[From the U.S. Government Printing Office, www.gpo.gov]
SHORE EROSION
CONTROL GUIDELINES
for Waterfront
Property Owners
$     TMA*k,
MARYLAND DEPARTMENT OF NATURAL RESOURCES
WATER RESOURCES ADMINISTRATION

'US Departmant of commerce
NOAA Coastal Services Center Library
2234 South Hobson Avenue
Charleston,  SC   29405-2413

SHORE EROSION CONTROL
GUIDELINES
for Waterfront Property
Owners
'j FM-0k
MARYIAND DEPARTMENT OF NATURAL RESOURCES
WATER RESOURCES ADMINISTRATION
Production of this report was made possible by funding provided by the Coastal Resources Division, Tidewater
Administration, Maryland Department of Natural Resources through a Coastal Zone Management Implementa-
tion Grant from the Office of Coastal Resources Management, National Oceanic and Atmospheric Administration.

EXECUTIVE SUMMARY


The Department of Natural Resources understands and respects waterfront property owners' rights to protect
their property from erosion. It is in the best interest of waterfront property owners and the health of the
Chesapeake Bay to select the most environmentally sensitive methods of combatting shore erosion.

Protection measures which best provide for the conservation of fish and wildlife habitat are encouraged by the
Department of Natural Resources. Erosion control measures should be considered in the following order of
preference:
* No action
* Relocation of threatened structures
ï¿½ Non-structural stabilization including beach nourishment, slope grading and marsh creation
ï¿½ Shoreline revetments
ï¿½ Offshore breakwaters
ï¿½ Groins
* Bulkheads

These recommendations are consistent with the objectives of the Chesapeake Bay Restoration Program and with
Maryland's Critical Area Protection Program which encourages the use of non-structural shore protection
measures in order to conserve and protect plant, fish and wildlife habitat.
2

PREFACE


This guidebook was developed by the Maryland Department of Natural Resources, Water Resources Administra-
tion, Tidal Wetlands Division, to assist waterfront property owners in understanding the various methods of shore
erosion control and assist them in selecting the method most appropriate for their property. The appropriate
shore erosion control method should be selected by considering the degree of erosion control needed, environ-
mental impacts and cost.
3

TABLE OF CONTENTS
Page
Executive Sunimary.......................................2

Introduction..........................................                                                           9
Maryland Shoreline Statistics and Characteristics
Understanding Shore Erosion
Erosion Rates
Preliminary Considerations for Erosion Control of Your Waterfront Property ..............13
Planning Considerations
Determining the Need for Shore Erosion Protection
Erosion Control Districts
State Assistance
Perm-it Requirenients
Federal Permiits
State Permits
How to Apply for Federal or State Permiits
Environmental Impact
Cost Assessmnent
Design Criteria

Types of Erosion Control.....................................16
Non-Structural .....................................16
No Action and Relocation...............................16
Beach Nourishment ..1.:..............................7
Slope Grading and Terracing .............................7
Marsh Creation ...................................19

Structural - Filter Type Structures.............................22
Stone Revetmients and Simailar Structures........................23

Structural - WallType Structures .............................24
Gabions ......................................24
Bulkheads .....................................25
Structural - Other ....................................29
Breakwaters................................... .29
Groins.......................................30
Reconimendations for Shore Erosion Control Structures ...................33

Other Controls .....................................34
Infiltration and Drainage Cont-rols
Combiniation Methods

Glossary ............................................35

References ...........................................39
5

FIGURES
Page
1. Wave erosion and transportation of sediments along a beach .....10
2. Seasonal changes in erosion and depositional patterns due to changing
wave direction exposing new surfaces ....................................I 1
3. The zigzag pattern of sand movement along a shoreline ........................I1
4. The combination of wave and groundwater erosion on a high bank ...............12
5. The single versus community approach to shore protection .....................13
6. Grading and terracing ................................................18
7. Potential role of vegetation in tidal shoreline stabilization ......................19
8. Profile of a stone revetment ............................................23
9. Gabion (used as a wall) ...............................................24
10. Basic design of a sheet pile bulkhead .....................................26
11. Cantilevered and anchored sheet pile bulkheads .............................26
12. Profile view of the two types of post supported bulkheads ......................27
13. Illustration of structural design considerations for bulkheads (from
U.S. Army Corps of Engineers (1981) .........28
14. Breakwater exhibiting the deposition of sand on the leeward side ................29
15. Groin field with typical sediment buildup ..................................30
16. Timber and stone groins ..............................................31


TABLE
Page
1. Vegetative treatment potential for eroding tidal shorelines in the Mid-Atlantic states.. .20
7

INTRODUCTION


This book provides guidance to waterfront property owners on the Chesapeake Bay and Atlantic coastal waters
(Atlantic shoreline and back bays) on how to protect their property frorm shore erosion. Each section builds on
the previous section in a logical progression for the assessment and selection of the appropriate technique for
protecting waterfront properties from shore erosion. Descriptions, site characteristics, construction materials,
design considerations, maintenance requirements, advantages and disadvantages are discussed for each type of
protection suggested.

The guidebook provides basic information for assessing erosion problems and selecting appropriate protection.
However, the services of a qualified engineer should be ermployed for designing a specific shore erosion control
project.

The appendix includes a glossary of terms conimonly used in descaiing shore erosion problems and associated
control measures.

The Maryland Department of Natural Resources (DNR), Water Resources Admainistration presents this guide-
book as a public service. The methods of shore erosion protection discussed in this guidebook are not guaranteed
to be successful for a specific site nor should regulatory approval from state or federal agencies be assurmed.
Further information maybe obtained from: The Department of Natural Resources, Water Resources Administra-
tion, Tidal Wetlands Division, Tawes State Office Building D-2, Annapolis, Maryland 21401, Phone: (410) 974-387 1.
9

Maryland Shoreline Statistics And Charactetistics
The Chesapeake Bay, Atlantic coastal waters (coast and back bays), and their tidal tributaries include4,360 miles
of shoreline which are subject to erosion. Approximately 1,341 miles of that shoreline are eroding. Statistics
compiled by the Department of Natural Resources show that 37 miles of shoreline are stabilized annually. The
remaining shoreline that erodes each year is a serious economnic and ecological problem because:
* Costs of shore erosion control and reclaimning lost property are beyond the means of some waterfront
property owners.
* Valuable structures such as homes and businesses are at risk to storm damage.
* Sedirments fromn the eroded shoreline smother important aquatic resources, contribute to the degra-
dation of water quality, and fll navigation channels vital to commerce and recreation.

Understanding Shore Erosion

Erosion and sedirnentation (the deposition of sedimnent) are natural processes, but often are in conflict with our
use of the shoreline. The most noticeable problem created by erosion is the loss of waterfront property. Waterfront
property values are high, so many owners spend considerable time and money protecting their shoreline fromn
erosion.

Shore erosion is caused primarily by wind driven waves and to a minor extent by wakes from passing boats. Wind
velocity, duration, and the expanse of open water (fetch) the wind blows over are the predominant factors
generating waves that attack and erode the shoreline. Wave height and strength are generally greater in areas
exposed to the main stern of the Chesapeake Bay than in rivers and creeks.

The basic progression of erosion resulting frorn wave action, diagrarrmned in Figure 1, includes: A) attack bywaves,
B) erosion of a bank and beach causing undercutting, C) slumping of the bank, and D) removal, transportation,
and deposition of the bank sediments along the shoreline.
Figure 1. Wave erosion and transportation of sedimnents along a beach.
10

Shallow bottoms near the shore reduce wave action. Therefore, a shoreline is likely to receive fewer waves if there
are shoals, tidal flats, offshore bars and/or a marsh near the shore. Also a wide beach can withstand more waves
than a narrow beach, therefore reducing erosion of the shoreline.
Water level also affects the amount of erosion. Water levels are influenced by the seasons, tides, storms, seiches
(sloshing action of water in a basin, similar to awave set up in a bathtub), droughts, floods and the general rise of
global sea leveL New areas of the shoreline are exposed to erosion by these changes in water leveL
Seasonal storms affect the level and movement of water, the intensity and direction of wind, and changes in the
patterns of erosion and deposition (Figure 2).
Figure 2. Seasonal changes in erosion and depositional patterns due to changing wave direction
exposing new surfaces.
Often, changes in the pattern of a shoreline are mistakenly measured as an overall net gain or loss of sand when
the changes are only seasonal.
Sand is carried onshore and offshore by the action of waves. Sand is also moved along the shore. Waves most often
arrive at an angle with the shoreline creating a current along the shoreline. These currents move sand along the
shoreline in a zigzag pattern as successive waves advance and retreat (Figure 3).
Zigzag movement of particles (littoral drift)
reponding to runup and return of waves
Downdrift
Chesapeake Bay
Direction of longshore curreht
Figure 3. The zigzag pattern of sand movement along a shoreline.
11

A stabilized beach is dependent on the balance between sand supplied from the bank or transported along the
shore, and sarid lost to erosion. The movement of sand is essential to mnaintaining beaches and deterring erosion.
The velocity (speed and direction) of water determines the amount of sand moved. Larger quantities and heavier
sands can be transported by larger waves or fast moving currents along the shoreline. Fie grained sedimnents
(silts and clays) are generally transported to the deeper sections offshore while larger grained sands are
deposited along the shoreline.

