TR(BR)-3/98-99 : Methodology for the water availability computations under different data availability scenarios

Abstract

Water availability generally refers to the volume of water available from a basin or stream at a specified point over a specified period of time. As it is computed for a specific time period it reflects the volumetric relationship between rainfall and runoff. Many factors viz. climatic and basin characteristics affect the water availability of a basin. Time and space distribution of rainfall, its intensity and duration, surface vegetation, soil moisture, soil characteristics, topography and drainage network are some of the important factors.

Determination of water availability or basin yield is required for solution of a number of water resource related problems: i) design of water resource projects, ii) determination of availability of water for irrigation, domestic, power supply or industrial use, iii) adjustment of long records of runoff for varying rainfall patters, and iv) reservoir operation planning

This report elaborates the different data availability scenarios for computation of water availability of a basin and also provides the available methodologies under such situations. Broadly such situations can be grouped under three categories. 1) availability of sufficient length of rainfall-runoff record; 2) availability of short term runoff record and; 3) no record availability. Report also highlights the use of water balance modelling and stochastic and statistical modelling mainly for extension of streamflow records.

It is expected that this report may prove a useful tool to the practising hydrologists and field engineer involved in water resources project formulation.