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Title: IMPACT OF FLOOD RETARDING STRUCTURES ON SIMULATED STREAMFLOW FOR VARIOUS SIZED WATERSHEDS UNDER VARYING CLIMATIC CONDITIONS

Author
item Van Liew, Michael

Submitted to: Hydrology and Water Resources International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2003
Publication Date: 10/1/2003
Citation: VAN LIEW, M.W. IMPACT OF FLOOD RETARDING STRUCTURES ON SIMULATED STREAMFLOW FOR VARIOUS SIZED WATERSHEDS UNDER VARYING CLIMATIC CONDITIONS. PROCEEDINGS OF GIS AND REMOTE SENSING IN HYDROLOGY, WATER RESOURCES AND ENVIRONMENT. 2003. v. 1. p. 1-9.

Interpretive Summary: Small earthen dams referred to as flood retarding structures (FRSs) represent one of the most effective methods for reducing damages caused by flooding and sedimentation from agricultural land. The Little Washita River Experimental Watershed (LWREW) in southwestern Oklahoma, which contains 42 FRSs, provides an experimental setting to better understand the impacts of the FRSs on streamflow characteristics. Five subwatersheds on the LWREW ranging in size from 33 to 610 square kilometers were investigated in this study. Thirty-three years of rainfall data, along with computer simulations, were used to determine changes in the annual, monthly, and daily streamflow characteristics at the outlet of the subwatersheds as a result of the FRSs for dry, average, and wet climatic conditions. Results of the study show that installation of the flood retarding structures has likely brought about small decreases in average annual streamflow of about 7.6%, 3.1%, and 0.6%, respectively, for the dry, average, and wet climatic conditions. On a monthly basis, the FRSs lead to greater reductions in streamflow for the three smaller subwatersheds than for the two larger ones. The largest reductions in streamflow caused by the FRSs occur during the peak runoff months of the year: September for the dry, May for the average, and October for the wet climatic conditions. On a daily basis, the most noticeable impact of the FRSs is the reduction of peak discharges on the day of a rainstorm. However, the size of the impact of the FRSs on a daily basis varies considerably from one subwatershed to another, depending on such factors as the number of flood retarding structures, how much water they store, and how close they are to the outlet of a subwatershed. Results of this study show that for the various sized subwatersheds, the presence of the FRSs leads to average decreases ranging from 8.9% to 31%, 20% to 34%, and 22% to 39% in the largest daily peak flow that occurs during a year for the dry, average and wet conditions, respectively.

Technical Abstract: Flood retarding structures (FRSs) represent one of the most effective methods for reducing damages caused by flooding and sedimentation from agricultural land. The impacts of these structures on the streamflow regime and their effectiveness in reducing watershed floods under dry, average, and wet climatic conditions were investigated in this study. The setting for the study was the Little Washita River Experimental Watershed (LWREW) in southwestern Oklahoma that contained 42 FRSs controlling 43% of the drainage area. The Soil and Water Assessment Tool (SWAT) was used to evaluate changes in annual, monthly, and daily streamflow characteristics as a result of the FRSs for five subwatersheds on the LWREW ranging in size from 33 to 610 sq km. Model simulations indicate that installation of the flood retarding structures has likely brought about small decreases in average annual streamflow of about 7.6%, 3.1%, and 0.6%, respectively, for the dry, average, and wet climatic conditions. Simulation results obtained on a monthly basis show that in general, the impoundment structures lead to greater reductions in streamflow for the three smaller subwatersheds than for the two larger ones. The largest reductions in streamflow caused by the FRSs occur during the peak runoff months of the year: September, May, and October for the dry, average, and wet climatic conditions, respectively. The greatest impact of the FRSs is on the daily flow regime and daily peak flows. The most noticeable difference in daily discharges as a response of the FRSs to rainstorms is the reduction of peak discharges on the day of an event. However, the magnitude of the impact of the FRSs on a daily basis varies considerably from one subwatershed to another, depending on such factors as the number of impoundment structures, their storage capacities, and their proximity to the outlet of a subwatershed. Results of this study show that the presence of the FRSs leads to decreases in annual peak discharges for the subwatersheds ranging from 8.9% to 31%, 20% to 34%, and 22% to 39%, respectively, for the dry, average and wet conditions.