Shoreline erosion and bluff stability along Lake Michigan and Lake Superior shorelines of Wisconsin

[From the U.S. Government Printing Office, www.gpo.gov]

10357
coastal Zone

Information
Center

SHORE EROSION STUDY

TECHNICAL REPORT

COASTAL ZONE
INFORMATION CENTER

JUN 14 1977

SHORELINE EROSION AND BLUFF STABILITY

ALONG LAKE MICHIGAN AND LAKE SUPERIOR

SHORELINES OF WISCONSIN

D.M. Mickelson, L. Acomb, N. Brouwer, T. Edil, C. Fricke,
B. Haas, D. Hadley, C. Hess, R. Klauk, N. Lasca, A.F. Schneider

FEBRUARY 1977

GB
459.5
M5
S5

WISCONSIN
Wisconsin Coastal Management Program

This report has been prepared through the cooperative
efforts of the Wisconsin Geological and Natural History
Survey, the University of Wisconsin (Madison, Milwaukee,
Parkside and Extension), the Wisconsin Department of
Natural Resources and the Office of State Planning and
Energy. Assistance was further provided by Owen-Ayers
and Associates.

This report is being reproduced quickly and in a limited
quantity for dissemination to local governments and
interested parties. The report will be broadly available
when reproduced in the fall of 1977 as an information
circular from the Wisconsin Geological and Natural
History Survey.

Financial assistance for this study has been provided by
the Coastal Zone Management Act of 1972 administered by
the federal Office of Coastal Zone Management, National
Oceanic and Atmospheric Admiiiistration.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . .. I. . . . . ... . . .

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . IV

LIST OF FIGURES AND TABLES . . . . . . . . . ... . . . . . . . . . . V

LIST OF APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . x

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . .

The erosion problem . . . . . . . . . . . . . . . . . . . . .

Determination of critiqal areas . . . . . . . . . . . . . . . . 3
Components of project 4 nd methods used . . . . . . . . . . . 6
SLOPE FAILURE AND BLUFF RET4EAT . . . . . . . . . . . . . . 25
Causes of slope failur4 . . . . . . . . . . . . . . . . .. . . . 25

Processes at the toe of the bluff . . . . . . . . . . . . . . . 25

Types of slope failure . . . . . . . . . . . . . . . . . . . . 29
Effects of groundwater . . . . . . . . . . . . . . . . . . . . 35
Effects of vegetation . . . . . . . . . . . . . . . . . . . . . 37
Changes in slope failure through time . . . . . . . . . . . . . 37

GENERAL SHORELINE CONDITIONS . . . . . . . . . . . . . . . . . . . . . 41

Glacial history . . . . . . . . . . . . . . . . . . . . . . . 41
Reach descriptions . . . . . . . . . . . . . . . . . . . . . . 55
Lake Michigan . . . . . . . . . . . . . . . . . . . . 55
Ln Lake Superior . . . . . . . . . . . . . . . . . . . . . ... 142

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . 161

Material properties . . . . . . . . . . . . . . . . . . 161
Stability analysis . . . . . . . . . . . . . . . .. . . . 174
Case studies . . . . . . . . . . . . . . . . . . . . . . . ... 181
Conclusion . . . . . . . ... . . . . . . . . . . . . . . . . 193

REFERENCES CITED . . . . . . . . . . . . . . . . . . . . . . . . .. . 196

GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l9a

US Denartment of COM"nerce
No" COalital @r@3317V`Ces COnter Libra17
2234 South J-*-@coson Avenue
Charleston, SC 29405-2413

LIST OF FIGURES AND TABLES

Page

Figure 1. Flow chart of shore erosion study . . . . . . . . . . . . . . 2

2. Outline map of Wisconsin showing location of reaches along
the Lake Michigan shoreline and the extent of the study
area on Lake Superior . . . . . . . . . . . . . . . . . . . 4

3. Example of form used for the description and evaluation of
structures. Completed forms are on file with the Depart ment
of Natural Resources . . . . . . . . . . . . . . . . . . .

4. Outline map of Wisconsin showing the location of
geotechnical drill holes used in this study . . . . . . . . . 13

5. Effective stress for sample GT-19, #9 . . . . . . . . . . . .. 17

6. Illustration of Modified Bishop Factor of Safety Method. . . 19

7. Diagram illustrating assumptions used for the position
@of the groundwater table under different conditions. 21

8. Oblique aerial photograph showing the effect of a
breakwater . . . . . . . . . . . . . . . . . . . . . .. . . . 28

9. Oblique.aerial photograph of the effect of al-groin on
shoreline erosion . . . . . . . . . . . . . . . . . . . . . . 28

10. Photograph of seawall showing old collapsed seawall in
foreground and new seawall in background . . . . . . . . . . 30

11. Oblique aerial photograph of collapsed seawalls . . . . . . . 30

12. Oblique aerial photograph showing bluff where shallow
slides and some flows are the common mode of failure. . . . 32

13. Oblique aerial.photograph showing relatively large slump
blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

14. Oblique aerial photograph of bluff showing numerous
closely spaced failure planes . . . . . . . . . . . 34

15. Oblique aerial photograph showing failure taking place
because of groundwater sapping beneath sand. . . . 36

16. Oblique aerial photograph of wooded bluff behind natural
@terrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

17. Diagrammatic sketch of slope evolution along the bluffs
at Kewaunee, Wisconsin. . . e . . . . . . . . . . . . . . . 40

18. Diagrammatic sketch showing slope evolution along the bluffs
at Port Washington in Ozaukee County . . . . . . . . . . . . 40

Page

cier ice in
Figure 19. Time distance diagram showing the extent o'f gla'*
the LakeMichigan basin during late Wisconsin time. . . . 43

20. Map of the Lake Michigan basin showing the approximate
extent of tills mentioned in this report . . . . . . . . . 44

21. Oblique aerial photograph of the bluff showing beach
littered with boulders where till is exposed at the base-
of the bluff . . . . . . . . . . . . ... . . . . . . . . . 45

22. Diagrammatic sketch showing the fluctuation of lake levels
in the Lake Michigan basin after the retreat of glacier
ice . . . . . . . . . . . . . . . . . . . . . . . . . . . 48,

23. Map showing the Q 'xtent of the Glenwood Stage (640'
elevation) of Gl4cial Lake Chicago . . . . . . . . . . . . 50

24. Glacial map of the state of Wisconsin . . . . . ... . . . 52

25. Diagrammatic sketch showing the fluctuations of lake
levels in the Lake Superior basin from glacial time to
present . . . . . . . . . . . . . . . . . . . . . . . . . 53

26. Map of Kenosha County showing the locations of Reaches 1,
2 and 3, and geotechnical site 9 . . . . . . . . . . . . 56

27. Longitudinal profile of bluff deposits in Reach 3 . . . . 61

28. Map o@f Racine County showing the locations of Reaches 3,
4, 5 and 6, and geotechnical sites 4, 5 and 10 63

29. Longitudinal profile of sluff deposits in Reach 4. �5

30. Longitudinal profile of bluff deposits.in Reach 5. . . . 68

31. Longtidinal profile of bluff deposits.in' Reach 6. 69

32. Map of Milwaukee County showing the locations of
Reaches 6, 7, 8, 9, 10 and 11, and geotechnical sites
1, 2, 3 and 8 . . . . ... . .. . . . . . . . . . . . . . . 73

33. Longitudinal profile of bluff deposits in Reach 7 . . . . . 74

34. Oblique aerial photograph of the bluff in the southern
part of Reach 7 . . . . . . ..
. . . . . . . . . . . . . . . 77

35. Oblique aerial photograph of the bluff in the northern
part of Reach 7 . . . . ... . . . . . . . . . . . . . . . 77

36. Longitudinal profile of the bluff in Reach 8 . . . . . . . 79

37. 'Longitudinal profile of bluff in Reach 10 . . . . . . . . . 82

VI.

Page

Figure 38. Oblique aerial photograph showing areas where rapid toe
erosion is taking place and failure is primarily by
shallow slides . . . . . . . . . . . . . . . . . . .. . . . 83

39. Oblique aerial photograph showing Nipissing Age (605'
elevation) terrace . . . . . . . . . . . . . . . . . . . . 83

40. Map of Ozaukee County showing locations of Reaches 11, 12,
13, 14, 15,16 and 17, and geotechnical sites 6 and 7. . . 85

41. Longitudinal profile of bluff in Reach 11 87

42. Longitudinal profile of bluff in Reach 12 . . . . . . . . . 89

43. Longitudinal profile of bluff in Reach 13 . . . . . . . . . 91

44. Oblique aerial p4,otograph showing very large..slump blocks
in Reach 13 . . . . . . . . o . . . . . . . . . . . . . . . 92

45. Oblique aerial photograph showing steep nearly,unvegetated
slope where most failure is taking place by shallow
translational slides and flow . . . . . . . . . . . . . . . 94

46. Oblique aerial photograph showing bowl-shaped depressions
in the bluff,top that have formed where groundwater sapping
is taking place . . . . . . . . . . . . . . . .. . . . . . 94

47.'..Longitud-inal profile of Reach,15 . ... . . . . . . . . ... 96

48. Oblique aerial photograph typical of the bluff in the
southern part of Reach 15 . . .... . . . . . . . . . . . . . 98

49. Oblique aerial photograph showing terraced areas typical.,
of Reaches 16 and 17 . . . . . . . . . . . . . . . . . . . 99

50. Oblique aerial photograph showing the exposure of dolomite
bedro.ck.at the.boundary between Reaches 16 and 17. 99

51. Map of Sheboygan County showing the locations of Reaches
18, 19, 20,'21, 22 and 23, and geotechnical sites 11, 12,
13 and 14 . . . . . . . . .... . . . . . . . . . . . . . . 102

52. Generalized longitudinal profile of T.15N . . . . . . . . 103

53. Generalized longitudinal profile of T.16N. 104

54. Generalized longitudinal profile of T.17N . . . 105

55. Generalized longitudinal profile of T.18N . . . . . . . 106

56. Generalized longitudinal profile of parts of T.18 and
.19N . . . . . . . . . . . .. . . . . . . . . . . . . . . . 107

VII.

Page

Figure 57. Oblique aerial photo of shoreline in Reach 18A. 109

58. Oblique aerial photo in Reach 18B . . . . . . . . . . . . ill

59. Oblique aerial photo of undeveloped shoreline in
Reach 18C . . . . . . . . . . . . . . . . . . . . . . . . 113

60.: Oblique aerial photo in Reach 19 . . . . . . . . . . . . . 115
61. Oblique aerial photo in Reach 19 ... . . . . . . . . . . . 116

62. Oblique aerial photo in Reach 19 . . . . . . . . . . . . . 117

63. Generalized long#udinal profile of Section 35, Reach 19. 110

64. Oblique aerial photo of Sheboygan Point, Reach 21. 120

65. Oblique aerial photo in Reach 21 . . . . . . . . . . . . . 122

66. Aerial photo of bluff near Pigeon River, Reach 21 . . . . . 123

67. Cross section through area of large slumps . . . . . . . . . 126
681. Oblique.aerial photo of slope failure, Reach 22 . . . . . .. 127

69. Oblique aerial photo of large slumps in Reach 22 . . . . . . 128

70. Map of Manitowoc County showing locations of Reaches 23,
24, '25, 26, 27, 28, 29 and 30, and geotechnical sites 15,
16, 17, 18, 19 and 20 . . . . . . . . . . . . . . . . . . .

71. Oblique aerial photo in Reach 23 . . . . . . . . . . . . . . 130

72. Oblique aerial photo of terrace in Reach 24 . . . . . . . . 133

73. Oblique aerial photo of gravel pits in Reach 25 . . . . . . 136

74. Longitudinal profile of Section 16, T.19N, Reach 27 . . . . 143

75. Oblique aerial photo of high bluff in Reach 27 . . . . . . . 145

76. Oblique aerial photo of protected shoreline in Reach 27. 146

77. Map o f Douglas County . . . . . . . . . . . . . . . . . . . 147

78. Map of Bayfield County . . . . . . . . . . . . . . . . ... . 151

79. Map of Ashland County . . . . . . .. . . . . . . . . . . . . 157

80. Map of Iron County . . . . . . . . . . . . . . . . . . . . . 158

81. Drained angle of internal friction vs. dry density for
sand and silt specimens . . . . . . . . . . . . . . . . . . 162

VIII

Page

Figure 82. Plasticity index vs. liquid limit . . . . . . . . . . . .. . 16@
834 Sand-silt-clay percentages of till.1 . . . . . . . .. . . . . 164.

84. Sand"silt-clay percentages of till 2 . . . . . . . . . . . . 165

85. Sand-silt-clay percentages of till 3. 166

86. Plasticity chart for all till units . . . . . . . . . . . . 171

87. Failure types documented in this study . . . . . . . . . . 175

88. Slope evolution example using critical circle criterion. 177

89. Slope evolution example using unstable circle criterioni 179

90. Profiles at geotechnical Sites 1, 4, 5, 8 and 11 . . . . . . 182

91. Profiles at geotechnical Sites.6, 7, 9, 10, 12 . . . . . . 183

92. Profiles at geotechnical Sites 13,.14, 15, 17, 19, 20 . . . 184

93. Profiles illustrating effects of groundwater, berm,
vegetation, cohesion, and overlying soil . . . . . . . . . . 185

94. Failure types and "typical profiles" . . . . . . . . . . . . 186

Table 1. List of reaches by priority and value/mile . . . . . . . . 5

2. Summary of engineering properties of materials in boreholes
1, 49 5, 63 7, 8, 9 and 10. .-i . . . . . . . . . . . . . . 168

3. Summary of engineering properties of materials in boreholes
119 12, 13, 14, 15, 17, 19, and 20 . . . . . . . . . . . . . 169

.4. Summary and correlation of laboratory results . . . . . . . 170

@LIST OF APPENDICES

(Note: small portions at borders of counties may be included in adjacent
county appendix. Copies of each appendix are available as separates from
the State Planning Office.)

Appendix

1 Kenosha Co4nty
Reaches 1, 2, 3

2 Racine Cou4ty
Reaches 4, 5, 6

3 Milwaukee County
Reaches 7, 8, 9, 10

4 Ozaukee County
Reaches 11, 12, 13, 14, 15, 16, 17

5 Sheboygan County
Reaches 18, 19, 20, 21, 22, 23

6 Manitowoc County
Reaches 24, 25, 26, 27, 28, 29, 30

7 Lake Superior
Ashland, Bayfield, Douglas and Iron Counties

8 Compilation of additional geologic and geotechnical
information in Milwaukee County

INTRODUCTION

The Erosion Problem

Shoreline erosion is a critical problem along Wisconsin's Lake Michigan and

Lake Superior Coasts. In recent years Wisconsin has suffered millions of dollars

in property losses as a result of erosion damage to homes, commercial and industrial

buildings and public facilities. These dama ges have increased from $4,591,000 in

1951-2 to an estimated $15,000,000 in 1973. Public concern has also intensified

with the increasing destruction to private and public property as repeatedly reflected

in telephone surveys, questionaires, public meetings and the news media. The

Coastal Management Program is a joint state/local effort formed to deal with the

many issues confronting Wisconsin's coastal areas, including shoreline erosion as

one of the highest ranking problems. The Shore Erosion Study forms an integral

part of the Coastal Management Development Program with a primary goal of developing

alternative plans for the prevention and abatement of shore damage to private and

public coastal property.

The foundations of the study were developed during the first year effort of

the Coastal Management Development Program with the initiation of basic data

inventories by state agencies, institutions, and, in-the second year effort, the

Re'ional Planning Commissions. A Shore Erosion Study Plan was developed following
9

a series of technical meetings that defined informational needs and delineated the

technical studies required for the formulation of alternative plans related to

shore eros
ion (Fig. 1).

The Shore Erosion Study may be divided into three major elements: (1) the

analysis of protective structural alternatives, (2) the analysis of non-structural

alternatives, (3) the field survey of erosion problem areas. This report represents

the field survey effort and is based directly on many of the preceding work elements

of the study, and forms the essential basis for the analyses of structural and

non-structural alternatives.

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Determination of Critical Areas

Critical erosion areas are defined as areas in which property of unusual

cultural, economic or scientific value is in danger of being damaged or destroyed

through the processes of coastal erosion. For the purposes of this study a

quanatative working definition of erosion problem areas was developed so that

the resources of the study could be directed toward the most serious erosion

problem areas. The criteria of this definition included; (1) public perception,

(2) shore recession rates, (3) shore damages, (4) protective structures, (5)

bluff height and (6) shore development.

The public perception of erosion hazard areas was obtained through regional

1workshops where the regional technical and citizen committees mapped known areas

where erosion threatened public safety, private or public property, historic or

scientific landmarks or environmental values. These maps were further detailed

through a canvas of Wisconsin Department of.Natural Resources and Department of

Transportation-field personnel. Shore recession rates were calculated from

measurements of changes in the shoreline on sequential aerial photographs. These

measurements were supplemented by historic recession rates as reported by previous

investigators. The dollar value of shore damages was obtained from the 1952.

Shore Damage Survey by the U.S. Army Corps of Engineers. This was the only year

for which damages could be obtained for all of Wisconsin's GreatIakes Shoreline.

Shore protection structures were interpreted from aerial photographs and

supplemented by field checks where available. Bluff heights and shore development

were estimated from U.S. Geological Survey topographic maps. All of this

information was quantified by reach in the Lake Michigan basin (Fig. 2) and mapped

on a series of shoreline base maps,(reproduced by reach in the Appendices).

The mapped values were then summed for each mile of shoreline and averaged for

reaches of the shore. The resulting values are shown in Table 1 and form a

priority list of serious erosion problem areas. Field work was concentrated in

areas with a high priority ranking.

superiOr
J,ay,e

no"k

ORE.-

,,N

LINCOLN
TAYLOR 7A-NGLADE OCONTO

MAR T- FEE FERNEE

CLAP.

SHAWANO

DOOR
WOOD 1. 'AGE WAUPACA K(WALINEE
IRIM-1-All 71A-IK111H OUTAGAMII

MANITOWOC
JUNEAU OANS WAUSHARA WsNNISAGO CALUME
... OF aches 24-25-
LA CROSSE 26-27-28-29-30
MAROUETTE GREEN LAKE

FOND OU LAC SHEBOYGAN
Reaches 18-19-
20-21-22-23
1AU. COLUM41A 0..,

RICHLAND WASHINGTON OEAUKU
Reaches 11-12--
CRAWFORD 13-14-15-16-17

DANE

JEFFERSON
IOWA WAUKESHA

Reaches 7-8-9-10
GRANT
P57- [AL*OIT. A
LAFAYETTE Reaches 4-5-6

KENOSHA
s 1-2-3

8006. 41e - XF

Figure@2' Outline map of Wisconsin showing location of reaches along
the Lake Michigan shoreline and the extent of the study area
on Lake Superior. For more detailed location of the reaches
consult the individual reach descriptions under General
Shoreline Conditions.

Table 1. List of reaches by priority and value/mile

GRID MILES N-S
PRIORITY REACH VALUE/MILE COUNTY TWNSHIP LENGTH LOCATION TOTAL

1 1 32 KEN 1 4.5 0-4.5 4.5
2. 12 27 OZA 9,10 05. 6 - 49.2-55.8 11.1
3 6 25 RAC-MIL 4-5 4.6 19.8-24.4 15.7
.4 7 23 MIL 5 2.8 24.4-27..2 @1&5
5 .11 23 MIL-OZA 8-9 2.6 46.6-49.2 21.1
_6 .10 20 MIL 7-8- 6.6 40.0-46.6 27 ' 7
7 13 18 OZA 10-11 5.2 55.8-61.0 32.9
8 18B 17 SHE 13-14 5.0 74.0-74.9 37.9
9 3 13 KEN-RAC 2-3 6.0 7.5-13.5 43.9
10 5 13 BAC 3-4 3.0 16.8-19.8 46.9
11 8 12 MIL 5-6 5.8 27.2-33.0 52.7
:12 -.5-6 12 OZA 11-12 3.0 65.5-68.5 55.7
13 '17 11 OZA 12 3.5 68.5-72.0 59.2
14. 14 10 OZA 11 1.0 61.0-62.0 60.2
15 15 10 OZA 11 3.5. 62.0-65.5 63.7
16 27 10 MAN 19 3.5 110.0-113.5 67.2
17 24 9 MAN 17 3.5 97.6-101.1 70.7
18 18A 7 .51ffi- 13 2.0 72.0-74.0 .72.71
19 191. 7 SEE. 14-15 2.2 82.0-84.2 74.9
20 -.25 7 MAN 17-18 5.9 101.1-107 ,0 80.8
21 29 7 MAN 20-21 .2.3 119.1-121.4 83.1
22 22 6 SHE 16 2.4 90.7-93.1 85.5
23 23 6 SEE-MAN 16-17 93.1-97.6 90.0
24 18C 5 SHE 14 3.0 79.0-82.0 93.0
25 21 5 SHE 15-16 3.5 87.2-90.7 96.5
@6 26 5 MAN 18-19 3.0 107.0-110.0 99.5
27 30 5 MAN 21 4.6 121.4-126.0 104.1
28 2 4 KEN 1-2 3.0 4.5-7.'5 107.1
29 4 3 RAC 3 3.3 13.5-16.a 110.4
30 28 3 MAN .19-20 5.6 113.5-119.1 116.0
31 20 2 SHE 15 3.0 84.2-87.2 119.0
32 9 0 MIL 6-7 7.0 33.0-40.0 126.0

Components of Project and Methods Used

The project was designed to provide information,at two levels of detail

for a variety of users. This report on general shoreline conditions and types

of bluff failure is for use by homeowners living on the Great Lakes, persons

concerned with the non-te-chnical-aspects of planning coastal areas, and other

interested citizens. More detailed information on critical areas in each county

is provided in the Appendices. This information will most likely be used by

engineers and planners in municipalities directly concerned with the erosion

problem and also will be used in the preparation of the final shore erosion plan

for the State of Wisconsin. The information in the Appendices does not provide

site specific information for all locations within the critical areas. It does,

however, provide a framework with a sufficient amount of information so that

relatively detailed planning of structures and slope stabilization projects

can be done before on-site field investigations are undertaken. For most projects

this site specific information will also have to be collected.

After bluff recession rates and critical erosion areas were determined, field

work was undertaken. Since beach erosion and slope failure on the adjacent

bluffs are intimately related, both aspects of the erosion problem were examined.

Field parties of geologists walked all of the shoreline in the most critical

.areas,measuring topographic profiles and mapping in as much detail as possible

the stratigraphy of materials in the bluff. The mapping also included a description

of the kind of slope failure that was taking place. All of these profiles and

maps are given in the Appendices by county and reach. Samples of many of the

materials were collected for laboratory analysis.

Another aspect of the project involved description of beach conditions

including nature of beach material and beach slope angle, beach width,. and the

distance from shore to the five-foot water depth. Since structures along the

shoreline play an important role in determining the width of the beach, all

structures were described, located, and evaluated for their effectiveness.

This information is also tabulated in the Appendices for the critical areas.

A fourth phase of the project involved the placement of engineering borings

at 20 locations along the Lake Michigan shoreline. Samples were collected with

shelby tube and split spoon samplers and were returned to the engineering laboratory

for analysis. The engineering data and drill-hole stratigraphy provided by this

phase of the study are also givea in the Appendices. In the next phase of the

study engineering data from the itest holes was extrapolated to include all of the

critical areas by using the geologic information derived from bluff descriptions.

This provides the basis for the mapping of factor of safety and stable slope

angles which are given in the Appendices.

The following methods were used in the collection and analysis of data.

Computation of Erosion Rates

Before a mapping of critical areas was undertaken, erosion rates were

measured for the Lake Michigan shoreline from Kenosha County north to Bailey's

Harbor in Door County. Additional measurements were made in all of Douglas

County, most of Ashland County, and parts of Bayfield County along the Lake

Superior shoreline. All of the shoreline recession measurements were done under

the direction of Mr. Charles Hess as the Department of Natural Resources,

contribution to the Coastal Management Program. Two types of shoreline recession

information were used in the determination of critical areas.

The first is the long-term rate of recession which integrates periods of

time when there was little or no erosion with those periods of time that have

had fairly high erosion rates. The long-term erosion rates were developed from

a variety of sources of data including the U.S. Army Corps of Engineers and other

specific studies along the Lake Michigan shoreline. Along the shoreline of Lake

Superior old maps from original surveys are available which accurately portray the

shoreline position at that time. These were used as the base line data for long-

term recession rates where they were available.

The second type of information is recession rate over the last 10 years.

In many cases these values are considerably higher but in some they are lower

because of the sporadic nature of some types of slope failure along the bluff.

These recession rates were measured from vertical aerial photographs at scales

1:12,000 to 1:20,000 that were taken during the last 10 to 15 years. The

measurements were made by plotting shoreline positions from the older photograph

onto the most recent photograph and measuring the distance of recession with a

Bausch and Lomb Microline Supergauge. Distances were measured to 5/10,,000 of an

inch. These were then converted to distance on the ground by determining photo

scale in comparison with U.S. Geological Survey topographic maps. The amounts

of recession were then divided by the number of years of record to produce a

recession rate in feet per year. Recession rates are shown on each reach map in

the Appendices.

Profile Measurements and Geologic Observation

In the areas which were determined to have high priority in terms of this

erosion study, field parties did detailed observation and profile measurements

during the summer of 1976. One field party, under the direction of Dr. Alan F.

Schneider, concentrated on Kenosha (Appendix 1) and Racine (Appendix 2) Counties.

Another field party, under the direction of Dr. David M. Mickelson, concentrated

on Milwaukee (Appendix 3) and Ozaukee (Appendix4) Counties, and a third field

party, under the direction of Dr. David Hadley, concentrated on Sheboygan

(Appendix 5) and Manitowoc (Appendix 6) Counties. Some measurements were also

done in Kewaunee and Door Counties on Lake Michigan. For the Lake

Superior counties (Appendix 7) some detailed profiling and stratigraphic descrip-

tion was available from previous investigations. Mr. Charles Hess collated this

information and also did detailed bluff descriptions in high priority areas.

All,of field work along Lake Michigan was done on a section-(one mile)

by-section basis. In each section where a bluff was present, 2 6 profiles

were measured. The topographic profiles were determined by measuring slope angle

with a hand-held Brunton compass and measuring distances with a tape'. All

significant slope breaks were recorded and are shown on the profiles. As the

topographic profile was measured, materials in the bluff were also described

where exposure of the materials Was available, and the thicknesses of the units

were noted on the profiles. Samples were collected for laboratory analysis from

all of the till units and some of the intervening lake sediment. The amount of

vegetation on the bluff was noted and the type of slope failure that was taking

place was'described for future incorporation with engineering data.

Because all of the shoreline between the profiles was walked by the field

parties, additional information.in the areas between the profiles was accumulated.

This information includes types of slope failure taking place, position of ground-

water discharge along the slope, changes in thickness*of types of material in the

bluff, types of toe material, and any other features of significance. All of

this information is provided either in narrative form or on maps in the Appendices.

In addition to description and measurement along the bluffs, beach widths

were.taped or paced.and the distance from the shoreline to a water depth of 5

feet was measured with tape or optical range finder at each profile. Beach width

and@material making up the beach (sand, pebbles, cobbles) was also described

in the areas between the profiles. Because the nature and width of the beach

changes with climatic,conditions, season of the year, and lake level, this

information only provides some basis for preliminary planning of structures.

Information on changes.in beach conditions with time, an important factor in

planning some structures, is not provided by this study. A generalized description

of the beach is also shown in each Appendix.

All of@the information accumulated was plotted either directly on vertical

aerial photographs at a scale 1:12,000 (about 5-j inches per mile), or on oblique

aerial photographs of the bluff and transfered to vertical photos. These were also

used for location, description of types of slope failure, and for the correlation

of stratigraphic materials in the bluffs. All of the information from the

photographs was then converted to maps at a scale of 1:12,000, and these maps

are provided in the Appendices.

Structure Mapping and Eval_uation

For each erosion control or bluff stabilization structure visible along the

shoreline a descriptive form waQ@ filled out (Fig. 3). Information given on the

forms is tabulated in the Appen4ices, and structure forms are on file at the

Department of Natural Resources. All structures were photographed to provide

additional description of the structures. The location of the structures is

shown by county, township, and range, section, and fraction of a mile north of

the south section line along the shoreline. The location of the structures is

also shown on maps in the Appendices.

Measurements of structure heights and widths were measured where possible

either by taping or pacing the distances. In some cases measurements were difficult

or impossible to obtain, and so estimates are provided. Definitions of the

structure types are given in the Glossary at the end of this report. Structure

condition was based on whether or not the structure was trapping sand and building

out a beach at the base of the bluff. Adverse effects were usually erosion on

the down-drift side (usually south) of the structure. In some cases, especially

with large structures, the beach has actually been removed by waves and currents

on one sideof the structure and considerable bluff erosion is taking place.

