Energy Dissipation in Eighteen-Foot Drop Broken-Back Culvert under Open Channel Flow Conditions

Abstract

This paper investigates reduction in degradation downstream of broken-back culverts by forming a hydraulic jump. A model was built in the laboratory focusing on a drop between inlet and outlet of 18 feet. Three flow conditions simulated included 0.8, 1.0 and 1.2 times the culvert depth. The hydraulic jump created in the culvert is classified as an "oscillating jump." To locate the jump near the toe, different sill and friction block arrangements were tested. The length of the culvert was 150 feet. In the broken-back culvert, a slope of 1 (vertical) to 2 (horizontal) was used for ease of construction, with the flat part at a one percent slope. The best option to maximize energy dissipation is to use one 5 foot sill located 43 feet from the outlet. The length of the culvert can be reduced by 40 feet. The calculated energy dissipation of the culvert was 66 percent.