Weko beach shoreline erosion study Bridgman, Michigan

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

MICHIGAN
OCZM GRANT #NA-80-AA-H-CZ157
SUBTASK 3r,>
Weko Beach
Shoreline Erosion Study

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September, 1981

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Property of CSC Library

WEKO BEACH

SHORELINE EROSION STUDY

U.S. DEPARTMENT OF COMMERCE NOAA
COASTAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
CHARLESTON SC 29405-2413

Bridgman, Michigan

September, 1981

This document was prepared in part
through financial assistance provided by
the Coastal Zone Management Act of 1972
administered by the Office of Coastal Zone Management
National Oceanic and Atmspheric Administration

TABLE OF CONTENTS

PAGE
SECTION I - GENERAL 1
INTRODUCTION 1

PURPOSE AND METHODOLOGY 1
SITE DESCRIPTION 2

ENVIRONMENTAL CONDITIONS 2

SECTION II - SHORELINE.EROSION ANALYSIS 5
GENERAL 5

PRIOR STUDIES 5
HISTORICAL SHORELINE CONDITIONS 6
LITTORAL MATERIAL AND TRANSPORT 10

SUMMARY AND CONCLUSIO NS 12

SECTION III - EVALUATION OF SHORELINE 13

EROSION CONTROL MEASURES 13
DESIGN CRITERIA AT WEKO BEACH 13
GROIN FIELD ALTERNATIVES 14

OFFSHORE BREAKWATERS 15
SUMMARY OF SHORE PROTECTION SYSTEMS 16
BEACH NOURISHMENT 16

SECTION IV - RECOMMENDATIONS 19
REFERENCES 20
LIST OF FIGURES FOLLOWS PAGE

Figure 1 - Weko Beach Project Vicinity 1
Figure 2 - Historical Shoreline Photographs 6
Figure 3 - Historical Shoreline Positions 6
Figure 4 - Long Range Beach Improvement Plan 19

LIST OF TABLES PAGE
Table 1 - Summary of Historic Shoreline Analysis 8-9
Table 2 - Orientation of Shoreline 11
Table 3 - Summary of Shore Protection Systems 17-18

SECTION I GENERAL

INTRODUCTION

The Weko Beach Recreational Area is located in the northwest corner of
Section 16, City of Bridgman, Berrien County, Michigan. The recreational
area shown on Figure 1 has approximately 3,000 feet of shoreline, and is
entirely within the coastal boundary as defined by the Michigan Coastal
Zone Management Program. The unique features of the site include sand
dunes and a natural Lake Michigan beach. The recreational area also contains
camping/picnic facilities, a swimming area and beach house, and a boat launch
ramp. The property is owned by the City of Bridgman. The city water intake
is located about 200 yard's offshore of the swimming beach.

The beach area has been experiencing normal erosion for many years. In the
early 1970's, the erosion accelerated, due in part to record high lake
levels. In 1973, the beach had been reduced to less than 50 feet wide in
front of the beach house. In an attempt to protect this structure, small
rubble groins were placed along the shore, and two sheet pile walls were
constructed. These measures were partially successful, and lower lake levels
resulted in a slight widening of the beach. By 1981, these temporary structures
were in poor condition, and were removed under the Michigan.Coastal Zone
Management Program.

PURPOSE AND METHODOLOGY

The purpose of this study is to analyze the shoreline erosion at Weko Beach,
and evaluate the feasibility of providing a long-term solution to the erosion
problem. The work was conducted under contract with the City of Bridgman,
Ind was partially funded by the Michigan Coastal Zone Management Program. The
investigation specifically emphasized three problem areas.

1. Protection of the Weko Beach House

2. Improvement of the boat launch ramp

3. Protection of the fresh water intake and sub-bottom pipeline

The study involved the following work tasks.

1. Collection of Data and Information

2. Analysis of Historical Shoreline Erosion

3. Evaluation of Current Shoreline Si-tuation

4. Evaluation of Alternative Shoreline Erosion Control Measures

5. Recommendations for Weko Beach

6. Report Preparation

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Throughout the study, low-cost shoreline improvements were given principal
consideration, due to the limited financial resources available for shoreline
projects.

SITE DESCRIPTION

The major features of the site are shown on Figure 1. The main access road
terminates at the beach house with parking provided on both sides of the road.
The beach house contains restroom facilities, a snack bar, and a large game
room. The lower level of the building is located on the beach, approximately
75 feet from and 5 feet above the water's edge (1981).

