جستجوی مقالات مرتبط با کلیدواژه « curve number » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Eskandari sub-watershed is one of the most important water supply sources for agriculture, drinking and industry in Isfahan region and province. Therefore, better understanding of the problems within this watershed is crucial for planning and proper management. Moreover, a concerted effort to engage all stakeholders in the integrated management of this watershed is necessary. This research aims to investigate the reasons for the increase of runoff in the years 2011, 2021, and 2031, providing management solutions with the active participation of stakeholders.

First, the height of the runoff was estimated using the curve number method. In this regard, Landsat 5 and 8 satellite images from 2011 and 2021 were used to prepare a land-use map of the Eskandari sub-watershed. Additionally, the prediction of land-use changes in the future (2031) was done using the Markov model. To prepare the curve number map, the combination of the land-use map and hydrological groups was used, and then the runoff height was estimated in the studied years. Following this, through collaborative workshops, stakeholders were asked to create a problems and objectives tree based on the main reasons for the runoff progress in the watershed, consulting with each other. Subsequently, based on the objective tree, the initial list of proposed solutions for the Eskandari sub-watershed was presented. The proposed solutions were then refined, classified, and prioritized by experts. Continuing with the goals of the current research, the most important indicators affecting the current situation of the Eskandari sub-watershed were selected based on the opinions of experts and stakeholders. To model, the multi-criteria decision-making method was used to select solutions and prioritize them. Therefore, initially, the researcher's questionnaire was distributed among stakeholders for scoring the selected solutions according to the assessment criteria. Finally, the results obtained from experts' scoring were prioritized using the TOPSIS method.

The results reveal a significant reduction in natural lands in the region. Consequently, by 2031, rangelands with good and mediocre cover have been completely destroyed, while those with poor cover, irrigation, and rainfed agriculture dominate the region. Based on soil science information, 57.18% of the area is related to hydrological group B with a medium runoff production capacity. Hydrological groups C and D, with percentages of 24.98 and 17.82, respectively, are the next priorities. Following this, by combining the hydrological group map of the watershed with the land-use map in GIS environment, the CN map with curve numbers ranging from 61 to 96 was obtained. Finally, the average infiltration in 2011, 2021, and 2031 was 79.15, 62.82, and 55.12 mm, respectively, while the average runoff in those years was 10.99, 13.15, and 13.38 mm, respectively. According to the results, the losses decrease over time, while the runoff increases. Residential lands and rocky outcrops have the highest amount of runoff production, i.e. 34.38 mm, whereas rangeland with good cover (0.33) has the lowest amount of runoff. In subsequent collaborative workshops, based on the opinions and consensus of stakeholders and experts, improper agriculture was identified as one of the main reasons for increase of runoff in the studied area. Due to a lack of water, insufficient income, and a lack of laws and supervision in the region, watershed farmers and residents are changing land use and cultivating low-yielding lands in an unprincipled manner. Also, in line with the research goals, 11 management solutions and 12 effective indicators (economic, social, and environmental sectors) were identified for the current situation of the watershed. The prioritization results based on the TOPSIS method showed that the solution of creating cover farming to increase surface coverage has been assigned the highest priority.

In this research, efforts have been made to address and mitigate the runoff in the study area. Management solutions have been presented based on the preferences and participation of stakeholders. Therefore, to prevent further runoff in the region, it is suggested to establish institutions tailored to the watershed's situation, considering patterns of cultivation and conservation agriculture, and integrating the cooperation of subordinate institutions and organizations.

Land use changes are one of the important factors in changing the hydrological status of the watershed and soil erosion, so the type of land use is one of the important and determining factors in the production of surface runoff. By knowing the process of land use changes, it is possible to manage the effects of land use changes in the hydrology of the affected areas and led the natural ecosystems towards balance. The following research was carried out with the aim of revealing land use changes using satellite data and analyzing its role in changing the hydrological situation.

The study area is the upstream part of the Siahroud river basin located in the south of Qaemshahr city. In this research, to extract land use maps of different time periods, integrated pixel-based and object-oriented methods, unsupervised and supervised classification of TM sensor images of Landsat 5 satellite related to 1998 and 2009 and OLI sensor images of Landsat 8 satellite related to 2015 and 2019 were used. After preparing the land use maps for each time period, the CN values for each land use were determined based on the standard instructions of the SCS method and the weighted average CN was estimated for the entire study area. At the end, the amounts of runoff production and depth of runoff resulting from rainfall are calculated.

