The Role of Geomorphology in Locating Underground Sandy Dams (Case Study: Gilan-e-Gharb)

The use of temporary runoff and underground dried-up water courses has been implemented by managers in recent years to compensate for water shortages in arid and semi-arid regions. One way to use this water is to set up an underground sandy dam in front of such water courses; selecting a suitable water course is the most important issue of such a purpose. In the present research, this matter was investigated using both library and field work methods during three stages in a part of the Gilan-e-Gharb basin. The following 11 variables were considered: lithology, structure, fault direction, length of water course, slope of water course, grade of water course, valley shape, granular of sediment, thickness of sediment, lithology of valley bed, and distance from habitation. First, 15 valleys were selected from aerial stereoscopic photos of 1:55000 over the hillsides dominating the plains of Gilan-e-Gharb; the variables considered were lithology, structure, fault direction, length of valley, slope of valley, and distance from habitation. Then, these 15 valleys were investigated through field study and paired comparison matrices considering the 5 factors of valley shape, granularity of sediment, thickness of sediment, lithology of valley bed, and grade of water course. As a result, 3 valleys over the hillsides of Mount Bar-e-Aftab were selected as suitable sites for the current study. The total reservoir volume for these 3 valleys was estimated by measuring the water volume of 1 cubic meter of sediment in a practicable and scientific method. Upon completion of an underground sandy dam project, between 2475 to 256 cubic meters of water could be stored in each valley.