جستجوی مقالات مرتبط با کلیدواژه "curve number" 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.

Given the growing population and the increasing need for food, water and soil conservation are of great value. In the context of conservation of soil and water resources, information on the amount of runoff production and erosion to achieve sustainable development is the basis for planning and decision making. Therefore, careful investigation of surface runoff and floods is an important and key step in planning and managing optimal water resources. One of the factors affecting the characteristics of surface runoff is land-use changes at different basin levels (Melesse and Shih, 2002). Land use is influenced by two components of human needs and environmental processes. Inaccurate land-use changes will disrupt the water cycle from natural equilibrium, resulting in devastating floods, including economic damage, loss of life, loss of water, and consequently reduced water resources (Jakeman et al., 2005). During the last two decades, the Qhareh-su watershed, particularly its downstream, has been experiencing rapid growth in the construction and expansion of residential structures. Human activities and changes in the basin have affected the natural arrangement of stream processes that transmit water and sediment from upstream to downstream. Human interventions are one of the major hazardous issues in this basin that causes changes in the pattern of surface currents and natural conditions of the catchments and encroachment on rivers and streams. In this regard, the present study aimed to investigate the role of land-use change on runoff in a part of Qhareh-su watershed in Ardebil province over a period of almost 20 years due to the availability of information and access to satellite images of different time periods.

The study area consists of a part of Qhareh-su watershed located in Ardabil province with an area of 2162.6283 km2. The minimum and maximum elevation of the mentioned watershed are 1280 and 3829 m respectively, and its average slope is 11.57%. Land use in this area often includes dry and irrigated agriculture, pasture, forest, and residential areas. The aim of the current research is to study the effect of different land uses and its changes during the years 1992-2012 on the surface runoff in a part of Qhareh-su, Ardabil watershed. At first, the maps of land use and curve number in the mentioned years were gathered and the area of each of the units was extracted. In the following, the process of land-use changes in the cases of the study period and its effect on changing the specific retention (S) and curve number were calculated and the height of runoff was estimated using the SCS method.

The results showed that during the case of the study period, area of forest, water farming, and wasteland land uses were decreased by 2.54%, 16.69%, and 1.19% respectively and the area of the rangeland, dry farming, and urban land uses were increased by 5.74%, 12.39%, 2.29% respectively. These changes have caused the increase of curve number from 78.57 to 79.77 in the years 1992 and 2012, respectively and following the decrease of the specific retention (S) from 69.28 mm in the year 1992 to 64.42 mm in the year 2012. Also, runoff height has increased from 263.4 mm in the year 1992 to 297.07 mm in the year 2012 (11.33%). Calculation of correlation coefficient between different land uses and curve number and runoff height showed that these
variables have a direct relationship with rangeland, dry farming, and  urban land uses while they have an inverse relationship with the forest, water farming, and wasteland.

In the present study, the results of the study showed that land-use change due to its effect on the curve number of the studied basin causes a change in the surface runoff. During this 20-year period, land use has changed and this land-use change has tended to decrease from 1992 to 2012 land use including residential, pasture and dryland areas increased by 2.29%, 12.39% and 5.74% respectively, as well as forest, water and wastewater land use decreased by 2.54%, 16.69% and 1.19%, respectively. As a result, its curve number has increased, followed by a runoff height of 11.33%. This shows that in a natural ecosystem, land use and environmental changes, especially vegetation and land use affect the hydrological responses such as flooding and erosion and sedimentation rate in the area. Ultimately, it will cause severe economic and social damages. Changes in the total volume of runoff and changes in hydrological balance are the most important effects of land-use change on watershed hydrology.

