hydrogeology
Rasool Hasan zadeh; Friba Esfandyari; sayyad Asghari saraskanrood; Zahra Miri
Abstract
the object-oriented method in preparing the land use map of Darre Rood catchment area using Landsat 5 and Landsat 8 images in a period of 30 years, from 1990 to 2019 and its effects on changes in Darre rood river discharge it placed. The images were classified into fourteen classes and the changes in ...
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the object-oriented method in preparing the land use map of Darre Rood catchment area using Landsat 5 and Landsat 8 images in a period of 30 years, from 1990 to 2019 and its effects on changes in Darre rood river discharge it placed. The images were classified into fourteen classes and the changes in the area of the classes revealed that the classes of irrigated agriculture, rainfed agriculture, rocky areas, residential areas, gardens and lakes with increased area and barren lands, pastures, forest lands and riverbeds decreased They were. To find out the changes in the river flow trend, SCS method was used which was implemented in SWAT model and according to land use in 1990 and 2019 in SWAT model was determined according to the digital elevation layer of the basin and all the necessary parameters to the model. Which included soil layers and land use changes and climate data were called into the model and two separate scenarios for 1990 and 2019 were used. The results showed that with the change of land use, the amount of CN in the second scenario compared to the first scenario increased by 5% and increased from 02.70 to 5.73, which due to the change in land use in favor of the basin becomes more impermeable to rain. Compared to 1990. Also, due to the increase in the type of vegetation, the amount of deep penetration has decreased from the first scenario to the second scenario from 257.09 to 97.9.
Mohammad Hossein Rezaei Moghaddam; Davoud Mokhtari; Nasrin Samandar
Abstract
Land use change is one of the important factors in changing the hydrological flow, basin erosion and biodiversity destruction. Therefore, knowing the effect of land use change on discharge and suspended load is an inevitable necessity. The main purpose of this study is the efficiency test of the model ...
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Land use change is one of the important factors in changing the hydrological flow, basin erosion and biodiversity destruction. Therefore, knowing the effect of land use change on discharge and suspended load is an inevitable necessity. The main purpose of this study is the efficiency test of the model and its usability as a simulation of the process of land use change on discharge and sediment is from the soil and water assessment model (SWAT) and SUFI2 program. Model simulation was performed for 29 years from 1987 to 2015, the first 5 years of which were selected for model calibration and the last 5 years for model results validation. Four statistical indices, r_factor, P_factor Nash-Sutcliffe (NS) and coefficient of determination (R2), the ratio of squared root-to-standard deviation (RSR) and the percentage of skewness (PBIAS) were selected monthly to evaluate the model. The accuracy of monthly simulation using NS evaluation index in the calibration and validation stage for flow and suspended load is equal to 0.65 and 0.49, respectively. The results of the study were considered acceptable according to the interpretive domains used in previous studies and indicate the satisfactory efficiency of the SWAT model in simulating the components of the impact of land use change on sediment and discharge in the Ojan Chay Bostanabad watershed. The results showed that the height of surface runoff increased by 1.15 mm and the sediment concentration increased by 1.5 tons per hectare per year.
Khodayar Zeiaei; abazar esmali; Raoof Mostafazadeh; Mohammad Golshan
Abstract
1-Introduction Watersheds are physical boundaries that include natural ecosystems and all human interactions. Land-use change in watersheds has been one of the major challenges in the 21st century. According to the findings of some researchers, the effects of land use on water resources are more severe ...
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1-Introduction Watersheds are physical boundaries that include natural ecosystems and all human interactions. Land-use change in watersheds has been one of the major challenges in the 21st century. According to the findings of some researchers, the effects of land use on water resources are more severe than climate change. The estimation of streamflow in watersheds with different land uses is one of the important issues in hydrological studies. In recent years, one of the most widely used methods to facilitate computation has been the use of computer models that represent the watershed response with high accuracy. Restrictions on access to sufficient hydrological data make the role of watershed simulation models more important. This study aimed at modeling monthly runoff using the SWAT model and assessing the effects of different land-use change scenarios on runoff components. 2-Methodology The Ahl-e-Iman watershed with 7770.86 ha area is located in Ardabil province, which was selected to predict the effects of land-use change on hydrologic response. The SWAT model has been developed to simulate different parameters of the daily, monthly, and annual hydrologic responses. The curve number method in the SWAT model was used to estimate monthly surface runoff and output runoff yield. The main inputs of the SWAT model, including daily precipitation, minimum and maximum temperature, relative humidity, and wind speed, were obtained from available data centers to prepare a digital elevation map (DEM), land use map, and soil map. The SWAT CUP program was used to calibrate the model. The input of this program is observational flow data and the output file is the SWAT model. The statistical indices of Nash-Sutcliffe coefficient (NS), correlation coefficient (R2), and mean square error (MSE) were used to evaluate the simulation results of the model. 3-Results and Discussion Sensitivity analysis and the model calibration were performed in 2003-2010. The validation of the SWAT model showed that this model had a high performance for predicting the hydrologic effects of management scenarios in the Ahl Iman watershed. The results showed that the model had high performance in both periods. The obtained land-use map was given to the model to simulate the effect of land use change. The results of runoff simulation with both land uses of the study scenarios compared with the base flow are given in Figure 1. Figure (1): Comparing base flow with streamflow in the first and second land-use change scenarios 4-Conclusion The performance of the SWAT model was evaluated in both the calibration and validation periods; therefore, this model was used to investigate different land use management scenarios. The results of the first management scenario showed that the average streamflow discharge was equal to 0.3 cms, which showed 17% decrease in discharge compared to the base land use discharge (0.6 m3). The streamflow discharge increased 36% compared to the base flow in the second scenario. Therefore, this scenario will reduce the water resources of the region in a long time.
