Virginia's programs and practices for shoreline erosion control.
Virginia's tidal shorelines include the Chesapeake Bay, southern shore of the Potomac, Rappahannock, York, and James rivers, as well as numerous smaller rivers and creeks. The four major rivers are tidal to the fall line, which occurs at Washington, D.C. for the Potomac River, Fredericksburg for the Rappahannock River, and Richmond for the James River.
In 1978, the Virginia General Assembly created the Coastal Erosion Abatement Commission to study shoreline erosion in Virginia. Recognizing that state tourist revenue results partly from the availability of public beach areas, the commission recommended establishing a state matching fund to help localities improve their public beaches. The commission also determined that erosion of privately-owned shoreline meant a loss of tax benefits. The commission recommended establishing a Shoreline Erosion Advisory Service to provide landowners with sound, environmentally acceptable advice and technical assistance regarding shoreline erosion|1~. In 1980, the General Assembly passed legislation to fund both programs.
Public Beach Program
Virginia promotes recreational opportunities and tourism through the Public Beach Program. A 50/50 matching grant fund for localities is administered by the Board on Conservation and Development of Public Beaches to help localities maintain and improve recreational beach access on tidal waters. The state's portion of the fund is allocated by the eight-member board, consisting of six citizen appointees and the Virginia Marine Resources Commission and Department of Conservation and Recreation. Localities are provided technical and financial help in planning and implementing beach projects. The Shoreline Programs Section of the Department of Conservation and Recreation provides administrative and technical help to the board. Virginia's 24 miles of public beach, as defined by the board, include the nationally known Virginia Beach resort area as well as small beaches in rural areas. Since 1980, over $5,568,000 in state grant monies and $553,000 emergency fund monies have been allocated for public beach projects.
All property owners along tidal shoreline can request and receive help from the Shoreline Erosion Advisory Service, better known as SEAS. SEAS assistance is available for all properties not designated as public beach, including private; federal, state, and local governmental; and commercial properties. SEAS engineers provide on-site inspection and technical analysis of shoreline erosion, followed by written recommendations detailing environmentally acceptable erosion control measures. Other services include contract review and construction inspection for properties previously assessed. SEAS provides technical assistance to marine contractors upon request. In addition, technical information is provided to localities developing and administering coastal zone management programs. SEAS can provide guidance in establishing setbacks, setting minimum construction standards for erosion control structures, and determining shorelines where non-structural measures are adequate for protecting private property. SEAS engineers have examined over 5300 properties since the program's start in 1980.
SEAS recommendations are also designed to be environmentally acceptable to the permitting agencies that regulate waterfront construction. In tidal Virginia, permits may be required from one or more regulatory agencies, depending on the nature of the project. The players include the U.S. Army Corps of Engineers, Virginia Marine Resources Commission, and local citizen wetlands boards. In some instances, permits are also issued by the Virginia Department of Environmental Quality and the Virginia Department of Health. Projects are also reviewed by each locality for compliance with the Chesapeake Bay Preservation Act, a land use law intended to protect the bay's water quality. SEAS advisory help has improved the overall quality of erosion control structures and measures being installed in Virginia. A staff member attends the bi-monthly joint processing meeting conducted by the Army Corps of Engineers in Norfolk and provides technical help to the regulatory agencies.
The types of erosion problem handled by the SEAS engineers include eroding banks, marshes, beaches, and dunes and failing shoreline structures. Recommendations are site specific for the conditions on a given piece of property. Both proper design and construction of shoreline erosion control measures are necessary to achieve a stable shoreline. Home remedies are often ineffective and are not recommended.
For river shores above the fall line, floods and currents are the primary agents of erosion. Below the fall line, shoreline erosion results from day-to-day wave and tidal action as well as storms. Storms such as northeasters and hurricanes often produce the most dramatic losses. The combination of storm-surge caused coastal flooding and larger than normal waves can quickly devastate an area. Other possible causes of erosion include boat wakes, the effect of neighboring erosion control structures, and sea level rise.
The SEAS staff use historical erosion rate data when advising the public and evaluating shoreline protection strategies. The rates help to determine the severity of the erosion problem and a time frame for taking action. Scientists at the Virginia Institute of Marine Science (VIMS) determined and published the erosion rates for the Chesapeake Bay and major tributary rivers in the mid-1970s|2~. The VIMS scientists divided the bay and tributary rivers into "reaches," with each reach representing a segment of shoreline with a given erosion rate. Erosion rate determinations were usually based on 80 to 100 years of data taken from old maps and aerial photography.