The land use changes of the studied area in the period of 22 years showed that 281%, equivalent to 657 hectares, was added to the area of citrus orchards. About 5% of the area of deciduous forest has decreased and the area of residential areas has increased by 57%. Due to the changes in land use during this 22-year period, the weighted average value of CN has decreased from 63.01 to 62.73. Also, the estimation of the amount of runoff for rainfall equal to 59.8 mm (average maximum rainfall of 24 hours during the period of 22 years) showed that the depth of runoff has decreased from 4.83 mm in the 1988 situation to 4.73 mm in the condition of 2019.

Considering the changes in land use and its effect on watershed runoff production, it seems that these effects have been moderated and land use changes have played a role in reducing runoff production over a period of 22 years. Therefore, it is expected that with the continuation of this process of land use changes, the production of runoff in the upstream of the Siahroud River watershed will decrease.

The main aim of this study is to estimate the Curves Number based on remote sensing and fuzzy methods for use in precipitation-runoff modelling. For this purpose, Landsat-7 satellite images were used for the second degree basin of Gorgan River, northern Iran. By making the corrections and satellite images processing using ENVI, the NDVI index of vegetation and the type of vegetation were extracted. Then, using soil map, obtained from the National's Resources Comprehensive Plan, and land slope map the type of vegetation, the CN of the sub-basins with fuzzy logic and non-fuzzy approaches calculated. To evaluate the calculated CN, a rainfall-runoff event was selected and by simulating the rainfall-runoff using HEC-HMS model, the runoff simulation was performed. The results showed that the calculated CN involving Landsat-7, using fuzzy logic simulated the runoff more accurately than non-fuzzy. So that the coefficients of determination between the observed and simulated hydrographs, obtained from non-fuzzy, fuzzy Gaussian and fuzzy trapezoidal functions were obtained equal 0.76, 0.94 and 0.84, respectively. Also, the maximum flow rate of the simulated hydrograph compared to the observed hydrograph in the fuzzy state has a difference of less than 2 m3/s compared to the non-fuzzy with a difference of 5 m3/s.

Due to the lack of discharge stations and rainfall in the Vazroud basin, it is not possible to have a relatively accurate hydrological behavior of the region. Therefore, by addressing the geomorphic features, this problem can be overcome to reduce the damage caused by floods in the future. In this study, in order to determine the flood risk of flood-prone areas, two geomorphic factors including topographic wetness index and stream power index were used.

Due to the lack of sufficient data related to the discharge of Vazroud watershed, the characteristics of historical flood risk were determined in this area. In the first step, the SCS method was used to simulate the peak discharge. After determining the quantitative characteristics of flood risk (peak discharge) in the next step, the qualitative risk of flood was predicted. In order to determine the qualitative risk of floods, a combination of two factors, the strength of the river and the level of floodplains, was used as the damage that could be caused. The amount of flood-prone regions with different return periods was determined by topographic moisture index threshold method.

The results of this method showed that with increasing the flood return period, the amount of flood-prone lands increases and the amount of topographic moisture index should decrease with increasing the flood return period. The results of flood risk maps with different return periods showed that as the flood return period becomes larger, the areas affected by flood risk in the hazard classes generally increase. The results of total lands that will be at risk of floods with return periods of 2, 10, 25, 50 and 100 years will reach 2.2, 3, 4.2 and 9.8% in the whole basin, respectively. Also, Vaz Tangeh, Nojmeh and Vaz olia villages with 20.6, 16.4 and 13.1% of flood-affected lands were determined as the most vulnerable rural areas in Vazrood watershed, respectively.

Flood risk prediction depends on the characteristics of the catchment and the hydrological and geomorphic factors of the region. So that in areas that have incomplete and low statistics as one of the non-structural flood management tools and complementary to structural methods, it plays an important role in flood control and reduction of potential damages.

The curve number (CN) method is one of the most common methods for estimating runoff in watersheds. The CN value depends on the soil infiltration, vegetation cover, and antecedent soil moisture content. According to the antecedent soil moisture content, three types of CN can be used: CN for dry soil moisture condition, CN for medium soil moisture condition, and CN for wet soil moisture condition. However, the determination of CN from the vegetation cover and soil infiltration needs high accuracy. In this study, 63 measured rainfall-runoff events in the Baghan watershed and 34 measured rainfall-runoff events in the Booshigan watershed were used for estimating runoff with seven conditions: 1) Calculating the CN value based on soil information and vegetation cover in different parts of the watershed. 2) Calibrating the surface storage coefficient of the runoff estimation equation by considering the medium condition for all events. 3) Calibrating the surface storage coefficient of the runoff estimation equation by considering the real soil moisture condition (dry or medium or wet) of each event. 4) Considering the average of observed CN in all measured rainfall-runoff events. 5 to 7) Calculating the relationship between the observed CN and measured rainfall as linear, power, and standard equation. For mentioned conditions, 48 measured rainfall-runoff events in the Baghan watershed and 26 measured rainfall-runoff events in the Booshigan watershed were used for calibrating the results, and the remained measured data in each watershed were used to evaluate the results. The results in two watersheds demonstrated that the linear, power, and standard conditions were better for runoff estimation. In the three mentioned conditions, the CN value depends on the measured rainfall data instead of using the soil infiltration information and vegetation cover of the watershed. Also, the results showed that it is not suitable to use the common method for determining the CN value (based on soil infiltration and vegetation cover of the watershed), and then estimating the runoff amount.