The single lane boat launch ramp, located at the northern end of the property,
is partially protected by a low sheet pile jetty on the north and a short
rubble groin to the south. In spite of these structures, sand continaully
covers the launch ramp, necessitating periodic cleanup. The material is
carried by both the water currents and wind. Sediment deposition problems
such as this are almost impossible to avoid at open coast locations.

The swimming beach extends from the launch ramp to the south for a distance
of 3,000 feet. The first 1,200 feet, between the launch ramp and water intake,
varies from 75 to 125 feet wide. Two small groins, extending less than 20 feet
into the water, protect the water intake pipeline. The section of beach between
these groins and the launch ramp extends farther seaward than the adjacent
shoreline, indicating that the structures have trapped sand moving along the
shore (littoral material).

To the south of the.water intake, a wide (200 feet) beach extends for 1,800
feet to the property line. This area is extensively used for swimming and
beach activities.

Behind the beach on both sides of the access road is a sand bluff, which is
undergoing moderate erosion. Measures to control this problem are being in-
vestigated under another program.

The fresh water intake for the City of Bridgman is located immediately off-
shore. Water is pumped from beneath the sandy lake bottom to the water
treatment plant about 1/4 mile inland. In the past, concern has been expressed
regarding the stability of the pipeline from the intake structure to the shore.
At present, the pipe is well covered with stable sand, and no problems are an-
ticipated.

ENVIRONMENTAL CONDITIONS

Shoreline erosion or accretion is dependent upon the interaction of many
environmental factors. These include wind And wave forces, water.level vari-
ations,2and ice, A brief-overview.of these conditions at.Weko Beach is given
on.the following page.

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Lake Level-s Fluctuations in the lake level may cause an extensive alteration
.of shoreline conditions. As the water level rises, waves more frequently
cross the previously stable beach, causing erosion of a shoreward bank. This
process frequently resul,ts in undercutting of steep bluffs and sloughing. For
a beach systemi the effects of rise and fall in water level do not balance.
High water level-s permit erosion of the bluffs whereas during periods of low
water level, these shoreline features are not replaced. Even a wide protective
beach will readjust to higher water levels by erosion of the berm and accretion
offshore. The changing lake level also upsets the previous shoreline balance
by permitting larger waves to break closer to shore.

The beach material in the wave breaking zone is moved more readily than material
offshore, which will only be subjected to oscillating, non-breaking wave forces.
A beach face will therefore readjust quickly to a change in water level conditions,
but offshore areas will adjust more slowly.
The orientation of the shoreline will not be significantly affected by variations
in water level unless refraction of the waves is altered; that is, unless ir-
regularities in bed topography occur through exposure or inundation of beach
material.

In the Weko Beach area, the Lake Michigan water level varies both seasonally
(1-2 feet) and long-term. The maximum Lake Michigan level was recorded in
June, 1973, at 580.9 feet (International Great Lakes Datum). The average
lake level is 578.3 feet (IGLD). Low water datum (LWD) is 576.8 feet. In
the following section, the significance of lake level variations on historical
shoreline position is shown.

Waves -- The dominant forces involved in shoreline erosion are winds and waves.
Bre ng waves impart energy upon the shoreline, resulting in erosion and
transport of beach material. At Weko Beach, the larger, steeper waves, created
by strong northerly winds, are the most effective in eroding and moving sedi-
mentary material. Smaller (less steep) waves.tend to push sediment onshore
and aid in building the beaches. It is the relative frequency of wave heights
and directions that determine the net effect on a shoreline.

The wave "climate" for a particular area depends on the wi-nds, the distance
over which the wind blows (fetch) and the shore and bottom configuration. In
the area offshore of Weko Beach, waves up to 10-12 feet have been observed
(Reference 1 ). However, it is the waves breaking nearshore that cause
longshore movement of sand. The relatively flat offshore slope of the beach
at Weko results in the larger waves breaking far offshore.(a wave will break
in water depth approximately equal to the height of the wave). Therefore,
the large waves are not a major factor in sand transport along the beach.

From analysis of the waves as they approach the shoreline, 3-4 foot breaking
waves are the maximum waves that.cause sediment transport. These waves result
from northwest storms, and occur two to four times each year. The shoreline
responds quickly to these events, followed by a gradual return to the equili-
brium situation.

-3-

Winds -- Winds act directly upon beaches by creating shear forces upon the
individual sand particles and thereby blowing sand off the beach (deflation)
or depositing sand in dunes. Winds move sand in three ways: 1) suspension
where small particles are lifted and held in the air stream; 2) saltation
where particles are carried in a series of short jumps; and 3) surface creep
where particles roll or bounce along the beach. Most particles move by salta-
tion. Sand moved seaward usually falls into the wave breaking zone and, al-
though lost to the beach, still remains in the littoral transport zone.

