Increased Roughness in Reinforced Concrete Box Culverts

This paper presents results of an experimental investigation to increase roughness within the barrel of a concrete box culvert using trapezoidal-shaped corrugations with a shape similar to pavement underlay on bridge decks. Half-scale corrugations were placed on the bottom and both sides of a tilting flume 21 meters long, 0.90 meters wide, and 0.53 meters deep in Albrook Hydraulics Laboratory at Washington State University. During the experiment, wood cut to the shape of bridge decking simulated the concrete forms expected to be used in the field. Experimental flow rates ranged from 24–144 L/s. Experimental slopes ranged from 0.3–10.1%. Depths were measured with a point gage in several points upstream of corrugations, within the corrugations, and downstream of corrugations. Depths were measured at both the crest and the trough within corrugations. Manning's n was found to be dependent on the submergence ratio in a power function. In a range of submergence ratios between 1.33 and 3.0, the Manning's n ranged from 0.03–0.05 after scaling to full size. This increase in Manning's n would lead to a 40–60% velocity reduction in full scale conditions.