Sara Heshmati; Bijan Nazari; Mohammadreza Nikoo
Abstract
Introduction
Climatic changes and human activities are among the key factors influencing river flow. Determining the contributions of climate change and human activities is essential for the sustainable management of water resources. Climate change is associated with variations in temperature and precipitation, ...
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Introduction
Climatic changes and human activities are among the key factors influencing river flow. Determining the contributions of climate change and human activities is essential for the sustainable management of water resources. Climate change is associated with variations in temperature and precipitation, leading to changes in the spatial and temporal distribution patterns of rainfall. Human activities, both directly and indirectly, affect water resources. The rational use of water resources, including runoff, is therefore critical. This study aims to quantify the contributions of climate change and human activities to runoff variations in the Qazvin Plain salt marsh.
Materials and methods
The Qazvin Plain, covering approximately 450,000 hectares, is located between longitudes 49°25′ to 50°35′ E and latitudes 35°25′ to 36°25′ N in Iran. In this research, the Mann-Kendall test was applied to analyze the trends in annual precipitation, runoff, air temperature, and potential evapotranspiration during the period 1990–2020. The Pettitt test and the double mass curve method for precipitation-runoff analysis were used to identify the change point in runoff values. Finally, hydrological sensitivity analysis based on the Budyko-Zhang hypothesis was employed to determine the respective contributions of human activities and climate change to runoff variations.
Results and discussion
The results of the Mann-Kendall test revealed a significant decreasing trend in runoff at a 0.01 significance level. Conversely, the average annual temperature and potential evapotranspiration exhibited significant increasing trends at the same significance level. Despite a reduction in average annual precipitation at the basin level, no statistically significant trend was observed for rainfall. The results of the Pettitt test and the cumulative precipitation-runoff curve identified 1996 (1375 in the Persian calendar) as the change point in the annual runoff series. Using hydrological sensitivity analysis based on the Budyko-Zhang hypothesis, the contributions of climate change and human activities to runoff variations were quantified as -0.21 mm (-161.2%) and 0.08 mm (61.2%), respectively.
Conclusions
Trend analysis in the study area demonstrated a decreasing trend in runoff and an increasing trend in average annual temperature and potential evapotranspiration. Runoff values in Shorezar identified 1996 as the change point in the time series. According to the Budyko-Zhang method, climate change has contributed to a decrease in runoff, while human activities have increased the water level in the salt marsh.
Nazli Zenozi Alamdari; Behrouz Sobhani; Mehdi Eshahi,; Masihallah Mohammadi
Abstract
Introduction
Climate is a complex system that is changing primarily due to the increase in greenhouse gases. To study the effects of climate change on agricultural, hydrological, and environmental systems, general circulation models (GCMs) are used to simulate climate variables. These models, based ...
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Introduction
Climate is a complex system that is changing primarily due to the increase in greenhouse gases. To study the effects of climate change on agricultural, hydrological, and environmental systems, general circulation models (GCMs) are used to simulate climate variables. These models, based on approved Intergovernmental Panel on Climate Change (IPCC) scenarios, enable the modeling of climate parameters over extended periods. Globally, various centers and models simulate future climatic conditions using different emission scenarios, physical structures, and computational approaches. The simulations from CMIP6 GCMs form the foundation for many IPCC conclusions regarding future climate changes. These data are utilized directly or after downscaling to evaluate local and regional climate changes (IPCC, 2021). This study analyzes and predicts trends in precipitation and minimum and maximum temperatures in East Azerbaijan Province under climate change conditions from 2021 to 2100.
Materials and methods
This study aims to investigate precipitation and minimum and maximum temperatures and their trends from 2021 to 2100 across stations in Tabriz, Ahar, Jolfa, Maragheh, and Miyaneh. Data from 12 CMIP6 models (ACCESS-CM2, BCC-CSM2-MR, CESM2, CNRM-CM6-1, CanESM5, MIROC6, MRI-ESM2-0, IPSL-CM6A-LR, GISS-E2-1-G, HadGEM3-GC31-LL, NESM3, and NorESM2-MM) were used under three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5). The Kling-Gupta Efficiency (KGE) method was applied to identify the best models for simulating precipitation and temperature by comparing historical model data (1989–2018) with observed data from selected stations. Bias correction of model outputs was then used to forecast climate variables under the SSP scenarios. Finally, the mean time series of precipitation and minimum and maximum temperatures for the future period were compared with historical data to quantify changes over the 80-year horizon (2021–2100) for East Azerbaijan Province.