Ice -- An ice cover along the shoreline can substantially reduce erosion by
reducing the wave energy imparted to the shore. For this reason, the analysis
of littoral drift is usually conducted only for ice-free periods.

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SECTION II - SHORELINE EROSION ANALYSIS.

GENERAL

The behavior of any reach of shoreline is dependent upon complex relations
between the numerous elements that make up that section of the shore. Such
factors as the natural forces that erode and transport material, the amount
of material available for the erosion or accretion, and the works of man in
the form of structures or other unnatural disturbances to the shoreline
balance must be considered.

The basic mechanism for erosion on the Great Lakes involves the constant
wearing away of the coast from wave attack on the shoreline over geologic
time. Wave attack breaks down the larger source rocks into small materials
which can be raised into suspension in the water and carried away by long-
shore currents (suspended load). Material that remains too large to be
raised in suspension may be moved along the bottom by wave forces (bed load).
This movement of sediment in the nearshore region is called littoral drift.
@et erosion within a specific reach of shoreline occurs when more material
is transported from the reach than is input into it, whereas net accretion
results from a surplus of input material. Creation of beach material in this
manner requires many years.

The amount of erosion and/or sediment transport occurring within the shoreline
reach depends upon the incident waves, material quantity and composition, and
shore slope. The volume of material within a shoreline reach may be comple-
mented by external source material from adjacent reaches or the offshore zone.

The source of material for Weko Beach is primarily the bluffs and beaches to
the north. During the past twenty years, man-made structures have interfered
with the natural north to south flow of sand in the area, thereby reducing the
amount of material available for building or maintaining a beach. The evidence
of this is shown in the analysis of aerial photographs presented later.

PRIOR STUDIES

Over the past ten years, a number of shoreline erosion studies have been con-
ducted for the eastern shore of Lake Michigan (see references 2, 3% 4.). The.
recession of bluff and beach shorelines has been well documented for many areas.'
However, there have been no prior studies of the sand beach at.Bridgman.

A Michigan Department of Natural Resources study in 1978 measured bluff re-
cession rates for areas immediately north and south of Weko Beach. The erosion
was characterized as.moderate, in the range of one to three feet per year.

The most relevant study was completed by the Coastal Engineering Research
Center in 1980 (reference 2). This investigation looked-at several sites

in the Berrien County area, and analyzed a series of aerial photographs for
bluff and beach erosion. The results documented the severe bluff erosion,
up to 10-20 feet per year in some locations.

For the purposes of this study, prior work provides insight into the ero-
sion processes in the area, but does not provide useful information for the
specific Weko Beach site. Therefore, a detailed analysis of the historical
shoreline erosion at this site was performed.

HISTORICAL SHORELINE CONDITIONS

The objectives of this analysis were:

1. Provide a record of shoreline alignment changes over the past
forty years..

2. Document the behavior of the shoreline with respect to lake levels
and structural improvements.

3. Provide a basis for predicting future shoreline changes.

MethodQlogy

The first step in the analysis was to obtain historic data on the Weko Beach
shoreline position and Lake Michigan water levels. Eight aerial photographs
of the beach were obtained from the U.S. Army Corps of Engineers and Soil
Conservation Service, covering a time period from 1938 to the present. Actual
recorded water levels were obtained from NOAA for the corresponding date of
each photograph. The shoreline photographs, with corresponding water levels,
are shown on Figure 2.

A baseline was established parallel to the shoreline, using objects common to
several photographs as reference points. Stationing was established along the
baseline, as shown on Figure 1, covering approximately 3,000 feet. The distance
from the shoreline to baseline was then measured on each photograph at selected
station locations.

The third step involved adjusting the measured shoreline positions, photographed
as they appeared at various lake levels, to a single lake level as a common basis
of comparison. The mean Lake Michigan level of 578.3 was selected for this pur-
pose. These adjustments were made assuming the slope of the shoreline did not
change significantly over the years. These adju-st-e-d--shoreline positions are
shown in Figure 3.

After adjusting the shoreline positions to a common water level, the yearly
change in feet per year was determined at each station for periods between
photography dates. It was also possible to calculate the total and annual

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volume of beach material eroded or accreted. A typical beach slope value
of 1:20 was assumed. The difference between the top of berm elevation and
limiting depth (lakeward limit of sediment transport) was assumed to be 14
feet. These simplifying assumptions allowed the cross sectional area of sand
movement to be calculated as the area of a parallelogram with a height of
14 feet and width equal to the positional change of the shoreline in feet.
The change in volume of material between stations was then calculated using
the average end area method.
The azimuth of the shoreline (angle measured clockwise from north) was also
noted at each station to aid in evaluating shoreline response.

