1. Our Source of Inspiration There is much that can be learned from a study of the past, for it enables us to view the present in its true perspective and is a basis for speculation as to the future. This is as true of science as of mankind. The science of hydraulics has a great history and one that is well worth recalling, in view of its service to man kind. Irrigation is the earliest form of hydraulics and has been practiced by mankind from the dawn of history. Archaeological discoveries have shown that canals, dams, and reservoirs existed in Egypt and Mesopotamia as early as 4000 B.C There have been many contributors, and space permits only a few of the more distinguished to be mentioned. Amplification is provided in the subsequent text where it is felt that knowledge of the detailed historical background would be helpful to the understanding of a particular analysis or empirical formula.

1.0 General  The design of canal involves following three major aspects:  A Irrigation and drainage canal network planning.  B Determination of discharge / capacities of  canals and drainages.  C Determination of shape and size i.e. geometrical dimensions of the proposed canal section, generally  known as design of canal section. More appropriately it can be called as design of internal section  of canal. It can be further divided in three following parts viz.  i. Design of unlined canals:  ii. Design of lined canals: or a canal may be partly lined and partly unlined.  iii. Choice between the unlined and lined canals. This aspect should be distinguished from the selection of type of lining. However, the scope of choice of lining may include both the aspects.  The design of canal section remains incomplete without the design of its embankments, either in lined or unlined canal, so the next aspect is  iv. Design of canal embankments. Still to complete the design of a canal one more aspect is required i.e.  v. Canal aesthetics and canal arboriculture.

Theoritical aspects of design has been discussed in chapter 1. Discharging capacity of canal is  computed by Manning Equation (1)and continuity Equation (2) (Para 1.4).  In the Manning's equation  V  =   R2/3  S1/2 / N (Eq. 1, Para 1.4);  N and R play most important role.  The effect of  R has been discussed in para 1.4.1, Chapter 1. In this chapter the complexities of Manning's n (or N, also known as Manning's rougosity coefficient  or simply rougosity coefficient) and some practical aspects of composite sections and velocity in best  Mehboob, trapezoidal or rectangular sectioned channels are discussed. 2.0 Manning's Rugosity Coefficient (n) Value of N depends upon a number of factors such as , surface roughness, vegetation, obstructions, type of lining, age of lining, erosion and damages in lining, curves, discharging capacity , perimeters, depth of flow, velocity etc. These are discussed below and commonly adopted values of n are given in tables 2.1 to 2.3.  

A canal of approximate discharge of less than 80 cumecs (3000 cusecs) discharge may be called a medium or low capacity canal). 3.1 Mehboob Section A Mehboob Section is only a modification of best trapezoidal section by making its complete bottom circular as shown in figure 3.1. Also see figure 1.6 and para 1.7. That is why these canals are also known as canals of zero bed width, or trapezoidal canals with curved bottom, or cup shaped canals. But these cannot be called as triangular canals with curves, as often spoken. In fact it is a truncated triangle circumscribing the semi circle. Trapezium is also a truncated triangle circum scribing a circle. More accurately it can be said as a combination of semi circular and best trapezoidal section so as to take full advantage of their hydraulic efficiency and practicability. This is such a beautiful section that the designer can never commit a mistake, even if he wants to commit a mistake. The dimensions are so geometrically fixed that no one can play with any dimension. The value of this section was realised for the first time by Er S I Mehboob (1943) in his Punjab Irrigation Branch Paper No.260" Lining of Canals". There after this canal section became well known as Mehboob Section after his name. He also stated that the most economical section i.e. the maximum area for the minimum perimeter is when the centre of the arc is at the full supply line of the section. This is also evident in figure 1.6. This is also the condition for all best hydraulic sections. This section is also useful to a higher silt carrying capacity than a wide shallow one..    

A canal of more than 80 cumecs (3000 cusecs) approximetly may be called as a high capacity canal. It has already been pointed out in chapter 1, that for the best section of any shape, R is always equal to d/2 only, and such depth is the most optimum depth. But such channels are not always practical or most economical due to many other practical reasons, (see para 4.1 and 6.3) and many times shallower depth then this depth is adopted. Typical examples are lining of existing earthen channels, given in para 6.3. All the best sections have fixed ratio of dimensions very near to the semi circle. For large discharges, radius of semi circle increases that, means depth of canal as well as velocity increases. But higher velocity is not permissible with every type of lining (see table 2.1 and para 2.3). Similarly depth also has limitation of construction, maintenance, stability of slopes, etc. see example–4.2. Because of limiting velocities and depth, deeper canal section are not practically feasible/possible. Therefore for large discharges, say more than 100 cumecs, Mehboob or best trapizodal sections are just not possible/practical, and recourse has to be taken to trapezoidal section with increased bed width then depth. This section is hydraulically inefficient or uneconomical. Larger the B/D ratio, larger is the inefficiency and section is more costly. (For Mehboob Section, B:D ratio is zero and for best trapizodal section it is much less than 1, see para 3.1, table 3.1 para 3.5 and table 3.4).

