|NOUWAKPO, SAYJRO - Purdue University|
|Huang, Chi Hua|
Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 1/31/2011
Publication Date: 9/18/2011
Citation: Nouwakpo, S.K., Huang, C. 2011. Tools for ephemeral gully erosion process research [abstract]. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE), September 18-21, 2011, Anchorage, Alaska, 2011 CDROM.
Technical Abstract: Techniques to quantify ephemeral gully erosion have been identified by USDA Natural Resources Conservation Service (NRCS) as one of gaps in current erosion assessment tools. One reason that may have contributed to this technology gap is the difficulty to quantify changes in channel geometry to assess the amount of erosion from the gully channels. Another reason that may have also contributed to the NRCS’ interest in ephemeral gully erosion assessment is the fact that fields implemented with reduced tillage or no-till may have mitigated the surface erosion problem but some of these fields still have ephemeral gullies. Since most conservation practices are designed to minimize erosion from raindrop impact and flow shear as a part of the surface hydrologic processes, gullies at no-till field indicates that subsurface hydrology may have contributed to the formation of gullies. Research efforts in ephemeral gully erosion are also lagging behind those invested into interrill and rill erosion processes. As a result, most hydrology and soil erosion models lack adequate tools to address ephemeral gully initiation and development. Most gully erosion researchers and land conservation specialists agree that there is a need for more research to better understand the processes involved in ephemeral gully initiation and development. Nevertheless, the data collection task is rendered difficult by the size and complexity of ephemeral gullies, thus creating a need for the development of research tools and methodologies suitable for studying these erosion processes. In our ephemeral gully research, we have developed and tested field and laboratory research tools and methodologies that address the specific nature of ephemeral gullies. To quantify soil loss, geometry and volume information on gully channels, we have developed a simplified photogrammetric procedure to reproduce the geometry of the gully channel. In the proposed procedure, the coordinates of ground control points, needed for conventional photogrammetry to provide a referencing scale, were acquired with an independent photogrammetric technique without using survey grade equipment. This simplification minimized the need to bring survey equipment to the field when acquiring photogrammetric images. We have successfully tested this procedure to digitize sections of two gully systems in Kansas and use it routinely in the laboratory on a soil box designed to track the progression of channel initiation and flow network. To better understand the relative contribution of surface and subsurface flows in ephemeral gully initiation and evolution, we have built a 9.75-m long by 3.66-m wide laboratory box with controllable surface and subsurface hydrology. The box was designed to represent a section of a hillslope where we can control all the surface and subsurface hydrologic components, i.e., near-surface drainage/seepage gradient, rainfall, surface runon and subsurface interflow from a hypothetical upslope segment. By varying surface and subsurface conditions in the soil box, we will be able to quantify the relative importance of surface and subsurface flow in the initiation and evolution of ephemeral gully. The development of a control system where we can quantify how surface and subsurface hydrology contributes to the ephemeral gully initiation and a field tool to acquire the geometry of gully channels will provide the needed data sets in developing a model to quantify ephemeral gully erosion.