جستجوی مقالات مرتبط با کلیدواژه « unconfined aquifer » در نشریات گروه « آب و خاک »

Determination of wells' capture zones are one of the important issues which must be considered in every aquifers. Methods used for depicting this area divides into two simple and complex methods. Through the simple one several mathematical equations utilized and in the complex method, numerical models are applied. In this study, for the first time, the capture zone of the extraction wells in a standard confined aquifer and Birjand unconfined aquifer was determined using Feflow simulation model. After the simulation procedure in the period of 1390-1391 with monthly time step, the groundwater head is obtained, then the capture zone for each well was depicted. In confined aquifer this area individually determined for 3 extraction wells in two periods of 50 and 180 days. The results showed that the extension of the capture zone for all three wells is toward the part of the aquifer with higher groundwater level. Also, the results revealed that, in areas of the aquifer with higher transmissivity coefficient, the zone is more extended and for the areas with lower transmissivity coefficient, its width decreases and becomes narrower. For instance in second well the width of capture zone in the third zone is 302.86 m, however, it is 267.46 m in the second zone. In Birjand aquifer which consists of 190 extraction wells, 5 wells were chosen randomly to depict capture zone for them in five years and thirty years period. The results revealed that the extension of the capture zones were corresponded to the flow direction. Also, extraction rate of wells and hydraulic conductivity coefficient were two effective parameters in the shape of these zones. As the fifth well in Birjand aquifer with the least value of discharge rate had the smallest length of capture zones among all the wells.

Having a pervasive knowledge about the groundwater balance conducts the engineers and managers to have an optimal management about these resources. In the present study, with using meshless local Petrov-Galerkin, one of the meshless methods in the field of fluid dynamic, groundwater balance is computed for a real field aquifer. The independency of this method from meshing the domain, removes the drawbacks and errors come from meshing state and improves the accuracy of results. The case study is Birjand unconfined aquifer located in South Khorasan province, east of Iran. After groundwater flow simulation and model calibration in one year 2011-2012 with monthly time step, the groundwater head is computed for each month and compared with the results of finite difference method (FDM). RMSE, MAE and ME criterion are calculated for both methods. They are 0.757m, 0.573m, -0.08m for MLPG method and 1.197m, 1.434m, 0.159m for FDM, respectively. The higher results of MLPG shows more correspondence of this method to real condition of aquifer. Finally, the input and output volume of water are computed for the aquifer. They are almost 91 and 88 MCM respectively. Therefore, the value of groundwater balance is computed. It was 3 MCM with minus sign which indicated the higher amount of output regarding to inputs.

Darcy's law is valid for laminar flow and its application is not recommended for turbulent flow. The turbulent flow equations are derived based on hydrodynamics principals with introducing turbulence effects. The purpose of this research is to derive the relationship between discharge and hydraulic potential in radial flow in unconfined aquifers under steady state. The basis of the relationship is fractional derivative approach of the velocity flow related to the hydraulic gradient. The previous study data was used for the verification of the derived equation. The profile of the water level was computed and plotted for different porous media with non-Darcy flow in unconfined aquifer for different discharges based on the extracted equation and compared with the results of the Darcy's law. The results showed with increasing the discharge values the highest and lowest increament of water level were 10 and 1.48% related to Darcy flow respectively. These values for increasing of hydraulic conductivity were 19 and 9.8% respectively. Overall, the difference between the Darcy and non Darcy flow in water level estimation increased with increasing discharge and hydraulic conductivity as well as the increase of both parameters, which water level was higher in Darcy flow than non Darcy flow in all water profile profiles.

Water is one of the most fundamentals demands of human society. Water consumption in industry, agriculture and household consumption, and also the lack of this source result in more extraction from groundwater sources. Irregular extraction from aquifers in dry condition of recent decades lead to significant drawdown in this sources. Recharging of the aquifer by injection wells is one of the solution for revival of the aquifers. The main purpose of this study is to investigate the effect of the injection well in recharging of the unconfined aquifer by using meshless local Petrov-Galerkin. The approximation and weight functions are moving least squares and cubic spline functions respectively. The groundwater table in unsteady extraction mode simulated. The achieved results compared with finite difference, finite element and analytical method. Small amount of error of meshless method indicated the suitable accuracy of this method. Then the aquifer simulated in recharge mode. The height of water rise in the aquifer because of injection well, computed. Finally sensitivity analysis carry out on transmission coefficient, specific yield and rate of flow parameters. The height of water has more dependency to transmission coefficient and rate of flow than specific yield.

GMS, is the software that simulate groundwater flow, with using ModFlow based on finite difference method. With comparing the acquired result from GMS and observation data, the existence of error is clear and obvious. One of the methods that decrease simulation error is the usage of filter kalman algorithm. In this study, extended non-linear filter kalman was used in order to improve the simulation results in Birjand unconfined aquifer in southern Khorasan province. The results showed that using this algorithm revealed satisfactory results in prediction of groundwater head. As the mean error (ME), mean absolute error (MAE) and root mean square error (RMSE) are -0.246, 1.125 and 1.341 meter respectively. With influencing extended filter kalman on results these errors decrease to -0.007, 0.015 and 0.019 meter. Also with investigation the results of extended non-linear filter kalman and non-linear filter kalman, it was found extended non-linear filter kalman is better choice for reducing simulation errors.

Tide induced head fluctuation has been considered by many researchers in coastal areas. In this paper, a numerical solution has been developed for an inhomogeneous multi-layered aquifer. This aquifer system comprises an unconfined aquifer on the top, a semi-confined aquifer at the bottom, and an aquitard between them. This coastal aquifer is bounded by coast in longitudinal direction; the coastal boundaries are parallel to each other. The results showed that the amplitude of unconfined aquifer head increases with increase of leakage, however, the amplitude of head fluctuation decreases in the semi-confined aquifer. In addition, the results of analytical solution, the head fluctuation in unconfined aquifer decreases with increase of dimensionless storage coefficient, however, it is almost constant in confined aquifer. Also, increase of dimensionless transmissivity increases the groundwater head fluctuation in both aquifers. Temporal head fluctuation illustrated that time lag has not significant changes, and is greater for semi-confined aquifer with respected to confined aquifer. Comparison between numerical and analytical solutions showed that there is little difference between.