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.