Abstract
The concrete and bricks when used for watercourse lining are not completely impervious and some seepage losses are likely to occur. Provision of some imperme-able layer like polyethylene sheet beneath some protective cover can guarantee complete check to the seepage losses for many years at a relatively very low initial investment. Trapezoidal watercourse with 7.6 cm thick layer of bricks as a protective cover laid over the plastic Film was 54% cheaper and gave complete seepage control as compared to the conventional lining (double brick lining in a rectangular design).
INTRODUCTION
Losses of irrigation water in con-veyance from mogha to the field outlets av-erage about 47% (Lowdermilk et at, 1978). Earthen improvement has been found to re-duce the delivery losses by about 50%, in-creasing thereby the delivery efficiency from SO to 75% (Reuse et al., 1975) but this is only short lived.
Lining is a long term effective method of controlling seepage losses from the wa-tercourse but the cost of conventional lining, technique is so high that this cannot be rec-ommended for a massive lining programme in the county. There is thus a strong need to develop alternate low cost lining techniques those can effectively control seepage losses from the watercourses.
The plastic film had failed when used as an exposed lining. However, it has proved effective and durable as buried lining as long as the protective cover remains intact (Anonymous, 1978). In India, the polyethy-lene film, when used for lining canals, with tiles as a protective cover has been found
relatively cheap, durable and highly imper-meable fulfilling all the requirements of a good lining (Anonymous, 1979).
Polyethylene film 0.2 mm thick was also used for lining a number of water-courses located in all the districts of Punjab during 1972.73 in rectangular design with 11.2 cm thick brick masonry protective cov-ers. The seepage losses were observed tO he cut off by about 99% (Anonymous, 1978a). Research was also conducted on polyethylene lining on trapezoidal water-courses at Niaz Beg Field Research Station, Lahore and found its performance efficiency satisfactory (Anonymous, 1978b). However, performance efficiency of lining decreased mainly due to mishandling of buried membrane by the cultivators during silt clearance. Experience on the country's watercourse system indicates that simple soil cover would not protect the film against the attack of rodent.
