Glossary

Sand Levee are embankment sections comprised of cohesionless materials that generally have a 1 V (Vertical) on 3 H (Horizontal) slope toward a river, 1 V on 5 H landward slope, and a 3.05-m (10-ft) top width.

Lockgate similar to a tainter gate, but it pivots about a vertical axis as does a miter gate. Sector gates have traditionally been used in tidal reaches of rivers or canals where the dam may be subject to head reversal. Sector gates may be used to control flow in the lock chamber during normal operation or restrict flow during emergency operation. Sector gates are generally limited to lifts of 3 m (10ft) or less.

A structure separating land and water areas, primarily designed to prevent erosion and other damage due to wave action. See also BULKHEAD.

The passage of water or other fluid througha porous medium, such as the passage of waterthrough an earth embankment or masonry wall.

Erosion caused principally by storm induced wave action and associated alongshore currents. Shore erosion problems become critical when high lake levels have submerged the beaches which protect the adjoining highly erodible upland areas. Raised above the beaches, wave forces can work directly on the toe of the bluffs and dunes, resulting in rapid erosion.

Areas in a community that have been identified as susceptible to a one- percent or greater chance of flooding in any given year. A one-percent-probability flood is also known as the 100-year flood or the base flood.

A detailed description of particulars, such as size of stone, quality of materials, contractor performance, terms, quality control, etc.

A term used by the U.S. Army Corps of Engineers to designate a flood thatmay be expected from the most severe combinationof meteorological and hydrological conditions thatis considered reasonably characteristic of thegeographical area in which the drainage basin islocated, excluding extremely rare combinations. The peak flow for a standard project flood isgenerally 40 to 60 percent of the probablemaximum flood for the same location.

The elevation that the surface of the water would assume if all wave action were absent.

A body of water flowing in a natural surfacechannel. Flow may be continuous or only duringwet periods. Streams which flow only during wetperiods are termed 'intermittent streams.'

Those physical or engineering measures employed tomodify the way floods behave, e.g., dams, dikes, levees, channel enlargements and diversions.

Sinking of the land surface, usually dueto withdrawals of underground water, oil, orminerals.

The rates which involvesubsidizations by the Federal Government toencourage the purchase of flood insurance onexisting structures at reasonably affordable costs.