Locating an Underground Dam in Roudan sub-Basin, South of Iran Tahereh Khorrami Department of Geology, Islamic Azad University, Bandar Abbas Branch, Bandar Abbas, Iran. e-mail: [email protected] Peyman Rezaei Department of Geology, Hormozgan University, Bandar Abbas, Iran. e-mail: [email protected] ABSTRACT Underground dams are one of the solutions proposed to provide arid, usually small-scale, arid lands that do not have access to common resources, such as permanent wells and rivers, or low resources. In terms of structural-sedimentary divisions of Iran, the study area lies at the end of the western part of the Makran zone. Rudan sub-basin in Hormozgan province due to having dry climatic conditions and special geological conditions has a suitable potential for construction of underground dam. In this study, digital elevation models, satellite data, topographic characteristics and hydrologic characteristics of the area in soft The GIS was evaluated in remote sensing and 9 locations were identified as prime points for underground dam construction. The selected sites were visited on two occasions in winter and summer; then, considering the need for water in the region, two sites were selected for further studies; other susceptible sites were rejected due to the distance from the centers of population and agriculture. The site (1), located 5 kilometers north of Faryab village, is located in the vicinity of a small village whose drinking water is supplied by a well within a distance of about 2-1 km. It can be a good alternative to the construction of an underground dam It will prevent groundwater pumping and also reduce surface water consumption and optimize their use. The site number (2) is located at the upstream of the industrial city of Roudan. By constructing a dam in this place, it is possible to provide the water needed for the settlement, while now it is used for water supply by drilling wells or using drinking water for use. Industrial is done. Reservoir deposits are (1) and (2) coarse grains of type GW, with a saving coefficient of 15%. The volume of dewatering of sites (1) and (2) is estimated to be 1785 and 518.1 cubic meters, respectively. According to the region's rainfall, it is possible to dewatering at least 2-3 times. According to Wilcox and Schuler diagrams, the surface waters of the area are suitable for agricultural and drinking purposes. KEYWORDS: Underground Dam, Feasibility, Rudan Sub-GIS, Geographic Information System, Geological Geology. INTRODUCTION Living on the planet depends on providing adequate water. Groundwater resources account for 14% of the total available freshwater available on the planet. Groundwater resources are important, especially in areas where there are no permanent rivers of great significance. Since the Rudan - 391 - Vol. 23 [2018], Bund. 02 392 catchment area is one of the Persian Gulf basins and is located in a region with a dry climate with limited rainfall, the main problem of this area, like other watersheds of Hormozgan province, is evaporating, which does not preserve the water capacity of the area. And water resources are immediately drained from the drainage area. Therefore, the feasibility, feasibility and location of the implementation of the methods of preserving small water resources with minimum evaporation are essential. A large part of the province's citrus and citrus is provided by the district of Rudan and even Hormozgan province. In recent years, due to the occurrence of droughts, water scarcity has caused many economic and social problems for farmers and villagers in the region. Rangeland poverty, lack of water for drinking and lack of agricultural water are among the problems that, if in the next few years, no solution to them is considered, there will be a risk of mass immigration and marginalization of the active population of these villages. In this research, GIS and Global Mapper software will be used to explore the proper site for the construction of an underground dam in the Rudan sub-basin (East Hormozgan). This sub-basin with an area of about 780.8 km2 is part of the Bandar Abbas-Sadiq catchment area. Because of its location in a dry area, irregular distribution of rainfall in terms of time and place, abnormal growth and increasing of various water needs (agriculture, industry, and Drinking water), the city of Roodan and the village of the subsidiary, the extreme limitations of surface water resources, climate change (drought period), and the increasing decline of underground water resources will face a severe and increasing shortage of water, especially in dry seasons. The study area is located in the east of Hormozgan Province, about 80 km northeast of Bandar Abbas, in southern Iran (Fig. 1). Figure 1: Roudan watershed in south of Iran (between Hormozgan and