جستجوی مقالات مرتبط با کلیدواژه « پهنه بندی سیلاب » در نشریات گروه « جغرافیا »

Flood is one of the natural phenomena and one of the most important and destructive hazards in the world, which is associated with loss of life and property every year in different parts of the world and Iran. Climate change has consequences and effects on global warming, reduction of  Agricultural production, changes in the diversity and vegetation of pastures, changes in groundwater levels, the occurrence of social and economic problems, and so on. The overall goal of this research is to zoning and model areas at risk and  flood risk for changing climates. The prevailing approach of the research is the approach of climate change and its effects on the hydrology of Gorganrood watershed. The key goal of the current research is to model and forecast regional flood risk under climate change conditions using fuzzy analysis algorithm, hierarchical analysis and SWAT model in the watersheds of Golestan province. In fact, it is possible to plan the water resources of the region more precisely and help to calculate the more precise management of the transfer of the region along with other environmental variables, including this research. There have been many research studies on the phenomenon of precipitation in Golestan province and Iran, but none of them have examined this climatic variable with the perspective of climate change together with environmental variables.                                                                                                      

Gorganrood Basin with an area of ​​10197 square kilometers is one of the northeastern basins of the country, a large part of which is located in Golestan province. It is bounded by the Atrak catchment area and the Caspian Sea and Qarahsu catchment area from the west. In the present study, flood zone changes in Gorganrood watershed based on the use of meteorological organization (synoptic) station information with a 30-year statistical period(1989 to 2018), land use, vegetation, topographic moisture index, slope, altitude, land lithology, Distance from river, river density, erosion, soil science, runoff, simulated data The average rainfall of HadCM3 model in LARS-WG under SRA1B scenario is estimated between 2011 and 2045. The evaluation criteria used in this study are defined based on parameters such as ME, RMSE, ASE, MSE. The most important criterion for estimating estimates is the square root of the mean error (RMSE). (ME) is the mean of the errors or the mean difference between the estimated value and the value observed at point I. The SWAT model is an extension under ArcGIS software that simulates the main hydrological processes including evapotranspiration, surface runoff, deep infiltration, groundwater flow and subsurface flows by the simulator model. The type of land use in the region, the type of vegetation in the region, the slope values ​​and the length of the slope in different areas, which is used through the Geographic Information System (GIS). The input spatial variables of the SWAT model in this study include the digital elevation model (DEM) information layers, the soil layer with soil texture information, and the land use layer with its descriptive information. Hydroclimatology and numerical variables of SWAT model include daily precipitation, minimum and maximum temperature related to stations inside and outside the basin and the average daily runoff of the basin outlet along with their geographical locations. Simulating large and complex areas with different management strategies can be done without spending a lot of time and money.                  

The results for SRA1B scenario therefore it can be concluded that in general for the next period, the  area under study will face a decrease in average flow rate. By analyzing the obtained results, it can be inferred that the phenomenon of climate change will have tangible effects on the studied  area over time and will change the values ​​of temperature and precipitation parameters and will reduce winter precipitation and increase the temperature of the studied area. results of the future discharge simulation show a decrease in runoff for October under the SRA1B scenario. Therefore, according to the results, it can be stated that in general, the SRA1B scenario predicts a decrease in discharge for the next period compared to the observed discharge. The simulation results of the basin output flow and observational flow measured by architect R2 and NS as well as the uncertainty parameters r-factor, pfactor were evaluated and analyzed. The optimal values ​​of R2 and NS coefficients are one and one. One of the goals of the SWAT model is to To reduce impotence. So that most of the observational data are at the level of 95%. In research, NS coefficient greater than 0.5 and p-factor greater than 0.5 have been introduced as satisfactory values. Examining the changes, it is expected that the runoff will decrease with increasing scenarios. This trend has decreased in RCP4.5, although its limit rainfall has also increased, and in RCP8.5 (with more rainfall) the runoff has increased. The reason for this change is that the incidence of precipitation in RCP4.5 was in summer and early autumn, which despite the high evaporation and lack of snowmelt (according to RCP8.5 which in spring coincides with snowmelt) runoff is less than the next  scenario.                             

