SPATIAL VARIABILITY OF RUNOFF AND SOIL PROPERTIES ON SMALLWATERSHEDS IN SIMILAR SOIL-MAP UNITS

摘要

Soil hydraulic property information is important for watershed modeling of runoff, water quality, and erosion. The source of soils information for these data 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 much higher on one watershed compared with the other. The soil map generally available to a practitioner for the watersheds 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 differences in watershed response to precipitation. Geologic conditions in the higher-yielding watershed may also be a factor. The results suggest that deterministic and random spatial variability of soil information within soil map units (at small scales) would be necessary for adequately modeling watershed runoff. The study has implications for watershed model development, GIS, and precision-farming applications.