How does land use/cover influence gully head retreat rates? An in‐situ simulation experiment of rainfall and upstream inflow in the gullied loess region, China

Abstract

AbstractLand use/cover plays a crucial role in gully head retreat (GHR). However, little is known about how land use/cover influences GHR rates. An in situ simulation experiment of rainfall and upstream inflow was conducted in a gullied loess region to investigate hydraulic erosion, mass movements, and linear GHR processes under three types of land use/cover (bare land, grassland, and shrub‐grass land). The results showed that the average linear GHR rates on grassland and shrub‐grass land were 87–89% and 72–81% lower than that on bare land (0.99–2.06 cm min−1), respectively. Gully heads retreat by hydraulic and gravitational erosion. In the case of hydraulic erosion, upstream runoff incision is dominant on bare land, while undercutting by on‐wall and jet flow dominates on grassland and shrub‐grass land. In the case of mass movement, collapse dominates with a frequency of 62–100%, of which gully sidewall collapse is most common, especially on bare land and it acts to widen the gully. Gully headwall collapse dominates on grassland and shrub‐grass land to cause retreat of the gully head. Overall, on bare land, upstream runoff incision dominates GHR. However, on grassland/shrub‐grass land GHR is mainly driven by the undercutting of on‐wall and jet flow and subsequent gully headwall collapses. As a consequence, the GHR length on bare land exponentially increases over time, while on grassland or shrub‐grass land, it discretely increases as an analogous step function. Moreover, the average linear GHR rate on grassland was considerably lower than that on shrub‐grass land, implying that an optimized vegetation restoration pattern enhances GHR control.