Flood discharge is of high importance in studies regarding water resource exploitation, flood control, construction of dams, basin management, and hydrologic studies (Alzahrani et al, 2017). Therefore, to a large extent the accuracy of these studies and the safety of water constructions depend on flood study methods. Flood is a natural phenomenon that threatens the life and properties of a large number of people all over the world, and it is impossible to manage water resources in basins without the accurate determination of the peak flood discharge (Badri et al, 2017). The advances in flood estimation techniques have made it possible to use rainfall-runoff models to assess the hydrographic properties of the flood in watersheds and decrease the risks of the flood. Therefore, this study was carried out to compare the SCS unit hydrograph and Uniform methods in determining the peak flood discharge with WMS model in Amughin basin of Ardabil province.

Amughin basin with an area of approximately 78 km2 is located in the northwest of Iran. The physiographic features were extracted using the basin map (scale: 1:25000) and WMS model. This study applied Arc GIS 9.2 and Idrisi32 software to obtain the properties of the studied basin using DEM (Digital Elevation Map) of the National Cartographic Center, NCC. Remote sensing methodology was utilized to study the geographical land use changes occurred during the study period. Landsat images of TM and ETM+ of Amughin basin area were collected from the USGS Earth Explorer web site. After image preprocessing, un-supervised and supervised image classification were performed to classify the images into different land use categories. In general, soil hydrologic groups were divided into three subgroups of B, C, and D and CN value of 78.7 was estimated for the Amughin basin based on the geological examination, permeability, vegetation, and hydrologic conditions of the basin soil.

The model calibration results showed that the simulated peak discharge and flow volume were in good correspondence with the observed values (RE%= 7.17, RMSE= 0.44). Thus, the calibration results were used for optimum values of parameters. The model was validated using two rainfall events and the model performance indices were acceptable in both cases (RE%= 2.51, RMSE= 0.0042) in SCS method. To evaluate and test model validation, two rainfall events, were used. That the model performance indices were acceptable. Distribution of CN amount in the area showed that the upstream flow had higher CN values and consequently increased flood volume in these areas. Based on the values of obtained CN, the amount of peak flood discharge was calculated for return periods of 25, 50, and 100 years.

Discussion and conclusion

According to the results, the SCS model has good agreement with experimental results among the different methods used for estimating flood discharge in the northwest of Iran. In fact, this model requires calibration in the study region. In small watersheds in the northwest of Iran, the SCS model yields better results than the Uniform method because the conditions required for using this model are satisfied in these basins. Moreover, the results obtained from this method can be closer to actual values provided that the watershed concentration time is calculated more accurately. Our results also showed that the SCS model has a high sensitivity to rainfall distribution across the region and that  the rainfall across the region needs to be analyzed to obtain desirable results. Besides, the rainfall distribution and its time distribution should be close to the corresponding values in the region. A comparison between the obtained results of peak discharge from the SCS and Uniform methods in return periods of 25, 50, and 100 years revealed that the average estimates of the Uniform were approximately 5% higher than the SCS method. According to paired T-test, the difference between Uniform and SCS values were not significant at a confidence level of 0.01. Overall, the results obtained from this method can be closer to actual values if the watershed lag time is calculated more accurately using the floods occurred in the studied basin.

The use of geographic information systems (GIS) and remote sensing is common to facilitate the estimation of catchment's runoff in the last century. This action is performed by using the rainfall-runoff model, which includes climate and geomorphological changes. One way to estimate the runoff height is the Curve Number (CN) method that shows the hydrological behavior of catchment. In this research, the Arc-GIS software was used for mapping curve number by integrating vegetation maps, land use and soil hydrological group, and then the annual runoff height map of Hesarak catchment was prepared. In addition, by using empirical methods, annual runoff of the study area was compared with I.C.A.R, Justin, Angeli di Sousa, and SCS-CN methods. The comparison of estimated runoff values in different methods with observations of runoff showed that the result of SCS-CN method has more adaptation to the observed runoff and discharge. The advantage of this model is the use of different parameters such as annual precipitation, soil holding, and permeability of the curve number of the basin, which causes the measured runoff to be closer to the observed value.