Flood risk zoning in the Gorganrood watershed, 345 villages with a population of 275,312 people are at high risk of flooding. square, it has a relatively low potential equal to 1425.46 square kilometers, a very high degree of flood risk equal to 884.68 square kilometers, and finally, an area with a low flood potential equal to 623.12 square kilometers from the entire surface of the Gorganrood watershed. It can also be concluded that most of the basin level equal to 89% is at risk of severe flooding. In all the stations, according to the predictions made by the LARS-WG model, the rainfall for the future scenario has increased in some months and decreased in some months compared to the base period . So that in the summer month, the rainfall will decrease and compared to the winter season, the rainfall will increase compared to the base period. The comparison of the monthly rainfall of the base period (2011-2007) with the rainfall simulated by the HadCM3 model for the SRA1B scenario (2011-2045) also shows a significant increase in rainfall in this series of scenarios in the months of September, October and November. It can be seen with a few changes. which can be investigated in terms of the effects of this phenomenon by studying the average percentage of precipitation changes for the SRA1B scenario in 2 periods; 2011-2045, 2045-2065 also shows the changes in rainfall from August in the period, 2011-2045 to 37.5% in November of the same period compared to the base period. The very high increase of precipitation changes in November can also be investigated and pondered for the cause of autumn floods.

Identifying flood prone areas is a key step in flood risk management and flood risk zonation provides a quantity measurement of flood risk, as a result of this, it is possible to send appropriate warnings in flood danger periods and facilitate rescue operations. In this study, the floods in the Abr watershed in several return periods were studied using Arc-GIS software and HEC-RAS hydraulic model. The cross sections were derived using the digital elevation model (DEM) in Arc/GIS environment and HEC-GeoRAS extension and the obtained outputs were entered into HEC-RAS hydraulic software. Manning roughness coefficients and flood discharge with five return periods of 2, 5, 10, 25, 50 and 100-year were entered into HEC-RAS model and water surface profile was computed in flow path and flood zonation for different return periods was derived using the HEC-RAS output information through geographical information system. results showed that in most sections of floods with a return period of 5, 10, 25, 50 and 100 years, it rises above the main section of the river and spreads around the river. Also, the agricultural lands along this river have been affected by the occurrence of floods with a low return period (2 years) and this will be dangerous for the residents of this village and agricultural lands.Area of flood zones for 5, 10, 25, 50 and 100-year return periods is 375, 476, 598, 759 and 1395 square kilometer respectively.

Flood zoning maps are among the basic and important sources of information for studying development projects in the world. In the conventional method of determining flood zoning maps, calculations are performed on the basis of a steady flow, assuming a fixed bed (without considering sediment transport). This study aimed to investigate the impact of river erosion and sediment transport on river flood zoning. So, the flood zoning calculations of Ajichai River were done using HEC-RAS model and the conventional method of steady flow with a fixed bed. In the next step, flood zoning calculations were performed using quasi-steady flow with moving bed and compared with the results of the previous step to determine the impacts of sediment transport on flood zoning. Comparison between the results obtained from steady flow (fixed bed) and quasi-steady flow with moving bed showed that in sedimentation sections, the width of the water surface increases in the flow mode with moving bed. The maximum rate of this increase in width is 19%. In other words, in the mentioned river, the width of flood zoning is less in the conventional method. This issue confirms the necessity of studying the river conditions in terms of erosion and sedimentation so that the amount of flood zone could be determined more accurately while the river is sedimentary. The increase of flood zone in sedimentation sections is due to the accumulation of sediments and consequently the increase of flow level and width of flood zonation. Therefore, it is suggested that in sedimentary rivers, a quasi-steady flow model (mobile bed) be used to prepare flood zoning maps for providing more safety.

Precipitation is one of the main factors of floods which due to the lack of proper dispersion of the rain gauge stations and the newly established some of these stations in most basins of the country, the use of these precipitation data faces serious challenges . Therefore , the use of remote-sensing methods is one of the ways that can be used for these fields. In the present study, the reanalysis rainfall data of ERA 5 for Kashaf rood catchment were evaluated in daily and monthly time steps and then its streamflow hydrograph was evaluated by using the rainfall data of Zoshk station and the Zoshk watershed parameters in the HEC - HMS software . The results showed that the reanalysis rainfall data of ERA 5 underestimated and overestimated and also had better accuracy in monthly time step (R = [ 0.87 - 0.99 ] ) than daily one ( R = [ 0.89 - 0.62 ] ) ; and its flow hydrograph compared to the observational hydrograph was satisfactory ( NSE = 0.49 and PBias = -26.46 ). The flood zone of reanalysis precipitation data ERA 5 in relation to the reference flood zone was obtained equal - 0.07 , which was obtained due to the underestimation of precipitation data and the subsequent underestimation of its hydrograph peak flow in the HEC - HMS model . Future studies can be used to evaluate the flood zone resulting from precipitation data of various products in the HEC - RAS model.

