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2 Landform Analysis

2 2011

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Impact of upstream sediment inflow on headcut morphodynamics

Wells R. R., Bennett S. J., Alonso C. V.

Landform Analysis

2011

Vol. 17

225-227

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 decreased markedly, but sediment discharge was less affected. The headcut erosion process was arrested as sediment inflow rates increased above a threshold value. As sediment feed rate upstream of the headcut increased, sediment size fraction downstream of the headcut also increased. 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.

Evolution of rill networks on soil - mantled experimental landscapes driven by rainfall and baselevel adjustments

Gordon L. M., Bennett S. J., Wells R. R.

Landform Analysis

2011

Vol. 17

57-63

Experiments were conducted using a soil-mantled flume subjected to simulated rain and downstream baselevel lowering to quantify the evolution of rill networks. Results show that: (1) headcuts formed by baselevel lowering were the primary drivers of rill incision and network development, and the communication of this wave of degradation occurred very quickly through the landscape, (2) rill networks extended upstream by headcut erosion, where channels bifurcated and filled the available space, (3) rill incision, channel development, and peaks in sediment efflux occurred episodically, linked directly to the downstream baselevel adjustments, and (4) sediment discharge and rill drainage density approached asymptotic values with time following baselevel adjustments despite continuous application of rainfall. These findings have important implications for the prediction of soil loss, rill network development, and landscape evolution where headcut erosion can occur.