Headcut retreat resulting from plunge pool erosion in a 3D landscape evolution model

Abstract

Headcut retreat produced by plunge pools is represented using existing concepts about this type of erosion. The model estimates retreat rates, given flow, height of the headcut, upstream slope and Manning's roughness, and the relevant soil parameters (erodibility and critical shear stress). The model was analyzed to study its behavior as its input parameters changed, and its output was compared to experimental observations. Next, the plunge pool mechanism was implemented in an existing 3D landscape evolution model (CHILD) that includes other mechanisms of erosion like fluvial erosion and diffusion. The effects of headcut retreat on the landscape and of the landscape on the headcut retreat mechanism were investigated to learn what factors promote gully erosion and the extent of the impact of this type of erosion on the landscape. The results indicate that headcut retreat is most significant in zones comprising either gentle slopes or large headcut heights. Additional hydraulic conditions promoting to headcut retreat due to plunge pool erosion were found.