Headwall Influence on Scour at Culvert Outlets

This study investigates headwall influence on local scour downstream of culvert outlets. Scour holes produced by discharging jets of varying duration and magnitude through circular culverts onto a horizontal sand bed were observed and mapped. The bed material was a uniform sand with a mean grain diameter d₅₀ = 1.86 mm and a standard deviation σ = 1.33. The culvert diameter was 102 mm (4 in.). A series of expressions are developed describing the depth, width, length, and volume of scour hole as a function of time, discharge intensity, and headwall conditions. Results are presented in equation and graphical form. A criterion is presented for the design depth of a headwall at culvert outlets.