Results and discussion
The performance of 12 CMIP6 climate models was evaluated for generating past and present climate data (1989–2018). Based on uncertainty analysis, the BCC-CSM2-MR and MIROC6 models were identified as the best for simulating precipitation and temperature. These models were used, with bias correction, to predict precipitation and minimum and maximum temperatures for the future period (2021–2100) under optimistic, moderate, and pessimistic scenarios for East Azerbaijan Province. The results revealed that in all scenarios, annual temperatures are projected to increase while annual precipitation will decrease. Annual maximum temperatures across the selected stations are expected to increase by 0.57–6.41°C, while annual minimum temperatures will rise by 0.46–4.89°C. Precipitation is projected to decrease by 2.3% to 9.18%. The highest temperature increase and precipitation decrease are expected at Jolfa and Tabriz stations, respectively.
Conclusions
This study demonstrates that CMIP6 models effectively simulate future climate parameters and align well with historical climate data for East Azerbaijan Province. The high accuracy of these simulations makes them suitable for forecasting future climatic conditions and facilitating macro-level management strategies. Such strategies can enhance resource productivity, particularly in water resource management, to address the challenges posed by climate change.
Abdorreza Vaezihir; Fatemeh Safari
Abstract
Introduction
The Goijeh Bel basin, with extensive outcrops of igneous, metamorphic, and sedimentary formations and adequate rainfall (342.2 mm annual precipitation), has significant potential for storing and transferring groundwater through fractured media. These hard formation units, located in elevated ...
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Introduction
The Goijeh Bel basin, with extensive outcrops of igneous, metamorphic, and sedimentary formations and adequate rainfall (342.2 mm annual precipitation), has significant potential for storing and transferring groundwater through fractured media. These hard formation units, located in elevated areas, can supply drinking water to Ahar city without the need for pumping stations. Most springs in the basin originate from hard formations, with their concentration in the center and north indicating the development of aquifers in these units. Overextraction of groundwater through wells and the limitation of alluvial resources have shifted water resource management toward utilizing hard formation water sources. This study investigates the quantity and quality of groundwater resources in the Goijeh Bel basin to identify methods for sustainable water management and assess their suitability as an emergency drinking water source for Ahar city.
Materials and methods
The study area is located 10 km southwest of Ahar city within the Aharchai River basin, which ultimately joins the Aras River. Remote sensing and GIS techniques, including the Analytic Hierarchy Process (AHP), Weighted Overlay, and Ordered Weighted Averaging (OWA) methods, were used for data analysis. Landsat 8 satellite images were processed to generate raster maps for the Normalized Difference Humidity Index (NDHI) and Normalized Difference Vegetation Index (NDVI). In the AHP method, criteria were ranked and compared pairwise, with weights assigned based on their importance. These weighted layers were overlaid to create a groundwater potential map. Fieldwork involved sampling five groundwater sources and Goijeh Bel River water, followed by hydrochemical analysis of eight major ions (Na⁺, Ca²⁺, Mg²⁺, K⁺, Cl⁻, CO₃²⁻, HCO₃⁻, SO₄²⁻), TDS, pH, SAR, %Na, and TH. Electrical conductivity (EC), dissolved solutes, and chloride ion concentrations were assessed to evaluate groundwater quality for drinking and agricultural purposes. Meteorological data from Ahar’s synoptic station over the past 20 years were also analyzed. The spatial distribution of springs was used to validate groundwater potential maps.
