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Mitigating Shore Erosion Along Sheltered Coasts E Glossary Accretion—the deposition of sediment, sometimes indicated by the seaward advance of a shoreline indicator such as the water line, the berm crest, or the vegetation line. Armoring—the placement of fixed engineering structures, typically rock or concrete, on or along the shoreline to reduce coastal erosion. Armoring structures include seawalls, revetments, bulkheads, and riprap (loose boulders). Beach—an accumulation of loose sediment (usually sand or gravel) along the coast. Beach nourishment—the addition of sand (sand fill) to a shoreline to enhance or create a beach area, offering both shore protection and recreational opportunities. Berm—a geomorphological feature usually located at mid-beach and characterized by a sharp break in slope, separating the flatter backshore from the seaward-sloping foreshore. Bluff—an elevated landform composed of partially consolidated and unconsolidated sediments, typically sands, gravel and/or clays. Breakwater— a single structure or a series of units placed offshore of the project site to reduce wave action on the shoreline.
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Mitigating Shore Erosion Along Sheltered Coasts Bulkhead—vertical shoreline stabilization structure that primarily retains soil. Convergence—zones where sediment deposition exceeds sediment loss and accretion of sediment occurs. Cumulative impacts—the impacts on the environment, which result from the incremental impact of the action when added to other past, present and reasonably foreseeable future actions regardless of what agency (federal or nonfederal) or person undertakes such other actions (40 CFR 1508.7 and 1508.8). Delta—a nearly flat plain of alluvial deposit between diverging branches of the mouth of a river, often, though not necessarily, triangular. Deposition—the process of sediment settling back to the bed or particles settling out of the water column. Divergence—zones where the amount of sediment mobilized and lost exceeds the amount deposited. Downdrift—in the direction of net longshore sediment transport. Dune—a landform characterized by an accumulation of wind-blown sand, often vegetated. Entrainment—the picking up and setting into motion of particles, either by wind or by water. The main entrainment forces are provided by impact, life force, and turbulence. Erosion—the loss of sediment, sometimes indicated by the landward retreat of a shoreline indicator such as the water line, the berm crest, or the vegetation line. The loss occurs when sediment grains are entrained into the water column and transported away from the source. Erosion mitigation—efforts to reduce or lessen the severity of erosion. Eustatic sea-level rise—results from changes in global sea level. Eustatic changes represent global sea level. The causes can be complex, such as ice sheet melting, increasing temperature of the surface waters, increasing the volume of the spreading ridge. Fetch—the distance that a wave travels from the point of origin to the shore where it breaks. In sheltered areas, the fetch corresponds to the distance across
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Mitigating Shore Erosion Along Sheltered Coasts a span of water over which wind-generated waves may grow before breaking on the opposing shore. Groins—a breakwater running seawards from the land, used on a variety of coasts including sheltered shores and open coasts, constructed to trap sand by interrupting longshore transport. A groin extends from the backshore into the littoral zone and is normally constructed perpendicular to the shore out of concrete, timbers, steel, or rock. Hardening—see Armoring. Infauna—animals that live in sediment. Inundation—the temporary submergence of typically dry lands when there is an exceptional rise of the sea surface, and floodwaters cover the adjacent low-lying land. Littoral cell—sections of coast for which sediment transport processes can be isolated from the adjacent coast. Within each littoral cell, a sediment budget can be defined that describes sinks, sources, and internal fluxes (sediment transport). Littoral zone—used as a general term for the coastal zone influenced by wave action, or, more specifically, the shore zone between the high and low water marks (USACE, 2002b). Longshore transport—sediment transport down the beach (parallel to the shoreline) caused by longshore currents and/or waves approaching obliquely to the shoreline. Marsh—a vegetated mudflat. Mudflat—an intertidal area with relatively fine sediment that may be vegetated by plant communities (marshes and mangroves) or colonized by microscopic plant communities (microalgae) and bacteria. Offshore—the portion of the littoral system that is always submerged. Open coast—tidal shores that have little or no protection from wave action. Planform—the outline or shape of a body of water as determined by the still-water line (USACE, 2002b).
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Mitigating Shore Erosion Along Sheltered Coasts Pore water—water filling the spaces between grains of sediment. Reach—a straight section of waterway that is uniform with respect to discharge, slope, and cross-section (USACE, 2002b). Relative sea-level rise—the sea level relative to the land, which relates changes in local water levels to local land elevations. The rate of sea-level rise relative to a particular coast has a practical importance because some coastal land areas are subsiding, resulting in a relative rise in sea level, while other land areas are rising, resulting in a slower or falling sea level. Revetment—a type of shoreline armoring that hardens the slope face and is often constructed from large boulders. A revetment tends to have a rougher (less reflective) surface than a seawall, and often is constructed with one or more layers of graded riprap but can also be constructed with precast concrete mats, timber, gabions (stone-filled, wire-mesh baskets), and other materials. Scarp—a steep slope, usually along the foreshore and/or at the vegetation line, formed by wave attack. Seawall—a vertical or near-vertical type of shoreline armoring characterized by a smooth surface. It retains soil, and reflects wave energy. Sheltered coast—a coastal area sheltered by headlands, coves, natural or harbor breakwaters, tidal inlets, and river mouths and estuaries which have a limited distance between banks (fetch) and hence limited exposure to wind-driven waves. This area is usually characterized by low wave energies and stresses. These lower energy conditions foster habitats and ecological communities, such as marshes and mudflats, not typically found on open coasts. Shore zone—the active volume of sediment affected by wave action. Sill—a generally semicontinuous structure (e.g., a barrier of rock) built to reduce wave action and preserve, enhance, or create a marsh grass fringe for shore erosion control. Storm surge—a temporary rise in sea level associated with a storm’s low barometric pressure and onshore winds. Wave attenuation—the power loss (the reduction in power density of a wave with distance) when a wave disperses over a larger area.
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Mitigating Shore Erosion Along Sheltered Coasts Wind fetch—the distance the wind blows over water with similar speed and direction. SOURCE: Most terms are defined by the authors of this report. Any additional sources are listed at the end of each item.