Glossary of Stormwater Management Terms and Acronyms
 

E



EPA
:  The United States Environmental Protection Agency.


Easement
:  An interest in land owned by another that entitles its holder to a specific limited use or enjoyment.  Example: power line easement, conservation easement.


Elevation
:  Distance above sea level that the point is. Necessary to determine slope and determine drainage. Example: Contour map, hydrometers.  


Embankment
A man-made deposit of soil, rock or other material used to form an impoundment.


Emergency spillway
A channel, usually an open channel constructed adjacent to an embankment, which conveys flows in excess of the design capacity of the principal spillway.


Energy dissipater
A device used to reduce the velocity or turbulence of flowing water.


Energy of water flow:  
(E = mv2). Water flow energy increases with the square of the velocity. A stream shows this energy change; silts low velocity, rocks high velocity.


Erosion
:  The wearing away of the land surface by running water, wind, ice or other geological agents.

        Accelerated erosion:  erosion in excess of what is presumed or estimated to be naturally
        occurring levels and which is a direct result of human activities.

        Gully erosion:  erosion process whereby water accumulates in narrow channels and removes
        the soil to depths ranging from a few inches to 1 or 2 feet to as much as 75 to 100 feet.

        Rill erosion:  erosion process in which numerous small channels only several inches deep are
        formed.

        Sheet erosion:  spattering of small soil particles caused by the impact of raindrops on wet soils.
        The loosened and spattered particles may subsequently be removed by surface runoff.


Eutrophication
The process of over-enrichment of water bodies by nutrients often typified by the presence of algal blooms.


Evaporation: 
The process of liquid water converting to water vapor.  The rate  of evaporation is determined by wind, temperature of air and water and relative humidity. Evaporation can significantly lower a lake. Evaporation contributes to rainfall.


Extended detention basin
A stormwater management facility which temporarily impounds runoff and discharges it through a hydraulic outlet structure over a specified period of time to a downstream conveyance system for the purpose of water quality enhancement or stream channel erosion control.  While a certain amount of outflow may also occur via infiltration through the surrounding soil, such amounts are negligible when compared to the outlet structure discharge rates and, therefore, are not considered in the facility's design.  Since an extended detention basin impounds runoff only temporarily, it is normally dry during non-rainfall periods.


Extended detention basin-enhanced
:  An extended detention basin modified to increase pollutant removal by providing a shallow marsh in the lower stage of the basin.


Exfiltration
:  The downward movement of runoff through the bottom of a stormwater facility and into the soil.