Results and discussion
Using AHP, Weighted Overlay, and OWA methods, groundwater potential maps were generated based on lithology, line density, elevation, humidity index, slope, drainage density, aspect, and vegetation index. The OWA method showed the highest agreement with spring locations, with approximately 50% of springs situated in areas of medium to high groundwater potential. Qualitative analysis revealed an increase in salinity and EC from upstream to downstream, with EC values ranging from 310 to 1,444 µS/cm. Chloride ion concentrations followed a similar pattern, suggesting a dominant role of sodium and chloride in groundwater salinity. Schuler’s diagram indicated that most groundwater in the basin is suitable for drinking due to the absence of pollutant formations such as salt, clay, or marl. These findings align with studies on hard and karst formations in western Urmia, which also report good-quality groundwater.
Conclusions
The southwestern part of the basin exhibits high groundwater potential. Validation of groundwater potential maps using spring locations confirmed the reliability of the OWA method. The groundwater quality assessment demonstrated increasing salinity toward the basin outlet, but most groundwater remains suitable for drinking. Watershed operations, such as biological measures or flood and sediment control structures, can enhance infiltration and aquifer recharge in the hard formations. To quantify aquifer potential and estimate extractable water volumes, geophysical surveys and exploratory drilling in high-potential areas are recommended.
Banafshe Yasrebi; Mehri Dinarvand
Abstract
Introduction
One of the key challenges in rehabilitating degraded lands in arid areas is ensuring adequate moisture to enhance biomass production. This water supply must be achieved without further straining the already limited water resources or causing social conflicts in the region. Utilizing runoff ...
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Introduction
One of the key challenges in rehabilitating degraded lands in arid areas is ensuring adequate moisture to enhance biomass production. This water supply must be achieved without further straining the already limited water resources or causing social conflicts in the region. Utilizing runoff from rainfall and creating water storage systems is an effective method for restoring and improving pastures, particularly in desert and dry regions. This study aims to evaluate the impact of pitting on the restoration of native vegetation in degraded lands and dust emission hotspots in southern Khuzestan province, specifically in Bandar Mahshahr city.
Materials and methods
The transect-quadrat method was employed to investigate changes in vegetation cover. Two transects were randomly established in opposite directions and perpendicular to the rows of pitting within the study area. Each transect included 15 plots, resulting in a total of 30 plots in pitting areas and 30 plots in the control area (between the pitting rows). Canopy cover and plant species were measured in all plots. Additionally, vegetation richness and diversity indices were calculated using PAST software. To examine the impact of pitting on soil properties, 60 soil samples were collected from pitting and control areas at three depths: 0–30 cm, 30–60 cm, and 60–90 cm. Laboratory analyses were conducted to measure organic carbon, salinity, and moisture. An unpaired t-test, following a normality test, was used to assess significant differences in vegetation cover and soil characteristics between pitting and control areas.
Results and discussion
The results revealed that species density in pitting areas increased by 81%, canopy cover by 14 times, the Shannon diversity index by 82%, and the Simpson diversity index by 67%, compared to control areas. Conversely, the dominance index decreased by approximately 60%. In terms of soil conditions, salinity decreased across all three depths, while moisture significantly increased at a depth of 60–90 cm. Furthermore, organic carbon content increased by 40% at a depth of 0–30 cm.
Conclusions
The implementation of pitting has successfully restored native vegetation and improved soil conditions by enhancing moisture storage. Field observations indicate that pitting not only facilitates desert restoration by reintroducing and establishing valuable native species but also enhances soil quality. This approach demonstrates the potential of pitting to act as a critical link between various ecosystem components, promoting ecological balance and sustainability.
Mohammadreza Kousari; forood sharifi; Alireza Majidi
Abstract
Introduction
In the context of climate change and global warming, the comprehensive management and productivity of water resources become increasingly important. Accurate measurement of existing water resources forms a critical foundation for effective water resource management. Precise measurements ...