Groundwater discharge through cracks (joints) in sediments as well as wave action contributes to shoreline
erosion by causing the slumping of sedirnents from high banks (Figure 4).
Figure 4. The combination of wave and groundwater erosion on a high bank.
Runoff of surface water also causes erosion of high and low banks and beaches. The amount and velocity of the
water, the height and slope of a bank, and the amount of vegetation detenmine the amount of material eroded and
deposited along the shoreline.
There are natural defenses for shoreline protection. Gently sloping shorelines, beaches and marshes are a good
defense against erosion. A beach prevents average high water from reaching upper areas of the shore. Marsh
plants decrease the rate of erosion by brealing up waves and trapping sediment carried by currents along the
shoreline. Where these features exist they must be managed wisely.
12

Erosion Rates
Erosion of the shoreline in Maryland varies from less than two to greater than eight feet per year. The rate is
dependent upon the erosional forces, mentioned previously, attacking the shoreline and the soil composition of
the bank, beach or marsh. The rate is also influenced by erosion control structures built along a shoreline. Often
the protection of a single waterfront property has a negative effect (increased erosion) on adjoining properties.
Therefore, coordinated protection of an entire segment of shoreline is highly recommended.

The Maryland Geological Survey (MGS) monitors shoreline changes both in the Bay and along the Atlantic Coast.
MGS has compiled erosion data on a series of maps, "Atlas Of Historical Shoreline and Erosion Rates" (1975). The
maps were produced at a scale of 1:24,000 and cover both the Chesapeake Bay and the Atlantic Coast. Individual
maps can be obtained from the MGS, 2300 St. Paul Street, Baltimore, Maryland 21108-5210 for $1 each [(410)
554-5505].

PRELIMINARY CONSIDERATIONS FOR EROSION CONTROL OF YOUR
WATERFRONT PROPERTY
Erosion problems are site specific. There are a variety of procedures and devices designed to protect against
erosion. Selecting an appropriate erosion control measure for your property requires planning.
Planning Considerations

DETERMINING THE NEED FOR SHORE EROSION PROTECTION

The loss of property resulting from shore erosion is a serious problem for manywaterfront property owners. It is
important to determine the degree of erosion to your waterfront property before you or your community decide
on a plan of action.

To determine if a shore erosion problem exists, you should consider the following questions.
* Has your shoreline noticeably receded during the last two years?
* If you have marsh along your shoreline, has it been disappearing?
* Do you have to step down to walk on your beach?
ï¿½ Are trees along your shoreline falling into the water?
* Is your beach submerged at high tide?
* Have your neighbors installed shore erosion control measures?
If you answer yes to one or more of these questions you should contact the Shore Erosion Control Program in
DNR, at (410) 974-3727, the Tidal Wetlands Division in DNR at (410) 974-3871, the local Soil Conservation District
Office or consult the telephone directory for engineering or marine contracting firms in your area.

EROSION CONTROL DISTRICTS
Erosion crosses propertylines, so a community approach is often the key to successful shore protection (Figure 5).
0-






COMMUNITY SHORELINE PROTECTION APPROACH

0)-







INOIVIDOAL APPROACH

Figure 5. The single versus the community approach to shore protection.
13

STATE ASSISTANCE
Waterfront property owners suspecting an erosion problem on their shoreline should contact the Department of
Natural Resources for assistance at (410) 974-3727 or (410) 974-3871. Shore Erosion Control personnel will1
inspect your property and suggest options available to prevent future erosion. These inspectors can provide a list
of engineers and contractors in the area, Property owners who have serious erosion problerms may also quabfy~ for
State financial assistance.

Individual landowners, mnunicipalities and counties may apply for grants or interest-free loans for projects
designed to control shore erosion. Financial assistance is awarded on the basis of available funds and a priority
assessment established by DNR. Priority ratings are based on the rate of erosion, amount of sedimentation, public-
benefit, type of erosion and date of application for the loan. Community based approaches carry a higher priority
for funding.

PERMIT REQUIREMENTS

Federal and State governments generally require that a permit be obtained prior to the construction of any
erosion control project. The Departmaent of Natural Resources and the U.S. Army Corps of Engineers should be
contacted if there is any doubt as to the necessity of a permit. Local (county or municipal) governments should
also be contacted because permit requirements vary widely.
Federal Permits

Federal permits for shore erosion control measures are issued bythe U.S. ArmnyCorps of Engineers. The Corps has
responsibility for the administration of Federal laws for protection and preservation of the waters of the United
States. Whether a permnit is issued will depend upon the impact of the proposed work on:
ï¿½ Navigation
ï¿½ Fish and w-ildlife
* Water quality
* Economics
ï¿½ Conservation
ï¿½ Aesthetics
* Recreation
ï¿½ Water supply
ï¿½ Flood damage prevention
* Ecosystems
* Needs and welfare of the people

The Corps circulates permtit applications for comment to the Environmnental Protection Agency, the U.S. Fish and
Wildlife Service, the National Marine Fisheries Service, and appropriate state and local agencies. Federal pernmits
will not be issued until State Water Quality Certification and State Coastal Zone Consistency determinations have
been provided to the Corps.
A pamnphlet, "U.S. Army Corps of Engineer Permnit Programn, a Guide for Applicants", describing the procedures for
applying for a federal permit, may be obtained free from the Baltimore Corps of Engineers' District Office.
For more information contact:
U.S. Armny Corps of Engineers
Baltimore District - Permnit Section
P.O. 1715
Baltimore, Maryland 21203
Phone: (410) 962-4500 eastern shore
(410) 962-4252 western shore
State Permnits
Shoreline protection projects usually involve construction at or channelward of the mrean high water line.
Waterfront property owners mnust apply to the Department of Natural Resources for a permit or license to alter
wetlands. Wetlands alteration includes:
ï¿½ FiDing
ï¿½ Dredging
* Construction of bulkheads, revetments, boat ranips, piers, below-ground utilities, storm drain
structures, groins, breakwaters, jetties, and simiflar structures or activities.
* Marsh creation.
14

Permnit approvals are based on an evaluation of the irnpact of the proposed project on varying ecological,
econornic, developmental, recreational, and aesthetic values. The law recognizes the right of waterfront property
owners to control erosion on their land, to gain access to navigable waters froni their land and to reclaimn land lost
to erosion since January 1, 1972.

How To Apply For Federal Or State Permnits
Only one application is necessary for a license, permnit or approval frorn both the federal and state governmnents.
This single application should be submitted to:
The Departmnent of Natural Resources
Water Resources Adnministration
Permnit Service Center
Tawes State Office Building, D-2
Annapolis, Maryland 21401
Phone: (410) 974-2755

The Permnit Service Center distributes copies of the joint application to all federal and State wetland regulatory
agencies for review and coniment.
In addition to federal and State wetland permits, a sedinient and erosion control plan, approved by the Soil
Conservation District, mnay be required before any work begirns. You should consult the local Soil Conservation
District for technical advice on how to address sedimnent control during construction of erosion control projects.
Projects mnust also be in compliance with the Chesapeake Bay Critical Area Protection Programn. Under that
Program's requirement, first preference is given to non-structural shore erosion control mneasures. For mnore
informnation on these requirements contact your city or county planning and zoning office.

ENVIRONMENTAL IMPACT
Shore erosion control mneasures can be harmiful to aquatic plants, invertebrates, fish, and wildlife. Therefore, the
impact on the environment by these maeasures mnust be midnimized. Installation of shore erosion control measures
should be placed landward of all marshes.

