Groundwater Mound Research Articles

Simulation of groundwater mounding at a West Australian mine site

Few studies exist that investigate the potential impact of groundwater mounding due to mining near an environmentally sensitive area in a real world scenario. This paper presents a case study in which the development and extent of groundwater mounding due to mining near the Shark Bay World Heritage Property (SBWHP) in Western Australia (WA) has been simulated. A numerical model was developed that enabled a detailed simulation of groundwater level response to the discharge of a water saturated sand slurry during mining at the project site near Coburn in WA. The simulations showed that after a mining period of around two and a half years, a groundwater mound of around 2.5 m would develop along the margins of the open pit at the SBWHP boundary. 500 m further into the SBWHP, the groundwater mound is predicted to be around 1 m high. A depth to water analysis showed that the groundwater may come within 4 m of the surface in the area of a sand dune swale that traverses from SW to NE near the SBWHP boundary. The results of these analyses provide a perspective of mine-related impacts in a unique environment. The results have been included in an environmental impact assessment (EIA) and used for mine water balance predictions.

Geotechnical Parameters Impact on Artificial Ground Water Recharging Technique for Urban Centers

Water scarcity is a serious problem throughout the world for both urban & rural community. Urban centers in India are facing an ironical situation of water scarcity today. This paper includes an Analytical solution, Numerical modeling, Empirical approaches, In-situ test results to predict recharge (rate) mound of the ground-water and capacity of recharge well which is essential for the proper management of suitable artificial ground-water recharge systems to maintain water balance and stop salt water intrusion. Authors have derived analytical equation for predicting growth as well as decline of the ground-water mound depending on the intensity of recharge rate qr with different value of permeability k, depth of pervious strata H and diameter of well d, also studying the effects of variation in the geotechnical parameters on water-table fluctuations. In this paper to study the impact of numerical modeling using quadratic equation for unconfined aquifer base on rainfall intensity P and a change in saturated thickness H with variation in piezometric level. Empirical approaches are for evaluation of correct value of k of an undercharged unconfined aquifer with drawdown s0, influence zone L, recharge rate qr. In-situ test results give actual correlation between value of recharging rate of well and permeability on field. Authors have verified recharging rate of installed well from all approaches. A result obtained from the various field case studies gives the validation of the derived equation. Scientific quality measures of aquifer water are also recorded.

Fluids’ dynamics in transient air sparging of a heterogeneous unconfined aquifer

Water table dynamics, dissolved oxygen (DO) content, electrical resistivity (ER) in monitoring wells and air pressure in the vadose zone are monitored in air sparging (AS) accompanied by soil vapor extraction (SVE) at a hydrocarbon-contaminated groundwater site in Oman, where a diesel spillover affected a heterogeneous unconfined aquifer. The formation of a groundwater mound at the early stage of air injection and potential lateral migration of contaminants from the mound apex called for an additional hydrodynamic barrier constructed as a pair of pump-and-treat (P&T) wells whose recirculation zone encompassed the AS and SVE wells. In all monitored piezometers the phreatic surface showed a rapid and distinct peak, which is attributed to the time of air breakthrough from the injection point to the vadose zone and a relatively mild recession limb interpreted as a decay of the mound. Tracer tests showed a layer of a relatively low hydraulic conductivity at an intermediate depth of the screened interval of the wells. Increased levels of DO and borehole air pressure that have been observed (as far as 50 m away) are likely mitigated by SVE and P&T. Radius of influence can be indirectly inferred from ER and DO changes in the AS operation zone. Salt tracer tests have shown that groundwater velocity within the AS zone decreases with the increase of air injection rate.

Hydrological impacts of rainwater harvesting (RWH) in a case study catchment: The Arvari River, Rajasthan, India. Part 1: Field-scale impacts

Rainwater harvesting (RWH), the small-scale collection and storage of runoff to augment groundwater stores, has been seen as a solution to the deepening groundwater crisis in India. However, hydrological impacts of RWH in India are not well understood, particularly at the larger catchment-scale. A key element to grasping RWH impact involves understanding the generated recharge variability in time and space, which is the result of variability in rainfall-runoff and efficiency of RWH structures. Yet there are very few reported empirical studies of the impact of RWH. Catchment-scale impacts are best studied using a water balance model, which would require a basic level of field data and understanding of the variability. This study reports the results of a 2-year field study in the 476 km2 semi-arid Arvari River catchment, where over 366 RWH structures have been built since 1985. Difficulties associated with working in semi-arid regions include data scarcity. Potential recharge estimates from seven RWH storages, across three different types and in six landscape positions, were calculated using the water balance method. These estimates were compared with recharge estimates from monitored water levels in 29 dug wells using the water table fluctuation method. The average daily potential recharge from RWH structures varied between 12 and 52 mm/day, while estimated actual recharge reaching the groundwater ranged from 3 to 7 mm/day. The large difference between recharge estimates could be explained through soil storage, local groundwater mounding beneath structures and a large lateral transmissivity in the aquifer. Overall, approximately 7% of rainfall is recharged by RWH in the catchment, which was similar in the comparatively wet and dry years of the field analysis. There were key differences between RWH structures, due to engineering design and location. These results indicate that recharge from RWH affects the local groundwater table, but also has potential to move laterally and impact surrounding areas. However, the greatest weakness in such analysis is the lack of information available on aquifer characteristics, in addition to geology and soil type.

