Groundwater In Unconfined Aquifer Research Articles

Numerical modeling of transient water table in shallow unconfined aquifers: A hyperbolic theory and well-balanced finite volume scheme

We present a new methodology capable of modeling transient motion of shallow phreatic surface of groundwater in unconfined aquifers. This methodology is founded on a new and comprehensive theory for water table motion and a corresponding efficient numerical scheme. In the theoretical aspect, we derived a new set of governing equations constituted by a depth-averaged continuity equation and momentum equations based on unsteady Darcy’s law. The derived governing equations are of the hyperbolic type and possess stiff terms in the momentum equations due to the inertia motion in a characteristic time scale that is relatively shorter than the time scale of seepage motion. To effectively solve the derived hyperbolic system with stiff terms, in the numerical aspect, we utilize f-wave propagation algorithm, an explicit finite volume method, that can ensure numerical convergence and well-balancing solutions when momentum is rapidly relaxing to an equilibrium of steady state. Verification is successfully performed by comparing the results with analytic solutions to the classic problem of multidimensional spreading of a groundwater mound. This study demonstrates that the proposed methodology can accurately and satisfactorily simulate the spatiotemporal distribution of shallow water table and its wetting front in unconfined aquifers.

Analysis on unconfined groundwater availability during dry and rainy season using dynamic approach in Ngemplak, Sleman, Yogyakarta, Indonesia

Groundwater is a natural resource with disparity across the different regions throughout time. In comparison to surface water, the groundwater in unconfined aquifers is easily accessible and generally of good quality. Groundwater macro zoning is classified into three, namely water catchment areas, transition areas, and groundwater discharge areas. Based on the macro zoning, previous research has mostly been carried out in catchment areas and discharge areas with a focus on groundwater potential and temporary groundwater conditions. The dynamics of groundwater availability, especially in the water transition zone, has not been studied much, even though the dynamics of groundwater availability in the transition zone plays a vital role for areas in the discharge zone. This study identified the availability of groundwater during rainy and dry seasons in groundwater transition zone. Groundwater availability was assessed through a dynamic discharge approach. The study variables included the hydraulic conductivity of the aquifer, the hydraulic gradient, and the cross-sectional area of the aquifer. Dynamic discharges were analysed during the rainy and dry seasons. The results showed that the availability of groundwater during the rainy season was 4,333,906.1 liters/day and 3,898,850.4 liters/day during the dry season. Based on the calculation of the dynamic discharge (Q), the decrease in the quantity of groundwater is affected by the variable hydraulic gradient (I) and cross-sectional area of the aquifer (A). The numbers of these two variables are smaller during the dry season than the rainy season. The decrease in the quantity of groundwater during the dry season is of course closely related to reduced rainfall which is a source of infiltration and percolation. Reduced rainfall causes the groundwater level to decrease, then technically reduces the groundwater hydraulic gradient (I) and aquifer cross-sectional area variable (A). There was no indication of groundwater scarcity in the study area. This study can serve as a reference related to the application of dynamic discharge theory to assess groundwater availability. Periodic monitoring of groundwater quantity, rainwater harvesting, and intensification of water infiltration wells can be carried out as a recommendation to anticipate problems related to groundwater availability in the study area. This study can serve as a reference related to the application of dynamic discharge theory to assess groundwater availability.

Capillary Impact on Tidal Response of Groundwater in Unconfined Aquifers With Finite Thickness, Anisotropy and Wellbore Storage—An Analytical Model

AbstractThis study develops a novel, two‐dimensional analytical model to study capillary effects on Earth tidal responses of groundwater in unconfined aquifers. It differs from the previous model by accounting for effects of finite aquifer thickness, anisotropy and wellbore storage. We test the present model against the previous model and numerical simulations and apply it to the field data. Several significant results are obtained: (a) At high conductivity ( m/s), the effect of capillary zones dominates tidal responses of groundwater and causes higher amplitude ratio and smaller phase shift compared with that predicted by the unconfined aquifer model without a capillary zone. At low conductivity ( m/s), the effect of capillary zones on the tidal responses diminishes. (b) The impact of the finite thickness on the tidal response is regulated by the anisotropy. If the anisotropic ratio is small (), the impact of thickness may be negligible; at high anisotropic ratio (), however, the amplitude ratio decreases and the phase shift increases, and the response differs substantially from that of the previous model, which is caused by a change in the flow pattern. (c) Wellbore storage have significant impacts on the tidal response at low conductivity ( 10−5 m/s) but negligible impact at higher conductivity. (d) The present model marginally improved the fit by the half‐space model to the field data from a well in SW China, showing that the remaining misfit to the field data by models with capillarity cannot be due to finite aquifer thickness, anisotropy, or wellbore storage.

Groundwater Quality Analysis to Determine Groundwater Facies in Pati-Rembang Groundwater Basin

Pati-Rembang Groundwater Basin is located in Pati Regency, Rembang Regency, and Jepara Regency. Industrial growth and groundwater utilisation increase every year in line with increasing population. Hence, it is necessary to evaluate the quality of groundwater both in unconfined aquifer and confined aquifer as drinking water and irrigation as well as to define groundwater facies as the goals of the research. The methods of groundwater quality evaluation are hydrogeological mapping to determine the geological surface condition, measuring water table of unconfined aquifer and confined aquifer, conducting a hydrogeochemistry analysis of 50 groundwater samples. The results showed that Pati-Rembang groundwater basin consists of 5 lithology units, i.e. Sandy tuff, Andesite Porfiri Lava, Tuff, Volcanic Andesite, and Alluvial Deposit. Groundwater in the unconfined aquifer flows from the west to the north, to the east, and the south. The confined aquifer flows from the west to the centre, and the north. There are five groundwater facies in the unconfined aquifer while in the confined aquifer consist of three facies. Magnesium bicarbonate dominates both of the unconfined aquifer and confined aquifer. Calculation of water quality index both unconfined aquifer and confined aquifer showed that groundwater is still suitable for drinking water.