The area most impacted by shore erosion control measures is the intertidal zone, located between high and low
tide. This zone includes nearshore shallow waters, associated marine soils, and marshes. Habitat, food and cover
for many species of fish and wildlife are the products of the intertidal zone, especially salt marshes. Marshes also
improve water quality by filtering upland runoff, absorbing excess nutrients and trapping sedimnents.

Selecting non-structural shore erosion control methods, such as beach nourishment or marsh creation provide
greater environmental benefits than structural control methods. In particular, marsh creation projects not only
reduce erosion but also enhance the fisheries value of the area and reduce pollutants entering the Bay.

Structural shore erosion control such as abulkhead muay cause erosion in front of the structure, endangering the
shallow intertidal zone and contributing to water quality problems. These adverse impacts can be minimized by
placing stone in front of the structure to break-up waves. Also bulkeads are chemically treated to retard the
growth of many marine organisms. These chemnicals may contribute to water quality degradation.

Stone or riprap revetments breakup waves allowing the marsh to survive channelward of the structure, They
provide habitat and cover for small fish. The use of stone or riprap revetments is environmentally preferable to
bulkheads.
Groins interrupt the natural flow of sand along a shoreline and may adversely change the characteristics of the
intertidal zone by accumulating sand in one area of shoreline while starving another.
COST ASSESSMENT
Costs vary for different types of erosion control and from contractor to contractor. The costs of protection, both
structural and non-structural, depend upon construction details, longevity of the type of protection considered,
the risk and consequence of failure, availability of construction mnaterials and degree of maintenance required.

Contracts for shore protection projects should clearly identify the responsibilities of both parties, the owner and
contractor. The contract should be based on plans and specifications and include prices for the work. It is
important that both parties understand the scope of work The property owner is encouraged to get estimates, or
bids frora several contractors to insure quality work at the lowest price.
15

Waterfront property owners should be aware that any mnethod of shore protection, if properly implemaented, is
expensive. Cost mnust be considered with respect to the amount of erosion currently experienced and the
amount
of protection that will be needed to control future erosion.

DESIGN CRITERIA

The contractor or property owner will be required to develop a final plan for an erosion control project that
includes a layout drawing, construction details, and material specifications. Design considerations will vary for
each method of shore erosion control and are diseussed in the next section.

TYPES OF EROSION CONTROL


This section presents typical shore protection mneasures with a discussion of site characteristics, construction
materials, design considerations, maintenance requirements, advantages, and disadvantages. A careful analysis
of the erosion control measures will reveal several that may be adequate to solve the specific problerms on your
property. Costs should be assessed early in the planning effort, because they will vary greatly among the
methods
of erosion control and the level of protection provided.

Protection measures which best provide for the conservation of fish and plant habitat are encouraged by the
Department of Natural Resources. Erosion control measures should be considered in the following order of
preference:
* No action
* Relocation of threatened structures
ï¿½ Non-structural stabilization including beach nourishment, slope grading and marsh creation
ï¿½ Shoreline revetments
* Offshore breakwaters
ï¿½ Groins
ï¿½ Bulkheads

These recommendations are consistent with the objectives of the Chesapeake Bay Restoration Programn and
with
provisions of Maryland's Critical Ar-ea Protection Programn which encourages the use of non-structural s-hore
protection measures in order to conserve and protect plant, fish and wildlife habitat.

NON-STRtUCTUJRAL

The first three protection measures mnentioned above fall into this category. The consideration of any of these
methods requires careful planning and design considerations to withstand the erosive forces that may be
encountered on your property.

NO AMTON AND RELOCATION

Description

A property owner should first consider taldng no action. Often, a property owner's reaction to shore erosion is
to
act immediately. The property owner is advised to estimate the losses if no action is taken, especially if the
land is
undeveloped or relatively inexpensive structures are at rislk In some circumistances, the property will have o-
nly a
very low erosion rate or experience erosion only dur-ing mnajor storms. It mnay be desirable under these site
characteristics to leave the shoreline in its natural condition. If the encroachmnent of the water on the property
threatens valuable structures, then relocation should be the next alternative considered.
Site characteristics
The shoreline is usually flat. The exposure to the forces of erosion must be minimal and the erosion rate low to
nonexistent. Sufficient land should also be present between the water and any structures to withstand the
erosion rate during the lifetimne of the structures.

Advantages

The advantages of this option are saving money and avoiding accelerating erosion on adjacent Ptoperties. The
relocation of any structures could cost less than erosion control measures.
16

Disadvantages
The loss of anywaterfrontpropertymaybe costly and this option provides no protection from erosion. Relocation
of structures takes special equipment and technical expertise and could cost as much or more than an erosion
control structure. The introduction of sediment from uncontrolled erosion into the water may also be harmful to
fish and aquatic plants.

BEACH NOURISHMENT

Description

Beach nourishment is the replacement of sand along the shoreline of an eroding beach. This method of control
takes advantage of the natural protection that a beach provides against wave attack Beach nourishment may
also be used in combination with other methods of shore erosion control such as groin fields and breakwaters.
Site Characteristics

Beach nourishment is appropriate where a gently sloping shoreline is present. It is also appropriate where the
erosion rate is low.

Construction Materials

The sand applied in a beach nourishment project should be identical to the original beach. A coarser sand may
erode more slowly than a finer sand. The sand may be dredged and pumped from offshore or transported from
upland sites by trucks and dumped.

Design Considerations

The erosion rate of the property is probably the most important element in designing a beach nourishment
project. If the rate is high then beach nourishment may not be appropriate.

The direction and rate of movement of sand along the shoreline should be determined. Sand may be placed
directly along the eroded shoreline or at a point updrift, allowing natural currents to move sand downdrift. The
resulting shoreline protects the area in back of it by sacrificing the newly deposited sand. If the added materials
are eroded their eventual fate should be considered, to avoid shoaling and filling of adjacent properties and
waterways.
Maintenance requirements
Periodic replenishment of the beach using appropriate size sand will help maintain the beach. The need to
replenish the beach depends upon the rate of erosion at the particular site. Although the original cost of the
addition of sand may be low, the cost of periodic replenishment may rival a more permanent solution.

Advantages
Beach nourishment provides effective protection without altering the recreationalvalues or natural integrity of a
shoreline. In providing protection, beach nourishment benefits rather than deprives adjacent areas. This option
maintains access along the beach for activities such as swimming and fishing.

Disadvantages

Along shorelines where no beach exists or removal of the sand is rapid it may be difficult or impracticable to
maintain a beach of sufficient dimensions to protect your property. Even well developed beaches do not provide
total protection during major storms.

The addition of sand may also result in shoaling of adjacent properties and waterways and increase turbidity
during the placement of the sand. This can cause temporary damage to fish and submerged aquatic vegetation.

SLOPE GRADING AND TERRACING

Description

A shoreline bank may be unstable due to the steepness of the slope. Slope grading and terracing (Figure 6) will
reduce the steepness, and therefore, decrease erosion caused by waves striking a steep slope.
17

Figure 6. Grading and terracing.
Site Characteristics

The shoreline must have a steep slope where erosion is presenit.

Construction Materials

No additional mnaterials are required for this type of shoreline protection other than top soil, vegetation and
mnaterials for surface/subsurface water mnanagernent such as ditches or drains.
Design Considerations

Iffwave energies are high, the use of slope reduction and terracing mnay not be enough to stop erosion. The slope of
the existing shoreline and the desired one must be determined. A recomimended design is 5:1 (average for
terracing), althoughi a stope of 3:1 is often satisfactory - especially if combined with other mnethods of shore
protection. It is recommended that regraded banks be stabilized with plants.

The control of surface and sub-surface runoff is necessary to maintain slope stability and to prevent the
destruction of any grading that is performed on the site. Generally, the cost for this procedure is low but varies.
The cost rises dramatically if materials need to be removed from the site.
Maintenance Requirerments

Periodic regrading and replanting may be riecessary depending upon the erosion rate. The use of additional
material may also be necessary to miaintain the proper slope.
Advantages
Slope grading and terracing can result in land that is more useful to the property owner and provides access to the
waterfront. The process can also be combined with erosion control structures for increased effectiveness at low
additional cost.

Disadvantages

Grading and terracing alone is generally not effective against intensive wave action by itself. It cannot be done
where bulkheads or revetments are adjacent to or in the proximity of your property.
18

MARSH CREATION
Description

Tidal marshes form the transition zone between open water and upland. They are recognized as vital links in the
food chain of the Chesapeake Bay. Tidal action in marsh areas provides nutrients that are converted to plant
material The plant material is grazed upon directly bywildlife and waterfowl, or is transported by the tide to open
water to nourish fish and other aquatic organisms.
Tidal marshes provide habitat for thousands of species of plants and animals. Many of these species, particularly
fish, shellfish, and furbearing animals are of direct commercial and recreational importance. Marshes also provide
natural shore erosion control, better water quality, and recreation and education opportunities.