Estimating runoff from atmospheric precipitation and its quantitative understanding of various production processes is considered as one of the important issues in hydrology knowledge. Since runoff in the watershed, due to several factors influencing it, is a complex issue, therefore, it is estimated that many researches, studies and various plans for development, use of water resources and hydrostructure. According to the above mentioned it was used, rain and discharge daily data of the Bar-Ariyeh area of Razavi Korasan province were used to estimate runoff from the extracted number curve method from the Natural Soil Conservation Service (SCS-CN). For this purpose, rainfall and discharge data of Bar and Ariyeh stations during the period of 56 years and in the daily scale, the value of the curve number in the three conditions of previous moisture in low, medium and high antecedent moisture conditions of soil was evaluated. The results showed that the maximum, minimum and average values of the curve number in summer and autumn were 93, 91, 92 and 85, 81, 83 percent, and in the spring and summer were 81, 79, 80 and 78, 76 and 77 percent in The domain was studied. The highest and lowest monthly average number of curve number for April and January were 93 and 76 respectively. In addition, the maximum and minimum amount of runoff was calculated for April and September with a numerical value of 12.45 and 1.29 mm in the statistical period.

Ephemeral Gully (EG) erosion is one of the most destructive types of water erosion, which contributes significantly to land degradation. EG erosion prediction is necessary to assess the magnitude of soil loss and to implement the appropriate conservation measures. The aim of current study  was to evaluate the efficiency of EGEM model for EG erosion prediction in Ghoorichay Watershed, Ardabil Province, Iran. For this purpose, a number of 17 EG erosion was identified and monitored between the years 2014 to 2016. The morphological characteristics and erosion rate of EGs were measured and recorded after seven effective rainfall events. In order to calculate the EG erosion, EGEM model requires four major categories of input data, including identification information, watershed data, soil data, and rainfall data. The model has two major components: hydrology and erosion. The runoff induced by a rainfall event in each gully catchment was determined by the Natural Recourses Conservation service (NRCS) Curve Number (CN). The result of EGEM model performance evaluation showed that the eroded soil volume and cross-section were predicted with a determination coefficient of 0.96 and 0.89, respectively. Sensitivity analysis revealed that the curve number was the most sensitive parameter, so that, with a 10% increasing and decreasing in CN, the volume of soil loss varied 22.98 and -18.92%, respectively. It can be concluded that EGEM model was suitable for event-based EG erosion prediction in Ghoorichay Watershed and it can be recommended for studying and planning on EGs in similar watersheds.

In recent decades, due to the importance of watershed management programs and the need for adequate information and correct estimation of rainfall and runoff, many conceptual models have been proposed. These models have parameters that must be estimated according to observational data. However, finding the optimal values for the parameters of simulation models has always faced uncertainty. One of the main methods for evaluating and predicting floods is the soil conservation methods provided by the Soil Conservation Service (SCS). This study aims to calibrate model parameters for three modified SCS models, i.e. 1- the Mishra and Singh model, 2- curve number model, and 3- modified curve number (MCN) model, in a basin in southern Chile using the evolutionary PSO algorithm. Comparison of the results was carried out using performance criteria such as Kling Gupta Efficiency (KGE), Nash-Sutcliff coefficient (NS), and mean square error (RMSE). Results revealed that simulated runoff is more efficient in MCN and Mishra and Singh models with KGE = 0.91 in rainfall-runoff simulations.

Human activities and changing in land-use can affect geo-hydrological processes. This paper investigates historical land-use changes over Golestan multilayer aquifer, Northern IRAN, and their impacts on recharges of both phreatic and confined layers. To achieve this goal, three historical land-use maps of 1984, 2005 and 2013 were used. Also the effects of land-use changes on runoff generation potential and groundwater direct recharge have been evaluated using SCS method. Results show deforestation in mountainous region and urbanization in the plain are the most critical problems of the studied area. Forest and rangeland areas in the mountainous district decreased 8.7 and 4 percent, respectively, and totally added to agricultural lands. Effect of land-use changes on groundwater recharge was found to be more than runoff generation and confined layer is more impressed. In recent 30 years, land use changes caused reduction in natural recharge of confined and phreatic layers up to 18.12 and 12.40 percent, respectively. On the other hand, runoff generation potential increased by 14.14 and 4.23 percent, respectively.