6.4.3. Channel Capacity The discharge capacity of the channel system should be decided on the concept of evapotranspiration rather than the ‘kor’ period. This has already been discussed in Secs. 3.8 and 5.8.
6.4.4. Canal Lining Lining of canals is a means to reduce the seepage losses from canals. In one typical case, the benefit-cost ratios of lining distributaries only, distributaries and watercourses, and field channels only were found (18) to be, respectively, 0.33, 0.608 and 2.303. As such, the lining of field channels is the most beneficial. Besides, it involves no dislocation in the operation of an existing system. In order to prevent damage to lining, the slope of a lined channel is reduced. This reduces the sediment carrying capacity of an existing channel which is being lined. Therefore, measures for sediment exclusion are to be considered whenever an existing canal is being lined. Alternative to the lining of canals is the conjunctive use of surface and ground water which should be opted for after comparing the unit cost of water saved by lining with the unit cost of pumped water. For a representative case, Chawla (16) has worked out the cost of water saved by lining as Rs. 25 for every 100 m3 of water against Rs. 7 to Rs. 12 for the same amount of pumped water.
