From the hydrologic records of over 50 years on a drainage basin of area 600 km2 , the average annual rainfall is estimated as 95 cm and the average annual runoff as 38 cm. A reservoir in the basin, having an average surface area of 1600 hectares, is planned at the basin outlet to collect available runoff for supply water to a nearby community. The annual evaporation over the reservoir surface is estimated as 120 cm. There is no groundwater leakage or groundwater inflow to the basin. Required:
Determine the available average annual withdrawal from the reservoir for water supply. (Hint: Do not include reservoir area when calculating surface runoff volume.)