Analysis of land suitability for small earth dams Using Multi Criteria Evaluation (MCE) in the Geographic Information System (GIS)

. In many parts of the world, especially in arid and semi-arid, one of the solutions to deal with the major flood season comes, is the dam, as well as water storage dams to store flood also reduced the flood peak flow and damages resulting from it. It must be built in places that best performance in terms of the volume of the reservoir and reduce their discharge. In this paper, using a combination of linear and GIS environment, the proportion of land for the construction of small earth dams in the watershed Kal Ajy in the East province with an area of 170.90 km, based on five criteria (slope of the stream bed, the distance from the village, away from sources of credit, apart from agricultural lands, areas with severe erosion) to assess and map the proportion of the land in the study area was prepared. This map priority areas for the construction of small dams and earthen offers. The results indicate that 27 percent of the region is important for small earth dams are suitable.


INTRODUCTION
Spatial analysis and geographic often have multivariate and multi criteria. Geographers, planners and decision-makers spatial (location) to solve their issues faced with a range of data and information that, due to the volume and nature of the integration and analysis of different, often very complex and difficult in some Despite good rainfall Average Golestan province, yet in some areas, especially eastern problem is dehydration. Kaul Ajay watershed is located in the eastern part of Golestan province that despite the many seasonal rivers, the people of the region with drinking water shortages for agricultural purposes as well as their health and are exposed during low rainfall. The small earthen dams and water storage is the way to deal with possible flooding. In this paper, two options weighted linear combination of GIS and we aim to achieve is the location for the dam (2). Geographic information systems, with numerous features and capabilities for collecting, storing, editing, data analysis and modeling, so a useful tool for spatial planners in the evaluation of a number of criteria are considered. Basically, the ultimate goal of providing GIS is support for planning and decision making (Nazri, 2006: 9-10). There are several ways to analyze and evaluate a measure of the proportion of land that is the most common method of weighted linear combination (1).
In this article it has been tried based on five criteria and using weighted linear combination, the proportion of land for the construction of small earth dams in the watershed Kaul Ajay, a GIS environment to be evaluated (3). The method For this reason selected The first is simple And one of the most common methods of multi-criteria evaluation, Secondly easily run in Geographical Information Systems Third, analysts can view information on the importance of benchmarks and review them to best apply (6). In the field of multi-criteria decision-making methods Solving problems in decision-making, numerous studies have been done in the world and Iran which some of them are mentioned below: (14). Tal Svoray and colleagues in a study on the integration of GIS and multi-criteria evaluation methods to assess ecological areas on land for four possible: Protection of natural forest areas, residential areas and industrial areas were used. The method proposed in this study, One layer for each of the four public events and a final layer Which can be the best use for each piece of land is proposed provides. The results of the model used in this study ( Figure 1) (5). In a study by Ron Store and Jyrki Kangas GIS data and spatial analysis, combined with modern techniques to improve the assessment decision on the habitats used in large areas. In this study, GIS as a platform to manage, combine and display data standards and data in order to produce new tools (especially by spatial analysis functions) was used. In this research, standardization, weighting and combining multiple criteria evaluation criteria by MCE)) was carried out. In the end, the proposed method has been implemented on a case study and the results ( Figure  2), respectively (4). Figure 2. The results of the study (kangas. Store, 2001) Cary Higgs in his research on the advantages of using multi-criteria evaluation integrated with GIS to enhance public participation in the debate stems (12). He is to demonstrate the benefits,

International Letters of Natural Sciences Vol. 42 39
challenges and opportunities that decision-makers in terms of increasing public participation in the process of waste management face saied And finally We concluded that the use of multi-criteria evaluation based on GIS can increase the efficiency of public participation in the plan have Bsyarbalayy (8). Habibi and others in research, using a combination of multiple criteria evaluation model and GIS to locate landfill proposed municipal solid waste. In this study, using data such as the distance from the city, away from roads, airports, land use, land capability and so on through the integration of models and maps based on fuzzy logic, the best place for the disposal of municipal solid waste the study sample ( Figure 3) was selected (7).

1.1.
Introducing the study area Kal Ajy basin with an area of 17099.93 hectares In the area east 55˚ 18 , 04" to 55˚ 29 , 32" And latitude 37˚ 35 , 44" to 37˚ 45 , 37" Almost in the north of Kalale city, is located in the East province. Villages in this area, including Akhjy, gachy sow and Kochak Gogche is that Located in the north of the basin, The villages surrounding this area Can be Named sojy and yoli badrag (10). (Figure 4). This area is located in the country and province show. Kal Ajy basin was divided into seven sub-basins and sub-basins hydrological conditions 1 to 6, and No. 7 in the basin is the area that can be seen in Figure 5(13).

