The Study of Drought on the Quality of Surface Water Resources in Kashkan Watershed

Drought is a phenomenon that threating water quality in addition to its shortage. In this paper we investigate the effect of drought on surface water quality of Kashkan watershed. For this purpose, during the collection of meteorological data and water quality data during 20 years (1987 to 2009) from Meteorology and Water Resources offices of Lorestan province, initially duration and severity of meteorological and hydrological droughts were determined by SPI, RDI and SDI Indices. Later in periods that intensity and duration of drought were more than other period, percent changes of water quality to the long-term average was calculated then agricultural and drinking water quality analysis in the form of two charts Schuler and Wilcox was performed. Also, the linear trend of data was investigated for highlighting the effect of drought on water quality changes. Results indicate that drought has significant changes in parameters of surface water resources especially EC, TDS, NA, CL and SO24.Also the results showed that water quality in terms of Schuler & Wilcox graphs has changed in effect of drought. The quality of Afarineh and Chan Anjir rivers drinking water has changed from ok classes to acceptable grade and for agricultural purposes has changed from C2S1 grade to C3S1 grade. Finally, the overall analysis of linier trend graphs shows that the increasing trend of drought has a negative impact on surface waters quality of Kashkan watershed.