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

Abstract

The use of temporary runoff and underground dried-up water courses has been implemented by managers in recentyears to compensate for water shortages in arid and semi-arid regions. One way to use this water is to set up anunderground sandy dam in front of such water courses; selecting a suitable water course is the most important issue ofsuch a purpose. In the present research, this matter was investigated using both library and field work methods duringthree stages in a part of the Gilan-e-Gharb basin. The following 11 variables were considered: lithology, structure, faultdirection, 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 aerialstereoscopic photos of 1:55000 over the hillsides dominating the plains of Gilan-e-Gharb; the variables considered werelithology, structure, fault direction, length of valley, slope of valley, and distance from habitation. Then, these 15 valleyswere 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 valleysover the hillsides of Mount Bar-e-Aftab were selected as suitable sites for the current study. The total reservoir volume forthese 3 valleys was estimated by measuring the water volume of 1 cubic meter of sediment in a practicable and scientificmethod. Upon completion of an underground sandy dam project, between 2475 to 2563 cubic meters of water could bestored in each valley.