The type of material used in the structure was given as the two major materials,

and the amount of maintenance needed was a subjective observation related to the

way in which the structure was being maintained. Shore parallel structures, such

as revetments and bulkheads, commonly fail by being over topped by large waves

or by being eroded at the toe; the latter failure usually results in collapse of

the structure. In some cases, breakwaters (shore parallel structures away from

DNR SHORE EROSION STU13Y
6-76 SHORE PROTECTION
EVALUATION
Report No. Observer

LOCATION
=F@, S,cED.[:] Mile[J-1 -1-1
county T RL

DATE PHOTO
Dsym Month[= YearM Hourm-1-1 Roll-Exp

PHYSICAL SETTING
Bluff: HeIght ft Slope = 0 Vegetation ED%
Beach: Width (--Mft slope Orientation =0
Neatshore: Distance to 6 ft depthF77 Depth 50 ft offshore
Wove beightEl-Oft Wave type El
1. Spilling, 2. Spilling/Plunging
Lake level ft 3. Plunging, 4. Surging, 5. Calm

STRUCTUPE

0. Permit
Type El Number n Length f t
1. kevetwent
2. Bulkhead Height= ft Maintenance[D
3. Groin 1. None required
4. Breakvater Material 2. Minor required
5. Pier I. Stone 3. Major required
6. other 2. Broken concrete 4. Rebuild
3 Steel
ConditionD 4: Timber Failures
1. Functional 5. Poured concrete 1. Toe undermiLled
2. Non-functional 6. Asphalt 2. Overtopped
3. Failing 7. Precast concrete 3. Flanked
'[], 8: WI r 4. Collapsed
Adverse Effects 9 Clo:h bp. 5. Faulty material
1. None 10. Tires 6. Vandalt am
2. Bluff erosion 11. other 7. None
3. ?,each erosion 8. other
4. Navigation hazard
5. other

Remarks

Figure 3. Example of form used for the description and evaluation of.
structures. Completed forms are on file with the Department
of Natural Resources.

the base of the bluff) also fail in the above-mentioned fashions. Shore

perpendicular structures, such as piers, occasionally collapse because of wave

or ice damage, but sometimes are so successful in trapping sediments that they

become buried in beach material and are not presently acting as sediment traps.

In these cases, the accumulation of beach material does protect the toe of the

bluff however, and the structures were rated as functioning and requiring none

or minor maintenance.

Geotechnical Subsurface Exploration, Sam2ling, and Field Tests.

Sites for engineering borings were chosen because they represent fairly

typical bluff composition, important stratigraphic units from an engineering

standpoint, and to some extent because they were accessible to the truck mounted

drilling equipment. Locations of the drill holes were monumented and detailed

slope profiles on the adjacent bluff were measured. This will enable more detailed

studies on slope stability to be undertaken in the future. Locations of all the

drill holes are shown on Figure 4, in more detail in maps showing reaches, and

in the Appendices.

Two separate drill rig units were used in the sampling of subsurface materials

each with a capacity of 120 to 135 feet of auger boring. Solid stem auger flights

five feet in length and four and one half inches in diameter were used to open

the hole and to determine general stratigraphy. Standard Penetration Resistance

was recorded at five foot intervals in Accordance with ASTM d 1586-67, by using

either a cathead and blocks system, or a Sate-T-Driver Hoist on the Mobile Drill

Unit. Thenumber of blows necessary for a 140-pound hammer dropping 30" to

penetrate a split barrel sampler (2 in. O.D., li in. I.D.)into the soil six

inches was recorded in three sets, the sum of the last two being the Standard

Penetration. Pocket Penetrometer readings were taken on the surface of the

split spoon samples thus obtained and averaged to give an estimate of the

unconfined compressive strength of cohesive soils. Three-inch Shelby tube samples

in lengths of 21 and 3 feet were pushed hydraulically into the soil approximately

III, W.S.80"N SAWY

ONEIDA

RUSK

LINCOLN

TAYLOR ocomTo

NIAR T.O. NIENONIN111

5-A.o

AU1I,L.f

DOOR
WOOD PoATAGE WAUPACA w. KEWAUNEE

@L. I-PIALtAU JACKSON OtTTAGAMIt

m.,Ulo.oc
JUNEAU ADA.5 WAUSHARA WINNEBAGO C.,UNET GT-20
MONROE GT-19
LA CAOS5( GT-1'7-, i6
MAROUEYTE G.- LAR GT-15 16
FOND ou LAC SMEPOYGAN GT-13
GT-14
-GT-11
M.D.

5AVK COLUMBIA DODGE
.IcHL.No WASHINGTON MA "It

z CRAWFORD
GT- 7
DANE 4EFFERsow WAUKESHA GT-6
GT-8
GT- 3
GRANT -GT-2

oc w LWOR" 4
GT-4
LAFAYETTE
GT-lP
.[**"A GT- 9

8006. 410, - XF

Figure 4. Outline map of Wisconsin showing the location of geotechnical
drill holes used in this study. For more detailed locations
consult the county maps under General Shoreline Conditions.

every 20 feet, or when a new recognizable layer was reached, as per ASTM D 1587.

The ends of the Shelby tubes were stopped with plastic caps, then covered with

cloth and sealed in paraffin, then stored horizontally in a moisture room in the

laboratory.

Piezometers were prepared in the lab consisting of a 3/8" I.D. perforated

plastic core and a lf" shell of an epoxy/ottawa sand matrix. The piezometers

were installed in each borehole at the estimated water table levels, or in

pervious strata, and connected to the surface by a 3/8" O.D. plastic tubing.

Bentonite "plugs" were used where appropriate to isolate the piezometer tip,

and sand filled in around the tip. Groundwater levels were determined approximately

,one month after the installation of the piezometers by registering the voltage

through a coaxial wire.

,,All boreholes were backfilled with soil refuse, capped with a 2j-inch

plastic'pipe and pipe cap fitting, monumented, and sealed in cement. The borehole

location.was roughly determined from nearby reference points.

Hollow-stem augers, casing, wash borings and slurry methods were not used

in the subsurface investigations. Due to the occurrence of high groundwater

tables, or saturated sand layers, it was often necessary to resort to obtaining

only "bag" samples from auger flights. These bag samples were used in classification

tests only.

Geotechnical Engineering Laboratory Testing

Standar d Classification and shear strength tests were conducted on split

spoon, J)ag,.and shelby tube samples obtained by the drilling crew. Atterberg

Limits (Liquid Limit and Plastic Limit) were determined by the procedure outlined

in W.T. Lambe's Soil Testing for Engineers as per ASTM D 423 and D 424. The

Liquid Limit was calculated by straight line least squares analysis of the water

content vs. the log of the number of blows of the liquid limit dish. The grain

size distribution of each sample was determined by wet sieving on standard sieve

sizes #10, #40, and #200, and the percentage finer than a particular grain size

determined by consecutive subtaction. Standard Hydrometer analysis as described

by W.T. Lambe was performed using 50 cc of AN Calgon solution (Sodium

Hexametaphosphate + Na2CO3 Buffer) with approximately 50 g of soil passing

#200 sieve in one liter of distilled water. A desk calculator (Monroe, Model

1880) was programmed to determine the equivalent corrected grain diameter and the

percentage finer for the particular hydrometer used, and the results were inter

,polated to obtain the percentage finer than .005 and .002 mm. Pipette analysis

was also used to determine the percentage of clay. Samples were prepared as

described above, then an appropriate volume of suspended material was removed at

specified depths and times as described by Tanner and Jackson (1947).- The results

were corrected for the concentration of Calgon, and the percentage of grain

sizes smaller than 0..5 and .002 mm were recorded.

The Unified Soil Classification System was employed as per ASTM D 2487-69

and APTM D 2488-69 using the following basis for grain sizes:

Gravel 2.0 mm
Coarse Sand -0.42 to 2.0 mm
Fine Sand -0.074 to 0.42 mm.
Silt -0.002 to 0.074 mm
Clay 0.002 mm

Natural water content, w, and natural unit weight, y, were determined for all

Shelby tube samples,.and many split spoon samples. Dry density was then

calculated as Y y (1+w) as a measure of the concentration of solid matter in
d.:

a unit volume of soil.

Shear,strength tests were conducted on all shelby tube samples. Sand samples

were tested.at natural densities determined either by Standard Penetration

results, or direct density measurements. The specimens (1.4 in. diameter, 3.0

in.high) were placed in triaxial compression test cells, an initial all-around

cell pressure applied,,and the axial load increased until failure at a shearing

rate of .03 to .06 inches/min (strain rate= .01 to .02 per inch). Drainage was

allowed, and dilatancy, or volume changes during shearing were used in determining

the shear strength. Compilation of the triaxial data and least squares determination

of the effective angle of internal friction was performed by a calculator program,

assuming cohesion zero and taking failure at the maximum principal stress

difference.

Clay sample were extruded from the shelby tubes, trimmed manually to a

speciman size approximately 3.6 cm in diameter and 7.8 cm in length. After

being enclosed in a rubber membrane, and placed in a triaxial testing cell, the

specimens were subjected to a confining pressure of 0.5 ksc and allowed to

consolidate. After equilibrium was obtained, B-checks were made wherby the cell

pressure was increased, and the subsequent increase in the internal porepressure

of the specimens noted. The backpressure, or applied porepressure, was then

increased to maintain a constant effective pressure of 0.5 ksc on the specimens.

This procedure was continued until saturation was achieved, i.e., the porepressure

increase was at least 907o of the increase in cell pressure. Backpressures of

3 to 5 ksc were generally required to achieve saturation. Cell pre ssure was then

increased and specimens allowed to consolidate in order to provide the desired

effective normal stress before shearing. All drainage due to consolidation was

recorded and the change in specimen height measured. Shearing was done at a rate

of about .004 inches per minute, (or a strain rate of .0013 per minute), and the

porewater pressure measured (drainage was not allowed during shearing). The

effective stress parameters were computed by calculator programs, based

on a least squres fit of points of maximum deviator stress. Effective stress

paths were plotted, and the corresponding failure envelope indicated for each set

of specimens (Fig. 5).

A Farnell automatic shear vane testing apparatus was used to estimate

the unconfined compressive strength of several shelby tube samples. The vane
had a diameter of 1.27 cm and a length also of 1.27 cm, and sheared at a rate of

about 8.50 per minute I(or about 40 minutes per rotation).

EFFECTIVE STRESS PATHS

CONSOLIDATED-UNDRAINED TRIAXIAL TEST'
3.0.. SAMPLE GT-14i Shelby V9, dcpth 55 feot
25.3%, y 102 pcf
jW
d

2.0--

T-1 T-2 T-3

0.0
0.0 1 0 2.0 3.0 4.0 5.'0 6.'0

CT + a
1 3
P 2 (ksc)

EFFECTIVE STRESS MOHR'S ENVELOPE
'SAMPLE GT-14 #9 . . . . . . . .
tri
3.0

@22.30

V, Z.0

1.0 ------ -T-3

t T-1 T-2
0.5 k c
-4-
0
1.0 2.0 3.0 4 .@O 5.,0 6.0
Notnlal StrE!Sncs, Cr (k8c)
1 3
T-1

Figure 5. Effective stress for sample GT-19, #9

Stability Analysis

The relative slope stability of the bluffs along the Lake Michigan shore-

line, its variations, extremes, and criticality due to changes in stratigraphy,

material properties, bluff height., and slope angle, were the ultimate concern

of the Geotechnical Engineering Group. Each bluff profile as measured by the

geologic field parties, was analyzed using the effective stress parameters

determined in the laboratory,

A modified Bishop method of slope stability analysis (Fig. 6) assuming,

circular, rotational failure has been found to model the slope fail;1re phenomena

along the coastline satisfactorily (Edil and Vallejo,' 1977) 'and was therefore also

used in this study. The procedure that this method follows is to divide the

failure zone into slices, analyze the effective forces on each slice, then sum

the Moment of these forces about the trial failure circle center. Groundwater

conditions and seepage forces are also considered in the stability'analysis.

The Safety Factor is then defined as the ratio of the sum of the moment of the

driving forces (shear stresses) to the sum of the moment of the resisting forces

(shear strength).. The computer program employed was developed by the New York

State Department,of Transportation giving intermediate moment values, 6 simplified

Factor of Safety, the modified Bishop Factor of Safety, and the critical failure

circle. It also employs a search routine which checks for the minimum Safety

Factor, and stops when this minimum is reached.
The ultimate angle of repose for a stable slope was determined by assuming
a long-range equilibrium condition of the bluff whereby the cohesion reduces
to zero.due.to weathering, and the angle of repose is then the angle of internal
friction of the soil. Below the groundwater table, the stable slope angle is
reduced due to theeffects of water pressure, so that the stable angle, B, can

SF YDb - shear stresses
94R shear strength

Figure 6.. Illustration of modified Bishop Factor of
safety method.

be computed by the equation

SAT
tanB BOUY tan itan

and results in a slope angle about half that of the angle of internal friction.

Artesian pressures and excess hydrostatic pressures due to seepage effects

tend to decrease this stable slope angle even more; however, these conditions

are not prevalent in the bluffs of this study.

Interpretation and Presentation of Results

The engineering properties of the soils along the Lake Michigan coastline

were determined only at particular sites where the boreholes were drilled. The

properties used in evaluating the slope stability of all the bluffs are a

combination of averaging the properties of all tests on a given stratum and

extrapolation ofthese properties over a large extent of shoreline based on

engineering judgement.

Soil properties were therefore considered constant and homogenous for any

given stratum. Stratification was considered horizontal at any given profile,

and variations in stratification along the coastline were determined using the.

section reports of the geologic field parties.

The locationQf the groundwater table at a given profile was assumed based

on the following criteria:

a. Stratification (Fig. 7). In fine-grained soils, the groundwater table

is characteristically higher than in coarse-grained m aterials.

b. Piezometric readings. Piezometers installed at the boreholes allowed

direct measurement of the actual groundwater level, which was then

assumed horizontal to the face of the bluff. Piezometric records

were applicable, however, only very near the borehole location.

c. Seepage zones. The lines or zones of seepage reported by the geologic

field parties were often assumed as the groundwater table since these

very often indicated a permeable layer over a less permeable one,

I;ne J
V.,

T
T
i) Clays ii) Sands iii) Sand/Clay interface

Figure 7. Diagram illustrating assumptions used for the position of the
groundwater table under different conditions.

as in case iii abovel in which the pervious stratum would conduct

the flow of water, and therefore be the highest critical groundwater

level.

Groundwater levels are generally much lower near the bluff than normally

expected further inland since the water is trying to reach a minimum potential

at the lake level, and therefore has a depressed water table. For the purposes
V
of this study, the water table was assumed to be'horizontal, since this is a

more critical condition than a gradual reduction to lake level, and is very

close to the actual,shape of the phreatic surface in sands and sand or silt

seams, a condition which frequently occurs in the bluffs of this study.

After extrapolating the stratigraphy, engineering properties, and ground-

water levels to the recorded profile locations, a safety factor was obtained

for each profile by computer analysis. This safety factor was then interpreted

and again extrapolated over a particular stretch of shoreline. Interpretation

of the Factors of Safety, and extrapolation of the results was based on the

following criteria:

a. Value of the Safety Factor: A Safety Factor less than or equal to one

was considered an Unsafe slope; that when water pressures build to an equili-

brium value will most likely cause failure along the failure plane indicated.

A Safety Factor between 1.0 and 1.25 indicated a slope of Questionable stability;

that if assumptions made are grossly in error, if groundwater conditions change,

or if wave erosion or surface degradation change the profile shape, that a

failure of a segment of the slope may be possible. A Safety Factor greater than

1.25 was considered to indicate a safe slope condition with little probability

of failure.

b. Vegetation cover. Vegetation affects the surface runoff conditions

and slope washing, increases the apparent cohesion of the immediate slope face,

and in general indicates a slope not undergoing active erosion. Therefore, the

amount and type of.,vegetation was often considered.in interpreting the stability.

of a particular stret,ch,of shoreline.

c. Nature of failure. Based on the principles outlined above in determining

stable slope angles, if the shape and nature of the slope profile seemed to

indicate a stable slope despite the calculation of a low Factor of Safety, as

in the case of accumulated. slump material at the toe of the bluff, this was

considered.in the interpretation of the results.

Descriptiveassessments of @he slope stability along a long stretch of shore-

line was made using the terms Unsafe, Questionable, or Safe, with modifications

noted where applicable. Divisions between areas of different safety indicators.

were based on-thelvisual observations described in the reach or section reports,

by the geologic field parties.

The level of confidence of the information available varies considerably,

along the shoreline, and is therefore also indicated on the section maps. The

engineering properties of the materials, the groundwater conditions, and slope

configurations are most accurate right at the boreholes, and are given the highest,

level of confidence. This information may be extended both north and South of

the borehole with reasonable accuracy so long as the stratigraphy is known and.

is consistent, or the lateral distances are not too great; thus, these areas

have been designated as a second level of confidence. The- lowest level of con-

fidence is then assigned to those areas where the stratigraphy is not at all

apparent, or that are far from any borehole.

% The stability line, . neglecting wave erosion, was obtaine d by extending
stable slope angles from the toe of,the bluff to the top of the bluff, and the

corresponding setback in feet of the bluff ridge measured. Thus., this setback

indicates a minimum retreat of the bluff top necessary to insure stable slope

conditions, provided the toe of the bluff is protected from further erosion.

There are a -number of assumptions that have been made in analyzing the

bluffs along the shoreline that require a certain amount of caution in assessing

the absolute reliability of@the engineering judgements made. All of the

engineering properties have been averaged, assumed homogenous and consistent

throughout any given stratum and the stratigraphy has been assumed horizontal

and continuous. These conditions may prevail at a particular site, but may be

drastically different from those in the near vicinity. Thus, the extrapolation

of data is precarious, and the apsignmefit of Unsafe or Safe slope designations

must be viewed with a certain degree of scepticism. These extrapolations are

to be used as a guideline or an indication of general Conditions along,the

shoreline, but should not exclude detailed geotechnical subsurface investigations

at any particular site to assess its slope stability. It should also be men-

tioned that these Safety Factors do not indicate large, dramatic failures, but

consecutive failures of a smaller extent' thus the term "Unsafe'.' does not mean

a catastrophic landslide always, but rather a high probability of subsequent

erosion by mass wasting. Finally, the methods used in analyzing the stability

of the slopes do not account for surface sloughing, solifluction, mass flows,

slope wash or wave eros ion which must also be considered in determining the

ultimate stability of the slope, or the ultimate rate of retreat of-the bluff

top.

SLOPE FAILURE AND BLUFF RETREAT

Causes of Slope Failure

On all hillslopes gravity acts to move,material on the slope to a lower

position., On most hillslopes which are undisturbed by man, and where streams

or waves are hot cutting at the base, an adjustment is reached through a.fairly

long period of time so that the slope Angle is adjusted to the stresses acting

to move material down the slope and.to the resistance of the materials in the

hill to the stresses. Thus on the bluffs on the Lake Michigan and Lake

Sup erior shorelines two major variables control the rate of bluff recession

and the angle of the slope at any given.time. The nature of the materialsz

(primarily the grain@size'distribution) and the amount of shear stress on the

materials in the slope. The detailed discussion of the engineering character-

istics of;materials in the.-bluffs and the engineering data presented in the

@appendicies is discussed under,engineering methods.

The shear stress of the materials.in the.,bluffs is primarily determined

by the.bluff height and the angle of the slope. Undercutting at the toe of

the slope by Waves,steepens the slope and increases the shear stress. Along

the Lake Michigan and'Lake Superior shorelines this is the process that is

primarily responsible for causing slope failure within the slope itself. In

the following section o,f.this report We will look at processes acting at the,

toe of the@'slope which tend to increase shear stress on slope materials and,

then examine the resulting slope failure.

Processes at the Toe of the Bluff

As pointed.out above, the basic cause of slope failure and bluff recession

on the Great Lakes-shorelines is wave erosion' at the base of the bluff. The

amount,of.waveerosion at the base of the,bluff. is directly related to the

type of material at the bluff base and also to the energy of the waves which

break against theltoe. Th6amount of energy going into toe erosion is, in turn,

related to the slope of the beach-and offshore areas, the orientation of the

beach as it relates to the orientation of large storm waves, the fetch or

distance of water over which the waves can develop and the elevation of the

water surface relative to the elevation of the base of the bluff. Both in

Lake Superior andin Lake Michigan, storms with northeast winds tend to produce

on average the largest waves, and therefore, beaches exposed to these waves

It
generally have the mostsevere erosion problems.

Materials on the beach are moved up and down perpendicular to the shoreline

as waves break and wash, then backwash,,on the beach surface. Since waves

usually strike,the beach at an angle, there is usually net transport of

material in one direction parallel to the beach. This movement is what is

called-longshore drift and occurs on the beach surface as well as in currents

just off shore, which are called longshore currents. Thus, at any given place

and time on the beach,material is being moved in from one direction and moved

out in the opposite direction. Because waves and currents responsible for this

sediment transport have a prevailing direction there is a net transport of sand

in one direction over a period of time. Along most of the Wisconsin shore of

Lake Michigan, the prevailing longshore drift is southward. In Lake Superior

the prevailing drift is westerly along most the Wisconsin shoreline.

Because of.the movement of sediment within.the wave zone, the width of,

the beach and, thesize of materials on the beach vary with time. In natural

situations where man has not interrupted the longshore drift system, the slope

and size of the beach is often adjusted so that the material on the beach can

be carried as longshore drift. Thus, beaches with coarse material are usually

steeper and waves strike the beach with greater force than sand beaches with

lower angles where waves break further away from the water's edge. Because most

sediment in the longshore drift system is derived from erosion of the bluffs

the volume. of coarse material in the bluffs is important. If sufficient amounts

of coarse sediment are available, a beach can be maintained and actual erosion

of the toe is reduced. If the bluff material is relatively fine-grained, a

large volume of bluff must be eroded for the waves to build a stable beach and

ifiaintain the longshore drift system.

Man-made structures can influence the longshore drift system in a number

of ways. Breakwaters, t hose structures which are shore parallel and built in

the water, prevent large waves from breaking against the shoreline. Thus,

material transported by the longshore drift system tends to accumulate behind

the breakwaters and the bluff behind the breakwater is protected. This can

be seen in a number of areas along the Lake Michigan and Lake Superior shore-

lines (Fig. 8). Groins and some piers also tend to stop sediment which is

moving.in.the longshore drift system. In these cases, sand accumulates as a

fairly wide,beach on the up-drift side (generally north on the Lake Michigan

shoreline) and the base of the bluff is protected from breaking waves.

Another result of these structures, however., is often an increase in erosion

on the down-drift side of the structure. This takes place because waves strike

the shoreline in this position and tend to move the sediment in the down-drift

direction. Because the sediment supply has been cut off by a structure, the

beach width is reduced or the beach is removed completely and increased erosion

takes place at the bluff toe (Fig. 9). Thus, knowledge of beach process and

the possible effect of any structure is necessary before structures are placed

along the shoreline to prevent increased erosion.

Another way in which man can attempt to reduce the amount of erosion at the

toe of the bluff in:volves direct protection of the toe from wave erosion.

Usually the kinds of structures used are revetments, which are commonly piles

of coarse rock debris, or concrete slabs along the toe of the slope, or

bulkheads, or seawalls, which are generally made of poured concrete. These

structures do not interrupt the flow of. sand in the longshore drift system.

?4.

.Figure 8. Oblique aerial photograph showing the effect of a breakwater.
Note vegetated slope behind the breakwater and active erosion
just to the left (south) of the breakwater. Location is
T. 5 N., R. 22 E., Section 24, Reach 7, Milwaukee County
(oblique R-21, 34).

-7j,

Figure, 9. Oblique aerial photograph of the effect of a groin on
shoreline erosion. Note the wide beach between the groins
and the narrow beach and actively eroding bluff to the
left (south) of the groins. Location T. 6 N., R. 22 E.,
Section 25, Reach 8, Milwaukee County (oblique R-20,23).

In many areas the beach in front of these structures is removed by erosion

and the structures absorb fairly high wave energies. This can result in under-

cutting of the structures as waves erode the loose sediment at the base. As

waves begin to break directly against the structure, the structures are often

overtopped and water from the breaking waves can erode material behind the

wall or infiltrate the area behind the wall and contribute to collapse of the

.structure (Figs. 10 and 11). Although at considerable expense, it is possible

to artificially nourish the longshore drift system when insufficient quantities

of material to form a beach are available.

The fundamental cause,then,of bluff retreat along our Great Lakes shore-

lines is erosion at the toe of the bluff. In most areas this is a natural

process which has been taking place for thousands of years, especially at

times of high water. In most situations any attempt at bluff stabilization

will also have to control wave erosion at the toe. Even when this is controlled,

however, bluff recession will continue until stable slope angles are reached.

In areas of high bluff with relatively weak materials, hundreds of feet of

bluff recession might be necessary before a stable slope angle is reached.

Thus, in areas which are already developed close to the present bluff top,

stabilization of the,toe is not the only solution. We must look at processes

on the bluff and materials in the bluff to predict what stable slope angles

might be and to develop possible methods of slope stabilization. Although

the methods of slope stabilization and estimates of cost will be discussed

in another report,'we will discuss the types of slope failure taking place and

the kinds of materials in the bluffs.

Types of Slope Failure

most bluff retreat takes place by slope failure (landslides in the

general sense) rather than by erosion by surface water crossing the bluff.

Although runoff from rainstorms can remove considerable material from the

4A.
Z

Figure 10. Photograph of seawall showing old collapsed seawall in
foreground and new seawall in background. Both walls are
being overtopped by waves (note gravels above wall and
erosion behind wall in center of photograph). Location
is T. 9 N., R. 22 E., Section 20, Milwaukee County
(structure 20.7)

Figure 11. Oblique aerial photograph of collapsed seawalls. Note
.the amount of erosion that has taken place since the sea-
walls were built. Location is T. 8 N., R. 22 E.,
Section 33, Reach 10, Milwaukee County (oblique R-17, 20).

bluff face if the vegetation cover is sparse, the lack of vegetation is an

indication that sliding of materials down the slope is also taking place at

a fairly rapid rate. The terminology used in this report to describe various

kinds of failure is that used by Varnes (1958).. Three major divisions of slope

failure are made in this classification. The first is rock or soil fall. This

type of failure takes place when undercutting is extreme and near vertical

cliffs are produced. Although some near vertical slope segments are present

in many of the profiles along the eroding bluffs, these ar e generally fairly

small and fall of material from vertical faces has relativelylittle impor-

tance except along some.bedrock cliffs in Door County and on the Bayfield

Peninsula.

The second type of-slope failure is sliding. In this type of failure the

material that is being moved is relatively undeformed and generally moves along

a@single slide plane. Two types of slides are very common along the bluffs

of Lake Michigan and Lake Superior. On most of the slopes which have very

little vegetation at the present time or vegetation is only present in

patches, translational sliding is taking place (Fig. 12). This type of failure

involves a surface layer several inches to one or two feet thick sliding either

rapidly or fairly slowly down the bluff. Where recent slides have taken place

slickensides or grooves left by the sliding mass are often present on the slope

above. The growth of ice crystals within the soil during winter-months weakens

the structure of the soil and increases the possibility for this type of sliding

and flows, especially during the-spring as the intergranular ice melts. Along

some part s of the shoreline, especially where much of the bluff is made up of

massive lake sediment and fine-grained tills, this failure type is probably

the most important in causing bluff recession. Without detailed measurements

it is impossible to quantify'the effects of this process, nor can the process

"'T
41 eel

Figure 12. Oblique aerial photograph showing bluff where shallow
slides and some flows are the common mode of failure.
Note the almost complete lack of vegetation on the slope.
Location is T. 10 N., R. 22 E., Section 3, Reach 13,
Ozaukee County (R-13,8).

be predicted in more than a general sense. Thus, the engineering analysis of

factor of safety which is given in the Appendices excludes analysis of this type

of slope failure and concentrates on another type of slide called slump.

The term slump is used when sliding of a fairly large mass takes place along

the curved surface. The slide mass is actually rotated and often the top of the

slump block is tilted back toward the hill slope (Figures 13 and 14). -Slumping
usually takes place fairly rapidly and the movement of one slump block*'can remove

up to 50 or 100 feet of bluff top. Slump blocks this large occur in southern

Ozaukee County (Reach 13) and remnants of large slump blocks are present in northern

Milwaukee County (Reach 10). Thus*, this type of failure could result in the loss

of human life and considerable property damage. The.analysis of prediction of

this type of failure is discussed under Engineering Methods.

The third major type of failure is flow. With this kind of slope failure

large amounts of.water are present and the soil mass actually liquifies and flows

like a fluid. Some flow commonly occurs at the toeof slump blocks during and

relatively soon after failure. Since slump blocks do show rotation and the top of

the block is often tilted back toward the bluff surface water can accumulate in these

depressions and saturate the underlying soil. This often creates an unstable situa-

tion and flows.away from the base of the slump block.are relatively common. Minor

shallow flows also occur when intense rains saturate the surface layer of soil or

in the spring as intergranular ice melts nearthe soil surface and.very.wet condi-

tions occur.

Minor flows can also be seen where groundwater discharges along the bluff

face in silt or fine sands. If these slightly more permeable units occur between

less permeable units, this removal of sediment by flow due to groundwater discharge

is referred to as sapping, and can cause undercutting which creates an unstable

slope in which slumping or sliding will occur.

W,4 ft,

;4 7. Pf d-

Figure 13. Oblique aerial photograph showing relatively large slump
blocks. Note the scalloped nature of the bluff top
produced by this mode of failure. In right center of the
photograph is a flow which took place after failure by
slumping. Location is T. 10 N., R. 22 E., Section 21,
Reach 13, Ozaukee County (R-13, 25).

Figure 14. Oblique aerial photograph of bluff showing numerous closely
spaced failure plains. These failures may be fairly deep-
seated. But failure is along numerous plains as opposed
to along a single plain as in Figure 15. Location is
T. 5 N., R. 22 E., Section 25, Reach 13, Milwaukee County
(R-22,12).

