Flood, levee, and erosion control glossary - H
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Habitable Room
A space used for living, sleeping, eating
or cooking, or a combination thereof, but not including bathrooms, toilet
compartments, closets, halls, storage rooms, laundry and utility rooms,
basement recreation rooms and similar spaces.
Habitat
The specific area or environment in which a particular type of plant or
animal lives. To be complete, an organism's habitat must provide all of the
basic requirements of life for that organism.
Photo courtesy of USDA NRCS.
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Photo of goose in natural habitat. |
Habitat Evaluation Procedure (HEP)
A methodology developed
by the U.S. Fish and Wildlife Service for quantitative evaluation of the suitability of wetlands and other habitat
types for fish and wildlife species.
Half Life
The time it takes certain materials, such as
persistent pesticides, to become chemically altered.
Hard Defenses
General term applied to impermeable coastal defense structures of concrete, timber, steel, masonry, etc, which reflect a high proportion of incident wave energy.
Hard Point
A slope protection technique whereby "soft" or erodible materials are removed from a bank and replaced by stone or compacted clay. These features may also occur naturally along banks where currents have removed erodible materials leaving nonerodible materials exposed.
Hard Structures
A type of bank protection structure
incorporating rock, riprap, sack concrete, gabion baskets and mattresses, or
concrete. These structures are inert and rigid.
Hardness
A characteristic of water caused by the measure
of various salts, calcium, magnesium, and iron that are dissolved in the water.
Hazardous Flow
Conditions that exist when the product of
the depth of the flow and its corresponding velocity are greater thatn10. For
example, a flow depth of 3 feet and a flow velocity of 4 feet per second (3 x 4
= 12) would be considered a hazardous flow.
Hazardous Waste
Waste substances which pose a substantial
or potential hazard to human health or the environment when improperly managed.
Hazardous waste possesses at least one of these four characteristics (or
appears on special U.S. EPA lists) - ignitability, corrosivity, reactivity or toxicity.
Headcut
The point at the upstream end of a channel where
it grows and lengthens; also called nick point.
Headcutting
The action of an upstream moving waterfall or
locally steep channel bottom with rapidly flowing water through an otherwise
placid stream. These conditions often indicate that a readjustment of a
stream's discharge and sediment load characteristics is taking place.
Headwater
A slope protection technique whereby "soft" or erodible materials are removed from a bank and replaced by stone or compacted clay. These features may also occur naturally along banks where currents have removed erodible materials leaving nonerodible materials exposed.
Health Advisories (HA)
Non-regulatory levels of
contaminants in drinking water at which no adverse effects would be expected.
Health advisories are used for guidance in the absence of regulatory limits.
Health advisories have been issued for children and adults for several
different exposure periods.
Heave
1. The vertical rise or fall of the waves or the sea. 2. The translational movement of a craft parallel to its vertical axis. 3. The net transport of a floating body resulting from wave action.1. The vertical rise or fall of the waves or the sea. 2. The translational movement of a craft parallel to its vertical axis. 3. The net transport of a floating body resulting from wave action.
Heaving
The partial lifting of plants out of the ground,
frequently breaking their roots as a result of freezing and thawing of the
surface soil during winter. Structures built on top of the ground may also
heave and become misaligned.
Heavy Metals
Metals of high specific gravity, present in
municipal and industrial wastes, that pose long-term environmental hazards.
Such metals include cadmium, chromium, cobalt, copper, lead, mercury, nickel,
and zinc.
HEC
Abbreviation for Hydrologic Engineering Center.
Herbicide
Chemicals used to kill undesirable vegetation.
Howe Document 465
The 1966 report of the Bureau of the
Budget Task Force on Federal Flood Control Policy, entitled A Unified National
Program for Managing Flood Losses, and advocating a broader perspective on
flood control within the context of floodplain development and use.
Human Intervention
The required presence and active
involvement of people to enact any type of flood proofing measure prior to
flooding.
Hundred Year Flood
More accurately referred to as a
"one percent chance flood," a flood of a magnitude which, according
to historical statistics, has one chance in 100 of occurring in any given year.
(This does not necessarily mean that, once such a flood occurs, the location
will not experience another for the next 99 years!) See 100-year flood.
Hurricane
A warm-core tropical cyclone in which the
maximum sustained surface wind (1 minute mean) is greater than or equal to 64
knots (73.6 mph).
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 onto the hillsides and provide gradient
breaks where sediments can be deposited and nutrients retained.
Hydraulic Depth
An average depth computed as the Flow Area
divided by the top width of the floodplain for a given water-surface elevation.
Hydraulic Head
Difference in water height between upstream
and downstream sides of a structure.
Hydraulic Mulching
Applying wood fiber mulch and often a
mixture of seed, water, and fertilizer in one application help retain soil and
moisture; also hydromulching.
Hydraulics
The science dealing with the mechanical properties
of liquids that describes the specific pattern and rate of water movement in
the environment.
Hydrodynamic Force
Forces imposed on an object, such as a
structure, by water moving around it. Among these loads are positive frontal
pressure against the structure, drag affect along the sides, and negative
pressure on the downstream side.
Hydrodynamic Loads
Forces imposed on structures by
floodwaters due to the impact of moving water on the upstream side of the
structure, drag along its sides, and eddies or negative pressures on its
downstream side.
Hydrostatic Loads
Forces imposed on a flooded structure due to the weight of
the water.
Hydrology
The science dealing with the properties, distribution and
circulation of water on the surface of the land, below the surface, and in the
atmosphere.
Hydrogeology
The part of hydrology that deals with the
occurrence, movement, and quality of water beneath the Earth's surface.
Hydrograph
A graph of runoff rate, inflow rate or
discharge rate, past a specific point over time.
Hydrologic Cycle
The circulation of water within the Earth
system and through the Earth's atmosphere by various processes including
evaporation, condensation, precipitation, runoff, ground water storage and seepage,
and re-evaporation into the atmosphere.
Hydrologic Unit Code (HUC)
Reference used by the USGS for
assessing hydrologic units throughout the United States.
Hydrology
The science of the behavior of water in the
atmosphere, on the surface of the earth, and underground. The science dealing
with the origin, distribution and circulation of waters of the earth such as
rainfall, streamflow, infiltration, evaporation, and groundwater storage.
Hydrolysis
The decomposition of organic compounds by
interaction with water.
Hydroperiod
A seasonal occurrence of flooding and/or soil
saturation; it encompasses depth, frequency, duration, and seasonal pattern of
inundation.
Hydrophytes
Specially adapted plants that grow in areas
having alternating wet and dry conditions. Examples of hydrophytes include
floating pond lilies, emergent cattails, many sedges, tamarack, and black
spruce.
Hydroseeding
A method of seeding by mixing seed with water and fertilizer and then
spraying the solution onto a seedbed.
Photo courtesy of USDA NRCS.
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Photo of hydroseeding. |
Hydrosphere
Water held in oceans, rivers, lakes, glaciers,
ground water, plants, animals, soil, and air.
Hydrostatic Force
Forces imposed on a surface, such as a
wall or floor slab, by a standing mass of water. The force increases with
increasing water.
Hyetograph
A graph of precipitation versus time.
Hypereutrophic
Murky, highly productive waters, closest to
the wetland status.
Hypolimnion
The lowest layer in a thermally stratified
lake or reservoir. This layer consists of colder, denser water, and has a
constant temperature where no mixing occurs.
Hypoxia
A condition where very low concentrations of
dissolved oxygen are in the water column.
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