Among all natural disasters, floods are the most frequent and affect the highest number of people. Flood risk is particularly severe in urban areas. Improving urban flood risk management has become a high priority at virtually all levels of governance. The proper design and evaluation of measures to enhance urban flood resilience should be based on the analysis of a range of scenarios, in which various hydro meteorological conditions and management options are tested. Human activities in varies forms has increased the flood events probability. These include: location of Iran's villages and cities in Foothills, destruction of vegetation, not respecting river privacy, excessive construction along the rivers, agriculture on the riverside and etc.  Therefore, the risk of flood is very high in urban areas. Urbanization also aggravates floods by increasing the amount of impermeable surfaces and redirect water flow. To describe the watershed hydrologic behavior are used from precipitation and runoff models. The curve number is one of the models for the calculation of runoff volume from rainfall. The curve number in comparison to other factors has the most impact on peak flow during various return periods. However, the rainfall volume has a great effect on peak flow and the intensity of this effect will increase by increasing the curve number.

The study area is located between 31° 51´ N to 31° 58´ N latitudes and 49° 46´ E to 49° 56´ E longitudes. The catchment study area is located in southwest of Izeh city that consists of three sub-basins: Sheykhan, Alahak and Tape- Shohada. Using the digital elevation model (12.5 m resolution), the boundary of watersheds and drainage system were extracted in WMS software environment. Land use map of the region was prepared, using Landsat Satellite Images. Then, field assessment in the region was done to measure cross sections, current velocity, and river slope and to determine the area affected by flooding in the rainy seasons. Furthermore, sediment sampling to identify soil texture was done aiming at characterizing soil hydrologic group. Curved number layer (CN) was prepared using soil characteristics, land use, and soil moisture conditions. Moreover, peak flow values and its duration for various return periods were measured using SCS Flood Calculator software and the data consists of basin extent, average of precipitation and its duration, curve number, river length and slope. To evaluate flooding of urban channels we prepared cross section profile, channel geometry parameters and hydrological features of each sections such as current velocity and discharge. Then, we used from Ghahreman and Abkhezr method (2004) to calculate the amount of rainfall intensity-duration in various return periods.

Based on the data obtained from the sub-basins, the curve number values were calculated and was prepared the curve number map. Based on maps prepared, most sub-basin area especially upstream of the basin have the highest curve number and the least permeability because the Asmari Formation and rock outcropping. Then, there are built-up areas and impenetrable surfaces, such as roads with a curve number of 87. Based on Ghahreman method in varies rainfall intensities, the expected amount of precipitation is calculated and intensities consistent with basin concentration time (30 to 120 minutes) were selected. In the following at the intensity of 30, 60 and 120 minutes, maximum precipitation volume was calculated in 2, 5, 10, 20, 50 and 100 return periods.

The intensity and duration of precipitation during different return periods were used to investigate the flood potential in upstream catchments of Izeh city. The results showed that Shahda Tapeh basin had the highest water withdrawal at the entrance reaches to the city. As a result, it has the most impact on flooding the streets and creating floods in Izeh City.In the second place, Elahak basin has the most effect on the flood in Izeh City, because the topographic slope of the area is high, also the channel was changed regardless of the hydrological parameters. Sheikhan Basin has the most negative impacts from flood damage on agricultural land because it is more distant from the city. The main causes of flooding in Izeh are: Change the natural channel of the river to artificial channels without considering the volume of inlet water, not increasing the width and depth of the channel at the city entrance (from upstream to downstream) and creating inappropriate transverse structures on the channel. Another reason for the increase in flood potential is the loss of the drainage network around the city; because the city has expanded. Also, alluvial fan cones between the city and the mountain were changed and converted into a city. Whereas in the past, alluvial fans have been used for flood spreading.

