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Coastal Erosion Near the Mouth of the Rappahannock River

Lillian Pitts and Monica Agudelo

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"The several thousand kilometers of coast on the Chesapeake Bay are both an asset and a curse, providing an extraordinarily rich and varied coastal area that is subject to extensive erosion"

-Richard A. Davis, Jr.

The Chesapeake Bay region and estuarine system, is continually eroded by wave action, tidal currents, and especially waves generated by high winds from hurricanes and large storms. These same processes of erosion affect the mouths of Bay’s tributary rivers in the same manner (Figure 1). Where the southern

erosionFigure 1: Areas of Significant Shoreline Erosion (Click to Enlarge)

shore of the Rappahannock River meets the Chesapeake Bay (in Middlesex County, VA), the coastline is facing severe erosion (Figure 1.A). These high erosion rates have become a threat to property owners along the coast. The Commonwealth of Virginia offers assistance to help it’s residents cope with this problem through organizations such as the Shoreline Erosion Advisory Service (SEAS), and through the local county planning offices of regions along the coast. At the southern shore of the mouth of the Rappahannock River, structures such as bulkheads, groins, and rip rap revetments have been erected to help retain the present position of the coast and stabilize existing property. Many of these structures have fortified these areas, but at the same time have upset the natural equilibrium of this delicate coastal environment by impeding the natural erosion process. It is important to understand that this coastal region along the Rappahannock is a dynamic system and erosion is only a problem when it encounters human activities or structures.

Erosion diagram

Figure1.A: Shoreline Erosion Along the Mouth of Rappahannock River (USDC 1986).

Prior to a major investment in a coastal region, it is important to evaluate the site. If the construction of a home or other building is close to a shore, than an evaluation is necessary. Many publications are available to the public through various federal, state, and local agencies. The US Army Corps of Engineers, Coastal Resources Division, or the Virginia Marine Resources Commission are just a few organizations employed to evaluate shorelines in the Chesapeake Bay area (Ward 1989). Shoreline Situation Reports document the erosion rates affecting local property owners. This information can be easily attained from the Virginia Sediment and Erosion Division of Soil and Water Conservation.

The Commonwealth of Virginia has a general approach toward shoreline erosion mitigation. First, they assess that the shore erosion requires federal assistance. If the property is involved, then funds can be allocated to protect the beaches through the Public Beach Conservation Act. However, if the land is privately owned, then the owner can receive planning and technical assistance from the Commonwealth through the Shore Erosion Control Act. This organization, however, provides no funds for the construction cost (USDC 1986).

The Shoreline Erosion Advisory Service (SEAS), established under the Shore Erosion Control Act, assesses the effects of shoreline erosion. SEAS can also provide a potential property owner with historical and recent erosion rates of the property. They also suggest types of erosion structures needed, prospective costs, and even give advice on where along the shoreline would be the best area for construction (USDC 1986). Potential property owners can also contact their local county planning office to get any pertinent information regarding the land.

Typically, in regards to erosion, the most desirable locations for homes and other human development are also the most vulnerable sites (U.S.A.C.E. 1971). The Commonwealth of Virginia issued a list of beach land use priorities. The number one priority of the Commonwealth is shoreline preservation. Preservation is followed by conservation, the systematic protection of natural resources. The third priority is the recreational use of beaches, and the fourth and final priority is development (USDC 1986). As the amount of people living along the coastline increases, the erosion hazard of that area also increases. Erosion is a natural process and is only classified problematic when human development interferes (Pilkey 1990).

There is not one single erosion control method that will perform well in every shoreline environment, so therefore each area must be assessed individually. The shores of the Rappahannock River ranges from a variety of different types of shorelines. The specific shores of the Rappahannock are classified into marshlands, wooded shores, clear beaches, sandy beaches, and developed waterfront property (U.S.A.C.E. 1971). Stingray Point, the most southeastern portion of the Rappahannock River shoreline, is classified as a beach with developed waterfront property.

The southern coast, at the mouth of the Rappahannock River in Middlesex, Va., has historically experienced erosion. This area along the Rappahannock is, for the most part, categorized as beach land. This area is also extensively developed; many people’s backyards extend to the shore. The combination of exposure to an open body of water, and widespread development promotes a problem to those property owners. Though erosion is a natural process, it poses as a threat to the many homes and buildings that populate the Chesapeake’s coasts. Areas along the Rappahannock like Grey’s Point, Regent Point, and Stingray Point (Deltaville) are heavily populated, are exposed to the tidal effects of the Chesapeake, and are experiencing elevated rates of erosion.

