ASSESSMENT OF EPHEMERAL GULLY EROSION PROCESSES
Watershed Physical Processes Research Unit
2009 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.
Using a large soil flume, rainfall simulator, and digital photography, gully network evolution was studied. Soil was packed into a large soil flume (approximately 4 feet by 8 feet), leveled then subjected to simulated rainfall. Digital photographs were taken at set intervals and used to create surface elevation maps. Initially, water infiltrated the soil then began to runoff. The runoff began to accumulate and erode the soil bed. The time sequence of photographs recorded the evolution of the gully network. Several key parameters in gully mechanics were obtained, including, but not limited to, gully width and depth, migration rate of the gully heads, and spacing of gully heads. Methods of monitoring included conference calls and email exchange of both data and experimental ideas.