Kerman provinces) Using the values of atmospheric precipitation and the average annual water temperature of the studied basin, the dormant drought stress values for the study area were calculated to be 4.44. Using the morphometric climatization and drought stresses obtained from the relationship, given that the Vol. 23 [2018], Bund. 02 393 average annual temperature and rainfall in the region is about 27.1 ° C and 202 mm respectively, the studied area generally has a semi-arid climate Close to dry. In Fig. 2, the climatic conditions of the study area are shown in the moratorium climatization. Figure 2: Watershed climatic conditions in de Martonne GEOLOGY The scope of the study is from the perspective of the division of Aghanbate (2004), at the end of the western layer of the Makranian structural zone. The dominant lithology in the region is Miocene deposits, Green unit, Waziris unit, Pliocene conglomerate, and Plio-Quaternary alluvial limestone (Aqanbaty, 2004). The most important fault in the area is the Rudan fault, which passes through the site. This inter-rhodan and Faryab fault with the NW-SE trend has driven the green schist rocks on colored mixtures. Its slope is about 32 degrees towards NE. Prison faults and Sabzevaran are also other faults in the region. Vol. 23 [2018], Bund. 02 394 Figure 3: Geological map of study area INFORMATION LAYERS Digital elevation and gradient In terms of topography, locations are suitable for building groundwater dams that have a slope of less than about 5%. In order to study the slope of the area, the digital elevation model of the area was prepared first (Map 2-4), then the slope map of the area was prepared. In the slope map, for the area affected by the dam, a slope of less than 2% was used. (Fig. 4). Figure 4: Digital Elevation Model (DEM) from Aster Sensor Vol. 23 [2018], Bund. 02 395 Figure 4: The slope map of the region along with the river system of the region (extracted from the Aster satellite image) Bedrock depth The depth map of the bedrock of the region is derived from geoelectric data (Fig. 5). Figure 5: Depth of bedrock in the sub-basin of Roudan Vol. 23 [2018], Bund. 02 396 Residential areas (urban and rural population concentration), agriculture and industry The decision on the dam construction site should be such that both the construction of the dam is avoided and its distance from the neighboring areas is evaluated, which is in terms of the use of the dam due to the interest And the use of human resources in the construction of the structure is also necessary. The threshold of site distance from adjacent areas is intended to reduce the cost of the distance of 5 to 10 kilometers. Figure 6: Information Layer Distance from target areas Vol. 23 [2018], Bund. 02 397 Locating susceptible areas by combining information layers After preparing the initial layers of information, the locations of underground dams were identified; then the sites presented with geological maps topography and satellite image, although there is a slight spatial difference due to the coordinate system error of the map scanned with digital data. Figure 7: Areas susceptible to being detected by remote sensing instruments INTRODUCING TOP PRIORITY SITES After locating by GIS and remote sensing, the introduced locations were field visits. In the first stage, after considering the points of interest, the following sites were selected as the preferred sites (Fig. 8) and geotechnical surveys were carried out. Site (1), due to its location near a small village whose drinking water is fed through a well at a distance of about 5 km downstream, could be a good option for the construction of an underground dam and prevent pumping of groundwater. As well as the removal of surface water and their optimal use. The site number (2) consists of three prime points for the construction of a subterranean dam located in the upstream of the industrial city of Roudan. By constructing even one of these sites, the Vol. 23 [2018], Bund. 02 398 water needed for the settlement can be provided, while now it is being supplied for the supply of water by digging a well Or using drinking water for industrial use. Figure 8: Selecting two high priority sites for the construction of an underground dam Site number (1) Site number 1 is located in the western sub-basin of Rudan and north of Faryab village. The site tank bed is composed of medium to coarse grains of GW type (Figures 9 and 10). The bedrock depth on both sides of the base is 4 meters on the ground and in the center. The supports of this site are sandstone and have good strength. The catchment area of this site has an area of 4.384 km2 (Figure 4- 5). Alluvial basins of the river border are, on average, 3 to 3 m thick, constitute the mainland margin lands and low-altitude new lowlands (Fig.