Runoff and soil loss relationships for the Texas Blackland Prairies ecoregion

Hydrological and soil loss data have been collected since 1937 at the USDA-ARS Grassland Soil and Water Research Laboratory near Riesel, TX. Data from the site, originally named the Blacklands Experimental Watershed, have played a vital role in the evaluation of conservation management practices to limit soil erosion and offsite herbicide transport and in the development of several watershed models used worldwide. The entire record of precipitation, runoff, sediment loss, management practices, and limited meteorological information is publicly available ( http://www.ars.usda.gov/spa/hydro-data). The data represent a valuable regional resource for use in water supply modeling, rural land development, and agricultural land management. Results of the present analyses confirmed the importance of soil–water phases to temporal runoff patterns in the Texas Blackland Prairies ecoregion. Little runoff occurs in the “dry” soil–water phase (avg. = 2–9 mm/month), but substantial surface runoff and lateral subsurface return flow occurs in the “saturated” phase (avg. = 19–28 mm/month). Strong linear relationships ( P < 0.0001) were determined between watershed size and annual peak flow rates for return intervals from 2 to 100 yr. Long-term data indicate a drastic reduction in soil loss from small grain production compared to row crop production due to the presence of soil cover in both the spring and fall high precipitation periods. Thus, utilization of a winter cover crop in row crop production or conversion from row crop to small grain production can be effective in reducing offsite transport of sediment and associated contaminants, which may be important in watersheds with substantial agricultural contribution to water quality impairment.