مجله هیدروژیولوژی
سال دوم شماره 1 (پاییز 1396)

Semnan plain with arid and semi-arid climate is situated in southern flank of Alborz range and north of great desert of Central Iran. In this study the result of analyses of major ions in 35 deep wells and qanats and oxygen-18 and deuterium stable isotopes in 5 wells and one sample of the river water have been used to access the chemical characteristics of groundwater. Hierarchical cluster analysis (HCA) has been used for classifying the water samples. The results show that the samples can be grouped into three main categories: (1) waters with highest bicarbonate content and lowest TDS, (2) waters with highest sulfate content and (3) chloride waters with maximum salt content. Checking the spatial distribution of the samples shows that the samples of each group are situated in a specific area; indicating similar affecting processes on water quality in each group. Mineral saturation index calculated with the PHREEQC software showed that the samples are super-saturated with respect to the carbonate mineral and under-saturated to saturated with respect to the gypsum and anhydrite and under-saturated with respect to the halite. Based on isotopic analysis, correlation coefficient and ion ratios, chloro-alkaline index and Gibbs plot of the chemical composition of the groundwater in Semnan plain are controlled by the intrusion of Abgram salt water and salt dissolution, groundwater residence time, silicate weathering, cation exchange, evaporation and agricultural return flow.

Water importance is obvious for each country especially for those which are located in arid and semi-arid regions. Water Shortage causes significant pollution and other continuous problems. Recently, groundwater as a main resource of fresh water, has been withdrawn more than the authorized limitation; Damghan Plain is located in south of Alborz mountains, and these days it is faced with serious water table drawdown. This research has been carried out to estimate appropriate well field in order to preserve water table from drawdown. By using Fuzzy Logic in three regions with different drawdowns of water table three models have been made. In each model inputs are hydraulic conductivity (K) and water table drawdown (D), and output is well field (R). The results show that in the first model with low drawdown of water table (0.5 m per year) the well field is about 285 m, in the second model with moderate drawdown of water table (3.5 m per year) the well field is about 371 m and in the third model with drawdown more than 3.5 m per year the well field is obtained about 457 m. It is implied that these well fields may prevent water table from extra drawdown.

Groundwater resources in Bushehr province aquifers are strongly affected by the factors of agricultural wastewater, closeness to sea, high salinity, and lying over oil and gas fields. Therefore, it seems to be important to evaluate groundwater quality in the study area. In this study, 360 water samples from different parts of the province were collected from wells, during 1387-1390. Cations and anions as well as chemical parameters were analyzed. Water Quality Index (WQI) and other effective chemical parameters were calculated. Ground water quality index (GWQI) map in the study area reveals that groundwater quality order is as Jam>Dashtestan>Dashti. Quality of water in Jam meets the highest quality among all and Kangan city has non-suitable drinking water. In general, groundwater quality in Bushehr province do not meet the water quality standards for some quality parameters and therefore it needs to be managed in Bushehr province.

By studying changes in the water levels of 359observation wells before and after the construction of 251 water reservoirs in Gorganroud watershed of Golestan province, water reservoirs effects were evaluated in improving the groundwater level. In this study some water reservoirs were selected that there were observation wells around them. All wells in which the water table levels were lower than the water levels of water reservoirs were evaluated. Among these, 31 Water reservoirs clearly showed there effects on 33 observation wells. Therefore, 12.4 percent of Water reservoirs have a positive effect on the level of groundwater. With providing a distribution map of all water reservoirs and observation wells and adapt them to each other and having observational data before and after the water reservoirs construction the effect of water reservoirs on the aquifer improvement were evaluated. In this study, parameters for evaluating effect of water reservoirs on the improving of aquifer included time of influencing the water level on observation wells levels, annual water rise and annual compensation of the water level. In this study the results show that water reservoirs had a positive effect on the groundwater level at the distance of 3.8 km, increasing the maximum groundwater level by 114 cm. The amount is of the annual compensation of the water level was 184 cm. Based on a rating scale the evaluation criteria were graded and so the performance of the water reservoirs at levels low (31.2%), average(20.4%), good(17.2%), good (21.5%) and excellent (9.7%) was evaluated.

