Surface depressions are important topographic features of watersheds, which can alter watershed water balance by affecting surface runoff generation and other hydrologic processes. To quantify surface runoff dynamics influenced by depressions, various efforts have been made to improve the surface delineation of depressions. However, it is a challenge to incorporate the spatial variabilities of land use and soil properties across identified contributing areas of depressions in a semi-distributed watershed-scale hydrologic model. To address this issue, the concept of hydrologic response units (HRUs), the basic modeling units in the Soil and Water Assessment Tool (SWAT), was employed and redefined by taking into account the spatial distributions of depressions and their associated contributing areas. The redefined HRUs were classified as (1) depressional HRUs and (2) regular HRUs. Both contributing areas and the variabilities of land use and soil properties among HRUs were considered in the simulation of inflows of depressions from the depressional HRUs. Specifically, a three-step process was performed. First, a surface delineation algorithm was utilized to identify the topographic features of depressions and determine the required parameters for all depressional HRUs. Next, a preprocessing program was developed to generate readable files for the redefined HRUs. The redefined HRUs were eventually incorporated into an enhanced SWAT model. This modeling approach was applied to a depression-dominated watershed in North Dakota. The results demonstrated the impacts of spatial variabilities of land use and soil properties on the modeling of the watershed hydrologic processes under the influence of surface depressions.
.jpg "Tiansong Qi (he/him/his) photo")