Results

The analysis of the historical photographs and adjusted shoreline positions
(Figures 2 and 3) shows a significant variation in the shoreline over the past
forty years. A general pattern of long-term erosion is evident. In 1938,
the beach in front of the beach house was over 500 feet wide. By 1960, the
beach width had been reduced to 250 ft. Further erosion continued until 1974,
when the beach was only 60-70 feet wide. This long-term erosion is a natural
phenomena for an open, unprotected beach. High lake levels, such as the record
levels of the early 1970's, increase the erosion. As the lake levels fell or
stabilized in the late 1970's, the beach accreted slightly, aided by the small
protective structures built during the high lake period.

The change in shoreline position at each station and the change in sand
volume between stations are shown in Table 1. Four time intervals are
shown, corresponding to periods of erosion or accretion. Total changes for
the period as well as average annual variations are indicated. It is empha-
sized, however, that beach erosion is sporadic, depending upon the occurrence
of major storms. It is estimated that over 75% of beach erosion occurs during
these relatively infrequent events (35 per year). Therefore, average annual
values are only indicative of long-term trends.

The data indicate that the most severe erosion occurred in the period from
1967-1974. Over 200 feet of beach was lost. The average erosion during this
time was almost double the rate experienced between 1938 and 1955. It is
likely that most of this occurred in 1971-1974, when lake levels rose rapidly.
Over the entire 3,000 foot reach of shoreline, over 330,000 cubic yards of
material was lost. About 46,000 yards of this material was returned to the
beach between 1974 and 1980, with most of the gain occurring in the western
half of the reach.

The erosion pattern at Weko Beach has resulted from a number of factors. The
relative frequency of storm events and water level of Lake Michigan are the
two most significant natural factors. The construction of facilities along
the shoreline and attempts to protect the beaches and bluffs with seawalls,

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TABLE 1
SUMMARY OF HISTORIC SHORELINE ANALYSIS
1938--1955 1955--1967
SHORELINE POSITIONI. VOLUME2 SHORELINE POSITION1
AVERAGE TOTAL AVERAGE AVERAGE TOTAL
TOTAL CHANGE CHANGE IN CHANGE TOTAL CHANGE CHANGE
CHANGE, PER YEAR VOLUME, PER YEAR CHANGE, PER YEAR VOLUME
STATION FT FT/YR. YD3 YD3/YR. FT FT/YR YD3

29+60 -69 -4.0 105 8.4
-82,660 -4,840 47,71
18+.90 -229 -13.4 67 5.4
16+90 -318 -18.6 .-28,370 -1,660 114 9.1 9,40
-31,650 -1,850 12,38
15+05 -342 -20.0 144 11.5
-31,840 -1,860 11,98
12+75 -192 -11.2 57 4.6
-33,180 -1,940 14,85
9+90 -257 -15.0 144 11.5
-47,880 -2,800 26,8(
6+10 -229 -13.4 128 10.2
-28,030 -1,640 14,91
3+45 -179 -10.5 89 7.1
-34,790 -2,040 17,OE
0+0 -210 -12.3 102 8.2

- - - - - - - - - -
1Ft from baseline adjusted to mean lake level; lakeward chang*e positive
2Accretion positive

TABLE 1 (Cont'd.)
SUMMARY OF HISTORIC SHORELINE ANALYSIS
1967--1974 1974--1980
SHORELINE POSITION1 VOLUME2 SHORELINE POSITION1 VOLUME2
AVERAGE TOTAL AVERAGE AVERAGE TOTAL AVERAGE
TOTAL CHANGE CHANGE IN CHANGE TOTAL CHANGE CHANGE IN CHANGE
CHANGE, PER YEAR VOLUME, PER YEAR CHANGE, PER YEAR VOLUME, PER3YEAR
STATION FT FT/YR. YD3 YD3/YR. FT FT/YR YD3 YD /YR

29+60 -282 -43.4 47 7.5
-152,010 -14,980 9.0 28,570 4,570
18+90 -266 -40.9 56
-26,180 -4,030 8,080 1,290
16+90 -239 -36.8 100 16.0
-20,860 -3,205 7,200 1,150
15+05 -196 -30.2 50 8.0
-20,635 -3,180 1,960 310
12+75 -150 -23.1 -17 -2.7
-25,270 -3,892 -1,920 -310
9+90 -192 -29.5 -9 -1.4
-38,725 .-5,965 -2,760 -440
6+10 -201 -30.9 -19 -3.0
-20,890 -3,220 -8,720 -1,400-
3+45 -103 -15.8 -108 -17.3
-26,840 -4,130 -11,720 -1,870
0+0 -197 -30.3 -23 -3.7

