Structures for Flow Diversion, Investigation Planning and Layout (Part - 1) - Civil Engineering (CE) PDF Download

Introduction 

In order to harness the water potential of a river optimally, it is necessary to construct two types of hydraulic structures, as shown in Figure 1. These are:

1. Storage structure, usually a dam, which acts like a reservoir for storing excess runoff of a river during periods of high flows (as during the monsoons) and releasing it according to a regulated schedule.
2. Diversion structure, which may be a weir or a barrage that raises the water level of the river slightly, not for creating storage, but for allowing the water to get diverted through a canal situated at one or either of its banks. Since a diversion structure does not have enough storage, it is called a run-of-the river scheme. The diverted water passed through the canal may be used for irrigation, industry, domestic water needs or power generation.

In this lesson, we shall discuss about the planning, layout and construction aspects of diversion structures, particularly barrages.  This is because a weir, which is a raised hump-like structure across the river usually associated with small shutters for flow control (Figure 2a), may be suitable for very small diversion works but for larger rivers with more flexibility on flow control, a barrage (Figure 2b)  is desirable. As may be observed from the figures, a barrage is actually a gated form of a weir and the table below lists the relative merits of each of the structure over the other.  

FIGURE 1. Structures for harnessing water resources potential of a river

Figure 2A. Section through a weir (with falling shutters) showing well foundation.

Figure 2B. Section through a barrage (with vertical lift gate) showing raft foundation and sheet piles.
 Gate hoisting arrangement not shown.

In general, the trend in India for most of the modern water resources project involving diversion of water through a canal involves construction of a barrage, since a slightly more investment can bring in much larger benefits in the long run.  Weirs may be used for very small scale hydraulic works.

In the subsequent sections of this lesson, we shall discuss only barrages and interested readers may refer to any standard textbook for details of weirs.