Effects of initial step height on the headcut erosion of bank gullies: a case study using a 3D photo-reconstruction method in the dry-hot valley region of southwest China

Headcut erosion has been recognized as one of the main processes involved in gully development in the dry-hot valley region of southwest China. To examine the effect of initial step height on headcut erosion processes, three headcuts were constructed ranging in height from 0.75 to 1.25m on an active bank gully head, and a series of scouring experiments were conducted under a flow discharge of 120Lmin(-1). The morphological evolutions of the plunge pools and soil loss volume were estimated by three-dimensional photo-reconstruction methods (3D-PR). As the step height increased, the experimental results showed that: (1) the transformed potential energy and shear stress would increase by approximately 4.89Js(-1) and 26.4Pa on average when the step height increased 0.25m; (2) the mean depth and width of the plunge pool exhibited obvious growth, and the morphology of the cross-section developed from approximately V-shaped to U-shaped; and (3) soil loss volume increased logarithmically, with total soil loss volumes of 0.076, 0.105 and 0.116m(3), respectively. Although the significant effects of the initial step height on headcut erosion were verified, further quantitative studies are required to quantify the mechanism of headcut erosion, especially for plunge pool erosion.