Erosion control methods recommended by SEAS engineers include both non-structural and structural measures. Non-structural measures include tree cutting, bank grading, and marsh and dune grass plantings. Structural measures include riprap revetments and other riprap structures, bulkheads, breakwaters, groins, and gabion basket structures. During on-site evaluations with the landowner, feasible options and rough, minimum costs associated with the various practices are discussed. A report is sent to the landowner that provides minimum construction guidelines, information about shoreline vegetation, cross-sectional drawings of shoreline structures, and lists of suppliers of plants and construction materials. A general description of some of the erosion control measures recommended by SEAS is discussed below:
* Tree trimming or cutting is often necessary for unstable, eroding slopes. Trees undermined by erosion displace large amounts of soil when they fall. In addition, tree removal should decrease the weight on the bank and reduce the chance of sloughing. The zone for tree clearing depends on the bank height, slope, and other site conditions.
* Bank grading is also recommended for unstable slopes. If bank grading is needed, slopes of 2:1 (horizontal/vertical) or flatter are usually recommended. Mulching and establishing low growing vegetation is recommended for graded banks.
* The feasibility of using marsh grass for erosion control is determined by the wave energy at the site, salinity, sunlight, and width of the beach area to be planted. Recommendations are made to landowners regarding possible species and planting methods. SEAS staff base their recommendations on experience gained during a vegetative research project funded by the Virginia General Assembly in the 1980s, as well as research conducted by the U.S.D.A. Soil Conservation Service and Army Corps of Engineers. Information about dune grass establishment and maintenance is also site specific and provided by SEAS engineers to the landowner.
* SEAS engineers provide information about the proper design and construction of riprap revetments and other riprap structures. For coastal areas, the structures must be designed to withstand the wave attack of an average storm. SEAS engineers determine the wave height associated with an average storm using the wave hindcasting methods provided in the U.S. Army Corps of Engineers Shoreline Protection Manual|3~ and historical storm wind-speed data. When SEAS staff recommend riprap, the report describes minimum design criteria for the structure, including slope, rock size, and toe depth, all based on the predicted wave height. Landowners are informed of the rock specification system of the Virginia Department of Transportation, which is used to obtain the correct size rock. In addition to providing information about riprap revetments, SEAS staff discuss riprap scour protection structures to protect bulkheads with undermining and scour problems and riprap structures to stabilize eroding marshes, when appropriate.
* Most bulkheads constructed on the Chesapeake Bay and its tributaries are timber, although aluminum, concrete, and steel bulkheads are occasionally used. SEAS engineers discuss proper bulkhead engineering and construction techniques with the landowner. Bulkheads in sheltered areas must be designed to withstand earth pressures, whereas bulkheads in exposed areas must withstand both earth pressures and wave attack. In both cases, proper design of the anchorage system is critical. Bulkhead design should also take anticipated scour into account by ensuring adequate pile penetration depths.
* Near-shore gapped riprap breakwaters are becoming more common in Virginia. The structures are usually designed to dissipate wave action and retain a beach. The beach functions both to protect the base of the bank from wave attack and to provide a recreational area. General information is provided on gapped breakwater design and anticipated results. Presently, gapped breakwater design is based on empirical performance data from existing breakwaters. The effectiveness of a system can never be fully predicted before construction.
* Groins have been installed along some shorelines to trap a recreational beach and reduce wave attack against the bank. To function properly, groins must be built correctly and have a sufficient sand supply to protect the bank. Past groin systems built in Virginia were often either improperly designed or ineffective. Some groins have impacted down-drift properties by preventing sand from migrating down the shore. SEAS does not normally recommend groins, although SEAS engineers will discuss proper design, construction, and placement, as well as possible down-drift impacts, when requested by the property owner.
* Gabions are PVC-coated wire baskets that are filled with rock to form protective structures, such as revetments, breakwaters, and groins. Because of the support provided by the basket, smaller rock and usually less rock can be used in the gabion structure than would be needed for a standard riprap revetment. Gabions are sometimes installed by land-owners who want to do the work themselves. Gabions may require more maintenance than other structural options because the baskets' longevity in saltwater is not well documented.
* Combinations of erosion control measures can also be implemented. Examples include installing a bulkhead and short groins, establishing marsh vegetation on the beach behind breakwaters, and installing groins in conjunction with bank grading and establishing dune grasses.
The Shoreline Programs Section also sponsors, conducts, and cooperates in generic and applied shoreline erosion control research with other state agencies, universities, and the federal government. Through annual contracts with VIMS, information is collected and databased on beach quality sand resources, public beach monitoring, and wave data collection. Research findings and information from these databases are available to local governments, engineering/design consultants, environmental interest groups, and the general public. Some of the Shoreline Program Section's past and present research projects are detailed below:
* From 1980 through 1984, the Virginia General Assembly funded a vegetative research project to study the establishment of estuarine marsh grasses for shoreline erosion control. The Shoreline Programs Section coordinated the project, a cooperative effort with VIMS and the U.S.D.A. Soil Conservation Service. VIMS prepared and published annual reports and a final report for the Shoreline Programs Section|4~. The results indicated that marsh plantings for erosion control appear to be best suited to low energy areas.
