Streambank and shoreline stabilization : techniques to control erosion and protect property

STREAMBANK AND SHORELINE STABILIZATION
- Techniques to Control Erosion and Protect Property -
Coconut logs, live stakes, toe of slope protection and riparian restoration Photograph courtesy of Register-Nelson Environmental Consultants.

Table of Contents

Introduction

2

Causes of Erosion

3

Planning

3

Preferred Practices

4

- Live Staking

5

- Live Fascines

5

- Branchpacking

7

- Vegetated Geogrid

8

- Brushmattress

9

- Coconut Fiber Roll

10

- Dormant Post Plantings

11

Acceptable Practices

11

- Joint Planting

11

- Live Cribwall

12

- Vegetated Gabion Baskets

13

- Tree Revements

14

- Log, Rootwad and Boulder Revetments

15

Discouraged Practices

16

- Rock Riprap

16

- Rock Gabions

17

- Bulkheads and Seawalls

17

Summary

18

Additional Resources

19

Appendix A Woody Plants

20

Appendix B Cuttings for Live Stakes

22

Appendix C Grasses and Forbs

22

1

Introduction
Appropriate selection and application of streambank or shoreline protection measures should vary in response to specific objectives and site conditions.
S treambank and shoreline stabilization consists of vegetative, structural and bioengineering methods to stabilize AND protect streambanks and shorelines. This document presents diagrams of the methods and practices listed in the Georgia DNR Environmental Protection Division's (EPD) July 2007 "Streambank and Shoreline Stabilization Guidance" document and provides information about preferred riparian vegetation for stabilization projects. Stabilizing streambanks with natural vegetation has many advantages over hard armoring such as riprap, seawalls and gabions. Streams with well-established vegetation on their banks provide for better water quality and fish and wildlife habitats. Vegetation is extremely important for the biological, chemical and physical health of the stream as well as the stability of the system. Vegetation is not a panacea for controlling erosion and must be considered in light of site-specific characteristics. When vegetation is combined with low-cost building materials or engineered structures, numerous techniques can be created for streambank erosion control. This document summarizes a number of methods that utilize vegetation and bioengineering.
Illustrated Streambank Restoration
NOTE: This handbook does not attempt to assume that bioengineering for streambank protection is a cure unto itself. First, streambed stability, another whole subject area, must be achieved before banks are addressed. Therefore, careful study should be made to determine the causes of erosion before bioengineering is considered. If streambeds are not stable, it does little good to attempt streambank stabilization. This document does not attempt to address the details of fluvial geomorphology involved in streambed stabilization.
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Causes of Erosion
Streambank and shoreline erosion is a natural process. Human activities often contribute to or accelerate the natural streambank or shoreline erosion process, exacerbating the negative effects. However, with thought and planning, such activities can be modified to avoid or reduce those effects. Human activities contributing to or accelerating the natural streambank or shoreline erosion process include:
Clearing Natural Vegetation
Often done by landowners to expand views or increase recreational areas, it destroys the roots of plants that provide significant streambank and shoreline stabilization.
Construction or Development (Urbanization)
Construction and development uphill of a streambank or shoreline can result in increased stormwater runoff, resulting in increased pollutant and sediment loads to the waterbody. Urbanization can lead to extensive loss of natural vegetation along the streambanks and shorelines, which increases the rate of erosion.
Impervious Surfaces and Structures (Stormwater Runoff)
Pavement, buildings, roofs, drainage ditches, etc. increase the amount, velocity and energy of stormwater, resulting in more runoff being routed to streams and lakes (and less into the ground), and increasing erosion.
Agricultural Practices
These can modify the rate of erosion and increase levels of nutrients in streams and lakes. Agricultural practices, such as plowing, drainage ditches, irrigation and grazing, can increase the rate of erosion.
Streambank or Shoreline Stabilization Projects
Erecting seawalls and other such projects reduce habitat and commonly affect other properties due to the redirection of waves and energy away from the area in which the seawall was installed.
Planning a Streambank or Shoreline Stabilization Project
Stream channel and shoreline erosion problems vary widely in type and scale, and there is no one measure that works in all cases. Stabilization structures and vegetative measures should be planned and designed by a design professional with experience in this field. Many of the practices involve the use of manufactured products and should be installed in accordance with the manufacturer's specifications. In ordered to determine what type of streambank or shoreline project needs to be implemented, you should first determine the severity of your erosion problem. Severe erosion covers a large area of bank (linear extent greater than three times average bank height) and is occurring at a rate in excess of one foot per year or a rate that is unacceptable for safety, environmental or economic reasons.
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If your streambank or shoreline is severely eroded, you will need to stabilize the soil to promote plant growth. There are three general approaches to bank stabilization:
Live Planting Bioengineering Hard Armoring
The best method for stabilizing and protecting your streambank or shoreline depends upon your specific situation. Factors to consider include the size and location of your stream or shoreline as well as the cause and severity of the erosion. In many cases, the best approach is to use a combination of methods. Before attempting any streambank or shoreline stabilization activities, you should obtain all applicable permits or approvals.
Preferred Practices
Preserving the Natural Streambank or Shoreline Stabilization of your streambank or shoreline can be as simple as not mowing the grass or not cutting the trees and shrubs along the edge of the banks. This allows natural vegetation to grow or become re-established. A naturally vegetated shoreline has many benefits. It prevents contaminants or excess nutrients from entering the water; it prevents erosion caused by rain, wind, wave and ice action; and it provides food, shade and cover for fish and wildlife. If some vegetation must be removed, limit the amount. Try to prune trees and shrubs back instead of removing them altogether.
Soil Bioengineering Systems Projects incorporating bioengineering practices using native riparian vegetation are preferred for streambank and shoreline stabilization. However, certain structural components of stabilization are highly effective and occasionally necessary. Natural approaches seek to restore hydrological and ecological balance by using methods that are structurally sound, economically feasible and ecologically sustainable. While there are many ways to protect an existing streambank/shoreline or restore an eroded one, choosing appropriate materials and design is important. Some methods may include planting native, deep-rooting vegetation, as well as bioengineering. Consult with a plant materials specialist for guidance on plant selection. Species that root easily, such as willows, are required for measures such as live staking and live fascines. Lists of Georgia's native vegetation for soil bioengineering and related systems are provided in the appendices.
Planting Densities EPD recommends that trees be planted at a density of 10 feet on center (ft o.c.) or 436 trees per acre. If planted alone, shrubs should be planted at an average density of 6 ft o.c. (1210 shrubs per acre) and groundcovers (4" containers) at an average density of 1.5 ft o.c. (19,360 containers per acre). When combined with planting trees, shrubs and/or groundcover may be planted at a density of 774 shrubs per acre and 18,150 containers per acre. Live stakes are typically planted at 2 ft o.c. Please reference http://www.soundnativeplants.com/calculator.htm for further planting density information.
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Soil Bioengineering Systems Some of the most common and useful soil bioengineering systems for restoration and protection of streambanks and shorelines are described in the following sections.
Live Staking
Live stakes are living, woody plant cuttings capable of rooted when inserted into the banks. These stakes, commonly willow species, can root and grow into shrubs that overtime will stabilize the streambank or shoreline and provide riparian habitat.
Figure 1. Live stake details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

