Modelling Primary Salinity of Water Resources using a Semi-distributed Hydrologic Model

Salinity of water resources is a common problem at many river basins all over the country. Helleh River Basin (HRB) with semi-arid climate located at south of Iran is one of such basins, where primary (natural) sources such as salt diapirs and salt formations are the main salinity sources. This paper deals with developing a model for basin-scale water resources salinity analysis. The model consists of two modules of water balance and salt balance where SWAT model takes role as water balance module and the salt balance module is developed in an external programming environment. It is worth mentioning that the original version of SWAT is not capable of modeling soil and water salinity. The model is applied to Shoor River a highly saline river located at upstream part of HRB and SUFI2 algorithm is utilized for calibration and validation. Calibration is based on monthly records of discharge and TDS at Shekastian hydrometery station (located on Shoor River) associated with 1995-2000 time period. Calibration results show that for the best (parameters’) estimation, goodness-of-fit measures of R-squared (R2) and Nash-Sutcliff (NS) respectively equal 0.76 and 0.73 for discharge and 0.63 and 0.56 for TDS. Also validation is based on 2001-2003 time period’s observation where R2 and NS related to the best estimation respectively equal 0.81 and 0.71 for discharge and 0.81 and 0.65 for TDS. Results demonstrate the reliable performance of model for analyzing river basin’s water and salt regimes.