عنوان مقاله [English]
Despite the progress made in identifying the various materials that can be used to lining of irrigation canals, a large parts of the country's irrigation canals are still unlined. On the other hand, last researches indicates that in some linings the expected target is not achieved and the amount of water loss in them is not significantly different from unlined canal. Therefore, it is necessary to evaluate the rate of water seepage losses in different bedsoil textures from the bed of the unlined canals and then, if necessary, linings should be carried out. The rate of water seepage losses in unlined irrigation canals and its relationship with the bedsoil textures in the Bahar plain from Hamedan province have been evaluated. For this purpose 6 unlined irrigation canals were selected. The technical characteristics, geometric dimensions and hydraulic parameters of the water flow were determined and the amount of water seepage losses measured with input-output method, in the early, middle and final stages of the agricultural season. Based on the average results, water seepage losses in selected canals are between 0.88 to 3.84 and averagely 2.38 m3/m2/day. The average seepage losses in the early, middle and final stages of the crop season are 2.61, 2.18 and 2.35 m3/m2/day. The evaporation losses with averaged of 0.01 m3/m2/day(to 0.3 percent of the total losses), were very small compared with seepage losses, and the remaining losses were due to seepage. The relationship between the amount of seepage from the substrate of the studied channels and the percentage of fine particles of the bedding soil (particles with diameter less than 0.75 mm) were extracted and presented as Sloss=5.394*e-0.0299*Fine. According to this relation, if the fine particles of bedsoil of canals increases to 35 present, the water seepage losses from this canal decreases to less than 50 of the present value.