جستجوی مقالات مرتبط با کلیدواژه « شماره منحنی(CN) » در نشریات گروه « جغرافیا »

Land use change is one of the most important factors affecting ydrological conditions, erosion and sometimes causing biodiversity destruction. The purpose of this research is evaluation of run off generation process in current land use condition in comparison to the optimized land use condition in Shiraz Nahre Azam watershed. To do this, after preparation of current and optimized (land use types regarding to land capability) land use maps, the effects of land use on run off generation was evaluated for the mentioned two conditions using SCS hydrological model. Comparison of the land uses in two conditions show that the area of agricultural areas do not show considerable differences. However, there is 8.1% decrease in urbanized area and 17.18% increase in range lands in optimized land use condition comparing to the current land use condition. Results also show that the overall value of CN in current land use condition is 82.6 where it is 75.2 in the optimized land use condition. The percentage of decrease in run off in optimized land use condition over the current land use condition decreases as the return period is increased, and the highest decrease of run off belongs to return periods of 2, 5, 10 and 25 years which is respectively 37.47, 29.97, 26.54 and 23.32%. The results of this research show that identification of the capability of the the lands is very important and the land use planning based on the land potential plays an important role on reduction of flood damages and run off loss.

Floods and their consequences, with the intensification of human exploitation of nature in the early twentieth century, have had negative effects on vital ecosystems. Also, adverse effects of erosion, while destroying the harvest site, lead to reduced production capacity and degradation of physical and chemical properties of soil in lands. To manage this phenomenon, the factors of production and flood must be identified and then areas with high potential in flood production must be identified to enable the possibility of executive and corrective operations at smaller and risky levels. The level of flood areas in the country is estimated at 91 million hectares, of which about 42 million hectares have moderate to very high flood intensity. Therefore, knowing the flood situation of the regions is a necessity to prepare strategic plans for sustainable management of basins. The purpose of this study is to estimate flood potential and determine the priority of flood areas by physical factors to combat erosion in Hajilar watershed by using a combination of data and information based on the CN-SCS method and also to determine critical flood areas.

In this study, in order to investigate the potential and zoning of flood risk in the basin, at first, by studying and examining the foundations and theoretical background of the subject, the physical factors affecting the occurrence of floods were identified.Then, the required information was collected and layers of each of the proposed factors were prepared in Arc GIS 10.7 software and Arc-Hydro and Arc CN-Runoff extensions. In this regard, the information layers of the waterway network, level lines, and elevation classes were prepared using a digital elevation model with a scale of 1: 120,000. Lithological information layers were obtained using the geological maps of Siah Rud, Tabriz, belonging to the Geological Survey of Iran. The precipitation map of the basin was prepared using data from meteorological stations within the study area and also adjacent stations using IDW interpolation method. Land use layers of the area were obtained using the area land use map and monitoring using Sentinel 2 satellite imagery. The soil map of the region has been prepared using studies of natural resources of Arasbaran basin prepared by the Forests, Rangelands and Watershed Management Organization of the country and controlled with lithological conditions and other environmental factors. Vegetation of the area was prepared through NDVI index. Then, by extracting the number of curves (CN) and the amount of penetration (S), the layers were combined and the runoff height of the basin was estimated by the runoff curve number (CN-SCS) method, the units were classified by SPSS software and the priority of areas in terms of floods in the basin was determined. In order to determine the peak discharge of flood through the obtained data, first based on the proposed Schwab relation, the water accumulation time of all sub-basins was prepared separately and, finally, the maximum peak discharge obtained from this runoff was obtained.

The results of the SCS-CN model which was intended to determine areas with different flood potential in the basin and compare it with environmental factors such as slope, lithology, land use, rainfall, etc in the basin indicate that this model is highly capable of estimating the flood potential in different areas of the basin. Results of changes in the number of curves based on effective environmental factors were also presented in Table 1.The potential for runoff production was high in high altitudes with poor pasture landuse or dryland agriculture with poor permeability soil, as well as in residential areas where the city surface consists of impermeable or low permeability surfaces.Also, there was a high flood potential in the  dense and medium pastures with hydrological group B. Irrigated and rainfed agriculture with hydrological group A has the lowest runoff potential and thus has the lowest amount of flooding in the basin.By obtaining the runoff height in different parts of the basin and determining the levels of changes in the values through quartering, it was found that mainly the central and lower parts of the basin are in the first priorities in terms of flood potential. Poor coverage, low permeability, and low rainfall in this area are some of the factors that increase flood potential. The southern and central regions are areas marked by low sensitivity to flooding. By prioritizing areas in terms of floods and mapping them, the results can be used in watershed management operations at the level of high-sensitivity units to reduce erosion and damage. Taking into account the values of runoff height relative to the sub-basins and water accumulation time obtained based on the Schwab estimation method, the results showed that the flood volume and maximum peak discharge in the basins have a good relationship with each other and the highest maximum peak discharge is related to H33 and H18 sub-basins with volumes of 51.44 and 48.67 and the lowest is related to H12 and H29 sub-basins with volumes of 3.77 and 3.86 m3/s.