Live Fascines (Fascine Rolls/Wattles)
Live facines are bound bundles of live branch cuttings that are buried onto the bank and staked into place along the slope contour. Willow branches are the most commonly used for this method.

Figure 2. Live fascine details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996) 5

Figure 3. Live fascine details

NRCS Engineering Field Handbook
Figure 4. Preparation of a dead stout stake

(210-vi-EFH, December 1996)

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996) 6

Branchpacking
Branchpacking is the process of incorporating alternating layers of live branch cuttings and compacted soils into a hole, gully or slump. This method is used to fill in depressions along the streambank or shoreline.
Figure 5. Branchpacking details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

7

Vegetated Geogrid
Vegetated geogrids are similar to branchpacking except that natural or synthetic geotextile materials are wrapped around each soil lift between the layers of live branch cuttings.
Figure 6. Vegetated geogrid details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

8

Brushmattress
A brushmattress system consists of live branch cuttings, live stakes, and live fascines installed to cover and stabilize the entire streambank/shoreline and secured in place. This method is installed above the normal stream flow and provides immediate protective coverage of the bank.
Figure 7. Brushmattress details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

9

Coconut Fiber Roll
A coconut fiber roll is a flexible "log" made from coconut hull fibers, staked at the toe of the bank. The technique is often used in conjunction with native plants to trap sediment and encourage plant growth.
Figure 8. Coconut fiber rolls detail