Planting a marsh along an eroding shoreline, therefore, provides shore protection and many environmental
benefits.

Site characteristics

The basic procedure for preparing and planting a marsh site is shown in Figure 7. The vegetation planted in this
procedure has the potential of trapping sediment lost from the eroding banks as well as from sand moving along
the shoreline. Over time, the band of trapped sediments mayincrease, resulting in the widening of the marsh. This
will cause the mean high tide line to move away from the front of the eroding bank and the dense buffer of
vegetation will protect the shoreline against waves.
Eroding Bank	Eroding Bank



Mean High Tide	'


Level of Sub    e	Level of Subs
without vegetation	without veget
BEFORE VEGETATIVE TREATMENT                IMMEDIATELY AFTER
Tide
Tide
strate -   '
tation
ANTICIPATED RESULTS
Figure 7. Potential role of vegetation in tidal shoreline stabilization.
Environmental factors affecting the success of the vegetative plantings on tidal beaches include the width of the
existing beach, depth and type of beach soil, shoreline geometry, and shoreline orientation.
Before choosing this type of shoreline protection you should decide if the site meets certain requirements. Table 1,
developed by the Soil Conservation Service, evaluates the potential for a particular site for successful marsh
creation.
19

DIRECTION FOR USE
1. Evaluate each of the first four shoreline variables and match the site characteristics of the variable to the
appropriate descriptive category.
2. Place the Vegetative Treatment Potential (VTP) assigned for each of the four variables in the right hand
column.
3. Obtain the Cumulative Vegetative Treatment Potential for variables 1, 2, 3 & 4 by adding the VTP for each.
4. If it is 23 or more, the potential for the site to be stabilized with vegetation is very good and the rest of the table
need not be used. If it is below 23, go to step 5.
5. Determine the VTP for shoreline variables 5 through 9 and obtain the cumulative VTP for variables 1-9.
6. Compare the cumulative VTP score with the Vegetative Treatment Potential Scale at the bottom of this page.

SHORELINE                                            DIRECTION FOR USE
VARIABLES                                      The Vegetative Treatment Potential (VTP)                        VTP
is Located in Upper Left Hand of Each Category Box
1. Fetch: Average distance in    8/             7/                0
miles of open water measured
perpendicular to the shore and	ess than	. tru                       Greater than  l
450 either side of perpendicular	0.5 miles	1 mile
to shore.
2. General shape of shore line    8                         3/	Headland or
for distance of 200 yards on              Coves                  Irregular shoreline	straight shoreline
each side of the planting site.
3. Shoreline orientation:            Aty	outh to          outh to          North to
}/Wentation G	uth to I/Sot to )0Nr~t
General geographic direction	rIe ion
the shoreline faces.	less tlan one-       North             West             East              East
half mile fetch
4. Boat traffic:Proximity of   5                 3/1-1oper        2/More           1/  -10per        0 /More
5~~~~~~~~~~~~1
site to recreational and com-       None             week             than 10	/w    week   than 10
r within ï¿½A nmi	per week within	within 100 yds.	per week within
mro~~ercial boat traf~c.  ~of shore	m     hore        of shore	100yds. ofshore

Cumulative Vegetative Treatment Potential for Variables 1, 2,3 & 4    __
If this score is 23 or above, the potential for the site is very good and the rest of the table need not be used.
If it is below 23, go to step 5 below.

5. Width of Beach	2	0
Above Mean High Tide             Greater than 10'	/     10' thru 7'           6' thru 3'	Less than 3'
in Feet
6. Potential width	3	2                     1	0
of Planting Area	/More than 20'	/    20' thru 15'              14' thru 10'	Do Not Plant
in Feet2                                                                 /
hl Feet2 ~~~~~~~~~~~~~~~~~~~~Do Not Plant

7. On Shore Gradiant:	6                    3	0
% slope from MLWto toe	/     Below 8%             8 thru 14%       / 15 thru 20%	over 20%
of bank

8. Beach
Vegetation                            Vegetation below toe of slope             No vegetation below toe of slope

9. Depth ofsand at                                          2                            0
Mean High Tide in                     More than 10"                 10" thru 3"                 Less than 3"
inches'
Table 1. Vegetative Treatment Potential for Eroding Tidal Shorelines in the Mid-Atlantic States.
(from U.S.DA, Soil Conservation Service)
20

Cumulative Vegetative Treatment Potential for Variables 1 - 9:
VEGETATIVE TREATMENT POTENTIAL (VTP) SCALE

If the VTP is:	Potential of site to be
Between	And	Stabilized with Vegetation
40	33	Good
32	24	Good
23	16	Good
below 16                  Do Not Plant

1 Do not plant.
2 If tidal fluctuation is 2.5 feet or less, measure from Mean Low Water to toe of bank. If greater than 2.5 feet,
measure from the Mean Tide Level to toe of bank.
Refers to the depth of sand deposited over the substrate.

Construction Materials
Adding sediments similar to the existing beach may be necessary before marsh creation can be performed.
The following marsh and beach grasses may be appropriate for protecting your waterfront property and are
commercially available in Maryland:
Marsh Plants;
Smooth Cordgrass (Spartina alternitlora). This plant is the dominant marsh grass from Newfoundland
to central Florida. This species ranges from 1.5-8 feet tall with soft and spongy stems often more than 0.5
inch thick Smooth Cordgrass can be planted with a better chance of success than any other coastal
marsh species native to the United States. This species will grow well in brackish or salt water(salinities
of 10-35 parts per thousand).
SaltmeadowCordgrass (Spartina patens). This species is common in the irregularly flooded high marsh
areas along the Atlantic coast. It is able to withstand extended periods of both flooding and drought,
growing in spots where the surface drainage is poor and water ponds during rainy periods. It cannot,
however, tolerate the daily flooding of the intertidal zone. Saltmeadow Cordgrass is avaluable stabilizer
in the zone between Smooth Cordgrass and upland grass species.
Smooth and Saltmeadow Cordgrass are strong sod formers, but relatively poor seed producers. The Smooth
Cordgrass usually grows in the area between high and low tides along brackish streams. Saltmeadow Cordgrass is
usually found between Mean High Tide and the area above any tidal influence. Both cordgrasses tolerate a wide
range of salinity and substrate textures, from coarse sands to silty-clay sediments. Both are well adapted to the
very wet, low oxygen soil conditions characteristic of most salt marshes.

Beach Grass (Ammophila breviliguata)
American Beachgrass is native to the mid-Atlantic coastal sand dunes from Maine to North Carolina. It
may be planted above the area commonly planted with Saltmeadow Cordgrass to provide additional
stabilization.

Further information on planting these and other species can be obtained from county offices of the Soil
Conservation Service.
Design Considerations
Marsh creation projects are particularly sensitive and adversely impacted by human traffic. Marsh plants should
be protected, where possible, from waterfowl grazing.
Careful selection of the varieties of plants with regard to local soil, water (salinity), and wind conditions, is
necessary to achieve successful erosion controL Native plants are more likely to thrive than imported vegetation.
Experience has shown that Spartina alterniflora and Spartinapatenswill grow well along most of the shoreline in
Maryland.                                                                                                /
The width of a marsh creation project is based on characteristics of the site including fetch, shoreline orientation
and the water depth of the nearshore area to be planted. At a minimum a marsh creation project should be 10 feet
wide. 'Typical marsh creation projects have widths of 20-25 feet.
I













i
I
21

When the water depths within the proposed planting area are too deep for creating a marsh, the addition of sand
and grading may be necessary.

The effect of shade from overhanging trees on marsh creation projects must be considered. All sites chosen for
marsh creation must receive at least six hours of direct sunlight daily throughout the growing season (April-
October). Trees must be pruned or removed to allow for the daily minimum amount of direct sunlight.
The State of Maryland considers the use of vegetation for shore erosion control to be an important part of its
Chesapeake Bay Restoration Program. The Shoreline Erosion Control Program (SEC), was created within the
Maryland Department of Natural Resources to encourage property owners who have shore erosion problems to
use non-structural techniques for which the state can provide a (50%) matching grant.

