Design of Irrigation Canals (Part - 2) - Civil Engineering (CE) PDF Download

Typical sections of lined channels

Though there may be a large number of combinations of the factors on which the cross-section of a lined canal depends, some typical examples are given in the following figures, which may give an idea of laying and a practical channel cross section.

                                               All dimensions in millimetres

FIGURE 5 (a). Typical cross section of canal when natural ground level is below bed level

                                           All dimensions in millimetres.

FIGURE 5 (b). Typical cross section of canal when natural ground level is between canal bed and full supply levels

                     All dimensions in millimetres.

FIGURE 5 (c). Typical cross section of canal when natural ground level is above the top level of lining

 All dimensions in millimetres.

FIGURE 5(d) Typical cross sections of canals when canal bed level is above natural ground level

FIGURE 5 (e). Typical cross sections of canals when natural ground level is between canal bed and full supply levels

FIGURE 5 (f). Typical cross sections of canals when natural ground level is above top of canal lining

The Bureau of Indian Standard code IS: 10430-1982 “Criteria for design of lined canals and guidelines for selection of type of lining” (Reaffirmed in 1991) may generally be used, in addition to special codes like IS: 9451-1985 “Guidelines for lining of canals in expansive soils (first revision)” (Reaffirmed in 1991), which may be used under particular circumstances. 

Subsurface drainage of lined canals

Lined canals passing through excavations may face a situation when the canal is dry and the surrounding soil is saturated, like when the ground table is very near the surface. Similar situation may occur for lined canals in filling when the confining banks become saturated, as during rains and the canal is empty under the circumstances of repair of lining or general closure of canal. The hydrostatic pressure built up behind the linings, unless released, causes heaving of the lining material, unless it is porous enough to release the pressure on its own. Hence, for most of the linings (except for the porous types like the boulder or various types of earth linings which develop inherent cracks), there is a need to provide a mechanism to release the back pressure of the water in the subgrade. This may be done by providing pressure relief valves, as shown in Figure 6. 

FIGURE 6a. Details of a Pressure Relief Valve (PRV)

FIGURE 6b. Possible locations of PRVs