Mechanics of jet scour downstream of a headcut

TLDR

Scour downstream of a headcut is studied by examining how jet diffusion detaches sediment. The authors derive analytical equations for equilibrium scour depth and scour‑hole development rate, applicable to diverse jet configurations and bed materials, and validate them experimentally on two noncohesive sands and a cohesive soil. Measured and predicted scour‑depth growth rates agree, revealing that scour does not grow semi‑logarithmically with time and that depth increases rapidly until reaching 95 % of equilibrium, with graphical solutions matching the data.

Abstract

Abstract Scour immediately downstream of a headcut is analyzed by considering the effect of jet diffusion on sediment detachment. The analytical development results in equations for: 1. the equilibrium scour depth; 2. the rate of scour hole development. These equations are applicable for a variety of jet configurations and any bed material including cohesive soils. The equations are tested in laboratory simulated headcuts on bed materials consisting of two noncohesive uniform sands and one cohesive natural soil. The agreement between measured and predicted rates of scour depth increase shows that scour does not increase as a semi-logarithmic function of time. The rate of scour depth increase is very rapid for depths less than 95% of the equilibrium scour depth. Graphical solutions for the rate of scour depth increase are in agreement with the experimental measurements.