- - - - - - - - - -
1Ft from baseline adjusted to mean lake level; lakeward change positive
2Accretion positive

groins, and breakwaters has also had a major effect. Structures that interrupt
flow of sand along the shore inevitably deprive downdrift shores of material,
resulting in accelerated erosion. To the north of Weko Beach, numerous struc-
tures have been built, particularly in the 1960's and early 1970's. These
have ranged from small groins to major installations (Cook Nuclear Plant,
completed in 1974). These structures have no doubt deprived Weko Beach of
some sand. The exact amount of loss is impossible to determine.

One interesting-observation from the recent aerial photographs is that the
beach between stations 3+45 and 16+90 extends farther seaward than the adja-
cent shoreline. This indicates that the existing small structures at Weko Beach
are serving their-intended purpose. Without the two groins.at stations 16+00
and 17+00, and the steel sheet-pile jetty at the launch ramp (3+50), the
beach would be expected to erode up to 50 feet. This would threaten the
beach house. Therefore, it is imperative that these structures remain intact.

The orientation of the shoreline over the past forty years is shown on Table 2.
It is apparent that shoreline orientation is quite variable, particularly at
stations in the vicinity of the groins (e.g. 16+90).. The shoreline angle is
primarily dependent on the angle of attack of the most recent erosive waves.
The values can be used to predict how the beach will respond to any proposed
structural improvements.

LITTORAL MATERIAL AND TRANSPORT

The erosion and accretion processes described above are the result of an
imbalance between sand being transported to an area and sand removed from
the area. If more material is removed than is brought into an area, erosion
results. The principal sources of beach material for Weko Beach are the eroding
bluffs and dunes 'to the north. Depending on bluff type, 20% to 30% of the
eroded bluff material is suitable for beach building. Beaches in the Weko
area are medium to fine quartz sand (reference 2

The net sand transport at Weko Beach is to the south, since the largest waves
come from the north and northwest. Movement of sand from south to north are
common during periods of southerly winds. The Corps of Engineers has estimated
that a net southerly transport of approximately 100,000 cubic yards may occur
in an average year (reference 4 ). However, this value represents the potential
transport of material, assuming sand is available in the littoral system. With
the numerous shoreline structures to the north, the supply of sand is limited.

The critical point is whether there is sufficient sand entering the system from
the north to maintain the existing beach. Only a small 'portion of the theore-
tical 100,000 cubic yards is needed to maintain equilibrium. The slight
accretion of the beach during the past few years indicates that a stable
equilibrium has been reached, particularly for the critical area in front of
the beach house.

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TABLE 2

ORIENTATION OF SHORELINE

AZIMUTH ANGLE IN DEGREES

STATION 1938 1950 1955 1960 1967 1974 1976 1980

29+60 28 35 15 25 31 38 33 26

18+90 10 29.5 36.5 27.5 25 11.5 25.5- 20.5

16+90 15 28 30 29 20 6.5 25.5 25.5

15+05 27 23 26.5 26 20.5 3 26 37

12+75 28 17 37 23.5 22 34 36.5 24

9+90 29 24 22 27 23 29 12.5 26

6+10 28 26.5 24.5 26 27 5.5 23 16.5

3+45 26 30 33 23 23.5 34 22.5 29

0+0 25 29 28-.5 30.5 24 38 38 31

SUMMARY AND CONCLUSIONS

The shoreline erosion analysis has shown that the Weko Beach shoreline has
experienced a general trend of erosion until 1974. From 1974 to 1980, the
beach stabilized, due to rising lake levels and the jetty at the boat launch
ramp and two groins at stations 16+00 and 17+00. Observations during the
summer of 1981 indicate a continuation of this stable beach.

The conclusion of this investigation is that the beach between stations 3+45
and 18+90 will remain stable for the forseeable future. The beach house will,
therefore, remain unthreatened. It is of critical importance that the existing
groins and sheet pile jetty remain in place. Even if Lake Michigan rises to
1973-74 levels, the shoreline structures wi-11 protect this reach. The stability
of this beach section would be threatened if any major shoreline structures
were built between Weko Beach and the Cook Nuclear plant.

