Analysis of the relationship between precipitation intensity and duration and the response of the stream discharge are aided by the concept of the unit hydrograph, which represents the response of stream discharge over time to the application of a hypothetical "unit" amount and duration of rainfall (e.g., half an inch over one hour). Because the peak flow also corresponds to the maximum water level reached during the event, it is of interest in flood studies. The stream rises to a peak flow after each precipitation event, then falls in a slow recession. In storm hydrology, an important consideration is the stream's discharge hydrograph, a record of how the discharge varies over time after a precipitation event. The river's discharge at that location depends on the rainfall on the catchment or drainage area and the inflow or outflow of groundwater to or from the area, stream modifications such as dams and irrigation diversions, as well as evaporation and evapotranspiration from the area's land and plant surfaces. The catchment of a river above a certain location is determined by the surface area of all land which drains toward the river from above that point. The equation implies that for any incompressible fluid, such as liquid water, the discharge (Q) is equal to the product of the stream's cross-sectional area (A) and its mean velocity ( u ¯ is the average flow velocity ( m/s or ft/s)įor example, the average discharge of the Rhine river in Europe is 2,200 cubic metres per second (78,000 cu ft/s) or 190,000,000 cubic metres (150,000 acre⋅ft) per day.īecause of the difficulties of measurement, a stream gauge is often used at a fixed location on the stream or river.
Ī commonly applied methodology for measuring, and estimating, the discharge of a river is based on a simplified form of the continuity equation. The units that are typically used to express discharge in streams or rivers include m 3/s (cubic meters per second), ft 3/s (cubic feet per second or cfs) and/or acre-feet per day. Measurement of cross sectional area and average velocity, although simple in concept, are frequently non-trivial to determine. The area is the cross sectional area across a river and the average velocity across that section needs to be measured for a unit time, commonly a minute.
For measuring the discharge of a river we need a different method and the most common is the 'area-velocity' method. Here the discharge might be 1 litre per 15 seconds, equivalent to 67 ml/second or 4 litres/minute. Thus the water discharge of a tap (faucet) can be measured with a measuring jug and a stopwatch. The quantity may be either volume or mass. 3 Catchment effects on discharge and morphologyĪ discharge is a measure of the quantity of any fluid flow over unit time.
0 kommentar(er)
