Irrigation Glossary

Water allotment A method to accurately and fairly estimate a total volume of water that should be allocated to a site.

Water allotment adjustment factor Factor used in the equation to predict Water allotment.

Water hammer Shock wave created when the flow of water in a piping system suddenly stops (or changes speed). Usually the result of a fast-closing (or opening) valve.

Water pressure In irrigation, pressure describes the amount of energy available to move water through a pipe, sprinkler or emitter.

Water holding capacity {in./in., in./ft, mm/m } Total amount of water held in the soil per increment of depth. It is the amount of water held between field capacity and oven dry moisture level. (NRCS, 1997)

Water meter Device used to measure to flow of water.

Water rights State administered legal rights to use water supplies derived from common law, court decisions, or statutory enactments.

Water table Upper surface of a saturated zone below the soil surface where the water is at atmospheric pressure.

Water window Time of day available for irrigation to occur.

Weir Flow measuring device for open-channel flow. Weirs can be either sharp-crested or broad-crested. Flow opening may be rectangular, triangular, trapezoidal (cipolletti), or specially shaped to make the discharge linear with flow depth (sutro weir). Calibration is based on laboratory ratings.

Wet weight (of soil sample) Weight of soil sample and included soil moisture.

Wetted area Surface area wetted at completion of irrigation.

Wetted diameter Average diameter of the area wetted by an irrigation sprinkler operating in still air. Preferred term diameter of throw.

Wetting agent Chemical used to reduce the surface tension of a liquid causing it to make better contact with the desired target.

Wiper seal A rubber or plastic gasket in pop-up spray heads that keeps dirt and debris out of the mechanism.

Wilting point Moisture content of the soil after the plant can no longer extract moisture at a sufficient rate for wilted leaves to recover overnight or when placed in a saturated environment.

Winterization Process of removing water from the irrigation system before the onset of freezing temperatures.

Wire gauge (One of several) standard units of measure for wire size. The larger the gauge number, the smaller the wire.

Work Work done by a force on a particle is defined as the product of the magnitud e of the force and the distance through which the particle moves. In hydraulic systems, it can be calculated as the product of the pressure and flow rate.

Working pressure Pressure of the irrigation system during operating. Synonymous with dynamic pressure.

Working storage Amount of water available in the soil profile for plant use after consideration of MAD.