NPDP Dam Dictionary

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Term AKA Definition
Habitat The area or type of environment in which a plant or animal normally lives or occurs.
Halophytic Salt-loving. Plants that thrive in soils that contain salt and/or sodium. A plant that grows in salty or alkaline soil.
Hardpan A hard, impervious layer, composed chiefly of clay, that is cemented by relatively insoluble materials and limits the downward movement of water. A cemented or compacted layer of soil near the surface that is essentially impermeable to water. A hard, tight soil. A hard layer that may form just below plow depth on cultivated land.
Harrow An agricultural tool that loosens and works the ground surface.
Haul distance The distance measured along the center line or most direct practical route between the center of the mass of excavation and the center of mass of the fill as finally placed. It is the distance material is moved. Average haul is the average distance a grading material is moved from cut to fill. See overhaul.
Haunch The outside areas between the springline and the bottom of a pipe. In pipe, the sides of the lower third of the circumference.
Hazard Classification The potential hazard to the downstream area resulting from failure or misoperation of the dam or facilities: 1. Low 2. Significant 3. High Definitions, as accepted by the Interagency Committee on Dam Safety, are as follows: 1. Low Hazard Potential: Dams assigned the low hazard potential classification are those where failure of misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property. 2. Significant Hazard Potential: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life, but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure. 3. High Hazard Potential: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life. (U.S. Definition)
Head Differential of pressure causing flow in a fluid system, usually expressed in terms of the height of a liquid column that pressure will support. The difference in number of feet between two water surface elevations. Height of water above a specified point. The back-pressure against a pump.
Head loss The energy per unit weight of water lost due to friction, transitions, bends, etc.
Heading In a tunnel, a digging face and its work area.
Headrace See forebay.
Headwall An upstream wall.
Headwater The source and upper part of a stream; water upstream of a dam or powerhouse.
Heap The soil carried above the sides of a body or bucket.
Heave The upward movement of land surfaces or structures due to subsurface expansion of soil or rock, or vertical faulting of rock.
Heel of dam The junction of the upstream face of a gravity dam with the ground surface. In the case of an embankment dam, the junction is referred to as the upstream toe of dam.""
Height of dam See hydraulic height or structural height.
Helical Spiral
Herpetofauna Reptiles and amphibians.
High hazard Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life. (U.S. Definition)
High-pressure gate A gate consisting of a rectangular leaf encased in a body and bonnet and equipped with a hydraulic hoist for moving the gate leaf.
Hoe A shovel that digs by pulling a broom-and-stick-mounted bucket toward itself.
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Hoist The mechanism by which a bucket or blade is lifted, or the process of lifting it.
Hollow gravity dam Cellular gravity dam A dam which has the outward appearance of a gravity dam but is of hollow construction.
Hollow-jet valve A valve having a closing member that moves upstream to shut off the flow. The hollow-jet valve discharges a hollow or annular jet dispersed over a wide area.
Homogeneous earthfill dam An embankment dam construction throughout of more or less uniform earth materials, except for possible inclusion of internal drains or blanket drains. Used to differentiate it from a zoned earthfill dam. An embankment type dam constructed of only one type of material.
Hopper A storage bin or a funnel that is loaded from the top, and discharges through a door or chute in the bottom.
Horsehead False set A temporary support for forepoles used in tunneling soft ground.
Horsepower hp A measurement of power that includes the factors of force and speed. The force required to lift 33,000 pounds one foot in one minute.