TABLE OF CONTENTS Hydraulic structures are used to control and manage the flow of water in natural and built systems. They include flow measurement structures such as weirs, conveyance structures such as culverts, and flood control structures such as dams. In this chapter, we will consider several types of hydraulic structures associated with open-channel flow.
Measurement of flow in open channels is essential for better management of limited supplies of water. Accurate measurement practices help provide equitable distribution of water between competing demands, and conserve the water supplies by minimizing waste due to excess delivery. Most flow measurement structures are emplaced in a channel. They are used to determine the discharge indirectly from measurements of the flow depth.
A sharp-crested weir is an overflow structure consisting of a thin, vertical plate with a sharp-edged crest mounted perpendicular to the flow direction, as shown in Figure 6.1. The flow accelerates as it approaches the weir, resulting in a drop ( drawdown) in the water surface. The water does not contact or cling to the downstream weir plate, but springs clear. The falling sheet of water springing from the weir plate is called the nappe. The section cut with a sharp upstream corner into the thin plate is called the weir notch or the overflow section. The depth measurements are taken at an upstream section not affected by the drawdown. This section is called the approach section, and is located at a distance...
