IMPACT OF LANS USE CHANGES ON STREAMFLOW AND FLOW CHARACTERISTICS OF PASAK BASIN

Abstract

The impacts of land-use changes on streamflow characteristic of Pasak river basin were investigated basing on nineteen-year of observed runoff discharge corresponding to changes of forest area during 1973 to 1991. The regression analysis was applied in determining their relationships, Results indicated that during studied period forest area decreased from 50 percent to 25 percent for the upper part and from 32 percent to 17 percent for the entire Pasak basin. Relationship between streamflow and rainfall was linear and varied directly to annual rainfall. Land-use change during the mentioned period increased quantity of wet flow in the upper Pasak but almost no effect in the lower part of the basin. It was observed that about 92 percent of annual flow was occurred in wet period while only 8 percent flowed in dry season. Watershed management by vegetative rehabilitation and reservoir construction are thus needed for mitigating water shortage in this basin.