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Introduction
In the context of climate change and global warming, the comprehensive management and productivity of water resources become increasingly important. Accurate measurement of existing water resources forms a critical foundation for effective water resource management. Precise measurements enable better and more fundamental planning. Surface water, particularly flood-generated water in large and small watersheds, plays a significant role in Iran's water resources. A major challenge in the country's water resource management is the lack of sufficient runoff data, especially for smaller watersheds. The use of hydrometric devices for stable water level measurements can substantially address this issue, improving the collection of surface and groundwater data. Several methods have been developed for water level measurement, which can be categorized as contact or non-contact methods, depending on whether the sensor interacts directly with the water. These methods may record data either automatically or manually. Selecting the appropriate method depends on specific conditions, such as the range of liquid level changes, the physical properties of the liquid (e.g., density, cleanliness, vapor or particle content, corrosiveness), process temperature and pressure, chemical composition, and environmental factors like moisture.
Materials and methods
Non-contact methods offer significant advantages, including independence from fluid type and non-interaction with the fluid itself. Among these methods are image processing using cameras, ultrasonic sensors, infrared sensors, and laser-based techniques. This research investigates the efficiency of the Sharp infrared module model GP2Y0A02YK0F in measuring water level changes in both laboratory and natural environments. The module includes a distance measurement sensor consisting of a Position Sensitive Detector (PSD), Infrared Emitting Diode (IRED), and a signal processing circuit. It operates within a voltage range of 4.5 to 5 volts and a temperature range of -10 to +60 °C. The analog output of this module corresponds to the measured distance, producing values between 0 and 1023. When an object moves closer to the sensor, the output approaches 0, and as the object moves farther away, the output increases toward 1023. Data calibration is required to relate sensor readings to actual values. The sensor's measurement range is 20–150 cm, utilizing infrared light for distance detection. To evaluate its performance, a low-power data logger suitable for watershed environments was employed. Since the method requires a non-reflective surface, it was combined with a traditional float-based method. The mechanical setup includes a polyethylene tube housing the sensor, enclosed within a metal body to resist flood conditions. Laboratory experiments involved measuring water level changes across 10 stages, where sensor data (independent variable) and actual water level values (dependent variable) were collected. Polynomial fitting (first to fourth degree) was applied to establish relationships between variables. Additionally, 30% of the data was reserved for model validation.
Results and discussion
An inverse relationship between sensor readings and actual distances was evident: sensor output values decreased as distance increased. The correlation coefficients (R) for one- to four-term polynomial fits were close to one, indicating a strong alignment between sensor data and actual measurements. The RMSE ranged from 2.16 to 1.89 cm, improving with higher-degree polynomials. In laboratory conditions, the sensor estimated water level changes with a 2 cm error, which was reduced to 1.34 cm by increasing the minimum measurement range to 30 cm. Given its affordability, this sensor is suitable for applications where high precision is unnecessary. For higher accuracy, alternative sensors should be considered. However, in flood environments, issues such as the obstruction and adhesion of floating materials in the tube pose challenges, making this method unsuitable for flood channel measurements. Incorporating additional sensors, such as pressure or ultrasonic sensors, could enhance the device's capabilities.
Conclusions
Various methods have been developed for measuring water level changes. The selection of a method depends on environmental conditions, accuracy requirements, and cost considerations. Given the lack of extensive water level and flow measurement networks in Iran's watersheds, the approach proposed in this research can significantly contribute to water resource management. However, the reliance on floating components within the tube is a critical limitation, as flood-induced sediment can hinder float movement over time. Future research should focus on methods that eliminate the need for floating parts, thereby overcoming these limitations. Additionally, the results of other measurement techniques will be explored in subsequent studies.
Mohammad Reza Sheykh Rabiee; Hamid Reza Peyrowan; Peyman Daneshkar Arasteh; Mehry Akbary; Baharak Motamedvaziri
Abstract
Introduction
Climate change is one of the most important challenges that affects natural ecosystems and different aspects of human life. The effects of global warming on the hydrology and water cycle in nature are very serious, and knowing these effects quantitatively creates more preparation to deal ...