In general, property owners whose shorelines meet the following site characteristics are eligible to participate in
the State SEC Grant program:
ï¿½ Presence of intertidal marsh grass growing on the shore within 500 feet of where the project will be
located,
and
* Less than a one mile fetch.

Waterfront property owners may call or write the SEC Program staff or their local Soil Conservation District office
to obtain further information.

State of Maryland
Department of Natural Resources
Shore Erosion Control
Tawes State Office Building D4
Annapolis, Maryland 2140
Phone: (410) 974-3727


Professional guidance in selecting plants for marsh creation projects is recommended to increase the likelihood of
success.
Maintenance Requirements
Plants that are removed or die during the early stages of growth must be replaced immediately to insure the
undisturbed growth of the remaining plants. The removal of debris and selective pruning of trees is also a good
maintenance practice. After significant growth has occurred only periodic inspections may be necessary.
Protection measures, such as fencing, must be taken to keep waterfowl from eating the young plants.

Advantages
For a minimum investment, marsh creation will help bind the soil against erosion and extend the life of erosion
control structures (revetments, bulkheads etc.). Where no structure exists it will slow down erosion. The cost for
this type of protection is much less than most other types of shore erosion controL
A created marsh along the shoreline not only reduces erosion but also enhances the fisheries value of the area. It
also provides an attractive natural shoreline. In many cases the newly created marsh will also serve as a buffer
strip. This strip can reduce the amount of sediments and nutrients entering tidal waters by filtering upland runoff.

Disadvantages

This method of erosion control may only be used along shorelines with low erosion rates.
STRUCTURAL
Structural erosion control devices are divided into two broad groups according to their purpose; 1) those
designed to stabilize a bank or fastland, and 2) those designed to stabilize a beach or promote accretion.
Two basic types of structures are designed to stabilize a bank: filter structures and wall structures. Filter
structures reduce the level of the wave's strength while keeping soil from passing through to the water. Wall
structures are impervious vertical walls that separate the natural shoreline from water and wave action. The
success of both types depends upon adequate design and construction.
22

FILTER TYPE STRUCI'URES (Stone Revetments and similar structures)
Description
Filter type structures are designed to reduce the energy of the incoming waves as they strike the surface of the
structure, while at the same time, hold the soil beneath it in place. Reduction of the energy of incoming waves is
accomplished bythe sloping shape of the structure and byits rough surface. Filtering qualities result from the use
of layers of varying sized stone and other materials. In construction, the bank is first graded to achieve the shape
required for the structure being installed. A filter cloth is placed on and attached to the graded bank. This cloth is
similar in weave and texture to tightlywoven burlap but is made of a non-deteriorating plastic. On top of the layer
of filter cloth is placed a six to eight inch layer of stone. This layer of stone holds the filter cloth in place and
becomes the bottom layer of the actual structure. A variety of outer layers are then placed on top of the stone. This
type of structure is preferred to bulkheads where groundwater is part of the erosion process.
A stone revetment (Figure 8) is constructed byplacing progressivelylarger blocks or pieces of stone on filter cloth
or fine gravel




Stone Apron for Protection

Bedding Stone Layer
 Existing Gound.   Backfl

Armor Stone Layer




STONE REVETMENT

Figure 8. Profile of a stone revetment.
The armor layer must be stable against movement by waves. The armor layer is typically made of rough angular
rock. The underlying filter layer supports the armor layer against settlement. It allows groundwater drainage
through the structure and prevents the soil beneath from being washed though the armor layer by waves or
groundwater seepage. Toe protection prevents settlement and protects the edge of the revetment from washing
away. In areas where large waves are expected, an overtopping (or splash) apron is sometimes added. Generally,
the apron is a layer of 10 to 12 inch stone about 10 feet wide that extends landward from the top of the revetment.

Site Characteristics
Revetments, to remain stable, must be built on gentle slopes (2:1 or better slopes).

Prior to construction, the ground should be graded to a gentle slope and fill material should be added only as
needed to achieve a uniform grade. The fill should be free of large stones and firmly compacted before revetment
construction proceeds.

Construction materials
Heavy armor stones with an interlocking design are needed for a revetment to withstand storm waves. There are
many types of materials that are used for the construction of revetments, however, quarry stone is the most
reliable type of revetment material
Design considerations
Important design considerations include the proper height and width of the revetment, protection from erosion
in front of the revetment, and analysis of the supporting soil characteristics. Revetments should be high enough to
prevent overtopping bywaves. To deter erosion along the sides, additional stone should be placed perpendicular
to the revetment. Erosion in front of the revetment can be prevented by the placement of additional stone. The
soils comprising the area under the revetment must be analyzed to determine if they can support the structure.
23

If a beach is present in front of the revetment, access should be considered for recreational activities. When access
to boats in front of a revetrment is desired, a pier constructed over the revetment may need to be designed.

Main ten an ce Req uiremnen ts
Periodic mnaintenance may be necessary to fill holes and restore the height and width of the revetment. These
maintenance activities are required because the individual stones cormprising the revetment may be subject to
mnovement and settling.

Toe protection should be monitored on a regular basis. The steeper a revetment the more frequently it should be
inspected because the toe is likely to erode more quickly. Other types of erosion control should be considered in
areas where movement of the structure may occur because of unstable slopes.

Advantages

Where the shoreline requires structural measures to control erosion, a sloping stone revetment is strongly
recommnended for the following reasons:
* Stone used in this type of structure does not degrade over time.
* Waves reflecting from sloping revetments usually cause only minor disturbance and scour of the
sediment offshore and at the toe of the structure.
* This type of protection is unlikely to fail completely during a storm. There is a possibility that stones
may be dislodged if waves wash over the revetment during a storm. However, the stones may be
recovered and replaced afterwards.
* Stone generally provides a better habitat for aquatic organims than the materials that are used in
most other types of structural shoreline protection.
* No preservatives are used in revetments such as those found in bulkheads which discourage the
growth of aquatic plants and anirmals.

Disadvantages
A large amount of stone is needed to properly build a revetment. Costs for buying and transporting the stone may
be considerable. It may be difficult to transport construction materials to the shoreline on properties where
access is limited by bridges or roads with low load limits, high banks, or shallow nearshore areas. Under these
circumstances another type of structure may be necessary.

STRUCTUTRAL - WALL TYPE STRUCTURES

Wall type erosion control structures generally form a wall to retain material on the upland side and separate
erodible land from daxnaging wave action. Two such structures, gabions and bulkheads, are described below.

GABIONS

Description

Gabions are rectangular wire baskets filled with stone. Gabions are veryversatile. They maybe used as revetments,
groins and offshore breakwaters. Figure 9 shows gabions being utilized as a wall type erosion control structure.
Figure 9. Gabion (used as a wall).           2
24

There are two types of gabions: mattresses and upper level baskets. Mattresses are baskets which are usually 9 to
12 inches thick and provide a foundation for the upper level baskets. Upper level baskets are available in 6, 9, and
12 foot lengths and 1, 1.5, and 3 feet heights.

At the construction site, gabion baskets are unfolded and assembled by lacing the basket edges together with wire.
Individual baskets are then laced together, stretched, and filled with stone. The lids are closed and then wired to
other baskets. The result is a large heavy mass that is not as easily moved by waves as single stones might be.

Site Characteristics

Generally, gabions are suitable on sites where bulkheads or revetments are acceptable.

Construction Materials

The baskets are made of galvanized and polyvinyl chloride (PVC) coated steel wire in a hexagonal mesh. The
stones used to fill the baskets are usually in the range of 4 to 8 inches.

Design Considerations

Gabions are suggested for use in brackish and freshwater environments, where corrosion of the wire will be
minimal.

The baskets should be staggered and joined, much like the courses of a brick wall, in order to form a stronger
structure. It is also recommended that the seaward end of the mattresses be anchored with large stones or
anchor screws.

Maintenance Requirements

Damage to the baskets should be repaired immediately. Missing stones should also be replaced from time to time
to maintain a tightlypacked basket. This will minimize stone movement which can cause abrasion damage to the
basket wires.

Advantages
The construction of gabions may be accomplished without heavy equipment. The structure is flexible and
continues to function properly even if the foundation settles. Adding stones to the baskets is an easy maintenance
procedure. The cost of using gabions may be low compared to other protection methods depending on the
distance of the stone from the job site.

Disadvantages
Gabion baskets mayopen under heavy wave action releasing the stones and scattering them. Water borne debris,
cobbles, ice, and foot-traffic can damage the baskets. Corrosion of baskets placed in salt water begins with the
smallest defect in the protective coatings.