Among the types of environmental hazards, flood is one of the most destructive natural disasters that causes a lot of damage (Yousef et al., 2011). Floods are a common natural disaster in Iran after an earthquake that endangers human life. Every year, terrible floods occur in the northern cities of Iran, such as the provinces of Mazandaran, Gilan and Golestan. Due to the occurrence of these floods, the places with the highest potential for floods (sensitive areas) should be identified before planning by flood sensitivity maps (Bobek et al., 2012) to the loss of life and property (Kurgalas and Karatazas, 2015). In case of excessive rainfall, especially in the form of showers due to the uneven conditions and vegetation of the region, most of it becomes runoff and after a short time flows as a flood and causes a lot of damage. The increasing trend of floods in recent years indicates that most parts of the country are exposed to periodic and destructive floods and the extent of flood damage and loss of life and property has increased, which is one of the reasons for the frequent recurrence of this phenomenon in the result is a disturbance of the hydrological and ecological balance (Miller et al., 1990) such as urbanization (along rivers), climate change (Tehrani et al., A 2015; Kjildson, 2010) and deforestation (Branastirt, 2003).

The research method is applied based on the purpose and descriptive and analytical in nature. The method of data collection is based on library, field, spatial data of the study area and questionnaires. First, the study area is determined and the identification of the basin and the status of the factors are considered. In flood zoning, many factors must be considered, each of which is of varying degrees of importance, but due to the limitations that existed in the preparation of some layers and the limitations due to their length. There is a model process, the use of multiple layers of information causes excessive complexity of the model, cost and long time in model analysis and processing (Mousavi et al., 2016). Therefore, according to these limitations and previous experiences, the factors that have had the greatest impact on the occurrence of floods in the Gorganrood basin and are more in line with our models have been selected. In this study, 11 effective parameters in flood zoning including slope, slope direction, altitude, geology, rainfall, distance from waterway and river, distance from roads, distance from residential areas, drainage density, NDVI index (cover density) and runoff coefficient (including land use, soil texture, soil hydrological group, curve number, surface maintenance and annual runoff height) were prepared and classified. After identifying the effective layers, the steps of the research method are as follows:

Table 14 also shows the area of each flood susceptibility class. As it is known, 40% of Gorganrood basin per hectare has a very high and high sensitivity and as about 41% of the basin has a low and very low sensitivity to floods. Therefore, the results indicate a high risk of flooding in the Gorganrood watershed.

The results of this study with the results of Amir Ahmadi et al. (2011) in the city of Neishabour who concluded that among these effective factors in floods, the distance from the river and thewater way has the highest weight and impact and also the study of Sheikh et al. (2015) in Malaysia, agree that soil type has the least impact on floods. According to the final map, the high-risk areas are mainly located in the flat and sloping areas located in the north and northwest of the study area, and the closer we get to the steep and mountainous areas, the greater the flood potential in the basin is reduced.Although slope is one of the most important factors in the occurrence of floods, it has the lowest weight in this study; This is because this research focuses on flood damage, not the factors that contribute to the flood itself. In other words, although the slope plays a role in causing floods, but the most damage has occurred in low-slope areas, because in these areas the water velocity decreases and flood accumulation occurs, and this is the case with the areas with the most damage due to the flood observed in it, it is coordinated. Also, Fernández and Lutz (2010) consider flood slope and poor maintenance of drainage canals as the most important causes of floods by preparing a flood risk map in two cities of Argentina. Other researchers have also considered other parameters important in the occurrence of floods, including Sani (2008) by examining the factors affecting the occurrence of floods in rivers in Nigeria and concluded that the annual rainfall has the highest weight and land cover the lowest weight and they have an impact on the occurrence of floods. Morley et al. (2012) examined the flood potential of the Arno River in Italy and concluded that urban development areas are more vulnerable to flooding.The results of the final flood risk map in Gorganrood basin show the fact that 19.97% of the basin has a very high risk situation, 19.98% has a high risk situation, 19.98% has a medium risk situation, 20.07% has a low risk situation, 20% have a very low risk of flooding. Therefore, the results indicate the high capacity of the basin in terms of flood risk, so there are many areas with high and high risk, which need protection and watershed management measures (such as: prevention of soil erosion and destruction, reducing water sediment load, reducing the speed and intensity of runoff flow, increasing flood concentration time, creating opportunities for water infiltration in the lower layers of the basin and feeding the aquifers, planting plants suitable for the geographical conditions of the slopes and rehabilitating rangelands and creating green spaces in the basin.