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Introduction
Climate change is one of the most important challenges that affects natural ecosystems and different aspects of human life. The effects of global warming on the hydrology and water cycle in nature are very serious, and knowing these effects quantitatively creates more preparation to deal with its consequences. It is necessary to evaluate these changes in order to reduce their effects on the basin and formulate a suitable strategy to minimize their adverse effects. This study uses a combined model of SDSM and SWAT to investigate the effects of climate change on the amount of runoff and sediment in Karganrood watershed in Gilan province in Iran. The water measuring station (Mashin Khaneh) is located inside this basin and has a long statistical history. Also, the least amount of land use changes has taken place in this basin, which can better show the results of revealing climate changes on the amount of runoff and sediment.
materials and methods
In order to investigate the consequences of climate change on runoff and sediment, SWAT hydrological model was used. The SWAT model was calibrated and validated by the SUFI-2 algorithm by improving the simulation results of discharge flow and basin sediment. After the implementation of SWAT model, 109 hydrological response units (HRU) were extracted in five sub-basins. After 500 steps of simulation, finally 22 parameters in runoff production and 6 parameters in sediment production of Karganrood watershed were identified as effective parameters. Then, according to the values obtained from NS, R² and RMSE evaluation criteria, it was found that CanESM5 climate model has better accuracy and efficiency than MPI-ESM1.2-HR and NorESM2-MM climate models. By introducing the time series of daily average precipitation and temperature resulting from the output of the CanESM5 climate model and using the SDSM downscaling model, the runoff and sedimentation of the Karganrood basin on a monthly basis at the Mashin Khaneh hydrometric station in the periods of 2026-2050, 2075-2051 and 2100- 2076 for two scenarios SSP2-4.5 and SSP5-8.5. Simulated.
Results and discussion
According to the values obtained from NS, R² and RMSE evaluation criteria, it was found that CanESM5 climate model has better accuracy and efficiency than MPI-ESM1.2-HR and NorESM2-MM climate models. The results of the CanESM5 model indicate that precipitation, maximum and minimum temperature will decrease in all future periods based on SSP2-4.5. Also, the examination of CanESM5 model results in connection with SSP5-8.5 shows that precipitation will decrease in all future periods and the maximum temperature will increase in the period of 2051-2075 and 2076-2100. Also, the results of climate data in all three climate models and in both scenarios SSP2-4.5 and SSP5-8.5 showed that the period of 2076-2100 will be drier and warmer than other periods. In order to investigate the consequences of climate change on runoff and sediment using the SWAT hydrological model and by introducing the time series of average daily precipitation and temperature from the output of the CanESM5 climate model and using the SDSM downscaling model, the runoff and sediment of the Karganrood basin on a monthly basis at the station Car house hydrometry in the periods 2050-2026, 2051-2075 and 2076-2100 for two scenarios SSP2-4.5 and SSP5-8.5. Simulated. The results of the SWAT model showed that the runoff changes for the SSP2-4.5 and SSP5-8.5 scenarios will decrease and the sediment changes will increase in all future periods.
Conclusion
Using the output data of the CanESM5 climate model related to the sixth report and under the SSP2-4.5 and SSP5-8.5 scenarios and using the SWAT model, the amount of runoff and sediment in three time periods of the near future (2026-2050), medium (2051- 2075) and period (2076-2100) was carried out. The amount of sediment at the exit point of the Mashin Khaneh water measuring station showed an increasing trend. Also, the results showed that the observed stream flow limit does not match with the SSP2-4.5 and SSP5-8.5 scenarios in the future periods, but the observed sedimentation is compatible with the future periods. The data of the SSP2-4.5 scenario showed that discharge will decrease in all periods and sediment will increase in all future periods. The largest changes in discharge are related to the future period of 2076-2100 and amount to -56.7 percent, and the lowest number of changes in discharge are related to the future period of 2026-2050 and amount to -48.5 percent. The highest sediment changes are related to the future period of 2051-2075 and amount to 54.3% and the lowest amount of sediment changes are related to the future period of 2026-2050 and amount to 5.12%. Also, the results of the SWAT model based on the data of the SSP5-8.5 scenario showed that discharge will decrease in all periods and sediment will increase in all future periods. The largest changes in the flow rate are related to the future period of 2076-2100 and amount to -56% and the lowest number of changes in the flow rate are related to the future period of 2026-2050 and amount to -52.8%. The highest sediment changes are related to the future period of 2076-2100 and amount to 113.27% and the lowest amount of sediment changes are related to the future period of 2026-2050 and amount to 29%. It seems that the decrease in rainfall in the coming periods will cause a decrease in vegetation, especially in late summer and early autumn and with the melting of the remaining snow in the highlands due to the increase in temperature; The amount of produced runoff increases, which will increase the sediment produced in the basin.
