Hydrology
- The science of hydrology deals with the occurrence and distribution of water over and above the earth’s surface.
- Such a study is based on meteorology, geology, agricultural physics, chemistry, botany and the various data obtained based on the observation and measurement.
- From the study of data, it is necessary to calculate the mean rainfall for a period of at least 20 to 30 years and to note the frequency of dry years.
- Various data obtained are useful in predicting the availability of yearly average of stream flow of water and its head at a particular site.
- It also helps in deciding the expected average output of a hydro-electric power plant.
- The minimum stream flow helps in estimating the availability of minimum power and the maximum stream flow data helps in the design of spill way.
- Such data is also helpful in the design of required capacity of storage reservoir.
Hydrological Cycle :
A hydrological cycle deals with the rainfall and run-off study. The cyclic movement of water involves the following :
- Evaporation of water from sea to atmosphere.
- Precipitation of vapour from atmosphere.
- Flow of water from rivers back to sea.
The water which precipitates from atmosphere may be in the form of rain fall, snow fall, dew and mist. Out of the total precipitation, some water is evaporated and infiltrated into soil to form underground storage. The remainder of the rain water flows on the ground surface of the catchment area to form the stream and it is called run-oft.
This rain water run-off over the ground surface which makes its way towards the streams, lakes, rivers and sea.
The run-off of a catchment area is the total quantity of water which flows into a stream or into a reservoir during a specified period. It is measured in terms of centimetre of water over catchment area. Thus the total volume of water can be calculated. It helps in designing and planning of power plants.
Flow Duration Curve and Power Duration Curves :
Flow duration curves are plotted by taking the magnitudes of run-off on the ordinate against the percentages of time taken on abscissa. Thus it is another method of representing the run-off data for a given of time.
If we take the potential power contained in a stream flow on ordinate and time on cs, such plot of curves are called power duration curves.