Effects of Land Use Changes on Water Balance in Taleghan Catchment, Iran

In recent years, changes in catchments water balance due to land use management have become the main concern of water resources authorities in Iran. Due to rapid population growth and land use changes, especially construction of Taleghan dam, Taleghan catchment has undergone rapid changes such as urban development, declining of rangelands, and deterioration of environment and erosion of soil resources by cultivating the hilly lands along the slopes for wheat or barely production. The extent of rangeland area shrinkage is substantial: from 83% during the early stages of dam construction down to 35% by the end of the study period. The 'good' rangeland area decreased to 5.90% from 34.49% while the poor rangeland increased from 19.04 to 23.35% during the period of 1987 to 2007. These changes could potentially have devastating impacts on water balance of the catchment. The main objective of this research was to examine the effects of land use changes on water balance of the Taleghan catchment before and after the dam construction. The Soil and Water Assessment Tools (SWAT) model was applied for predicting water balance in the middle and outlet of the catchment. The main input data for simulation of SWAT are Digital Elevation Model (DEM), soil type, soil properties, and hydro-climatological data. Comparing the water balance for 1987's land use for the middle station (Joestan) and the outlet station (Galinak) showed that surface runoff was 21% of the precipitation for the upper part of the catchment and 33% at the outlet. Total groundwater and lateral flows were 37 and 19%, respectively. The water balance at the outlet was predicted for two other scenarios of 2001 and 2007. The results showed 7.3% increase in surface runoff and 11.3 and 11% decrease in the lateral flow and groundwater flow, respectively. These results indicated progressive increase in surface runoff and decline in interflow and groundwater flow. Therefore, one of the main challenges facing development planners is the control of the accelerated degradation of the natural resources that has been taking place during the last decade.