Hydraulics of Closed Conduit Spillways Part 1. Theory and Its Application

Abstract

The closed conduit spillway is any conduit having a closed cross section through which water is spilled. The inlet and outlet may be of any type. The barrel may be of any size or shape and may flow either full or partly full. Also, the barrel may be on any slope. This broad definition includes the smallest culvert as well as the largest morning glory spillway.

The basic theory of the flow is the same for each of the many forms which the spillway may take. This paper discusses the control of the flow through closed conduit spillways by weirs, the barrel exit, tailwater, pipe, orifice, and short tube, since each of these controls may govern, at some time or other, the rate of flow through the spillway. The effect of these various controls on the performance of the spillway is explained. A means of developing a composite head-discharge curve is given. Pressures within the closed conduit spillway must sometimes be determined, so the methods for this determination are presented. A selected bibliography useful to the understanding and for the design of closed conduit spillways concludes this technical paper.