Improved Hydrologic Modeling for Depression-dominated Areas

Abstract Modeling of overland flow for a depression-dominated area is a difficult task due to the spatial distribution of depressions. Particularly, the hierarchical relationships of depressions and their variable contributing areas make the hydrologic modeling more complicated. In traditional hydrologic modeling, however, digital elevation models (DEMs) that are used to represent surface topography are often edited by filling depressions before delineation, and the impacts of depressions are considered by using certain simplified and lumped approaches. Due to such flaws, these hydrologic models fail to account for the actual dynamic influences of surface depressions. The objective of this study is to improve hydrologic modeling for depression-dominated regions by developing a new modeling framework to quantify the influence of spatially distributed depressions. To achieve this objective, a new puddle-based unit (PBU) probability distributed model (PBU-PDM) is developed and coupled with the existing Soil and Water Assessment Tool (SWAT). The PBU-PDM facilitates separate simulations for non-depressional and depressional areas, and accounts for the hierarchical relationships of depressions, their filling and spilling processes, and the dynamic variations in their contributing areas. The PBU-PDM enhanced SWAT was applied to the Upper Maple River watershed in North Dakota, and calibrated and validated using the observed data. In particular, it was also compared with the original SWAT model, which demonstrated the abilities of PBU-PDM to mimic the filling-spilling overland flow dynamics and the threshold behavior. The PBU-PDM provides improved watershed-scale hydrologic modeling, especially for depression-dominated areas.