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(210-vi-EFH, December 1996) 10

Dormant Post Plantings (Live Posts)
Dormant post plantings form a permeable revetment that is constructed from rootable vegetative material placed along streambanks in a square or triangular pattern.
Figure 9. Dormant post details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

Acceptable Practices
Integrated Bioengineering Practices Acceptable stabilization methods are integrated bioengineering with one or more structural component useful in areas with higher velocity flows and/or wave action. This is most often appropriate at the "toe" of the bank or shoreline to prevent additional bank slumping. Structural components should be minimal and only used when necessary to ensure long-term success of the stabilization efforts.
Joint Planting
Joint planting or vegetated riprap involves tamping live stakes into joints or open spaces in rocks that have been placed on a slope. Vegetation, especially deep rooting species, planted above and immediately behind the rock will greatly increase the stability of the slope
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Figure 10. Joint planting details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

Live Cribwall
A live cribwall is a box-like structure with a framework of logs or timbers, rock and live cuttings that can protect eroding streambanks or shorelines. Once live cuttings become established, mature vegetation gradually takes over the structural functions of the logs or timbers.

Figure 11. Live cribwall details

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(210-vi-EFH, December 1996) 12

Vegetated Rock Gabions
Gabion baskets are rectangular containers fabricated from a heavily galvanized steel wire or triple twisted hexagonal mesh. These empty gabions are placed in position, wired to adjoining gabions, filled with stones, and then wired shut. Vegetation is incorporated into rock gabions by placing live branches on each consecutive layer between the rock filled baskets.
Figure 12. Vegetated gabion details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

13

Tree Revetments
Tree revetments are rows of cut trees anchored to the toe of the bank. This is a low cost method, often used for toe protection with other bioengineering techniques.
Figure 13. Tree revetment details

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(210-vi-EFH, December 1996) 14

Log, Rootwad, and Boulder Revetments
These revetments are systems composed of logs, rootwads, and boulders selectively placed in and on streambanks.
Figure 14. Log, rootwad, and boulder revetment details

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

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Discouraged Practices
Discouraged practices are structural practices with limited or minimally functional vegetation, or no re-vegetation. These are traditional and conventional methods of hard-armoring streambanks and shorelines to address erosion problems. These methods often degrade the quality of aquatic habitat and contribute to erosion in other areas, either downstream or along other shorelines. Since newer practices are available and more contractors are familiar with better stabilization practices, the use of hard armoring is discouraged, however, there are severely eroded locations where hard-armoring is necessary.
Rock Riprap
Riprap stabilization designs should include appropriate bank slope and rock size to protect the bank from wave and current action and to prolong the life of the embankment. A final slope ratio of at least 1:2 (vertical to horizontal) is recommended, and a more stable 1:3 slope should be used where possible.
A layer of gravel, small stone, or filter cloth placed under and/or behind the rock helps prevent failure. In many cases, only the toe of the slope may need rock reinforcement; the remainder can be planted with native vegetation.
Figure 15. Rock riprap details

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Rock Gabions
Rock gabions with vegetation are a more acceptable stabilization practice. See details for gabion baskets on page 13.
Bulkheads and Seawalls
Bulkheads and seawalls are not encouraged and generally are not approved. These structures (typically sheet steel, concrete or wood) produce a sterile, vertical, flat-faced object that is of little use to aquatic organisms and other wildlife. They also tend to reflect wave energy rather than dissipate it, usually resulting in erosion problems in front of the "fix" and elsewhere.
However, when erosive forces are severe, existing building foundations or structures are threatened, and other stabilization approaches would not be effective, a new or replacement retaining wall may be warranted. In these cases, rock should be placed at the toe to reduce the adverse impacts of reflected wave energy.
Figure 16. Timber bulkhead detail

NRCS Engineering Field Handbook

(210-vi-EFH, December 1996)

