ADVANTAGES AND DISADVANTAGES OF CANAL LINING
The lining of an irrigation canal has the advantages (i) Reduction in seepage losses from canals reaching water table and raising it resulting in waterlogging and reduction in yield, (ii) Reduced seepage losses by as much as 75 per cent means saving of water which otherwise would have required construction of bigger reservoir and dam for the same amount of actual
water delivered to the field which implies more capital expenditure without much gain, (iii) Reduction in losses and thereby making available more water for extension of irrigation to new areas and improvement of irrigation facilities in the areas afready under irrigation, (iv) Flatter slope in lined canal system results in low height of dam and consequent saving in cost of dam construction, (v) Stable channel section, (vi) Brings more area under command due to very flat slope possible, (vii) Steeper side slopes and bed slope possible as the lined section is immune from erosion, (viii) Higher velocity permissible, resulting in proportionate saving in cross sectional area, land width, quantum of earthwork excavation and construction of bridges and cross drainage works which in certain cases may offset completely the extra cost of lining, (ix) Possibility of breaches are remote owing to sound structural stability of lined section, hence improvement in operational efficiency, (x) More hydel power generation possible with saving in water from losses and conservation of head losses due to flatter bed slope possible, (xi) Low coefficient of rugosity resulting in high velocity with the same slope and hence reduced cross sectional area compared with unlined section, (xii) Lined canal water does not pick up harmful salts from the soil through which it passes because canal water does not come in contact with the subsoil, (xiii) Permits more winding alignment resulting in saving in embankment and cutting costs, (xiv) Prevents weed growth thereby resulting in saving of expenditure incurred on weed removal in the case of earthen channels, (xv) Stable section which in the case of distributaries and minors reduces remodelling and alteration of outlets, (xvi) Theft of water by cultivators is stopped, (xvii) High velocity provided in lined section shall carry forward the blown in sand in sandy tracts, (xviii) Recurring charges on silt clearance inherent in unlined canals are avoided in the case of a silting canal, with the same slope. Existing silting channel when lined at the same slope generates higher velocity to carry forward the sediment, (xix) Considerable economy in the acquisition of cultivable land due to relatively narrow section of the canal, (xx) Improvement in cropping pattern, (xxi) Environmental bettennent, (xxii) Greatly reduced maintenance and operational charges of the canal, (xxiii) Reduction in evaporation and transmission losses due to reduced exposed area, (xxiv) Reduction in erosion which occurs in unlined channels constructed in steep lands.
Disadvantages of Lining
The widely publicized lining of channels is not free from disadvantages, some of which are (i) Higher initial investment; a lined canal is 3 to 4 times costlier than an unlined one of the same capacity, (ii) Costly repairs, (iii) Shifting of outlets is very costly because it involves dismantling and relaying of lining, (iv) Longer construction period, and (v) More sophisticated construction equipment and skilled labour are required.