Effects of Groundwater on Slope Stability

Rainwater falling on the ground surface landward of the bluff face often

percolates through the soil, and enters the groundwater system. In most areas

along the Great Lakes shorelines this water moves toward the lakes and discharges

either at or below the base of the bluff directly into the lake, or out oi the

bluff at some position above lake level. The presence of groundwater in soil

mat erials of the bluff can affect stability in several ways. Just the presence

of water below the water table where all of the pores,between grains are filled

with water decreases the grain-to-grain contact pressure in the soil And reduces

the frictional resistance of the material to a stress. If water is removed

from.the soil the bluff materials become more resistant to slope failure. if

the groundwater table slopes toward the lake, as it does in most of the bluff

areas, groundwater moving-between the grains also creates a seepage pressure

in the direction of water flow. 'This pressure is especially important in gran-

ular soils such as.,sands and silts and is less important,when the-con.tent of clay

is fairly hig4, Assumptions made'in the engineering analysis about the ground-

water movement and water level are discussed in the section on engineering

methods.

If groundwater actually discharges along the bluff face some undercutting,

of materials also occurs. If the amount of water is sufficient, sapping of

material will actually take place and this contributes to the amount of bluff

recession. Removal of bluff materials by ground water is especially important

when sand units are either interbedded with fine grained materials or are

present at.the bluff top. When present at the bluff top large amounts of water

percolate through the sand until a less permeable material is reached and the

water then travels laterally toward the bluff face. In some cases relatively

large semi-circular ravines are cut along the bluff top due to this process.

An excellent example of this (Fig. 15) is just north of Grant Park in southern

Milwaukee County.

Figure 15. Oblique aerial photograph showing failure taking place because
of groundwater sapping beneath sand. Water enters"the ground-
water system through sand which is the surface material here
and flows outward along fine-grained material. Sand is then
carried by flows to the beach as groundwater discharges along
the edge of the bluff. Location is T. 6 N., R. 22 E., Section 36,
Reach 8, Milwaukee County (oblique R-20, 34).

Effects of Vegetation

The presence of vegetation, especially forest vegetation, along the bluff

face indicates fairly long term stability. Bluff faces in the protected terrace

areas (Fig. 16) show.a nearly continuous vegetation cover and very little evidence

of active slope failure. It should be noted that the vegetation cover is present

because the toe is not being undercut and because the slope is stable and not that

the slope is stable because of the presence of vegetation. The presence of vega-

tation does affect the amount of erosion that takes place by sheet wash or overland

flow of rain water. It probably also has some effect in decreasing slow types of

mass movement s,uch as soil creep. The vegetation will not, however, decrease the

amounts of bluff recession that are due to sliding and relatively deep-seated slumps

unless the toe of the.slope has been protected and,the slope angle has reached a

fairly stable position.

Changes in Slope Failure and Bluff Recession through Time

Changes.in rates of bluff recession and types of slope failure take place

over time. Lake level fluctuations change rates of toe erosion. In addition,

styles of failure on the bluffs change over even shorter periods of time.

It has been shown (for example, Berg and Collinson, 1976) that high water

levels in the Great La kes cause more rapid recession of the bluffs. When water

level is low, wave energy is expended as waves break along the beach. When water

levels rise, waves begin to beat directly on the toe of the bluff and energy

from the waves erodes the bluff material. The base of the bluff is.then undercut

creating unstable conditions in the slope above. This is followed at some

later time by'slope failure and the movement of material down to the base of the

bluff. As water levels in the Great Lakes decrease, the beach again widesn and

much of the wave energy is taken up by beach sediment transport. There is a

time lag, however, after the water drops because materials in the bluff take time

to form a stable slope. It is for this reason that recent that studies (Berg and

Figure 16. Oblique aerial photograph of wooded bluff behind natural
terrace. Most of the terrace edge is protected from erosion
by revetments. The bluff behind the terrace is stable. Loca.-
tion is T. 8 N., R. 22 E., Section 21, Reach 10, Milwaukee
County (oblique R-16,27).

Collinson, 1976) have shown that there is about a 4-year time lag:between w .ater

level highs and corresponding high rates of erosion and water level lows and

corresponding low rates of erosion along the Illinois shoreline of Lake Michigan.

Thus, even after water levels begin to fall and wave erosion is.decreased, bluff

recession aDntinues at a fairly high rate until the bluffs have reached a stable

slope angle.. It can be seen then that knowledge of the nature of the material in

the bluffs and the kinds of failures that are taking place is important in determining

any short-term measures to reduce the rate of bluff retreat.

Short-term changes in rate@ of toe cutting and bluff retreat also occur.

During the'winter, ice often protects the toe from wave erosion and relatively

little cutting takes place. In spring, melting of intergranular ice.produces wet

conditions and shallow slides and flow are common., Edil and Vallejo (1977, in press)

have done detailed studies of bluff retreat at Port Washington and Kewaunee. They

suggest that in moderately high bluffs at Kewaunee where the middle and lower bluffs

consist of silty clay, slope-evolution is by nearly parallel retreat in the middle

parts of the slope, caused by shallow translational slides an d flow (Fig. 17). Port

Washington, where higher bluffs occur, the slope seems to begin evolution by a

series of slumps working their way from the toe up to the bluff top. This changes

a convex bluff profile to a concave one with a steep top and a flatter lower por-

tion (Fig. The next phase is retreat takes Place by slumping in the upper

parts of the bluff terminating in a uniform slope.

Parallel
Retreat

Removal of 4%
Too Material

Wate
prin

Weathering Non-Parallel
and Retreat
Mudflow

Figure 1.7. Diagramatic sketch of slope evolution along the bluffs
at Kewaunee, Wisconsin (from Edil and Vallejo, in press).

Too Ero*Lm Shallow Slidas. Composite
Removal of Toa Slope.
material

Top Retreat Removal of Uniform
Too Material Slope

Figure 18. Diagramatic sketch showing slope evolution along the
bluffs at Port Washington in Ozaukee County (from Edil
\ Et&

and Vallejo, in press).

GENERAL SHORELINE CONDITIONS

Throughout the reaches studied during this investigation, a wide variety

of shoreline types and associated erosion processes were described. Although

detailed information about specific localities is available in the appendices and

should be used if available, in this section we discuss general shoreline cond'i-

tions of Lake Michigan and Lake Superior, and'provide some specifics'on reache s

examined'in detail.

Very little of the shorelitle is bedrock. In Bayfield County, especially on'.

the Bayfield Peninsula, bedrock makes up the lower or sometimes,the complete bluff.

This bedrock, primarily Precambrian-age sandstone, is somewhat more resistant to

wave erosion than the unconsolidated glacial desposits., There are, however, areas

where erosion of the sandstone is taking place. Similar sandstone bluffs occur

on Madeline Island and other of the Apostle Islands. Paleozoic age dolomite bed--

rock outcrops occur on the beach in a few places in Racine, Milwaukee, Sheboygan,

and Manitowoc Counties, but bedrock does not make up a substantial amount of the

bluff in any of those areas. In Door County numerous bluffs are made up of dolomite,

but these areas were not studied in this project.

Since past glaciation is primarily responsible for the pres ence of bluff.

materials, the glacial history of the Great Lakes is discussed before the individual

reach descriptions.

Glacial History

The Great Lakes basins were deepened and widened during glaciation which

took place over the last one to two million years. Glaciers flowed out of the

north and northeast down the Lake Michigan basin into Illinois, down the Green Bay-

Lake Winnebago lowland to a position near Madison, and down the Lake Superior basin

into northern Wisconsin And Minnesota (Fig. 24). Successive ice advances and

retreats have left a series of unconsolidated deposits which, except in the bedrock

areas of Door County and the Bayfield Peninsula,,make up the bluff materials.

Lakes larger than today's formed in the basins between each succeeding glaciation and

so the layering which is observed in the bluffs records a geologic history of al-

ternating.lake,� and glacial cover. In some places where glacial deposits.are

relatively thick or are-at higher elevations, the height of the bluff is well over

100 feet. In other places where glacial deposition and erosion left the land surface

at lower elevations the bluff heights are considerably lower or are nonexistent.

Lake Michigan

Although numerous ice advances contributed to the formation of the Lake

Michigan basin, only the last few have left a record of deposits which are now

exposed in the eroding bluff. Materials deposited directly by glacial ice are called

till. Till is usually poorly sorted (has,a large range in grain size) and it usually

does not show stratification or layering that is typical of water-deposited sedi-

ment. The till deposited by a single ice advance is usuall y relatively uniform

over a fairly large area and thus mapping and correlation of the tills allows the

development of a stratigraphic framework which gives some order and predictability

to the aerial and vertical distribution of deposits.

Details of the distribution of glacial deposits in the area along Lake Michigan

are given in Alden (1918), Goldthwait (1907), Thwaites and Bertrand (1957), Brunning

.(1970), and Mickelson and Evenson (1975). Many tills have been named in Illinois

(Willman and Frye, 1970; Lineback, Gross, and Meyer, 1974), but in this report

tills will be numbered and correlation with Illinois.tills will be suggeste d.

A summary of these units is shown in Figure 19. Grain size of the tills is given in

Figures 83, 84, 85.

The oldest till exposed along the Lake Michigan shoreline is a coarse, sandy

till (usually over 40% sand) with a large number of cobbles and boulders (till lAt

Fig. 19, 20, 21). This was probably deposited before 14,000 years ago, and

probably correlates with the Haeger till of Illinois. In the southern part of

TIM.E- STRATIGRAPHIC ROCK - S TIRA71GRAPHIC
UNITS (SUBSTAGES) UN17S

io3yr
420 N 43ON 440N 4501N 4 6 ON

z SOUTH END CHICAGO IV, H-W A U K E TWO CREEKS MACKINAW CITY
L. MICHIGAN
< Sands -Sturge" JVCrGl@fle -r
_j
0 30 60 90 120 Km
<
Maii7LckeAlgoiqui'nsedimen,",__-.

LL
T'v%'O RiVERS.111
12- T WOCREEKAN X TCFB L A K E SE D TI
and FOREST BE'DS
Inner Port Huron

MAN!TOVVCC TILL IVEIR.'.
Outer Port Huron 3 C

13- '.''SHOREWOCD T !L L M, R. 0
z
< Cary -Port Huron interstode CBB x----7,-

0.
LL
0 Q B.Loke Border Drifts
0
1.4- 0 Tinley Drift WADSWORTH TILL IVIBR.. Q@

VdIparciso Drifts
i@ - Z4
AlAef_G@F 7/

Figure 19. Time distance diagram showing the extent of glacier ice i.n-the Lake Michigan basin
during late Wisconsin time. Terminology used on the right . i:s that used in Illinois,
in.
with the exception.of the Two Rivers till which has been formally named in Wiscons,
The numbered units are used informally in this report. Note that distances of
advance are in center of lake and extent on Wisconsin sho.re.is somewhat less than
@e Bo@der 6,1fts.

shown. Modified from Evenson (et al., 1976).

Mockinac Sl i

+
SANDS- STURGEON MORA INE' . CBB,
Indian River
SL f Little Traverse Bay 0
ACK
19166,J
0

010 VALDERS of
MELHORN, 1954
MICKELSON and P0
EVENSON, 1975
4CF8
THWAITES TWO RIVERS M. c)
19143 VaIders a Rivers Manistee
TWO RIVERS
TILL LIMIT
..... .- Ludington
VALDE Sje@@"%
TILC MANITOWOC TILL ""-SAGINAW
Of BRETZ
1991 LOBE
LAKE
Muskegon BORDER
MORAINES
Milwaukee SHOREWOOD TILL
I (TI 113 A,
CARY P11
TILC

Wisc.
Fl F

WADSWORTH TIL
HAEGE
TILL
(Till 2.)
Mich.
(1r, I Chicago - - - - - - -
I ncf.
50 MI.
4- 80 KM

Figure 20. Map of the Lake Michigan basin showing the approximate.
extent of tills mentioned in this report. Modified
from Evenson et al.., 1976.

Figure 21. Oblique aerial photograph of the bluff showing beach
littered with-boulders where till 1 is exposed at the
base of the bluff. Location is T.6N., R.22E.,
Section 24, Reach 8, Milwaukee County (oblique R-20,
14).

the state, in Racine and Kenosha Counties, this till is below lake level and the

southernmost exposure of the till is just south of the city of Milwaukee.in

Reach 8, Sections 23 and 24 (see next chapter). Here it is exposed in the lower

.10 feet of the bluff where it contributes a great deal of coarse material to the

adjacent beach (Fig. North of the city of Milwaukee, till 1 is exposed more

commonly near the base of the bluff all the way into Kewaunee County.

Till 1B, a thin, grey, usually sandy-silty till (Fig. 19) directly overlies

till 1A at many localities. This till is generally much less cobbley and bouldery

than 1A. It is usually only 6-10 feet thick. It is not cleat whether,a till

correlative with this occurs to the south in Illinois or on the surface west of

Lake Michigan in Wisconsin. Since no large amount of lacustrine sediment has been

seen between tills IA and 1B, they may represent the same,episode of glaciati on.

As the ice which deposited this till retreated into the lake basin an ice marginal

lake existed for a short period of time throughout the area of the present lake.

However, another glacial advance which took place approximately 13,500 years ago

came out of the lake basin at all points and destroyed much of the evidence of these

former lake s. This later advance deposited a much finer grained till, (till 2),

probably because of the. incorporation of the lake sediments which had been deposited

earlAer (Fig. 19). This till (till 2) is called the Wadsworth till in Illinois

and it makes up much of the bluff in Kenosha, Racine and Milwaukee Counties. it@

is.also present, although much thinner, towards the northat least into Ozaukee

County. The ice advance which deposited the Wadsworth till was actually probably

several ice advances very closely spaced in time and in some places lake sediment

is between nearly identical till units (Fig. 19).

Units A, B, and C of till 2 can be distinguished in some places such as

southern Milwaukee County (see next chapter) but, because the units are so nearly

identical, they cannot be separated without physically tracing the units. In

.northern Racine County and north of Milwaukee, exposure is insufficient to sub-

divide the units within till 2. For all practical purposes, the units are the

same 'as far as their physical and engineering properties.

As the glacier which deposited this till retreated into the northern part

of Lake Michigan Basin, a lake (called Glacial Lake Chicago) filled the southern.

part of the basin anddrained through an outlet near Chicago into the Mississippi

River. The elevation of the highest shoreline features and lake deposits from this

lake are now at an elevation of 640 feet (called the Glenwood Stage, Fig. 22) or

about,60 feet above the present lake level. Fairly well developed beaches are

present in Racine and Kenosha Counties and also in southern Milwaukee County where

they exist as ridges of sand roughly parallel to the 640-foot contour. Thus, all

of the bluff south of Milwaukee which is at an elevation of less than 640 feet.

has till 2 capped by sediments deposited in this lake. The grain size of-the

sediments varies from sand near the edges of the former lake to silts and clays

which were deposited-in deeper, quieter water.

Approximately 13,000 years ago glacier ice again advanced (Fig.19 down the

Lake Michigan basin and this time st.opped just at the city of Milwaukee. The tex-

ture of. the till of this advance (till 3A) is roughly'the same as that of till 2

although it has more sand and a reddish cast which is not present in Racine and

Kenosha Counties (Fig. 19). South of the glacial border of this so-called Port

Huron advance (Fig. 22), glacial Lake Chicago remained at the Glenwood (6401) level

throughout the time ice was in the Lake Michigan basin. Another similar reddish

till (till 3C) was deposited by a slight readvance of ice very shortly after this.

In a few places between (see reach reports) a sandy unit (till 3B) exists.. This

may represent a readvance of ice or simply debris dropped from floating ice.

As the ice finally retreated out of the northern part of the basin a new

outlet developed at the Straits of Mackinac and the level of the lake dropped from

the Glenwood Stage to some level below present water level. At this time

LAKE STAGES OF THE MICHIGAN. BASIN

4 '00

WtW
-j zz
0
0 0 04Z 0 0@
0 .2
0
01

Ir D 0
<z
WUj L' 0
01 0 > n1d W*
M, M 0: x
to W @L' ,
x0- 'x :3
Wz x W
_5 9L

Figure 22. Diagrammatic sketch showing the fluctuation of lake
levels in the Lake Michigan basin after the retreat
of glacier ice. From Hough, 1958.

49,

(about 12,000 years ago) spruce forests were present along the e.dge.of Lake Michigan

,and as ice again advanced into the Lake Michigan basin near the Straits of Mackinac,

the northern outlet was blocked and the water level rose flooding the spruce forest

and killing the trees. Parts of this buried forest are preserved today in the

lake bluff in Manitowoc and Kewaunee.Counties (Black, 1970). At onelocation at

the Manitowoc-Kewaunee county lines (Black, 1974) this Two Creeks forest bed, is

being preserved as a state park. When lake level rose again it probably returned

to the Glenwood level, but while ice was still at its terminal moraine near the

city of Two Rivers the water level dropped to the lower Calumet stage at approxi-

mately 620 feet (Fig. 22). The level of the lake did not rise again to the Glenwood

level; thus, there are no Glenwood shorelines north of the city of Two Rivers

(Fig. 23). This ice advance (Fig. 19) which covered the Two Creeks forest bed,

deposited a clayey, red-brown till (Two Rivers Till) with very few pebbles or coarse

material. After about 11,000 years ago ice retreated from the Lake Michigan basin

for the last time.

Since that time, lake levels in Lake Michigan have fluctuated because of

changes,in outlet position, erosion of the outlets, and changes in elevation of the

outlets due-to glacial rebound. Although for short periods of time the lake was at

a variety of different levels the best beaches that developed in these later lake

stages are at an elevation of about 605 feet (Fig. 22). These were cut during

three stages of Lake Michigan, the Toleston stage, the Algonquin stage, and the

Nipising stage. At the present time, old lake bluff and a wave cut terrace at

this elevation at some locations. Most of the terraces which are 15 to 20 feet

above.present lake level in the Lake Michigan counties are due to erosion at this

time.

Lake Superior

Early glacier advances of the Lake Superior lobe into northern Wisconsin

deposited a sandy, bouldery till much-like that deposited in the 15,000 year old

Kewounee

r -
Manistee

\Two Rivers
OVAL"Its Manitowoc

-OLudington

Pentwoter
Sheboygan

A-4

Port Washington

Muskegon

MILWAUKEE

Racine Hollan

Kenosha

South Haven
Waukegan
North Chicago

Benton Harbor

GREATER
CHICAGO

MICH. I
Michigan City . .. . ..
IND.

Gary

0 10 20 MILES
k
0 10 20 30 KILOMSTERS

Figure 23. Map showing the extent of the Glenwood Stage (640' if
elevation) of Glacial Lake Chica o. The dashed line
9
represents the furthest extent of ice which deposited
the Two Rivers till and destroyed earlier beaches at
this elevation. From Evenson, 1973.

103.57
COASTAL ZONE
INFORMATION CENTER

ACKNOWLEDGEMENTS

The Shore,Erosion Administration Committee, consisting of S. Born,,

G. Hedden, T. Lauf, A. Miller, M. E. Ostrom, G. Pirie, P. Tychsen,, N.

Laska, and several of the authors, assisted greatly in the planning and

initial-phases of this-project. We especially wish to thank S. Born

and A. Miller for assistance in the planning and for advice and sugges-

tions throughout the study eriod. M. E. Ostrom, State Geologist, also
'IF
contributed a great.deal to the planning and operational phases as well

as the administration of thp project.

Wewould also.like to thank those who assisted the authors in the

field and laboratory; 0. Brouwer, R..Chiang, E. Domack, R. Goodwin, R.
,Guzman, M.@C. McCartney, G. Morris, J. Pelham, R. Peters, T. Smart and

E. Smith.. Their help in the field parties, with drilling, sample processing,

and with drafting, is greatly appreciated. We thank Norman H..,Feverson,

technician in the Geotechnical Laboratory at the University of Wisconsin-

Madison for greatly assisting in the processing of samples. Students that

worked under his direction were G. Hossein Bahmanyar, Tom Wolf, and David

Bennett. We would also like to thank Luis Vallejo for his discussions and

ideas on the project and also for computer processing some of the later data.

Thanks also go to J. Mengel, who provided information on Lake Superior.

Thanks also go to Mr. John Perry of Owen Ayers Associates for his

suggestions in the early phases of the project, his comments in the field,

and his comments on an early version of part of this report. W. Rehfeldt

of Donahue and Associates also contributed helpful comments on an early

part of this report.

We would also like to acknowledge municipal employees and private

citizens who gave permission to drill geotechnical holes on their property.
V@

Additional geotechnical information was provided by M. Harrigan of the

Village of Shorewood, A. Wagner of Soil Testing Services of Illinois, Inc.,

the City of Milwaukee, Department of City Development, J. Rose, Mrs..E.

Knaack, L. Sivak, of the City of Oak Creek, D. Weiss of the Village of

Whitefish Bay, and W. Murphy of Marquette University.

The Technical and Citizen Advisory Committee on Coastal Management

in southeast Wisconsin (Southeast Regional.Planning Commission), the Bay.

Lake Citizens Advisory Task Force on Coastal Zone (Bay Lake Regional

'Planning Commission), and toe Coastal Zone Intergovernmental and Technical

Advisory Council (Northwest Regional Planning Commission) also helped in

providinginformation on the public perception of the erosion problem.and

contributed to developing a study plan.

Financial assistance for this study has been provided through the

Wisconsin Coastal Man agement Program by the Coastal Zone Management Act

of 1972i administered by the Federal Office of Coastal Zone Management,

National Oceanographic and Atmospheric Administration. Financial assis-

tdrice was also provided by the Wisconsin Geological and Natural History

Survey, University ofWisconsin-Extension.

advance in the Lake Michigan basin* except that it is red-brown ins.tead of buff

in color. This till extends to a terminal moraine which enters the state from

Minnesota near the town of Hudson and continues eastward just north of Eau Claire

to the town of Antigo in Langlade County (Fig. 24),. Although the date of this

advance is not confirmed,,'@radiocarbon dates in Minnesota (Wright, 1971).suggest

that ice was at its terminal position between 16,000 and 18,000 years ago. As in

the Lake Michigan basin, the ice retreated from its,maximum position in a series of

steps with minor readvances between. Most of the till present along the shoreline

of Lake Superior in Wisconsin is more clayey and silty than earlier tills and was

deposited during these later stages of ice retreat. The extent of these readvances

has been well documented in Minnesota (Wright, 1969), but relatively little is.

known about the extent of these advances in Wisconsin, although some work has been

doneL(e.g., Leverett, 1929; Farrand, 1969; Mengel, 1970).

At.some point.during the retreat of glacial ice, a lake called Glacial-Lake

Duluth (Fig. 25) formed along the Ice margin and this lake was present throughout

much of'.1'ate glacial time in the Lake Superior basin. The highest shorelines of

this lake'4xceed 500 feet above present lake level and can be seen on topographic

maps in Douglas, Bayfield and Ashland Counties. In this areaa thick,sequence of.

lake sediment primarily composed of silt and clay makes up the bluffs. In some,

-locations the underlying@till is exposed fairly close to water level. Compared to

Lake Michigan very little coarse material is available to the longshore dirft

system within the.lake, and with the exception of areas around incoming streams,

....shoreline erosion is prevalent in the areas where unconsolidated material makes

up the bluff.

The great extent of fine-grained lake sediment and till back from the shore-

line creates a large volume of suspended material which enters the stream system

and then enters Lake Superior. Silts and clays in the eroding bluffs also contribute

Figure 24. Glacial map of the state of Wisconsin. Note the extent
of lake sediment around the Lake Superior shoreline.

WISCONSIN GLACIAL DEPOSITS
2 after Thwaites, 1956

0 40 80

SCALE OF MILES

. . . . . . . . . . . . . .

LEGEND

End Moraines

Ground Moraine

F7771 Outwash, unpitted

Outwash,'pitted

Lake Basins

Drumlin Trends

University of Wisconsin
Wisconsin Geological and Natural History Survey
George F. Hanson, Director and State Geologist

LAKE STAGES OF THE SUPERIOR BASIN

Uj
>

> 2
>
W

t.-O

UJ
C, 4
jj.
0
0

Ir
7
z W Co
0. 6 La
0 > S
a.

Cr
.".3 W :) 0@ Qj
0-
0 IL

Figure 25. Diagrammatic sketch showing the fluctuations of lake
levels in the Lake Superior basin from glacial time
to present. From Hough, 1958.

to a high-suspended sediment load in coastal Lake Superior water, especially off

Douglas and western Bayfield Counties.

Glacial Lake Duluth did not rise and fall in a series of stages as Lake

Michigan did,but remained at a fairly high level (about 1,000 - 1,100 feet above

sea level along the Wisconsin shoreline) (Farrand, 1969) while drainage from the

lake went through the St. Croix River system and into the Mississippi drainage.

As the retreating glacier ice reached the Keweenaw Peninsula water from the ice-

dammed lake began to drain across the Michigan Peninsula and into the Lake.Michigan

basin. A minor readvance, possibly correlative with the post-Two Creekan readvance

in the Lake Michigan basin evidently took place at about this time because in

eastern Ashland and Iron Counties a thin, red-brown, clayey till overlies the lake

sediment in the bluff.

As the ice continued to retreat lake levels in Lake Superior dropped in a

series of short-lived stages (Fig. 25) to an unknown level when water began draining

out the present Lake Superior outlet. By this time glacier ice had retreated from

the Lake Michigan basin and Lakes Michigan and Superior stabilized at a level of

605 feet (Nipissing stage). Since that time lake level probably dropped for a few

thousand years and then has risen to its present level of about 600 feet above sea

level. Throughout much of the lakeshore, lake level continues to rise very slowly

(with fluctuations due to climat e) because of the glacial rebound of the lake outlet.

REACH DESCRIPTIONS

This chapter includes a general description of the shoreline from the Illinois

state line to Manitowoc on Lake Michigan and the Wisconsin part of the Lake Superior

shoreline. Much more detailed information is available in county appendices (see

list of appendices at beginning of this report) which can be obtained fran the

State Planning Office,

Reach 1

Erosion reach I of the Lake Michigan shoreline is located in southern Kenosha
County, in Township 1 North, Range 23 East (Fig. 26.). The reach is about 4-L
2

miles long and extends from the Illinois state line on the south to the Kenosha

city limits on the north; it thus includes the entire stretch of shoreline known

locally as Carol Beach. This 4-L-mile segment is considered to be the most critical
2

reach of the entire Lake Michigan coast in terms of.shore damage and recession rates;

it has the highest priority of all reaches, with a per-mile value of 32. The

reach is discussed in detail in Appendix 1.

The northernmost half-mile of the reach is owned by the Wisconsin Electric

Power Company and is currently unused except by trespassing motorcycle enthusiasts,

who have desecrated a beautiful and scientifically valuable coastal area of sand

dunes and natural prairie. Except for this power company property and the Trident

Marina development at the extreme south end of the reach, the entire reach is sub-

divided into residential lots. Although the density of houses is considerably

lower than in some other n.on-urban segments of the shoreline, new home construction

was very apparent during the summer of 1976. In contrast, during the past few

years a number of houses have been destroyed as a result of shoreline recession or

have been relocated in order to prevent their destruction.

Beach widths in Reach I range from 0 to about 110 feet. Variations in beach

width over short distances are common throughout the reach, most of the changes

being controlled by shore protection structures. In one area, for example, the

12 X
R 61CH 3
Paris PA I OR 13 s9m RS
hWn S 43 LAKE
i2

- -----------------
2 30

REACH 2
J
a-d 50 Kenosha

R ------------------

P
@MICHIGAN
Maui
EA N RAIRIE
REACH 1
Tim A -a
23 174
Tobi h

42'M
MCC j----jj I, - - - - - - - - - - - - -
U%4 32
STATE OF ILLINCiS
0-21-E + B-22-E

RE-NOS11 A CO
0 DEPARTMENT OF TRANSPO-R-tATIO-N
DIVISION OF 11IGHWAY9
STATE MKI BV" 0111C
#Asp. v#Wmj4

-Figure 26. MaP Of Kenosha county showing the locations Of Reaches
2 and 3, and geotechnical site 9.

beach widens from 15 feet to 110 feet in less than a quarter-mile; at another

locality, the width increases from 10 to 100 feet in a still shorter distance.

In both situations virtually no beach is present immediately to the north or south.

Man's extensive modification.of the shoreline is largely responsible for those

changes. Natural beach materials everywhere consist mostly of sand with smaller

quantities of gravelly constituents (pebbles and small cobbles).

The bluff in this reach is low. Typically, it is only'4 or 5 feet high and

nowhere does its height exceed 20 feet. In many places a bluff, as such, does not

actually exist, the rise from lake level to the upland surface being nothing more

than a gentle beach slope. In other places, however, a distinct bluff is present,

generally ranging in height between 5 and 10 feet. The highest bluff-occurs in

section 17 at the north end of the Carol Beach area adjacent to the,power company

property, where the bluff is 18-20 feetbigh.

Throughout this entire reach, the bluff is composed of fine-to coarse-grained

sand. Genetically, most of the sand is beach sand deposited during an earlier and

higher 1.ake stage (Fig. 22), but in some places, particularly where the bluff is

higher, the upper part of the bluff is made of dune sand. Thin organic horizons,

mostly organic sands, are interbedded with the beach sands at several exposures.

No deposits of till or fine-grained lacustrine deposits were observed in any of

the bluff exposures.

