DNREC Online

Question: Can vegetation hold the slope?

Thick healthy vegetation contributes greatly to slope stability by holding soil in place with its root system. Even oversteepened banks can be held in place by existing vegetation. Once vegetation is cut or removed from oversteepened banks, revegetation may be very difficult to do without some regrading and/or stabilization with a structural alternative such as rip-rap.

Solutions:

Maintain as much of the naturally occurring vegetation on the banks, where possible.
Remove all dead vegetation and debris which may kill vegetation by smothering it.
Where there is no vegetation or regrading is necessary, select the best vegetation for the site, plant it, protect it and foster its growth until it is well-established.
For sites where vegetation alone has been unsuccessful in stabilizing a slope, install some combination of rip-rap and vegetation
Keep foot traffic to a minimum around eroding slopes and revegetated areas. Stable foot paths or constructed walkways work well to achieve this goal.

Question:Should I use vegetation alone or with rip-rap?

There are many factors which will determine if plantings alone will be successful in stabilizing a bank. In addition, these factors will also determine what combination of vegetation and rip-rap should be applied to any given shoreline.

Solutions:

Before investing your time and money, evaluate the site (or consult with a professional) for the following factors:

Existing vegetation - The presence of native vegetation below the toe of slope is a favorable indication that further plantings will be successful.
Fetch: How many miles of open water does wind blow across before reaching your property? This distance, and the dominant direction from which it blows is important in designing a project. If fetch is greater than 5 miles, it is unlikely vegetation alone will successfully halt erosion. Vegetation alone is most successful where the fetch is less than half a mile.
Shape of shoreline: Orientation of the shoreline helps to determine what the forces of erosion are, and whether vegetation alone (such as in protected coves or lagoons) or some combination of vegetation and rip-rap will work to halt erosion.
Boat traffic: The numbers of boats and how close they travel to a shoreline will help to determine the choice of a solution for a given site.
Width of beach above mean high tide: Beaches which are greater than 10 feet above the mean high tide, or which can be regraded to create 10 feet in width above the mean high tide line have the best chance for successful vegetation growth.

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