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Summary
Streambank and shoreline work should be proposed only when a problem exists and needs fixing (i.e., to stabilize identified erosion areas) - not to decorate, landscape or reclaim land. When work is necessary, natural approaches should be considered first. Permits and buffer variances may be required from the following agencies:
U.S. Army Corps of Engineers Savannah District
100 W. Oglethorpe Avenue Savannah, GA 31401 (912) 652-5279/5770
U.S. Fish and Wildlife Service Southeast Region
1875 Century Blvd, Suite 400 Atlanta, GA 30345 (404) 679-4000
Georgia DNR - Environmental Protection Division Watershed Protection Branch
4220 International Parkway, Suite 101 Atlanta, GA 30354 (404) 675-6240
Georgia DNR - Coastal Resources Division One Conservation Way Brunswick, GA 31520 (912) 264-7218
Georgia DNR Historic Preservation Division 254 Washington Street SW Atlanta, GA 30334 (404) 656-2840
Local Governments (Cities, Counties)
Other Entities (Utilities, Authorities)
Please contact appropriate agencies BEFORE beginning any stabilization activities.
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Additional Resources
Plants
Calculating Plant Quantities for Restoration Projects http://www.soundnativeplants.com/calculator.htm Sources for Native Plants and Seed http://gnps.org/resources/Native_Nurseries.php
Streambank and Shoreline Stabilization
Guidelines for Streambank and Shoreline Restoration http://www.files.georgia.gov/SWCC/Files/Guidelines_Streambank_Restoration.pdf Natural Resources Conservation Service Handbooks Part 650 Engineering Field Handbook, Chapter 16 Streambank and Shoreline Protection http://directives.sc.egov.usda.gov/ The Shoreline Stabilization Handbook http://nsgd.gso.uri.edu/lcsg/lcsgh04001.pdf Streambank and Shoreline Stabilization Guidance http://www.gaepd.org/Files_PDF/techguide/wpb/Streambank_and_Shoreline_Stabilization _Guidance.pdf
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Appendix A Woody Plants for Soil Bioengineering and Associated Systems in Georgia

Scientific Name Acer negundo Acer rubrum Alnus serrulata Amorpha fruitcosa Aronia arbutifolia Asimina triloba Betula nigra Carpinis caroliniana
Carya cordiformis Catalpa bignonioides Celtis laevigata Celtis occidentalis Cephalanthus occidentalis Chionanthus virginicus Clethera ainifolia
Cornus amomum Cornus florida
Cyrilla racemiflora Diospyros virginiana Fraxinus caroliniana Fraxinus pennsylvanica Gleditsia triacanthos Hibiscus aculeatus Ilex coriacea Ilex decidua Ilex glabra Ilex opaca Ilex verticillata Ilex vomitoria Juglans nigra Juniperus virginiana Leucothoe axillaries Lindera benzoin Liquidambar styraciflua Liriodendron tulipifera Lyonia lucida

Common Name boxelder red maple smooth alder false indigo red chokeberry pawpaw river birch american hornbeam bitternut hickory southern catalpa sugarberry hackberry buttonbush
fringe tree
sweet pepperbush silky dogwood flowering dogwood titi persimmon carolina ash green ash
honeylocust hibiscus sweet gallberry possomhaw bitter gallberry american holly winterberry yaupon black walnut eastern redcedar leucothoe spicebush sweetgum
tulip poplar
fetterbush

Plant Type small to medium tree medium tree large shrub shrub shrub small tree medium to large tree small tree
tree tree medium tree medium tree large shrub
small tree
shrub
small shrub small tree
small tree medium tree large tree medium tree
medium tree shrub small to large shrub large shrub to small tree small shrub small tree small to large shrub large shrub medium tree large tree small to large shrub shrub large tree
large tree
small to large shrub

Region *
M, P, C M, P, C M, P, C M, P, C M, P, C M, P, C M, P, C
P, C P, C P, C P, C M, P, C
P, C
P, C
M, P M, P, C
C M, P, C C M, P, C
P, C C C P, C C M, P, C M, P C M, P M, P, C C M M, P, C
M, P
C

Establishment Speed
fast fast medium fast fast fast slow
fair slow slow medium
medium fair
fair fast fast fast
medium
fair medium
fast

