M. Motallebian; H. Ahmadi; A. Rauf; N. Cartwright
Abstract
Introduction: Aquifers are the major source of freshwater in many parts of the world. Saltwater intrusion (SWI) is a serious environmental issue since 80% of the world’s population live along the coast and utilize local aquifers for their water supply. Globally, coastal aquifers are under threat from ...
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Introduction: Aquifers are the major source of freshwater in many parts of the world. Saltwater intrusion (SWI) is a serious environmental issue since 80% of the world’s population live along the coast and utilize local aquifers for their water supply. Globally, coastal aquifers are under threat from saltwater intrusion (SWI). SWI is caused by changes in coastal aquifer conditions resulting from ground water extraction, climate drivers, sea-level rise, oceanic over topping events, and land use change. Under natural conditions, these coastal aquifers are recharged by rainfall events, and the regional groundwater flow towards the ocean counters the intrusion of saltwater into the freshwater region. However, over-exploitation of coastal aquifers in some regions has resulted in a reduction in fresh groundwater levels (and hence reduced natural flow) and this has led to an increase in saltwater intrusion. Saltwater intrusion degrades the quality of coastal aquifer groundwater resource which can lead to a reduction in crop yield efficiency, limitation on the drinking water resource as well as soil fertility and salinity of operated wells. Such problems are more crucial where groundwater aquifers are shallow.
Materials and Methods: The aim of this study is to investigate the effect of Lake Urmia water-level fluctuations on groundwater table and rate of the intruding or receding of salt water to the coastal aquifer. In order to achieve this purpose, Rashakan coastal aquifer in the vicinity of Lake Urmia in the northwest of Iran was simulated. In this study, SEAWAT model was used to simulate the problem. SEAWAT was specifically designed for the simulation of SI, although it has many other applications as well, notably the combined simulation of groundwater flow and heat transfer. SEAWAT as a widely used, three-dimensional variable-density groundwater flow and transport model has been developed by the USGS based on MODFLOW and MT3DMS and includes two additional packages: Variable-Density Flow (VDF) and Viscosity (VSC). First, the model was calibrated and then the simulations were defined in four scenarios as follows: a) The rate of the intruding or receding of salt water to the coastal aquifer during recent years b) The effect of the drop-in lake water level on groundwater level changes trend regardless of changes in lake water density c) The effect of the drop-in lake water level on groundwater level changes trend in view of changes in lake water density d) The effect of the drop-in lake water level on the rate of the intruding or receding of salt water.
Results and Discussion: In this study, simulations were carried out under four scenarios in order to investigate the effect of Lake Urmia water-level fluctuations on groundwater table and rate of the intruding or receding of salt water to the coastal aquifer. In the first scenario, in order to assess the rate of the intruding or receding of salt water to the coastal aquifer in recent years, three profiles have been investigated in the north and the center and south of the study area, and the results showed that in recent years there has been no significant change in the displacement of the salt-water wedge and this change was less than 50 meters and only the upper part of wedge connected to the lake was more affected by dropping water level of lake, which was due to retreat of the boundary imposed by lake water recession. In the second scenario, the effect of the drop-in lake water level on groundwater level changes trend, regardless of changes in lake water density, was investigated. The findings of the study showed that if the concentration of lake water is considered constant, the increase and decrease in groundwater level across the aquifer would be almost equal to the increase and decrease the lake water level. In the third scenario, the effect of the drop-in lake water level on groundwater level changes trend in view of changes in lake water density was investigated and the findings was also made with the second scenario, where the results showed that when the effect of the density changes is neglected, the groundwater level is affected by the lake water level changes more than about 2 times that when the density changes are considered. However, increasing and decreasing concentrations, and consequently increasing and decreasing the density, may have a great effect on the reduction and increase of groundwater levels. In the fourth scenario, the effect of the drop-in lake water level on the rate of the intruding or receding of salt water was also investigated. It can be concluded that when concentration changes and as a result of variations in density are affected, by decreasing the level of the lake, saltwater wedge would be intruded and when the effect of the density changes is neglected, saltwater wedge would be receded.
