The Selection of Susceptible Reservoirs to Flood Storage with an Emphasis on Landform Characteristics and Spatial Multi-Criteria Decision-Making Methods in Qomroud Watershed.

Introduction
A flood is an exceptional stream that may be flooded from the natural bed of the river. Usually, the maximum observed discharge during a year is named a flood or an annual flood. It is one of the natural disasters which has the highest damage in the world, after an earthquake. Losing life, land, and property, especially along the river, are among its most perilous environmental hazards. A comprehensive flood management seeks to use structural and non-structural methods to prevent flood intensity and minimize its human and financial losses. Although we can minimize their damage, there is not any possibility of controlling floods. Qomroud Basin with an area of 3563 km² (356300 hectares), is located in provinces of  Markazi and Qom and in a geographical position of  50°  2 33 to 50°  54 29 East and 33° 57  37 to 34°  39 28 north latitude. Its minimum and maximum heights are respectively 964 m and 3145 m and its average slope is 13.6 %.  The perimeter of the basin is 452.7 km and is part of the main catchment area of Iran's central plateau. After several destructive floods with significant damage in recent years, especially after the huge flood of April 2009, the  need  for  desirable flood management in the Qomroud
 
 

 

River basin is very urgent.
Methodology
The purpose of this research was to control the floodwaters of the Qomroud Basin by determining the appropriate flood conservation areas using a multi-criteria decision-making technique. Flood diversion and storage is a well-known method for dealing with the risks and damage of a flood.  It can also improve the quality and quantity of underground water. In fact, flood control and artificial feeding of aquifers are among its important results. The Weighted Aggregates Sum Product Assessment (WASPAS) model is a new multi-criteria decision-making technique (MCDM) that was introduced in 2012 and can be effective in complex decision-making issues. It is based on the combination of two models of multi-criteria decision making WSM (weight aggregate model) and WPS (weighted production model) and is more accurate and has the ability to rank. Its application has four stages. In this hybrid model, it has been attempted to use a combined benchmark to determine the final importance of each option, which combines the parity contribution from WSM and WPS for the final evaluation of the options. In this study, the variables of gradient, soil, land use, groundwater depth, landform, surface permeability, roughness, accumulation flow index, lithology, elevation, and drainage density as effective factors in location for diversion and flood storage were used. The model (WASPAS) which is one of the most recent multi-criteria decision-making models was used to calculate the indicators' weights and rank the options and prepare the final map.
Result
The results obtained through this model have identified the areas susceptible to flood storage, with high accuracy and in the least possible time. Scoring each criterion is based on their relative importance. After determining the score of each criterion, a multi-criteria evaluation of the GIS was obtained using the overlapping

 
operation, WASPAS model, and the final map (synthesis) of land potential relative to the flood reserve. The relative heights of slope and land use were respectively 0.136, 0.12.  The relative weights of the height and the density of drainage were respectively 0.06 and 0.04, with the least importance for zoning susceptible flood reservoirs.
Discussion and conclusion
By combining their results with the WASPAS model, it was possible to identify the susceptible areas to storm-storing with high precision and in the least possible time. The results showed that the Qomroud basin was divided into five classes including very high with 24 percent, high with 28.2 percent, moderate with 24.9 percent, low with 15.2 percent, and very low with 7.7 percent. Thus, there were nine very suitable areas found in the central, south, northwest and eastern parts of the basin for flood diversion and storage. The aforementioned areas were also recognized for field purposes for the desired purposes.