Flood is defined as “streamflow with high discharge which spreads temporary on the lands nearby the main river” and consequently there will be some risks. Due to proper conditions, most of the economic and social activities take place in these areas. Therefore, it is important to determine flood zonation due to flood discharge with different return periods in these areas. In this regard, the Cheshmehkileh River located in Tonekabon Township has vast river boundary zones and most of the economic and social activities are carried out in its neighborhood, which is susceptible to flood hazard according to flood conditions and occurred floods. The cross sections were derived using the digital elevation model (DEM) with scale of 1:1000 in Arc/GIS environment and HEC-GeoRAS extension and the obtained outputs were entered into HEC-RAS hydraulic software. Manning roughness coefficients and flood discharge with five return periods of 2, 5, 10, 25, 50 and 100-year were entered into HEC-RAS model and water surface profile was computed  in flow path and flood zonation for different return periods was derived using the HEC-RAS output information through geographical information system. The obtained results showed that the longer the return period, the wider the surface affected by flood. Also, the highest flood area is related to agricultural land use with an area of 6.24 ha and after residential land uses with an area of 3.94 ha, forest with an area of 2.9 ha and orchard of an area of 0.8 ha were located at the following ranks.

The Leilan alluvial fan in the northwest of Iran has been exploited by humans due to its topographical, geological and climatic conditions and has established many cities (Leilan and Miandoab) and many villages on its surface. Over-use of alluvial fan capacity by its residents over many years has made the alluvial fan vulnerable to geomorphic hazards. The most important geomorphic hazards that threaten the alluvial fan are flood risk. The development of agriculture on the alluvial fan surface and river encroachment has increased the risk of flooding on the margins and floodplains of the Leilan Chai River. The flooding of the Leilan River in the spring causes a lot of damage to the farmland around the river. The Leilan alluvial fan is also at risk of flooding the Leilan Chai Seasonal River. The purpose of this study was to evaluate the flood risk dynamics at the surface of this alluvial fan. Therefore, the flood hazard assessment of the Leilan Chai River with a length of 15.4 km was carried out using HEC-RAS hydraulic model.

The study area is located in thewestern and eastern Azerbaijan provinces, and the cities of Leilan and part of the Miandoab city are located on it. This alluvial fan is located between 36o 55′ 10″ to 37o 00′ 40″ N and 46o 06′ 17″ to 46o 17′ 17″ E. The following data, software, and methods were used to dynamically analysis flood risk and prepare flood risk maps with different return periods in the study area: - Landsat 8 OLI satellite image for 2019 (path and row 168-134). - Topographic maps 1: 20000 and 1: 25000 of the study area. - Digital Elevation Model (DEM) with 12.5 m spatial resolution. - Shirin Kand hydrometer station data including daily and monthly discharge. - HEC-RAS hydrodynamic software for simulating flood in alluvial fan surface. - HEC-GeoRAS extension to provide the required parameters for the HEC-RAS model. - ENVI software for land use mapping. - ArcGIS software to generate maps.

HEC-GeoRAS extension was used in ArcGIS software to determine the geometric characteristics of the Leilan Chai River and The layers required for model implementation such as centerline, river banks (right and left bank), flood plain, cross-sections, bridges, and floodgates were prepared. Due to the floodgate on the river to perform flood simulation, the Leilan Chai River is divided into two reachs (upstream and downstream of the floodgate). In this research, after field surveys and gathering the required information, 151 cross-sections with a distance of 100 m and a width of 1000 m were created on Leilan Chai in ArcGIS software. It was also found in field surveys that in the second reach most of the rivers were occupied by humans and converted to agricultural land and as a result, the river width in this area was significantly lower than the first. Land use map and field studies were used to determine the coefficient of roughness in the bed and shores of the Leilan Chai river.

