Rill network development on loessial hillslopes in China

Authors: SHEN, HAIOU - Jilin Agricultural University; ZHENG, FENLI - Northwest A&f University; Zhang, Xunchang; QIN, CHAO - Northwest A&f University

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2020
Publication Date: 8/1/2020
Citation: Shen, H., Zheng, F., Zhang, X.J., Qin, C. 2020. Rill network development on loessial hillslopes in China. Earth Surface Processes and Landforms. 45(13):3178-3184. https://doi.org/10.1002/esp.4958.
DOI: https://doi.org/10.1002/esp.4958

Interpretive Summary: Rills are defined as small channels of a few inches wide on slopes. Rill network development not only potentially affects hillslope and drainage network evolution, but also causes severe soil degradation. This study aimed to investigate the temporal and spatial development of hillslope rill networks with laboratory rainfall simulations and field observations. A soil pan (10.0 m long × 3.0 m wide × 0.5 m deep) on a 20 degree slope was applied three successive simulated rains at two intensities of 50 and 100 mm/h. The field observations were performed on two hillslope runoff plots at 20 degree inclination (10 m long by 3 m wide) in the bare and fallow surface treatments. Three typical erosive natural rainfall events were observed in the field, and rills were measured in detail, similar to the laboratory rainfall simulation. The results indicated that with increases in rainfall events, the rill network morphology varied from emerging formation to maturity. The index of rill bifurcation number described rill network development well. Rill networks on loessial hillslopes generally evolved into dendritic rather than parallel forms. The development characteristics of the rill network were relatively similar between the laboratory simulation and natural field conditions. The morphology of eroding rills evolved over time and space, which led to corresponding rill network development from infant to maturity. The finding will be useful to erosion modelers to simulate rill network development and to predict soil erosion using computer software

Technical Abstract: Rill network development not only potentially affects hillslope and drainage network evolution, but also causes severe soil degradation. However, the studies on rill network development remain inconclusive. This study aimed to investigate the temporal and spatial development of hillslope rill networks and their characteristics based on rainfall simulations and field observations. A soil pan (10.0 m long × 3.0 m wide × 0.5 m deep) on a 20° slope was applied three successive simulated rains at two intensities of 50 and 100 mm/h. The field observations were performed on two hillslope runoff plots at 20o (10 m long by 3 m wide) in the bare and fallow surface treatments. Three typical erosive natural rainfall events were observed in the field, and rills were measured in detail, similar to the laboratory rainfall simulation. The results indicated that with increases in rainfall events, the rill network morphology varied from incipient formation to maturity. Four rill network development indicators (rill distribution density, distance between rills, rill bifurcation number, and merging point number) exhibited different changes over time and space. Among the four indicators, the rill bifurcation number was the best indicator for describing rill network development. Rill flow energy increased and decreased cyclically on a slope ranging between ~3–4 m. Moreover, rill networks on loessial hillslopes generally evolved into dendritic rather than parallel forms. The development characteristics of the rill network were relatively similar between the laboratory simulation and natural field conditions. Over time, rill erosion control measures become increasingly difficult to implement as the rill network develops. The morphology of eroding rills evolved over time and space, which led to corresponding rill network development. Further study should quantify the impacts of rill network development on soil degradation and land development.