Glossary

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Glossary terms for letter: H

Hazard Adjustment:

See 'structural' and 'nonstructuralfloodplain management measures.'

Heads of bavs:

In the approximate center of a bay between the two points or headlands which form the bay.

Hinged-Crest Gates:

Hinged-crest gates are known by a variety of names including Bascule, Pelican, and flap gates. These gates are hinged at the base to a dam sill and are raised to retain pool and lowered to pass flows. They can be straight or curved to fit the dam sill crest when in the lowered position. The plate is reinforced with vertical and horizontal members and is fitted with a torque tube at the base or separate hinges. These gates are normally sealed at the base and edges when in the raised position.

Hydrodynamic Loads:

Forces imposed on structuresby floodwaters due to the impact of moving wateron the upstream side of the structure, drag alongits sides, and eddies or negative pressures on itsdownstream side.

Hydrograph:

A graph that charts the passage ofwater as a function of time. It shows flood stages, depicted in feet above mean sea level or gageheight, plotted against stated time intervals.

Hydrology:

The science of the behavior of water inthe atmosphere, on the earth's surface, andunderground.

Hydrostatic Loads:

Loads or pressures resulting from the static mass of water at any point of floodwater contact with a structure. They are equal in all directions and always act perpendicular to the surface on which they are applied. Hydrostatic loads can act vertically on structural members such as floors, decks, and roofs, and can act laterally on upright structural members such as walls, piers, and foundations.