Due to population growth and human activities and increasing water demand, water availability will be critical and water resource assessment and planning for sustainable use become more complex. The dynamic and long-term laws of runoff are important and have practical value for the sustainable development and planning of water resources. On the other hand, the traditional methods of runoff estimation should be improved regarding the accuracy and spatial variations. The application of GIS extensions is needed to provide water resource assessment data. Therefore, the application of such new techniques has greatly increased in recent years to estimate the runoff characteristics. The SCS method is the most commonly used method for estimating surface runoff, whose accuracy has improved through employing advanced GIS-based tools. The applicability of Arc-CN Runoff tool was tested in different internal and external studies which emphasized the quantitative evaluation of the model results. In this study, the accuracy of runoff estimation by Arc-CN Runoff tool was evaluated based on the land use map in two different time periods (1996-2011). The Landsat satellite images of 1996 and 2011 were processed and analyzed for land use mapping. Map of soil hydrologic groups was prepared in GIS environment using slope and soil texture maps. The annual rainfall calculations were done using rainfall daily data of several years for stations within the basin. The curve number map was used to estimate runoff using SCS method within ArcCN-Runoff tool in GIS environment. The runoff observations of Karehsang Station were calculated using daily flow data and the base flow was separated. Finally, the accuracy of the estimated runoff was assessed by estimating the percent relative error. According to the accuracy assessment of land use maps using the ground-based map, the best overall accuracy and kappa coefficient were respectively 90% and 88%. The results showed that the maximum likelihood algorithm and the combination of main and synthetic bands, classified the land use classes of the study area with an acceptable accuracy. The highest percentage of the area was classified as range and dry farming (62.74%) in 2011. The percentage of rangeland, dense forest, and water zones decreased in 2011 compared with 1996.The map of the hydrological groups shown in this study, consisted of groups B, C and D, respectively covering 15.5, 44.5 and 40% of the study area. The average CN in the years 1996 and 2011 was estimated to be around 79.6 and 81.6.
The average estimated rainfall of the study area using the arithmetic mean, inverse distance weighting, and kriging methods in 1996 were respectively 486.24, 424.4 and 486.1 mm. The estimated annual rainfall values were equal to 521.5 (arithmetic mean), 514.6 (inverse distance weighting) and 521.5 (kriging) mm. Runoff height was the highest in bare lands and residential uses, and the minimum of runoff height values were estimated in good and medium rangelands. The mean values of total runoff, base flow, and surface runoff have increased in 2011 compared to 1996. The highest CN values in both periods consisted of bare lands and residential area. The runoff height in different land uses and the total runoff height increased in 2011 (11.38 mm) compared to 1996 (8.8 mm), which can be partly due to the degradation and land use change. The results of this study showed that the ArcCN-Runoff tool improved the accuracy of potential runoff estimations, while the relative error of runoff estimation in both periods was relatively low and acceptable. Thus, the implemented tool can be used to assess and estimate runoff height. The results showed that the relative error of runoff estimation in both periods was in agreement and the error amount was relatively low (10%). In addition, the used methods and tools were evaluated with 90% accuracy in both periods and can be used for runoff estimation in data-scarce watersheds.

The process of precipitation – runoff of each basin, is influenced by hydrologic, geomorphology conditions, geological formation and vegetation. There are different methods in drainage basins. One way to estimate the runoff height is Curve Number (CN) method. That reperesents the hydrological behavior of basin. data were collected for statistics of climate and then topographic map of 1: 25000 and geological map of 1: 100000 by GSI was used. Smada software for calculate the short – term rainfall at different return periods. As well as Arc GIS software for mapping Curve Number by combining maps of land use, soil hydrological groups and moisture of soil with using the table of America Soil Conservation Service (SCS). And then modeling related in the GIS mappings of runoff height of Hesarak catchment was prepared. The aim of this study, was to determine Curve Number and estimate runoff coefficient and maximum discharge runoff with SCS method in various units catchment is. The results showed, hydrologic condition and soil hydrological groups are the most important parameters to determine the CN and affect on runoff. The most potential for runoff is in downstream of basin that specified with urban land use. Also average weight of Curve Numbers those obtained for each sub catchments, Chapdareh sub catchment (S2) with 88 Cure Number and mean of runoff 28.15 mm had the highest volume of runoff, Dochenaran sub catchment (S3) with 89.3 Curve Number and mean of runoff 24.54 mm and sub catchment of the twin branches (S1) with 90.1 Curve Number and mean of runoff 17.36 mm had The lowest amount of runoff probability and spill potential. But in general potential runoff in this basin is relatively high. The maximum amount of runoff Curve Number in condition of high humidity is 99 and 78 is the lowest.

