SECTION 4: Management Measures

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4.4. SHORELINE AND STREAMBANK STABILIZATION

Management Measure for Shoreline and Streambank Stabilization:

Where shoreline or streambank erosion is a nonpoint source pollution problem, shorelines and streambanks should be stabilized. Vegetative methods

are strongly preferred unless strectural methods are more cost-effective,

considering the severity of wave and wind erosion, offshore bathymetry, and

the potential adverse impact on other shorelines, streambanks, and offshore

areas.

Protect shorelines and streambanks from erosion due to uses of either the

shorelands ar adjacent surface waters.

Management Measure Description

Streambank erosion is used in this guidance to

refer to erosion along nontidal streams and rivers.

Shoreline erosion is used here to refer to erosion

in tidal portions of coastal bays and estuaries.

Erosion is a natural process that results from

water acting on streambanks and shorelines.

Erosion along a river or stream removes material

from one area and deposits it elsewhere, and

beaches are constantly and naturally eroded and

resupplied with sediment from other areas.

Streambank and shoreline stabilization may be

needed where natural erosion is occurring to

protect shoreline structures.

Induced erosion often occurs where soil,

streambanks, or shorelines have been disturbed.

Removing vegetation from any streambank or

shoreline exposes soil to the erosive energy of

waves and currents. Altering a watercourse (for

instance, by installing a breakwater or a dam) or

artificially affecting the course of water (perhaps

by channelizing a river) can cause erosion because

the manner in which energy is transmitted through

a waterbody can be affected. In the latter case,

erosion sometimes occurs far from the location of

the channelization. Properly designed erosion

control measures and structures can reduce natural

as well as induced erosion.

In a marina, structural elements are often necessary to protect boats and the marina perimeter

from waves or water current energy. Hence, the

marina basin is often a fairly calm, nonerosive

environment. Erosion can still occur along the

perimeter, however, and wave energy reflected

off a structure, such as an improperly designed

breakwater, or from boat wakes may be a

contributing factor. Bank erosion may result

where it is desirable to hold a given slope. Scour

along the bottom of a structure such as a breakwater or at the abrupt junction of two unlike

materials, such as river bottom sediments and a

cement boat ramp, can also be a problem. Bank

erosion and scour can result in sediment filling

in a marina basin (and the need for maintenance

dredging) or erosion at the edges of a boat ramp.

Minimizing shoreline erosion can protect marina

shorelines and can reduce the need for or frequency of maintenance dredging. Less frequent

dredging also reduces the need for proper and

potentially costly disposal of dredged material.

A vegetated shoreline can minimize the transmission of wave energy to other locations. Vegetation

is also a relatively low-cost means to stabilize a

shoreline, and it can add a natural, attractive

element to an otherwise engineered environment.

Used by itself, vegetation is most effective where

waves or currents are low in energy and the soil
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National Management Measures Guidance

is stable enough for plant growth. Another site

factor conducive to vegetative stabilization is

shallow sloped banks. Where wave or current

energy is too strong for vegetation to gain a

foothold, temporary structures can be used to

protect vegetation until it can establish itself, or

permanent structures might be necessary.

Permanent streambank or shoreline protection

structures could be needed where wave or

current energy is too great for establishing and

maintaining vegetation. Some structural methods

to stabilize shorelines and navigation channels are

gabions, riprap, sloping revetments, bulkheads,

jetties, and breakwaters. The first three dissipate

incoming wave energy more effectively than the

rest and usually result in less scouring than the

last three. Bulkheads are appropriate in some

circumstances where other preferred alternatives

are not feasible. Vegetation can often be added at

the edges of these structural elements to control

erosion from storm water runoff and to serve as a

landscaping element.

The type of perimeter stabilization might be

dictated in both inland and coastal marinas by

local variations in water level due to dam

drawdown in a reservoir, natural fluctuation in a

lake, or tides along the coast. In some of these

instances, shoreline stabilization might not be

practical. Because rivers are hydrographically

complex and many factors need to be taken into

account when determining how to correct erosive

problems, shoreline stabilization might not be

sufficient to eliminate an erosion problem.

Streambank and river restoration projects, of

which erosion is usually only a small part, can

encompass anywhere from a small section of a

river or stream to the entire watershed.