Wave action is the primary source of erosion in the Chesapeake Bay. The southern sides of the tributary estuaries, like the Rappahannock, have the highest relative erosion rates. This can be attributed to shoreline exposure to the north, northeast, and northwest directions from which the most severe seasonal winds blow (U.S.A.C.E. 1990). Waves or wave-induced currents are also primary movers of near shore sediment, or littoral drift. During periods of increased water levels or wave heights, the sand above low water level on a typical beach is eroded and carried offshore. Stingray Point is exposed to the open bay from three directions and as a result is categorized as an area of severe erosion (>3ft/yr) (Ward 1989).

The tidal currents and rising sea levels greatly affects the erosion rates in the Chesapeake Bay. Higher sea levels equate to more land that is submerged under water. The higher sea levels drown existing beaches and cause the shores to retreat. To prevent shoreline retreat, people can either nourish the beach with more sediments, or build structures to prevent or reduce the effect of erosion.

Along its lower reaches, where the Rappahannock River meets the Chesapeake Bay, a variety of shoreline protection structures have been erected to reduce erosion. The area of study consists of the shoreline of Middlesex County on the southern shore at the mouth of the river. These structures include bulkheads, groins, and rip rap revetments. Each of these erosion control measures serve unique functions and interacts with its surrounding environment in a different manner.

Property owners in the study area have built bulkheads to stabilize the foundations of their land where it meets the shoreline. The primary purpose of a bulkhead is to retain and prevent the sliding downslope of upland soil while providing minimal protection from low energy waves (CBS 1990). Bulkheads (Figure 2) are vertical structures that protect only the

Bulkhead

Figure 2: Bulkhead (Virginia Marine… 94).

land directly behind them that they support and offer no protection to the adjacent areas, and actually promote the erosion of nearby shorefront. Bulkheads do little to dampen the wave energy and effectively transfer the energy laterally along the face of the structure itself (BMP's). This transfer of energy in turn contributes to the degradation of adjacent property. In some cases, erosion may actually be accelerated due to wave reflection off these structures (CBS 1990). An example of a bulkhead in our study area is found near Stingray Point where an owner has built a bulkhead to retain a grassy lawn just one meter above an already eroding sandy shoreline. In this instance, the natural shoreline equilibrium has been upset, and erosion of the adjacent area is being promoted.

Other structures that we found utilized along this reach were groins and groin fields. A groin is a structure that juts into the water perpendicular from the shore, with the intent of trapping sand as it travels down the coast (Figure 3, BMP's). Many of the structures look as if they have withstood many years of weathering and are just barely functioning. A properly

Groin structures

Figure 3: Groin Structures (Virginia Marine… 1994).

designed groin should be constructed with such materials as treated timber, steel sheet-pile, quarrystone, or sandbags (CBS 1990). Many of the groins built along the Rappahannock appear to be constructed of timber, but have failed as they were unable to effectively resist the wave action, currents, etc. with time. A groin must be durable and be suited to the environment where it is built. Generally, materials moving along the shore accumulate on the updrift side of the structure. Once the sediments fill the groin cell, future sediments will continue past that region without being deposited (BMP's), but groins are only effective when sufficient amounts of sand are being transported in the littoral transport system. When sediments are of a smaller size than fine sand (i.e. silt/clay), they remain suspended in the water and are not deposited (CBS 1990). The spacing between these groins is an important factor in that they must be far enough apart to trap sediments. The proper interval can be determined by examining existing structures and their success/failure rates, as well as by calculating the distance using a simple correlation ration between the groin length and shore width (BMP's). Groins are found on property all along the river's edge in this region.

The most numerous feature that we see in the study area are rip rap revetments (Figure 4). These revetments are generally preferred over bulkheads because of their ability to absorb and divert wave energy, and thus reducing the erosion to adjacent property

Rip Rap Revetments

Figure 4: Rip Rap Revetments (Virginia Marine… 1994).

(BMP's). Also the sloped nature of revetments provide a greater surface area to counter the forces, as opposed to vertical structures like bulkheads (BMP's). In order to be effective, revetments must be built on a stable foundation. A rip rap revetment consists basically of a filter cloth base, with multiple layers of various-sized stone-like materials on a slope along the waterfront (CBS 1990). Nearly every erosion control structure found in this region is reinforced by a rip rap revetment to some degree. Although sometimes unsightly to many naturalists, rip rap revetments are arguably the most environmentally sound structures of the previously stated.

Erosion control structures can be found along nearly every stretch of land along this reach of the lower Rappahannock River. In attempt to preserve their property, owners have erected these structures in hopes that they will reduce the erosion that is taking place along the shore. Although there is a broad range of success of various structure types in different localities, nearly every piece of waterfront property has been fortified in some way by some form of structural shoreline protection.

Bibliography (Back to Top)

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