New Model for Simulating Hydrologic Processes under Influence of Surface Depressions

Abstract

Surface depressions significantly influence hydrologic processes. In traditional semidistributed models, however, the entire area is connected to the outlet of a watershed and surface depressions are often lumped as a single depth to control runoff water release. As a result, hydrologic processes related to topographic characteristics of depressions cannot be directly simulated. The objective of this study is to quantify the impact of depressions on rainfall-runoff processes and the mechanism of dynamic water release from depressions. To achieve this objective, a new semidistributed depression-oriented hydrologic model (HYDROL-D) is developed. Unlike the traditional methods, a unique modeling framework is proposed in HYDROL-D to facilitate separate modeling for the depressional area (DA) and nondepressional area (NDA) of each subbasin. A DA is further divided into time-varying contributing area (CA) and ponding area (PA). A depression-dominated delineation (D-cubed) algorithm is utilized to provide specific characteristics of surface depressions (e.g., maximum depression storage and maximum ponding area at various depression levels for all subbasins), which are processed to define the characteristic areas (i.e., NDA, DA, CA, and PA), varying functions of CA and PA, and the hierarchical control thresholds for water release in HYDROL-D. The model was applied to a site in North Dakota, compared with the widely-used hydrologic modeling system Hydrologic Engineering Center, Hydrologic Modeling System (HEC-HMS), and calibrated using the observed data. The results demonstrated that because of the discontinuity caused by depressions, only a small portion of the study area contributed water directly to the outlet. The new modeling framework was able to effectively account for the dynamic processes associated with surface depressions. In addition, compared with the single threshold, multiple hierarchical control thresholds showed a better ability to reveal the mechanism of dynamic water release from depressions.