NPDP Dam Dictionary

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Term AKA Definition
Eddy Circular current of water moving against the main current
Effective peak ground acceleration That acceleration which is most closely related to structural response and to damage potential of an earthquake.
Efficiency Ratio of useful energy output to total energy input, usually expressed as percent.
Effluent Partially or completely treated wastewater flowing out of a treatment facility, reservoir, or basin.
Effluent limitation The maximum amount of a specific substance or characteristic that can be present in effluent discharge without violating water quality standards in receiving waters.
Electric power system Physically connected electric generating, transmission, and distribution facilities operated as a unit under one control.
Electrical conductivity A measure of the salt content of water.
Elevation The height of a point above a plane of reference. Generally refers to the height above sea level. See datum.
Elongate An increase of the vertical diameter of a flexible pipe.
Embankment An earth structure the top of which is higher than the adjoining surface. A shaped earth or rockfill dam. Fill material, usually earth or rock, placed with sloping sides and with a length greater than its height. An embankment is generally higher than a dike
Embankment dam Fill dam Any dam constructed of excavated natural materials. See diaphragm-type earthfill, earth dam or earthfill dam, homogeneous earthfill dam, hydraulic fill dam, rockfill dam, rolled fill dam, or zoned earthfill. See also berm and fill.
Emergency Action Plan EAP A formal document that identifies potential emergency conditions at a dam and specifies pre-planned actions to be followed to minimize property damage and loss of life. It contains procedures and information to assist the owner in issuing early warning and notification messages to responsible downstream emergency management authorities of the emergency situation. It also contains inundation maps to show the emergency management authorities the critical areas requiring action in case of an emergency. In the NPDP Dams Directory and the National Inventory of Dams, it is indicated whether there is an EAP (Yes) or not (No), or if one is not required (Not Required).
Emergency spillway A spillway which provides for additional safety should emergencies not contemplated by normal design assumptions be encountered, i.e., inoperable outlet works, spillway gates, or spillway structure problems. The crest is usually set at maximum water surface.
Endangered species A species or subspecies whose survival is in danger of extinction throughout all or a significant portion of its range.
Energy Force or action of doing work. Measured in terms of the work it is capable of doing; usually electric energy is measured in kilowatt hours (kWh).
Enhancement Improvement of a facility beyond its originally designed purpose or condition.
Enhancement flow Improved flows that result in better stream conditions for aquatic, terrestrial, and other resources.
Entrainment Process by which aquatic organisms, suspended in water, are pulled through a pump or other device.
Environment All biological, chemical, and physical factors to which organisms are exposed.
Environmental analysis Systematic process for consideration of environment factors in land management actions.
Environmental Effects Description Decscribe the environmental impact of the dam incident, such as release of sediment into stream, or release of toxic materials, damage to wetlands, animal habitat, etc.
Eolian See aeolian.
Ephemeral creek A creek or stream that flows briefly only in direct response to precipitation and whose channel is above the water table. See intermittent stream.
Epicenter Focal point on earth's surface directly above the origin of seismic disturbance.
Epifauna Animals which live on the benthos.
Epilimnion The upper layer of a lake or reservoir with essentially uniform warmer temperatures. See stratification.
Erode To wear away or remove the land surface by wind, water, or other agents.
Erosion A gradual wearing away of soil or rock by running water, waves, or wind. Concrete surface disturbance caused by cavitation, abrasion from moving particles in water, impact of pedestrian or vehicular traffic, or impact of iceflows. Surface displacement of soil caused by weathering, dissolution, abrasion, or other transporting.
Escapement Unharvested spawning stocks that return to the streams.
Escarpment A cliff or steep slope that separates two level or gently sloping areas.