MATERIALS AND METHODS
In this paper, effective measures earthen dam at the location where they will be discussed in more detail below were prepared in the GIS environment.

Slope of Stream bed
Framework for dam embankment slope gradient of less than 5%, because the slope is inversely related to the size of the tank. Figure 5 shows the map of the region and set the drainage channels with a slope of less than 5% of the show (11).

The distance from village
Near the dam site and the village can be used as an indicator easy to find skilled manpower for the construction of the dam is raised. The dam was built close to residential areas and rural areas, access to and transfer of stored water is easier and less costly. Figure 6 shows the location of villages and Privacy intervals (16).

Areas with severe erosion
It covers areas gully erosion and alluvial terraces of the old and make Palyvsvl that Production of sediment and erosion can be a problem for dam construction and fill the reservoir from sediments as well as a platform for the structures are weak and permeable, so in other areas, the figures are wrong. In Figure 7, these areas can be seen and considered optional (15).

Distance from Borrow
Clay sources of research carried out in the past that were identified by spectral analysis were extracted and the distance to the radius of 5 km from the dam were considered as optional. In Figure  8, and access resources within the limits of the resources shown.

The distance from Agriculture land
Areas intended for the construction of the dam should be close to agricultural lands up to Water is readily available to farmers and ranchers affected and the cost of transferring water from the reservoir to agricultural land and reduce intubation in these areas. Figure 9 (9). For spatial analysis and multi-criteria evaluation software was used Idrisi and raster format. For this purpose, the layers were collected in Idrisi and for all maps UTM coordinate system is considered the same and the size of each picture element (pixel) in the maps of 30 * 30 m (14). Criteria and variables considered for analysis in this study include 5 standard is the fit. For standardization and unification of the value scale map layers of fuzzy and weighting criteria weighting method analytic hierarchy process (AHP) was used (15). In the final analysis, multicriteria evaluation (to match the ground) technique Vzn¬Dar linear combination (WLC) was used.
The overall process integration model of multi-criteria decision making (MCDM) and GIS to solve problems is in Figure 10.

RESULTS
The results of this study are as follows:  Multi-criteria decision-making strategies in combination with GIS can be a useful framework to solve complex problems of decision-making (especially spatial decisions) provide.  Using multi-criteria decision-making based on GIS is so simple and flexible that any number of criteria can be used to solve a problem. Although it should be noted that with the increasing number of criteria, decision makers may face difficulties in giving weight to these criteria.  The multi-criteria decision-making process based on GIS, in steps of evaluation criteria, can be given in terms of different groups interested in the issue of the role and functions of each area of use. This process can lead to increased public participation in municipal decisionmaking. Future research in this area could test the efficiency of this method. The diversity and complexity of the subject information and spatial analysis has led to the GIS is widely used in solving problems. Multi-criteria evaluation method for comparing the relative importance of various characteristics together and integrating data according to their importance in the decision (16). In this paper, the evaluation criteria and weight scales comparable standard method of analytical hierarchy process (AHP) was determined as follows. The distance from the village (0.26), distance to Borrow (0.23), tilt Bstrabrahh of (0.13), areas with severe erosion (0.312), and distances of agricultural land (0.068).
Run the MCE method in GIS environment, including the following (11)

CONCLUSION
Map of the evaluation of several criteria to determine the suitability of the land in the watershed Kal Ajy (with the aim of locating suitable areas for small-earth dam), map compilation raster format values are those values between zero and one. Higher values (to one) in the map indicates suitability for the construction of a dam and lower (zero indicates the proportion of land is less important. The map shows the location of red earth dams that 27% of the total area included. As the results show, GIS capability in the field of collecting, editing, modifying and analyzing massive amounts of data and information, spatial and non-spatial, the tool Support for spatial analysis and planning (3). Functions of basic and advanced the implementation of a wide range of statistical and mathematical operations on data and spatial algorithms makes it possible. The operation largely limitations and complications of the large volume of information, the nature of the measures to reduce discrepancies caused by variation analysis to reduce computation time. (Carver, 1992: 105-127) While relatively good accuracy as well. In connection with the analysis of physical fitness of land for development, in addition to procedures Multi Criteria Evaluation (MCE), can be fuzzy methods and methods based on Boolean logic was also helped, while the number of evaluation criteria to match the features and This increased restrictions.