Flooding is a major natural disaster. This phenomenon becomes more important when it is occurring especially in the city. Therefore, prevention of the communities from the impacts is inevitable. The high level of awareness of potential runoff area for flood management is important. Given this importance, this paper deals with the calculation of runoff with SCS method in Meshkinshahr city and its surrounding area, For this purpose, we used GIS software and the accession of the ARC-HYDRO, especially Arc-CN-RUNOFF software. Finally, the layers of soil hydrologic group, the integration of land use and rainfall averages were compared with the index table, then the resulting map was obtained. Curve number Map (CN), which was proportional to the permeability of the 20 classes. Curve No (32) for areas with high permeability and low runoff and curve number is high (98) for areas with low permeability and high runoff. Dimensional map of the height map is runoff from zero to areas with very high permeability and high runoff starts 99/0, including the use of low permeability to continue. Check the map showed that both CN and RUN-OFF lot to do with the type of the user, so that the use of man-made and synthetic runoff curve number and height are more.

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 hazard that takes place more frequently in recent years. In order to better flood mitigation and control, it's needed to recognize flood production factors and determine the high potential flood areas. Hydrological model is a simplified representation of natural system and the rainfall-runoff model is one of the most frequently used events for flood simulation. HEC-HMS is one of the computer models and for its ability in simulating short time events become very popular. The aim of this research is to investigate spatial prioritization of flooding in Beheshtabad sub-catchments using HEC-HMS software.
Material and Behashtabad Basin located in Chaharmahal-va-Bakhtiary Province, Iran, is 3866 km2 and its mean altitude is 2317 meter above sea level. It is divided into 6 sub basins according to 6 hydrometric stations. Land use categories of study basin extracted using ETM Images for 2009. Using 170 ground control points land use map of Beheshtabad basin was prepared with total accuracy of 99.34 and Kappa Index equals to 0.81. Rangelands covers most of the study area. Soil Hydrological groups and land use data used for mapping sub basin's curve number considering antecedent moisture of past five days as well. The mean curve number of study basin is 72.69. Daily precipitation data of 6 rain gauges in study area used for analyzing maximum 24 hr precipitation in different return periods. Rainfall hyetographs of flood events derived from recording rain gauges data. CN method used for estimating initial loss, SCS method used for runoff hydrograph simulation, and Muskingum method used for flood routing simulation. HEC-HMS model was calibrated using 2 Flood hydrographs and corresponding hyetographs for each sub-basin and validated for 1 flood event.
Rainfall loss in Beheshtabad sub basins varies from 0.13 to 0.19, curve number varies from 69.73 in Kooh-Sookhteh sub-basin to 73.71 in Kharaji sub basin, and lag time varies from 0.99 hr in end Beheshtabad to 5.72 hr in Kharaji sub-basin. Using optimized rainfall loss index derived from calibration stage, HEC-HMS validated for one flood event for each sub basin. Model validation shows very little difference (below 1%) between estimated and recorded data in all sub-basins. Among sub basins, Darkesh-Varkesh has the most and end Beheshtababd has the lowest peak discharge in all return periods. Priorization of sub basins according to their areas show that bigger sub basins havent essentially highest amount of the rate of Qsub/Qtotal. In this comparison Darkesh-Varkesh sub basin with a rate of Areasub/Areatotal of 0.13 has the highest rate of Qsub/Qtotal. Flood routing in streams showed that the rate of participation of sub-catchments in output flood is not proportional to sub-catchment peak discharge. Therefore, in order to eliminate the effect of area in participating sub-catchments, the rate of influencing each unit of sub-catchment area in output flood was calculated as well. The results of prioritization with respect to peak discharge, based on having participation of each sub-catchment in output location of watershed, indicates that Darkesh-Varkesh and Beheshtabad sub-catchments with 29.16 and 2.5 percent, have maximum and minimum of participation in output flood peak discharge of watershed, respectively Results of prioritization based on reducing discharge per unit area show that Beheshabad sub-catchment with having lowest area in comparison to other sub-catchments has highest participation and Tange-Dehno has lowest role and contribution.
In the present study, rainfall-runoff modeling is carried out using HEC-HMS hydrologic model. Results of simulation in 18 events and comparison of simulated and observed hydrographs showed that the model can applied for simulation of rainfall-runoff in study area. Other researches like Kumar and Bhattacharjya (2011) and Hegdus et al (2013) have same results as our findings. Ranking sub basins according peak discharge without flood routing show that Darkesh-Varkesh has the most and end Beheshtabad has the lowest peak discharge. According contribution in total discharge also results are the same. Soleimani et al (2008) and Zehtabian et al (2010) also found the same results. Finally, according to decrease in total Q per unit area, ranking show that end Beheshtabad sub basin despite of having the smallest area, has the highest contribution in total Q per unit area Nasri et al (2011) also concluded that areas are located near the outlet of study basin have the most contribution in flood production. This research show that the Darkesh-Varkesh sub basin need the most attention in selecting management practices especially in optimizing flood control and flood mitigation solutions.