Conclusion: The results of this study indicated that during recent years there has been no significant change in the location of the salt water wedge, and this change is less than 50 meters. The upper part of wedge connected to the lake is more affected by dropping water level of lake, which is due to retreat of the boundary imposed by lake water recession. Also, the findings of the study showed that if the concentration of lake water is considered constant, the increase and decrease in groundwater level across the aquifer will be almost equal to the increase and decrease of the lake water level. When the effect of the density changes is neglected, the groundwater level is affected by the lake water level changes more than by about 2 times that when the density changes are considered. Despite the decreasing of about 7 meters of lake Urmia water level, due to increase the density of water, the wedge has intruded. This research shows that in the event of an increase in the water level of Lake and consequently a decrease in water density, Saltwater wedge would be receded.
Hojjat Ahmadi; Mohammad Hemmati; Mehdi Motallebian
Abstract
Introduction: Coastal aquifers are major source of freshwater in many parts of the world. Saltwater intrusion is a serious environmental issue since 80% of the world’s population live along the coast and utilize local aquifers for their water supply.Under natural conditions, these coastal aquifers ...
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Introduction: Coastal aquifers are major source of freshwater in many parts of the world. Saltwater intrusion is a serious environmental issue since 80% of the world’s population live along the coast and utilize local aquifers for their water supply.Under natural conditions, these coastal aquifers are recharged by rainfall events, and the recharged water flowing towards the ocean would prevent saltwater from encroaching into the freshwater region. However, over exploitation of coastal aquifers has resulted in reducing groundwater levels (hence reduced natural flow) and this has led to severe saltwater intrusion. Saltwater intrusion from the sea into below the freshwater of aquifer impairs the quality of these resources. Cause ofthe complexity of saltwater intrusion issues and generally they cannot be solved analytically, so numerical methods can be useful tools for simulation and prediction of salt water intrusion.
Materials and Methods: CTRAN/W is a finite element software product that can be used to model the movement of contaminants through porous materials such as soil and rock. The comprehensive formulation of CTRAN/W makes it possible to analyze problems varying from simple particle tracking in response to the movement of water, to complex processes involving diffusion, dispersion, adsorption, radioactive decay and density dependencies. SEAWAT is a three-dimensional variable density groundwater flow and transport model developed by the USGS based on MODFLOW and MT3DMS. SEAWAT is based on MODFLOW and MT3DMS. SEAWAT includes two additional packages: Variable-Density Flow (VDF) and Viscosity (VSC).In this study, the precision of CTRAN / W and SEAWAT models to simulation and prediction of saltwater wedge were investigated in three states: a) steady state salt-wedge data observed underdifferenthydraulic gradient conditions; b) transient salt-wedge data observed underintruding-wedge conditions; and c) transient salt-wedge data observed under receding-wedge conditions. Both models were initially calibrated and then the models were performed for the above conditions. The simulation results of the two models with the experimental results of Goswami and Clement (2007) have been compared. For comparing the measured data and simulated data, statistical indicators were used: root-mean-square error (RMSE), a measure of Nash-Sutcliffe (CE), the Correlation Coefficient (R^2), the ratio of difference (r) and the General Standard Deviation (GSD).