The present study, using the HEC-RAS hydrodynamic model, simulates the Leilan chai River flow on the Leilan alluvial fan during different return periods. The peak daily discharge data recorded at Shirin Kand hydrometer station were used to predict peak discharge values. Study of the flood maps show that flood risk does not pose a risk of flooding during the 2 and 5 year return periods of agricultural lands and residential areas around the river. But in return periods of 10 years or more, we see flooding of agricultural lands and residential areas around Leilan Chai. During the 25-year return period, 120.2 hectares of agricultural land and about 9.1 hectares of residential areas along the river are affected by the risk of flooding. The village of Mullah Shahabuddin is one of the areas developed along the river and as a result is at risk of flooding in the event of heavy rainfall. The most vulnerable areas are in the second reach due to the occupancy of the river bed by residents of the region and converting their marginal land into agricultural land and residential areas. Therefore, it is necessary to carry out a serious review of the riverbed in order to prevent accidents and the possible financial and casualties in the event of flooding in the Leilan Chai River, and that the river's privacy should not be further confiscated. It was also found in field surveys that in the second reach most of the rivers were occupied by humans and converted to agricultural land and as a result, the river width in this area was significantly lower than the first. Land use map and field studies were used to determine the coefficient of roughness in the bed and shores of the Leilan Chai river.

Floods are the most common natural hazards, the recurrence of which is increasing and the associated risks in urban and rural areas are of global importance, although their importance is not well understood for developing countries. The aim of this study was to zoning the flood risk of Dinevar River in Kermanshah province. Therefore, the HEC_RAS numerical model was used to simulate the flood and was used through the HEC-GEORAS. Using SMADA software, the peak flow rate was calculated and the flood zone with different return periods of 2 years, 10 years, 25, 50, 100 and 200 years is simulated area and with the help of digital depth model Water and land use layer, the amount of damage was calculated using the equation of depth function and damage in the return period of 25 years, 50 and 100 years. The results of this study show that the area of flood expansion zone in the return period of 25 years is 40.34 square kilometers, in the return period of 50 years is 43.51 and in the return period of 100 years, 44.28 square kilometers is endangered in terms of damage. 25 years is considered a baseline flood that shows significant damage, covering all farms, but floods affect parts of farms at lower returns. But it is controllable, while 25-, 50-, and 100-year-old floods have completely endangered many rural centers and farms. 50 years has been an average of 85% more, which requires flood control for sustainable management.

Varkesh-Chai River with approximately 69 kilometer and north-south trend, in one of the main and permanent rivers of Tabriz city, That 10 villages with worn out texture have established in its main bed. Field studies show that, villages’development has been without knowing the rules governing hydraulic behavior, prediction of river hydrological behavior, and no respecting the main bed of river, it has been conserved to the agricultural land or garden. Lack of knowledge and attention to the above-mentioned cases and river bed manipulation has increased the vulnerability of villages, agricultural land or other human facilities of the flood risk in the catchment area. Therefore, it is necessary to study the areas potential to the flood occurrence and to prepare floodplain maps in district. In present study, flood levels were determined along the main river, during the return periods of 25 and 50 years. For this purpose, geography information systems (GIS) and HEC_RAS model and HEC_GEO_RASextension were usedto simulate earth geometry, river plans, left and right rivers shores, and flow rate obtained then, the villages exposed to flood with these return peaks were identified and then, hydraulic behavior of the river was simulated. Finally, solution to reduce the damages caused by flood along the main river were identified.