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Scientific Name Common Name

Plant Type

Region *

Magnolia virginiana sweetbay

Myrica cerifera

southern

waxmyrtle

Nyssa aquatica

swamp tupelo

Nyssa ogeeche

ogeeche lime

Nyssa sylcatica

blackgum

Ostrya virginiana hophornbean

Persea borbonia

redbay

Platanus occidentalis sycamore

Populus deltoides eastern

cottonwood

Quercus alba

white oak

Quercus laurifolia swamp laurel oak

Quercus lyrata

overcup oak

Quercus michauxii swamp chestnut

oak

Quercus nigra

water oak

Quercus palustris pin oak

Quercus phellos

willow oak

Quercus shumardii shumard oak

Rhododendron

coast azalea

atlanticum

Rhododendron

swamp azalea

viscosum

Salix nigra

black willow

Taxodium distichum baldcypress

Tsuga canadensis eastern hemlock

Viburnum nudum swamp haw

*M=Mountain, P=Piedmont, C=Coastal

small tree small shrub
large tree large shrub to small tree tall tree small tree small to large tree large tree tall tree
large tree tree medium tree medium tree
medium tree large tree medium to large tree large tree small shrub
shrub
small to large tree medium tree large tree large shrub

P, C C
C C M, P, C M, P, C C M, P, C M, P, C
M, P, C C P, C M, P, C
M, P, C M M, P, C P, C P, C
P, C
M, P, C C M M, P, C

Establishment Speed
slow
slow medium slow slow slow fast fast
slow fast slow fair
slow fast medium slow
fast fast slow

NOTE: EPD recommends that trees be planted at a density of 10 feet on center (ft o.c.) or 436 trees per acre. If planted alone, shrubs should be planted at an average density of 6 ft o.c. (1210 shrubs per acre) and groundcovers (4" containers) at an average density of 1.5 ft o.c. (19,360 containers per acre). When combined with planting trees, shrubs and/or groundcover may be planted at a density of 774 shrubs per acre and 18,150 containers per acre. Live stakes are typically planted at 2 ft o.c. Please reference http://www.soundnativeplants.com/calculator.htm for further planting density information.
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Appendix B Plants Suitable for Rooting as Cuttings (Live Stakes) in Georgia

Scientific Name Common

Name

Acer negundo

boxelder

Asimina triloba

pawpaw

Baccharis halimifolia groundsel bush

Cephalanthus

buttonbush

occidentalis

Cornus amomum silky dogwood

Cornus sericia

red osier

dogwood

Gleditsia triacanthos honeylocust

Populus deltoides eastern

cottonwood

Robinia sp.

black locust

Salix discolor

pussy willow

Salix nigra

black willow

Salix purpurea

purpleosier

willow

Sambucus

american elder

canadensis

Viburnum dentatum arrowwood

Viburnum lentago nannyberry

*Rooting ability from cutting

Plant Type
small tree medium shrub large shrub small shrub
medium tree tall tree
large shrub small to large tree medium tree
medium shrub medium to tall shrub large shrub

Rooting Ability*
poor to fair good fair to good
fair
poor to fair very good
very good good to excel excel
good
good fair to good

Region
M, P, C M, P, C P, C M, P, C
M, P M, P
P, C M, P, C
P, M
M, P, C M, P, C
M, P
M, P, C M, P, C

Appendix C Grasses and Forbs Useful in Conjunction with Soil Bioengineering and Associated Systems in the Southeast

Scientific Name
Ammophila breviligulata Andropogon gerardii Arundo donax Herarthria altissima Panicum amarulum
Panicum virgatum Paspalum vaginatum Pennisetum purpureum Spartina pectinata Zizaniopsis miliacea

Common Name
american beachgrass big bluestem giant reed limpograss coastal panicgrass switchgrass seashore paspalum elephant grass
prarie cordgrass giant cutgrass

Soil Preference Drought

Tolerance

sands

fair

loams sandy sandy sands to loams

good good poor good

loams to sands good sandy

sands to loams good

loam

poor

Shade Tolerance poor
poor poor poor poor
poor poor
poor
fair poor

Flood Tolerance
fair poor good good
good good
fair good

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Georgia Environmental Protection Division Watershed Protection Branch 4220 International Parkway, Suite 101 Atlanta, GA 30354 (404) 675-6240 www.gaepd.org
Georgia Soil and Water Conservation Commission State Headquarters 4310 Lexington Road P. O. Box 8024 Athens, GA 30603 (706) 552-4470 www.gaswcc.georgia.gov
The publication of this document was supported by the Department of Natural Resources, Environmental Protection Division and was financed in part through a grant from the U.S. Environmental Protection Agency under the provisions of the Section 319(h) of the Federal Clean Water Act of 1987, as amended. April 2011.
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