Watershed Sediment Yield Reduction through Soil Conservation in a West-Central Oklahoma Watershed

Soil conservation practices on the Fort Cobb Reservoir watershed in West-Central Oklahoma were limited before the 1950s. However, extensive soil conservation measures were implemented in the second half of the 20th century to protect agriculturally fertile but erosion-prone soils. Fortuitously, the U.S. Geological Survey (USGS) collected instantaneous suspended-sediment and discharge measurements on major tributaries within the watershed in 1943-1948 and again in 2004-2007, called pre- and post-conservation periods. These measurements offered the opportunity to compare channel suspended-sediment yield before and after implementation of conservation practices. With these measurements, a separate suspended sediment-discharge rating curve was developed for each the pre- and post-conservation period. Average annual suspended-sediment yield at a U.S. Geological Survey gauging station near the watershed outlet was estimated by evaluating each sediment-discharge rating curve with the 18-year long daily discharge record at that gauging station. Average annual suspended-sediment yield was estimated to be 760 [Mg/yr/km2] and 108 [Mg/yr/km2] for the pre- and post-conservation periods, respectively. The substantial reduction in suspended-sediment yield was related to land use and management changes and the wide range of conservation practices implemented in the second half of the 20th century. Even though it generally is difficult to identify impacts of upstream conservation practices on sediment yield at the watershed outlet during the short time span of a particular conservation project, targeted and widespread conservation efforts in the Fort Cobb Reservoir watershed have led, over 60 years, to a sizable and measurable reduction in watershed sediment yield