Every year we see natural disasters causing major financial and human losses to human societies, and unfortunately, our country also has a bitter taste of it every now and then. Floods, earthquakes, droughts, frostbites, storms, and so on ... There are a lot of financial and financial losses to the country, which will require measures to reduce the damage caused by these disasters. Definitely, the first step is to understand and understand these phenomena. The development of the process of urbanization and degradation of vegetation, soil erosion, and global climate change has already paid attention to the importance of addressing the issue of the urban flood. This research was carried out to determine the risk of flooding in Sari using multi-criteria decision-making techniques. Using nine criteria, the distance from the river, runoff coefficient, CN coefficient, population density, residential density, slope, land use, the age of the building and outdoor space were developed. By preparing the required layers, determining the weight of each layer based on their importance in the occurrence of a flood. After the final weighing, the layers were compared in two to two by Expert Choice software and the matrices derived from these comparisons were transferred to Idrisi software and the final coefficient was determined for each layer. Finally, by applying these coefficients, ArcGIS software provided a flood risk zoning map in the city of Sari. The results show that flood risk in the center and south of the city has been the highest. Flood risk zoning map shows that 12.24% of the map area is in a very high danger zone and 37.05% in very low-risk zoning. To reduce the risk of retrofitting buildings around the river to reduce flood damage.

Nowadays floods are considered as one of the greatest threats in terms of social security and sustainable development which affect 20 to 300 million peoples each year (Hirabayashi & Kanae, 2009). In recent decades, many studies have been carried out on floods which have mainly approached to flood risk management. Flood inundation models are defined as the tools which could simulate the rivers hydraulic and also occurred floods in flood plains (Horrit, 2007). In other words, flood inundation models are useful tools for flood plain management. This ability in flood prediction, and also flood damage reduction by protecting of near river land use, improving the knowledge of indigenous people of flood plain, and preventing the construction in banned area of flood plain is very useful (Di Baldassarre, 2010). In this study the risk of flood occurring for different return period along 72 Kilometer in Qaraso River have been investigated.

This research is based on filed studies and 1:2000 scale topographic maps that provided by Ardabil regional water authority. The 1:100000 scale geological maps, satellite imagery such as IRS and Google Earth and also hydrometric data of Dostbaglo and Arbab Kandi hydrometric station, considered as essential data. The HEC-RAS model could calculate the water surface profile in stable flow gradual variable in rivers and artificial channels in the subcritical, supercritical and complex regimes. The calculation of water surface profile carried out from one cross section to other cross, step by step, solving energy equation in standard way.

In this study in order to estimate the frequency distribution of floods we used Pearson Type III distribution in logarithm base 10, which provided by USA federal organizations of rivers reconstruction. Then flood peak discharges with different return period and its probability of occurrence has been calculated for important hydrometric station namely: Dostbaglo and Arbab kandi. According to the flood-prone zonation map, we observed the maximum wide of flood-prone area in reach2 to reach4 of river (from Qadirlo Village to Lalganj Village) in different period. In these reaches the width of flood-prone area in 25 years return period is about 500 meter on average. In first and some parts of reach6 and reach7, due to narrowing of channel and some obstacle the wide of flood-prone area was decreased and instead the water depth has been increased. Regarding to the placement of the Qadirlo, Kangarlo, Agh¬ Darag and Dostbaglo villages in the margin of the Qaraso River, the flood zonation in this rivers should be considered. The main landuse of Qaraso riparian is assigned to agriculture and orchards. By overlay the flood zonation maps with satellite imagery we observed that the main portion of this agriculture lands, has been located in the river bed and riparian zone (according to 25 years return period), are at risk of flooding. This could lead to heavy damage for farmers. For example, the flood events with 25 years return period, affected about 1085 hectare of farmland and orchard that located beside Qaraso River and lead to heavy damages.

Regarding to notable encroachment by farmers in the Qaraso river bed, the Flood risk is very important. The flood-zoning of Qaraso River shows that wide part of farmlands and orchards and also part of the facility located around the Qaraso River (nearby the village of kangarlo) have been exposed to floods with 25 years return period. Therefore, according to article 10 of regulation of bed and riparian of rivers the regional water authority of Ardabil should determine the condition of this high risk area. Accordingly, the floodplain management should be considered as an important and essential issues.

