Erosion Control Structures

picture of erosion control structure

beach with rip rap on it

Many state and local governments regulate the type of shoreline stabilization structures allowed as one way to limit shoreline hardening. In some cases, rip rap (top) is permitted whereas bulkheads (bottom) are not.


Case Studies:


Overview:

Many state and local governments regulate the type of shoreline stabilization structure allowed as one way to limit shoreline hardening, yet still allow some types of structural stabilization to protect existing development, or maintain water-dependent uses such as marinas or boatyards, where needed.

There are many ways to regulate erosion control structures. For example, specific types of engineered structures, such as bulkheads, can be prohibited entirely. Bulkheads often have more environmental impacts then other hard structures, such as rip rap. State or local governments could also decide to prohibit hard structures throughout a portion of their shoreline. For example, engineered structures are often prohibited in designated ecologically sensitive areas or important sand source areas, but are allowed along more developed shorelines. Hard structures can also be permitted as a last resort where all other alternative methods would be ineffective. For example, states such as Washington, Rhode Island and Massachusetts require the property owner to first demonstrate an existing structure is imminently threatened by erosion and that non-structural, soft or hybrid approaches would not be effective erosion control methods before a structural stabilization method is permitted.

The size, design and placement of shoreline stabilization structures can also be regulated to minimize environmental and public access impacts. For example, to allow for some sand transport and over-topping during strong storm events, Florida requires that hard structures be designed to withstand a 5-10 year storm, but not a severe (100 year) storm event. Similarly, Massachusetts encourages shoreline structures to be low enough to allow the upper bank or bluff to slump over the structure and feed the beach below.

One of the problems with hardened structures is that many of the negatives associated with the structure, such as beach scouring or increased erosion down drift occur on adjacent properties. The property owner that installs the erosion control structure does not necessarily recognize these costs. To address this problem, Pennsylvania regulates the length and location of groins so that the benefits (sand accumulation in front of the groin) and costs (beach starvation below the groin) are both realized on the owner's property. (See also Pennsylvania case study below.)

Benefits: Helps protect ecologically sensitive habitats. Limiting or regulating erosion control structures allows structural stabilization techniques to be used along high-energy or highly developed shores. However limiting the size, type or placement of structures can also help maintain natural shoreline dynamics where needed.

Drawbacks: Requires good scientific data to identify sensitive shoreline areas or determine that non-structural or hybrid alternatives would not be suitable to manage erosion at the site. May be politically difficult to achieve, especially in areas that are already fairly well-developed.


Case Study:

Pennsylvania Controls Groin Height and Placement

Pennsylvania's Coastal Management Program allows property owners to install small groins -- structures built perpendicular to the shore that trap sand -- to stabilize eroding shorelines that threaten upland development. To ensure that groin impacts on public access and neighboring properties are minimized, the Pennsylvania Coastal Management Program has developed guidance for the placement and design of these structures: Criteria and Methodology for the Proper and Consistent Placement of Shoreline Stabilization Structures along Pennsylvania's Lake Erie Shoreline.

The guidance stipulates that groins cannot extend beyond four feet of water depth. This is known as the "breaker zone" for Lake Erie. Extending beyond this depth would impair littoral sand transport. In addition, groins cannot be closer than two groin lengths from the next groin or less than four groin lengths from an adjoining property. This way any beach loss that occurs down drift from a groin will occur on the owner's property and not the neighbor's. The guidelines also recommend that groins be low-profile groins (no more than 18" above the mean water level at the landward end), to allow for over-topping of littoral material during storm events. Low-profile groins are also easier to step over, so they don't significantly impair lateral public access along the shoreline.

(top)

Rhode Island Prohibits Structural Stabilization Along its South Coast

Rhode Island recognizes that its barrier beaches are dynamic areas.  Natural currents and storm events continuously transport sand from one area to another. Updrift beaches provide important sand sources for those downdrift.  However, shoreline stabilization structures such as groins and seawalls can significantly alter these natural sediment processes.  To protect the sediment source of its beaches and preserve natural sand transport, the Rhode Island Coastal Resources Management Council banned the installation of hard structural stabilization devices along all barriers and Type 1 water (all of the RI ocean facing coastline) (RICRMP Section 300.7). The Council also prohibits using shoreline protection structures for habitat preservation or restoration on beaches (Section 210.1), barriers (Section 210.2), and dunes (Section 210.7).  Recognizing that some hard shoreline stabilization structures existed at the time the Council adopted the regulations, the regulations allow existing shoreline stabilization structures to remain. However, any structure that is more than 50 percent damaged by a storm event or other process must comply with current programmatic requirements. Property owners are prohibited from rebuilding shoreline stabilization structures on barrier islands or Type 1 waters (Section 300.14).