عنوان مقاله [English]
Locating temporary settlement based on flood hazard in Shiraz
Natural hazards, especially floods, as recurring and destructive phenomena, have always existed throughout the life of the planet and have always been a danger to humans. The experiences of developing countries in this field indicate that they are more vulnerable to natural hazards. Due to its natural and human characteristics, Iran has suffered many crises and is one of the most vulnerable countries to natural hazards.
Rivers are one of the vital arteries in attracting population and creating urban and rural settlements, especially in arid and semi-arid regions. The Khoshk and Rahdar River in the metropolitan area of Shiraz has been one of the dangerous geomorphic areas of the city in recent years. The location of Shiraz urban area due to the location of a significant part of it on the geomorphological field of floodplains of rivers is associated with the threat of flood risk, which is evidenced by floods in 1986, 2001 and 2019 and the damage caused by them. Therefore, the necessary environmental management in this field before, during, and after the flood in the urban area of Shiraz is essential. This study aims to help by locating temporary settlements based on flood risk in the urban area of Shiraz, which is doubly important with a population concentration (population of 1.5 million people) and significant economic capital.
Materials and methods
In this research, digital topographic maps of 1: 25000, geological 1: 100000, digital model of altitude 10 meters, detailed study map, aerial photographs, and satellite images have been used. Statistics of hydrological stations were provided by the Regional Water Organization. To calculate the average annual discharge of stations in the 25-year index period (1989-2014), at first, the statistics of stations with a statistical period of more than 10 years have been reconstructed by establishing a correlation between the annual discharge of these stations and the reference stations. Annual discharge statistics in stations with a statistical period of 10 years or more have been reconstructed and supplemented using the correlation between them and base stations.
The research method used in this research is descriptive-analytical. First, flood zoning was done for the study area and then suitable places for temporary settlement were determined. Flood zoning was determined using Hec_GeoHMS and HEC_GeoRAS models for Khoshk and Rahdar Rivers.To select suitable neighborhoods for temporary settlement, first the necessary criteria for this location are prepared and after preparing these criteria, in the location stage, according to experts, scoring frameworks are determined based on these criteria. Determining suitable places for temporary settlement during flood risk in the study area has been done using multi-criteria decision-making models and the AHP model using ArcGIS software.
Results and Discussion
Flood zoning was performed using HecGeoHMS and HECGeoRAS models for Dry River that flows seasonally. Due to the lack of information on the flow of the river, the flood zone of the Rahdar River has been determined by field visits and the opinion of the experts of the Water Regional Organization (average radius of 150 meters).
According to studies, the main criteria for locating temporary settlement are: 1) distance to the flood zone, 2) distance to the border of mountains and plains, 3) distance to empty spaces (land without construction, garden, park and space Green, and agricultural lands), 4) building density, 5) distance to waterway and river, 6) distance to fire station, 7) total population, 8) vulnerable population (less than ten years and over 65 years) 9) compatibility of land uses, 10) distance to main thoroughfares, 11) distance to health centers, 12) distance to military-law enforcement points, 13) ground level, 14) land slope, 15) slope direction and 16) distance To the entrance of waterway and river.
The steps for analyzing the data are as follows:
1- Preparation of raster layers of criteria
2- Reclassify the raster layers of the criteria
3- Converting raster layers to vector layers
4- Calculation of relative weights of sub-criteria by Analytic Hierarchy Process (AHP)
5- Calculating the relative weights of sub-criteria the use compatibility
6- Preparation of raster layer of relative weights of sub-criteria
7- Determining the relative weight of criteria
8- Combining the layers of relative weights of the sub-criteria and determining the spatial utility index
9- Determining the average spatial utility index in empty spaces
10 - Determining the best areas for the construction of emergency settlement
Shiraz has seen heavy and torrential rains 5 times in the last century. The water flowed out of the dry river and flowed in the passages and streets, causing major damage to houses and commercial places along the river. Many people needed a place to live temporarily. The uncontrolled expansion of the city, especially in the northwest axis, and the loss of natural areas absorbing runoff and precipitation and reducing vegetation in the region has caused that in high rainfall (more than 70 mm in 24 hours) and intermittent, water can not penetrate the soil. Slow and eventually flow in the path due to lack of drainage and proper disposal system. Among the effective human factors are land-use change, commercial, recreational and residential constructions, tampering with waterways or blocking these waterways completely, construction in the area of canals, construction of communication bridges on canals and narrowing of waterways.
Locating temporary settlement before the hazard occurs and in the planning stage can help managers have a written action plan after the hazard occurs .One of the differences between this research and other researches is the type of criteria considered and that so far no comprehensive study has been conducted on the subject of research for Shiraz. Suitable places for temporary settlement during flood risk in the study area were determined using multi-criteria decision- making models and the AHP model using ArcGIS software. The combination of criteria for locating suitable areas for temporary settlement in Shiraz (Figures 9, 10 and 11) shows that areas in the southeast and central areas are among the areas with high potential for temporary settlement.
Keywords: AHP, flood, settlement,