Do upland conservation measures reduce watershed sediment yield?

Authors: Garbrecht, Jurgen; Starks, Patrick

Submitted to: Environmental and Water Resources Institute World Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2008
Publication Date: 5/31/2008
Citation: Garbrecht, J.D., Starks, P.J. 2008. Do upland conservation measures reduce watershed sediment yield? Proceedings of the Environmental and Water Resources Institute World Congress, May 17-21, 2008, Kansas City, Missouri. 2008 CD-ROM.

Interpretive Summary: Past soil and water conservation research has demonstrated the effectiveness of conservation practices on cropland to reduce overland soil erosion and sediment delivery to channels. However, soil conservation and channel stabilization may not always translate into an immediate sediment yield reduction at the outlet of a large watershed. Hence, the apparent disconnect between upstream conservation practices and reduction of watershed sediment yield, at least within customary project durations of a few years. In this study, impacts of conservation activities on reducing sediment yield was demonstrated by contrasting sediment yield and discharge measurements taken by the USGS on the Fort Cobb Reservoir watershed during 2004-2008 with similar measurements taken more than half a century earlier. A substantial reduction in annual sediment yield between 1943-1948 and 2004-2008 was uncovered and related to conversion of cropland to rangeland and to the targeted implementation of conservation practices in the second half of the 20th century. Thus, while it may be difficult to identify immediate impacts of upstream conservation practices on watershed sediment yield, this study demonstrated that targeted and sustained conservation efforts in Oklahoma can, in time and with some delay, lead to a sizable reduction in sediment yield at the watershed outlet.

Technical Abstract: Implementation of conservation measures do not always result in an immediate and measurable sediment yield reduction at the outlet of large watersheds. In this study, instantaneous suspended sediment and discharge measurements, taken in 1943-1948 and again in 2004-2008, in the Fort Cobb Reservoir watershed were used to estimate the downstream cumulative effects of 60 years of conservation practices on sediment yield. The analysis showed a substantial reduction in mean annual sediment yield between 1943-1948 and 2004-2008. This reduction was attributed to the gradual implementation of land use conversion and broad range of conservation measures over a 60 year time span.