عنوان مقاله [English]
The flood is considered as a natural disaster with the highest financial losses according to the Report of the United Nations Development Program. The floods are harmful to the urban and suburban areas. River floods and flood plains have been a source of great interest in the past while the flood has been considered less in the urban environment. The socio-economic consequences of flood in the urban environment have affected inevitably more than 2.49% of the world inhabitants.
Construction of buildings on urban areas is increasing impermeable surfaces. Development of built surfaces in the urban areas can also decrease permeable levels of the basin that is useful for absorbing runoff. It has increased the total volume of runoff in the city. Until now, flood risk zoning with the aim of flood control in Urmia has not been considered greatly. This topic received not remarkable attention in the form of a research project. Therefore, flood risk zoning and controlling is essential to predict the extent of flood damage in different economic and social circumstances.
Materials and methods
In this research, we have used linear weighted Combination and fuzzy multi-criteria analysis and Geographic Information System (GIS) for zoning of flood hazard in urban areas of Urmia. The weighted linear combination method is the most commonly used technique in multivariable analysis. This technique is called either simple additive weighting or scoring method. This method is based on the mean weight concept. The analyst directly estimates the criteria based on the "relative importance" of each criterion. After multiplying the relative weights in the values of each criterion, a final value for each alternative is obtained. After determining the final value of each alternative, the alternative with the highest value will be selected for the goal. The weighted linear composition method is an averaging technique that simplifies the hard decisions of the Boolean method and avoids excessive estimation. The linear weighting method consists of four steps: 1) First, to determine a set of evaluation criteria (map layers) as well as a set of possible options; 2) to standardize each map variable; 3) Third, to determine directly the relative importance of weights of each criterion; 4) at the end, to create a standardized weighted map. In this research, various natural and human criteria have been used to achieve the goal. At first, we have prepared nine natural and human effective indicators including distance to river, runoff coefficient, building age, construction density, population density, slope, CN coefficient, open space availability and land use condition. After digitizing the maps, since each map has a different measurement scale, for the analysis and evaluation of several criteria, we need to make same measurement scale for all of our variables. Standardization of data converts all values of the maps into the same domain, for example, between 0 to 1 or 0 to 255. Then, by defining the binary comparison matrix, using the Hierarchical Analytic Hierarchy Model, the significance of the weights was determined with 0.07 inconsistency ratio in the Expert Choice software. According to the final map of flood risk zonation, the central areas of the Urmia City are more susceptible to floods. This problem has been exacerbated by the proximity of urban areas to densely populated areas and buildings in flood prone area where increase the amount of runoff and accumulation of surface waters. The WLC technique using weighting method has provided powerful solutions for researchers in multi criteria problems like flood zoning. On the other hand, this model is one of the commonly used methods for evaluating environmental problems with the MCDM fuzzy method that have been widely used in the GIS environment.
Results and discussion
After creating a flood risk zoning map, it was declared that the central areas of the Urmia City had the highest flood potential. The flood risk map shows that from all the total area of the Urmia City, about 22.31% is located in the very high danger zone, 29.08% in the high risk zone, 26.45% in the middle danger zone, 17.52% in the low risk zone, and 4.64% in the very low risk zone. Urmia Urban Development strategy should be planned with regarding the flood potential map of the city. The map showed that over 50% of the urban areas are categorized in very high and high risk zones. Given the flood potential map, it is suggested that it is required to create underground and diverse canals in flood-prone areas for discharges of surface runoffs to secure vulnerable areas, especially in the central parts of the Urmia City.
According to the results of this research, more than 50 percent of the Urmia city is very highly and highly at risk of flooding. Therefore, it is necessary to the flood prone areas for municipal activities and urban management. To secure vulnerable areas, underground canals and flood diversion route, especially in the downtown areas, can be constructed to discharge surface runoff to avoid the flood damage.