A simulation of rill bed incision processes in upland concentrated flows

Authors: QIN, CHAO - Northwest Agricultural & Forestry University; ZHENG, FENLI - Northwest Agricultural & Forestry University; Zhang, Xunchang; XU, XIMENG - Northwest Agricultural & Forestry University; LIU, GANG - Northwest Agricultural & Forestry University

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2018
Publication Date: 2/21/2018
Citation: Qin, C., Zheng, F., Zhang, X.J., Xu, X., Liu, G. 2018. A simulation of rill bed incision processes in upland concentrated flows. Catena. 310-319. https://doi.org/10.1016/j.catena.2018.02.013.
DOI: https://doi.org/10.1016/j.catena.2018.02.013

Interpretive Summary: Quantifying rill bed incision provides fundamental information for process-based erosion modeling, while the mechanisms before, during and after headcut incision are still unclear. Thus, experiments were conducted to examine rill bed incision processes in upland concentrated flows. DEMs (2 mm × 2 mm resolution) obtained by photogrammetry were used for rill bed morphology analysis. Rill channel (2.0 m-long, 0.08 m-wide and 0.15 m-deep) with two slope gradients (15° and 20°) and four inflow rates (1.0, 2.0, 3.0 and 4.0 L min-1) were subjected to clear-water overland flow. The results showed that sediment delivery, rill bed incision rate and average final rill depth increased with inflow rate and bed slope. Sediment delivery increased from 0.060 to 0.226 kg min-1 per 1 L min-1 inflow increase and from 0.043 to 0.207 kg min-1 when bed slope increased from 15° to 20°. In a well-developed rill channel, rill bed incision could be divided into three phases: the pre-headcut formation, headcut incision and post-headcut incision. Headcut incision phase, which only accounted for less than 15% of total experimental time, produced more than 65% of rill bed sediment. In the pre-headcut formation phase, rill flow velocity, shear stress and stream power increased with increases of inflow rate and slope gradient. Conversely, flow velocity showed no evident trend with increased inflow rate and bed slope during headcut incision phase. Rill depth could be predicted by a non-linear function based upon soil characteristics, rill flow shear stress, headcut height and advancing rate. Sediment delivery showed a power function with the product of inflow rate and squared bed slope. Because rill bed incision is dominated by headcut advancing and incision, practices for controlling headcut initiation should be implemented to decrease hillslope soil loss. This information would be useful to soil conservationists to manage rill erosion in agricultural fields.

Technical Abstract: Quantifying rill bed incision provides fundamental information for process-based erosion modeling, while the mechanisms before, during and after headcut incision are still unclear. Thus, experiments were conducted to examine rill bed incision processes in upland concentrated flows. DEMs (2 mm × 2 mm resolution) obtained by photogrammetry were used for rill bed morphology analysis. Rill channel (2.0 m-long, 0.08 m-wide and 0.15 m-deep) with two slope gradients (15° and 20°) and four inflow rates (1.0, 2.0, 3.0 and 4.0 L min-1) were subjected to clear-water overland flow. The results showed that sediment delivery, rill bed incision rate and average final rill depth increased with inflow rate and bed slope. Sediment delivery increased from 0.060 to 0.226 kg/min per 1 L/min inflow increase, and from 0.043 to 0.207 kg/min when bed slope increased from 15° to 20°. In a well-developed rill channel, rill bed incision could be divided into three phases: the pre-headcut formation, headcut incision and post-headcut incision. Headcut incision phase, which only accounted for less than 15% of total experimental time, produced more than 65% of rill bed sediment. In the pre-headcut formation phase, rill flow velocity, shear stress and stream power increased with increases of inflow rate and slope gradient. Conversely, flow velocity showed no evident trend with increased inflow rate and bed slope during headcut incision phase. Rill depth could be predicted by a non-linear function based upon soil characteristics, rill flow shear stress, headcut height and advancing rate. Sediment delivery showed a power function with the product of inflow rate and squared bed slope. Because rill bed incision is dominated by headcut advancing and incision, practices for controlling headcuts initiation should be implemented to decrease hillslope soil loss.