A. Rectangular Canals 5.1 Design of Best Rectangular Canals After the Mehboob and Trapezoidal canals, next best section is rectangle. This section is also generally adopted for small discharges say upto 10 cumecs (350 cusecs). This section ranks at No. 4. Yet, this is the only section most commonly adopted for flumes of discharges upto140 cumecs (5000 cusecs). Typical example is Orsang acqueduct, 1 km. long for 1140 cumecs (40000 cusecs) in ractangular sections on Narmada Canal Project, Gujrat, India, built in the years from 1990 – 2000. Such sections are common in power house canals due to limitation of space and very sharp curves. It is free from the effect of change of side slopes as in the trapezoidal canals (see para 3.3) Still some small side slope (batter) is adopted in thick masonry / concrete lining. It adds to structural stability with economy in thickness of wall and as well as hydraulic efficiency. It may still be called as rectangular section. Details of its hydraulic efficiency in comparison to semi circle, Mehboob and trapeziodal sections are discussed in chapter 1, para 1.8

6.0 General No lessons can be drawn without the experiences of the past. In fact, much of engineering, rather all sciences have developed in bits and pieces from the experiences of the past. The engineers by and large have never become wiser in one day. They have become wiser slowly and slowly with their own experiences and from the experiences of past engineering works. Wisdom lies to gain wisdom from experiences/draw lessons from the marvellous engineering works constructed so far. It helps us in a direction for further development of technological skills. Here an effort is made to draw lessons from experiences of the canals constructed in the past.  There are several aspects of such experiences. A few important aspects of studies are:  (i) Internal hydraulic sections of the canal with respect to discharge, topography, stability of side slopes, type of lining, operation and maintenance problems and their solutions etc.  (ii) Design of canals banks (embankment) with respect to discharge, depth of flow, depth of cutting /filling, below/above natural ground level, type of soil, topography, operation and maintenance, drainage of banks etc.  (iii) Canals aesthetics and arboriculture  (iv) Other utility/service of canal such as multi-objectives of hydropower, irrigation, drinking/industrial water supply, social needs of recreation, forests etc.

A brief description of IGMC is given in Para 6.6 with details of the canal sections. Here an attempt is made to review the hydraulic performance of the Main Canal. 7B.1 Study of Flow Characteristic of the Main Canal The main canal is designed for a maximum discharge of 524 m3/s at head i.e. at Km. 0. Large of number of branches, distributaries and minors off take from the main canal at different location all along the canal. These are shown in the L- section, Figure 7B.1 and a statement off taking canals is given Table 7B.1. Many distributaries such as lift canals have been planned subsequently. Also discharges of few off taking channels have been changed. A clear and updated data are not readily available. So data available are indicated in the Table and plotted in the L - section. A half bottom plan of the canal is also shown in Figure 7B.2

8.1 Design of Canal Embankments  There are two aspects of canal embankment design.  (i) The general requirement, such as free board, dowel, service/inspection road, drainage of banks etc. The aspect of free board is discussed in Para 8.2 to 8.3 and that of service/ inspection road in Para  8.4 and drainage of banks in Para 8.5 in this chapter.  (ii) Safe design of embankment i.e. Hydraulic and structural requirement. It includes stability of inner and outer slopes, Structural safe design of inner cut slopes in deep cuttings in different types of soils/rocks of varying nature and ground water conditions. Stability of slopes may include drainage, so as to prevent rock falls/debris in canal. For outer slopes in embankment (filling sections) hydraulic gradient/pharetic line, toe drains etc, similar to the earthen dams, on different types of soil/rock foundation with respect to varying ground water level conditions are important. The canal embankments in filling may even fail through its foundations by sloughing or liquefactions. All these aspects of canal embankments are discussed in this chapter in Para 8.4 to 8.9.

So far much have been talked about the best hydraulic sections, as these appeared to be most economical sections. But as it appears may not be always true and there are exceptions to each individual site conditions. 9.1 Suitable and Economical Cross Section Best hydraulic sections are most economical in lined and unlined canals. In lined canal this section is economical as long as the cost of earth work (excavation and embankment) is less than the cost of lining per unit length of channel and this is the most usual case. These sections, besides having least area and perimeter also have minimum top width. Therefore land width required is also minimum, in comparison to other wide sections. But if the cost of earth work / excavation is more, such as in rocks, or in very heavy cutting/filling, best hydraulic section do not remain most economical, and recourse to alternative section must be worked out. Even in unlined channels in deep excavation or in deep filling recourse must be taken to narrower and deeper sections as far as possible. Also the type of lining in the bed may be cheaper than the lining on sides and in such cases, lining of best section is no more most economical and cost economics of various alternatives including increase in bed width has to be worked out, see para 4.1 and 6.3.