BULKHEADS
These structures are walls designed to protect the shoreline by providing a barrier to waves. They are most
appropriate where fishing and boating are the primary uses of the shore, and for deep water commercial, port
applications.

Description

There are two basic types of bulkheads: sheet pile and post-supported. Sheet pile bulkheads (Figure 10) consist of
interconnecting very tightly-spaced sheets of material driven vertically into the ground with special pile driving
equipment.
25

Figure 10. Basic design of a sheet pile bulkhead.
The sheet pile bulkhead may be cantilevered or anchored (Figure I 1). A cantilevered bulkhead is a sheet pile wall
supported solely by the depth to which it is buried in the ground. The anchored bulkhead is supported by
embedded anchors or tilted structural bracing on the water side.
Figure II. Cantilevered and anchored sheet pile bulkheads.
There are two types of post-supported bulkhead: batter pile and tie back (Figure 12). They both consist of evenly
spaced piles (usually timber) driven into the ground with an attached facing material that forms a retaining wall.
The posts support the bulkhead and may be of the carntievered or anchored type.
26


TIE-BACK TIMBER BULKHEAD


.-..-~~~~~~~~~~~~~~.
4'~~~~~~~~~~~~~~
~ I
Figure 12. Profile view of the two types of post-supported bulkheads.
Bulkheads are not generally needed along shorelines with low fetch where large waves are not common.

Site characteristics
In general bulkheads should be limited to sites where the use of marsh creation or stone revetments to provide
shore erosion control is inappropriate. Bulkheads may be the preferred shore erosion control option under the
following circumstances:
ï¿½ High energy shoreline
* Inaccessible shoreline
ï¿½ Adjacent bulkheaded shoreline
ï¿½ Commercial vessel berthing (Deep water application).
Construction Materials
Sheet-pile bulkheads may be constructed of steel or timber. The type of soil at a site determines the type of
sheet-piling that can be used. Steel sheet piles can be driven into hard sediments and some soft rock Timber sheet
piles can be driven into softer sediments. Steel bulkheads are constructed of a marine alloy to resist corrosion by
salt water. Ends of the metal sheeting that protrude above the bank are covered by an a cap that is bolted on.
Treated timber bulkheads are generally less expensive than steel. There are several different types of treatments
for the timber used in marine structures including creosote, chromated copper arsenate and a combination of the
two.
Design Considerations
Factors influencing design are: exposure to waves, depth of water, height of bank foundation conditions,
penetration of the piling, height and alignment, and the need for erosion protection in front of the bulkhead.
Figure 13 depicts a typical bulkhead cross section with many of the necessary structural design precautions.
27




























t
1. Heavy timber sheet piling
and anchor pile provide needed strength.
2. Woven plastic filter cloth stabilized
against ultraviolet light and sized to mnatch
backfill and beach mnateriaf.
3. Stone toe protection to prevent scour.
4. Drain holes to relieve hydrostatic pressure.
S. Flank protection ties structure into existing bank.
6. Splash apron to protect against anticipated overtopping.
7. Corrosion-resistant or galvanized steel fasteners-
no combination of different metals.
8. Galvanized anchor rod with turnbuckle,
Figure 13. ilustration of structural design considerations for bulkheads
(from the U.S. Army Corps of Engineers (1981)).

Bulkheads most comamonly fail because of (a) inadequate design or construction using poor qualit materials to
withstand waves or to prevent overtopping, and (b) undercutting of the front of the structure. The pressure of the
soil and water on the landward side can also topple the structure.
Main ten ance requirements
Sheet pile bulkheads should be inspected regularly to check for sheet failure and possible loss of soil behind them.
Faiures may be caused by freezing and thawing, direct wave impact, or debris imnpact.
The protective coatings on the hardware, sheeting, and pile tops of tirnber bulkheads should be maintained. Splits
in the wood need to be mended on aging bulkheads. Soil washing out frorn behind the bulkhead should be
replaced.
Advantages
Steel bulkheads that are properly designed and built are quite strong and are suitable where severe conditions are
expected. Construction materials are available in a variety of sizes and shapes. Steel bulkheads have been in use
for many years and design and engineering data are time tested and readily available.
Materials for a timber bulkhead are readily available. The structure will usually provide adequate protection if
properly constructed and maintained.
Disadvantages
Steel bulkheads are susceptible to corrosion after a time depending upon the grade of the steeL These structures
reflect waves causing erosion at its base (toe).
Timber bulkheads are also susceptible to erosion at the base unless toe protection, such as stone, is used. The
creosote and chromnated copper arsenate used to prevent i-nfestations by borers and rot can cause burns and may
adversely affect other marine organisms. The structural members of timber bulkheads can splinter. Wave
reflection off the vertical face of timber and steel bulkheads produces unsuitable habitats for marine organisms.
The cost of constructing steel sheet pile bulkheads is much higher than that for a timber bulkhead. Bulkheads may
also cause increased erosion to adjacent properties.
28

STRUCTUJRAL - OTHER








I
BREAKWATER~S

Description
Breakwaters are structures, made of various materials, placed offshore to reflect or decrease wave energy,
creatirng a low energy zone, between the structure and the existing beach. Decreases in wave strength significantly
affect the transport of sarid by a wave. Sand moving along the shoreline may be slowed or deposited on the beach
side of the structure (Figure 14). The decrease in sand rmoving along the shoreline may cause increased erosion to
adjacent properties. This erosion can be mninimized by adding sand between the breakwater and the beach.
Breakwaters may be used to protect selected areas of shoreline, headlands or harbors.
Figure 14. Breakwater exhibiting the deposition of sand on the leeward side.
Breakwaters are structures that extend from the bottom to a designied height above the normal water leveL

Site Characteristics
A gently sloping beach with an unacceptable rate of erosion is the basic type of site suitable for offshore
breakwaters. Movement of sand along a shoreline is necessary to produce the desired effect, a build up of sand
between the structure and the beach. If the mnoverment of sand along the shoreline is not to be interrupted, then
proper design of the structure is essential. In addition, the placement of sand between the structure and the beach
may be necessary to offset erosion to adjoining properties.

Construction Materials
Breakwvaters may be constructed of laxge stoines, gabions, concrete rubble, concrete form structures, mnetal or
wood sheeting or sand filled bags. Other mnaterials, such as plastics, are also occasionally used.
Design Considerations
The effectiveness of a breakwater depends upon its height, am~ount of water and sand allowed through, distance
from shore, length, spacing of each unit, type of soil under the structure, structural weight, and foundation type.
The most important of these is the height, because it controls how mnuch of each wave reaches the shoreline.
Breakwaters are usually installed in shallow water (less than 4 feet deep) due to the cost.

The service of a professional engineer is advised for the construction of offshore breakwvaters due to the complex
nature of their design.

Maintenance Requirements
The maintenance required for breakwaters is the saxne as that for revetments and bulkheads.
29

Advantages
Protection is accomplished without the placement of a structure on the shoreline. Recreational use of the
shoreline for swimming and sunbathing is preserved and may be irnproved. Minimal impact on the environment
occurs when stone is used in the construction of a breakwater.

Disadvantages
These structures are subject to erosion at the base and physical damage from large waves.

GROINS
Groins are structures that interrupt the flow of sand for the purpose of widening an already existing beach and
thus provide additional protection for the beach. They are not designed for the purpose of creating a beach.
Description
Groins are narrow structures of varying lengths and heights that extend, fingerlike, into the water and are usually
constructed perpendicular to the shorelinae (Figure 15).
Figure 15. Groin field with typical sediment buildup.