Floods are among the most important environmental hazards that cause human and financial losses every year. In the meantime, using the SCS-CN experimental model, as a method for estimating floods in basins with different environmental conditions, and the inter-environmental approach in it can be a useful solution in watershed management studies. Considering that human intervention has caused an increase in floods in all areas, providing methods for accurate flood estimation is one of the basic needs of the relevant responsible organizations. Accordingly, the present study was conducted to determine the priority of areas in terms of flood potential and the results showed that 9% and 51% of the basin areas are in the very dangerous and high-risk flood categories, respectively. According to the final map obtained, Areas with very high risk and high risk are mainly located in residential areas and in the lower areas of the basin, which are the first priority in programs related to water resources, especially flood control and watershed management in the upstream units. Also, according to the results, areas with medium risk potential occupy 23% of the area and 17% of the area has low risk potential. The results of the study confirmed the high potential of the studied area in terms of flood risk, so lands with very high and high risk are lands that should be protected and appropriate watershed management measures must be conducted to control the speed of floods and reduce soil erosion.

Introduction and Background: The development of urbanization and the transformation of rural areas into cities are accompanied by land use changes and pressure on natural systems. One of the natural systems is the rivers that are affected by human activities in urban areas. The purpose of this study is simulation and estimation of the variations of geohydro-logical parameters including surface runoff, river discharge, permeability and evapotranspiration. his research has been conducted using the semi-distributed SWAT model in the last two decades of the past twenty years (1998) and present (2018) in the catchment area of Darband. In this study, the SUFI2 algorithm was used to calibrate the model. The results of the research show that after optimizing the parameters used in SWAT-CUP, the value of Nash-Sutcliff (NS) and R2 coefficient of year 1998 in the calibration stage is equal to 0.34 and 0.43, respectively, for the validation period, the coefficient value Nash-Sutcliff and the coefficient of determination are respectively 30/0 and 39/0 respectively. Also, the SWAT-CUP model was studied and evaluated in the current situation of Darband-Golad-Dare Basin for 2018. The results of observational and simulated hydrographs are presented and the performance evaluation values of the model are presented below. The value of nisoscatheff (NS) and coefficient of determination (R2) were estimated to be 0.31 and 0.46 during the calibration period, 0.33 and 0.39, respectively, during the validation period. According to the results of the performance evaluation, the model based on Nash-Thaw (NS) coefficient and determination coefficient (R2) shows the ability of the swat model to simulate the runoff of the basin. Similarly, the simulation results show that changes in the range of the study area caused a change in CN values, runoff and evapotranspiration at the user level over a period of 20 years.

The most appropriate option for flood control in accordance with environmental conditions is watershed management, which has different effects on the hydrological factors, including the amount of surface runoff, sedimentation rate and the permeability in the watershed. The purpose of this study is to simulate and assess changes in surface runoff, sedimentation rate and the permeability using semi-distributed SWAT model in two periods before and after watershed management in the Anbaranchay Watershed. The results showed that the rate of sedimentation in the upstream before watershed management was 22.14 T/ha and after watershed sediment yield per hectare has decreased to 1.84T. Also, the simulation results showed that the amount of CN has changed from 75.68 to 61.24 in watershed and an increase in permeability and the flow lateral is observed. The SWAT model estimated the evapotranspiration 157.4 mm to Anbaranchay watershed. Changes in the hydrological cycle in plain sedimentary region has left the greatest impact. It seems that the SWAT model is able to simulate the hydrological cycle processes and geomorphological studies and provide valuable information.

