Optimization of a SWAT model by incorporating geological information through calibration strategies

Abstract

Hydrological models are frequently used for water resources management. One of the most widely used is the Soil and Water Assessment Tool (SWAT). However, one weakness of SWAT is its simplicity in modeling groundwater, which might affect the representation of hydrological processes. Therefore, modeling strategies that are geared towards achieving more realistic simulations would increase the reliability and credibility of SWAT model predictions. In this study, the performance of a SWAT model in a geologically heterogeneous basin was optimized by incorporating geological properties through semi-automatic calibration strategies. Based on its geology, the basin was split into four regions, and a default calibration (Scheme I) was compared with three designed calibration schemes: a zonal calibration (Scheme II), obtaining a parameter set in each of the regions, a zonal calibration after introducing an impervious layer in an aquifuge region (Scheme III), and a final calibration scheme (Scheme IV) where an aquifer region was re-calibrated, changing a parameter controlling the required content of water in the aquifer for return flow to increase groundwater flow. The results from the four schemes were evaluated both statistically and by assessing their plausibility to determine which one resulted in the best model performance and the most realistic simulations. All schemes resulted in a satisfactory statistical model performance, but the sequential optimization in the final scheme realistically reproduced the heterogenous hydrological behavior of the geological regions within the basin. To the best of our knowledge, our work addresses this issue for the first time, providing new insights about how to simulate catchments including aquifuge substrates.