Glossary of Common Terms

Glossary of Common Terms Used in the Beach Industry

Accretion—The seaward growth of land; opposite of shoreline erosion or shoreline retreat.

Backwash—The seaward return of a wave in the intertidal zone. Backwash carries sand in a seaward direction.

Barrier Island—An elongate island of sand bounded by inlets at either end and separated from the mainland by a lagoon. Barrier islands front most of the U.S. coast from Long Island, New York, to the Mexican border.

Barrier Island Migration—A process of island movement caused by rising sea level and/or insufficient sediment supply, in which a barrier island rolls over itself like the tread on a bulldozer. Simultaneous shoreline retreat of the open-ocean beach and increase of the land area by overwash on the lagoon side of the island results in island migration.

Beach—A strip of unconsolidated sand or gravel found at the seaward margin of the coast and accumulated in the zone affected by wave action along the shoreline of a body of water.

Beach Replenishment (Beach Nourishment)—The replacement of sand on an eroded beach from an outside source such as an offshore sand deposit, an inlet tidal delta, or an upland sand quarry. One of the responses to shore- line retreat.

Berm—A term used by coastal engineers to describe the artificial dune built on the landward side of a replenished beach for the purpose of reducing storm damage to a community.

Borrow Area (Borrow Site)—The source of beach replenishment sand. In the early days of replenishment, lagoonal areas behind islands were commonly used as borrow areas. Today, the preferred borrow areas are inlets or off- shore sand deposits.

Bulkhead—Relatively low and small seawalls designed not to protect buildings from waves, but to keep land from eroding from behind them.

Closure Depth—The water depth beyond which, it is assumed, little beach sand will be transported in a seaward direction. Typically assumed by coastal engineers (on the U.S. Atlantic and Gulf coasts) to be somewhere between 12 and 30 feet.

Coast—Biologically, the zone where land, ocean, and air interact, extending inland to the limit of tidal or sea spray influence. Politically, the inland limit of the coastal zone varies by state, sometimes defined as the band of counties that border the sea.

Continental Shelf—The section of sea floor between the beach and the point at which the sea floor begins to slope steeply (the upper continental slope). Typically, ocean depth at the edge of the shelf is 300 to 400 feet.

Downdrift—The direction of net longshore transport of sand on an annual basis. Analogous to downstream in a river.

Dredge Spoil—Material dredged from channels and harbors.

Dune—A sand hill, landward of the high-tide line formed by the deposition of windblown sand. In coastal areas, dune sand is almost always derived from the beach.

Dynamic Equilibrium—The four major controls that govern a beach: (1) wave and tidal energy; (2) quality and quantity of sediment supply; (3) beach shape and location; and (4) relative sea level. As any of these four factors change, the others adjust accordingly.

Ebb Tidal Delta—The body of sand in a lagoon pushed seaward by the out- going (ebb) tide. The ebb tidal delta is the location of most shipwrecks in inlets.

Estuary—A coastal water body that is connected to the sea so that fresh and salt water mix. Commonly, estuaries occupy former river valleys flooded by the sea during sea level rise.

Flood Tidal Delta—A body of sand that extends into the lagoon formed by sand carried by the incoming (flood) tide. Flood tidal deltas add to barrier island width when the inlet migrates or opens somewhere else. The delta is usually colonized by salt marshes or mangroves.

Groin—(sometimes spelled “groyne”) A wall built perpendicular to the shoreline intended to trap sand traveling laterally in the surf zone. It can be built of almost anything and is often successful in building up a beach in place, but, in so doing, it causes a sand deficit and erosion downdrift.

Inlet—The waterway that separates barrier islands and allows passage between the open ocean and an inland harbor. Inlets generally form during storms, usually when storm surge ebb cuts a channel through an island.

Jetty—A shore-perpendicular wall, usually much longer than a groin, built at an inlet to stabilize a navigation channel. Usually severely interrupts the longshore transport of sand.

Lagoon—Coastal water body separated from the sea by a low-lying strip of land, often a barrier island. Commonly, the term lagoon is used inter- changeably with bay estuary and sound.

Littoral Drift—See longshore current.

Longshore Current—Longshore currents are surf zone currents formed as breaking waves strike the shoreline at an oblique angle, forcing some of the surf zone water to move laterally along the beach. Also called littoral drift.

Mathematical Shoreline Model—Mathematical equations intended to describe beach processes that are combined to predict beach behavior.

Nearshore—The innermost continental shelf, comprised of the surf zone and the shoreface.

Net Direction of Longshore Transport—The direction along a shoreline toward which the longshore current carries more sand on an annual basis. Corresponds to downdrift direction. Also called the dominant direction.

Newjerseyization—The process of stemming shoreline retreat at the price of the beach through shoreline armoring. The result is loss of the recreational beach and a completely armored shoreline.

Nourishment Interval—The predicted length of time between necessary additions of sand to a replenished beach, usually based on the assumption that one-third to one-half of the beach will be lost during this time.

Offshore Breakwater—A coastal engineering structure built offshore and parallel to the shore to reduce wave energy and slow net longshore transport by forming a wave shadow on the beach. Sediment is deposited in the lee of breakwaters such that a tombolo may form.

Overwash—The process of waves washing over an island during a storm. Overwash produces deposits of sand called overwash fans that increase is- land elevation.

Relocation—The practice of moving buildings or infrastructure back from retreating shores, one of the responses to shoreline retreat. Includes actually picking up and moving buildings intact, demolishing and rebuilding else- where, and rebuilding storm-destroyed buildings elsewhere.

Revetment—A common type of seawall built directly on a surface such as the seaward slope of a dune. They are frequently constructed of boulders; the large rocks provide ample interstitial cavities that absorb some of the water from a breaking wave, reducing sand-removing wave reflection and back- wash.

Scarp—A small bluff, in the unconsolidated material of a beach, usually parallel to the shoreline.

Seawall—A coastal engineering structure built on the beach, parallel to the shoreline, intended to protect buildings from wave action.

Shoreface—The nearshore zone extending from the low-tide line to a typical water depth of approximately 30 feet.

Shoreline—The wet/dry boundary of the beach, which naturally moves up and down with the tide. For mapping purposes, the shorelines location is determined by some mean position such as the mid-tide line or mean sea level.

Shoreline Armor—Fixed structures, such as seawalls, groins, and offshore breakwaters, built on the beach and designed to hold the shoreline in place, i.e., to stabilize it. Another term {‘or stabilization.

Shoreline Erosion—Land loss caused by wave or wind action. Commonly shoreline erosion is used interchangeably with shoreline retreat. The latter is the scientifically preferred term.

Shoreline Retreat—The landward movement of a beach.

Stabilization—One of the human responses to shoreline retreat, in which attempts are made to hold the shoreline in place. Stabilization may be “hard” (armoring the shoreline with erosion-control structures) or “soft” (beach replenishment).

Storm Surge—The temporary rise in local sea level caused by a storm.

Storm Surge Ebb—The seaward return flow of storm waters that were forced onto the upland or into the lagoon. Usually the ebb starts when winds reverse direction as the storm moves ashore.

Surf Zone—The linear zone adjacent to the beach where waves break. The size of the surf zone varies, widening from several yards in calm weather to hundreds of yards during storms.

Tidal Delta—A body of sand formed at an inlet by tidal currents (see flood and ebb tidal deltas).

Tombolo—A seaward bulge of the beach connecting the land with an offshore island or to a human-built offshore breakwater.

Updrift—The opposite direction from the net direction of longshore transport of sand on a beach. Analogous to upstream in a river.