Erosion and Sediment Pollution Control Program Manual.pdf

Hyetograph -----A chart showing the distribution of rainfall over a particular period of time or a
particular geographic area.
Hygroscopic -----The ability to attract, absorb, and retain atmospheric moisture.
I
I or i -----The symbol for Rainfall Intensity used in the Rational Equation (Q = C I A).
IECA -----International Erosion Control Association.
Illuvial Material -----Soil material, usually minerals and colloidal particles that is removed from the
upper soil horizon to a lower one. These can form a hardpan.
Impact Basin -----A device used to dissipate the energy of flowing water to reduce its erosion potential.
It generally uses baffles to accomplish this.
Impermeable Material -----A soil or material whose properties prevent movement of water through the
material.
Impervious Surface -----Hard ground cover that prevents or retards the entry of water into the soil and
increases runoff, such as asphalt, concrete, rooftops, etc.
Implied Easement -----An easement for the benefit of lots necessary to provide passage or provision of
water supply or sewerage over land or buildings in a subdivision. The easement is specified in
words, not dimensions, on a plan of subdivision
Impoundment -----1. A water body upstream of a structure such as a sediment basin, trap, or detention
pond constructed for the purpose of holding water. 2. An artificial collection and storage area
for water or wastewater confined by a dam, dike, floodgate, or other barrier.
Improvements -----Roadways, building, utilities, etc. built upon a tract of land.
Incised Stream ----- A stream in which scouring causes the channel to degrade or down-cut to a point
where the stream is no longer connected to its floodplain.
Inclinometer -----A device used to measure the change in inclination, or tilt, of a casing in a borehole.
Individual NPDES Permit -----A construction permit issued separately due to concerns about a special
protection watershed, potential for disturbing toxic materials, or a history of lack of compliance.
Infiltration -----The portion of rainfall or surface runoff that moves downward into the subsurface soil
and rock.
Infiltration Basin -----An excavated area that impounds stormwater runoff and allows it to gradually
infiltrate the subsoil beneath the basin floor.
Infiltration Capacity -----The maximum rate at which the soil, when in a given condition, can absorb
falling rain or melting snow.
Infiltration Rate -----The maximum rate at which water can enter a soil under specified conditions.
Infiltration Trenches -----Shallow excavations that have been backfilled with a coarse stone media.
The trench forms an underground reservoir that collects runoff and allows it to infiltrate into the
subsoil.
Inflow -----Water that enters a BMP or other hydrologic system.
Influent Stream -----A stream above the water table that contributes to groundwater recharge.
Infrared Photography -----A type of aerial photography useful in detecting subtle geologic features like
fracture traces, sinkholes, groundwater seepage, etc.
Infrastructure -----1. An underlying base or foundation, especially for an organization or system.
2. The basic facilities, services, and installations needed for the functioning of a community or
society, such as transportation and communications systems, water and power lines, sewer
lines, etc.
Initial Loss -----The sum of interception and depression loss, excluding blind drainage.
Initial Storage -----In TR-55, it is that portion of precipitation required to satisfy interception by
vegetation, the wetting of the soil surface, and depression storage.
Inlet -----A drainage passage, as to a culvert or storm sewer.
Inlet Control -----In culverts, it is the condition when the culvert barrel is capable of conveying more
flow than the inlet will accept.
Inlet Filter Bag -----A geotextile bag designed to fit inside a storm sewer inlet for the purpose of filtering
sediment from runoff entering the inlet. See Standard Construction Detail #s 4-15 and 4-16.
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