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Document Type

Thesis - University Access Only

Award Date

2012

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Suzette Burckhard

Abstract

Soil erosion has negative effects including: 1) loss of soil productivity, 2) water quality degradation, and 3) reducing capacity of reservoirs by deposition. For this research, the Soil and Water Assessment Tool (SWAT) model was used in the estimation of flow and sediment yield on a daily time step to evaluate the water quality improvements achieved through the implementation of best management practices (BMPs) in Ash Creek. Ash Creek is a small un-gauged watershed located in western South Dakota and is a tributary to the Bad River. Watershed characteristics, management information, and weather data was collected for a period of October 1, 1991 through September 30, 1993. Delineation of the watershed was based on the three primary inputs: digital elevation model (DEM), land use-land cover, and soils map. Erosion of gullies on rangeland and falling streambanks are the primary sources of sediment. Overgrazing of rangeland in the Bad River watershed disturbs the soil which increases runoff, accelerates erosion, and increases sediment yield. Two different land use scenarios were performed in this study to determine the effects of varying grass species on streamflow at the outlet. Scenario 1 is the baseline scenario and represents rangeland dominated by western wheatgrass, a mid-grass species. Scenario 2 was performed using a mix of warm and cool season grasses to symbolize a range seeding BMP. Rangeland management BMPs were simulated by altering the runoff curve number to represent areas of poor, fair, and good ground cover. Implementation of stream BMPs, such as riparian zone management, was simulated by modifying Manning’s n roughness coefficient. The model outputs were then compared to the baseline condition. A direct comparison of simulated flow and observed flow could not be performed for this study, due to lack of a monitoring station at the outlet. Results of this analysis show that annual average discharge and sediment yield at the outlet of the sub-watershed was greater during the pre-BMP condition as compared to the post-BMP condition, indicating the effectiveness of BMPs at reducing discharge and sediment. This reduction in flow and sediment yield occurred due to improved vegetation, which increased infiltration rates. As vegetative cover increases the sediment filtering processes are enhanced and infiltration takes place. An increase in evapo-transpiration (ET) through Scenario 2 also demonstrated reduced surface runoff and decreased streamflow. The results are presented as percent reductions in annual average streamflow and sediment yield, as measured at the outlet of Ash Creek, to represent the efficiency of BMPs in reducing nonpoint-source pollution.

Library of Congress Subject Headings

Streamflow -- South Dakota -- Bad River Watershed -- Simulation methods
Sediment transport -- South Dakota -- Bad River Watershed -- Simulation methods
Runoff -- -- South Dakota -- Bad River Watershed -- Simulation methods
Range management

Description

Includes bibliographical references (pages 82-85)

Format

application/pdf

Number of Pages

129

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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