Estimating Culvert Scour in Cohesive Material

An investigation of scour at culvert outlets in a cohesive bed material is presented. Twelve experiments of 1000 minutes duration were conducted using a cohesive bed material. Culvert 27.3 cm (10-in.), 35.6 cm (14-in.) and 45.7 cm (18-in.) diameters were tested with discharges ranging from 0.054 m³/sec + 0.824 m³/sec (1.91 cfs to 29.13 cfs). The tailwater elevation was maintained at 0.45 D ± 0.05 D above the culvert invert where D is the diameter of the culvert. The results yielded a series of empirical relationships expressing the depth, width, length and volume of scour as a function of the culvert diameter, culvert outlet velocity, soil plasticity index, soil shear strength and fluid density. General observations concerning scour hole formation, growth and stabilization are reported.