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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).

catchment area

See drainage basin.

calibration

The process of using historical data to estimate parameters in a hydrologic forecast techniques such as SACSMA parameters, routings, and unit hydrographs.

capillarity

1. The degree to which a material or object containing minute openings or passages, when immersed in a liquid, will draw the surface of the liquid above the hydrostatic level. Unless otherwise defined, the liquid is generally assumed to be water.
2. The phenomenon by which water is held in interstices above the normal hydrostatic level, due to attraction between water molecules.

capillary fringe

The soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches to a few feet (few centimeters to couple of meters), and it depends on the pore sizes of the materials. The capillary fringe is also called the capillary zone.

capillary zone

The soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches to a few feet (few centimeters to couple of meters), and it depends on the pore sizes of the materials. The capillary zone is also called the capillary fringe.

catchment area

An area having a common outlet for its surface runoff.

Same as drainage basin.

caution stage

The stage at which some action needs to be taken.

Centralized Automated Data Acquisition System (CADAS)

A system of two minicomputers at National Weather Service headquarters that interrogates LARCs by telephone every 6 hours and transmits the data to NWS forecast offices and river forecast centers.

channel

An open conduit either naturally or artifically created which periodically or continuously contains moving water. "Watercourse," "river," "creek," "run," "branch," and "tributary" are some of the terms used to describe natural channels.

channel inflow

Water, which at any instant, is flowing into the channel system form surface flow, subsurface flow, base flow, and rainfall that has directly fallen onto the channel.

channel lead

An elongated opening in the ice cover caused by a water current.

channel routing

The process of determing progressively the timing and shape of the flood wave at successive points along a river.

channel storage

The volume of water at a give time in the channel or over a flood plain in a drainage basin or river reach. Channel storage is large during the progress of a flood event.

channelization

The modification of a natural river channel,; may include deepening, widening, or straightening.

closed basin

A basin draining to some depression or pond within its area, from which water is lost only by evaporation or percolation. A basin without a surface outlet for precipitation falling precipitation.

closed basin lake flooding

Flooding that occurs on lakes with either no outlet or a relatively small one. Seasonal increases in rainfall cause the lake level to rise faster than it can drain. The water may stay at flood stage for weeks, months, or years.

coastal flooding

Flooding which occurs from storms where water is driven onto land from an adjacent body of water. These can be hurricanes, "nor'easters," or tropical storms, but even a strong winter storm or thunderstorm can cause this type of flooding.

columnular ice

Ice consisting of columnar shaped grain. The ordinary black ice is usually columnar-grained.

composite hydrograph

A stream discharge hydrograph which includes baseflow, or one which corresponds to a net rain storm of duration longer than one unit period.

conceptual model

A model which represents a physical process such as accumulation and ablation of a snowpack with explicit mathematical functions. Each significant physical component is represented separately rather than using a single index to explain several processes.

cone of depression

The depression, roughly conical in shape, produced in a water table, or other piezometric surface, by the extraction of water from a well at a given rate. The volume of the cone will vary with the rate of withdrawal of water. Also called the cone of influence.

cone of influence

The depression, roughly conical in shape, produced in a water table, or other piezometric surface, by the extraction of water from a well at a given rate. The volume of the cone will vary with rate of withdrawal of water. Also called the cone of depression.

confined groundwater

Groundwater held under an aquiclude or an aquifuge called artesian if the pressure is positive.

conservation storage

Storage of water for later release for usual purposes such as municipal water supply, power, or irrigation in contrast with storage capacity used for flood control.

consolidated ice cover

Ice cover formed by the packing and freezing together of floes, brash ice and other forms of floating ice.

contents

1. The volume of water in a reservoir. Unless otherwise indicated reservoir content is computed on the basis of a level pool and does not include bank storage.
2. The actual water contained in a SACSMA soil zone.

control points

Small monuments securely embedded in the surface of the dam. Any movement of the monument indicates a movement in the dam itself. Movements in the dam are detected by comparing control points location to location of fixed monuments located off the dam using accurate survey techniques.

cooperative observer

An individual (or institution) who takes precipitation and temperature observations -- and in some cases other observations such as river stage, soil temperature, and evaporation -- at or near their home, or place of business. Many observers transmit their reports by touch-tone telephone to an NWS computer, and nearly all observers mail monthly reports to the National Climatic Data Center to be archived and published.

conveyance loss

The loss of water from a conduit due to leakage, seepage, evaporation, or evapotranspiration.

corn snow ice

Rotten granular ice.

conservation pool

Storage of water for later release for usual purposes such as municipal water supply, power, or irrigation in contrast with storage capacity used for flood control.

creek

A small stream of water which serves as the natural drainage course for a drainage basin of nominal, or small size. The term is a relative one as to size, some creeks in a humid region would be called rivers if they occurred in arid regions.

crest

1. The highest stage or level of a flood wave as it passes a point.
2. The top of a dam, dike, spillway, or weir, to which water must rise before passing over the structure.

crest gage

A used to obtain a record of flood crests at sites where recording gages are installed.

crest (top) of dam

The elevation of the uppermost surface of a dam excluding any parapet walls, railings, etc.

crest width (top thickness)

The thickness or width of a dam at the level of the crest of the dam. The term "thickness" is used for gravity and arch dams and "width" for other types of dams.

critical_depth

A condition of flow where the mean velocity is at one of the critical values, ordinarily at Belanger's critical depth and velocity. Another important usage is in reference to the Reynolds' critical velocities which define the point at which the flow changes from streamline or nonturbulent to turbulent flow.

critical_rainfall_probability

The probability that the actual precipitation during a rainfall event has exceeded or will exceed the flash flood guidance value.

cross-sectional area

The area perpendicular to the direction of flow.

cubic foot per second (cfs)

The flow rate or discharge equal to one cubic foot of water per second or about 7.5 gallons per second.

cfs-day

same as second-foot day. The average flow in cubic feet per second for any time period is the volume of flow in cfs-days. Also called day-second feet.

cubic meter per second (cms)

The flow rate or discharge equal to one cubic meter of water per second.

current meter

A device used to measure the water velocity or current in a river.

curtain drain

A drain constructed at the upper end of the area to be drained, to intercept surface or ground water flowing toward the protected area from higher ground, and carry it away from the area. Also called an intercepting drain.