Shore protection structures are very abundant in Reach 1. Approximately 175

such structures,were identified and described, despite the fact that a single

structure--a newly constructed dolomite rip-rap revetment--protects the shore for

the full half-mile of the electric company's shoreline at the northern end of the

reach. For the remaining.4 miles of the reach, the density of protective struc-

tures averages about 42 per mile; in one section alone (section 17) there are

nearly 60 individual shore protective devices. This is undoubtedly the highest

density of individual structures along the entire Wisconsin coast.

Slope,failures in Reach 1 occur main ly through the mechanism of slump,

induced by oversteepening of the bluff face by wave action at the toe. Asa

result, the bluff edge in many places is finely scalloped, particularly where

shore protection structures are absent. Sand slides and sandflows do not appear

to present a severe problem, despite the presence of seep zones within the sand

units that compose the bluff.

Reach 2

Reach 2, in Townships 1 and 2 North, Range 23 East, covers 3 miles of

shoreline in central Kenosha County (Fig. 26). It is virtually coextensive with

the City of Kenosha, extending from the southern end of Southport Park northward

through the downtown and harbor area to the north end of Lake View (Kennedy) Park.

The entire shoreline is protected with stone revetments and other structures, with

the exception of short segments of public bathing beaches at Southport and Simmons

Island Parks. For this reason and also because of the low rank accorded this reach--

priority rank number 28 with a per mile value of 4, the only part examined systemati-

cally was a half-mile stretch of shoreline at Southport Park. Data on beach condi-

tions and shore protection structures were also obtained in Eichelmann Park. These

are given in Appendix 1.

Except for the bathing beach area, where the beach is 50 to 100 feet wide,

no beach is present in the Southport Park segment. The bluff is only 5 to 10

feet high, and both bluff and toe materials are everywhere concealed by a continuous

stone revetment. Although materials are not exposed, the bluff is probably composed

of sand. The segment is marked by approximately 12 additional structures, most of

which are old groins that.are today largely non-functional and in need of repair.

Small areas of sand accumulation are found adjacent to one or two of these groins,

but even here the beach is less than 5 feet wide.

Reach 3

Erosion reach 3 of the Lake Michigan shoreline is located in northern

Kenosha and southern Racine Counties, in Townships 2 and 3 North, Range 23 East

(Fig. 26). It is one of the longer reaches of the shoreline, having a grid
length of exactly 6 miles and an actual shoreline distance of approximately 621

miles. Geographically, the reach can be thought of as a suburban coastal corridor

that connects the City of Kenosha on the south with the City of Rneine on the north.

Except for only three or four small areas, including the Town of Mount Pleasant

fire station and park property near the north end, the entire northern three-fourths

of the reach is subdivided; most of the lots are occupied by single-family residences.,

but a few are used for apartments and small businesses. Immediately to the south

is the campus of Carthage College, which extends along the shoreline for a distance

of more than one-half mile; the rest of the southern quarter is reserved for rec-

reational use and is the site of Alford and Pennoyer Parks, which together are about

6,000 feet in length.

Reach 3 was ranked as the ninth most critical stretch of Wisconsin's Lake

Michigan shoreline, with a per mile value of thirteen. In view of the considerable

property damage and shoreline recession that is currently taking place throughout

much of this reach, it would appear that the reach should be assigned a somewhat

higher priority. Details on the reach are given in Appendix 1.

Beach conditions in this reach are extremely variable. Beach width, in

particular, exhibits great variability, ranging from complete absence of a beach

in many places to the presence of an extensive beach that exceeds 275 feet in

width. The most marked change in conditions occurs near the south end of the

Carthage College campus, approximately 6,000 to 6,500 feet north of the southern

boundary of the reach. North of here the beach generally ranges from 0 to 40 feet

high, but at the south end it is generally 10 feet or less in height. Whereas

the bluff is virtually continuous throughout most of the reach, in the southernmost

mile it is distinctly discontinuous, as a result of the upland surface near the

shoreline having been narrowed and in places completely removed by normal erosional

processes near the mouth of the Pike River.

Bluff and toe materials in this reach also exhibit a systematic change from

north to south. In the upper part of the reach the lower two-thirds to three-

fourths of the bluff is composed of calcareous silty clay till (till 2); the till

is overlain by interbedded fine sands, silts, and clays of lacustrine origin (Fig. 27).

Nearly one mile south of the Racine-Kenosha County line the till-lacustrine con-

tact descends to lake level, with a corresponding thickening of the lacustrine

sediments, and thence disappears below lake level to the south (Fig. 27.). still

farther south, the lacustrine deposits tend to become more massive in character and

also finer grained. The bluff is everywhere capped by fine to coarse-grained sand

deposits, which were probably deposited in a beach environment. At the southern end

of the reach, however, the low bluff appears to be composed almost entirely of sand,

suggesting that the contact between the sand and the underlying lacustrine sediments

has also dipped below modern lake level.

Shoreline protection structures are very abundant in the northern three-fourths

of reach 3. Approximately 180 individual structures were identified and described

in the 5-mile segment of shoreline that lies north of Carthage College. These

structures consist of a great variety of both shore-parallel and shore-normal devices,

as well as earthen and man-made materials used for fill. The Carthage campus is

protected by a continuous dolomite rip-rap revetment. South of here, in Alford

and Pennoyer Parks, modern shore protection structures are absent, the only struc-

tures being a series of 40-year old semi-permeable groins that are largely des-

troyed or buried beneath the broad accretional beach deposits described above.

Except for the Alford and Pennoyer Park areas, shoreline recession and slope

failure are serious problems throughout the entire reach. Some houses have, in

fact, collapsed during the course of the present study and many additional homes

T. 2 N. Kenosha Co. Racine Co.

I C) U

43*

LZ 2 A

30 19 18 8 5 32 28

CGvM RED OR Figure 27. Generalized longitudinal
SAND I LT section showing bluff
UNA'-' CES SiCLE
stratigraphy in Reach 3.
Numbers along base of
GRAVEL CLAY TILL diagram are geographic
(1 mile) sections.
SAND AND D
E L SP-TY CLAY S ED, I M -P IN T S

situated near the bluff edge are in danger of being destroyed within the near

future. Toe erosion by wave action, gully cutting by small streams and by storm-

water drainage spilling over the bluff, rotational and planar motion of small to

moderate si ze slump blocks at the bluff edge, sapping and undercutting within the

bluff caused by water issuing from the more permeable layers-espec1ally at the

contacts between layers of differing permeability within the 1acustrine sequenc e,,.

and mudflows in the clay-rich till and fine-grained lacustrine sediments are all.

active mechanisms of slope failure-in this reach.

Reach 4

Erosion reach 4 extends through the southern and central parts of the city

of Racine in Township 3 North, Range 3 East, Racine County (Fig. 28);. It is

approximately 3-1 grid miles and 3 3/4 shoreline miles in length. The northern two-
4

thirds of the reach is marked by continuous shore protection structures, principally

in the form of offshore breakwaters and shoreline revetments. These structures

provide protection for the Racine harbor facilities aid industrial sites on the

north, Pershing Park and the downtown business district in the central part, and

residential properties farther south. As a direct and indirect consequence of

these structures, reach 4 received a relatively low priority for the purpose of

this study, ranking twenty-ninth on the priority list with a low valueper mile

figure of three. Accordingly, only the southern half of the reach was examined in

our investigation and the following summary of conditions is restricted.to this

portion. The northern and southern parts of this segment are residential in

character, with the longer intervening strip being occupied mostly by the City

of Racine sewage treatment plant and the J. I. Case Co. tractor plant. Detailed

maps are given in Appendix 2.

Most of the shorelinehas no beach, mainly because of man's past and current

activities. For the most part, the shore is.armored with extensive stone

(dolomite) revetments constructed at the base of the bluff and steel (sheet piling)

Oak Cmk z

T REACH 6
D C

Bay
Fca IREACH
9r4f

-- - - - - - - - -

38
IREACH .4
[Racine

Ur*W nt

T NT
Al I Pod ItEACH 3
;d nk K

Two d fti 7 M
41
1W

RACINE CO.
'UPAItTMEN Oil TRANSMUTIN 4
olvillam OP NIGMAVI
IrAll G"E BUILM"

aches
unty showing the locations Of Re
28-: Map of Racine CO si es 4 5 and 10
Figure 4, .5 and 6,:and geotechnical tI

bulkheads built some distance offshore and completely backfilled to form made

,land. In some places, however, notably south of the Case tractor plant, a narrow

and discontinuous beach does exist. Nowhere was it found to be more than 10 feet

wide and generally It is between 0 and 5 feet in width. Beach materials consist of

gravel, broken concrete, stone, broken asphalt, dead trees, old lumber, cinders,

iron, and slag from the old Case foundry.

The height of the bluff in the southern part of reach 4 nearly everywhere is

about 40 feet. Bluff materials and toe materials in all.but' the southernmost 1,500

,feet of the reach appear to consist mostly of artificial fill composed of stone,

brick, glass, concrete, iron, slag, and garbage. In places where natural deposits

can be seen, chiefly at the south end of the reach, the bluff is made of inter-

bedded clays, silts, and sands of lacustrine origin overlying calcareous gray silty
clay till (till 2).' The contact between the till. and:the overlying lake sediments

occurs about a third to hal,f-way down from the top of the bluff (Fig. 29).

Although much of the bluff has been graded and grassed and appears to be fairly

stable, slope failure is evident in several places. It is most severe along the

virtually unprotected shoreline south of the Case factory at the southern end of

the reach. Much of the failure is directly related to the presence of multiple

seep zones within the more permeable beds, especially the sand layers, in the

lacustrine sequence, particularly where the more permeable layers.rest on the clay

till and on a massive pink clay layer in the lower part of the lacustrine unit.

Failure occurs mainly in the form of flows and small slump blocks. Toe erosion

is. also an important erosional process.

Reach 5

Reach 5 runs through the northern part of the City of Racine, through the

village of North Bay, and about half-way through the village of Wind Point, in

Townships 3 and 4 North, Range 23 East, extending from the north end of the Racine

harbor structure to the mid-line of the Wind Point headland (Fig. 28). The grid

(Arcl)

OD @t.

OD
F1

0 x 0 <
;@ I n 0 m
0 7J
rn

C'L Z M (A rt 0 CD
F- H. r- ?1 :3, r- (D
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rm u :4 H. m
" m Fj* z @lt
F- W " 0 D) 43
m El co m H CD
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length of the,reach is 3 miles; the shoreline distance is 3-@ miles
2

About 55% of the reach is public land. The southern mile is occupied by

the Racine public beach, Lake View Park, and the Racine Zoological Park. Shoop

Park to at the north end of the reach. The remaining 45% of the shoreline is

residential in character, with most of the properties In northern Racine and North

Bay being in,the $100,000-plus category. Reach 5 was rated tenth in the ranking

of critical erosion areas, with a per-mile value of 13, the same as Reach 3.

Detailed mpas are given in Appendix 2.

The beach in Reach 5 ranges in width fran 0 to almost 300 feet. It is widest

.at the south end, where the north-south longshore current is obstructed and the

sand supply is effectively trapped by the harbor structure. Low dune ridges indi-

cate that some of the sand has been reworked by the wind. Northward the beach

gradually narrows to zero within a mile. Elsewhere in the reach, however, abrupt

and very substantial changes in beach width are common.

Much of the shoreline is heavily armored with various types of shore-parallel

and shore-normal protective structures, especially in the residential segment.

Approximately 85 such structures were identified and described in slightly less

than 2 miles between the Racine Zoo and Shoop Park. The effectiveness of these

structures, especially the more recently built groins, is readily apparent from

the abrupt changes in beach width and the locations of eroding and non-eroding shore-

line segments. Virtually all of the well constructed groins are trapping sand on

their updrift (north) sides, and it is this process that accounts for the common

and abrupt changes in beach conditions. Poorly protected and unprotected segments

of the shore are subject to severe wave erosion at the toe of the bluff, debris

fall and flowage higher on the.slope, and slump at the top of the bluff; scalloped

bluff edges are not uncommon in this reach, even though much of the bluff has been

graded and grassed.

Bluff height ranges from slightly under 20 feet to just over 30 feet.

67 COASTAL ZONE
INFORMATU CENTER

Exceptions occur at stream mouths, in places where the bluff has been terraced or

otherw ise modified by man, and at the northern end of the reach in Shoop Park.

Here the bluff splits, and a low natural terrace separates the shoreline from the

main upland surface. At the northern end the terrace is about 750 feet wide. The

shore bluff along the terrace is generally between 5 and 10 feet high, but it is

virtually absent at the northern boundary of the reach.

Much of the bluff is covered by vegetation, and in many places it is composed

of artificial gray (where unoxidized) or tan (where oxidized) silty clay till (till 2)

overlain by lacustrine deposits (Fig. 30). At several places a thin layer of water-

bearing sand or sand and fine gravel occurs slightly above mid-bluff height, between

the till and pinkish-brown lake clay. Water seeping from this horizon, and also

from other zones within the lacustrine beds, are undoubtedly a major cause of slope

failure involving slump.

Reach 6

'Erosion reach 6 is located in Townships 4 and 5 North, Range 23 East, in

northern Racine County and southernmost Milwaukee County (Fig. 28). It extends

from the mid-line of the Wind Point headland northwestward to the north end of

the bulkhead that protects the coal stockpile for the Oak Creek power plant.

Although the north-south grid distance of the reach is about 4.6 mile s, the coastal

distance is fully one-third again as long--more than 6.1 miles-due to the northwest-

southeast orientation of the coastline. Detailed maps are given in Appendix 2.

Reach 6 has one of the highest priorities of the entire Lake Michigan shoreline,

ranking third in the listing of critical erosion areas, with a value per mile of

25. Land use and shoreline characteristics cover a wide range. Much of the land

is residential property, but some is used for agricultural,purposes, some is un-

developed to partially developed recreational land (including both County of Racine

and Town of Caledonia park properties), some is industrial land, and until recently

some of the shoreline was owned by educational institutions.

ril

10, @,;i
1;00ili

ef
El.

EEO,
ox 0
<
in 0
0

D@,o

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13
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T4N Rod ne -Co. Mi1w au ke e Co.

80,

40'

20
0 -.4;1
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21/22 16/17 7/8 6

Figure 31. Generalized longitudinal
F=7-71 COWERED OR bluff
section showing
_T I
I V A C C E Sl S I E, LE in Reach 6.
SAND L stratigraphy
Numbers along base of
geographic
diagram are
CLAY TILL
GR, AV C L (l mile) sections.

:-4 C,LAYEy Sit T,
M I X E D
SAND AND I =:4
E-li-TY CLA. SEDIMENTS

Beach width ranges from 0 to 75 feet; much of the beach is between 10 and 40

feet wide. The beach is widest,just south of the mouth of the small valley near the

middle of the reach, where a compound shore-protection structure consisting of

four on-shore groins attached to a dolomite stone revetment is responsible

for active beach accretion. In contrast, numerous segments exist where either no

beach whatever is present or where the beach is less than 10 feet wide. Beach

materials also exhibit a wide range in caliber, from nearly pure sand to nearly

pure gravel. The coarsest beach in all of Kenosha and Racine Counties is that at

Wind Point just north of the lighthouse, where beach sediments consist almost entirely

of pebbles and cobbles.

Much of the coastline in Reach 6 lacks shore protection structures of any kind,

some of it is moderately well protected, and part is marked by a fair abundance of

protective devices. Except for the compound bulkhead that protects the Oak Creek

power plant at the north end of the reach, only three protective structures, none

of which is effective, are present in the entire north half of the reach. The

density of structures is therefore about one per mile (in contrast to segments of

several other reaches farther south, where the density is 40 or more per mile).

Structures are much more abundant and generally well constructed, however, in the
southern part of Reach"6.

Bluff height ranges from 5 to 85 feet. The bluff is highest in the northern

part of the reach where the shoreline intercepts the proximal slope of the inner-

most Lake Border moraine; in this area the bluff nearly everywhere is very steep

and in excess of 70 feet high. In the southern part of the reach, on the other

hand, at and just north of Wind Point the low terrace that separates the shoreline

from the main upland surface is generally 8 to 14,feet above lake level, and in

most places no real bluff exists along the shore; where present, the bluff is only

5 to 10 feet high. The terrace is.also,present as a narrow belt half a mile

upshore. Throughout most of the reach,,between the north end of this low terrace

and the Lake Border moraine, the bluff is moderately to very steep and ranges

from 30 to,70 feet high, progressively increasing in height from south to north.

The upland surface-behind the bluff in this segment is a lacustrine terrace that

represents the Glenwood stage of glacial lake Chicago.

The materials.in-!the bluff consist mainly of fine-textured sediments, including

compact silty clay till (till 2) and silt and clay of lacustrine origin, with

lesser amounts of fine-grained sand (Fig. 31). Individual till and lacustrine

units range in thickness up to.abbut 55 feet, but unit thicknesses appear to be

highly variable. The upper part of the bluff commonly exposes sand or gravel or

sand and laminated lacustrine silts-and clays, which overlie.the much thicker till

and lacustrine deposits below. Except for this general relationship, no-cbnsistent

stratigraphy is apparent,; in some places lacustrine sediments overlie till, at

other sites.the relationship is reversed, and at still other localities the de-

posits are,interbedded. Jn the southern third of the reach, however, no till what&ver,

seems, tobe present in the bluff (Fig..31).

Slope-stability also shows a range in conditions. In places where the bluff,

has been terraced or graded and sodded, the slope appears to be quite stable. In

a great many other places, however, bluff failure is rapid and severe. Moderate-

sized to massive slump blocks,commonly of a compound character, impart a, distinctly

scalloped pattern to the raw, sharp bluff edge through much of the reach. Mudflow,

debris slide, debris fall, seep sapping, gully cutting, and toe erosion are all

significant processes causing bluff failure and shoreline recession. Single pro-

files commonly showevidence of slump at the. bluff edge, flow in mid-bluff, and

wave erosion at the base of the cliff.

Thus, in virtually all categories, the Reach 6 shoreline'presents,a wide
variety of con.dit'ions--undoubtedly.the widest range of conditions of any reach in

Kenosha and.Racine Counties.

Reach 7, South Subreach

The south subreach of Reach 7 is defined as a.segment of shoreline, approxi-

mately 3,500 feet long, that extends from the end of Oakwood Road to the south

boundary of the reach in section.31, Township 5 North, Range 23 East, at the north

end of the bulkhead that encloses the coal stockpile for the-Oak Creek power plant

(Fig. 32). Detailed maps are given in Appendix 3.

Bluff conditions in this subre.ach are generally similar to bluff conditions

in the remainder of the. reach. The bluff is approximately .100 feet high, and

bluff materials consist mainly of compact silty clay till (till 2) and interbedded

lacustr.ine deposits that include clays, silts, and fine sands (Fig. 33). Several

of the coarser, more permeable layersact as seep horizons from which water issues

at the bluff face, thereby contributing directly to slope failure by sapping and

flow processes. Flowage appears to be the mostAmportant mechanism of bluff failure

in..the subreach at this time. Slump is also a significant mechanism, however, as

indicated by the presence of scalloped bluff margins and abundant slump blocks,. most

of which pass,downward into flow-structures.. Toe eros:ion and debris fall are impor-

tant where the beach isnarrow.

Beach conditions in the northern third of the subreach are also similar-to

those elsewhere in the reach..-The beach is quite narrow, generally ranging in

width from,10 to 20 feet, although in a few places it is less than 10 feet wide.

Beach materials.consist of sand and gravel. No shoreline protective structures

exist.

Approximately .1,000 feet south of Oakwood Road a definite change in shoreline

aspect occurs, a change that becomes progressively more pronounced toward the

south, with the result that the south end,of the subredch is quite different from

the north end. The major differences are in beach width, in-distance from the

shore to the base of the bluff, in the character of the sediments in this shore-

bluff zone, and in vegetation. Whereas wave erosion and a narrow beach characterize

%a I e uon
C,

River REACH 11
F i
; I Hills 11 Bayside
Spo EER RD
1;5, @Brown
@-l ----- ;---------------
Deer U*
41 100
t .0 45,
""OPP 4 . . . . . Fox Point
115 T-"
len
ale

@LVER VC. DR. Whitefish Bay REACH 10
41
KAM,
Co
-ml CAMTOL 190 @Shorewoof
ISO 61t-
R
- - - - - - - - - - - - - - - - - - - -
141 1.-
X
45 100 t@ 4 &,@V
37 %,71%.
1b sa AVE

C3
13
U1 C3
XLUE
113. 94
4 s.l. FVY. (.9 P
fo . ..... -A, Nilwaukee ,EACH 9
GREEN FIF, a
Qj AVE
C59 41
c:
Al K de

-OK
A VQRGAN AV -Fi@ C71 - - - - - - - - - - - - - - - -
NOVARO VF 32 T44

F".
894 G @3
A4F
toil
Gr en
9 1 t: .REACH 8
'Field @,Cudahy.
Hales n dale
rOMLLF.CE A
24
RAMA AV .F -C11 outh
Milwaukee
0 -----------

Franklin - T-54

A
- @,V' .- . REACH 7
7
RYAN R06 too 10
36
Oak Creek
'T I
- - - - - - - - - - - - - -

........ REACH 6
94 41 %A
38 32
To" al Rayw*W Tom a cwwmois
:Gr

R-21-1

Fig. 32. Map of Milwaukee County showing the locations of Reaches
6, 7, 8, 9, 10 and 11, and geotechnical sites 1, 2, 3,

t.4ji 7'0@0
S

N) 'IM)

ril

1-0

cn aq o- ro cr z

V1
ID

0 m 0

r) li@- 0 0 (D
z z
M
09 &0
"r 0

00
H a) ::r ta. 1.4 m

the northern part, active accretion of beach material is,occurring in the southern

part, where the beach is nowhere less than 20 feet wide. The width of the shore-

bluff zone progress.ively increases from less than 10 feet in the north to several

hundred feet in the south, thereby forming a distinct wedge-shaped area. This area,

in addition to recent beach deposits, consists of a flow terrace, underlain mostly

by water-logged silts, at-the base of the bluff and an abandoned beach and d une

complex between the flow terrace and the modern beach. A progressive north-south

change in the vegetative pattern is also obvious. This marked difference in shore-.

line character between the north and south ends of the subreach is attributed to the

Oak Creek power plant complex and particularly to the coal stockpile, which acts

as a massive groin that serves to interrupt the longshore transport of beach de-

posits from north to south and traps the sediment on its north side. The situation

is generally similar to that involving the Racine harbor structure and associated

beach accretion in Reach 5.

Reach 7, North Subreach

Reach 7, approximately 41.mil,eslong,,extends fr.om the Oak Creek Power Plant
2,

near the southern boundary of Milwaukee County north to the Water Treatment Plant

in Section 12, T. 5 N., R. 22 E. (Fig. 32). It is ranked number 4 on the priority

list, and it has a value per mile of 23 (see introduction for discussion of

priority determination and value per mile). Erosion rates within the reach are

up to 2 feet/year over the long term and 6 feet/year over the short term. The

reach is discussed in detail in Appendix 3. Much of the southern third'of the

reach is in Bender Park owned by Milwaukee County. This land is wooded or pasture

land.and some.areas are. in row crops. North of this a sewage disposal plant and

several industries are located along the shoreline.

In the southern part of the reach the beach width is 5 to 20 feet and there

are no structures present...In the central and northern parts of the reach, beach

width is considerably narrower, except where structures such as groins and small

breakwaters have created a beach up to or greater than 25 feet wide.

The bluff height within the reach ranges from 125 feet in the southern part

of the reach to about 60 feet in the northern quarter. In the southern part of

the stratigraphic section (Fig. 33), the bluff consists of a lower, gray, silty

clay till with few pebbles (till 2A). Where exposed, the till ranges from 6 to

20 feet -thick and contains a few inclusions of lacustrine material. This till is

overlain by a sequence of lacustrine deposits consisting primarily of silts inter-

bedded with fine sand. This sequence changes laterally to some extent within the

reach. Near the middle of the reach some interbedded fine gravels are present and

silt is fairly thin (15 feet).

The silts are overlain by till (till 2B) in all locations except in part of

Section 25. Here a wedge of medium sand and silt interbedded with fine sand is

about 60.feet thick. This wedge is local and was probably deposited in front of the

advancing ice front which deposited the upper till. The upper till (till 2B),

identical in the field to the lower. till (till 2A) in sequence, ranges from 10 feet

thick.to'nearly 70 feet thick within the reach. The thick till is located at the

intersection of the bluff with a moraine and it coincides with the highest part of

the bluff in the,reach. In the very northern part of the bluff, sediment from Oak

Creek is present in terraces at a level of 640 feet (Glenwood Stage of Glacial Lake

Chicago).

In the southern part of the reach the bluff top is scalloped (Fig. 34) and

fairly large..slump blocks displace material at regular intervals. Failures are

seated in or, at the base of the silt and the interbedded fine sand unit just above

the lower till. Northward in the central part of the reach few discreet slumps are

present, but numerous small slump blocks are present down the bluff surface (Fig. 14).

Because of the rotation of the block surface, these trap water and there are many

wet areas along.the-bluff. In the northern third of the reach most of the eroding

slopes are straight and the primary type of failure is sliding. In places the bluff

1; 0

4
f t@ z,

Figure 34. Oblique aerial photograph of the bluff in the southern
part of Reach@ 7. Note the scalloped nature@of the
bluff top because of shallow slumps in the upper part
of the bluff'. Location*is T.5N., R.22E., Section 259
Reach 7, Milwaukee County (oblique R-22, 13).

RWI
Ki,

Figure 35. Oblique aerial photograph of the bluff in the northern
part of Reach 7. Note the revetment of concrete
blocks dumped from the top ofthe bluff. Location is
T.5N., R.22E., Section 24, Reach 7, Milwaukee County
(oblique R-22, 2).

is protected by concrete rubble dumped from the bluff top (Fig. 35), and in

places the slope has been graded.

Reach 8

This reach is located in townships 5 and 6 north, Range 22 East in southern

Milwaukee County (Fig. 32). It is.approximately 5 miles long and is discussed in

more detail in Appendix 3. Its'priority in the ranking of critical 'areas was

eleven, with a value per mile aE twelve (see introduction for discussion of priority

determination and value per mile). Long term erosion rates measured are up to 1

foot/year and short term rates are up to 2 feet/year. Although some of the land

near the top of, the bluff is used for industrial development, much of this reach

is in open space. Grant Park is in the southern part of the reach and Sheridan Park

is near the northern part of the reach.

Beach width through the reach is variable and.in-places is up to 50 feet

where groin fields interrupt the longshore drift. A wide beach has developed in the

South part of the reach just updrift from a fairly large groin at the mouth of Oak

Creek. The bluff height in the reach varies from less than 60 feet along the Glen-

wood terrace near the mouth of Oak Creek to slightly over 100 feet in the central

part of the reach. The Glenwood stage shoreline (640 feet elevation) again inter-

sects the present shoreline. in the northern part of the reach just north of Sheridan

Park.

In thesouthern part of the reach two grey, silty clay tills (tills 2A and B)

are present with interbedded silt and fine sand (Fig. 36). The upper till is over-

lain by interbedded silts and sands up to 20 feet thick. At the base of the bluff

in Grant Park approximately 10 feet of sand occurs just above beach level beneath

till 2A (Fig. 36).. About half-way through the reach another grey, weathering

to buff or pink clayey, silty till (till 2C) appears. This is then present at

or very near the top of the profiles almost to the northern end of the reach. In

the northern part of the reach a sandy till with many cobbles azid boulders appears

@T 5 N. T6KI.

@100'

S.
2 C City of Milwaukee -80,

60'

77
wer Rant 4 0'
-. @7
A
20'
IB
17@
I A
12 1
36 25 24 14

LE%";% END

COVER-ED OR Figure 36, Generalized longitudinal
S- I LT
E
SAND F-I I N' A C C tc- S S! BE LE
section showing bluff.
stratigraphy in Reach 8.
F- T-@q Numbers along base of
GRAVEL CLAY -1 1. L L diagram are geographic
(1 mile) sections.

SAND AND CLAYE'Y SILT, M I X E D
G R AW E L I,:,!T-TY CLAY S D I s"Is EN T S

at the base of the bluff. This till is referred to in this report as till 1A and

may be correlative with the Haeger till of Illinois (Fig. 19). The bouldery nature

of this till can be seen by the large number of boulders present.in the bluff

along the beach at this location (Fig. 21). Directly above this a thin, fairly

sandy till with fewer boulders is present (till 1B). The erosion rates in the

.reach are lowest in Grant and Sheridan Parks Where groin fields and associated

beaches protect the base of the bluff. At the south end of the groin field at

Sheridan Park a marked change in bluff stability can be seen as the beach narrows

(Fig. 9). Most of the failure on the bluffs in this reach is shallow sliding and

flows where water is present. In the central part of the reach the gravel unit

contains water and sapping occurs in this unit causing collapse of the overlying

silts and till. Some sapping also occurs in the southern part of the reach where

sands and silts make up the top of the bluff (Fig. 15)., Small ravines due to

sapping cut approximately PO feet backinto the top of the bluff.

Reach 9

Reach 9 (Fig. 32) covers the.Milwaukee Harbor.area which is entirely protected

by a large breakwater system. Because of the shore protection structures this

reach was not examined in detail. The reach,has a priority of 32 and a value per

mile of 0 (see introduction for methods used in determining priority.and value

per mile).