The beach area to the south of station 18+90 is unprotected, and may erode
further if high lake levels return and coincide with a period of severe storms.
However, this erosion will be retarded by the groin at station 17+00t, and
should not proceed significantly inland from the 1974 location. This area
presently has a large beach, and protective structures are not recommended
at this time.
'It must be remembered that prediction of shoreline erosion is not an exact
science. Therefore, several possible alternative erosion control measures
are evaluated in the following section. In the event that unexpected conditions
occur on the beach, a low cost, emergency solution may be implemented. At rel-ine
this time, however, the predicted stability:of the beach indicates that sho
protective structures would not be cost effective.

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SECTION III - EVALUATION OF SHORELINE EROSION CONTROL MEASURES

DESIGN CRITERIA AT WEKO BEACH

This section presents a review of possible shoreline erosion control plans
for Weko Beach. Since financial resources are limited and the beach appears
to be stable, emphasis is placed on low cost measures that could be imple-
mented on an emergency basis. Recommendations will be made for the most
appropriate system for Weko Beach. This information.-can be retained for
possible future use, if the need for beach protection develops.

The fol.lowing general design criteria will serve as a basis for the evaluation.

1. It is assumed that existing shoreline structures will remain in-
tact, and that no additional major structures will be built to
the north.

2. The area immediately in front of the beach house, approximately
200 feet long, is the only area that might need-protection.

3. The water intake and pipeline are currently functioning well.
There is no need for additional protection in this area.

4. Some inexpensive measures may be considered for preventing sand
from encroaching on the boat ramp.
5. Construction of large shoreline structures are not warranted;*City
officials and the people of Bridgman do not want large structures,
based on financial and aesthetic considerations.

The basic types of shoreline protection under consideration include:

1. Construction of a groin field to trap a protective sand beach.

2. Construction of an offshore breakwater, to shield the shore from
waves and trap sand moving along the beach.

3. Beach nourishment to periodically replenish sand eroded away.

4. On-shore reinforcement, such as a stone revetment or seawall.

Onshore reinforcement would dramatically change the appearance and use of the
beach in that area. Since this is contrary to the desires of the City officials,
onshore reinforcement was not further considered.

Groin fields and offshore breakwaters may be of various types and materials.
Several patented systems are available. The following discussion summarizes
systems that have been successfully used or that show particular promise for
locations such as Weko Beach.

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GROIN FIELD ALTERNATIVES

1. Stone Rubble - Rubble groins have been used for years as a durable shore
protection device. The structure normally has a core of small stone and
rock, capped by an armor stone layer designed to withstand the wave forces
at the specific location. The groin may be designed to project any dis-
tance (normally perpendicular to the shore) out into the water. The
existing groins at Weko Beach are rubble, and have stood up well to wave
attack.

For the Weko Beach area, a groin would be designed to extend 50 feet into
the water, to a water depth of 3-4 feet. The armor stone layer would be
approximately 1-2 ton stone (3-4 feet in diameter). The cost of such a
structure would be about $12,000 - $15,000. In an emergency, a smaller
structure, costing proportionately less, would be adequate.

The major advantages of a rubble mound groin are durability and no main-
tenance.

2. Timber Crib Groin - Timber cribs, filled with stone rubble,. have been
effectively used at many locations, as an inexpensive means for shoreline
protection. Again, a structure may be custom designed for a specific
- location. Cost of a 50 ft timber crib groin would be about $5,000.
However, the structure would not be as durable as a stone rubble groin,
and the appearance is not as natural.

3. Steel Sheet Pile - For open lake areas with heavy wave action, a double
sheet pile structure, filled with stone or earth fill would be required
at a cost of $150 - $200 per foot. Such a structure would provide
durable protection comparable to the stone groin, at a similar cost.
The appearance may be somewhat less appealing.

4. Longard Tube - The Longard Tube shore protection system has been suc-
cessfully used in Europe for many years. Made in either 40 in. or 69 in.
diameter, the impermeable, flexible, polyethylene tubes are covered with
custom woven synthetic*fibre. The tube is filled with sand on the site
to provide a stable barrier to wave action and/or sand movement. The
tubes may be used either as a groin or as a nearshore breakwater parallel
to shore.

At Weko Beach, twin 40 in. Longard Tubes could be installed as a groin,
extending about 50 feet from shore. The cost for such a system would
be $8,000 - $12,000, including mobilization.

Longard Tube groins and breakwaters have been successfully used for shore
protection along the Great Lakes. The major problems have been settling
of the tubes and questionable durability. Debris can tear the tubes,
particularly in areas of high wave attack. In several instances, vandals

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have also destroyed tubes. Since the system is only slightly less costly
than a rubble groin, Longard Tubes are not recommended for small projects
such as Weko Beach.

