A STUDY OF CONVEYANCE LOSSES IN CHANNELS

Abstract

Conveyance losses in canals mainly constitute seepage losses. Seepage losses can be determined by direct methods or analytical methods. Direct methods include, inflow—outflow, pending ,seepage meter and tracer technique. Ponding is the most accurate method and seepage losses in Gamti—Kalyani Doab on two minors has been assessed by this method. It has been seen that the seepage in the minors is of the order of 1.5 m3/sec/1O m Direct methods can be applied on existing canals only, whereas analytical methods can be employed for assessment of seepage losses from canals even in planning stage.. Due to inadequate facilities and other limitations, it has not been possible to apply direct methods to determine seepage losses from distributaries and branches in Gomti--Kalyani Doab. Seepage losses through distributaries and branches have therefore, been estimated by analytical methods. It is seen that seepage losses through. distributaries very between ,00724 & .01926 m3/sec/ken , and from ©.498.m3/sec/million sq.m. to 1.747 m3/sac/million sq.m. Seepage' lasses appear to increase from head to tail of the canals if expressed per unit area of wetted area of canal. In the reaches where seepage is negligible, lining of canal is not justified from seepage consi-derations. In the reaches where significant water is lost through seepage, the canal may be lined to prevent this seepage. An alternative to lining could be to store the seepage water into underground reservoir, to be used when surface water is in short supply. The lining of canals for seepage prevention could he consi-dered economical only if the cost of water saved as a result of lining is less than the cost of pumping the seepage water from underground reservoir. In Gomti-Kalyani Doeb the depth of t ater table .varies from 2 to 12 metres! Total head through which water to be lifted shall range between 5 and 15 meters. The cost of pumping unit volume of water against a lift of 15 m is approximately Rs.0.09/m3. The cost of water saved per unit volume as a result of . lining the channels in this area works out to Rs.1.10 or more. It is seen that lining of branches and distributaries in Gomti Kalyani Doab 'is not economical.