The report discusses the water availability computations under different data availability scenarios. Water availability generally refers to the volume of water available from the basin or stream at a particular point over a specified period of time. Volumetric relationship is reflected between rainfall and runoff. Many factors like 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.
There is no standard method available that can be assigned for a particular case. Choice of a methodology is made based on the availability of catchment information & purpose for which the information is being collected. The computing facilities that are available also determine the choice of the methodology.
Rainfall-runoff relationship and runoff process being a complex process varies from catchment to catchment and from time to time. As data availability becomes poorer, results obtained using the data becomes more uncertain. However, nowadays with research and development in the area of hydrology, more and more methods are being proposed to deal with scanty data availability situations.
Determination of water availability or basin yield is required for solution of a number of water resource related problems: design of water resource projects, determination of availability of water for irrigation, domestic, power supply or industrial use, adjustment of long records of runoff for varying rainfall patterns and 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: availability of sufficient length of rainfall-runoff record, availability of short-term runoff record and no record availability.
It also highlights the use of water balance modeling, stochastic and statistical modeling mainly for extension of stream flow records. The report is expected to prove a useful tool for the practicing hydrologists and field engineers involved in water resources project formulation.
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