Reach 10

Reach 10 is located in Townships 7 and 8 north, range 22 east in northern
Milwaukee dount (Fig. 32). The reach is about 6.5 miles long and extends
Y

northward from the structured part of Milwaukee Harbor to Fox Point. Land use

in the reach is limited to residential areas (Shorewood, Whitefish Bay, Fox Point)

and parks and open space (Shorewood, Buckley, Big Bay, Silver Springs, Klode and

Doctors Parks). The reach is ranked number six on the priority list and has a

value per mile of twenty. Long term erosion rates in the reach are up to 3 feet/year.

No short term rates were measured. Beach conditions in the reach vary greatly

depending upon the protective structures present. Where groins exist, wide (60

foot) sand beaches protect the toe of the slope. Where only sea walls exist, there

is a small sand and cobble beach or the waves are breaking against the front of

the sea wall (Fig. 11). In front of most of the revetments thereis no beach

unless the shoreline is also protected by a groin.

The bluff height in Reach 10 varies from 116 feet in the southernmost section

to about 70 to 80 feet in the central areas and then rises to almost 120 feet in

the northernmost parts of the reach.

The characteristic stratigraphy of the entire reach is an upper red-brown

clayey, silty till .(till 3A) separated from three lower tills by a sequence of silt

and interbedded sand and silt (Fig. 37). In the southernmost section the natural

exposures are very poor but from boring logs the upper till is at least 60 feet

thick and the lower tills extend upward to a few feet above lake level. Between

the lower tills and the upper tills 20 to 30 feet of lacustrine silt and sand are

present. About one quarter of the way northward through the reach the lower tills

1-ise until they are almost in contact with the upper red-brown till (3A). North

of this point to the end of the.reach the lower.tills drop in elevation and are

separated from the upper red-brown till by an increasingly thick wedge of

lacustrine deposits. About three quarters of the way northward through the reach

the lacustrine silt and interbedded. silt and sand reach a thickness of 90 feet.

The southernmostmile of the reach is relatively stable and most of the

bluff is tree covered. North of this, bluffs are intermittently wooded but some

failure is taking place. Two types of slope failure are taking place within the

reach. In one type rapid toe erosion at the base of the bluff causes steep

lower slopes and shallow translational slides.on the more gentle upper slopes

(Fig. 38). In this case the toe material is usually in place (tills one or two

T7N.
CO

.@Z 3A
A

2
1A
I A
IC) 33/34 243 16
0
=-!=j

SAND COVLPED 0 R Figure 37. Generalized longitudinal section showing
SILT
14NACCESSMELE bluff stratigraphyin Reach 10. Numbers
along base of diagram are geographic
U miJe) sections.
GR AVEL CLAY TILL

SAND AND cuy-=Y- S I LT, MIXED
-L SII-TY CLAY SED11,12ENTS

Figure 38. Oblique aerial photograph showingareas-where rapid
toe erosion is taking place and failure is primarily
by shallow slides...Location is T.M, R.22E., Sec-
tions 33 and 34, Reach.10, Milwaukee County (oblique
R-17, 13).-

Figure 39. Oblique aerial photograph showing Nip ising Age (605'
elevation) terrace. Terrace is protected'by revetments
and seawalls. The bluff behind the terrace is vege-
tated and stable. Location is T.8N., R.22E., Section
21, Reach 10, Milwaukee County (oblique R-16,28).

or slit). The slide material is.carried away as rapidly as it falls from the bluff.

Less often there is a small quantity of upper red-brown till or silt debris covering

the toe.

Slumping, the other type of failure is caused by toe erosion coupled with

the presence of seeps and lubricated rotational failure planes. Slopes exhibiting

this type of failure usually have large blocks of slump debris covering the toe.

Slump blocks pile up at,the base of the bluff and then are slowly removed by way

of action. The topographic profiles (Appendix 3) of these-slopes show a gentle

lower slope and a steep upper slope4 Small scarps were observed on even the most

stable appearing slopes such as those protected by seawalls, groins and terraces.

These may be at the heads of old, very large, deep-seated slumps because remnants

of old slump blocks are present along the base of the bluff in places.

Throughout the reach several minorseeps occur in the low part of the bluff

either on top of the tills (tills 1A or B) or over a less permeable silt or-clay

layer., The presence of the seeps with their sapping action probably does not

greatly add to the erosion problem.

The northern one-quarter of the reach-in Fox Point has a natural terrace

which is probably Nipissing in age (elevation 605 feet). This old wave cut

terrace is based on the lower two tills (till IA and B) and has a thin (3 to 6.

foot) layer of sand above. Most of the terrace is protected by revetments and

small groins. The bluff in back of the 200 to 300 foot wide terrace is vegetated

and stable (Fig. 39). Slopes on the bluff range from 19 to 240.

Reach 11

Reach 11 (Appendix 4) is about 3 miles long and extends north from Fox Point

in northern Milwaukee County to Virmond Park in southern Ozaukee County (Fig.

32, 40). It is in townships 8 and 9 north, range 22 each. Reach 11 is number 5

on the priority list of erosion reaches with a value/mile of 23 (see introduction

for disucssion of priority and value/mi le). Land use at the top of the bluff is

either residential or is park land.

R-n-9
13 Tom C1 T"A d motwd
- - - - - - - - - - - - - - - - - - - - 7- - -
10acada
PRE-
11 J6,
DoNIA REACH 17
12

4f -W
ELGIUM lqi", CW T-1241
4 - - haRAGWR
ONO --------------------

Holy REACH 16
'%.Waubi-ka 30 Q
AN S

PORT r, -- -------------------
WASH.

KW
33 REACH 15
84
-8 SAU
1 0
'VILLE Z6 K1%
qauk%fi a 0 Pmt Washington,
Low -4-4

141
REACH 13

----------------------------------------

C
AF_ 8ON
REACH 12

Thiensville
Mequon
T-M
...........

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

REACH 11

57 River
@w 32 41 Bayskle
hills
uke a

Figure 40 Map of Ozaukee County showing
locations of Reaches Ils 12,
13, 14, 15, 16 and 17, and
geotechnical sites 6 aad 7.

The width of the beach varies from less than 5 feet in the central part in

northern parts of the reach to greater than 20 feet in other areas (Appendix 4).

Several small groins and revetments protect the toe of the bluff in some areas

but much of the reach is unprotected. The southernmost third of the reach is
wave-cut terrace Of NiPissing age that is 100 to 200 yards wide (similar"to

Fig. 39). Much of this is vegetated although some small dunes have blowouts

where active wind erosion is@taking place. The terrace here is within the Audubon

Bird Sanctuary and there is no residential development as there is on the terrace

south of Fox Point. Vegetation.covers the bluff above the terrace.

Bluff height in the reach ranges.from approximately 70 feet at the northern

end of the terrace area to 140 feet at the northern edge of the reach. Several

large gullies cut the bluff although no large perennial streams enter the lake

within the reach.' No 6tratigraphy is visible In the bluff in the terrace area.

North of this, red-brown silty till (till 3A) up to 60 feet thick is present at

the surface throughout the reach (Fig. 41). This is underlain in the central part

of the reach by a sand and gravel sequence ranging in thickness from 10 to 30 feet

which overlies silts and interbedded fine sand.. In the north central part of the

section till 1B.is exposed just above water line in a few places.

The bluff adjacent to the terraced area in the southern part of the reach

is relatively stable. North of this through the rest of the reach shallow slides

are common. Lacustrine material from the middle and lower parts of the profiles

slides off the bluff and is accumulating at the toe where it is not being actively

eroded. As the bluff rises to the north sliding continues to take place on the

lower parts of the profile but shallow slumps also occur in the upper part of the

bluff and seem to be seated at the base of the till unit. Small scarps and rotated

masses of soil occur along the upper and middle parts of the bluff. At the northern

edge of the reach, wave erosion is taking place at the base of the bluff and slopes

are very active.

G,
cn

M 0 (1)

rtl
rrl (D

boo CD
CD,

U4 0

It.

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I

Reach 12

Reach 12 is located in townships 9 and 10 northl range 22 east in southern
Ozaukee County (Fig. 40). The reach is about 6-1 Miles long and extends from Virmond
2

Park north to a point east of the towns of Cedarburg and Grafton. Land use in the

reach is primarily residential although there are some parks. The reach is ranked

second on the erosion priority list with a value per mile of 27 (see introduction

for discussion of priority ranking and value per mile). The high priority in based

on short term recession rates which range from 2 to 6 feet per 10 year period,

the very high bluffs present, and the large number of residences located along

the bluff top (up to 29 per mile). Throughout much of the reach the beach is narrow

but is very variable and is best viewed on the section maps in Appendix 4.

The bluff height in reach 12 ranges from 140 feet in Virmond Park at the south

edge-of the reach to about 75 feet in the central part of the reach. In the northern

end of the reach the bluff rises to over 100 feet and the entire reach has a

uniformly high-bluff character. Tills 2 and 3A are present in nearly all profiles

through the reach and in many places make up most of the bluff section (Fig. 42),

Ih.the southern part of the reach they are separated by about 20 feet of sand,

gravel and silt which wedges out within the first mile north of the southern edge.

In the next two miles north, nearly all of the bluff is made up of tills 2 and 3A

although till 1H is exposed at the very base of the bluff in the northern part of

section 17. North of this to the northern part of the reach a unit consisting

of sand, sand and gravel and sand interbedded with silt appears between tills 2

and 3A in the central part of the bluff and reaches a thickness of nearly 80

feet (Fig. 42).

The slope failure type in this reach includes both sliding and slumping.

In general the bluff in the southern part of the reach is more subject to sliding.,

The area around Virmond Park owes its rapid recession rates primarily,to this

type of failure. The northernareas seem to be marked by more slumping There

co 0 0
C,a

illD

Of
G) cn
34

Tel
r1i

P; )'v-

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qv
I ; I -@@ '11,
11 Y"
Ofl i
1Y ! I; ) , Z". - G %
'i Ili Mil'ill'i @11 11 0.
bd

it ri-10 6
00,
'ab

uc; 0.0 D'a
It c @j.D 0. b
Q,(JQ d '11 ,
-po"

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OO'd
CA -q -7;, c *1 OD 'W;45@1 4.
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(IQ ,13
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68

are large slump blocks resting at the base of the bluff and erosion of these

blocks is now taking place'(similar to Fig. 44). These evidently represent very

large slumps, possibly seated below the water level of Lake Michigan. Their age

is unknown.

Vegetation within the reach is partly dependent on failure type. Where the

slope has failed,by sliding there is very slight vegetation cover and surface

erosion during rain storms is great. In the areas of slump the bluff is more highly

vegetated, especially on the slump block. There. are however barren scarps and the

toes of the slopes which are being eroded by waves are vegetation-free.

Reach'13

This reach begins in Section 21, T.10N., R.22E. and extends through Section

33, T.11N., R.22E. in Ozaukee County (Fig. 40). The reach is approximately

5 miles long and is No. 7 on the shore erosion priority area list with a value

per mile of 18 (see introduction for discussion of priority determination and

value per mile). The land use in this reach is almost entirely agricultural,

but new homes are built fairly close to the top of the. bluff in a few places.

within the'reach,, bluff height varies from 100 feetto 125 fee t.. Much of

the reach has, s6attered vegetation along the bluff, and stratigraphy is difficult

to interpret in many places. The sur face stratigraphic unit is red-brown silty

till (3A) up to 40 feet thick overlying interbed ded sands, sand and gravel, and

silt (Fig. 43). Beneath this, in the southern part of the reach, slightly more,

gray silty till clay@,(till 2) underlies the sand and silt units.. Throughout

the southern part of the roach large slump blocksare located at,the toe of the

bluff and no stratigraphy can be seen (Fig. 44). In the central and northern

parts of the,,bluff, where the toe is exposed, the more gray silty till (Till 3A)

is present just.above water level.

T ION. Ozoukee Co. T I I N.

-120

C;
3 A -3-
3 A
7n, 0,p, C, 0 e, @@
C5 C
3 A
p -e.
4": -3 Port
cD @!o
C@ fo -%@1>0 b -o -p Wasiihingtcn

7- -Z.
40
--@- 4
B,
21 16 10 33

L E(Z" E N D

COVERED OR Figure 43 Generalized longitu-
SAND SILT dinal section showing
I N A C C E S S 16 LE
bluff stratigraphy in
Reach 13. Numbers
along base of diagram
are ge
G R AVEL CLAY TILL
ographic (l,mile)
sections.
C L AV) E" Y' 1,3 1 L%
SAND AND M 1 D
17.= -:a-- @4
GRXIEL 'SF-TY CLAY EIL-- SEDIAMIENTS

Ai@

77,
7@
7W, @@-

Figure 44. Oblique aerial photograph showing@very large slump
blocks in Reach 13. Much of the slump block is
vegetated and is presently being eroded at its toe.
Location is T.10N., R.22E., Section 16, Reach 13,
Ozaukee County (oblique R-13, 20A).

In the southern third of the reach, slope failure is primarily by large deep-

seated slumps. The base of the bluff, like that in reach 12, is made up almost

entirely of slump materialwhich is still vegetated and which traps wnter coming

out of and down the-bluff (Fig. 40. This slump block (Fig. 44) is being eroded

presently by waves along its shoreward edge; At one location,. where stratigraphy

near the base can be seen, sands overlie a fine-grained till or lacustrine unit, and

excessive sapping takes place in the sands. In the northern two-thirds of the

reach, failure is primarily taking place by shallow translational slides down the

bluff face (Fig. 45). Very few'slump blocks are present along the toe, and in

places where the,beached narrow, in-place materials at the toe can be observed.

In places where the beach is wider, a thin layer of low and slide debris occurs

along the toe. In this part of the reach several bowl-shaped cuts (Fig. 46)

extending from the surface two-thirds of the way down the bluff are vegetated

and stand out as distinctly different from the steeper bluffs on either side.

These have formed where undercutting due to sapping in the sands and surface water

flowing over the bluff top have cut through the till and produced wide, roughly

equi-dimensional gullies.

In the southern part of the reach, beach width is narrow and waves are eroding

the toe of slump material in many places. In the central part of the reach the

beach widens to about 20 feet and is primarily sand, although a cobble line does

exist at water level. North of this, toward Port Washington, the beach narrows,

coarser materials are present, and much of the beach is made up of pebbles and

cobbles. An exposure of dolomite bedrock creates a small point in the northern

part of Section 3. Very few structures exist in the reach.

Reach 14

Reach 14 is.the harbor area of Port Washington in Ozaukee County (Fig. 40).

,The harbor is protected by a power plant and groins on the south side, and by a

large breakwater attached to the shore on the north side. There are no natural

.exposures within this reach.

-v k

17-
IWgUMONM

Figure 45. Oblique aerial photograph showing steep nearly un-
vegetated slope where most failure is taking place by
shallow translational slides and flow. Some small
slumps.oc,cur near the top of the bluff. Location is
T.10N., R.22E., Section 3, Reach 13, Ozaukee County
(oblique R-12, 33).

1 _717 - %_
A

Figure 46. Oblique'aerial photograph showing bowi-shaped depres-
sions in the bluff top.that have formed where ground-
water sapping is taking place. Location is T.10N.,
R.22E., Section 10, Reach 13, Ozaukee County (oblique
R-12,32).

Reach 15

Reach 15 is located in T.11N., R.22E. in central Ozaukee County (Fig. 40).

The reach is about 4.5,miles long and extends northward from structures in the

Port Washington harbor to a lake terrace (6051) in Section 1, T.11N. Land use

on the bluff top and terrace.is either residential farm land or forest.

Reach 15 is ranked 15th on the priority list with a value per mile of 10 (see

introduction for discussion of priority determination and value per mile). This

value is based on short term recession rates thatvary from 3 to 8 feet per.10

year period and a fairly high rankin,g.of importance by the public.

The beach width in the reach varies greatly. In places it is over 70 feet

wide (Section 22), but in many areas it is 5 to 20 feet wide; and in sane places

waves are..eroding the toe of the bluff throughout much of the year. Most of the

beaches are made up of coarse-grained material such as pebbles and cobbles,

although 'sand is present in some areas, especially high on the beach.

Bluff height varies from a maximum of 116 feet to about 85 feet in the

southern@two`sections of the reach. The northern 3 sections have a bluff height

between 50and 85 feet. Within the reach are 3 areas of old lake terrace

(Nipissing, @or 605 feet elevation). The largest occupies the middle of Sections

14 and 15,,and 11. At the northern end of the reach iris'ections 2 and 1 theterrace

begins again and continues northward through reaches 16, '17, and 18..

The stratigraphy within the reach is rather uniform (Fig. 47). At the base

of the bluff, in most localities, is a gray, silty sandy till with many cobbles

and pebble s (Till 1B). At'the top of the bluff, throughout reach 15, is a red-

brown, silty, pebbly till (Till 30. Sandwiched between these two tills is a

variable sequence of lacustrine and fluvial.silts, sands@yand gravels. The thickness

of the units@'changes greatly, depending on the location, but in general the lower

gray silty till increases-,from 4 feet at the southern edge of the:reach to about

27 feet in Section.'22.., The till then decreases in elevation so that it is not

cl
-:;p cn
z 0
D.
m
r Icy.,
OD
Osj.

61 > ..I
p f
ts

0.0
<

@j
0 CA .0 r,
. I I v1-;
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.C,

z
0
tD g r 4
0 < .'I
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0 frl
m 0 rri M

tj I Ulu

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CL Zri)
M (D
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m M 0 M*0
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exposed in the northern quarter of the reach. The separating fluvial and lacustrine

sediments are generally about 40 feet thick with most of the thickness (about 30

feet) being made up of silt in the southern half of the reach, and most being made

up of gravel in the northern half of the reach. In many places the gravel layer

is highly cemented into a hard dense conglomerate. The upper red-brown till (3C)

varies in thickness with bluff height and is thickest (40 to.50 feet) in the

high bluff area in the southern part of the reach. In the northern half of the

reach the thickness varies between 30 and 40 feet.

Slope failure within the reach is primarily slumping with a, little sliding

in the southern half (Fig. 48) and sliding only in the mrthern half. Many of the

slump blocks are vegetated and there are few completely bare slopes, as there are

in reaches to the south.

Reach 16

Reach 16 is a 3-mile stretch of Nipissing Age lake terrace (605 feet elevation).

The reach is located about halfway between Port Washington and the Ozaukee-

Sheboygan County line (Fig. 40). The reach is ranked No. 12 on the priority list

of erosion areas, and has a value per mile of 12. Land use on the terrace in

this reach is entirely park land and residential. About half of the homes are

used in the summer only and half have year-round occupancy.

At the southern boundary of reach 16 is a small but prominent point formed

because of an exposure of resistant dolomite bedrock. At the point itself there

is no beach, but a 20 foot wide shelf of bedrock dissipates the wave energy.

North of this point the beach is made up of cobbles and pebbles, except for a

small sand beach just north of the point.

The terrace ranges in width from about 250 feet to 500 feet. Behind the

terrace the bluff is about 50 feet high and is entirely vegetated and stable

(Fig. 49). Very little stratigraphy is exposed in the terrace and probably much

of the terrace material is sand. At the north end of the reach a bedrock point

extends into the lake from the terrace (Fig. 50).

'k:

Reach 48. Oblique aerial photograph typical of the bluff in the
southern part of Reach 15.- Slumping takes place in the
upper part of the bluff and shallow slides are more
typical of the lower,part of the bluff., Locatio*n is
T.11N., R.22E., Section 22, Reach 15, Ozaukee County
(oblique R-121, 8).

Figure 49. Oblique aerial photograph showing terraced areas
typical of Reaches 16 and 17. The low bluff behind
the terrace is vegetated and stable. Location is
T.12N., R.23E., Section 25, Reach 16, Ozaukee County.
(oblique 9,14)

7
4't

7 t
--%w -0 IIC;I

tA@' 4A.

Figure 50. Oblique aerial photograph showing the exposure of
doloraite bedrock at the boundary between Reaches 16
and 17. Location is T.12N., R.23E., Section 19,
Reaches 16 and 17. (oblique 9 35)

100.

Reach 17

Reach 17 is a 3-1 mile long reach of Nipissing Age lake terrace (605 feet
2

elevation). Tt is located at the northern end of Ozaukee County and extends from

the point at Harrington Beach north to the OzaukeeSheboygan County line (Fig. 40).

Reach 17 is ranked No. 13 on the erosion study prioritylist and has a value per

mile of 11. Like reach 16, the land use on the terrace is residential and park.

.At the southern boundary of the reach, a bedrock point extends into the lake.

Here there is no beach, but a 20 foot wide bedrock shelf extends a short distance

north to a sand beach. Extensive sand bars also occur offshore and are probably

present because the bedrock point acts as a natural groin. These conditions occur

northward throughout the reach. The terrace is over 500 feet wide in the southern

part of the reach, and is approximately 1,000 feet wide near the northern edge

of the reach.

The bluff, where present behind the terrace, is vegetated and stable. No

stratigraphy was observed within the reach, and probably most of the terrace

materials are sand overlying bedrock.

101

Reach 18A-

Reach 18A lies in Sections 30 and 31 of T.13N., R.23E., in extreme southern

Sheboygan County. It is roughtly two miles in length, extending from the county

line on the south to a point directly east of the town of Cedar Grove. The

reach has,an overall priority of 18 which is the fourth highest priority of

those reaches lying north of the Sheboygan County line (Fig. 51),

Figures 52 through 56 constitute a generalized longitudinal profile of the

high bluff area lying between the cities of Sheboygan and Manitowoc. These are

supplemented by Figures 63 and 74, which are profiles of isolated area.s of high

bluffs elsewhere in the st
udy area.

Reach 18A (along with Reaches 18B and 18C) lies on the prominent terrace

that extends from north of Port Washington to near the southern city limits of

Sheboygan. This terrace was formed by shoreline erosion along the shores of an

ancient glacial lake at a time when the lake level was about 605 ft. above sea

level. This is about 25 feet higher than modern Lake Michigan. The surface of

the terrace is made up of a series of roughly parallel ancient beach ridges and

is bordered on the west by an ancient wave cut bluff. This bluff is identical

in origin to the steep bluffs that are found along many sections of the modern

Lake Michi*gan shoreline in Sheboygan County and elsewhere. The terrace is of

Nipissing Age.

At the Sheboygan-Ozaukee County line, which is the southern border of this

section, the terrace is roughly 1000 feet in width and terminates to the west at

a relatively steep and well defined bluff which is between 30 and 40 feet high.

Although the ancient bluffs were not studied in detail,.the few exposures that

were studied indicated 10 to 20 feet of red till over lacustrine sand and gravel.

102

n3z 42 +
.41
R R I N'E7
REACH 23
mos L 61-13
WU S S EL L

is ii
------------

7`7
J,
42
It
HERVAN@

32
S;H E 84) Y GAN is H o..XEACH 21
Y x

AJ
W47
oil REACH 20
beboygan

@71 19
@1 J I AN to) 0
- - - - - - - - - - - - -
Lim 'OF dov
W I
to,

rl
C

-7

E
SHERMAN.
REACH 18

r'7'@ hJ11k'
Ra;;-.l 1; m)i.!DLLAND
Gr

- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Tan, W Fyn-ON gTome of NO" TOM 4134"
+ 1.22 E

SHEBOYGM CO.

mvnmm S. -0--

Figure 51. Map of sheboygan County showing the locations of Reaches 18, 19,
20, 21, 22 and 23, and geotechnical sites 11, 12, 13 and 14.

Figure 52. Generalized longitudinal profile of bluffs..

T 15 N.

0-
-6@

SEC. 14 SEC. 11 SEC. 2-

1000 f t.
---------- REACH 21
Vertical Exaggeration 50X

LEGEND

COVERED OR
SILT
SAND- INACCESSIBLg

GRAVEL CLAY TILL

SAND AND CLAYEY SILT, MIXED
SEDIMENTS
GRRIEL _SILTY CLAY 1:S:

Figure 53. Generalized longitudinal profile of bluffs.

T. 16 N.

7,0

0
,q

0,-QO

C @6 3A
:Zq 3A
.00,
9,*-!@. 0 *
zi:rl -bb,
SEC. 34 SEC. 2-7 SEC. '22

REACH 21 REACH 22

T 16'N.

3C
.3c
-Mr

_0
ca P

slit

SEC. 15 SEC. 10 SEC. 3

REACH 23
1000 ft. SHEBOYGAN CO.

Vertical Exag4eratidn 50 x

Figure 54. Generalized longitudinal profi le of bluffs.

T. 17 N.

3c
3c

3A
0
of 0.:-0 A
000 h
-7 0.

SEC. 34 S EC. 27 SEC. 22

REACH 23 REAC H 24
Cn
am"ANITMOC CO.
T. 17 N.

A (3 @A7=@ 3A
SEE C. 14 SEC. I I SEC. I

1000 f t.
REACH 24 REACH 25.
Vertical Exaggeration 50 X

Figure.55. Generalized longitudinal profile.of bluffs..

T 18 N.

Wf,
0
-A, ON
P70 -0- OT
0
00-, .0 0
C,
00 :0: ;qE!
6
.0 -0
076 N
0 b,
6

SEC. 36 SEC. 25 SEC. 24

1000 f t.

Vertical Exaggeration 50X

Figure 56. Generalized longitudinal profile of bluffs.

T. 18 N.
3B

00
'0' 0,0.g ,.,0, a 0
-0 po.q..
-0
V
d" .76
ej 6. 0
O-P

?
TILL
SEC. 18 S EC. 7 SEC. 5
REACH 25 REACH .26,

T. 19 N.

SEC. 36
1000 ft.
REACH 26
Vertical Exaggeration 50 X.

108

Land use within Reach 18A is almost exclusively private residential, although

a small township park is located on the northern end of Sec. 31. Some summer

cottages or second homes were observed, but most of the properties appear to be

permanent residences. Housing density averages 12 residences per mile.

Beaches along this section of terrace are well developed, ranging from about

30 to more than 100 feet in width. They are striking in that they are made up almost

exclusively of sand. Particles of pebble size or larger are almost completely

absent.

Throughout much of Reaches 18A, B, and C, there are three very well developed

sand bars lying off shore. At the time the shoreline was studied one of these

sand bars merged with the beach in the southern portion of Section 31. Because

of this, the water is quite shallow immediately off shore. Five foot water depths

lie between 100 and 200 feet from the shoreline throughout section 31, and between

85 and 165 feet from shore in section 30.

Erosion along this reach is the result of the removal of sand from the beaches

by storm waves. Measurements of erosion rates at two stations in the reach

showed rates of 1.2 and 2.7 feet/year over about the last ten years. At the

northern station, however, one hundred year averages show a small overall accretion.

Figure 57 is an oblique aerial photograph showing the general character of

the shoreline in Reach 18A. The lack of beach in front of the revetment protecting

the home in the foreground demonstrates the retreat of the shoreline in the

reach.

Reach 18B

Reach 18B encompasses all or part of Sections 19, 20, 17, 8, 9, and 4 of

T. 13 N., and Sections 33 and 34 of R. 14 N., R. 23 E. The reach has an overall

priority rating of 8 which is the highest of any reach north of the Sheboygan

County line. Land use is almost exclusively private residential. Housing

density varies from a low of 10 to a high of 45 residences per mile with an

average density of about 27 residences per mile.

109

Figure 57. Oblique aerial photograph showing the general character
of the shoreline in Reach 18A. The absence of beach in
front of the revetment protecting the home in the fore-
ground demonstrates the retreat of the shoreline:along
this reach. (oblique 8,19)

110

in the southern portions of the reach the beaches are well developed but as,

one progresses northward, the beaches narrow and many of the residences in the

northern portion of the reach would suffer rapid and severe erosion losses if they

were hot heavily protected. The beaches are still predominately sand when present

with pebbles and cobbles significantly more abundant in the northern portion of

Reach 18B than was true to the south. In the extreme northern portion of the

reach, beaches once again are present and range up to 65 feet in width.

As was the case in Reach 18A, the near back shore area is made up of sand

dunes and beach ridges with cut faces ranging up to 18 feet in height.

Ancient bluffs lie approximately 1000 feet to the west of the present

shore line in the southern portions of the reach. These bluffs are sharp and

well defined in this area., As we move to the north the terrace broadens to about

a quarter of a mile and the bluffs become obscured due to erosion by streams

tributary to the Black*Rivek. Annual erosion over about the last 10 years has

been measured at between 2 and 3 feet per year while 100 year averages are

significantly lower with values of about 0.5 feet per year.

Figure 58 is an oblique aerial photograph showing the nature of the shoreline

in the northern portion of Reach 18B. Storqi waves have gone over the low revet-

ments in this area, causing some structural damage.

Reach 18C

Reach 18C extends for a distance.of 3 miles and consists of the shoreline

along sections 27, 22, and 14, T. 14 N., R. 23 E. The reach has an overall

priority rating of 24, and ranks ninth out. of- the twelAw. reaches north of Ozaukee

County. This low ranking is primarily due to the fact that a large proportion

of the shoreline within the reach is incorporated in the Terry Andrae-Kohler

State Park Complex. As a result there are only 20 private dwellings along the

shoreline of the total reach, leaving much of this reach undeveloped and essentially

in its natural state.

k-I

41
.Miftn':

Figure 58. Oblique aerial photograph showing the nature of the
shoreline in the northern portion of Reach 18B. Storm
waves have gone over many of the low revetments found
in thislarea resu,lting.in considerable erosion and some
damage to homes. (oblique 6,33)

.112

In contrast to the more highly developed area immediately to the south in

18B) the beaches in Reach 18C are relatively wide, ranging up to 100 feet in width,

Pebbles are much more abundant than in Reaches 18A and 18B, The back shore area

consists primarily of terrace sands, In some areas send dunes in excess of 30

feet high have developed. Erosion behind,the beaches has produced cut faces in

many areas which, when present, are normally between 10 and 16 feet high.