Mohammadreza Goodarzi; Atiyeh Fatehifar
Volume 6, Issue 20 , December 2019, , Pages 57-78
Abstract
1-Introduction The assessment report fifth of the Intergovernmental Panel on Climate Change shows that global warming has led to a change in the water cycle due to increased greenhouse gas emissions. In the present time, with the increase of industrial activities and the neglected environmental issues, ...
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1-Introduction The assessment report fifth of the Intergovernmental Panel on Climate Change shows that global warming has led to a change in the water cycle due to increased greenhouse gas emissions. In the present time, with the increase of industrial activities and the neglected environmental issues, the effects of climate change have become more evident and poses this phenomenon as a global difficult. Increasing the probability of occurrence of extreme climatic events such as flood and increasing the frequency and intensity of the effects of climate change. Due to changes in climate and global warming, the probability of heavy rainfall and consequently the risk of flood due to incorrect drainage system and physical and environmental factors have increased. Therefore, the study of the region's climate is important given the new scenarios and flood frequency analysis with suitable statistical distributions for future planning. 2- Methodology In the present study, the effects of climate changes on the runoff of Azarshahrchay Basin with CanESM2 model under RCP2.6, RCP4.5 and RCP8.5 release scenarios assessment report fifth (AR5) of the Intergovernmental Panel on Climate Change (IPCC), with Statistical down scaling model (SDSM), for the period 1976-2005 and 2059-2030 by the hydrologic model SWAT have been investigated. The accuracy of the simulation was evaluated with three indicators: Root Mean Square Error (RMSE), Coefficient of Determination (R2) and Nash–Sutcliffe Efficiency (NSE). An analysis of the frequency of maximum annual flood for both base and future periods using their probability distribution function (PDF) and the Easyfit model. In this model, 5 types of probability distribution including Normal, Normal Log, Pearson, Log Pearson Type 3 and Weibull were used. The best distribution for each basic and future time series were ranked and selected by using three Chi-square, Kolmogorov–Smirnov, Anderson–Darling tests. In order to study how the maximum flood discharge regime changes in the base and future periods were used two indices: 1) The probability and the return period in the equal flows 2) Intensity of flow in the equal return periods 3- Results The obtained factors of the three RMSE, R2, and NSE indicators showed the good performance of the SDSM model in the down scaling the large-scale data. Investigating the performance of the SDSM model in the downscale of the Azarshahr station's climate data with a Coefficient of Determination and Nash–Sutcliffe of 0.99 and 0.98 for temperature for the period 1990-2001 and 0.86 and 0.83 for precipitation in the period 1976-2005. The simulation results showed a rise in temperature during the period 2030-2059 under scenarios and the highest increase was related to RCP8.5 (0.23°c). Also, rainfall at a station increased by 7.44 percent to RCP2.6 and at another station decrease by 7.57 percent to RCP8.5. The performance analysis of the SWAT model indicates a good accuracy of the model in runoff simulation with R2 and Nash 0.6 on average. The results of the 2.1% increase in runoff and the maximum flood peak and the probability of flood events in March and April (late winter and early spring) have been shown by the SWAT model. Results of the study of the regime of maximum annual flows (frequency and intensity) by fitting probabilistic distributions with the lowest error rate for the base distribution period of the Weibull, future period RCP2.6 distribution Log Pearson Type 3, RCP4.5 Log Normal and RCP8.5 Log Normal as best distribution are selected. Also, the frequency and intensity of flood have increased. In the return periods of constant, the maximum discharge increased, and in maximum discharge constant, with increasing return period (1000 years), the discharge rate significantly increased. So, in the 500-year return period is expected a 98% increase in maximum discharge RCP8.5 future period than base period. The most critical scenario is RCP8.5 scenario. 4- Discussion and conclusion The results indicate the impact of climate change on the basin in the future period. Therefore, knowing the increase in precipitation intensity, the flood risk increases. The occurrence of terrible floods due to climate change have caused many damages in different parts of the world in recent decades. The results of this study, like other previous studies, confirm that climate change is significant, especially with the increasing frequency of floods, governments, organizations, and educational centers need to take appropriate measures to eliminate or reduce the effects of climate change and adaptation to extreme events such as floods.
