Erosion and Sediment Pollution Control Program Manual.pdf

Holding Structure -----Any excavation, pond, or closed embankment used to contain water or another
solution until needed.
Horizon -----A layer of soil with different color or composition than the layers above and below it.
HQ Watershed -----High quality watershed.
Humic Acid -----The alkaline-soluble portion of organic material — humus — that precipitates from
solution at low pH and is of high molecular weight. A breakdown product of cellulose from
vascular plants.
Humus -----Organic materials resulting from decay of plant or animal matter.
100-Year Flood -----A flood level with a 1 percent or greater chance of being equaled or exceeded in
any given year.
HWM -----High water mark, a mark indicating the highest level reached by a body of water.
Hybrid Terrace -----A method of planting on slopes to prevent soil loss and landslides; mulches, trees,
vetiver grass, and rock walls are combined on the terraces to tie soils on the hillsides and
provide gradient breaks where sediments can be deposited and nutrients retained.
Hydration -----The chemical reaction between water and cement.
Hydraulic Gradient -----A line which represents the relative force available due to the potential energy
available. This is a combination of energy due to the height of the water and internal pressure.
In an open channel, the line corresponds to the water surface.
Hydraulic Head -----1. The height of the free surface of a body of water above a given point beneath
the surface. 2. The height of the water level at an upstream point of a waterway above the
water surface at a given point downstream.
Hydraulic Jump -----An abrupt rise in water surface that occurs in open channel flow when water
flowing at a high velocity is retarded. This occurs as the flow changes from supercritical flow to
sub critical flow.
Hydraulic Mulching -----Applying wood fiber mulch and often a mixture of seed, water, and fertilizer in
one application to help retain soil and moisture. Also called “hydromulching.”
Hydraulic Radius -----The cross-sectional area of a channel divided by its wetted perimeter (A/P). For
a circular pipe flowing full, it is ¼ the pipe diameter.
Hydraulics -----The study of water in motion.
Hydric Inclusions -----Relatively small (unmapped) areas of hydric soil located within larger areas
(mapped) of otherwise non-hydric soil.
Hydric Soil -----A soil that is saturated, flooded, or ponded long enough during the growing season to
develop anaerobic-conditions. When such a soil is located in an area that has hydrophytic
vegetation and wetland hydrology, a wetland is present.
Hydrograph -----A graphical representation of the rate of flow, stage, velocity or other property of water
at a specific point over a period of time (usually during a storm or flood event).
Hydrologic Balance -----An accounting of all water inflows to, water outflows from, and changes in
water storage within a hydrologic unit over a specified period of time. Inflow = outflow +
changes in storage.
Hydrologic Cycle -----The circuit of water movement from the atmosphere to the earth and back to the
atmosphere by various processes such as precipitation, runoff, infiltration, evaporation, and
transpiration.
Hydrologic Soil Group ---A classification of soils according to infiltration rates. Group A soils have the
highest infiltration rates, and therefore, the lowest runoff potentials, while Group D soils have the
lowest infiltration rates and (highest runoff potentials).
Hydrology -----Study of properties, distribution, and circulation of water on the surface of the land as
well as underground.
Hydrophytic Vegetation -----Plants adapted to life in wet environments.
Hydroseeding -----Application of seed and soil amendments (sometimes with a paper mulch) to an
area to be stabilized by spraying it in a water mixture onto previously prepared soil (seedbed).
Hydrostatic Head -----A measure of pressure at a given point in water in terms of the vertical height of
a column of water which would produce the same pressure.
Hydrostatic Water Testing -----High pressure water testing of pipelines (intended for gas or other
product transport) to check for possible leaks.
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