Some specialized locations along the banks of

rivers, reservoirs, and lakes, however, may be

ideal candidates for shoreline stabilization. Such

locations may be severely eroded soils around a

storm sewer discharge point, disturbed soils

where a boat ramp has been installed or is in need

of maintenance, or overused shoreline areas in or

next to established recreational areas.

Examples of vegetative and structural methods

are presented below. Before selecting any of

them for a particular erosion problem, it is important to identify the cause of the erosion, which,

especially in rivers and coastal environments,

could be extremely complex. Selecting the

appropriate technique to remedy an erosion

problem might require analysis by a professional.

Applicability

This management measure is applicable to new

and expanding marinas where site changes might

result in shoreline erosion.

Best Management Practices

♦ Use vegetative plantings, wetlands,

beaches, and natural shorelines where

space allows.

Vegetative plantings, wetland enhancements,

beaches, and preservation of natural shorelines,

where feasible, can be the most effective means

of shoreline stabilization. Plantings can be in the

form of a grassed buffer strip that serves the

triple purpose of shoreline stabilization, establishing a visually aesthetic area, and controlling

polluted runoff. If natural wetlands are found or

were present within the boundaries of a marina

before its development, their preservation or

re-creation can protect shorelines, dissipate low

wave energy, provide wildlife habitat, and filter

pollutants out of the water and storm water

Herrington Harbour Marina South

(Maryland) retained and enhanced much of

the natural shoreline during a recent

rebuilding, modernization, and expansion

program. An old, failing bulkhead was

removed, and rock riprap and filter cloth

were placed on the regraded shoreline.

Native shore species were planted along

the shore, and nearby wetlands were

cleaned and restored to native marsh

grasses. Over a few years, the shoreline

vegetation filled in and created a very

attractive and effective buffer that helps

control erosion and storm water runoff.

Wildlife diversity also increased in the

surrounding shoreline area, including

several blue herons that have taken up

year-round residence.
SECTION 4: Management Measures

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runoff. A sloping beach is the best surface for

attenuating wave action, though such beaches can

occupy more space than other perimeter stabilization

methods.

Establishing a “no wake zone” in nearshore,

shallow aquatic areas can also be effective to

reduce impacts from boat wave energy.

♦ Where shorelines need structural stabilization and where space and use allow, riprap

revetment is preferable to a solid vertical

bulkhead.

In some cases, primarily because of space

limitations or elevation differences between the

land and water surface, steep slopes are necessary within marinas. Riprap is a common and

economical revetment that can withstand substantial wave energy. Its irregular surface also

reduces wave energy transmission better than a

solid vertical bulkhead does. Natural rock is the

best material. Concrete rubble can be used, but its

many flat surfaces transmit more wave energy

than do irregular natural rocks. Gabions (rock in

heavy-duty wire mesh baskets) can be used

where a slope steeper than that which can be

obtained with riprap is needed. Gabions function

best where waves do not exceed 12 inches. The

irregular surface of riprap revetment can provide

habitat for shore and nearshore plants and

animals.

♦ Where reflected waves will not endanger

shorelines or habitats and where space is

limited, protect shorelines with structural

features such as vertical bulkheads.

Vertical bulkheads reflect waves and are not a

good choice for shoreline stabilization where

waves or surges occur in the marina basin and

are not mitigated in the stabilization design. They

are usually more costly to install than other forms

of shoreline protection but might be necessary

where boats are hauled and launched, where the

marina cannot be moved farther into the water,

and where valuable real estate needs protection.

They can be constructed of concrete, treated

timbers, steel, aluminum, or vinyl. Vertical bulkheads can be combined with riprap by placing the

former at the upper portion of a bank and riprap

along the lower edge. Scour protection at the toe

of the bulkhead should be incorporated into the

structural design.

♦ At boat ramps, retain natural shoreline

features to the extent feasible and protect

disturbed areas from erosion.

Near boat ramps, shorelines can be damaged

during ramp construction. Shorelines are also

susceptible to erosion from runoff that is channeled alongside the ramp (especially if the site has

been sloped for the ramp), boat wakes, waves,

and currents after initial installation. During boat

ramp construction, therefore, retention of natural

shoreline features to the extent possible generally

saves maintenance or corrective costs later.

Natural-appearing shorelines are also aesthetically

appealing, and they can minimize the likelihood of

invasion by unwanted or exotic plant species later.

BMP Summary Table 4 summarizes the BMPs

for Shoreline Stabilization mentioned in this

guidance.
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