Feasibility study and construction of an underground dam in the Daryan watershed (Case Study Mashnaq Underground Dam)

The water crisis in arid and semi-arid regions is a limiting factor for human activities and sustainable agricultural development. One of the new solutions in this field is the construction of underground dams. Underground dams compared to conventional dams that store river water in open reservoirs; block the subsurface flow of water in the cross-section of the river and store it under the riverbed. In these dams, water losses through evaporation are controlled and the possibility of environmental pollution is minimal. In the present study, the feasibility of constructing an underground dam in the seasonal Meshnaqchai River for agricultural water harvesting has been studied. After basic studies, the main location was finalized with geophysical and geotechnical studies. In the main axis of the dam, the width of the bed is 130m and the alluvial thickness in the location of the axis and the lake of the dam is 14m and 22m, respectively. The cross-sectional design of the dam is trapezoidal and consists of fine-grained materials in the dam core and a filter layer with a thickness of one meter in the dam shell. The length of the dam crown is 160.30m and its height in the center of the dam axis is 15m. By moving towards the sides of the river, the depth of the bedrock decreases, and the depth of the dam decreases accordingly. The area of the aquifer, including the 5% slope of the river, is 39,000 square meters. By calculating the depth of alluvium, the volume of the reservoir is 546,000 cubic meters and according to the total porosity of alluvial deposits (35%), it is possible to harvest 163,800 cubic meters of water of the aquifer. The purpose of this study is to assess the feasibility of constructing underground dams in coarse-grained alluvial rivers to manage floods in watersheds. By achieving this goal, the problem of the agricultural, sanitary, and drinking water supply in Meshnaq village will be solved.