As was the case in Reach 18D to the southo the ancient bluffs marking the

western limit of the terrace have been largely destroyed by the erosion of streams

tributary to the Black River,

The principal mechanism of erosion throughout this reach is the removal of

easily eroded sands through the action of storm waves. Ten year erosion averages'

were determined at two stations within the reach, and values of 2.2 feet/year

and 1.4 feet/year were obtained, A single hundred year measurement was made within

,the reach, giving a value of 0*6 feet/year, A typical shoreline segment is shown

on Figure 5.9.

Reach 19

Reach 19 is a little over 2 miles long in a north-south direction and includes

the shoreline along Sections 11 and 12 of T. 14 Nao R. 23 t.i and of Section 35

and a portion of Section 26 of T, 15 N., R. 23 S. The reach has a priority of

19, making it the 5th highest ranking reach in the Sheboygan-Manitowoc study area.

This reach is a zone of transition in terms of geology, geomorphology and

in its land use. The southern portions of the reach are a continuation of the

terrace that extends southward almost to Port Washington. Northern portions of

the teach are in an area of moderately high bluffs, typical of much of the area

north of Sheboygan,

In terms of land usagej the southern portion of the area is one of year around

beach residences, fronted by a moderately wide sand beach,. Housing density is

.61 residences per mile. In the central portion of the reach this residential.

113

P@
"V,
AM

Figure 59. Oblique aerial photograph showing-typical undeveloped
shoreline in Reach 18C. (oblique 4,19)

114

area gives way to the grounds of the Edgewood Power Plant and the sewage disposal

facilities for the City of Sheboygan. Immediately north of the sewage plant the

land is largely urban in character, consisting of roughly a quarter mile of park

lands which give way to closely spaced urban housing on top of the bluff.

Figures 60, 61, and 62 show the contrasting nature of the shoreline in

these three areas.

Till is first encountered in this study area at the southern boundary of the

sewage treatment plant,'where about a foot of highly oxidized red till, believed

to be till, 3C., is exposed. The till is exposed intermittently for a short

distance along the shoreline. Throughout this small area the till is overlain

by sand. North of this point, the bluff attains a height of about 50 feet, and

the stratigraphy of the bluff is almost totally obscured by fill that has been

dumped over the edge of the bluff, as well as granular fill placed behind a large

revetment and groin complex that protects this portion of the shoreline. A boring

taken at the crest'of the bluff revealed 20 feet of sand, which became progressively

finer with depth, overlying a till unit (W) about 20 feet thick. The till

was found to be underlain by sand to well below the lake level. A generalized

longitudinal profile of the northern portion of the reach is included as Figure 63.

A ten-year average erosion rate of 2.5 feet per mile was obtained in the

southern portion of Reach 19, with a one hundred year average of about one foot

per year. In the northern two-thirds of the reach, the shoreline is almost

completely protected by structures and little if any evidence of erosion wasnoted. 21

Reach 20

This reach consists of the area including and immediately surrounding the

harbor at Sheboygan and is fully protected from shoreline erosion by structures.

It is the second lowest priority reach in the total project and has the lowest

rank of any reach in the Sheboygan-Manitowoc study area. it was therefore

excluded from the study with the exception of about 1000 feet which was included

in order to complete the southernmost section in Reach 21.

115

-75411

Figure 60. The southern portions.of Reach 19 are typified'by year
around residences fronted by sand beaches along the terrace.
(oblique 4,6)

116

Figure 61. In the central portion of Reach 19, the ground elevation
increases and land use is largely industrial.
(oblique 3,19)

117

d%X

Figure 62. The northern portion of Reach 19 is an area of well-
protected high bluffs and is densely populated.
(oblique 3,9)

9TT

119

Casual examination while driving through Reach 20 reveals the shoreline to

consist almost entirely of fill, lying behind massive protective structures.

Reach 21

This reach includes the shoreline portions of sections 4, 11, and 2 of T.15N.,

R.23E., and about.the southern two-thirds of section 34 of T.16N., R.23E.,

It has an overall priority ranking of 25, which gives it the tenth highest

priority of those reaches north of Ozaukee County.

Land use within this reach is quite vari able, ranging from urban residential

in much of the two southernmost sections, to largely agricultural or undeveloped

lands to the north where only scattered, small subdivisions indicate the close

proximity of Sheboygan.

In its southern@sectiohs, the shoreline is composed primarily of granular

fill placed behind heavy,revetments with a moderately high bluff to the rear.

Throughout the urban portions of this reach, study of the stratigraphy of the bluffs

is extremely difficult due to the extensive placement of fill on the bluff face as

well as a heavy vegetative cover in many areas protected by revetments.

In the less highly developed areas to the north, the shoreline generally

has a moderately wide cobble beach, normally ranging between ten and thirty feet

in width. In some areas in which till appears in a basal position, however, the

beaches are very narrow, or, in some cases, nonexistant. The height of the bluffs.

throughout the reach is, for the most.part, between forty and fifty feet.

Near the southern boundary of the reach bedrock is very shallow or exposed

in the nearshore area. This body of dolomite at or near the water surface is

known as the "Sheboygan Reef". The promintory, Sheboygan Point, that marks the

southern reach boundary is almost certainly due, in part, to.the protection

provided by this natural breakwater. These features are shown on Figure 64.

120

Figure 64. Oblique aerial photograph of Sheboygan Point at the southern
boundary of Reach 21. The disturbed water in the fore-
ground is the result of waves breaking on the exposed
dolomite of the Sheboygan Reef. (oblique 53,6)

121

Along most of the shoreline in Reach 21 the bluffs are made up largely of
lacustrine sediments. These sediments display a regressive sequence, with silty

clay at the base grading upward to sand at the top of the section. A typical shore-
line segment with a steep bluff cut in lacustrine sediments is shown on Figures Oj66

in portions of sections 11 and 1@ till 3A is exposed.in a basal position, and

till 3C is exposed at or near the bluff top in section 2. In section 34, till 3C

is exposed at the base of the bluffs near the center of the sectiont where it.is

seen to rise rapidly to the north. At the northern reach boundary, till 3C is

once more at the surface, where it overlies till 3A.

Several types of slope failure were noted along this reach. in those areas

in which lacustrine sediments appeared to extend down to the toe of the slope,

failure was often in the form of very closely spaced slumps occurring at a steep

angle. The slumped fine grained lacustrine material was subsequently greatly

modified by flows, especially where a thick sand sequence occurred along the

bluff top, leading to extensive ground water seepage. In areas in which the slumped

.material was removed through wave action, undercutting and subsequent Boil falls

became important mechanisms for slope failure.

Where tills 3C or 3A were exposed at the base ofthe bluffs, failures often

took the form of very large scale slumps, with the scarp often lying several

hundred feet behind the roe of the slope.

Where thick till sequences were exposed at the base of the bluff, and

especially where the exposed till was till 3A, failure occurred primarily through

undercutting and subsequent soil fall, resulting in near vertical cliffs bordering

the beach.

Erosion rates were not determined for the extreme southern regions of

Reach 21, probably due to the.fact that this area is.almost completely protected

by revetments.

122

AIL

Figure 65. Oblique aerial photograph of a typical shoreline segment
in north and central Reach 21. The bluff is composed
entirely of lacustrine sediments with silty clay at the
base grading through clayey silt to sand at the bluff
top. Slope failure here is primarily through under-
cutting and soil fall with some high angle slumping.
(oblique 52,14)

123

Figure 66. Oblique aerial photograph at the northern valley wall
of the Pigeon River in Reach 21. Erosion of a massive
silt along the base of the bluff has created a series
of "sea eaves." (oblique 52,22)

124

in the central portions of the reach the results are anomolous, with readings

of 14 feet/year and 1.6 feet/year for the ton year average taken in close proximity.

to a site that showed a ten year erosion rate of only 06,3 feet/year.

in the northern portion of the reach# bear the till hard point that marks

its northern terminus) the ten year erosion rate was only 0.1 foot/yeart although

.a one hundred year average of 9.0 feet/year was obtained for the same point,

Reach 22

Reach 22 is made up of the shoreline in the northern quarter of section 34

and all of that along section 27 and 22 in To 16 N,j R, 23 The reach has a

priority ranking of 22, making it the seventh highest ranking reach in the

Sheboygan-Manitowoc study area.

Land use throughout the reach is primarily agricultural, although the

Wisconsin Electric Power Company hag large holdings in the@'area and may be

planning future development of a nuclear power plant,

Cobble beaches of about,20 to 30 feet are commonly'fou'nd along the shoreline

in this reach# and the bluff height is normally between forty-five and fifty feet.

in the immediate vicinity of the unnamed point that,marks the southern

boundary of the reach, the bluff is made up almost entirely of till with till 3C

lying directly on till 3A As we move northwardt the normal intervening lacus-

trine sediments once more appear., At the south section line of section 27,

twenty feet of lacustrine sediments separate tills 3C and 3A. An additional

ten feet of lacustrine sediments overlie till 3C at this point. The same general

stratigraphy carries northward throughout Section 27. The shoreline along this

part of the coast is a relatively uniform and steep bluff. At about the south

section line of section 22, there is a dramatic change in the nature of the

shoreline". The steep, bare bluff found immediately to the south gives way to a

series of massive slumoso some of which approach a tenth of d mile in length

125

and are more than 100 feet from searp to toe. This dramatic change in mode

of failure appears to coincide with the pinching out of the lacustrine beds

between the two tills. A profile at right angles to the bluff in a very similar

area in Reach 23 is shown in Figure 67 and the contrasting failure modes are

shown on Figures 68 and 69.

At the extreme northern end of the reach, the lacustrine sediments overlying

till 3C begin to thin, becoming completely absent at the northern boundary.

Ten year average erosion rates at the southern and northern ends of the

reach are 1.7 and 1.2 feet/year respectively. A somewhat anamolous figure of

0.1 feet/year was obtained for a site near the center of the reach, One hundred

year average figures of I foot/year in the south, 1 f6ot/year in the center, and

2 feet/year in the northern portions of the reach were also obtained.

Reach 23

Reach 23 lies in Sheboygan and Manitowoc Counties and includes the shoreline

in Sections 10, 15, 3 in T. 16 N., R. 23 E., and of Section 34 and a portion of

Section 2 in T. 17 N., R. 23 E. This is the area lying between Seven Mile Creek and

Centerville Creek. The reach has a-priority ranking of 23, and is the eighth

most highly ranked reach in the area north of Ozaukee County (Fig. 51,70).

With the exception of the town of Cleveland, which lies at the extreme

northern end of the reach, the shoreline is almost exclusively agricultural land..

Average density of dwelling within the reach, excluding the Cleveland area, is

less than 5 homes per mile.(Fig. 71).,

At the southern boundary.of the reach., the bluff plunges sharply into the

valley of Seven Mile Creek. North of the valley, which is about 1000 feet wide,

the bluff once again rises steeply, attaining a height of about 50 feet. The

bluff is very uniform north from this point, showing a very slow rise to the

north where it reaches a height of almost 60 feet before reaching the valley of

Centerville Creek at Cleveland. Throughout the reach, beaches are predominantly

of cobbles, and normally 20 to 30 feet in width..

0 M m
0 @-j 1- I-j I-ft @-j
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127

Fig4re 68. Oblique aerial photograph showing steep, unvegetated bluff
typical of the southern portions of Reach 22.,
(oblique 51,35)

128

Figure@69. Oblique aerial photograph showing:the large scale sequential
slumping typical of the northern portions of Reach 22.
(oblique 51,25)

129

fd" 10 Mi-

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at I
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-0 REACH 30
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REACH 28
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REACH 27

-----------------
PIDS,
REACH 26

------------------------
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REACH 25

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Figure 70 Map of Manitowoc County showing locations of Reaches 23, 74,
25, 26,, 27.. 28, 29 and 30, and geotechnical sites 15, 16, 17,
18, 19 and 20.

t LTDXOC Co.

nmm" Mae"

130

15,

Figure7l. Oblique aerial photograph showing the contrast between
the unprotected shoreline shown at the right and the
largely stable and erosion free slope lying behind a
well designed and constructed stone revetment on the
left. Reach 23, Sec. 15, T. 16 N., R. 23 E.
(oblique 51,20)

131

Immediately to the south of the Seven Mile Creek, till 3C is roughly 10

feet thick, and -lies directly on the surface of till 3A. Just north of the valley,.

till 3C is absent and the erosion surface that marks.the top of till 3A is within

5 feet of the bluff top under a thin cover of silty Eind'sandy lacustrine deposits.

Moving northward, the surface of till 3A makes a slow,and irregular descent with.

the overlying lacustrine sediments showing.a commensurate increase in thickness.

The contact is, ho wever, extremely irregular throughout the reach.

Till 3C once again appears in Section 10 of T.17N R.23E. Rather than

being present as a persistent bed, it occurs as lenses,of till completely surrounded

by sandy sediments in the upper portion of the lacustrine sequence. This is

thought to be the mode of occurrence of the upper till throughout the remainder

of the reach.

Despite the abrupt change,,.,in stratigraphy that occurs at the south end of

Reach 23, the slope failures along the shoreline continue to be in the form of

very large scale slumping with the resulting slump blocks of the type found in

the northern portions of Reach 22. This type of failure makes the study.of the

stratigraphy through this reach extremely difficult, since very little of the

stratigraphic sequence.is exposed.

Only two ten year. rec ession rate determinations were available for Reach 23,

the southernmost of which was 1.7 feet/year, and the other, which was taken in

Section 3, was 0.3foot/year. The one hundred year average recession rates for,

the reach were about I foot/year.

Reach 24

Reach 24 includes,the area between Centerville Creek at Cleveland and

Point Creek, three and one-half miles to the north. The reach includes the

shoreline of the northern half of section 27 and that of all of sections 22, 14,

and 11, T.17N., R.23E.

132

Reach 24 has a priority ranking of 17, and is the third highest reach in

priority of those reaches lying north of the Ozaukee County line.

The reach includes an area of substantial residential development at its

southern end, associated with the town of Cleveland, and large portions of the

remainder of the reach are the property of land developers and will probably

see substantial residential development in the future.

The shoreline in the extreme southern portion of Reach 24 consists of the

remnants of an ancient terrace. This terrace is about two hundred feet wide

near the southern reach boundary, and pinches down to the modern bluff line

about a mile to the north. Beaches in-this terrace area are predominantly of

sand, and between thirty and fifty feet wide. Figure 72 is an oblique aerial

photograph of a shoreline segment lying on the terrace.

In the area between the terrace and Fischer Creek, which lies about half

way up the reach, cobble beaches predominate and beach widths are in the range of

20 to 30 feet in most areas. North of Fischer Creek, the beaches once again

become predominantlycomposed of sand with beach widths normally between 20 and

35 feet.

The bluff height throughout the reach is about 50 feet, except in those areas

where the modern ground surface slopes down into the stream valleys.

The backshore area along the terrace in the southern portion of the reach

is composed of-sands of mixed origin. At the point at which the ancient bluff,

behind the terrace begins to join the modern bluff line, till 3A once again is

exposed. The erosion surface on the till is well developed, and in some areas

there is a prominent stone line visible. The till is overlain by 1-3 feet of

sand and rises to the north..

133

77,

Figure 72. Oblique aerial photograph of a portion of the terrace
that lies in southern Reach 24.

134

At the point where the terrace has fully rejoined the modern bluff line, the

till is about twenty feet thick and is overlain by thirty feet of silt and sand.

These stratigraphic relationships hold northward for about a half mile at which

point the surface of the till plunges Into the valley of Fischer Creek. The

bedding in the overlying lacustrine sediments conforms to the till surface.

For a distance of about a mile north of Fischer Creek, the section is composed

entirely of lacustrine sediments. These sediments are complex and contain many

highly contorted beds. in the northernmost section of the reach, till 3A once

again emerges from the subsurface. The top of the till is extremely irregular

with the contact between the till and the overlying lacustrines dipping below the

surface in a number of areas.

Along the terrace, the mechanism of erosion is simply the erosion of the

highly vulnerable sand by storm waves. In the area between the terrace and the

point at which the full bluff height is obtained, the mechanism of erosion is

undercutting of the exposed till through wave action, leading to soil falls.

once full bluff height has been obtained, slumping becomes the predominant

mechanism. Slumps in this area are, however, extremely steep and do not normally

involve the full face of the bluff. In many areas, slumping is confined to the

till and overlying fine grained lacustrines, with the silts and sands that make

up the upper portion of the bluff in this area remaining undisturbed under a

vegetative cover.

In the area of lacustrine sediments north of Fischer Creek, slumping is

once again the predominant mechanism. In this area, slumps are full face with

many secondary slumps occurring in those areas in which the sandy sediments have

been partially removed through wave action along the toe of the slope. This type

of slope failure continues to be most abundant in the northern mile of the reach,

especially in those areas in which the basal till is below the beach surface.

135

No ten year average recession data were available for this reach. One

hundred year averages ranged from 0.3 foot/year in the southern portions of the

reach to 2 feet/year in the north.

Reach 25

Reach 25 is located in southern Manitowoc County, covering a north-south

distance of 5.9 miles. It consists of section 1 of T. 17 N., and sections 36,

25, 24, 18, and 7 of T. 18 N., R. 23 E. Land use is predominantly agricultural

with sparsely spaced rural housing. A small amount of sand and gravel extraction

occurs in section 24 (Fig. 73). The reach ranks 20th on the overall priority

list. Erosion rates vary from 2 feet in the north to between .2 and .3 in the

central and southern portions over a 100 year average as computed by the Army

Corps of Engineers in their 1952 Shore Damage Survey.

The highest bluffs in the reach are found in the far southern and the far

northern portions where they obtain heights of 80 feet and 60 feet respectively.

Between these two areas the bluff generally maintains a height of between 40

and 50 feet.

A red/'brown silty clay till (till 3A ) from 0 to 55 feet thick is found

along nearly the entire length of the reach at the base of the bluff. Except

in sections 1 and 36, the till is overlain by sand with smaller amounts of gravel.

In these two sections silts and clay lie between the sand and the red/brown

silty till. A second thin, sandy till (till 3B ) lies in several locations

above the red/brown silty clay till (sections 1, 7, 18), but it does not form

a continuous unit.

Seeps are often noted at the contact of the surficial sand and the silty

clay till (3A ). The sand is usually dry and holds a nearly vertical face. The

steepness of the face of the sand is aided by a vegetative cover and, in places,

by compaction. Where sand composes a large portion of the bluff, failure occurs

most often by slumping. Masses of clumped sand entangled in roots also slide down

the face of the bluff (southern part of section 1, northern part of section 24).

136

Figure 73. Oblique aerial photograph showing gravel pits in a
body of pitted outwash in Sec. 24, T. 18 N., R. 23 E.
The floor of the pit in the foreground is at the
contact between the outwash and the underlying till
3A. (oblique 48,16)

137

vegetation covers large portions of the bluff face in some sections as the

result of relatively stable conditions.

Where little or no vegetation is established on the silt, clay, or till,

sliding and flow occurs. In places where undercutting occurs, soil fall results

in steep Cliffs, some measured to be as great as 56 degrees even with a 51

foot high bluff (southern part of section 18). Large slump blocks have also

been noted in this reach in the northern portion of Section 18'

Beach widths variable, ranging from 5 to 50 feet. The Predominant beach

material is sand sized material although gravels do constitute a significant

portion in some places; espcially at the immediate lakeshore.

The geology and stratigraphy in section 7 of T. 18 N.are probably the most
complex encountered in the area north of Ozaukee County. The section is unique

in that it is the only place known to the authors in which all of the tills that

have been recognized in the area are exposed (Fig. 56).
.'The southern boundary of the section lies just south of the south valley

wall'of Calvin Creek. At the section line the stratigraphic section consists of

a bed of very sandy till till 3B, overlying a thick exposure of till' 3A. In

the immediate vicinity of the south section'line, the two tills are often

separated by a thin sand bed. On the north side of the valley of Calvin Creek

till 3B, rather than occurring as a continuous and well developed unit, is found

as prominent lenses of till within a sequence of mixed lacustrine sediments

between 5 and 10 feet thick. At 'several locations, this lacustrine sequence was

also found to cont again what appeared to be a red-brown till. This material could

either be highly oxidized till 3A, till 3C, or a lacustrine clayey silt with

a high pebble content. Faint indications of bedding would indicate that the

latter possibility is the most likely.

138

At the north section line, the stratigraphy differs greatly from that in

the southern portions of the section. The observed sequence is a thick bed of

coarse sand overlying till 3C which in turn overlies a thick unit of sand and

gravel. The widely differing stratigr%*Lc sequences that occur.at the two section

boundaries can each be traced readily towards the central portion of the section.

The geologic relationships where these two differing sequences meet are extremely

complex and are not yet fully understood. Unfortunately, Section 7 was the last

section investigated and the early advent of winter weather conditions, especially

the presence of a snow cover on the high, steep bluffs that are found in this area,
forced a termination of field activities in mid-Decem.ber before the geology had

been fully worked out.

The authors' preliminary'interpretation of the geology in Section 7 is shown

graphically on the longitudinal profile. As can be seen from this profile, the

authors now believe that till 3A represents the oldest unit exposed and that the

very sandy till 3B was deposited upon the erosion surface that marks the top of

this till, probably in a shallow lacustrine environment. The sand and gravel

that occupied the basal position in the narthern portions of the section are

believed to lap up on an erosion surface,that was cut an both till C and the

overlying till B with its accompanying lacustrine beds. Till 3C is believed

to have moved across the.sand and gravel and up the erosion surface on tills 3B.

and 3A. The bed of coarse sand that lies over till 3C in.the northern portions

of the section is thought to be the youngest unit present in the section.

If this interpretation is correct, it would lend support to the view that

the sandy till 3B is intermediate in age between the two red-brown tills,

tills 3A and 3C.

139

One investigator has reported the presence of a fourth till unit (till 1A?)

in this section. This till was described as being up to 20 feet thick, and was

said to occur within the sand and gravel that is the basal unit in the northern

portions of the section. The relative stratigraphic position of this till, if

present, has not been established..

Reach 26

Reach 26 extends from about J mile.south of the city limits of Manitowoc at

Silver Creek Park to the northern jetty at the Manitowoc Harbor. It includes

Section 5 of T. 18 N., R. 24 E. and Sections 32 and 29 of T. 19 N., R. 24 E. This

is a north-south distance of 3 miles. The reach has a priority ranking of 26

and is therefore the eleventh most highly ranked reach north of Ozaukee County.

At the southern boundary of the reach land use is primarily agricultural with

a scattering of private residences along the shoreline. Within I mile, the
2

shoreline is in parkland and at the northern end of Section 5, the shorefine is

occupied by the campus of the UW-Manitowoc Center. Moving northward the reach

passes through residential areas until reaching about the center of Section 32

at which point it enters Red Arrow Park. From the north end of the park to the

end of the reach land usage is primarily industrial.

At the south.ern,end of Section 5 the bluffs are 70 feet high and are made

up of 14 feet of coarse sand overlying 10 feet of till 3C which in turn overlies

almost 50 feet of sand and gravel. Moving northward from this point both the

upland surface and. the contact.between the stratigraphic units drop rapidly.

At the south valley wall of Silver Creek the contact between the lower sand and

gravel unit and till 3C, for example, is 40 feet lower than at the south section

line, 0.6 miles to the south.

At the south section line of section 32 the bluffs are 18 feet high and are

composed entirely of sand. The bluffs rise steeply to the north and at the site

of boring GT-19, the bluffs have risen to a height of almost 30 feet and till 3C

is now exposed overlying the sand. North of this point the bluffs are heavily

140

vegetated and where exposures are present it is usually found that the surface

of the bluff is veneered with fill material that has been pushed over the edge

of the bluff.

The surface continues to rise to the north until about the middle of the

section at which point the bluffs are about 60 feet high. Northward from this

point the bluffs lose height rapidly and by about the north section line have

completely given way to a low sand plain along the shoreline.

The beaches along the southern half of Reach 26 are of sand and cobbles and

are from 20 to about 40 feetwide. North from here to the north end of Red

Arrow Park, sand beaches predominate. Many of them are more than 50 feet wide.

North of this point the beaches are either absent or obtain a maximum of about

20 feet..

Fromithe south section line of section 5 to about 0.15, erosion is very

rapid and slumping and sliding of the lower sand and gravel in this high bluff

area appears to cause quite rapid retreat of the bluffs. From 0.15 to about 0.7

at the mouth of Silver Creek.Blope failures occur mainly as slumps which often

involve most, if not all, of the face of the bluff. From Silver Creek north to

the end of Silver Creek Park at about 0.9 there are no bluffs and shoreline

erosion occurs through the action of waves against the low lying shoreline. From

this point north to the section line slopes are gentle and completely vegetated

with grasses.

Slumping is again common in about the southern 0.2 mile of see. 32. North

of this area, the slopes are veneered with fill, fully vegetated and appear to

be largely stable. From Red Arrow Park to the end of sec. 32, there are no

bluffs.

As part of a separate investigationthe author inspected the south half of

Section.29 (the remainder is Manitowoc Harbor) and photographed the structures

lying along the shoreline in this area. It was found that the entire shoreline

141

is armored by heavy revetments or bulkheads and that the bulkheads were backed

by sand, some of whic h is undoubtedly fill. Since this is a fully armored sectio n,

Section 29 has been deleted from this investigation.

Two long term recession measurements both gave values of one foot per year.

Reach 27

Reach 27 consists of-the area between the northern Jetty of the harbor at

Manitowoc and the town of Two Rivers. The reach includes the shoreline in portions

of Sections 20, 17, 16, 10, 11, and I of T. 19 N., R. 24 E. The reach has a

priority rating of 16, and is the most highly ranked reach in the'Sheboygan-Manitowoc

study area.

Over most of this reach, the shoreline consists of a well-constructed revet-

ment with either sand, fill, or both behind. The immediate shore zone is separated

from residential, commercial, or park lands bv a four lane highway in most of the

reach.

A few small, scattered beaches are found in this reach, but many appear to

be ephemeral. Some of the beaches present when the reach was inspected were not

found to*be visible on the air photographs taken earlier in the year, and some

beaches shown on the photos were no longer present.

The reach is, with the exception of a single section to be discussed later,

protected by heavy structures which over large areas are backed by fill.

Significant exposures of stratigraphy and unprotected shoreline segments are,

however, present in section 16. The remainder of this discussion will, therefore,

be confined to this section.

The bluffs in section 16 rise to a maximum height of about 30 feet above the

beaches. In the southwestern portion of the shoreline in the section, very little

stratigraphy is exposed due to heavy vegetative cover and the large amount of

slumped silt that covers the greater part of even actively eroding areas. About

3 feet of bluff silt over 2 feet of silty clay was the maximum section observed in

the southwestern portion of section 16 (Fig. 74).

142

In the northeastern portion of the section, several excellent exposures were

located from which it was possible to determine the stratigraphy from the top of

the bluff to beach levels The section was found to consist of basal lacustrine

sandpt which were overlain by a one to three foot thick bed of till 380 which was

in turn overlain by roughly 10 feet of the same red silty clay observed to the

southwest, The silty clay was in turn overlain by the buff silt found in the

equivalent stratigraphic position in the southwestern exposure, The silt was

overlain by a highly oxidized till identified as till 3Cj and the section was

capped with about a foot of sand, A thin greenish-gray sand layer in this unit

was found to make an excellent marker bed.

Although essentially flat lying where first observed, all of the units des-

cribed were found to plunge to the northeast at the wayside on top of the hill

in Section 16. The beds were then overlapped by a horizontally bedded sand.

The top of the bed of till 3C dipped into the subsurface at the north section line,

Figure 74 is a generalized longitudinal profile of Section 16; figure 75

is an oblique serial photograph of a portion of the high bluff shoreline in

section 16; and figure 76 shows a low-lying and heavily protected area# typical

of most of Reach 27.

Lake superior
Reach Descriptions

Reach 1

Reach 1 extends southeasterly 3A miles from the Wisconsin-Minnesota state

line at Superior Entry to the base of Wisconsin Point (Fig. 77). The reach is

located in sections 27, 28, 34, and 35 of township 49 north, range 13 west in

Douglas County and is the most northwesterly reach in Wisconsin. The reach is a

low-lying sand spit that ranges from 3 to 15 feet above lake level which together

with Minnesota Point, to the west, forms a bay mouth bar that is the longest

fresh water spit in the world. The spit separated Allouez@ Bay from Lake Superior.

Beaches are made up predominantly of sand and pebbles and range in width from

Prof Ile2
sand
GT-20
buff ilty
silt clay
till 3C
zone contains many large
red silt
Inclusions of highly
contorted buff silt
-0
?
lacustrine sand
revetment
horizontal bedding
C):
Prof Ile I i.nterbedded. Stoney brown till 3B
sand andsilt very hard, many boulders
silt and cobbles

SCAM
Horizontals I inch 1000 feet
Vertical i I inch 20 feet

Figure 74. Generalized longitudinal prof ile of se
C. 16, T. 19 N., R. 24 E., Reach 27.

144

Figure 75. Oblique aerial photograph showing a portion of the high
bluff area: in Sec. 16, T. 19 N., R. 24 E., Reach 27.

