Prioritization of suitable axes for underground dam construction in the Doostbeiglou watershed

Water resources management in arid and semi-arid areas is very important to provide of water for stakeholders. In recent decades, construction of underground dams have been considered, because of its advantages. These dams have many advantages, e.g., unlike a surface dam, land is not submerged to store water and there is no danger of breaching due to natural or manmade disasters. The surface area can be used in the same way both before and after construction of the underground dam. A subsurface dam is a facility that stores groundwater in the pores of strata and uses groundwater in a sustainable way. Underground dams are used for various purposes such as preventing of combining salt water and fresh water, reserve water for management using and creating an obstacle against of influencing waters to structures. The water gathered in subsurface dams is good quality for drinking, as it has been filtered by the sand and is stored underground away from contamination. The aim of this research has been to identify areas suitable for underground dam construction, so that in these areas there is no limit to the underground dam and then appropriate priorities in these areas.

Doostbeigloo watershed with an area of 7461 square kilometers is located in the Ardebil province (North Western Iran). In this research, we consider several criteria for suitable site selection of underground dams in watershed, including: topography, hydrography, hydrogeology, geology and land use. These factors were used to initial mapping suitable regions for underground dam construction. Firstly, for this purpose were used Boolean logic and fuzzy logic models. Then, using the analytical hierarchy process to priorities suitable axes in appropriate areas for underground dam construction.
Boolean logic: Boolean (logic) algebra is the branch of algebra in which the values of the variables are the truth values true and false, usually denoted 1 and 0 respectively, 1 for suitable areas and 0 for unsuitable areas. The maps of different factors that involved in locating underground dam, in the GIS environment were combined using Boolean logic. Therefore, the map of suitable areas for underground dam construction was created.
Fuzzy logic: In a Fuzzy logic the weighted of layers is between zero to one, which gives more data than Boolean method. This method defined as Fuzzy AHP in many studies. In this research with regarding donned studies was used of 0.9 fuzzy gamma operator in order to locating suitable areas for underground dam construction.
Analytic Hierarchy Process (AHP)

The analytic hierarchy process (AHP) is a structured technique for organizing and analyzing complex decisions, it provides a comprehensive and rational framework for structuring a decision problem, for representing and quantifying its elements. In this step after determining the suitable areas for underground dam construction, AHP method was used for prioritization of appropriate axes. The AHP method is based on analysis, binary compression, summarizing, prioritizing and selection among alternatives. After determining the subject, it’s divided to many criteria, and many various sub criteria. In this method assessment the selecting criteria, performed with consistency index (C.I). Based on previous studies the (C.I) must be less than 0.1value.

The extracted results showed that, areas in the southeast and northwest are unrestricted for underground dam construction. Locating underground dam with using Boolean logic and Fuzzy logic showed that suitable area in 3 stream rank are more than other stream ranks that is accordance with previous studies. The compatibility rate value for AHP method was obtained 0.03 that this rate in AHP method is acceptable value. The results from prioritizing of selected dams in this area showed that water criteria is the most important factor to prioritize the proposed axis. The water quantity and quality criteria with 0.11 and 0.104 weights, respectively have highest important than other criteria. The 9 number axis located in Meshgin shahr plain and 30, 33 and 34 number axis in Ardabil plain have prioritize than other axis.

Construction of underground dam and using of surface runoff is an appropriate way to secure and expand water supplies. The Boolean logic and Fuzzy logic showed suitable areas for construction of underground dams with acceptable accuracy and between these methods the Fuzzy logic model showed higher performance than Boolean logic method. With using of AHP method, determined the axis that have more prioritize for performing underground dam than other axis. Can be said that using GIS and satellite images to locate underground dams have a significant impact, because the maps are produced in this process can be used at a later stage and as an executive guide map for underground dam construction to be considered. Thus, with utilization of this methods we can showing suitable areas and axis for underground dam construction in the Doostbeigloo Watershed.