A valid estimation of runoff volume and maximum discharge in the dried and semiarid regions which lack data is important for flood management. One of the estimating methods of runoff volume is related to curve number (CN) of American soil conservatives services (SCS). In this study, the drainage basin of Darrehshah Sarab has been studied with regard to its runoff volume potentiality, maximum discharge and effective factors. To estimate the runoff volume and maximum discharge of the sub-catchments, the curve number method has been used. First, the layers and the needed data including the land use, soil hydrological groups and a maximum 24 hours precipitation was prepared for basin. Then the CN values, infiltration (S), runoff volume (Q) and maximum discharge (Q max) were calculated for the entire basin and each sub-basin. Finally, factor analyses based on 19 parameters were used to identify the effective factors on maximum discharge at sub-basins. The results showed that among the used parameters in sub basins, two physiographic parameters (area and drainage density) were effective parameters in flooding potential of the drainage basin of Darrehshah Sarab.

Landuse and land cover changes have direct effect on hydrological regime of basin.Iincreasing bare lands and similar landuses make flooding and increasing of orghard landuse area has effective role on reduce of runoff discharge. In this study using of soil hydrolic group map that indicat sensitive lands, and landuse map of 1987, 2000, and 2013 periodes curve number (CN) map of study area was extracted and then using of this map amunt of soil water retention was calculated and finally the rate of runoff from simulated 100 mm rainfall was estimated bye SCS model. The results indicate an increase in runoff or in other words, inceasing flooding rate of basin because of landuse and land cover changes. According to existence of the relationship between rainfall and runoff discharge at specified intervals, landuse change to orchard development as one of the effective factors on decrease of runoff rate was studied,then after of separation of base flow and flow from snowmelt of the entire flow using MODIS satellite images processing, the residual flow was considered as the discharge of rainfall. the result of analysis of covariance indicated that increasing of orchard area reduce the relationship between rainfall and discharge from it.

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.