Fariba Karami; Maryam Bayati Khatibi
Volume 6, Issue 18 , June 2019, , Pages 115-137
Abstract
IntroductionSoil erosion is one of the most serious environmental degradation problems that adversely affects many natural and human-managed ecosystems. In agricultural watersheds, soil erosion not only removes nutrient-rich top soil on site, but also degrades water quality as a result of transported ...
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IntroductionSoil erosion is one of the most serious environmental degradation problems that adversely affects many natural and human-managed ecosystems. In agricultural watersheds, soil erosion not only removes nutrient-rich top soil on site, but also degrades water quality as a result of transported sediments off site. The estimation of soil erosion is often complicated due to the complex interplay of many factors such as climate, land cover, soil, topography, lithology, and human activities. Erosion models can be used as predictive tools for soil loss assessment, conservation planning, soil erosion inventories, and project planning. Moreover, models can be used as tools for understanding erosion processes and their impact. They are basically categorized into three types of empirical, conceptual, and physical based models. Empirical models are usually statistical in nature and generally applicable only to conditions for which the parameters have been calibrated. The commonly used empirical soil erosion models are USLE, RUSLE, and MUSLE. Soil erosion based- physical models include AGNPS, WEPP, SWAT, and the like. One of the most widely applied watershed models is SWAT which has been extensively used for simulating hydrologic and water quality processes in watersheds with a wide range of scales and environmental conditions. Iran is among the most affected countries in the world in terms of the extent and intensity of soil erosion. Current estimates suggest that soil erosion in Iran is around 25 tons per hectare annually which is four times greater than the world average. In the Northwest of the country, the Sattarkhan Dam has been constructed on the Aharchay River, which is the source of drinking water, agriculture, and industry in the region. In the catchment area of the Sattarkhan Dam, which includes the Aharchay upstream, physical conditions such as being mountainous and the unstability of land management such as the spread of rainforests with plowing in the direction of gradient and developmental activities cause soil erosion, sediment production, damping reservoir capacity reduction and increasing reservoir sedimentation costs. The goal of this study was to model and evaluate the spatial distribution of soil erosion in the Sattarkhan Dam basin. In this study, Soil and Water Assessment Tool (SWAT) and MUSLE models were served for simulating sediment yield and identifying critical areas of soil erosion in the Sattarkhan Dam basin, located in the North West of Iran.MethodologyThe SWAT model is a continuous-time, semi-distributed, process-based river basin or watershed scale model. It was developed to predict the impact of land management practices on water, sediment and chemical yields in agricultural watersheds with varying soils, land use, and management conditions over a long period of time. It divides a watershed into sub watersheds. Each sub watershed is connected through a stream channel. In addition, each sub watershed is divided into Hydrologic Response Unit (HRU). HRU is a unique combination of soil, land use, and slope type in a sub watershed. SWAT predicts the sediment yield within each HRU using Modified Universal Soil Loss Equation (MUSEL). Sequential Uncertainty Fitting-2 (SUFI-2), a SWAT-CUP2012 sub-module computer program, was applied to optimize the parameters of the SWAT using monthly observed sediment yield data at a monitoring site in the Sattarkhan Dam basin. In this study, sediment discharges data series during 2004-2009 and 2010-2013 were respectively used for model calibration and validation. To evaluate model performance, the statistical methods consisted of the determination coefficient (R2), Nash-Sutcliffe coefficient (NS), and root mean square error observations standard deviation ratio (RSR).Results and DiscussionSeven highly sensitive parameters were recognized for sediment yield simulation including CN2, ESCO, CH_K2, SMFMN, CH_N2, PRF, and USLE_K. The calibration outputs for simulation showed a very good model performance for sediment yield where the values of R2, NS and RSR were respectively 0.76, 0.95, and 0.06. During the validation period, the annual sediment yield simulation of R2, NS, and RSR values were respectively 0.96, 0.93, and 0.1. Also, the results showed that the spatial pattern of the regions differed in terms of the erosion and sediment production. The critical areas were located in the upper part of the basin and sediment production was very high and high, which included about 34.15% of the area of the Sattarkhan Dam basin.Conclution This study showed that the SWAT model is competent of predicting sediment yields and, hence, can be used as a tool for water resource planning and management in the study watershed. The prediction of sediment yield at ungauged watershed with SWAT could be possible under comparable topography, land use, soil management, climate condition for the purpose of soil erosion assessment, scenario analysis, and recommendation of best management practices to support watershed management initiatives in the semi-dry mountainous regions of Iran.
