عنوان مقاله [English]
Floods are the most common natural hazard in the world that affect many people in the world every year, and population growth and urban development and human settlements have caused floods to become hazards for humans and to reduce casualties and financial losses. From floods, flood risk management seems essential in this regard
In this study, 5 factors affecting the occurrence of floods including: rainfall map, slope, topography, vegetation and physiographic characteristics have been considered.Then, according to the mentioned factors, the layers are included in the model, and the flooding zoning of the area is done. A standard criterion for judging or a rule for testing the desirability of decision-making options is the choice of general rule evaluation criteria that determine these criteria in relation to the situation of the problem; The set of criteria should have characteristics that represent the multi-criteria nature of an evaluated problem
Floods occur mainly in conditions with high rainfall. The map of the basin has been prepared from eleven rainfall stations located in Fars province over a period of 30 years. First, the data were edited in Excel, then imported into the GIS environment, and in the next step, using kriging, the map of the study area was cut from it.
In this regard, using the Topsis model, the above-mentioned criteria have been classified and determined in order to determine the areas vulnerable to flood risk in the hydrogeomorphic basin of Shiraz and the civil basin of Shiraz. Each of these criteria has its own characteristics that have been extracted according to the following methods. Information such as library studies, topographic maps of Shiraz 1.50000, geological maps of Shiraz 1.100000 and 1380 as well as information about altitude digitals taken d aerial photographs of the Shiraz civic area during the four decades of 1330, 1350, 136 from the study area In order to study the behavior of Shiraz hydrogeomorphic basin and also how the development process of Shiraz urban area, using the normal distribution curve, and then the analogical analysis of the results of the above topics on how the flood coefficient of the basin has behaved.
Results and Discussion
According to the studies, the cybernetic coefficient of flooding coefficient of Shiraz hydrogeomorphic basin is as follows:
B) Cybernetics of flooding coefficient of Shiraz hydrogeomorphic basin and spatial development of its civil basin from 1330 to 1380.
In the study basin, the compaction coefficient was 1.79, which indicates the average trend of flooding coefficient of the basin and its elongated shape. The behavior of flooding coefficient of Shiraz hydrogeomorphological basin has varied between 1 to 1.9 Gravilius coefficient.
This means that approximately 50% of the development of Shiraz basin is located on the minimum part of the flood incidence coefficient, and 50% of it is located on the middle areas up to the maximum flood incidence coefficient.
C) Normal distribution
1- Normalized limit of flooding in the whole Shiraz basin
The normal limit of flooding coefficient of the whole basin on the coordinate system between 1 to 3 flooding coefficient and the peak of this axis is equal to 2 (arithmetic mean) of flooding coefficient and according to the calculation formula for the whole basin, the integral interval between 1.73 to Calculated -1.73, that the risk of flooding in the whole basin is equal to / 916 or 92%, which is rounded.
2- Normalization limit of flooding in Shiraz civil basin in 1330s
The rate of flooding in this decade was between 1.876 and 1.854.
In other words, the risk of flooding in Shiraz civil area in the 1330s is equal to 1.5%.
3- The norm of flood normalization in the civil area of Shiraz in the 1350s.
The flooding rate of this decade is between 1.88 to 1.67 flooding coefficient and in other words, the risk of flooding in the 1350s is equal to 14%. Of course, the percentages are rounded and indicate the further movement and development of Shiraz towards the areas of maximum flooding.
4- The norm of flood normalization in the civil area of Shiraz in the 1360s
According to the normalization limit of floods in the civil area of Shiraz in the 1980s, the coefficient of floods was between 1.88 and 1.46. The risk of flooding in this decade is equal to 24%.
And indicates the proximity of the urban area to the area is the maximum risk of flooding.
5- Normalization limit of flooding in Shiraz civil area in 1380.
In the 2001s, the normalized limit of flooding of this decade is between 1.96 to 1.4 of the flooding coefficient. The risk in this decade is equal to 32% and in the process of development, the risk of flooding is increasing, and in general, it has led the civil sphere to the areas with the maximum flooding rate.
The results of the studies showed that the Shiraz basin, based on calculations, has a flooding coefficient of 1.79 and a branching ratio of 2.88, and in the equivalent rectangular section has a length of 130.765 km and a width of 16.035 km, which generally indicates It is a moderate trend in terms of flood risk. Analysis of the urban development trend of Shiraz during the four decades of 1330, 1350, 1360 and 1380 according to the flood zoning map shows a minimum in terms of flood risk. However, by examining the flood risk level of Shiraz hydrogeomorphic basin and Shiraz civil basin using normal distribution model and calculations, and considering the urban development course on this model in the range of 1 to 3 flood factors, and 1.73% of the area under the curve, It turned out that, in principle, the trend of urban expansion to 1 flooding factor in the left part of the curve, and indicates a higher risk of flooding.