Zoning flood in the rivers and watercourses within different return periods and identifying and introducing areas at risk of flooding are non-structural, important measures in the flood management discussion. The aim of this study was to identify natural areas prone to flooding in the region and to review the hazards and consequences of its occurrence in order to identify floodgate lands at the river bed. In this study, the HEC-RAS model, HEC-GEORAS appendix, and ArcGIS software were used to simulate the river flow, and to calculate and determine water surface profiles and other hydraulic characteristics of flows. According to the results of the floodgate zone, it can be said that the area of land at risk of flooding has increased at the entire study area due to the increase of return period and has also dramatically changed at different study region due to the geomorphological conditions of the area. So that, if we consider the area of the floodgate zone with a 25-year return as our basis, 3607/43 hectares are at risk of flooding in all the regions, of which 2129/69 hectares are in the region 3.The region 3 can be introduced as the most critical region of floodgate, so that the largest area of arable lands, garden areas and residential areas of this region are at the risk of flooding in the river bed. The average maximum power of the river in the returns course 1.5-100 years old has the highest value in the region 2 (573/7 watt per square meter). So this region, the harmful effects and damages are taken into consideration rather than the power of the river, which can be considered as the most critical region of erosion.

Prediction, controlling, and reduction of the flood plain have crucial role in integrating watershed management. The flood damage analysis and designing control plans need to identify floodplain limits around the main river according to different return periods. Kashkan River in Lorestan province has been challenged frequently by dangerous floods. Since numerous villages and also agricultural lands are existed near the both sides of the river, they are exposed in flooding hazard. The aim of this study is preparing the floodplain maps of this river for a reach length of 5000 m using HEC-Geo-RAS for different return periods. For this purpose, digital elevation map (DEM) with scale of 1:150, topographic map with scale of 1:50000, cross-sections geometry, and peak discharge data recorded in the hydrometric station in upstream of the reach were incorporated. The peak discharge corresponding to return periods 2- to 1000-years are estimated as 227 to 5000 m3/s using fitting a three parameters person distribution. Simulation of the hydraulic behavior of the Kashkan River using the HEC-RAS model indicates that the floodplain area for discharge with return period 25-years are 75% of one obtained for 1000-years. Additionally, the floodplain area for the upstream of the study reach is greater than the other where. This reveals that construction of the villages and changing the land use in the river borders threaten with low period floods (e.g. 25-years).

Flood risk zonation is necessary to Control and predict the amplitude of flood damage.The purpose of this research is to evaluate the rate of flood risk vulnerability and the flood damage assessment in Tabriz. Specific variables of this study are land use, population density, river beds, slope classes residential density, CN coefficient, runoff coefficient, open spaces and old buildings.Methodologically speaking, having determined the necessary layers, the weight of each layer was obtained based on the importance of layer in flood occurrence. After weight determination phase of the research, layers were compared with each other in two–by–two basis by the Expert–choice software, then the resulted matrices of these comparisons were analyzed by Idrisi software and final coefficients for layers were calculated. Finally, by applying these coefficients through Raster Calculation menu to ArcGis software, the map of flood risk zonation of Tabriz suburb was prepared. The critical zones vulnerable to flood and inundation were determined. oreover, the possible flood loss was estimated by developing the flood damage map.thus,flood critical zones of urban texture and inundation were preparedand the flood loss was determined by producing the map of flood damage evaluation. the flood risk zonation map reveals thata bout 3/34% of study zone is located in the class of very high flood risk, 15/87% in high flood risk class, 70/84% in medium flood risk class and 9/95 percent is in the low flood risk class. Moreover, there was a compatibility of 85% between the classes of flood damage evaluation map and those of flood risk map.

Flood is a natural phenomenon, which human being has experienced from very old times. In Iran, due to its very large area, several climates, and time and local density of Precipitations in most watersheds, there are many great floods of the country. In this study, run-off coefficient, maximum debit of flood, identifying the factors and elements that are effective on bloodiness, and zoning of the area of Leilan chai watershed based on its flood bearing are analyzed. The curve number method was used for this watershed. To do this, firstly, the needed data and information including the statistical situation of the area climates and satellite images were gathered Inputted to the GIS data system. Compiling these data and information by the SCS method and the CN of the watershed, The infiltration level and run-off volume were prepared.Finally, the zoning map of the annual flooding potential of the area were produced using weighting model and compiling the area Precipitation, hydrological groups of soil, slope level, land use, etc.

