Introduction

Flood, as one of the important natural crises, causes a lot of damage to the affected areas. In order to manage floods, first the factors of its production and creation must be identified, then the areas that have a great potential in generating floods should be identified. Floods are the most common natural disasters that affect urban areas around the world and their effects in developing countries are due to social and economic inequalities, poor development infrastructure, unplanned change in land use patterns, Climate conditions, insufficient flood mitigation systems and increasing urbanization rate are intensifying. Like many urban areas of the country, vulnerability to flooding in Shiraz is difficult due to low drainage standards, poor drainage capacity, rapid housing development, etc. The most important role of the dry river, which is flood control, has become a problem with the creation of a bypass across the river. On the other hand, the dumping of construction waste along the river has created the ground for more flood risk

Methodology

The data required in this research is between 2010 and 2020 and using Landsat satellite images and SCS model, the maximum possible runoff in the basin has been calculated using the SCS method. To obtain the CN of the hydrological group of the soil, land use, type of agriculture and hydrological status, the maximum possible precipitation was calculated by using the meteorological data and the geostatistics method, and the maximum runoff was obtained by running the SCS model. By obtaining the maximum runoff, the maximum discharge was calculated with the physiographic data of the catchment area, and with the discharge and the shape of the riverbed, the simulation of floods and floodplains was carried out, and finally, with the information layer, the floodplains at risk were identified.

Discussion

The time for the flood to reach its peak in this river was between 8 and 12 hours, but with the construction measures and the changes in use in the upper part of the basin, this time has been reduced and the response time for managing the flood crisis has been reduced. By covering the roads that end in the dry river, including the Koran gate road, which was turned into an entrance road by the Shiraz municipality, this problem has been further exacerbated. As in the flood of 1998, 21 people were injured and 119 people were injured. Due to this flood, the areas around the river were dry, including Haft Ton and Saadi areas, suffered damages due to this flood. In general, it can be said that unprincipled actions such as land use change, encroachment on the river course, unprincipled constructions and close to the river bed, pouring construction materials on the river course, creating bypasses on the river bed have created more flood risk. And the more these measures increase in the western part of the basin, i.e. in the Golestan, Khollar and Gardneh Shul parts, the more damage will be caused to the middle and eastern part of the basin, which is inside the city of Shiraz, because first of all, the slope of the basin is also from the west side. It is to the east, secondly, the amount of rainfall decreases from west to east. Also, by pouring construction materials, etc., the load of the river has increased along with the sediments that the river itself carries in the form of alluvium and uplift. This city will be very dangerous, including the flood that happened in 1965 and caused heavy damages. On the other hand, vegetation can be effective in this river when the width-to-depth ratio is less than 16, which is a potential factor in the western part of the basin. But unfortunately, not only this factor is not strengthened in the western part of the basin, but with the creation of constructions, the ground for it has been reduced. If the flow rate entering the river bed is between 100 and 250 cubic meters per second, according to the width of the river and Other factors can be very dangerous unless there is a ground to reduce the flow in the upstream of the basin, and one of the solutions is to create vegetation in the western part of the basin.

Conclusion

Based on the obtained results, in the upper reaches of the basin, which has a high slope, bare lands, impermeable soils, there is more dispersion, the soil retention is low, and as a result, the amount of runoff production is also higher. With the increase of runoff at the level of the upper basin, the maximum discharge has also increased, and with this increase, the floodplains are submerged with a greater extent. Through the surveys conducted on the dry river, it was found that the amount of erosion and destruction of the river banks in the routes Direct and meander are far more in places without vegetation than in places with vegetation. If the flow entering the river bed is between 100 and 250 cubic meters per second, considering the width of the river and other factors, it can be very dangerous. Also, the more land use changes in the western part of the basin, i.e. in the Golestan, Khollar and Gardane Shul parts, will cause more damage to the middle and eastern part of the basin, which is inside the city of Shiraz, because first of all, the slope of the basin is also from the west side. It is to the east, secondly, the amount of rainfall decreases from west to east