چکیده:
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 2563 cubic meters of water could be stored in each valley.
خلاصه ماشینی:
In this research, therefore, the above factors were considered and geomorphologic studies were used in an attempt to select a suitable place(s) to build an underground sandy dam in the Gilan-e-Gharb basin in order to compensate in part for the shortage of drinkable water the residents of villages in this region face.
Based on the results, 3 valleys were selected as the best sites in the study area to construct underground sandy dams.
4. Theoretical Principle of the Research An underground dam is described as a barrier and/or any kind of obstacle constructed in order to control the sub-surface currents inside the alluvium of valleys (Nilsson, 2003; Baghdadi, 2008; Mokhtari, 2008).
In the current research, an attempt was made to select an appropriate place(s) which comprises the above- listed conditions based on the geomorphologic variables and features for the purpose of building a sandy dam in the Gilan-e-Gharb basin.
5. Research Results Analysis Based on the results obtained from all 6 variables in the first stage and the 5 variables of the second stage, 3 valleys were selected as sites for underground sandy dams in the Gilan-e-Gharb basin and numbered 13, 14, and 15 (Fig. 3).
The current research showed that such valleys that have not been settled along a fault and have stone beds that are impermeable or have little permeability- in case of availability of other criteria - are suitable locations in which to construct underground sandy dams.