Glossary of Hydrologic Terms - H
Glossary of Hydrologic Terms - H
These definitions have been compiled from various sources, including the USGS's Water Resources Data, Weather Service Operations Manual, Chapter E-90, and Glossary of Meteorology (AMS, 1959).
- Hydrometeorological Automated Data System (HADS)
- Software which replaced the GOES Data Distribution System (GDDS) to process and distribute the GOES DCP data and CADAS data collected from DCPs and LARCs.
- hanging (ice) dam
- A mass of ice composed mainly of frazil or broken ice deposited underneath an ice cover in a region of low flow velocity.
- head
- The difference between the pool height and tailwater height, expressed in a height or in a force per area.
- head loss
- The decrease in total head caused by friction.
- head race
- A channel which directs water to a water wheel; a forebay.
- headwater erosion
- Erosion which occurs in the upstream end of the valley of a stream, causing it to lengthen its course in such a direction.
- headwaters
- Streams at the source of a river.
- Headwaters Advisory Program (ADVIS)
- A program which uses the antecedent precipitation index (API) method of estimating runoff, unit hydrograph theory and stage-discharge ratings to produce hydrologic forecasts for headwater basins.
- Headwaters advisory table
- A table developed by a river forecast center for a headwater guidance point. A precomputed matrix of values allows a forecaster to ascertain an anticipated crest or rise on a small river or stream for a variety of rainfall events and soil moisture conditions.
- headwater basin
- A basin at the headwaters of a river. All discharge of the river at this point comes only from within this basin.
- hinge crack
- Crack caused by significant changes in water level.
- hummock
- A hillock of broken ice which has been forced upward by pressure.
- hummocked ice
- Ice piled haphazardly one piece over another to form an uneven surface.
- hydraulic fill dam
- A dam constructed of materials, often dredged, that are conveyed and placed by suspension in flowing water.
- hydraulic grade line
- A line whose plotted ordinate position represents the sum of pressure head plus elevation head for the various positions along a given fluid flow path, such as along a pipeline or a ground water streamline.
- hydraulic head
- The height of the free surface of a body of water above a given point beneath the surface.
- The height of the water level at the headworks, or an upstream point, of a waterway, and the water surface at a given point downstream.
- The height of a hydraulic grade line above the center line of a pressure pipe, at a given point.
- hydraulic mean depth
- The right cross-sectional area of a stream of water divided by the length of that part of its periphery in contact with its containing conduit; the ratio of area to wetted perimeter. Also called hydraulic radius.
- hydraulic permeability
- The flow of water through a unit cross-sectional area of soil normal to the direction of flow when the hydraulic gradient is unity.
- hydraulic radius
- The right cross-sectional area of a stream of water divided by the length of that part of its periphery in contact with its containing conduit; the ratio of area to wetted perimeter. Also called hydraulic mean depth.
- hydrograph
- A graph showing the water level (i.e., stage), discharge, or other property of a river with respect to time.
- hydrograph separation
- The process where the storm hydrograph is separated into baseflow and surface runoff components.
- hydrograph survey
- An instrumental survey to measure and determine characteristics of streams and other bodies of water within an area, including such things as location, areal extent, and depth of water in lakes or the ocean; the width, depth, and course of streams; position and elevation of high water marks; location and depth of wells, etc.
- hydrologic budget
- An accounting of the inflow to, outflow from, and storage in, a hydrologic unit, such as a drainage basin, aquifer, soil zone, lake, reservoir, or irrigation project.
- hydrologic cycle
- The natural pathway water follows as it changes between liquid, solid, and gaseous states.
- hydrologic equation
- The water inventory equation (inflow = outflow + change in storage) which expresses the basic principle that during a given time interval the total inflow to an area must equal the total outflow plus the net change in storage.
- hydrologic focal point
- The person in a WFO responsible for maintaining the hydrologic program when a service hydrologist is not present.
- hydrologic model
- A conceptual or physically-based procedure for numerically simulating a process or processes which occur in a watershed.
- hydrologic service area
- A geographical area assigned to weather forecast office which embraces one or more rivers.
- hydrologic services
- A general term referring to the operations, products, verbal communications, and related forms of support provided by the NWS for the nation's streams, reservoirs, and other areas affected by surface water.
- hydrologic unit
- A geographical area representing part or all of a surface drainage basin or distinct hydrologic feature such as a reservoir, lake, etc.
- hydrology
- The applied science concerned with the waters of the earth, their occurrences, distribution, and circulation through the unending hydrologic cycle (precipitation, consequent runoff, infiltration, and storage; evaporation; and condensation). It is concerned with the physical and chemical reaction of water with the rest of the earth, and its relation to the life of the earth.
- hydrometeorologist
- An individual who has the combined knowledge in the fields of both meteorology and hydrology which enables him or her to study and solve hydrologic problems where meteorology is a factor.
- hydrometeorology
- The interdisciplinary science involving the study and analysis of the interrelationships between the atmospheric and land phases of water as it moves through the hydrologic cycle.
- hydrosphere
- The region which includes all the earth's liquid water, frozen water, floating ice, frozen upper layer of soil, and the small amounts of water vapor in the earth's atmosphere.
- hydrostatic head
- A measure of pressure at a given point in a liquid in terms of the vertical height of a column of the same liquid which would produce the same pressure.
- hyetograph
- A graphical representation of rainfall intensity with respect to time.
Return to the WGRFC Home Page
Glossary of Hydrologic Terms - H
http://www.srh.noaa.gov/wgrfc/glossary/h.html
This page maintained by SR-FWR.Webmaster
Updated June 1, 2003
www.srh.noaa.gov
