Outlet Structure Design for Conduits and Tunnels

Abstract

This paper describes the analysis and experimental work leading to the development of design criteria for an outlet structure. The recommended design consists of a transition and stilling basin with straight diverging sidewalls. The rate of sidewall divergence is expressed as a function of the width ratio and Froude number. Design values were determined from model tests carried out for both round and square conduits. Design criteria were based upon observations on the effective position of the hydraulic grade line at the outlet, head losses in the transition, depth and velocity distribution in the transition, stability of the hydraulic jump, downstream velocity distribution and scour tendencies in the discharge channel. A major portion of the paper is devoted to details of the recommended design procedure, including the rationale behind the various recommendations. An example is worked to illustrate the procedure, and the performance data for one of the test models is included.