Sediment reduction due to conservation practices at the watershed scale

Authors: Garbrecht, Jurgen; Starks, Patrick; Moriasi, Daniel

Submitted to: National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment
Publication Type: Abstract Only
Publication Acceptance Date: 7/15/2008
Publication Date: 9/5/2008
Citation: Garbrecht, J.D., Starks, P.J., Moriasi, D.N. 2008. Sediment reduction due to conservation practices at the watershed scale [abstract]. National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment, September 3-5, 2008, Oxford, Mississippi. 2008 CD-ROM.

Interpretive Summary: Abstract only.

Technical Abstract: In large agricultural watersheds, upland conservation practices and channel stabilization may not result in immediately measurable sediment reduction at the watershed outlet. Measurable reduction in watershed sediment yield depends on placement, or targeting, of conservation practices and on the fraction of cropland that is treated. Also, channels deprived of upstream sediment sources tend to respond by eroding previously stored sediment as well as their boundaries, thereby concealing conservation impacts by shifting sources of sediment. Thus, expected watershed-scale benefits are difficult to demonstrate in the field within customary project durations. Hydrologic watershed model applications can alleviate some of the cited short-comings. However, years of prior sediment storage and subsequent re-mobilization potential, channel morphologic adjustment and associated response lag are not well simulated. Thus, hydrologic watershed simulations, while practical, do not tell use how long it may take and what fraction of the full sediment reduction potential will be felt at the watershed outlet. In this study, a unique opportunity to demonstrate conservation impacts on the Fort Cobb reservoir watershed is seized upon by contrasting runoff and sediment yield measurements from the 1940s with related measurements during 2004-2007. Differences in runoff and sediment yield would be attributable to the aggregated effects of land use changes, and implementation of conservation practices. Preliminary results show a substantial reduction in sediment yield as a result of land use changes and conservation practices. While it may be difficult to measure and identify watershed conservation impacts at the short time span of a project duration, it is believed that targeted, widespread and sustained conservation efforts can lead, in time, to measurable impacts at the watershed outlet, as was the case for the Fort Cobb reservoir watershed.