|Wells, Robert - Rob|
Submitted to: Congress of International Association for Hydraulic Research Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2009
Publication Date: 8/9/2009
Citation: Wells, R.R., Bennett, S.J., Alonso, C.V. 2009. Effect of upstream sediment load on headcut morphodynamics. 33rd Congress of International Association for Hydraulic Research Proceedings -- Water Engineering for a Sustainable Environment. pp 6375-6382. 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 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.
Technical Abstract: 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 they were subjected to an upstream sediment load composed of sand. As the upstream sediment feed rate increased, the size and migration rate of headcut decreases markedly, but sediment discharge is less affected. The headcut erosion process is arrested as sediment inflow rate increases above a threshold value (0.6SY). This research demonstrates that headcut erosion can be greatly modulated by an upstream sediment source, further complicating the prediction of soil erosion on upland areas.