Results and Discussion: In this study, the precision of CTRAN / W and SEAWAT models to predict saltwater wedge wasinvestigated. At first step, both models were calibrated and the best values for longitudinal and transverse dispersion were obtained 0.5 and 0.05, respectively.Then simulation was performed with both models for all three modes(a- steady state salt-wedge data observed underdifferenthydraulic gradient conditions; b- transient salt-wedge data observed underintruding-wedge conditions; and c- transient salt-wedge data observed under receding-wedge conditions). The results showed thatCTRAN/W and SEAWAT models have high precision for simulation of position and movement of saltwater wedge in steady state with average of root mean square error (RMSE) equal to 1.05 and 1 cm, respectively and Both models have a higher estimate than the actual value for a steady state. As well as for transient state under the underintruding-wedge conditionsCTRAN/W and SEAWAT models have high precisionwith average of root mean square error (RMSE) equal to 0.65 and 0.44 cm, respectively and other statistical indicators were acceptable. The results of prediction of position and movement of saltwater wedgeunder receding-wedge conditionswith average of root mean square error (RMSE) equal to 0.54 and 0.56 cm, respectively provided acceptable estimates of both models. Finally, in order to determine the accuracy of the models in estimating the flow rate from the source of fresh water to the source of salt water, a comparison was made between the results of the models and the laboratory data, which showed that The CTRAN/W revealed appropriate estimation of amount of transferring discharge from freshwater reservoir to saltwater reservoir in compared with SEAWAT model. In general, according to statistical indicators, the results of both models were acceptable
Conclusion: The results showed thatCTRAN/W and SEAWAT models have high precision for simulation and prediction of position and movement of saltwater wedge with average of root mean square error equal to 0.67 and 0.58 cm (less than 10% of the average of measured data), respectively. The CTRAN/W revealed appropriate estimation of amount of transferring discharge from freshwater reservoir to saltwater reservoir in compared with SEAWAT model. In general, according to statistical indicators, the results of both models were acceptable.
Hassan Rahimi; H. Ahmadi
Abstract
Introduction: Cracking of earth dams is a one of the main threat causes of stability of embankment dams. In this research by modeling of the behavior of an embankment dam and employing conditions of the earthquake, the reasons of cracking were inspected using by modeling of earth dam behavior. Based ...
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Introduction: Cracking of earth dams is a one of the main threat causes of stability of embankment dams. In this research by modeling of the behavior of an embankment dam and employing conditions of the earthquake, the reasons of cracking were inspected using by modeling of earth dam behavior. Based on the literature, one of the main causes of dam failures is sliding and cracking of the dam structure during earthquake. Localized liquefaction of foundation soils was one of the causes of the observed post-earthquake distress within these dams.
Material and Methods: In order to study the causes and the results of crack on earth dams, Mahmoodabad earthen dam with a height of 19 m, is located in Zanjan province, northwest of Iran, which suffered a longitudinal crack on the crest and slight sliding of the upstream slope due to 2001 Avaj earthquake was studied. This dam has faced earthquake two times with an interval of two years. During the first earthquake with the magnitude about 6.6 in Richter scale small longitudinal cracks had created on the crest. The developed cracks had been repaired by injecting the cement and then has been hidden by passing the time. After the second earthquake with the magnitude about 6.5 in Richter scale the hidden cracks had been appeared again and the slight movement of the upper slopes of dam reported. Based on the site investigation and documented information about dam, including maps and parameter data, the behavior of the dam has modeled by using Plaxis as a finite element model. In order to check the accuracy of the design of dam, the stability analysis has been conducted using by Xslope as a limit equilibrium model. The foundation conditions and the Geotechnical properties of the layer beneath the dam has been inspected by open excavation.
Results and Discussion: Underground investigation about Geotechnical properties of dam foundation has showed that there is a thin sandy layer confined in alluvium material of the river base beneath the dam structure. In fact , this layer has not been considered in the analysis as well in design. Because of fully saturated condition of this layer in an operation period of dam it might subjected to liquefaction during the happening of the earthquake. Evaluation of liquefaction potential of this layer based on Seed and Idriss (1971) diagram showed probability of this phenomenon. To prove this hypothesis, the stability analysis had been conducted in two different conditions by including the thin sandy layer and without considering the mentioned layer. The analysis showed in the case of absence of sandy layer the required safety factor was satisfied, but including the sandy layer leads cause the safety factor dropped to 0.84 that means accruing of liquefaction in the thin layer would lead to structural instability of the studied dam. The simulation of the behavior of dam by employing the accrued earthquake acceleration confirmed the liquefaction has been accrued in the thin sandy layer. The results of finite element simulation showed the depth of the cracks on the crest is about 2 meters and also the upstream slope has slipped about 81 mm to the reservoir of the dam. These results was consistent with the observed values. To overcome the next risks, also to repair the damaged parts of the dam, 3 different methods had been proposed. The curing technics was deploying of the reservoir and removing of the damage part of the dam and as well the thin sandy layer and reconstructed that part of dam, Deploying of reservoir of the dam and adjusting the slope of the upper shoulder to stable condition and at least repairing the developed cracks by injecting cement slurry and tolerate the current condition without imposition any additional costs to the project. The third method has been selected, but for any probable risky condition monitoring of the dam has been advised.