5. Permagroin - A patented groin section, manufactured by Permagroin, Inc.
of Dania, Florida, consists of a 30 ft long, 6 ft high, 5 ft wide,
reinforced concrete structure. The sides are perforated to enhance
dissipation of wave energy. Such a structure could be installed at
Weko Beach, at a cost of about $10,000.

6. Sand/Concrete Filled Bags - As a low-cost emergency system, sand bags have
proven temporarily effective in stopping shoreline erosion. Placed as
either a groin or onshore protection, sand bags can reduce wave energy
and hold beach material in place. Wave action and debris severely limit
the useful life of this system. Therefore, it is not recommended for
Weko Beach.

In an attempt to improve durability, concrete filled bags have been used
in place of sand bags. The concrete "blocks" will continue to function'
after the bag is torn. Again, this system should only be considered as
an emergency measure. The cost of such a system would be variable, de-
pending on the site requirements.

OFFSHORE BREAKWATERS

In this context, offshore breakwaters are structures placed parallel to shore
at any distance from 20 feet to 200 feet from shore. The breakwater serves
two purposes:

1. To shield the threatened shoreline from erosive wave action.

2. To trap sand moving along the shore behind the structure, thereby
enhancing the protective beach.

The cost of offshore breakwaters is highly variable, depending on the water
depth of the installation. Several types of offshore breakwaters are de-
scribed below.

1. Stone Rubble - Most offshore breakwaters in water depths greater
than 3 feet are made of stone rubble. Successful installations have
have been completed at Geneva Park and Lakeview Park, Ohio, and
at Presque Isle State Park, Pennsylvania. In each case, the
objective was to increase and protect an eroding beach; a similar
situation to Weko Beach. As with rubble groins, the breakwaters
are built with a core of small rock (6 in. - 12 in.) and capped
with armor stone.

At Weko Beach, a 100 foot long offshore breakwater, located in front
of the beach house at station 10+50 to 11+50, in a water depth of

-15-

3-4 feet would expand the beach from station 9+50 to station
12+50. One to two ton armor stone would be required. The
estimated cost would be $30,000 to $40,000. It is apparent
that a rubble offshore breakwater is considerably more ex-
pensive than a small groin. Additional protection is pro-
vided, but the additional cost is not justified at Weko
Beach.

2. Sta-Pods - The Sta-Pod system, consisting of interlocking con-
crete units with four legs, may be installed in shallow water
to protect a reach of shoreline. The system has proven to be
quite effective. However, the high cost ($250 per foot) and
significant visual impact on the shoreline preclude use of this
system at Weko Beach.

3. Miscellaneous Shore Protection units - Several other patented
precast concrete units have been used for shore protection. These
include surgebreaker, sandgrabber, Z-wall, and Nami Rings. Each
is installed on or close to shore, with the purpose of dissipating
wave energy and retaining sand. Costs range from $110 to $250 per
foot of shoreline protected. None of these systems are appropriate
for use at Weko Beach.

SUMMARY OF SHORE PROTECTION SYSTEMS

Table 3 summarizes prior experience with the systems described above. Es-
timated 1981 cost information is presented, along with comments regarding
feasibility at Weko Beach.

BEACH NOURISHMENT

As an alternative to installing protective groins or breakwaters, nourishing
the beach by simply adding sand would provide at least temporary protection.
Assuming that such a project would extend a 300 foot length of beach 50 feet
seaward, (5 ft average depth) a total of 2,800 cubic yards of sand would be
required. At an average cost of $3.00 per cubic yard, this nourishment
project would cost $8,500 to $9,000

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TABLE 3

SUMMARY OF SHORE PROTECTION SYSTEMS

1981
PROTECTION SYSTEM LOCATION YEAR INSTL. LENGTH COST/FT COST/FT FEASIBILITY AT WEKO BEACH
Groins
Stone rubble Various $200 50' groin - good long-term
protection

Timber crib Sanilac, Mi. 1975 <50' $ 30 $ 50 Technically and economically
feasible - 50' groin <$5,000

Double steel sheet Various $150 Good long-term protection
pile, filled

Longard Tube
Twin 40" Sanilac, Mi. 1973 100, $ 55 $100 Low durability, subject to
Single 69" Sanilac, Mi. 1973 501 $ 71 $130 vandalism, not for high wave
locations, consider as emergency
measure

