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United States Department of Agriculture

Agricultural Research Service

Title: Spatial Variability of Runoff and Soil Properties on Small Watersheds in Similar Soil-Map Units

Author
item Bonta, James

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 1998
Publication Date: N/A

Interpretive Summary: Experimental watershed data at the North Appalachian Experimental Watershed at Coshocton, Ohio were found to be significantly different for two small, adjacent agricultural watersheds that are visually similar. The generally-available soil map for the watersheds show no difference in soil map units that would explain the differences in watershed responses. This is a problem because, without knowledge of the actual differences in watershed response to precipitation, a practitioner would simulate runoff from one or both watersheds in error, costing money for purposes of the particular study. Available hydrologic and soil physical characterization data suggest that part of the explanation difference in response are soil characteristics and persistent moisture differences upstream from the outlets of the watersheds, and possibly geologic conditions in the higher-yielding watershed. The results highlight the need for including spatial variability in soil map units for use in watershed models. Furthermore, watershed models are needed in practice that incorporate the spatial variability of soil properties as input to be able to simulate the observed differences in watershed response to precipitation. Geographic information systems are often used to provide the inputs to models, and must also incorporate the spatial variability of soils information for watershed models. Users that will benefit from this investigation are the NRCS, engineering firms, and scientists working with models.

Technical Abstract: Soil hydraulic property information is important for watershed modeling of runoff, water quality, and erosion. The source of soils information is often soil-survey maps. Runoff data from two small, adjacent agricultural watersheds at the USDA-Agricultural Research Service experimental watershed facility near Coshocton, Ohio, that are visually similar, show that annual runoff can be significantly higher on one watershed compared with the other, yet the soil map available to a practitioner shows the soils for both watersheds to be mapped in the same soil series. Available hydrologic and soil-characterization data were analyzed and suggest that the soil characteristic and moisture differences in areas upstream from each watershed outlet are responsible for at least some of the difference in watershed response to precipitation, as well as geologic conditions in the higher-yielding watershed. The results suggest that spatial variability of fsoil information within soil map units would be helpful to adequately mode watershed runoff, provided a suitable model that used these types of inputs was used, and would enable persons using GIS data bases to include this variability for watershed model inputs.

Last Modified: 11/23/2014
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