145

Ik'

Figure 76. Oblique aerial photograph showing a typical heavily protecte d
segment of the shoreline in Reach 27.

146

REACH REACH
5 6

REACH
4

REACH
REACH REACH 3 1

R A SII
2

j,c
,LAX.; SIDI,

41H.

I t
I ..
It

@TA 7
N D 111? U L F.
g
TI:
APLE

It,
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DOUGILAS CO.

Figure 77. Map of Douglas County.

147

more than 300 feet on the west to 3 feet on the eastern end of the reach. Although

accretion is dominant in this segment of the coast the amount of accretion decreases

from a maximum of more than 10 feet/year at Superior Entry to an erosion rate of

about two.feet/year near the base of the spit. Breaches of the spit have

periodically exposed the marshes on the east end of Allouez Bay to direct wave

action. The reach-is also one of the few shore areas on the western arm of Lake

Superior where the sand supply is sufficient to allow the formation of sand dunes.

'Much of the reach is a low developed recreational area largely owned by the

City of Superior. The abandoned Coast Guard Station adjoining Superior Entry is

occupied as a study center by the University of Wisconsin-Superior. The only

shore protection or navigational structures in the reach are the jetties protecting

Superior Entry and a dock adjacent to the Coast Guard Station.

Reach 2

Reach 2 extends 4.9 miles east from the base of Wisconsin Point to the mouth

of the Amnicon River in sections 35 and 36 of township 49 north, range 13 west

and sections 31, 329 33, and 34 of township 49 north, range 12 west in Douglas

County (Fig. 77). The reach has an erodible, high bluff ranging from 40 feet to

65 feet above lake level. The bluff is composed predominantly of red clay and

silt with occasional sand lenses. The bluff is dissected by Dutchman Creek,

Morrison Creek, six unnamed streams and the Amnicon River. Along this shore the

rivers emanate from south of the Douglas fault some 6 to 10 miles inland and flow

predominantly on bedrock across the intervening coastal plain. The creeks and

unnamed streams are still down cutting through the red clay of the coastal plain

and are frequently subject to damming by long shore drift during low flow

conditions. Beaches in this reach vary from a maximum width of 65 feet to being

absent. The widest beaches are almost always in the vicinity of a river or

creek mouth and are frequently covered with draftwood, a typical feature of the

Lake Superior Coast. The beach is composed of sand and pebbles with occasional

148

boulder erratics, Frequently the beach offers no protection for the bluffs and

relatively low waves cross,the narrow beaches to act directly on the toe of the

bluff. The wave action destroys the stability of the slope subjecting the bluff

to almost constant erosion in the form of slides, slumps and earth flows, During

rainy seasons the bluff material flows across the narrow beach and the near shore

area becomes highly turbid with the fine materials. Spring sapping is also

frequent, particularly in areas of the bluff having sand lenses. The erosion rates

in this reach range from 8.7 feet/year to 2.7 ieet/year. The reach is largely

undeveloped with a few seasonal or permanent residences in the vicinity of road

ends and stream mouths. There are no shore protection structures or bedrock

outcrops in this reach,

Reach 3

Reach 3 extends 3.2 miles east from the mouth of the Amnicon River to the

mouth of the Poplar River and is located in sections 34, 35, and 36 of township

49 north, range 12 westo and section 30 of township 49 north, range 11 west in

Douglas County (Fig. 77). The height of the bluff in this reach ranges from 55

feet to 65 feet and the bluff is composed predominantly of red clay and silt,

The bluff is dissected by Hanson Creek, Middle River andthree unnamed streams in

addition to the Amnicon and Poplar Rivers.

Beach width in this reach varies from about 30 feet at the mouth of the

Amnicon River to nothing at intermediate points between stream mouths, The

beach is composed of sand and pebbles, occasional cobbles and frequently driftwood.

With the narrow beaches the waves frequently impact directly on the bluff

instigating slope failures such as slides, slumps and earth flows.

The reach is mostly undeveloped and the only access is by three town roads.

The only shore protection structures in the reach are located on the east side

of the Amnicon River. A timber groin and a sunken barge were placed at that

point to protect a now abandoned sand and gravel operation. These structures

are almost completely destroyed and offer little shore protection.

149

Reach 4

This Reach 4 extends 9.7 miles east from the mouth of the Poplar River to the

mouth of the Bois Brule River in Douglas County, and is located in sections 13,

14, 21, 22, 23, 28, 29, and 30 of township 49 north, range 11 west, and sections

8, 9, 10, 17 and 18 of township 49 north, range 10 west (Figj 77). The reach has

an erodible, high bluff ranging from 40 feet to 75 feet above lake level. The

bluffs decrease in height from west to east. The bluffs are primarily red clay

and silt with occasional sand lenses. Beaches are composed of sand, pebbles and

driftwood. The beaches vary in width from about 100 feet at the mouth of the" Bois'

Brule River to nothing at many locations. Waves consistently cross the narrow

beaches to cause massive slides, slumps and earth flows. Frequent slide scars

indicate the movement of large trees from the bluff crest to the water's edge.

The bluff through this reach is highly dissected by Bardon, Pearson, Haukkala,

Nelson, Fisher and SMith Creeks, and sixteen unnamed streams as well as the Poplar

and Brule Rivers. An unusual feature in this reach is the very long spit that

frequently develops at the mouth of the Bois Brule River. The spit extends

westward from, the east bank of the river mouth and may at times attain a length

of over one-half mile, sometimes adding a neighboring stream as a tributary of the

Brule by extending across that stream entrance. The reach is relatively undeveloped.

except near the mouth of-the creeks and rivers. Access is generally restricted

to the section line roads except at the mouth of the Bois Brule River which is

served by a state forest road. There is a precast concrete groin immediately

west of Bardon Creek that is in excellent condition and a beach has formed on its

easterly side. There are no other structures in the reach except for a boat ramp

near the mouth of the Bois Brule. Erosion rates in this reach range from nearly

six feet per year to about two feet per year. Minimum erosion along the western

arm of Lake Superior coincides with the entrance of rivers.into the lake because

maximum beach widths also occur at the mouth-of the rivers. There are no bedrock

outcrops in this reach.

150

Reach 5

This reach extends 2,0 miles northeast from the mouth of the Bois Brule River

,to Brule Point in Douglas County. The reach is located in sections 2. 3, and, 10

of township 49 northi range 10 west (Fig. 71). Bluff height in this reach varies

from 10 feet to 40 feet and averages about 35 feet. The bluff is primarily made

up of red clay and silt except in the lower portions where the sand content

increases. Beach widths range from absent to 30 feet and the beach is composed

of sand.and pebbles. Bedrock outcrops are not readily visible in this reach but

sandstone outcrops do occur in the immediate.near shore zone hear'Brule Point and

may control the location of that promintory. The reach is largely state owned and

undeveloped except near the mouth of the Brule. Cleared fields near Brule'Point,..

are evidence that some cultivation has been tried and abandoned. Access to the

area is limited to the western end of the reach and five trails neat the east

end... There are no shore protection structures in this reach, but there is a boat

ramp on the Bois Brule near its mouth. Erosion processes are similar to other seg- J

ments of this "Red Clay" shore,-waves cross the narrow beaches to directly attack

the base of the high erodible bluffs. This action keeps the bluffs' slopes

unstable and promotes various forms of mass movement such as slides, slumps and

earth,flows.

Reach 6

This reach extends 4.4 miles easterly from Brule Point to a rock prominence'

700 feet west of the mouth of the Iron River and is located in sections I and@2

of township 49 north, range 10 west; sections 4, Sj and 6 of township 49 north,

range 9 west; and section 33 of township 50 north, range 9 west .(Fig. 78).. The

western 1.1 miles of this reach are in Douglas County and the balance is in,

13ayfield County, The bluff height ranges from 20 feet to 40 feet and the bluff
is predominantly red clay with some interbedded* sands. The bluff is dissected by

Fish Creek, Reefer Creek and two unnamed streams. Erosi.on,r.ates in this reach

vary from a high of about 10 feet/year to a low of about 7,feet/year. Beach

151

REACH
REACH 13 14 REACH
-4 " 15
REA CH 12 V!,@-

REACH
REACH
10 11
1 16
REACH

REACH
@,7 REACH
8
BA Y, I EU 17
REACH
REACH
18
7
REACH
6 REA
T
CH 19

REACH 20

All
Am"

-1k
REACH 21

77
REACH 22
I E

Figure 78. Map of Bayfield County.
r@PXA,

152

widths in the reach vary from 30 feet to nothing and are composed-mostly of sand

and pebbles-although an increasing number of boulder erratics arealso.present.

The westernmost bedrock outcrops along the south shore occur in this reach in the

form of flat-bedded sandstone about 1000 feet west of the Iron River-. This outcrop

is visible near the level of the lake. Erosion processes are visibly similar to

other "red clay reaches" with wave action causing direct erosion of the bluff in

areas with narrow beaches and also causing bluff failures such as slides, slumps-

and earth flows. The evidence of these failures is not as spectacular as it is

farther west in-the areas of higher bluff.

Reach 6 is highly developed with primarily seasonal residences between the

shore and state highway 13. There are no shore protection structures in this

reach of the Lake Superior Coast.

Reach 7

Reach 7 extends.five miles northeasterly from a point 700 feet west of the

mouth of the Iron River to Quarry Point in Bayfield County. The-reachis,located

in sections 33, 134P 35,- and 25 of township 50 north, range 9@west@;- and sections-

30 and 19 of townihip-50'north, range 8 west.. The reach is a medium to,,high

bluff (average 25 feet) shore. The bluff is composed mainly of red clay and silt.

The bluffs are dissected by the Iron River, Jardine Creek and two unnamed streams

in this reach. The beach varies in width from 110 feet on,the wes*t bank of the

Iron River to absent at other locations'. Where present, itlis. composed of, sand

and pebbles, some boulders, and localized sandstone@shlngle,and cobble, one-

frequently finds clay@balls formed'by wave action =piece'&of clay-fromthe.bluff.

The erosion rates in this reach range from 4.4 feet/year to 1.0 foot/year-and,

average about 2.0 feet/year. The erosion processes are,dominated by wave action,

on the bluffs and the-resulting slope failures. in the form of silumps, slides,

and flows.

153'

one of the-unusual features in this reach is a shingle-cobble spit damming

the mouth of Jardihe Creek. The material is well rounded sandstone that is a

deep-reddish brown. The source of the material may be a sandstone outcrop on

the west side of,the creek mouth or other outcrops in the near shore zone. A

major sandstone outcrop occurs at Quarry Point, west of Port Wing. This outcrop

was quarried, as the name would imply, for building stone used in Superior and

Duluth near the turn of the century.

There is a bo at ramp on the Iron,River near its mouth but no shore protection

structures in this reach. :The reach is sparsely developed with seasonal and

permanent residences located between the shore and Highway 13.

Reach 8

This,reach extends from Quarry Point 7.1 miles east and northeast to a,rocky

promontory 1.1 miles west.of the mouth of the Cranberry River and includes the

harbor entrance at Port Wing in Bayfield County. The reach is located in

sections Ili.12, 14, 15, 19, 20, 21, and 22 of township 50 north, range 8 west;

and sections 6 and T,of township 50-north, range 7 west (Fig. 78). This-reach

is marked.by-highly contrasting shore types. At each end of the reach low sandstone

cliffs are present, the westernmost two miles of the reach are low-lying sand

spits forming a bay mouth.bar at the mouth of the Flag River, and the remainder.

of the reach has the@'.highest (over 200 feet above lake level) bluffs on Wisconsin's

Great Lakes Coast.i Sin unnamed streams dissect this extremely hi gh bluff segment

of the reach. Quarry Poi.n.t,averages only about 10 feet in height while the Port-

Wing spit,is generally less than 10 feet above the@present lake level. one of

the highest.shore recession rates occurred west of the entrance to Port Wing when

the spit was completely eroded following the extension of the jetties At the

harbor entrance. This'shore retreat amounted to almost 2000 feet and occurred in

about a 10 year period during.and after World War II. The spit has since been

rebuilt, with the,aid of the westerly long shore drift, although it remains narrower

than the spit to the east of the harbor entrance.

154

The extremely high bluffs to the east of Port Wing are very different in

appearance and composition-from the high bluffs to the west. The bluffs appear

to be either reworked glacial till or outwash and take on a "flat iron"' appearance

when viewe&from the lake. The bluffs are composed of interbedded sandf silt, and

clay with abundant gravels and cobbles. This bluff is undoubtedly -the source of

most of the beachematerial at Port Wing because of the much higher percentage of

coarse material than the "red clay bluffs." Although recession rates are lower

than many other areas, 2.0 feet to 6 feet per year, the volume of material eroded

probably exceeds an: other segments of Wisconsin's Lake Superior shore of similar
y

length, because of the greater bluff height. Beach widths vary from about 50 feet

at Port Wing to absent at the rocky points. Beach widths along the high bluff

segment average less than 10 feet inwidth because of the steep near shore slope.

The high bluff area is'undbVeloped in contrast to the Port Wing area where the

harbor was developed in the latter part of the 19th Century in connection with

a saw mill'operat6d in,-*that area. There is good public-access at Port Wing but'

the high bluff.shoreline is totally inaccessible by road. The only 'shore

protectibin@structures in this reach'are the-steel sheet pile jetties protecting

the entrance to the Flag River and Port Wing.

Reach 9

This reach extends from the rocky prominence one mile east of Herbster

northeast 6.9 miles to Bark Point and is located in sections 4., 5., and 6 of

township 50 north, range 7 west; and sections 24, 26, 27, 33, and '34 of town-ship

51 north, range 7 west in Bayfield County (Fig.78). The bluff in thi-s.reach is

quite variable ranging in height from 150 feet to 10 f,eet and averaging about

40 feet above the-level-of theIake., The low bluff areas' are a sand spit at the

mouth of the Cranberry River. This area also has greater beach widths than the

rest of the reach (about 70 feet) and the only structure. The structure was

originally a jetty or pier at the mouth of the Cranberry River but a:ll that

155

remain are a few timber,pilings in very poor condition and nonfunctional. The

bluff is composed of sand, clay, and gravel while the beach is mostly sand and

pebbles.

Beach widths along the higher bluff areas are generally less than 10 feet-wide.

Sandstone bedrock outcrops at each end of the reach and its height in the bluffs

is usually higher to the east.. The reach is moderately developed with seasonal

and permanent residences. Public access is excellent at Herbster where the

village maintains a public park on the lake front. Bark Point is a mixture of

residentiali recreational.and agricultural development.

Reach 22D

This reachois, located on the east side of the City of Ashland and extends

2.1 miles east from the west boundary of Lake Park to a road end two miles east

of the city limits. It is located in sections 27, 23, 24, and 19 of township 48

north, range 4 west. The top of the bluff in this segment ranges from 20 feet

to 4Q feet@above, the lake level and,much of the bluff is composed primarily of

red clay and.silt.. Beaches are composed of sand and pebbles but are relatively-

rare in this.-reach.

The reach is largely residential except for the city park and there are many,

shore protection structures in.the reach of highly variable construction@' The

most common structural form is rock-filled timber cribs used as groins or revetments.

Some of the most interesting and substantial structures are "home made'? from salvaged

timbers of the-old ore docks in Ashland that float ashore after heavy storms. The'

most serious erosion problems occur in those properties that have not constructed

shore protection structures. This also creates a major problem for those property

owners that have protective structures because of the difficulty of protecting

the existing structures from flanking (wave attack on the unprot .ected sides of the

structure). Shore,recession.rates in the unprotect ed segments of this reach have

averaged as@high as five feet per year, even though this reach is semi-protected

156

by the offshore breakwater in'Ashland and the arm of Chequamegon Point and Long

Island. These sand spits protect the reach from the open lake and decrease the

effective fetch of waves approaching this shore.

Reach 27

Reach 27 extends from the base of Chequamegon Point eastward 4.8 miles to

Marble Point, in sections 26, 27, 35, and 36 of township 48 north, range 2 west;

section 1 of township 47 north, range 2 west; sections 5 and 6 of township 47 -

north, range I west and section 32 of township 48 north, range 1-west (Fig. 79, 80).

The western 2i6 miles are in Ashland County and the eastern 2.2 miles are in Iron

County. Bluff heights range from 20 feet to 80 feet above lake level, but average

bluff height.is about 60 feet above the lake. Although this reach i .s in the "red

clay" area, samples of the bluff material indicate-that these materials are

primarily coarse silt and,very fine sand with little if any clay size material.

The composition of these bluffs is however.highly variable.

The beaches,, composed-of sandand pebbles, range from 30 feet to 10 feet in

width and are particularly susceptible to rapid changes in dimension because of

their openness to large northeast storms off Lake Superior. There are no shore

protection structures in this reach, but a demonstration site using.various

patterns of,Lo,ngard..tubes is to be constructed in this reach in 1977. The reach

is generally undeveloped except for a recreational site on the west end of the

reach..and a picnic.ground at Madigan Beach. Erosion rates in this reach average

about.one to two feet per year.. This reach is entirely within the Bad River

Indian Reservation.

Reach 28

This1reach extends 4.4 miles from Marble Point easterly to the Wisconsin-

Michigan state line.at the mouth of the Montreal River. It is located in sections

3$ 4, IOV 11, and 12 of.township 47 north, range 1 west;@and section 7 of township

47 north, range 1 east in Iron County (Fig. 80). The westernmost mile of the

157

REACH
REACH 32
31

'REACH 30
tv REACH 33

REACH 29
REACH 34

REACH
25
REACH
24
REACH
26

REACH
Y
2 2, X
REACH
27

-,Or

H's I F.

"A 41i LL@1

ASHLAND CQ@

Figure 79. Map of Ashland County.

158

REACH REACH
21

RIE

I
!rot

k h

'8A
IUR
F@ wt
10

IRON Co.
'-TALNT OF TRANSPORTITIM -4

X.LE

Figure 80. Map of iron County..

159

-80,
reach is in the Bad,River Indian Reservation. The reach has a high bluff (10

'feet) shore with narrow beaches and several bedrock outcrops. Most of.the bluff

is composed of interbedded sands and a clay cap in the-upper 10 feet.
silts with

Sandstone bedrock outcrops at Marble Point and as steeply.dipping strata in the
vicinity of' the Montreal River, Slumpsi slidea and,earth flows are promoted'by

the eroding waves that cross.the narrow beaches to attack the toe of the bluffs.

The bluff is dissected by Graveyard Creek, Sturgeon Branchi Carpenter Creek, Parker-

Oronto Creek and the Montreal River.

The reach forms a large open embayment known as Oronto Say. At the aipex of

the bay A small boat marina, Saxon Harbor, is located adjacent to the mouth of

Parker-or6nto.Creek., Beaches in the reach are narrow varying from 30 feet to

and are composed primarily of sand and pebbles with increasing Amounts of

iwell-.-rounded pebbles and cobbles to the east. The only shore protection structure

in this reach is a kiprap revetnient immediately west of the entrance to Saxon

Harbor, The revetment has not been adequate to protect this site from further

erosion. The harbor entrance is protected by a sheet pile nozzle And a@caiss6n.

arm. The mouth of Oronto-Parker Creek is also protected by sheet piling in an

effort to prevent the damming of the stream by long shore drift.

Reach 33

This reach extends from Big Bay Point easterly 5.6 miles to Amnicon Point

on Madeline Island in Ashland County in sections 12, and 13 of township 50 north,

range 3 west; sections 19t 7, 8, 5,.4, 3, and 2 of.township 50 north, range 2

west; and sections 35 and 36 of township 51 north, range 2 west (Fig. 79). Bluff

heights.in this reach range from 5 feet to,20 feet above the level of the lake.

The bluff material is highly variable and includes red clay, till, sand and

sandstone. The sandstone bedrock outcrops at Big Bay Point, Amnicon Point and

on both sides of Big Bay., Big Bay has a spit forming a bay mouth bar on its western

side that forms Big Bay Lagoon..'Beach widths range from more than 60 feet to

160

absent. The beaches are composed of sand and pebbles and occasionally sandstone

cobbles and erratic boulders in the near shore area. The reach is lightly developed

on the western end of the reach on Big Bay where the use is primarily recreational

in state andcounty parks. From Big Bay east to the vicinity of Amnicon Point the

reach is primarily residential although there are also several fishing camps. The

easternmost end of'the reach, at Amnicon Point, is in theBad River Indian Reserva-

tion. There ar e many shore protection structures associated with the residential

area bordering County Highway H. The structures are quite variable but the most

common form is rock filled oak cribs used as piers, groins and revetments. The

structures"aie economical and usually functional. A portion of Highway "H" in

section 8 of township 50 north, range 2 west has been repeatedly threatened by

erosion damage creating a major problem in this reach.

161

SUMMARY AND CONCLUSIONS

Material Properties

A really intensive investigation of the material properties of the

soiles along the shoreline and especially their statistical variations

and interdependencies, was not undertaken in this study. However, sev-

eral general observations can be made through an interpretation of the.

laboratory results obtained.

Standard Penetration numbers for the sand deposits indicate in most

instances relatively dense sands. A plot of all the triaxial test re-

sults on sands and silts shows a strong relationship between the dry den-

sity of the sands and their drained angle of internal friction (nee

Fig. 81). For most of the sands, maximum and minimum void ratios were

not determined, so that a conparison based on relative density is not

possible; however, with respect to their absolute density, there is still

a reasonable dependence of on Yd' with the points falling in a fairly

narrow range of values. Maximum and minimum angles are 34.7 and 41.0*

respectively, with the angle of internal friction at any given density

falling within a range of values varying by less than 4.5% The values for

the silts tested as a dry powder in triaxial tests indicate a lesser

angle of internal friction for the same density, while the cohesion,

obviously could not be measured.

For clayey soils, the values of the Liquid and Plastic Limits for

all the samples tested have been plotted on a plasticity chart, Fig. 82.

.This@chart shows the relatively narrow range in the classifications of

these materials; all samples tested were either low-plasticity silts or

clays. The grain size distribution of the tills is shown in Figures 83,

84 and 85.

162

400
T;
L

4-
T-]
L

350
44

T
30" 77

SaO 1 s0ecim4 ris
Ti j@;
P
ec i' n iI
, T

25"
J-

20" 80 90 100 110 120-----* --"'130
Dry density as tested (psf)

Figure 81. Drained ang-le of internal friction vs. dry
density for sand and silt specimens.

PLASTICITY INDEX, Ip, M

77,
71-T 77 7

Al
r'T
1. LJ
4- J:
if

Co
IJ i

-1 -Q4
rt

rt
14 ij
co

-1 !JJ-

T
Lo
Lp I

40
rt
T7T

0 n En
(D

(IQ (A
m H.
(J) @-A
0 rt
0 1

tyj
> >

179T

00
NI,

clr rr
<
F@ (D H-
rj) @-j
to
0 1

to C")

F- m

99T

S,I-,JD too% Figure 85. Sand-silt-clay per7
centages of samples
of till 3.

X = Till 3C
0 = Till(?)3B
= Till 3A

0
ON

'ZO
A !PO

too% 40 To 4c 20 to C,%A4 too?,
/\U@
7@

V
I\A
- A/\

167

.Inspection of the Atterberg limits, and strength characteristics-of

the clayey soils, leads to a distinct differentiation of the.tills and

lacustrine deposits. A summary of these properties based on the aver-

ages of all of the samples tested within a given layer or unit at each

borehole is shown in Table 2,3. The till layers have been groupe d-accord-

ing to their geologic similarities, and their properties statistically

correlated. The results are tabulated in Table 4, and drawn on a plas-

ticity chart, Fig. 86. Difference in the material properties within a

particular unit arise in the fact that local chemistry may alter the clay

,characteristics, source material from the same glacial unit may vary

somewhat with location, and the local stress history at any particular

site (e.g. glacial overburden, overlying lake deposits, etc.) may change

the strength parameters significantly.

With reference to the above correlations, the following generaliza-

tions or observations can be made:

1. The entire range of the Atterberg limits. of all the specimens

tested is relatively small, comprising mostly low-plasticity clays and,

clayey silts. This is even more striking when the average values for the

till units is observed--practically all of the averages have Liquid

Limits between 22 and 32 per cent, with corresponding Plasticity Indices

between 9 and 15 per cent.

2. A correlation cannot be made between the Att.erberg limits of a

particular sample and its drained strength parameters. The southern grey

till unit (2A,B) in Rapine and southern Milwaukee Counties has drained

strength parameters approximately equal to those of the red till unit

OA) of northern Milwaukee and Ozaukee counties; but the averages of

their Atterberg limits (wL 24.1 & 30.7%; Ip 10.1 & 14.1%, respectively)

Sr.. 11 U, 0

L
En <
C,

Al H

4
OD

ca IV "IV
11 "It CHI IL3@
0
ti
m
W. LA
0
m An H
4t d4 G. .
SO M
1 4
I F-, w 14 1-4 N
La N
H :4 1@
P

r!F 04
-Et
10 IV,
13
'"4 LA
0 co
rl Z. :0 11 1" r,4 @l
4 cl, t3 $- Ld
61

@41 11 IE: .6, 1
Co

E. g -4 LA >

rIF G.
131
PHI
:0 41 r
w

nr
L. 0)
03 n
n
i a
H ti F @- @ .. S Jo
cc :0 N %L.4 0. C6 .4 IL
8- ;4
to 14 t4
a, CD go w

99T

I to 0
.0.
ft @L
(D CIO :,1 0 17
to 1-
to

CAI 1-4 Ir
I." lo
to '0
-t4 @D
to to (n ID 0
to to -3 Z' U, to 0
C. 10 0 1- CL 0
14
to

ro
1@
to I',
:0 11 11 :J2 C. '1 0 '1 OD r, C.
0 l'o
Ll . I- - pv 0, ;o I
V" 'I to I, - w :3 tI, C, r 4
rD I N 14 @o 1- 0 @n @O 0 0 l<
0 to to

FJ*
I'd lo
to to In C)
to V@ 11 U1 0 'W'
1.o , . P@ S@"
10
100 wn .1 W'4 CL W 1-1 -4
110 1,4

m
Fl to "i
(D - .3 m
W C, 0.
IJ Lj

0 Fl

I'A
Fl 1-1,4ww 14 w C3 10 w
I to to I- 'I (b r CL I-
-:4

If 11 0,
to " 0@ w0 m F@ .91
F- I CL
, 'iM n
to C. 0 10
CL

Old
11 11 p I m ii o o 2
1'. w rj F-1 W 1-- W 01- W 0
10 1, C', L, ID w P.

69T

170
Table 4
Summary and Correlation of
Laboratory Results on Glacial Till Units

Grey till. Racine and Milwaukee Counties. (Till 2)
Strength: (GT-4) 31.2 (GT-1) 31.4 (GT-1) 31.0
C 0 0 0
Average-- 0 = 31.2 + .2
c= 0
Atterberg GT-10) w= 24.4 - (GT-4) W-23.2 GT-1) w= 25.1
Limits 1 0 9.66 a 9.45 1 0 10.06
P pi P
(GT-1) w -25.8 (GT-8) w-22.8 (GT-6) w - 23.0
L 6q%
10.9 1 =10.0 1 10.7
P
Average-- w L - 24.05 �1.13%
IP . 10.13 �.52%
Red-brown till. North Milwaukee and Ozaukee Counties. (Till 3A)
Strength! (GT-8) 32.5 (GT-6) 0- 30.50 (GTm7) 0'- 31.30
C! - 0 cd0 c
Average-- 0 31.4 .80
cl 0
Atterberg (GT-8) w L- 29.8 (GT-6),w L-31.3 (GT-7) w L- 31.0
Limits: IPW 12.6 1P.15.0 1 Pa 14.7
Average-- wLft 30 7 � .65%
I W 14:1 �-1.07%
P
Lower Red-brown till. Sheboygan and Manitowoc counties. (Till 3A) J
.strength: (GT-12) 28.70 (GT-12)' 0'- 30.0- (GT-8q47) 31.@50 d
C'- 511 psf c'- 696-psf c- 380 psf
- (GT-13) 0
(GT '14) 22.30 31.30 (GT-15) 31.30
C' 1023 ppf c), 530 psf c0 530 psf
Average--- 0'-29.18 �@ 3.20 30.56 1.17; (if GT-14 ignored)

C' 612 206 paf c'- 529 1 0 ps
Atterber Limits.:
Average- w L 30.93 �3 97% (all samples of till unit, including
IP 14.53 3:24%
boreholes GT-8,6,& 7)

w 29.8 31%
IL (lower till unit in-Sheboygan & Manitowoc)
13.6 2:4%
P
Upper red till. Sheboygan and Manitowoc counties. (Till 3C)
Strength:
Average-- 4@q'- 29i55 �'.390 (GT-14&13) 29.83*. (GT-20) 29.0*
cl- 578 � 151 0psf c'- 471 psf 792 psf
Atterberg Limits.,
Average-- w L 27.34 � 4 08% (all samples of till unit)
0I0P 12.7 � l.2i6%
Note; Averages are mean values of the average properties assigned to each
till layer at each borehole, with the standard deviation indicated.

-1 T- 1 1 '1 --- I F j I I I I j
-4-4-

-T
=LLD-
FT I
30
T-4
;IF
- - - - - - - - 0- 4L I
I J-
-IL i -14
e V1 an
A4
ik-de'- -t--r
20 t
1,Up rL p

;
;Oo
Oo

Aj
10

0
0 .10 20 30 40 50 60 70

Liquid Limit

Figure 86. Plasticity Chart for averages of till units. (average for
unit in solid color)
-4-

172

do not agree well with one another. Conversely, the Atterberg limits for,

the red till of Ozaukee County (3A) compare closely to the averages of

several samples of the same till unit exposed in the lower bluff reaches

of Sheboygan and Manitowoc counties; but their drained strength parameters

vary considerably 31.4* & 30.6% c' = 0.0 and 530 psf, respectively).

