Above ground plots at the MAFES-Holly Springs Experiment Station for studying impacts of seepage on erosion

Authors: Wilson, Glenn; Wells, Robert - Rob; Dabney, Seth; Momm, Henrique; Hudspeth, Joe; Gregory, Edgar; SAUNDERS, RANDY - Mississippi Agricultural And Forestry Experiment Station (MAFES)

Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 4/25/2012
Publication Date: 4/25/2012
Citation: Wilson, G.V., Wells, R.R., Dabney, S.M., Momm, H.G., Hudspeth, J.A., Gregory, E.A., Saunders, R. 2012. Above ground plots at the MAFES-Holly Springs Experiment Station for studying impacts of seepage on erosion. Laboratory Publication. pp. 1-83.

Interpretive Summary: Sediment is the most common contaminant causing impairment of streams in the United States. In many areas, the dominant source of sediment is gully erosion. Consideration for subsurface flow contributions to these erosion processes has largely been neglected in assessments and prediction technologies due to the lack of experimental observations and insufficient understanding of the governing processes. A common feature often associated with subsurface flow contributing to gully initiation is the occurrence of a water-restricting layer that perches water. The objective of this report is to describe the facilities constructed at the North Mississippi Branch of the Mississippi Agriculture and Forestry Experiment Station (MAFES) at Holly Springs, Mississippi (HSES) to study seepage effects on runoff, erosion, and gully formation under a variety of topographic, soil, landuse, and erosion control conditions. Six existing plots at HSES were selected for conversion into above ground seepage erosion plots because of the existing runoff collection and measurement systems. By utilizing a common inner wall, the new above ground plots were enlarged to 5.49 m wide and elongated from the endplate upslope to 18.29 m to produce a 0.1 ha plot area. In addition, the side walls were elevated with distance from the endplate to change the slope from the original 3.1% to 10.0%. The back wall was designed to contain a water reservoir for inducing seepage into the plot center (convergent) area. A 15 cm thick compacted clay layer was placed above a base layer and extended from the back wall to 10.7 m downslope then tapered off to 0 m thick at 12.2 m downslope. Loess topsoil material was placed above the clay layer with the depth tapering off from between 45 to 60 cm thick at the back wall, depending upon the surface configuration, down to 0 cm thick where the clay layer reaches the surface at 10.7 m downslope. The above ground facilities described in this report were designed and constructed to fill the knowledge gap in the area of subsurface flow impacts on ephemeral gully erosion. Ephemeral gully erosion is a critical problem that significantly damages and deteriorates agricultural lands worldwide yet little mechanistic work has been done on the subsurface flow processes contributing to gully initiation. Basic research and resulting prediction technology are still in the developmental stage. These facilities will enable the quantification of the impact of seepage on erosion rates and gully formation under controlled hydrologic conditions for a wide range of soil and landuse conditions.

Technical Abstract: Sediment is the most common contaminant causing impairment of streams in the United States. In many areas, the dominant source of sediment is gully erosion. Consideration for subsurface flow contributions to these erosion processes has largely been neglected in assessments and prediction technologies due to the lack of experimental observations and insufficient understanding of the governing processes. A common feature often associated with subsurface flow contributing to gully initiation is the occurrence of a water-restricting layer that perches water. The objective of this report is to describe the facilities constructed at the North Mississippi Branch of the Mississippi Agriculture and Forestry Experiment Station (MAFES) at Holly Springs, Mississippi (HSES) to study seepage effects on runoff, erosion, and gully formation under a variety of topographic, soil, landuse, and erosion control conditions. Six existing plots at HSES were selected for conversion into above ground seepage erosion plots because of the existing runoff collection and measurement systems. By utilizing a common inner wall, the new above ground plots were enlarged to 5.49 m wide and elongated from the endplate upslope to 18.29 m to produce a 0.1 ha plot area. In addition, the side walls were elevated with distance from the endplate to change the slope from the original 3.1% to 10.0%. The back wall was designed to contain a water reservoir for inducing seepage into the plot center (convergent) area. A 15 cm thick compacted clay layer was placed above a base layer and extended from the back wall to 10.7 m downslope then tapered off to 0 m thick at 12.2 m downslope. Loess topsoil material was placed above the clay layer with the depth tapering off from between 45 to 60 cm thick at the back wall, depending upon the surface configuration, down to 0 cm thick where the clay layer reaches the surface at 10.7 m downslope. The above ground facilities described in this report were designed and constructed to fill the knowledge gap in the area of subsurface flow impacts on ephemeral gully erosion. Ephemeral gully erosion is a critical problem that significantly damages and deteriorates agricultural lands worldwide yet little mechanistic work has been done on the subsurface flow processes contributing to gully initiation. Basic research and resulting prediction technology are still in the developmental stage. These facilities will enable the quantification of the impact of seepage on erosion rates and gully formation under controlled hydrologic conditions for a wide range of soil and landuse conditions.