Conclusion: Based on the overall results of the investigations, it was concluded that cracking and sliding of upstream shell is mainly due to the presence of a loose, fine sandy layer under the base of the dam which was liquefied during the earthquakes. In order to overcome the problem, one of the three offered solutions, including modification of cracks by injecting cement slurry, was applied and after roughly 9 years, the provided reports confirmed the adequacy of the applied solution.
vahid Rezaverdinejad; M. Hemmati; H. Ahmadi; A. Shahidi; B. Ababaei
Abstract
In this study, the FAO agro-hydrological model was investigated and evaluated to predict of yield production, soil water and solute balance by winter wheat field data under water and salt stresses. For this purpose, a field experimental was conducted with three salinity levels of irrigation water include: ...
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In this study, the FAO agro-hydrological model was investigated and evaluated to predict of yield production, soil water and solute balance by winter wheat field data under water and salt stresses. For this purpose, a field experimental was conducted with three salinity levels of irrigation water include: S1, S2 and S3 corresponding to 1.4, 4.5 and 9.6 dS/m, respectively, and four irrigation depth levels include: I1, I2, I3 and I4 corresponding to 50, 75, 100 and 125% of crop water requirement, respectively, for two varieties of winter wheat: Roshan and Ghods, with three replications in an experimental farm of Birjand University for 1384-85 period. Based on results, the mean relative error of the model in yield prediction for Roshan and Ghods were obtained 9.2 and 26.1%, respectively. The maximum error of yield prediction in both of the Roshan and Ghods varieties, were obtained for S1I1, S2I1 and S3I1 treatments. The relative error of Roshan yield prediction for S1I1, S2I1 and S3I1 were calculated 20.0, 28.1 and 26.6%, respectively and for Ghods variety were calculated 61, 94.5 and 99.9%, respectively, that indicated a significant over estimate error under higher water stress. The mean relative error of model for all treatments, in prediction of soil water depletion and electrical conductivity of soil saturation extract, were calculated 7.1 and 5.8%, respectively, that indicated proper accuracy of model in prediction of soil water content and soil salinity.
H. Ahmadi; V.R. Verdinejad; M. Hemati
Abstract
The main objective of this research was to find the stable side slope of irrigation canals, considering type of subgrade materials as well as canal depth. For this purpose two methods of limit equilibrium and finite element methods were used for stability analysis. In respect to the geotechnical properties ...
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The main objective of this research was to find the stable side slope of irrigation canals, considering type of subgrade materials as well as canal depth. For this purpose two methods of limit equilibrium and finite element methods were used for stability analysis. In respect to the geotechnical properties of subgrade materials, the Unified Soil Classification System as well as the technical properties of each soil group such as cohesion, angle of internal friction and unit weight was used based on the recommendations given in the literature. To consider operation conditions, three cases namely: steady seepage, rapid drawdown and end of construction of canal were taken in to consideration. The results of investigation showed that stability of side slopes in canals is a function of type of subgrade material in respect to its cohesiveness, operation conditions and depth. In non-cohesive materials, the safety factor is not related to the canal depth and is normally less. Based on the mentioned functions safety factor of side slopes of canals with depth up to 8 meters were calculated. For non-cohesive soils stable slopes were about 1:0.6 and for cohesive soils it was determinate around 1:3.