High arsenic groundwater in the Guide basin, northwestern China: Distribution and genesis mechanisms

High arsenic (As) groundwater has been found in Pliocene confined aquifers at depths from 100 to 300 m of the Guide basin, but little is known on the main hydrogeochemical processes leading to its elevated concentrations. Ninety-seven water samples and fifty-three sediment samples were collected for chemical and/or isotopic analysis. Concentrations of As in groundwater of confined aquifer range from 9.9 to 377 μg/L (average 109 μg/L), which generally show a sharply increasing trend along with NH4+, HCO3−, CO32− and TOC along the inferred flow path, while NO3−, SO42−/Cl− and redox potential (Eh) have decreasing trends. Results of sequential extraction show that As bound to amorphous and crystalline Fe oxide minerals are the main As forms, accounting for around 50% of total As in sediments. Reductive dissolution of As-bearing Fe(III) oxide minerals under reducing conditions in confined aquifers lead to the mobilization of As in groundwater. In addition, alkaline environment and high concentrations of HCO3− and CO32− may make contributions to As enrichment in groundwater. High As groundwater in confined aquifer continuously flows out on the ground surface through tens of artesian wells, which may potentially contaminate low As groundwater in unconfined aquifer. Thus, further investigation is needed to evaluate long-term variations of water chemistry of low As groundwater and assess vulnerability of unconfined aquifer to As contamination.

Spatial Correlation Analysis of Land Subsidence and The Water Table Changes in Unconfined Aquifers Using Sentinel 1-SAR Image and Geographic Information Systems (Case Study: Semarang City – Indonesia)

Groundwater has a very important role both in terms of environmental, social and economic. The consumption of groundwater continuously can affect the physical condition of the environment such as land subsidence, especially in Semarang City. The spatial correlation of land subsidence and water table changes was analyzed in this study using remote sensing and geographic information systems. PS-InSAR method is used to process Sentinel-1 SAR image satellite to get the result of land subsidence during in 2014-2017. The annual average of vertical land subsidence in Semarang City, with the range 0 ± 3.4 cm to 4.5 ± 3.4. The spatial relation between the land subsidence and the water table decreased is obtained using the rules of the spatial correlation matrix. The study area was dominated by a very high correlation with the percentage (47.58%), which located in several areas in Genuk District, Tembalang District, Pedurungan District, Tugu District and Mijen District. The potential of groundwater in unconfined aquifers in Semarang City is nihil potential and low potential of groundwater quality. The very high correlation between land subsidence and water table decreased, which located in the low potential of groundwater in unconfined aquifer mostly located in Tembalang District.

Pumping from unconfined aquifers of limited saturated thickness with reference to wellpoints and horizontal wells

Groundwater in unconfined aquifers of limited saturated thickness can be a valuable resource but frequently it is not developed because conventional boreholes are unsuitable. However, successful exploitation of shallow unconfined aquifers has been achieved using either a line of wellpoints or horizontal wells extending for more than 100 m. The flow processes by which wellpoints and horizontal wells collect water from unconfined aquifers are explored by developing conceptual and computational models. Several representative examples are considered and it is found that similar discharges occur if the wellpoints are closely spaced. The sensitivity of the yield to physical dimensions of the wells and aquifers is explored; the impact of alternative aquifer parameters is also examined. Results from these computational models are used to identify the causes of air entry into wellpoint systems; the prevention of air entry into horizontal wells is also considered. This evaluation demonstrates that wellpoint systems and horizontal wells can efficiently abstract water from unconfined aquifers of limited saturated thickness provided that precautions are taken to prevent air entry.

Hydrogeochemistry of volcanic hydrogeology based on cluster analysis of Mount Ciremai, West Java, Indonesia

Summary Hydrogeochemical analysis has been conducted on 119 spring locations to portray volcanic hydrogeological system of Mount Ciremai, West Java, Indonesia. Cluster analysis on 14 parameters has extracted three clusters. Cluster 1 (112 springs) is distinguished by normal temperatures, low TDS, EC, and high bicarbonate concentrations. Cluster 2 (five springs) has moderately high temperature, TDS, EC, and high concentration of chloride. Cluster 3 (two springs) exhibits high temperature, anomalous high TDS, EC, and chloride concentration. Three hydrogeological systems have been pictured based on the 3 clusters consecutively. The 1st system is developed in shallow unconfined aquifer, with domination of high bicarbonate (4.2 me/L) meteoric water. The 2nd system is predominated with mixing processes, between groundwater in unconfined aquifer and hot groundwater from deeper aquifers. The 3rd system is primarily dominated by groundwater flow from deep formation. The hot – deep seated groundwater flow also carries mud particles. It has anomalous high TDS (>1000 mg/L), EC (515 μS/cm), and chloride (99 me/L) from interaction between groundwater with clay formations, interpreted as Kaliwangu Formation.

Groundwater and stream water interactions in Widden Brook, Upper Hunter Valley, N.S.W.

INTRODUCTION Stream and groundwater connectivity plays a vital role in the health of riverine ecosystems, which currently face stresses from current unsustainable land management practices such as overgrazing, groundwater extraction, and sand mining (Hancock 2002). Extended drought conditions related to El Nino episodes and higher evaporation rates have significantly altered the hydrology of catchments in south-east Australia. The key benefit of restoring hydrological connectivity of stream flows with shallow groundwater in unconfined aquifers is increased groundwater recharge, leading to increased stream flows in dry seasons and enhanced ecological function of the hyporheic zone (Boulton 2000).