Effect of execution and operation Issues on the Efficiency of Geomembrane lining in Control of Water seepage (Case studies in Isfahan, Hamedan, Khuzestan, Semnan, Alborz provinces)

Geomembranes is a kind of geosynthetics that is used to control water losses in water storage ponds. and conveyance irrigation canals with a a fast growing rate. This lining material, in addition to the ease and speed of execution, can control water seepage losses completely. In this research, the role of execution and operation issues in control of water seepage losses in geomembrane linings was investigated. For this purpose, in 5 provinces of Alborz, Isfahan, Khouzestan, Semnan and Hamedan, 15 cases (ponds) were selected. All of these ponds were lined with HDPE geomembrane sheets with a thickness of 1.5 mm , made in Iran, with a lifetime of 8 years and ponds depth was 3 meters. Total water losses in these ponds were determined in three stages of one crop year. . Based on the results, the amount of water seepage losses from geomembrane lining is between 0.1 to 37.6 and on an average 13.9 liters/m2/day, which is about 125 times lower than the seepage losses in concrete lining. The lowest seepage losses were in Hamadan and Khuzestan provinces with 0.3 and 0.2 liters/m2/day ,respectively, and the highest value belonged to Alborz, Isfahan and Semnan provinces with 23.1, 16.2 And 29.6 liters/m2/day, respectively. Due to the uniformity of the geomembrane sheets and the geometric conditions of the ponds, the difference in the amount of seepage losses was found to be related to the quality of the execution and operation issues of geomembrane lining in the ponds. The most important issues in the ponds with high value of water seepage losses were the lack of attention to the slopes of the bed in design and execution, sediment accumulation and the need for dredging during operation, inadequate bed prepration and compaction, the presence of rocks and sharp objects under the lining, the formation of wave, the cuts due to the absence of under lining in the weld sides and the corners of the pond and human destruction during the lining.