پهنه بندی مخاطره سیلاب در حوضه رودخانه کلات (زیرحوضه منتهی به شهر کلات)

Introduction
Flood is one of the most important natural disasters in the world. More than half of the global flood amage occurs in Asia. One of the types of hazards that affects a large part of the country each year is the flood. Iran is in the high-flood region of the world. The city of Kalat, with its linear pattern along the Kalat River, was affected by the severe flooding of the river and its changes in the urban development process have increased the intensity of flooding. The flood, dated April 24, 1398, was an example of a flood that caused significant damage to agricultural land and residential buildings in the city due to the intensity of rainfall. The purpose of this research is to assess and quantify urban flood risks in the basin area extreme to Kalat Naderi city.
Data and research method
This paper relies on field, library and documentary research methods. First, using the topographic maps, the study area was determined. Topographic maps 1: 50000 and 1: 250000 Kalat for mapping elevation, slope, slope direction, drainage network and communication paths (Mapping Organization of Khorasan Razavi) and geological map of 1: 100000 Kalat for geological formations , Lithological and lithological units of the range and main and secondary faults (Geological Survey of Khorasan Razavi), from precipitation data of synoptic stations, climatology, and evapotranspiration for precipitation and temperature maps (Weather Administration of Khorasan Razavi province), from Soil map of the scale with 1: 50000 scale (Research Center of Natural Resources and Agriculture of Khorasan Razavi province) and land use 1: 50000 (Administration The total natural resources of Khorasan Razavi province, satellite images, aerial photos of Band 1 of Mashhad (Kalat Block) with a scale of 1: 40,000 geographic organizations of the Armed Forces were used and the maps of the study area were drawn using the GIS software. To assess areas at risk of flood in the town of Kalat Naderi, and the study area, using the natural and morphological characteristics of the seven effective factors in the occurrence of flood include: hydrologic factor (runoff), geology (lithology), slope, roughness (altitude) Drainage density, distance from main canal or waterway and land use. The factors used in this study were chosen for their general relationship with the dangers of flood and based on Shaban et al method, (2001).
Results and discussion
The final map of hazard zonation of the study area of Kalat city using the hydrologic layers (runoff, drainage density, distance from the waterway). Lithology, slope, altitude, land use using a combination of weights obtained from Shaban method with each layer And their overlay in the environment (GIS Model Builder). Of the total study area, 10.14% are very low, 30.15% are low-risk, 20.35% are in medium risk, 26.42% are at high risk and 12.66% are at very high risk. Therefore, the hydrologic factor (runoff, drainage density, distance from the waterway) is the most valuable and the most important source of flood hazard in the region with value of 49.69 % and the land use agent with a value of 7.67% is the lowest weight It is dedicated to.
Conclusion
The purpose of this study is to zonate the flood risk areas in the Kalat Naderi study area in Khorasan Razavi province. The results indicate that hydrologic factors (runoff, drainage density and distance from the waterway), geology (lithology), elevation and slope have the most important role in the occurrence of hazards in this area. In the study of seven factors, it should be stated that: The runoff factor and rainfall intensity, especially rainfall over 300 mm, were the most important factor in the occurrence of flood hazard in the city of Kalat and the study area. In terms of lithology, clay formation, Neogene red sediments and quaternary alluvium play the most role in the occurrence of flood hazard in the study area. For the gradient, the maximum weight and frequency are in terms of the area of the class (0-10%). For the height class parameter, the maximum weight is for the class of 497- 1000 meters and the lowest weight for the height class 1500-1709 meters. In terms of distance from the waterway and drainage density, the highest score is found in the 0-100 meter waterway. The distance from the main flow of the Kalat River and the greater density of the northern boundary of the city to the main Kalat River has provided critical conditions for the city and the urban infrastructure. For land use, residential areas at high risk of flood have the highest weight. According to the results of the research, the total area of the study area in the city of Kalat was 10.14% in very low risk, 30.15% in low risk, 20.35% in middle class risk, 26.42% in high risk category and 12/66 is in very high risk. Hydrological factor (runoff, drainage density, distance from the waterway) is the most valuable and most important source of flood risk in the studied area in the region with the highest value of 49.69% and the most important land use factor of 7.67% has the lowest weight and impact have given. Also, based on the results of flood risk zoning and according to Shaban method, a large range of Kalat city is at risk of flood, which is more At the entrance to the city and the Darband area and under the northern sub basin, overlooking the city of Kalat, it provides critical conditions for the city and should be given special attention in future plans.