On calculation of amount of available surface water

This paper presented a method for calculating quantity of available surface water based on evaluation of other presently usable methods. Difference obtained by subtracting amount of unavailable surface water from that of total surface water corresponds to the available portion. Unavailable water is composed of ecological runoff and discardedwater in flood season. Least basic flow in non-flood season turns to ecological runoff. A part of the discardedwater serves as ecological runoff in flood season and the other part is unmanageable water. The calculation of discarded water is based on discardedwater coefficient. Reasonableness of this method has been proved by our investigation in various regions.