Scour at culvert outlets in mixed bed materials.

"The study of localized scour at culvert outlets has been on-going to control and manage erosion along highway embankments. Herein is presented an investigation of scour at culvert outlets which refines and extends the state-of-the-art of predicting the dimensions of scour holes. Over 100 experiments ranging from 20 to 1000 minutes in duration were conducted in cohesive and non-cohesive bed materials. Culverts having 4-inch (10.2 cm), 10-inch (25.4 cm), 14-inch (35.6 cm) and 18-inch (45.7 cm) diameters were tested with dis- charges from .11 cfs (.003 cms) to 29.13 cfs (.82 cms). Tailwater elevations were maintained at zero, 0.25D and 0.45D +- 0.05D above the culvert inlet 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 and discharge. parameters including the shear number, equivalent depth, pipe shape, soil gradation and extent of scour were investigated. General observations concerning scour, hole formation, growth and stabilization were reported."\n