In this study, to investigate the influence of clay blanket on reducing seepage a computer model has been developed in which general equation of fluid flow through soil has been solved numerically by finite elements method. At the end, a complete and comprehensive relation for the effect of clay blanket on leakage from foundation of dams has been presented. To do this, all effective parameters have been modeled by the SEEP/W 2012 software in 350 models. One of these important parameters is the horizontal to vertical permeability ratio in foundation that has not been applied in any other research so far. This ratio should have been calculated for giving a precise relation applicable in construction works. Other parameters include thickness, length and permeability ratio of the clay cover, foundation thickness and width of the core. In the following, the results of modeling by the SPSS 23 software have been analyzed and finally, the results of the proposed relation have been compared to the results of the software and relation of the American Army Civil Engineers. The result of this comparison testifies the completeness of the proposed relation and trivial difference with the results of the modelings. Based on the analysis, the effective length for the clay blanket four times the height of water behind the dam is proposed. Also, when thickness of clay blanket is low, the impact of different levels of permeability coefficient is almost identical in reducing leakage and permeability reduction of clay blanket is effective when its thickness increases.

Seepage and water flow is one of the most important factors in design of earth and rockfill dams. The seepage through the foundation of earth dams can be controlled using the cut off walls. The hydraulic head reduces in the connection zone of the cut off wall and core of the dam that results in high hydraulic gradients. Therefore, this study investigates the efficiency of cutoff wall on some design parameters in Sabalan rockfill dam. For this purpose, different hypothetical positions of cut off wall with various depth and permeability were used and analyzed in the foundation of dam. The results showed that the maximum hydraulic gradient in foundation of Sabalan dam, occurs at the cutoff wall. Change in cutoff wall position for obtaining minimum hydraulic gradient showed that the optimal position of cut off wall for reducing the hydraulic gradient is in the toe of the core and the optimal position of cut off wall for reducing the seepage is in the heel of the core. By reducing the permeability and increasing the depth of the cutoff wall, the hydraulic gradient is increased and the seepage is decreased. Comparison of the effect of permeability and depth of the cutoff wall on seepage with corresponding values in Karkheh embankment dam, showed proper agreement between them.

Knowledge of hydraulic parameters is certainly important for groundwater resources management and development. Geoelectrical method is one of the newest methods with acceptable accuracy and low cost. It can play an important role in determining these parameters. In the present study, 100 vertical electrical sounding (VES) were carried out using the Schlumberger electrode configuration to determine the status of Chahardoli plain, located in Kurdistan province. Pumping test data prepared by Kurdistan Regional Water Authority, were analyzed to determine hydraulic parameters. The number of 28 VES points were chosen based on their locations to determine aquifer hydraulic parameters. After interpreting the VES points using IPI2Win software, thickness and electrical resistivity of the subsurface layers, as well as transverse resistance and modified transverse resistance were determined. Hydraulic parameters are estimated using geoelectrical method on the basis of calculations given by Sri Niwas and Singhal. The present studies show that the values of Kσ^' remain fairly constant in 3 independent lithostratigraphic units within the study area. As Singhal and Sri Niwas noted, it is possible to estimate hydraulic coefficients according to the zoning of the region. The results of geo-electric method were compared with the results of Step-Drawdown test. The t-test results indicate that Transmissivity values in both geo-electrical method and Step-Drawdown test have no significant difference. Correlation of the Transmissivity and modified transverse resistance revealed a direct relationship (with a correlation coefficient above 8.5) which indicates an acceptable accuracy of the experiments in the study area and it also confirms previous studies of Singhal and Sri Nivas.

To achieve an appropriate management of groundwater resources, the accurate estimation of aquifer parameters is essential. In this study, several artificial intelligence models including, Artificial Neural Network (ANN), Generalized Regression Neural Network (GRNN) and Radial Basis Function (RBF) neural network have been developed to estimate the hydraulic parameters of a confined aquifer. One of the many reasons in using the artificial intelligence models to estimate the aquifer parameters, is their high flexibility, especially in non-linear problems. In order to implement these models, after gathering the pumping test data and reducing the dimensions of the data using the Principle Component Analysis (PCA), the artificial neural networks are trained and tested. Under the condition that the well function’s error as the output of the artificial intelligence models, lies within an acceptable limit, then the values of aquifer parameters can be determined. The models are applied to a pumping test data in a confined aquifer and the results are compared with those of the graphical Theis curve method. Several statistical errors considering the results of the proposed artificial intelligence models and the graphical Theis curve method are compared and the performance of the models is examined. As an example, the Mean Absolute Relative Error (MARE) in estimating aquifer parameters for ANN model and graphical Theis curve method are 0.5564 and 1.1320 percent, respectively. To this regard, the GRNN is more precise and has much less computational time than the others and may be selected as a superior model in the estimation of confined aquifer parameters.