Permagroin $300 30' long section

Sand filled bags Slaughter Beach 1979 618' $ 55 $ 70 Bags lost; short-term solution
Sanilac , Mi. 1973 60' $ 30 $ 55 only

Concrete/sand bags Fountainbleu, La. 1979 ? $ 48 $ 60 Function after bags torn; low
Alameda, Ca. 1978 600, $ 36 $ 50 cost short-term measure

Double Sta-Pod 751 $250 Quote, Permagroin, Inc.
Cleveland, Ohio

Offshore Breakwaters
Stone rubble Various $300 High cost, not necessary at
$1,000 Bridgman
Sta-Pods Geneva St. Pk., OH. 1978 31 $116 $250 Permeable, limited protection;
-depth high cost

O"Imm OWN" "Wow M me OM

1981
Offshore Breakwaters (Con't) YEAR INSTL. LENGTH COST/FT CO$T/FT FEASIBILITY AT WEKO, BEACH
Sandgrabber Basin Bayou La. 1979 240' $120 $145 Costly for small job.
Surgebreaker Basin Bayou, La. 1979 200' $125 $150 Costly for small job.

Z-Wall Geneva Park, Oh. 1978 150' $206 $250 5-6 year life; expensive.
Sand bags Kitts Hummock, N.C. 1978 336' $155 $200 Poor durabil-ity, short-term
measure.

Cement/Sand Alameda, Ca. 1978 $ 23 $ 35 Cost highly variable; emergency
filled bags measure

Nami Rings Little Girls Pt., Mi. 1974 3001 $ 63 $110 High cost, poor durability

SECTION IV - RECOMMENDATIONS

The conclusion of the shoreline/beach erosion analysis is that the beach
has likely reached a state of relative equilibrium. The existing small
groins and boat ramp jetty prevent more sand from eroding from the area
in front of the beach house. The beach south of the groins may erode
slightly, but not enough to seriously affect use of the area. The two
groins also provide adequate protection for the water pipeline.

Based on these findings, the recommended approach for Weko Beach is to take
no action at this time. In the unlikely event that unexpected conditions,
either increased shoreline construction to the north or extremely severe
storms combined with record high lake levels, occur then measures may be
taken to protect the facilities. rt would not be cost effective to con-
struct protective works at this time.

Based on our evaluation of available erosion control options, the following
11contingency" plan has been developed. If needed, a single rubble mound groin,
extending approximately 50 feet into Lake Michigan would trap sand on the north
side and provide protection for the beach house. The location of this groin
is shown on Figure 4. The estimated cost is $15,000 (1981 dollars), including
mobilization and miscellaneous costs and fees. Alternative construction
materials for the groin are shown on the-figure for comparison. The superior
durability, natural appearance, and no maintenance justify the slight additional
cost for the rubble structure.

It is also suggested that an attempt be made to build up the jetty on the
north side of the boat ramp. Since the few rocks to the south of the ramp
are of no value at that location, efforts could be made to move those to
the north side. The effectiveness of the north jetty would be improved by
increasing the height-by 4-6 feet.

_19-

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AT,

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@PXJ TING
GR INS
RE AIN

GROIN CONSTRUCTION OPTIONS

LONGARD TUBES- TWIN 40" $100-150 PER FT
STONE RUBBLE $ 200 PER FT
SAND SAGS $50 PER FT (EMERGENCY ONLY)
TIMBER CRIB $50 PER FT.
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REFERENCES

1. National Oceanic and Atmospheric Administration, Summary of Synoptic
Meteorological Observations for Great Lakes Areas, Volume 3, Lake Michigan,
Asheville, N.C. 1975.

2. Birkemeier,- William, The Effect of Structures and Lake Level on Bluff and
Shore Erosion in Berrien County, Michigan, 1970-74,. U. S. Army corps f
Engineers, Coastal Engineering Research Center, Miscellaneous Report 80-2.
April, 1980.

3. Michigan Department of Natural Resources, Bluff Recession Study, Lincoln
Township, Berrien County, Michigan, August, 1978.

4. U..S. ArnW Engineer District, Detroit, Sect-ion 111 Detailed-Project Report
on Shore Damage at St. Joseph Harbor, Michigan, May, 1973.

5. Michigan Coastal Zone Laboratory, The Michigan Demonstration Erosion Control
Program in 1976, Michigan Sea Grant Program..Technical Report No. 55,
February, 1977.

6. Davis, Jr., R.A., Coastal.Changes, Eastern Lake Michigan, 1970-73, U. S.
Army Corps of Engineers, Coastal Engineering Research Center Technical
Paper No. 76-16, October, 1976.

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