Majid Mohammady; Mojtaba Amiri
Abstract
IntroductionHuman activities are at the core of global environmental change and Humans play a key role in global warming, land degradation, air and water pollution, rising sea levels, eroding the ozone layer, extensive deforestation, and acidification of the oceans. Soil erosion and degradation is a ...
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IntroductionHuman activities are at the core of global environmental change and Humans play a key role in global warming, land degradation, air and water pollution, rising sea levels, eroding the ozone layer, extensive deforestation, and acidification of the oceans. Soil erosion and degradation is a natural phenomenon altering the relief of the landscape. Erosion is often capable of causing several on-site and off-site impacts. Erosion and soil loss are common in hilly areas, but their severity will vary depending on the geoenvironmental factors including, Steep sloping, geological characteristics, vegetation and climatic factors making it more vulnerable to erosion. One of he most important kind of erosion is badland erosion. The term of badlands currently refers to areas of unconsolidated sediment with little or no vegetation, which are useless for agriculture because of their intensely dissected landscape. Badland erosion is observed mostly in arid and semi-arid regions, and the interaction of precipitation with geological materials is responsible for the development of badlands in arid and semi-arid regions. Because soil erosion is a complicated process that is influenced by the properties of the land surface and the soil as well as by environmental factors, quantitatively accurate forecasts of soil erosion and susceptibility mapping are challenging. The main goal of this research is to map badland erosion suscepibility in Firozkuh watershed using frequency ratio model. Materials and methodsFirozkuh watershed was selected as study area because in this watershed, badlands are the most important contributors to soil erosion because of the condition of climatic, hydrologic, topographic, and reduced vegetation conditions, and as well as presence of susceptible soil and geology formations in this region. The first step in this research is to prepare distribution map of the badlands and determine their location on the map. This was done using Google Earth imagery and field surveys. The maps of condiioning factors were prepared from different sources and entered into the GIS environment. Digital Elevation Model (DEM) map with the cellsize of 30 meter was prepared using the elevation points and lines in the topographic maps prepared by the National Cartography Center of Iran. Slope aspect, slope degree, plan curvature, TWI and elevation classes maps was creaed using DEM map in ArcGIS10.3 and SAGA-GIS environment. The geology map of the watershed was extracted from the geologic map of Iran with the scale of 1:100000. River and road maps were extracted from 1:25000 topographic map and the distance from these features was calculated in ArcGIS10.3 environment. The land use of Firozkuh watershed was created from LANDSAT 8 images of year 2020 using a synthetic method. To map soil characteristics, 30 samples were taken from depth of 0-30 centimeter and analyzed in the laboratory. Aaverage annual rainfall map was developed using rainfall data from meteorological stations. After classifying conditioning factors maps, the weight of each map was calculated using the frequency ration model. In the next step, by combining the weights, the final badland erosion susceptibility map was prepared. The ROC curve and the area under the curve were used to assess the accuracy of the frequency ratio models. Results and discussionThe relationship between badland erosion and conditioning factors was investigated using the frequency ratio model. The results showed that the highest weight of the frequency ratio is related to the elevation class of 1710 to 2286 meters, rainfall 400 to 550, slope more than 35, northwest aspect, distance less than 1150 meters from drainage network, marl, limestone and shale formations, ranglands, Convex and concave slopes, clay 25 to 33%, silt 27 to 35%, hydrological group C, soil depth 57 to 120 cm, pH 7.6 to 1.8, TWI class 6 to 11. Accuracy assessmen of the freency ratio model was done using ROC and area under this curve. The area under the ROC curve was 0.71 that showed frequency ratio model is acceptable for badland erosion susceptibility mapping in the Firozkuh watershed. Despite its simplicity, the freqency ratio model provides acceptable results due to the creation of a logical connection between the badlands and conditioning factors. Other studies, including investigating the potential of underground water, landslide susceptibility maping, and the vulnerability to floods, have also been conducted with this model, and its accuracy has been confirmed. ConclusionsBecause of topographical, climatic and geological conditions, the badland erosion is a dominant phenomenon in the Firozkuh watershed. In this research, badland erosion susceptibility map was prepared using the frequency ratio model. Accuracy assessment showed that frequency ratio is a suitable model for badland erosion susceptibility maping in this watershed. The results showed that about 50% of this region has high and very high susceptibility to the badland erosion, so it is necessary to pay attention to this phenomenon and prepare a susceptibility map.
