Development of alternative SWAT-based models for simulating water budget components and streamflow for a karstic-influenced watershed

Abstract

Most semi-distributed and distributed hydrological models can potentially be applied for comprehensive catchment simulations, but these models may require modifications to capture dominant hydrological processes. The Soil and Water Assessment Tool (SWAT) ecohydrological model, an open source program, provides flexibility for modification to capture different components of hydrological processes in a given catchment. In this study, two new approaches were tested to simulate the hydrological processes of a karst system in the Zagros Mountains, Iran. The major modifications used in these two methods included adjusting the percolation rates in karst hydrologic response units (HRUs) using SWAT-Maharlu Lake (SWAT-ML), and modification of the crack flow module using SWAT-Crack Flow (SWAT-CF). Hydrological datasets from 1980 to 2013 were used for calibration and validation of surface runoff, baseflow, crop yields, and actual evapotranspiration. Both modified models outperformed the standard SWAT model in simulating runoff. The respective average Nash Sutcliffe Efficiencies of the original SWAT, SWAT-ML and SWAT-CF were 0.64, 0.68 and 0.66. Also, the results showed that higher deep aquifer infiltration values were estimated in the modified models versus the standard SWAT for a karst HRU, which reflects more accurate levels of recharge to the deep aquifer. However, the results showed that karst conditions and geometry of sinkholes in karst zones did not play a major role in creation of runoff.