Therefore, no "rule-of-thumb" simplification is possible.

3* This is not to say that there is complete scatter in the re-

sults obtained. In fact, t@e geotechnical properties are relatively con-

stant for samples of a givep glacial unit under similar conditions, i.e.

in a similar geographic location. The drained angle,of internal friction

for all, samples of the Racine-Milwaukee grey till unit (2A,B) vary by

only 0.2 degrees, while their average Liquid Limits vary by only 1.13

per cent, and their Plasticity Indices vary by only 0.52 per cent. Also,

the red upper till (U). of Ozaukee County has a variation in 0' of only

0.80, and in Atterberg limits of 1.07 and 0.65% for wL and Ip, respec-

tively'.. Even the somewhat more variable lower red till unit (3A)'of

Sheboygan and Manitowoc counties has drained strength parameters varying

by onl 1.07 degrees for and 100 psf for c', which is relatively
y

small in comparison with the lab inaccuracie s. The upper red till unit

(30 of Sheboygan-Manitowoc varies by only 0.39* in and by only 151

psf in c'.

4. Lacustrine deposits follow no set trend in their properties,, so

that their drained strength parameters cannot be predicted. As a casual

observation, the drained angles of internal friction of lacustrine clays

are generally smaller, the cohesion generally larger than those of the

till units in the same area, but this is not true in every-case. The

clay of GT-5, it may be noted, has Atterberg limits very close to those

173

of the grey till of Racine-Milwaukee (2A,B) which lies on either side of

it; likewise, in GT-7, the lower red-brown lacustrine clay has limits

very similar to those of the upper red till in Ozaukee county. In other

instances, the limits of neighboring till and lacustrine deposits may

vary considerably, as in GT-l and GT-20.

In summary, it can be stated that the Atterberg limits of the till

deposits along the Lake Michigan shoreline do, in many cases, exhibit

signific ant similarities, when they are of the same glacial unit, and

are subjected to similar influences. The drained strength paraneters can

be roughly predicted for the southernmost tills (2, 3A in Racine, Milwau-

kee and Ozaukee counties) within relatively narrow*.limits at about 31*

for @', and c' = 0. The n"orthenmost tills show greater variability, but

all have considerably more cohesion (c' 300-700 psf), while their

drained angles of internal friction are slightly lower (01= 29-30*).

Atterberg limits alone cannot be used to estimate and c'.

There are a number of problems and inaccuracies that have arisen,

in the sampling and lab testing of the samples reported. First, insuf-

ficient equipmen t and experience in the field made proper sampling tech-

niques impossible, and therefore, proper geotechnical identification and

testing erroneous or incomplete. Too many boreholes were drilled where

the only samples obtained were disturbed samples off the auger flights,

or Shelby tubes filled withsand of questionably intact relative density.

Often tubes were filled with slump, or only enough "undisturbed" sample

to run one triaxial test, thus giving a poor estimation of the actual

strength. In the lab, there were major differences in the results ob-

tained by direct shear and triaxial tests on sand specimens, so that

direct shear results had to be disregarded. Hand carving and trimming

174

of silt specimens was found to be too difficult for the technicians, so

the silts were too often disturbed, dried, and tested as sands, thus

losing any assessment of their cohesive strength. Finally, vane shear

tests provided an unreliable measure of the unconfined compressive

strength of cohesive materials, since the values obtained on the surface.

.of just one Shelby tube sample were found to vary by more than 100 per

cent.

Stability Analysis

The stability analysis of the bluffs covered in this study yielded

a number of distinct types of failure processes, which are'shown sche-

matically in Fig. 87. These failure types shall be referred to as follows:

1. Toe failure.. This is the most common type of failure en-

countered, in which the failure circle indicates a shallow

slip failure at the toe of the bluff.

2. Face failure. Analysis on many bluffs resulted in broad,

shallow zones of failure, indicating a trend slope wash or

translational failure of the slope, which itself could not

be analyzed by the particular computer program used.

.3. Erosion of the top of the bluff face. Shallow back-cutting

of the top of the bluff was often indicated, however, was

not always the most critical condition for the bluff, nor

investigated in every case.

4. Removal of toe material. In mostly stable bluff, where

slope debris (slump blocks) were accumulated at the toe of
7

the bluff, the failure circle indicated the removal of this

toe material, while not affecting the stability of the

bluff as a whole.

5. Stable slopes. Minimum Safety Factors for stable bluffs

were either for shallow or deep-seated circles, but indi-

cated no tendency to fail.

. . . .........

Ii Toe fa*
ilure
2. Face f ailure 3. Top retreat

-Ij

4. Removal of toe' material 5. Stable slope

Figure 87. Types of slope failure and face configuration.

.17(1

Computer analysis resulted in almost all cases in computing a mini-

mum Factor of Safety for a circle indicating a small, surficial slump.

This is due mainly to the fact that the cohesion was relatively small for

many of the materials encountered. Thus, the slope material behaved like

..a sand; the Safety Factor decreases as the inclination of the failure

plane increases, giving a small, steep failure circle. As the cohesion

increases, the depth of the failure circle increases, as does the value

of the Safety Factor itself. The term "deep slip" shall be used in de-

scribing the failure of natural bluffs that result in failure zones that

are deeper than the small surficial slumps described above. In many in-

stances, the two act together.

The "critical circle" shall be defined as that failure circle.having

the lowest factor of safety, as calculated by the computer. This.indi-

cates the most unstable surface of sliding, or the smallest ratio of the

assumed shear strength of the material to the shear stresses. However,

any trial failure circle may be considered "unstable" if its safety factor

is less than one. This results in two criteria, or explanations, of the

progressive failure of the bluffs.

1. Critical circle criterion. According to this criterion, the

process of failure of the bluffs is seen to follow a succession of small,

rotational slides which progress from the toe to the top of the bluff.

(Edil & Vallejo, 1977). An example of this was.investigated at borehole

GT-6, and outlined in Fig. 88. Each time a critical circle with a Safety

Factor of less than one was obtained, failure was assumed to occur, and

the slumped materi al was assumed to be removed by waves and surface ero-

sion. The resulting profile was re-analyzed, and each consecutive failure

allowed to occur. This sequence of successive failures showed a pro-

30. 40 existing slope
s A
C 10.0 f
Y'= 135 P f

15 - 0' 'V'= 104 Def
C =1 0. 1) rsf
29.6-
Y'=.138 P--f
=.82 P@f- . .....

- 29. 60'
stable slope
C = 32 usf corfiguration

'5.6 c f
P

Figure 88. Slope evolution example showing sequence of successive failures .at Profile 2,
Section 2.8, T9N.

178

gression of small, surficial slides which progressed up the face of-the

bluff, continuing until 'a Safety Factor greater than unity was encountered,

and a stable slope'Configuration was reached.

2. Unstable'circle criterion. An example of the unstable circle

criterion was studied for a slope in Reach 13; Profile 2, Sec. 33, TION,

and is outlined in Fig. 89. Failure was assumed to occur throughout the

zone where the computer analysis indicated a Safety Factor less than

unity, for each failure circle try. This zone was bounded by the largest

failure circle with a Safety Factor less than one, which was then assumed

to rotate, but not to be completely removed. This criterion resulted in

failures which also progressed up the slope, but each failure was ofmuch

larger extent, and a stable slope configuration was reached after just

three failures.

It is believed that the actual erosion of the bluffs involves both

of these criteria. The critical circle indicates the particular surface

where incipient failure is likely, and will probably occur first. Where

subsequent failures occur, and if they,occur, depends on the local vari-

ations of the soil, weather influences, groundwater conditions, vegeta-

tion cover, surface wash, and other factors. There is a danger'of failure

whenever the Safety Factor is less than one, but only when assumed condi-

tions prevail in the field at the time of failure. Also, an absolute

time scale is not available for the events described above. The unstable

circle criterion may be thought of as a culmination of smaller criterion

circles that fail at approximately the same time. In other words, the

failure zone may be undergoing internal failures and deformations,

so that failure occurs everywhere within the unstable zone, not just on

the largest failure surface.

Aviv--

A MIR -R@AUUV--@- 7

-7 ---7
FIZESS-K-t -KU@wa@)U-I 5wipt

i 9F Avs

Figure 89. Slope evolution model showing series of progressive failures using tIhe l'unstable.
circle" criterion (profiles.1 and 2, Section 33, T10N.

180 J

In addition, solifluction-, surface wash, mudfl.ow, or other forms of

mass wasting may be occurring in conjunction with the processes above.

The undrained failure of the 'bluffs, that is, a stability analysis using

total,stresses and the undrained strength parameters of the soil, was not

investigated in this study,.but may be of major importance in many in-

stances.

The ultimate angle of repose for a stable slope was determined by

assuming a long-range equilibrium condition of the bluff.whereby the co-

hesion reduces to zero due to weathering, and the@angle of repose is

then the angle of internal friction of the soil. Below the groundwater

table, the stable slope angle.is reduced due to the effects of water

pressure, so the stable angle, @, can be computed by the equation
YSAT
tan' tan@' 1/2tan@'
YBbUY
and results in a slope angle about half that of the angle of internal

friction. Artesian pressures and excess hydrostatic pressures due to

seepage effects tend to decrease this stable slope angle even more-, how-

ever, these conditions are not prevalent in this study.,

Where the coh esion of a slope is high, it is not necessarily logical

to assume that the cohesion will weather to zero causing shallow slides

until a low-angle stable slope is reached. Instead, higher stable

angles may be maintained safely; these were determined by using charts

presentedly Edil & Vallejo (1976) which related the stable slope angle

to the cohesion for 30* and for various bluff heights with varying

water table.

The*ultimate stable angle of a bluff, and the corresponding amount

of regrading required, depend on a number of assumptions and influences.

If wave action is prevented, face degradation will flatten the slope to

181

-an angle corresponding to the zero cohesion condition described above due

to weathering of the surface, and other slope processes. Stabilization

measures for slopes of higher cohesion and.consequently higher slope

angles, require that the Safety Factors using both drained and@undrained

strength parameters be greater than 1.3 to 1.5, and also that proper

drainage of the surface and sufficient vegetation cover.is provided to

prevent face degradation. Protection of the toe from wave action is im-

perative.

Case studies

Evaluation of the results of the stability analysis permits a number

of observations and comments to be made. Example profiles to be used as

.case studies are made reference to in an attempt to explain the various

phenomena occurring in the erosion of the shoreline. These profiles are

drawnin Figs. 90-94, with their assumed strength parameters and critical

failure circles.

Effect of lowering the lake level.

The,lowering of the lake level will by itself cause.no change in

the stability of the bluff, but may induce an indirect change in the sta-

bility by affecting other factors in the bluff, such as the height of the

bluff, the groundwater conditions,,or the wave action. As is evident in

practically all of the bluff profiles of Figs.,90-94, the critical failure

circle does not intersect the bluff beyond the toe; thus, the bluff above

-7 77 711

7 :>

t>
CO

Figure 90. Profiles,at geotechnical sites showing critical failure circles. See.
Fig. 94 for meaning of symbols.

SIP

V
--i@ . ....... .

5F- -55-1
r
-7

00
qT- 10 LJ

-7
>

-jl@

V-1
r I"

Figure, 91. Profiles at geotechnical sites showing criti'cal failure circles. See Fig. 94
for meaning. of symbols.

G,,7 - IS

1.30

-7
7
5
F -

Figure 92. Profiles at geotechnical sites showing critical failure circles. See Fig.-94
for meaning of symbols.

C" 0

1 7 2@

vee@cA
70: --@- 0%

-'00
N7

OD
5 -Ar kp
U: ILI

10
S11 -T S2e5 T VA

Clir-
V

CF'- 14

I@A
(f - -E i 6 T5N
77

T@'. P2 S11 nK F Z "7

Figure 93. Profiles illustrating effects of groundwater,-berm, vegetation, cohesion and
S't -T5"

:>
4.

overlying cohesive soil. See Fig. 94 for meaning of symbols.

rt H
H '4 F'
0 10 1--
I-h M r-

(D lb
En 0
CL rt
LA

rt
.10 0 LP

rt 4
4-

rT 0 ED U)
'13
ri @ I '@j
ru

98T

187

the beach acts as a separate unit since the slope of the beach is so low.

Should the waves begin to encroach on the base of the bluff by eroding,

the beach, the effect will be to increase the height of.the bluff in the

long run, and thereby decrease its stability. If the initial beach is

very steep,, porepressures may remain high in the bluff, while the rela-

tive height is increased rapidly; thus, the lowering of the lake level

may have a direct affect on the stability of the bluff. Porepressures

are often kept high for extended periods due to the stratigraphy of the

bluff and the forced position of the groundwater table. Also, as the

groundwater table decreases, and the height of the bluff is increased due

to the lowering of the lake level, some weak layers which were originally

below the bluff base may now become part of the bluff face and may in-

duce failure.

Effect of high groundwater table.

Raising the groundwater table decreases the stability of the bluff,

while increasing the size of the failure circle in proportion to the in-

crease in the height of the groundwater table. The profile at borehole

GT-6 (Fig. 91) shows the water level at about one-third of-the height of

the bluff, with a Safety Factor of 0.69; Profile A in Fig. 93, with ap-

proximately the same slope angle'. and a slightly higher 0', has a ground-

water level at about 3H, with a Safety Factor of only 0.64.

It is typical for the failure surface on straight bluffs with no

cohesion to intersect the bluff at the toe of the slope, and just above

the level of the groundwater. This can be seen in the two profiles dis-

cussed above as well as many other bluffs along the shoreline. The net

result is to slough away the saturated material at the toe, thus decreas-

ing the stability of the overall bluff, and initiating a progressive

188

failure sequence, as 'investigated at borehole GT-6.

Effect of slope angle.

(Fig. 93, Profiles C, D, E, & F) Increasing the slope angle de-

creases the Safety Factor of the critical circle, as can be seen in the.

above profiles each with similar stratigraphy, and cohesion equal to

zero. The amount of vegetation also gives an indication of their rela-

tive stability, and decreases with an increasing slope angle.

The profile at borehole GT-6 (Fig. 91), and Profile C (Fig. 93) both

have low-angle slopes with 100% vegetation. At.this angle, the critical

criterion is of greatest concern, and the effects of the vegetation, and

actual groundwater levels must be taken into account to assess the ulti-
mate stability 'of the bluff. A series of progressive shallow slides may

be expected.

As the slope angle increases, the critical circle,.criterion becomes

of less interest than the largest unstable failure circle*criterion.

Profile D (Fig. 93) shows the limiting case where the critical circle is

also the'largest unstable circle; note that the slope angle is approximately

equal to At this slope angle, also, the vegetation has decreased sub-

.stantially and the critical failure circle is much@deeper than for slopes'

.of a lesser angle.

In Profiles E & F (Fig. 93), the slope angle is so large, that the

largest unsafe circle criterion controls, indicating a deep-seated

failure mode for the bluff. This condition would suggest that failure,

when it occurs,will progress very rapidly up the slope, causing a net

failure of the entire slope.

Effect of a berm-type post-failure slope.

.If we try to reconstruct the pre-failure shape of the given profile,

189

we find that the maximum amount of regrading required is much greater

.than that which would now be estimated from the present slope configura-

tion. The reason for this descrepancy is that as the slope fails, and

the "berm" is created, the slope toe actually extends further into the

lake. Thus, the amount of regrading required may be estimated from a

point further lakeward, and the net loss of the top of the bluff is cal-

culated less. It can be seen from Profile B (Fig.93), that there is

100% vegetation at the top qf the berm, and on the slope above the berm,

but that the face of the slope below the'top of the berm has little or

no vegetation, suggesting a lower stability. The critical failure circle

does indicate an unsafe condition at the toe of the berm, and is an ex-

ample of the removal of slump material at the toe of the bluff. The

berm will be eroded back until evidence of it has disappeared; thus, the

effect olf the berm is not to stabilize the slope, for the ultimate angle

of stability will not-change, but rather, the presence of the berm

shifts the stability line, so that a lesser amount of regrading required

is likely. With a greater:amount of cohesion, however, the berm will

tend to stabilize the slope somewhat, since the berm will act as a sepa-

rate unit of lower total height, and the ultimate angle of stability for

this height will be greater.

Effect of stratigraphy.

A greater amount of cohesion of the soil making up a bluff will cor-

respondingly increase the Safety Factor and the size of the critical

failure circle. The critical circle becomes most important in*the sta-

bility of the bluff, but Safety Factors may often exceed unity, as can

be seen in Profile G Fig. 93). Profiles A and H have approximately the

same slope angles, and drained angles of internal friction, but their

190

Safety Factors vary considerably. The profiles it boreholes GT-5-and GT-I

(Fig.-90) both have lacustrine,clay deposits over a significant portion

of the slope, and the safety factor is high in both cases. Higher cohe-

sion may, however,.make uhdrained failure critical, particularly where

artesiqn-pressures are present.

When a cohesive-'layer in the upper part of a slope overlies a non-

cohesive layer, there is little effect on the critical.failure circle in

the lower part of the bluff. Therefore, sloughing of the lower material

is likely,'undercutting thetoe of the bluff. The stability of the whole

bluff is, however, much greater, so that typical failure circles.are deep-

seated with higher Safety Factors, as shown in Profiles I (Fig. 93) and

GT-14 (Fig. 92).

The effect of the presence of a-cohesive material overlain by a

cohesionless material, is common in many of the northern profiles (see

boreholes GT-13, GT-15, GT-12). Characteristically, these bluffs are

stable-or questionablysafe, with no slumping at the toe; but rather,-a

considerable amount of. top retreat.. Overall Safety Factors are higher,'

with a,deep-seated failure mode indicated.

Near-stability.

Very often a critical failure circle less than one will be calcu-

lated for a slope that will undergo no top retreat to achieve a stable

slope configuration. Erosion of the face of the slope involves a "smooth-

ening-out" of certain unstable features., without affecting the overall

shape of the bluff. An example of this can be seen readily in Profile J

(Fig. 94), where there is little vegetation, and a low Safety Factor,.

but a slope angle very close to;the stable configuration. Another 6x-.

ample of*this type is the process of the removal of slumped material from

191

the toe of the bluff.

False instability.

When a Safety Factor less than one is calculated for a uniform slope

having 100%.vegetation and'where the ultimate angle of stability paral-

Lels the slope face, the failure mode indicatedis often misleading. The

critical failure circle must be interpreted as an indication of barren

slope-forming processes. If the failure indicated is a shallow slide,

then the vegetation will 'retain the slope in its present configuration.

If, on the other hand, an unstable circle involves a deep slip, then the

vepetation may give a false sense of security,'and the slope may be in

danger of incipient failure. An example of the former case is the pro-

file at borehole GT-6 (Fig. 91),, and of the latter case of false security,-

is Profile K (Fig. 94).

Wave Erosion.

A former stable bluff configuration may be subjected to the forces

of wave erosion,, and subsequently become unstable, as in Profile K. The

Safety Factor indicates an unsafe critical circle causing a shallow slide

near the base, which will initiate a progressive failure of the bluff.

Top Retreat.

Top retreat may be caused by two different conditions, either a

difference in the material properties at the top of the bluff, or the

final stages in a progressive failure of the slope. Profile L (Fig. 94)

is an example of a cohesionless bluff which is stable at its toe, but un-

stable at the top, the critical failure circle indicating shallow slides

at the top of the slope.

192

Typical slope profiles.

The term "typical slope profile" is actually a misnomer, for every

slope is-in itself unique; subjected to different environmental influ-.

ences, shape-forming processes, stratigraphic variations,.material prop-

erties,,groundwater conditions, and vegetation cover. However, some

very generalized shapes or failure modes appear more frequently than

others for different segments of the shoreline.

Profile M (Fig. 94) is more-or-less typical of many of the bluffs

of Racine and Kenosha counties. Where the stratigraphy consists of co-

hesionless till, sands, or silts, there is often a stepped slope undergo-

ing both, toe-erosion and top retreat.. The groundwater table is typically

high. Where.the bluffs are either uniform, or straight, theyare either

stable, or undergoing some undercutting at the toe. The bluffs are low

in height, so that the net retreat of the top of the bluff for astable

angle is small to negligible. Lacustrine clay deposits have high cohe-

sion, and generally add significanly to the stability of the slope.

Lower Milwaukee county may be typified by Profile N (Fig. 94). The

bluffs are of cohesidnless materials with lower angle slopes that are

actively undergoing progressive failure sequences. Slumping at the toe

is common, with moderate setback of the top to achieve a stable slope

angle. Interspersed lacustrine clays of high cohesion allow.stable

slopes at higher angles. Wave erosion and subsequent slumping at the toe

is typical.

r
Further north, the slope angles become very steep, danger of deep-

seated failures by the unstable circle criterion is evident; also failure

by an undrained analysis is possible. Interbedded lacustrine deposits

vary from high-cohesion clays to dense sands which retain surprisingly

193

high-angle slopes with a considerable amount of surface sloughing. Pro-

files D, E, and F (Fig. 93) may be common.

Northern Milwaukee and Ozaukee counties are typified by profiles at

boreholes GT-6 and GT_7 (Fig. 91), and CT-8 (Fig. go), where thick de-

posits of cohesionless tills are subjected to progressive failures of

shallow slides, according to the@critical circle criterion, Bluffs are

generally high, with angles varying between safe slopes to steep, highly

complex, and slumped surfaces.

The bluffs in Sheboygan and Manitowoc counties consist generally of

tills with higher cohesion overlain by cohesionless sands and silts. Top

retreat is active in .many areas, but the slopes as a whole are able to

maintain high angles'at moderate heights, with relatively high Safety

Factors. Face degredation and wave action are prevalent*. (see GT-14 to

CT-17, Fig. 92)

Conclusion

The Factor of,Safety analysis for the natural bluff,slopes along,the,

coastline indicates the most critical conditions affecting the stability

of the slopes. The presence of a shallow slide at the toe of a slope

suggests sloughing of saturated, cohes.ionless material below the ground-

water table when the groundwater is at, a high level during the spring.

The failure of this lower toe material alters the stress conditions af-

fecting the rest of the slope, and subsequent erosional failures, either

shallow or deep-seated may result, which progress up the slope. This

cycle may repeat year after year if the slumped material is removed by

the waves, or undercutting of the toe by waves is allowed.

Critical failure-circles showing shallow surface slides may indicate

surface wash or a.parallel retreat of the slope face. In high-.angle

194

slopes, these may.bel.of lesser importance than the larger, deep-seated

failure circles, as characterized by the unstable circle criterion. Cohe-

sion tends to,deepen the critical failure circles, and in crease the Safegy

Factor for a,given,value of the drained friction angle.

The slope-forming processes assumed take into account a number of

conservative assumptions and observations. Therefore, the Safety Factors

and the stability line,--values are reflective of the worst possible condi-

tions thought probable for the given slope.. The-two most important con-

siderations.of any given profile are the engineering properties governing

the type of failure suspected, and the porepressure within,th.e bluff.

one cannot,accurately assess the "true" Safety Factor of a slope, but can

only try to get,ahandle on the type of failure mode probable, and.the,

relativechance.of this failure occurring. This can only be done by,

properly interpreting the Safety Factor.

Not all failure modes have been investigated for every profile.

Thus, top retreat or the largest unsafe failure circle may not be drawn

for a particular profile, but still may be of major importance. The,in-

terprefer must look at-other similar profiles, or compare the given slope

with the failure processes described herein to determine if the slope

has modes of failure other than those drawn, or originally calculated.

The stability line is generally a conservative estimate of the max-

imum retreat of the bluff top probable to insure a Safety Factor greater

than one. 'However, the vegetation cover, beach protection, drainage

controls, lakeward advance of the toe of the bluff, or the presence of a

greater amount of cohesion than assumed will reduce the amount of regrad-

ing required.

All of the engineering properties have been averaged, assumed homo-

genous and@consistent throughout any given profile, and the@stratigraphy

195

has been assumed horizontal and continuous. These conditions may not

prevail ata particular site, but may be drastically different from

those in the near vicinity. Thus, the extrapolation of data is precar-

ious, and the assignment of Unsafe or Safe slope designations must be

viewed with.a certain degree of scepticism. These extrapolations are to

be used as a guideline or an indication of general conditions along the

shoreline, but should not exclude detailed geotechnical subsurface in-

vestigations at any particular site to assess its slope stability..

Finally, the methods used in analyzing the stability of the.slopjes

do notiaccount for surfacesloughing, solifluction, mass flows, slope

wash, or wave erosion which must also be considered in determining the

ultimate stability of the slope, or the ultimate retreat of the bluf.f,,.

top. Nor has the Safety Factor against an undrained failurebeen ana-

lyzed which may be critical in many cases.

196

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U.S. Geol. Survey Prof. Paper 106, 356 pp.

Berg, R. C.and,Collinson, C., -1976. Bluff erosion, recession rates,

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Black, R.F.,-1970. Glacial geology of Two Creeks Forest Bed, Valderan

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Leverett, F., 1929. Moraines and shorelines of the Lake Superior region.

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198

GLOSSARY

BREAKWATER A protective structure built off shore and parallel to the
shoreline. Incoming waves crash against the breakwater instead of
direetly on the beach; this lowers.their erosive power,

CALUMET STAGE Stage of Glacial Lake Chicago which is recorded by beaches
at'an elevati6 n of 620 feet above sea level (40 feet above the present
lake surface) throughout most of the Lake Michigan Basin.

CLAY Very fine grai ned sediment. In this report-clay refers to the less
than .002 millimeter fraction.

FETCH - The distance over open water which the wind blows. The fetch'i ,s a
partial determinate of.wave height.

FLOW A type of downslope movement where the soil mass, saturated with
water; moves like a viscous liquid under the influence of gravity.

GLACIAL LAKE CHICAGO The lake which existed at several different stages
(elevations) in-the southern part of the Lake Michigan basin during
late glacial time.

GLENWOOD STAGE A stage.of Lake Chicago which is recorded by beaches at an
elevation of 640 feet above sea level (60 feet above the present lake
surface). This is highest level of glacial Lake Chicago.and is in
part responsible for the lacustrine sediment high in the bluff.

GROIN - A structure built of concrete, steel pilings, rocks or other
materials which extend into the water perpendicular to the beach.
Groins trap the sediment. moved by the.longshore drift forming beaches
.,on the updrift side.'

GROUNDWATER DISCHARGE - The flow of water from the ground as spr ings onto
the ground surface or into water bodies. Also referred to as.seeps..

LACUSTRINE SEDIMENT - Sediment deposited in a lake. Usually refers to
fairly fine grained (sandy silt and clay) sediment.

LONGSHORE DRIFT.- The transport of sediment (usually sand) along the beach
andjust off shore by the prevailing currents'and oblique waves.

NIPISSING STAGE - One of several fairly long-lived stages of Lake Michigan
at an elevation of 605 feet above sea level. Many of the terraces and
sand areas along Lake Michigan 20 to, 25 feet above present lake level
represent wave action during'the Nipissing stage. These stages occurred
after glacier ice had left the Lake Michigan basin.

PIEZOMETER - A small observation well open to the groundwater system at some.
depth which is used to measure the depth to the water table.

199

REACH A segment of shoreline which has somewhat uniform characteristics
and orientation. Reaches of any length can be defined.

REVETMENT - A shore parallel erosion control structure generally built at
the base of the bluff and top of the beach. It differs from a sea
wall in that it is usually made of rip rap.(large chunks of rock)
and its surface is generally inclined in the direction of the water
as opposed to a sea wall which is generally vertical.

SAFETY FACTOR - The engineering factor of safety as used in this report
refers to the likelihood of slope failure by slumping. A discussion
of how safety factor is calculated is given in the text.

SAND Sediment with a grain size between .0625 and 2 millimeters.

SAPPING - The removal of sediment (generally undercutting) by discharging
groundwater.

SEA WALL A wall generally of concrete or sheet piling. It generally has
a vertical face, although in some cases, the faces are stepped on the
beach side.

SHELBY TUBE - Thin walled steel tube which is forced into soft sediment to
collect relatively undisturbed samples.

SILT Sediment with a grain size between .002 millimeters and .0625
millimeters. This material is intermediate in size between clay and
sand.

SLIDE A type of downslope movement which takes place along a definable,
relatively flat surface of failure. Usually the sliding mass is not
deformed as it is in flow.

SLUMP - A type of slide where failure takes place along a curved surface
and the moving mass rotates backwards in the upslope direction. It
leaves a scalloped bluff top of amphitheater shaped scars. This is a
very common type of failure along the bluffs of Lake Michigan and Lake.
Superior.

SOIL CREEP - A very slow movement of unconsolidated material downslope.,
Very often this is measured in millimeters per year and is not
observable to the naked eye. When this process is occurring, however
trees, fence posts, telephone poles etc. become tilted, and making the
effect of soil creep is observable.

SPLIT-SPOON SAMPLER - A tubular sample collecter which is attached to the
end of a drill rod and pushed or driven into the sediment. This is
generally used on harder sediment than the shelby tube.

STRATIGRAPHY In its classical use refers to the study of the formation,
composition, sequence and correlation of sedimentary materials. In
this report it refers to sequence of materials making up the bluff.

TILL - Poorly sorted, poorly stratified material depos ited directly by
glacier ice..

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