V. R. Verdinejad; H. Ebrahimiam; H. Ahmadi
Abstract
A transient drainage simulation model, SWAP, was used to evaluate the performance of subsurface drainage system. SWAP model was calibrated by measured daily data including water table depth, drain discharge rate and soil and water drain salinity collected from Behshahr Ran drainage system for 120 days ...
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A transient drainage simulation model, SWAP, was used to evaluate the performance of subsurface drainage system. SWAP model was calibrated by measured daily data including water table depth, drain discharge rate and soil and water drain salinity collected from Behshahr Ran drainage system for 120 days during 1385. Calibration of SWAP model was done by inverse modeling via linking with WinPEST model. In order to calibrate drainage quantity parameters, two objective functions were defined to minimize difference between measured and simulated values of the water table depth and drain discharge rate, simultaneously. To calibrate drainage quality parameters, another objective function was also defined to minimize difference between measured and simulated values of soil salinity. There were good agreements between measured and simulated values of drain discharge rate and water table depth. The absolute error of estimation was 7 and 4 % for water table depth and drain discharge rate, respectively. Measured cumulative drainage was 7.5 % (5.3 mm) greater than its simulated value. The SWAP model could also simulate soil and drainage water salinity with a reasonable accuracy. The results of this study indicated that the performance of the SWAP model could be considerably improved using inverse modeling.
H. Ahmadi; H. Rahimi; A. Soroush
Abstract
Abstract
At present study constant rate of strain (CRS) consolidation under Non-Darcy condition was investigated. In this study a governing conditions of drainage pore water were investigated using proposed equation. The CRS experiments under different rates of strain were conducted on different soil ...
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Abstract
At present study constant rate of strain (CRS) consolidation under Non-Darcy condition was investigated. In this study a governing conditions of drainage pore water were investigated using proposed equation. The CRS experiments under different rates of strain were conducted on different soil samples. Results these experiments and there comparison with proposed equation showed that flow of pore water drainage in the most part or each test was Non-Darcy and changed to Darcy condition in the final one forth of test. According to the results the threshold that Non-Darcy flow changes to Darcy is dependent on variations of relative pore water pressure versus total strain and it can be determined based on variations in inclination of relative pore water pressure-total stress curve.
Keywords: Consolidation, Constant strain, Non-Darcy flow, Pore pressure
V.R. Verdinejad; S. Besharat; H. Abghari; H. Ahmadi
Abstract
Abstract
To optimal use of available water, irrigation scheduling is important to over scarcity of water resources in arid and semi-arid area. In this research to estimate of maximum allowable deficit (or: management allowed depletion) and irrigation scheduling of Fodder Mays based on canopy-air temperature ...
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Abstract
To optimal use of available water, irrigation scheduling is important to over scarcity of water resources in arid and semi-arid area. In this research to estimate of maximum allowable deficit (or: management allowed depletion) and irrigation scheduling of Fodder Mays based on canopy-air temperature difference, a field study was conducted in agricultural faculty of Karaj. The lower limit baseline (potential transpiration) and upper limit baseline (zero transpiration) were estimated by a wet treatment: (keeping soil water content at Field Capacity) and a dry treatment: (complete depletion of available water), respectively. To estimate the maximum allowable deficit, four soil moisture depletion to permanent wilting point treatments were applied in four different growth stages including settlement, vegetating, flowering and ripening of Fodder Mays with three replications. The measured data were wet and dry air temperature, canopy temperature, air relative humidity, root depth, soil water content in root depth and air vapor pressure and based the measured data, equations were extracted for lower and upper limit baselines of Fodder Mays. By comparison of canopy-air temperature difference of four treatments of soil moisture depletion with wet treatment, the maximum allowable deficit for four growth stages were estimated 42.8, 59.2, 58.9 and 67.5 percentages, respectively. The location of upper limit baseline (zero transpiration) was obtained +3.2 °C based on dry treatment. To irrigation scheduling in different growth stages by canopy-air temperature difference, crop water stress index was used and irrigation time was determined by direct method of canopy temperature.
Keywords: Canopy temperature, Evapotranspiration, Fodder Mays, Irrigation scheduling, Karaj