Location: Watershed Physical Processes Research2013 Annual Report
1a. Objectives (from AD-416):
The objective of this effort is to assess the processes associated with ephemeral gully development through the study of: ephemeral gully evolution pertaining to ephemeral gully widths and networks; soil resistance to gully erosion; and the effect of agricultural practices on gully erosion across a range of temporal and spatial scales including the influence of above and below ground biomass. These studies will lead to new or enhanced algorithms for use in ephemeral gully erosion models. Ephemeral gully erosion represents an important and often dominant sediment source within watersheds in the U.S. and worldwide that is often overlooked when evaluating the effect of conservation practices in controlling erosion.
1b. Approach (from AD-416):
Develop and execute novel experimental programs to understand the processes leading to the initial growth and development of gullies under varying hydrologic and topographic conditions. Define the key pedologic, hydrologic, and hydrodynamic parameters that control the magnitude, morphology, and rate of soil loss, gully erosion, and landscape degradation due to gully development. Develop theory and equations to predict soil loss and gully erosion on hillslopes and agricultural fields under different management practices and integrate these into USDA watershed and soil erosion models.
3. Progress Report:
Research has been conducted to assess the efficiency of engineered log jams (ELJ) to reduce suspended sediment loads in the Big Sioux River, SD. These ELJs will be placed along the streambanks where excessive erosion is taking place. The idea is to reduce loads through bank stabilization. Laboratory experiments have shown that ELJs have a positive influence on the flow, i.e. velocities near the bank are reduced while velocities near the channel centerline accelerate; although mean flow depth and velocity remain unchanged. Research has been conducted on the location, magnitude, and spatial evolution of rill networks and ephemeral gullies on hillslopes and agricultural regions. Experiments using a large, soil-mantled flume were conducted with simulated rainfall to quantify growth, development, and spatiotemporal evolution of rills and rill networks. Rill development and extension occurred due to actively migrating headcuts. Degradation occurred very quickly and in nearly uniform bed incision throughout the network. Although supply-limited, most of the sediment was directly linked to headcut development and migration.