The dimensions, shapes and the patterns of natural rivers change according to their dynamic properties. These unavoidable changes cause the rivers imbalance and a new balance will be formed. The around lands will be affected by this dynamic and dangers such as instability of the bed. In this research we used chronological inference method to study Kashkan River morphology. Kashkan river is located in a region between Lorestan province and Gavmishan bridge in a reach of 25 kilometers. The aero photos of 1334, 1376, the sensing images of liss3 obtained from IRS P6 satellite in 1385 and the Geo Eye image of the land were digitized in Arc GIS software. In the second step geometrical parameters such as wave length, valley length, sinuosity, central angle and radius tangent on the river arch were calculated. Then these geometrical parameters were statistically analyzed and were compared in 4 stages. We Using HEC-RAS investigated flood zonetion as an important factor in river bed changes. The results of this study and comparing these parameters during the 4 reaches showed that in the abovementioned year's kashkan river pattern was meandering in the reaches of 1, 4 and 5 and also it was developed meandering form in the reaches of 2 and 3. Those river’s arcs which had the most changes in those years were located in the reaches of 2 and 3. At the end it was concluded that the geology factor and the river’s flood in the reaches of 2 and 3 were the most important factors in forming the bed’s changes and bank erosion. Topography factor was the most important factor in causing the most changes in the reaches of 2 and 3 which were located in floodplain.

Flood risk zonation is necessary to control and predict the amplitude of flood damage. The purpose of this research is to evaluate the rate of flood risk vulnerability and the flood damage assessment in Sabzevar. Specific variables of this study are land use, population density, river beds, slope classes, residential density, CN coefficient, runoff coefficient, open spaces and old buildings. Methodologically speaking, having determined the necessary layers, the weight of each layer was obtained based on the importance of layer in flood occurrence. After weight determination phase of the research, layers were compared with each other in two-by-two basis by The Expert- Choice software, then the resulted matrices of these comparisons were analyzed by Idrisi Software and final coefficients for layers were calculated. Finally, by applying these coefficients through Raster Calculation menu to ArcGis software, the map of flood risk zonation of Sabzevar suburb was prepared. The critical zones vulnerable to flood and inundation were determined. Moreover٫ the possible flood loss was estimated by developing the flood damage map. Thus, flood critical zones of urban texture and inundation were prepared and the flood loss was determined by producing the map of flood damage evaluation. The flood risk zonation map reveals that about 15 % of study zone is located in the class of very high flood risk, 45 % in high flood risk class, 25 % in medium flood risk class and 15 percent is in the low flood risk class. Moreover٫ there was a compatibility of 80 % between the classes of flood damage evaluation map and those of flood risk map.

Flood is a natural phenomenon, which human being has experienced from very oldtimes. In Iran, due to Its very large area, several climates, and time and local density ofPrecipitations in most watersheds, there are many great floods of the country. In thisstudy, run-off coefficient, maximum debit of flood, identifying the factors andelements that are effective on floodiness, and zoning of the area of Leilan chaiwatershed based on its flood bearing are analyzed. The curve number method was usedfor this watershed. To do this, firstly, the needed data and information including thestatistical situation of the area climates and satellite images were gathered Inputted tothe GIS data system. Compiling these data and information by the SCS method and theCN of the watershed, The infiltration level and run-off volume were prepared.Finally,the zoning map of the annual flooding potential of the area were produced usingweighting model and compiling the area Precipitation, hydrological groups of soil,slope level, land use, etc.

A region of 390 square kilometers of Neyshabour was selected for flood zoning. This region is divided into the city and hydrographic networks. This confined area includes three geo-morphological part namely mountain, plain head (along alluvial fans) and lowland. A part of the city is located in Plain geomorphology unit and the other part is laid in the mountains area that covered surface of alluvial fan. The study on the desired area was conducted as follows: The study area is too wide therefore, it is divided into 3 sub-basins; then, the effect of urban development on the basin was estimated through topographic maps, aerial photographs and field visits. The maximum flood event of every basin is calculated by a 100- year return period. The purpose of this calculation is estimating the maximum flood volume which is entered into the urban of the mentioned basins. By providing the required layers for both the city and the basin area of the study, the weight of each layer is determined based on its importance in the occurrence of floods. (Importance of each layer was determined based on the opinions of experts in various organizations of Neyshabour). After the final weighing, the layers were compared with each other and the resultant matrix of these comparisons is used in Idrisi and eventually final coefficients were determined for each layer. Finally, by applying these coefficients through Raster calculator in ArcGis, maps of flood hazard zoning in the basin were determined and the boundaries of Neyshabour were specified separately.Thus, the critical boundaries of urban area against flood were defined and flood damages in the form of the maps of the damage assessment were presented.