Flood is among phenomenon which brings about considerable damage each year. This has been attracted greatly by hydrologists. The factors such as physiography, geomorphology and human factors can accelerate this phenomenon in basins. For using water source, flood management, damming, watershed management and the most basic hydrologic studies, peak discharge is important, so accuracy of studies and the safeties’ level of the hydraulic structures and establishments are independent to it. In this research potential flood Kharashk basin were studied by using of SCS method. So Basin Hydrograph dimensions calculated by using of 24 hour rainfall, time of concentration, Curve Number, rainfall excess, time to peak and peak discharge. Then was design Hydrograph for basins in 2,5,10,25,50,100 period time . Results show, because of form of Kharashk basin, it has not ability for making flood, but because of narrowness of basin, runoffs in short time arrive to main drainage and fill it. So it will have ability for making flood where that the river gets out of mountain.

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.

In this research the runoff coefficient and effective elements that affect the floods risk of Balekhlo basin were estimated and studied. In this area (Balekhlo River basin) to estimate the amount of runoff the curve number method (CN) were used. This method is the most common method to predict runoff volume. For this purpose, the data and information required includes: the maximum daily rainfall statistics, maps Density of vegetation, soil and Hydrologic Soil Groups were prepared and entered into Geographic Information System (GIS) environment. Combining these data with the model (SCS), maps (CN) basin, the amount of precipitation (S) and runoff (Q) was prepared. Finally, the hierarchical analytical process was used and six factors include: runoff, hydrological soil groups, slope, vegetation density, land use and drainage density were weighted using AHP method. Finally, the zonation map of flood potential produced with different return periods (5, 15, 25 and 50 years) by weighed layers. Results showed that about 40 to 47 percent of watershed areas, during periods of 5 to 50 years have moderate flooding potential.

One of the most common methods for estimating direct runoff from 24 rainfalls is The Soil Conservation Service of America methods (SCS) that is known number of curves (CN). This method estimated quantity of runoff obtained from precipitation in different parts of the basin with considering the soil characteristics, hydrological status of land and land use. In this paper quantity of runoff was calculated for 24-hour rainfall dam catchment Yamchi (Ardabil) with using this method and the effective factors has been studied in runoff production in different parts of the basin. In this study is using 24-hour rainfall with return periods of 5, 25, 50 and 100 years. Also, using the combination of hydrologic soil groups, land use and hydrological conditions, the curve number (CN) was obtained which with Using existing relationships in the model was calculated keeping quantity of soil surface and penetration for catchment basin and finally quantity of runoff produce. The results of study indicate that the greatest potential to produce runoff is in the northern and western parts of the basin that is marked with arid and low permeability. Also estimate the volume of rainfall becomes runoff for several period indicate which with increasing return period a greater percentage of rainfall becomes runoff. For example, the quantity of runoff produced by precipitation of 5 years, from 39 percent to 55 percent in the period is 100 years old.

The one of the natural hazards is Flood that affects almost all of the country and brings financial and human damages; therefore recognition of the areas with flooding potential is one of the most important measures to decreasing these damages. In this research Darrehshahr drainage basin has been analyzed in view of flooding potential and identifying efficient factors in flooding potential. The run-off has been estimated by using curve number method (CN) of American Soil Conservation Service (SCS).For this purpose, in the beginning the needed data and information including land use and hydrologic groups of basin soil maps were gathered and inputted to GIS system. The CN and the infiltration maps were prepared by using of SCS method and compilation the data and information, then were calculated the run-off volume (Q) for basin using of SCS formula and maximum 24 hours precipitation of basin. Finally, the basin study were divided into 4 classes in view of flooding potential according to first quarter, median and third quarter of values of the run-off volume that 9.1 km2 of it included the very high flood potential, 7.8 km2 of it high potential,13 km2 of it average potential and 6.6 km2 of it had also low potential.

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.

Flood is amongphenomenon which bring about considerable damage each year.This has been attractedgreatly by hydrologists. The factors such as physiography,geomorphology and human factors can accelerate this phenomenon in basins. Forusing water source, flood management, damming, watershed management and themost basic hydrologic studies, peak discharge is important, so accuracy of studies andthe safeties’ level of the hydraulic structures and establishments are independent to it.In this research potential flood Zilaki and Firehrud drainage basins were studied byusing of SCS method and finally were compared together. So BasinHydrographdimensions calculated by using of 24 hour rainfall, time of concentration, CurveNumber, rainfall excess, time to peak and peak discharge.Then was designHydrograph for basins in 2,5,10,25,50,100 period time Results show, because ofphysiography of Firehrud basin, It has more ability for making flood than Zilaki basin.