INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS
Location: Watershed Physical Processes Research Unit
Title: Modulation of headcut soil erosion in rills due to upstream sediment loads
Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2010
Publication Date: December 11, 2010
Citation: Wells, R.R., Bennett, S.J., Alonso, C.V. 2010. Modulation of headcut soil erosion in rills due to upstream sediment loads. Water Resources Research. 46:W12531, doi:10.1029/2010WR009433.
Interpretive Summary: Soil erosion and sedimentation by water are major problems that reduce cropland productivity, degrade water quality, and clog water conveyance structures. The objectives of the current study were to determine experimentally the effect of an upstream sediment (sand sized) point source on the development, upstream movement, and soil losses associated with actively migrating gully headcuts (a discontinuity in the soil surface where the slope changes abruptly and is the focal point of intense erosion, similar to a water fall) in flows typical of upland and agricultural areas. This was accomplished using a laboratory flume specially designed to create actively migrating gully headcuts within soils packed under precisely controlled and quantifiable boundary conditions. The results of the study demonstrate that increased upstream sediment inflow into ephemeral gullies can influence gully dimensions, but does not impact the sediment production downstream from the gully. Downstream gullies may disappear when 60% of the total eroded sediment is added into the system upstream of the erosion site as a result of sediment filling the gully from the upstream source. This research demonstrates that gully headcut erosion is influenced by upstream sediment sources and as a result, the development of gully erosion prediction technology should include headcut erosion components that consider upstream sediment sources. As conservationists implement and select appropriate sheet & rill and gully erosion control practices they should carefully consider sediment source effects on the formation and migration of gullies as a result of these practices.
Headcut erosion can severely accelerate soil loss in upland concentrated flows and lead to significant soil degradation in agricultural areas. Previous experimental work has demonstrated that actively migrating headcuts display systematic morphodynamic behavior, and impinging jet theory can provide an excellent theoretical foundation for this erosional phenomenon. This research sought to examine systematically the effect of an upstream sediment inflow on the morphodynamics of actively migrating headcuts in upland concentrated flows. Using a specially-designed experimental facility, actively migrating headcuts were allowed to develop, and then subjected to an upstream sediment load composed of sand. As the upstream sediment feed rate increased, the size and migration rate of the headcut decreases markedly, but sediment discharge is less affected. The headcut erosion process is arrested as sediment inflow rate increases above a threshold value. As sediment feed rate upstream of the headcut increases, sediment size fraction downstream of the headcut also increase. This research suggests that headcut erosion can be greatly modulated by an upstream sediment source, further complicating the prediction of soil erosion on upland areas.