Curve Number (CN) is one of the required parameters for runoff calculation using SCS method. Considering spatial variability of factors affecting this parameter, different values of CN is expected within different parts across a catchment. The present research aims to map CN in Navdar catchment, Kermanshah province, Iran. Therefore, modern technologies such as geographical information system (GIS) and remote sensing (RS) have been used. First, land use map of the study area was determined based on Landsat satellite images (TM) using ERDAS software package. Then ground coverage density was determined based on Normalized Difference Vegetation Index (NDVI). The map of soil hydrological groups was prepared in GIS environment based on the available soil map in the study area. Finally, CN map was prepared based on SCS table and the maps of land-use, ground coverage density, and soil hydrological group. Average curve number under intermediate humidity conditions in the study area was calculated as 78. Simultaneously, CN in the catchment was determined as 76 by the analysis of recorded runoff events using HEC-HMS model. Results of this study indicate that the accuracy of calculated curve number via RS and GIS technique is high, so the obtained curve numbers using RS and GIS method across this catchment are reliable. Based on the determined curve number in the catchment (78), it can be concluded that this catchment has high potentials in terms of runoff generation.

Flooding is a natural hazard events and Survey data from the annual losses due to flood in Iran and the world show the extent of the flood damage caused on natural and human resources. To estimate height of the runoff and discharge maximum in basins and stream erosion، there are various experimental methods and mathematical models that one of these models، SCS model is. Thus، the aim of this study was to estimate the Runoff coefficient and Maximum discharge by Curve Number method with different units forming the Fyruzkla Kojoor basin and zoning maps of potential runoff and stream erosion in the drainage basin is. After mapping the watershed CN and S، to calculate the volume of runoff produced in the region، short-term rainfall for different return periods were calculated using Pearson distribution of type III. According to the map of potential runoff in the basin، forest land has the lowest runoff potential and pasture lands have the greatest potential to generate runoff and erosion is occurring and also has the lowest penetration. The middle part of the basin، the most prone to runoff and erosion and gully formation in the region are. After determining the height of the basin surface runoff، peak discharge was calculated for various hydrological. The highest values of maximum flow rate are based on rangeland with hydrologic group D.

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.

This research was carried out in the catchment basin of Varband River in Larestanlocated in Fars Province in an area of 925.5 km2 by the use of IRS satellite pictures andthe measurer P6 (2006) so that through the use of the software ERDAS8.7, the localcorrections of the related pictures with 15 points and Afain equation with RMSE=0.42 andradiometric corrections with the algorithm of the equivalent rectangles were implemented.The best band combination was selected by the use of a suitable index factor and we usedthe classification under the supervision of the Maximum Similarity Probability Algorithmin order to provide the utilization map. The utilization layers were estimated 0.90 and 0.88by the use of general correctness test and Kapa statistics respectively. The co-precipitationmap was prepared in the environment of ARCGIS9.2 by the use of TPSs algorithm andaltitude-precipitation gradient as well as the map of Curve Number by the use of the mapof hydrologic and utilization groups. The height of the catchment basin slope,inappropriateness of formations, high evaporation and perspiration, soft soil tissue,severity of thundershower, utilization change, low compression of the covering crown andpoorness of pasturelands are among the effective factors in the exposure of the catchmentbasin to the floods. The analysis of each morphometric parameter of the catchment basinindicate that slope, area, shape, time of concentration, and percentage of waterwaycompression are the major effective factors in the exposure of the catchment to the floods.The presence of the rainfalls with duration of 15 minutes for 6-hour thundershowers arethe main factors in the destruction of soil structure and acceleration in the cumulativecurrent of the surface flowing water in Varband catachment basin . The phating map ofthe catchment exposure poteantial to the floods were offered in four classes of very low,low, average, and high. The results of this research showed that the whole productiveflowing water in this catchment basin is 42283746.6 m3 from which the sub-basins M, K,and A with 11.7, 11.3, and 10.01percent have a high exposure respectively and those of Cand G with 4.3 and 5.3 percent have the lowest exposure to the floods respectively.