Mohsen Armin; Hamide Zahedikhah; Maleeha Mozayyan
Abstract
Introduction
Check dams are simple and relatively low-cost structures that are widely used to control sedimentation in watersheds due to the lack of special materials and technology. These types of dams have the largest amount of watershed improvement operations in Iran. Therefore, considering the frequency ...
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Introduction
Check dams are simple and relatively low-cost structures that are widely used to control sedimentation in watersheds due to the lack of special materials and technology. These types of dams have the largest amount of watershed improvement operations in Iran. Therefore, considering the frequency of construction and as a result the cost of construction, it is necessary to investigate their performance in watersheds to identify their strengths and weaknesses. Evaluation of sediment trapping of check dams and correct selection of parameters affecting their sedimentation performance is the main goal of this research.
Materials and methods
In this research, the evaluation of check dams from the perspective of sedimentation performance in the Nehzatabad watershed in Kohgiluyeh county has been investigated. For this purpose, after determining the parameters related to the volume of sediments deposited behind 11 selected check dams and calculating their volume, the amount of sediment yield was first measured and then estimated by calculating three different sediment trapping coefficients. Finally, by calculating the sediment delivery ratio, the measured and estimated sediment yield was converted into its equivalent soil loss on the surface in the upstream sub-watershed of the check dams.
Results and discussion
The results showed that the amount of specific sediment yield measured in check dams is from 0.001 to 1.08 and on average 0.13 tons per hectare per year. Considering the ratio of sediment delivery, which varied from 18 to 51 percent for selected dams, this amount of sediment yield is equivalent to 0.01 to 2.1 and an average of 0.3 tons per hectare per year of soil loss in the upstream sub-watersheds of check dams, which is a very small number compared to the figures presented for the average soil loss in most of Iran's watersheds. Taking into account different coefficients of sediment trapping, the estimated average values for specific sediment yield in check dams are 2.88, 7.46 and 0.87 tons per hectare per year, which are equivalent to 9.41, 30.5, 3.49 tons per hectare per year of soil loss respectively, which compared to the average amount of soil erosion in Iran's watersheds, seem more reasonable and logical numbers.
Conclusions
Considering the factors affecting the sediment trapping coefficient, it can be said that if check dams are built at a point in the waterway where the ratio of the storage capacity of the dam reservoir to the area of the sub-watershed upstream of the dams is higher, the sediment trapping coefficient in the dams will increase, which it is more favorable in terms of sedimentation efficiency. By examining the amount of sediment trapping coefficients in the investigated check dams in the Nehzatabad watershed, which are relatively low, it can be said that one of the reasons for the low coefficients is the reduction in the ratio of the storage capacity of the dam reservoir to the area of their upstream watershed. Therefore, if the scientific principles are not observed in the correct selection of the effective parameters for the placement of check dams, the implementation of such projects does not have the necessary and sufficient effectiveness, while the sediment measured in these dams and the soil erosion equivalent to it are a basis for the implementation of other watershed management measures are in watershed areas and if they are not accurate, It can lead to ineffectiveness of these measures and incorrect calculations.