* The Chesapeake Bay Shoreline Erosion Study|5~ was a cooperative effort of the Army Corps of Engineers and the states of Maryland and Virginia. Virginia's part of the study involved examining gapped breakwater systems and headlands at seven sites. Project design, installation, and monitoring were conducted by the Shoreline Programs Section, VIMS, and the Army Corps of Engineers. The research provided a greater understanding of design parameters and performance of riprap breakwaters and gabion basket breakwaters.
* Coastal Zone Management grants were obtained from the National Oceanographic and Atmospheric Administration to conduct two studies on the contribution of nutrients and sediments from shoreline erosion to the non-point source pollution of the Chesapeake Bay. Prior to the research, the contribution of nitrogen and phosphorus to the Chesapeake Bay from shoreline erosion had not been studied. Because the 1987 Chesapeake Bay Agreement's participants sought to reduce nitrogen and phosphorus contributions to the mainstem of the Chesapeake Bay by 40 percent by the year 2000, research into the contribution of nutrients from shoreline erosion was needed. VIMS assisted the Shoreline Programs Section with project design, sampling, and laboratory analysis. The research culminated in two reports: Sediment and Nutrient Contributions of Selected Eroding Banks of the Chesapeake Bay Estuarine System|6~ and Eroding Bank Nutrient Verification Study for the Lower Chesapeake Bay|7~. The findings from the study can be used in conjunction with shoreline stabilization data as a management tool to help achieve the 40 percent nutrient reduction goal for the Chesapeake Bay.
* The Shoreline Programs Section is currently participating in two wave measurement projects. The Chesapeake Bay Wave Measurement Program is funded through VIMS and involves two wave gages, one in the lower Chesapeake Bay and the other in the Atlantic Ocean, near the mouth of the bay. The Virginia Beach Wave Gage Program is a cooperative effort with the Army Corps of Engineers, Old Dominion University, and the city of Virginia Beach, which operate a gage in the Atlantic Ocean off Virginia Beach. Government agencies, universities, and consultants use the data obtained by these wave measurement programs to improve our beach management and coastal design capabilities.
* The development of Shoreline Erosion Assessment Software or SEASware, was a joint effort between the Shoreline Programs Section and VIMS. SEASware is a computer-based decision matrix that local regulatory agencies can use to evaluate the cost-effectiveness of bulkheads and riprap revetments in managing wetlands and waterfront development. Funding for the project was obtained from a National Oceanographic and Atmospheric Administration Coastal Zone Management grant.
1. "Report of the Coastal Erosion Abatement Commission to the Governor and the General Assembly of Virginia." Senate Document No. 4. 1979. Commonwealth of Virginia, Division of Purchases and Supply, Richmond, Virginia. 52 pages.
2. Byrne, R.J. and G.L. Anderson. 1977. "Shoreline Erosion in Tidewater Virginia". Special Report in Applied Marine Science and Ocean Engineering No. 111. Virginia Institute of Marine Science, Gloucester Point, Virginia. 102 pages.
3. U.S. Army Corps of Engineers. 1984. Shore Protection Manual. (Two volumes) U.S. Government Printing Office, Washington, D.C.
4. Hardaway, C.S., G.R. Thomas, A.W. Zacherle, and B.K. Fowler. 1984. Vegetative Erosion Control Project: Final Report. Virginia Institute of Marine Science, Gloucester Point, Virginia. 275 pages.
5. Chesapeake Bay Shoreline Erosion Study. 1990. Baltimore District of the U.S. Army Corps of Engineers, Baltimore, Maryland. 111 pages.
6. Ibison, N.A., C.W. Frye, J.E. Frye, C.L. Hill and N.H. Burger. 1990. Sediment and Nutrient Contributions of Selected Eroding Banks of the Chesapeake Bay Estuarine System. Department of Conservation and Recreation, Division of Soil and Water Conservation, Shoreline Programs Bureau, Gloucester Point, Virginia. 71 pages.
7. Ibison, N.A., J.C. Baumer, C.L. Hill, N.H. Burger and J.E. Frye. 1992. Eroding Bank Nutrient Verification Study for the Lower Chesapeake Bay. Department of Conservation and Recreation, Division of Soil and Water Conservation, Shoreline Programs Bureau, Gloucester Point, Virginia. 79 pages.
Ms.Ibison is a Shoreline Engineer with the Department of Conservation and Recreation, Division of Soil and Water Conservation, Shoreline Programs Section, Gloucester Point, Virginia.
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|Author:||Ibison, Nancy A.|
|Date:||Dec 1, 1993|
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