Used singularly, or in groups know-n as groin fields, their prirnary purpose is to trap and retain sand, filing the
areas of shoreline between them. Groins i-nterrupt the movement of sand along the shoreline. Ideally, the area
between the groins is filled, then sand can continue mnoving along the shoreline. Sand usually accumulates
between the groins with rmore accumulation on one side than the other dependent on the direction of the
movement of sand along the shoreline. The accumulation of sand between the groins acts as a barrier that waves
can attack and erode without damnaging upland areas. An adequate quantity and mnovemnent of sand along the
shoreline is necessary to produce accumulations of sand between the groins. If sand transport is equal in both
directions, groins may not be effective.
Site Characteristics
The shoreline should be a gently sloping beach. It is irnportant to consider the direction and araount of sand
moving along the shoreline before choosing groins as a mnethod of shore erosion control.
Constructdon Materials
Stone, concrete, gabions, timber and steel are the primnary mnaterials used in the construction of groins (Figure 16).
Many other mnaterials are also used but are not as dependable as these. Quarry stone should be considered where
locally available. The structural form of a stone used in construction of a groin is about the same as for a stone
revetment. Filter cloth should be installed under any stone or rubble groins.
30

...-  ,,"'      ,z:;.5--.	-  ..:r  Bedding gtot
STONE GROIN   ï¿½W.. Beach "	24              , Water
Figure 16. Timber and a stone groins (the view of a steel sheet groin would be similar to the timber
and the view of a concrete rubble groin would be similar to the stone groin).
Timber and steel groins do not require the use of filter cloth. Recommendations for construction materials
contained in the section for sheet pile bulkheads applies to groin construction.
If the movement of sand along the beach is mixed with too much clay or silt, filling the area between the groins
with sand from an outside source is necessary.
Design Considerations
Important design considerations for groins include:
* Height
* How far they should extend into the water or onto the land
* Spacing between structures, if you are constructing a groin field
ï¿½ How much sand and water should be allowed to pass through the groins
Groins may be built either high or low in relation to the existing beach profile. High groins effectively block the
movement of sand along the shoreline, provided sand cannot pass through them. Low groins, built so waves can
wash over them, permit sand to pass over the structure and nourish adjacent beaches.The extension of a groin
must be sufficient enough to create a desired beach while allowing adequate passage of sand around the end. A
groin extending beyond the area of the shoreline where the waves break, forces sediments too far offshore to be
returned to the adjacent shorelines. The groin should extend inland far enough so that storm waves cannot erode
around the upland side, making the structure ineffective.
The correct spacing of groins depends on their length, wave strengths in the area, the amount of sand moving
along the shoreline and the desired firal shoreline shape. Properly designed groins are spaced so that sand
accumulates along the entire length of the area between groins. The shoreline erodes in some areas between
groins that are positioned too far apart. Groins placed too close to one another may not allow for sand
accumulation. Generally, groins are spaced two or three groin lengths apart.
The use of groins must be carefully considered. Many of the regulating agencies do not approve groin construction
due to possible erosion of the adjacent shoreline.
31

Maintenance Requirements
The maintenance requirements for groins are essentially the same as discussed for those of revetments and
bulkheads. In addition, the area between groins in a groin field should be monitored for sand loss. The addition of
sand, if necessary, into the area between groins will protect upland a-reas and decrease the araount of time
required for the area between the groins to fil naturally.

Advantages

Increasing the size of a beach provides a buffer, where wave energy may be absorbed, resulting in protection for
upland areas. The stabilization of a beach may possibly add to the recreational value of the beach.
Disadvantages

Sand moving along a shoreline is interrupted by a groin, usually resulting in sand starvation of adacent
properties. Groin placement does not necessarily guarantee sand accumulation.
32

RECOMMENDATIONS FOR SHORE EROSION CONTROL STRUGJI'RES
Several important recommendations whih should be considered in designing or maintaining all shore erosion
structures are discussed below.

I1)Select the proper crest (top) elevation for an vertical structure. Consider the combination of
maximum tide and waves (run-up) that can be expected in the lifetimae of structures. The height of
structures necessary to preveint overtoppinig by waves depernds upon the water depth and the
maximum potential wave height at a site. Increases in the height and depth of structures increases
the costs for materials and labor. The structure should be designed to withstand the forces of a storm
that would occur once every 20 to 30 years on the average. An adequately designed structure
provides protection for most storm conditions encountered without the undue higher costs of a
more elaborate structure.
2) Select the proper stone armor weight fo-r revetments. Shore protection structures must be strong.
This can be accoraplished by using heavy and mnassive components unlikely to be dislodged by waves
or ice. The stone for revetraents should be clean, hard, dense, durable and free of cracks and
cleavages. For sloping revetments built in Maryland's Chesapeake Bay, a minimurm stone weight of
650 pounds is recommnended, unless the water depth fronting a particular structure is shallow,
limiting the wave heights attacking the shore.

3) Alwaysincludefilter cloth in the design. The purpose of filter cloth is to prevent soil from washing out
behiind or under the erosioni control structure. The life of fiter cloth is not well established, its use is
certainly reconimended. Filtering, one of the most ixmportant design details, is probably the most
neglected and, therefore, poorly designed fiters have caused more structures to fail than any other
contributing factor. A properly designed filter allows water but not sand to pass through. Water must
flow through a structure in order to eliainate the buildup of water pressure. Filtering can be
provided through the use of graded stone on gravel in a range of sizes, or through woven, or
non-woven synthetic filter cloths.
4) Provide a bedding of smrall stone covered Rith armor stone at the toe of bulkheads. Advantages
gained by providing armor stone toe protection for bulkheads include:
ï¿½ Reduction in the number of waves hitting the bulkhead
* Less water will spray over the top of the bulkhead
* Erosion of the soil at the base of the bulkead will be eliminated, therefore maling it more
structurally sound
ï¿½ Creation of a more favorable habitat for mnarine organisms
The installation of armor stone toe protection should include filter cloth and a bedding layer of small
stones. The small stones will reduce the potential for rupture of the filter cloth. Ideally, the armor
stone should be piled as high as the highest storm waves expected. In many places the cost of using
armor stone may be nearly as costly as a revetment. Under these circumstances it may be more
prudent for the property owner to just construct a revetment instead of a bulkead.

5) Provide erosion control structures along propertylines to preven t erosion along the side and behind
the erosion control struct are. If a specified reach of beach has been protected completely, erosion on
the side and behind the erosion control structures will not occur at those properties within the
reach. However, if only a segment of the shoreline has been protected, adjacent shoreline could erode
rapidly. The increased erosion could possibly endanger the shore protection structure. To prevent
this, structures should be designed to protect the side and back of the erosion control structure
consistent with the erosion rate and design life of the structure. Lengthening these structures may be
necessary depending upon the erosional rate.

6) Finall,y more frequent maintenance of many erosion control structures should be performed.
Periodic mnaintenance of structures is necessary due to annual storm and winter damage. The
maintenance varies with the structural type, but annual inspections should be made by property
owners. For stone revetments, the replacement of stones that have been dislodged is necessary. For
timber bulkheads, protective coatings should be maintained on hardware, sheeting and pile tops.
Splits in the wood should be mended on aging bulkheads, and any backfil that has washed out
should be replaced. Steel bulkheads should be inspected foy sheet pile deterioration and for loss of
backfil Gabion baskets should be inspected for corrosion failure of the wire (the plastic coating can
be removed by improper handling during construction or abrasion by stones inside the baskets).
Baskets that are damaged should be replaced because waves will quickly empty therm. Through
periodic monitoring and maintenance, erosion control structures will protect the shoreline longer.
33

OTHiER CONTROLS

INFILTRATION AND DRAINAGE CONTROLS

The erosion of steep bluffs alo-ng the shorelfine may require the use of infiltration and groundwater drainage
controls. Infdltration controls are designed to promote downward percolation of surface runoff while drainage
controls divert water already present on the surface and in the soil. An example of an infiltration method: Water
comning off the roof of a structure is collected by a gutter system and then diverted into a dry well. A drainage
control could be a ditch or a swale on the surface. Subsurface drainage controls are complex and require the
assistance of an engineer to analyze site conditions and offer a solution.

COMBINATION METHODS

The erosion controls described in this docurnent mnaybe used in various combinations, to complement each other
and accormplish the desired protection when a single method is not enough. The nature of the erosion and desired
extent of protection suggests which methods should be cormbined.

Marsh creation and beach nourishmnent mnay be considered for use with other methods to produce effective
protection measures depending upon wave strength. Beach nourishment may be used in combination with groin
fields and breakwaters.

Large waves can damage new marsh vegetation. Therefore, it may be necessary to provide temporary structural
protection such as groins until the vegetation becomes established.
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GLOSSARY
While not all of these terms are used in this book, many are used by shore erosion control profes-
sionials.
Accretion
Accurnulation of sand or other beach miaterial at a point due to the natural action of
waves, currents and wind. A build-up of the beach (see Deposition).

Parallel to and near the shoreline; same as longshore (see Littoral drift, Longshore
Current).

Predominantly used in stone revetments, referred to as "splash apron", to prevent loss
of earth materials supporting the structure.

The rising ground landward of a beach, whether it be a bluff bank or gentle slope.

A fully or partly submerged mnound of sand, gravel, or other unconsolidated sedirment
built on the bottom in shallow water by waves and currents.
Generally a timber pile; driven into the bottom to provide lateral support to a vertical
protective structure.
A shoreline of unconsolidated material; extending from the low water line to a point
landwa-rd where either the topography abruptly changes or permanent vegetation
first appears.

