COMPARISON OF WATER LOSSES BETWEEN UNLINED AND LINED WATERCOURSES IN INDUS BASIN OF PAKISTAN

The issue of water losses through irrigation systems has a major impact on surface water supplies and management. Although a number of national and international organizations have attempted to assess the degree of losses from the watercourses, the impact of lining on the same command on the water losses had not been addressed. A study was carried out to assess the differences in water losses through the lined and unlined watercourses in the particular area of Indus Basin of Pakistan. The selected watercourses were located on the same distributary; therefore, it was considered that all of these watercourses would be subjected to same hydrogeologic characteristics of soil. It was observed that for the lined watercourses, the irrigation water losses ranged from 35 to 52 percent and for the unlined these were from 64 to 68 percent. Comparing the average water loss of 43.5 % from lined to the average water loss of 66 % from unlined watercourses, it was concluded that the lining reduced water loss by 22.5 %. It is emphasized that the studied watercourses were quite old with poor maintenance conditions. Lining was deteriorated badly with frequent cracks in the walls. The excess leakage of water through these watercourses was probably due to cracks, eroded mortar and structural failure of the lined walls. Moreover, the lined watercourses were raised, which accelerated the leakage phenomena. In addition, the capacity of watercourse was reduced due to silting, resulting in overtopping of flows at many locations. Consequently, the lined watercourse could not effectively save the water losses and resulted in higher water loss than the normal.