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item Bingner, Ronald - Ron

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/5/2002
Publication Date: 7/5/2002
Citation: Yuan, Y., Bingner, R.L. 2002. Determination of topographic parameters for application of hydrologic and water quality models on flatland watersheds. ASAE Annual International Meeting, ASAE Paper No. 02-2161, 19 pp.

Interpretive Summary: A significant amount of agricultural crops are grown on flatland watersheds. Unfortunately, existing elevation maps are not detailed enough to capture the field slopes needed for use in large-scale watershed models through automated topographic tools. Thus, alternative methods are needed to determine topographic parameters from flatland watersheds for use in watershed models. The watershed models can then be used to evaluate the best management practices (BMPs) that are suitable for any particular watershed in order to reduce non-point source pollution entering rivers and streams. This paper details a procedure that combines the use of digitized land-use maps with on-site surveys to quickly develop the database needed to simulate a flatland watershed system. Comparisons of simulated and measured runoff and sediment yield for a Mississippi Delta watershed were nearly identical. This approach, when used with watershed modeling technology, is important to local, state, and federal watershed management planners who are required to determine the impact non-point source pollution from agricultural watersheds has on the impairment of rivers and streams.

Technical Abstract: Watershed models have been recognized as a powerful tool in watershed evaluations for Best Management Practices (BMPs) recommendations and Total Maximum Daily Loading (TMDL) allocation. However, determining the required input parameters for model application can be difficult and time-consuming, especially for large watershed systems. Geographic Information Systems (GIS) provides tools to generate, manipulate, and spatially organize disparate data for distributed modeling. Unfortunately, for many areas, existing digital elevation models (DEMs) do not adequately represent a watershed because the elevation resolution of the watershed is not sufficient for flat areas to use tools for automatic watershed delineation; in addition, DEMs may not reflect the current condition of watershed because of human activities such as farmers leveling their lands and forming their own drainage ditches. In this paper, an alternative method is introduced to produce the needed topographic parameters for the application of AnnAGNPS on the Mississippi Delta MSEA Beasley watershed in central Mississippi. The simulated 25-year annual average runoff and sediment yield was 21.7 inches and 3.57 tons/ac,yr., respectively, compared to the monitored three-year annual average runoff and sediment yield of 22.3 inches and 4.1 tons/ac.yr, respectively. Providing long-term annual runoff and sediment yields simulations from agricultural watersheds is vital in determining the most appropriate BMPs that reduces non-point source pollution into rivers and streams.