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Title: RUNOFF AND SOIL LOSS RELATIONSHIPS FOR THE TEXAS BLACKLAND PRAIRIES ECOREGION

Author
item Harmel, Daren
item RICHARDSON, CLARENCE
item King, Kevin
item ALLEN, P - BAYLOR UNIV

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2006
Publication Date: 12/15/2006
Citation: Harmel, R.D., Richardson, C.W., King, K.W., Allen, P.M. 2006. Runoff and soil loss relationships for the Texas Blackland Prairies ecoregion. Journal of Hydrology. 331(3-4):471-483.

Interpretive Summary: Runoff and soil erosion data have been collected since 1937 at the Grassland Soil and Water Research Laboratory, which was originally known as the Blacklands Experimental Watershed. These data have been valuable in the evaluation of agricultural conservation management practices to reduce soil erosion and loss of herbicides and in the development of several watershed models used worldwide. The entire database of rainfall, runoff, soil loss, management practices, and weather data is publicly available on the world wide web. The data represent a valuable regional resource for use in water supply modeling, rural land development, and agricultural land management. Results of this study confirmed the regional importance of changes in soil moisture within the year. Little runoff occurs in the “dry phase” when soils are dry and cracked, but substantial runoff and seepage flow occurs in the “saturated phase” when soils are saturated. Annual peak flow rates were also determined to be directly related to watershed size. Long-term data indicate a drastic reduction in soil loss from oats and wheat production compared to corn, sorghum, and cotton production due to the presence of soil cover in the high rainfall months in the fall. Thus, a return to the use of fall/winter cover crops may be warranted in watersheds where excess erosion from agricultural lands contributes to water quality pollution.

Technical Abstract: The historical discharge and sediment transport database is presented for the Grassland Soil and Water Research Laboratory, originally established in 1937 as the Blacklands Experimental Watershed. Data from the site 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://arsserv0.tamu.edu/hydata.htm). 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 (2-9 mm/month) occurs in the “dry phase,” but substantial surface runoff and lateral subsurface return flow occurs (12-28 mm/month) in the “saturated phase.” Strong linear relationships (p <0.0001) were also determined between watershed size and peak flow rates for return intervals from 2-100 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 the high rainfall months in the fall. Thus, a return to the use of fall/winter cover crops may be warranted in watersheds with agricultural contribution to water quality impairment.