High, steep, broad-face bank at the water's edge (see Cliff).

Large stones with diameters greater than 10 inches. Larger than cobbles.

A wave as it spills, plunges or collapses on a shore.

Area offshore where waves break.

A structure aligned parallel to shore, designed to protect any landform or water area
behiind them frorm the direct assault of waves.
A structure that retains or prevents the sliding of land or protects land from wave
darnage.
Extremely fine-grained soil with individual particles less than 0.00015 inches in
diarmeter.
fHigh steep face of rock at the water's edge (see Bluff).
Rounded stones with diameters ranging from 3-10 inches. Cobbles are larger than
gravel but smaller than boulders.

Upper edge or limit of a shore protection structure.

The flow of water in a given direction.

An accuraulation of sedirment on a beach, samne as accretion.
The mninimium period of timne a structure is expected to function, commonly estab-
lished through an engineering design procedure.
Alongshore


Apron


Bank

Bar


Batterpile


Beach



Bluff

Boulders

Breaker

Breaker Zone

Breakwater


Bulkhead


Clay


Cliff

Cobbles


Crest

Current
Deposition

Design Life
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Period or cycle lasting approximately one day. A diurnal tide has one high and one low
in each cycle.
A hill or mound of loose, wind-blown material, usually sand.
The wearing away of land by the action of natural forces.
Land that is not regularly inundated by high water.

The linear distance of open water where waves are generated by the wind of a certain
direction, speed and duration.
Synthetic textile with openings for water to escape, but prevents the passage of soil
particles.
Small, rounded granules of rock with individual diameters ranging from 0.18-3 inches.
Gravel is larger than sand but smaller than cobble.

A shore protection structure built perpendicular to the shore to trap sand and retard
shore erosion.

Series of groins acting together to protect a section of the beach. Also called a groin
system.

Intersection of the level of mean high water with the shore. Shorelines on navigation
charts show approximations of the high water line.

Not having openings large enough to permit water to freely pass.

The land area alternately inundated and uncovered by tides. Usually considered to
extend form mean low to mean high water
Structures used at inlets to stabilize the position of the navigational channel, to shield
vessels from wave forces, and to control the movement of sand along the adjacent
beaches so as to minimize the movement of sand into the channel.
Sheltered, the area located on the side facing away from the wind.
Direction toward which wind is blowing or waves are traveling.
Off, on, or along the shore. The region along the shore.

The sediments moved along the shore by waves and longshore currents.

The movement of sediments in the nearshore zone by waves and currents. Transport
of sediments can be, either parallel or perpendicular to the shoreline.
Parallel to and near the shoreline; same as alongshore.

Current in the breaker zone moving essentially parallel to the shore and usually caused
by waves breaking at an angle to the shore (also called alongshore current).

The rate of the transport of littoral drift parallel to shore; usually expressed in cubic
yards per year (see Littoral Drift).
The minimum elevation reached by each falling tide.
An area of soft, wet, or periodically inundated land, generally treeless, and usually
characterized by grasses and other low growth.
Average height of the daily high waters over a 19-year period. For semidiurnal or
mixed tides, the two high waters of each tidal day are included in the mean. For
diurnal tides, a single daily high water is used to compute the mean.
Diurnal

Dune
Erosion

Fastland

Fetch


Filter Cloth


Gravel


Groin


Groin field


High Water Line


Impermeable

Intertidal Zone


Jetty


Lee
Leeward
Littoral

Littoral Drift
Littoral Transport


Longshore

Longshore Current

Longshore Transport
Rate

Low tide
Marsh

Mean High Water








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Mean Low Water
Average height of the daily low waters over a 19-year period. For semidiurnal and
mixed tides, the two low waters of each tidal day are included in the mean. For diurnal
tides, the one low water of each tidal day is used in the mean.
The process of replenishing an existing beach either naturally, by longshore transport
or artificially by materials dredged or excavated elsewhere.
The passing of water over a structure from wave run-up or surge action.

Residual product of partial decomposition of organic matter in marshes and bogs.
Having openings large enough to permit free passage of appreciable quantities of sand
or water.
Long, heavy section of lumber, concrete or metal driven or jetted into the earth or
seabed as support or protection (see pile sheeting).

Pile with a generally slender, flat cross-section driven into the ground or seabed and
meshed or interlocked with like members to form a diaphragm, wall, or bulkhead.

A group of piles.

Plastic material that forms a resilientcoating suitable for protecting metal from
corrosion.

A facing of stone, concrete, etc., built to protect a scarp, eroding bank or shore
structure against erosion by waves or currents.

Layer, facing, or protective mound of stones randomly placed to prevent erosion,
scour, or sloughing of a structure of embankment; also, the stone so used.
Loose, angular, stones along a beach. Rough, irregular fragments of broken rock or
concrete.
Particles with diameters between 0.003-0.18 inches. Sand is larger than silt but smaller
than gravel.
The accretion of sediments trapped by a groin or other protrusion in the littoral zone.

The removal of underwater material bywaves or currents, especially at the base or toe
of the shore structure.
A structure separating land and water areas primarily to prevent erosion and other
damage by heavy wave action (see Bulkhead).

An occasional rhythmical movement from side to side of the water of an enclosed
basin, with fluctuations in water level.
A tide with two high and two lowwater in a tidal day, each high and low approximately
equal in stage (see Mixed Tide).

The narrow strip of land in immediate contact with the sea, including the zone
between high and low water lines (see Beach).

The intersection of a specified plane of water with the shore or beach (e.g., the high
water shoreline would be the intersection of the plane of the mean high water with the
shore or beach). A line delineating the shoreline on National Ocean Survey nautical
charts and surveys approximates the mean high water line.

Low offshore barrier structure whose crest is usually submerged, designed to retain
sand on its landward side.

Generally refers to particles having diameters between 0.00015-0.003 inches. Silt is
larger than clay but smaller than sand.
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Nourishment

Overtopping
Peat
Permeable

Pile


Pile Sheeting


Piling

Polyvinyl Chloride(PVC)


Revetment


Riprap


Rubble

Sand

Sand Fillet
Scour


Seawall

Seiche


Semidiurnal Tide


Shore


Shoreline




Sill


Silt







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Detailed description of particulars, such as the size of stone, quality of materials,
contractor performance, terrms, and quality controL

The rise above normal water level on the open coast due to the action of wind on the
water surface. The storm surge resulting from a hurricane also includes the rise in level
due to the atmospheric pressure reduction as well as that due to wind stress.

The periodic rising and falling of water resulting frorn gravitational attraction of the
moon, sun and other astronomical bodies acting upon the rotating earth. Although the
accompanying horizontal movement ofthe water resulting from the same cause is also
somnetimes called tide, it is preferable to designate the latter as tidal current, reserving
the namnenTde for vertical movernent.

Refers to piles and rods set in the backfil area to provide lateral support to a vertical
protective structure.

Steel rod used to tie back the top of a bulkhead or a seawall.

The channelward base of a structure.
Specifications


Storm Surge



Tide





Tie Backs


Tie Rods

Toe
The configuration of a surface, including relief, position of streams, roads, buildings,
etc.

Juncture of land and sea. This line migrates with the changing of the tides or other
fluctuations in water level. Where waves are present on the beach, this line is also
known as the limit of backrush (approximnately the intersection of land and the
stfliwater level).

A ridge, deformation, or undulation of the surface of a liquid.
Topography


Water line




Wave
Direction from which a wave approaches.

Direction from which the wind blows.
Wave Direction

Windward
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REFERENCES
Rogers, Golden and Halpern, Inc., 1981, Low Cost Shore Protection, Philadelphia, Pa, contract DACW 61-81-
D0012 by United States Army Corps of Engineers, 36 p.
United States Army Corps of Engineers, 1981, Shore Protection Manuag Vols.1-2 (Vicksburg, Mississippi: United
States Army Corps of Engineers Coastal Engineering Research Center).
United Sates Army Corps of Engineers, 1973, Shore Protection Guidelines, in National Shoreline Study, Vol. 1,
Washington D.C., United States Government Printing Office.
United States ArmyCorps of Engineers, Low CostShore Protection.. .A Guide forLocal Government Officials, 108 p.
United States Department of Agriculture, SoilConservation Service, Vegetation for TidalShorelineStabilization in
the Mid-Atlantic States, 18 p.





























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