فهرست مطالب سیدسجاد مهدی زاده

Excessive exploitation of groundwater in Damghan plain has caused many problems such as land subsidence in the study area, along with the reduction of the groundwater level and the loss of a part of the aquifer and the reduction of the specific yield of aquifer. Therefore, in order to control the withdrawal from the aquifer and as a result to reduce the drop in the groundwater level in that plain, it was investigated. For this purpose, in this research, the mathematical modeling of Damghan Plain was done for the optimal management of exploitation and providing the optimal cultivation pattern in order to save water consumption with the focus on controlling the groundwater level and limiting land subsidence.

In this research, Damghan plain aquifer was first simulated using MODFLOW mathematical model. Then, taking into account different scenarios of aquifer exploitation, using the NSGAII genetic algorithm, optimization of multi-objective exploitation of water resources and optimal management of water supply and demand in the agricultural sector was done. The results of the model were evaluated based on statistical error parameters to predict the ground water level.

The results of this research showed that the MODFLOW numerical model was able to simulate the groundwater level of the studied plain well in steady and unsteady conditions in the calibration and validation stages. Also, the results of the simulation-optimization algorithm showed that by changing the cultivation pattern and also by changing the type of irrigation system from traditional to modern irrigation and as a result of increasing the irrigation efficiency (90 percent), the average drop of the groundwater level of the plain can be reduced. It reduced the groundwater level of the study area from 0.49 m in existing conditions to 0.07 m in optimal conditions. This will compensate the deficit of the aquifer from 31.90 to 5.1 million cubic meters per year.

Using management strategies such as changing the cultivation pattern, increasing irrigation efficiency, and also by controlling surface water and injecting it into groundwater, the process of reducing the groundwater level in the studied plain can be completely controlled and provided 100% of the water needs of the plain.

Identification of homologous hydrological groups is one of the fundamental topics in hydrology in both applied and research dimensions. One of the common methods to achieve homogeneous hydrological zones for estimating flood zones is the use of clustering methods. In this study, the using, evaluation and comparison of statistical methods and methods based on artificial intelligence for clustering Karkheh catchment have been investigated. SOM, K-meansand hierarchical clustering were used for the study area. In the following, the study of hydrological homogeneity of the obtained areas was evaluated using the linear torque method and the heterogeneity adjustment was evaluated using the methods proposed by Husking and Wallis. The results show that the study area can be converted into two clusters. The values ​​of homogeneity statistics for the first and second clusters were calculated to be 0.33 and 0.17, respectively, which indicates the homogeneity of each region. Due to the short statistical period in some stations, statistical shortcomings and the reliability of the results of regional frequency analysis, this method should be used in estimating floods in other catchments.

Watershed management strategies can be considered in mitigating water pollution issues. In this study, using SWAT as a semi-distributive hydrological model, runoff and nitrate amounts have been investigated according to management scenarios in Hashtgerd plain, Iran. After runoff simulation, three hydrometric stations were used for calibration in the period (1990-2013) and validation in the period (2014-2018). The results of R2 and NS statistical indices (greater than 0.6) show that the simulation results in this catchment have been done with good accuracy. The results also indicate that applying the first scenario (changing the crop pattern) and the second scenario (increasing irrigation efficiency) reduced the water usage in the agricultural sector from 85.3 MCM to 59.8 MCM in the present condition, which also will improve the fertilizing efficiency. It was demonstrated that changing the crop pattern can help reduce the deep percolation. On the other hand, using drip irrigation, the leaching requirement, and irrigation water loss will be reduced. Comparing the amounts of observed nitrate in the hydrometric station in the base period with the simulation results in the first scenario revealed that, by applying the first scenario, the amount of nitrate simulated has relatively a decreasing trend except in winter and early spring. The results of the second scenario show that by changing the irrigation method, the amount of nitrate leaching has decreased significantly compared to the base period. In general, the second scenario is more effective in reducing nitrate leaching and is recommended.

In recent years, iron nanoparticles have been successfully used to remove water pollutants. Fecal coliform is one of the parameters that reduces water quality and its removal is essential. The aim of the present study is using nanoscale zerovalent iron particles to enhance the usual sand filters in removal of fecal coliform of groundwater in Ilam city.

Water samples were collected from several active wells in Ilam city. The parameters of hardness, probable and fecal coliforms were measured. Afterward, samples of fecal coliform contaminated-water were passed through filters with different values of zerovalent iron nanoparticles (0.5-3 gr) and parameters were remeasured.

The results of this study showed that by increase of iron nanoparticles, the removal efficiency of coliform was increased, so that, in most samples, by increasing the iron nanoparticles to 3 gr, the coliform content reached to zero. The degree of hardness was initially reduced when the amount of iron nanoparticles increased, but over time, the reduction trend was halted.

In general, the results indicate that not only zero-valent iron nanoparticles are capable enough to remove microbial contamination from water, but also they can be used to completely purify the groundwater and also to reduce other contaminants including chemical pollutants to a permissible threshold, especially in small regions where complex water treatment plants may not be available.

Investigation on available freshwater below the sea in offshore aquifers (i.e. part of the coastal aquifer is stretched beneath the sea) can provide a resource for ecological demand in the future. In this study, to understand the response of intruded seawater to freshwater recharge that is leaked from the riverbed, various scenarios with different aquitard length and permeability or river conductance have been introduced. SEAWAT dispersive code is used for seawater intrusion simulation and saltwater wedge toe position, mixing zone thickness and saltwater volume were estimated. The results showed that the river conductance influences the volume of freshwater in offshore aquifers significantly. Thereby, small conductance value (i.e. 0.0025 m2/d in this study) leads to a negligible impact on saltwater characteristics but as this coefficient grows up to a specific amount, more freshwater is released from the riverbed which could significantly affect saltwater characteristics (60% reduction in brackish water volume). Nonetheless, extra-large conductance (i.e. 375 m2/d in this study) cannot sharply affect seawater recession due to high-velocity magnitude of recharged freshwater and limited contact time with the saltwater wedge. Hydraulic conductivity and length of aquitard also affect the results; so that the extension of aquitard length to the dry land boundary will cause reduction in the recharged freshwater and consequently reduce the intruded saltwater especially in the vicinity of aquifer bed.

Sea level rise and groundwater extrapolation lead to freshwater head changes at boundaries of coastal aquifers and causes further intrusion of seawater into aquifers. In the present study, the behavior of unconfined coastal aquifer to instantaneous sea level rise and freshwater head decline is investigated by physical and mathematical dispersive modellings. Three laboratory models have been conducted in a sand tank and salt wedge shape has been photographed over time. Salt wedge toe position, area of transition zone and volume of intruded seawater are measured for this purpose. The numerical results are in good agreement with experimental observations. The outputs derived by both modellings indicate that the instantaneous rise of head in sea boundary or significant decline of freshwater head in landside deforms the wedge shape of saline water, so that the seawater encroachment velocity at its tip will be faster than other regions. Moreover, establishment of an inverse hydraulic gradient (hydraulic gradient from sea to land) causes significant seawater delivery from sea into the aquifer. As a result, the salt wedge can even be stretched up to land boundary. Results of dispersive simulations demonstrate that when the velocity of saline water rises inside the aquifer, the advection role will be highlighted rather than dispersion. However, the longitudinal and transverse dispersivity will also increase and that consequently will widen the transition zone. Nevertheless, the increase rate of saline water volume has been achieved much higher than the growth rate of toe position and transition zone area.