The validation of a gully headcut retreat model in short-term scale based on an in-situ experiment in dry-hot valley

Abstract

How to predict gully erosion rates was one of the most important issues at present. A model implemented in the Channel Hillslope Integrated Landscape Development (CHILD) model based on the shape factor (Sf) of the plunge pools, which successfully predicted the headcut retreat rates over a long timescale. But whether this model was also valid in the short-term scale? What factors affected the prediction effects of the model? These issues still need evaluation. Four gully head plots with consistent initial topography and soil types were constructed for conducting in-situ scouring experiments with different flow discharges. Eighteen tests were conducted in each plot to monitor the plunge pool growth and headcut retreat rates using an unmanned aerial vehicle (UAV) to create high-precision topographic data. The topographic parameters of the plunge pools generally increased with scouring duration and were strongly correlated with the total runoff energy consumption (0.55 < R2 < 0.92, P < 0.01). In contrast, headcut retreat was an intermittent process that suddenly migrated in a short time after relatively long stable periods lasting from 20 to 130 min. The relationships between the headcut retreat rates and total energy consumption were weaker than those with the plunge pools. As the timescale shortened, the contribution of mass failure due to gravity to headcut migration significantly increased, leading to the pool effects of the model to influence the prediction of the gully headcut retreat rates, which assumed that flow hydraulics were the key dynamics.