Surface depressions are one of the important impact factors of overland flow, infiltration, and other hydrologic processes. Depressions undergo filling, spilling, merging, and splitting processes under natural conditions, resulting in discontinuous overland flow and variable contributing area.

In this study, a new depression-oriented watershed hydrologic model will be developed to simulate the variation of contributing area and threshold-controlled overland flow dynamics, and this new model will be applied to the upper portion of upper Sheyenne River Watershed in the Prairie Pothole Region (PPR) in North Dakota. In the new model, the depression-dominated intrinsic changing pattern of contributing areas and the probability distribution function of their occurrences are quantified first. Such information is further used in the model to determine the contributing area, depression storage, surface runoff, and their occurrence probabilities under different rainfall conditions. The performance of the developed model will be evaluated in this study.

Project Objectives:

The objective is to develop a new depression-oriented watershed hydrologic model to simulate the variation of contributing area and threshold-controlled overland flow dynamics.

Progress:

Development of a depression-oriented hydrologic model

A depression-oriented variable contributing area (D-VCA) model has been developed in this study. The D-VCA model contains two major loops: time loop and subbasin loop. For each subbasin, a surface topographic analysis procedure was developed to estabilish the depression-dominated intrinsic dynamics of contributing areas and the relationship curves of contributing area and depression storage based on the surface topographic characteristics of the subbasin. In addition, the probability distribution of contributing areas was also determined in the surface topographic analysis procedure. The developed relationship curves and the probability distribution of contributing areas were further incorporated into the D-VCA model to simulate the threshold-controlled surface runoff generation processes.

Application to a depression-dominated watershed in North Dakota

The study area is the upper portion of upper Sheyenne River Watershed in the Prairie Pothole Region (PPR) in North Dakota, and the USGS gaging station #0505300 was selected as the final outlet of the watershed. The 10-m DEM data for the watershed has been downloaded from the USGS Nation Map. Based on the DEM data, the watershed was divided into 12 subbasins, and the topographic characteristics (e.g., depression storage capacities and areas of depressions) were calculated for each subbasin. The land use land cover and soil type for the watershed were downloaded from the National Land Cover Database (NLCD 2011) and the State Soil Geographic (STATSGO2) dataset, respectively. Based on the DEM, land use, and soil data, the SCS curve number of each subbasin was calculated. The climate data for the watershed was also acquired from the North Dakota Weather Network (NDAWN), and the observed discharge data at the watershed outlet was downloaded from the USGS National Water Information System.

Significance:

A large portion of North Dakota is dominated by pothole lakes, wetlands, and depressions, which can affect hydrologic processes and further are important to agriculture activities. This study proposes a new rainfall-runoff model for depression-dominated areas, which can be used to quantify the influence of depressions on hydrology under the changing climate. The new modeling approach would also improve our understanding of the evolution of contributing area and the mechanism of surface runoff generation.

Conference/Seminar Presentations:

     Zeng, L. and X. Chu. 2019. Modeling of Dynamics of Runoff Contributing Areas in Depression-Dominated Areas. AGU Fall Meeting, December 9-13, 2019, San Francisco, CA.

     Zeng, L. and X. Chu. 2020. Improved Hydrologic Modeling for Characterizing Variable Contributing Areas and Threshold-Controlled Overland Flow in Depression-Dominated Areas. Department of Civil and Environmental Engineering Seminar, April 8, 2020, Fargo, ND.

     Zeng, L. and X. Chu. 2020. Improved Hydrologic Modeling for Characterizing Variable Contributing Areas and Threshold-Controlled Overland Flow in Depression-Dominated Areas. Department of Civil and Environmental Engineering Ph. D. defense, November 13th, 2020, Fargo, ND.