Groundwater recharge in arid areas induced by tropical cyclones: lessons learned from Gonu 2007 in Sultanate of Oman

Younger groundwater found in some Omani aquifers is a result of recent recharge from cyclonic and storm events [Weyhenmeyer et al. (Science 287:842–845, 2000); Young et al. (J Appl Geophys 57:43–61, 2004)]. The analysis of the meteorological data in Oman indicates an anomalous rainfall on a decadal interval whereas cyclones frequency is expected to increase due to global climatic changes. The cyclone Gonu has severely struck the eastern Omani coasts in 2007 resulting in devastating floods. Huge volume of water (3,672 mm3) spread over the coastal plain calling for an assessment of potential groundwater recharge subsequent to this event. The present study evaluates groundwater recharge with respect to Gonu 2007 to assess the potential of recharge induced by such cyclones in the arid zones. The hydrographs of several piezometers sited along the coastal plain in Muscat Province have been studied and variation in water table rise has been analyzed. Significant water table rise is indicated for areas with geological and structural settings favoring rapid infiltration of water yielding considerable groundwater mound, whereas piezometers located in less favorable zones show minimum rise of water table. However, soon after the floods the aquifer hydrodynamics has readjusted to attain equilibrium and the groundwater mound dissipated. The cumulative rise of the water table on an areal extent does not exceed a few centimeters indicating lesser volume of recharge. Comparatively, recharge from frequent precipitation along favorable zones produces more significant recharge compared with cyclonic events where surface water residence time is shorter to allow for efficient infiltration.

Use of geochemical, isotopic, and age tracer data to develop models of groundwater flow for the purpose of water management, northern High Plains aquifer, USA

Abstract A prolonged drought in the High Plains of Nebraska prompted the use of groundwater for cooling at the largest coal-fired power plant in the State. Prior to the drought, groundwater was used primarily for irrigation and the power plant relied exclusively on surface water stored in a nearby reservoir for cooling. Seepage from the reservoir system during the past ∼75 a has resulted in the buildup of a large mound of water in the underlying unconfined aquifer. A well field was installed during the drought for the purpose of tapping the groundwater mound as a supplemental source of water for cooling. Concentrations of dissolved Cl − and SO 4 2 - indicate 65–100% of shallow groundwater and 0–100% of deep groundwater (saturated thickness ∼115 m) in the immediate vicinity of the reservoir was from seepage out of the reservoir system. Hydrogen and O isotopic data indicate most surface-water seepage occurred in the late spring and early summer when reservoir stage was at its highest level. Tritium/ 3 He apparent groundwater ages imply horizontal flow velocities from the reservoir were on the order of 60–600 m/a. These diverse data provided information regarding the spatial distribution, timing, and rate of seepage from the reservoir that could not have been obtained from the available geologic, hydraulic head, and conductivity data. In particular, mixing fractions of surface water and regional groundwater in the aquifer could not have been determined using hydraulic information. Mixing fractions were of special interest in this study because of the management objective to maximize the capture of surface-water seepage in the cooling water wells. Groundwater-flow models developed as well-field management tools were calibrated using inverse modeling techniques and observations of groundwater age, surface-water flow, reservoir stage, and groundwater levels. The age data only accounted for 6 of the 2574 field observations used to calibrate the groundwater-flow models, yet they were among the most influential for refining estimates of hydraulic conductivity, recharge, and seepage from the reservoir. Results from this study demonstrate the benefits of using geochemical, isotopic, and age tracer data to develop conceptual and numerical models of groundwater flow for the purpose of water management.

東京市西郊保谷村上宿附近の地下水堆と聚落、淺い窪地 (武藏野臺地の地下水-第五報)

東京市西郊保谷村上宿附近の地下水堆と聚落、淺い窪地 (武藏野臺地の地下水-第五報)

Nonlinear aspects of phreatic water filtration

Horizontal gravity filtration of groundwater in soil is considered. Under Boussinesq approximation, the problem is reduced to a one-dimensional nonlinear parabolic equation in phreatic water level. The problem of linearizing the original equation is discussed. The comparison of gravity-filtration problem solutions in the nonlinear and linearized formulations shows considerable discrepancies to exist between the solutions, especially, for boundary problems with mixed boundary conditions, when the value of the function is not fixed on the right boundary. An analytical solution is obtained for steady-state flow from a water body into the soil with subsequent leakage into underlying beds. Two regimes are shown to exist: one with an infinite exponential tail, and another in the form of a finite groundwater mound. A new approach is proposed to the linearization problem—quasilinearization with the use of the Burgers equation.

Simulation of Groundwater Mound Resulting from Proposed Artificial Recharge of Treated Sewage Effluent Case study – Gaza waste water treatment plant, Palestine

Mounding of the groundwater table beneath recharge sources is of concern as the raised water table approaches closely to near-surface facilities or features. The shape and height of the mound depend on several factors including the recharge rate, hydraulic conductivity and thickness of the aquifer. The objective of this paper is to evaluate the suitability of the study area for a rapid infiltration system of treated wastewater effluent without causing excessive mounding of the water table. A comparison was made between two methods used to estimate ground-water mounding: an analytical approach and a numerical approach. Both approaches incorporate each of the saturated and the unsaturated zones. Results predicted that after 1400 days of groundwater level simulation, the maximum rise of the mound was 18 m in the center of the infiltration pond, and it was almost 17 m at the edges of the pond. As the natural average groundwater level was about 35 m deep in the area of the study, the groundwater mounding caused no problem on the groundwater level. Thus, the planned infiltration was feasible.

Modeling Surface Water‐Groundwater Interaction with MODFLOW: Some Considerations

The accuracy with which MODFLOW simulates surface water-groundwater interaction is examined for connected and disconnected losing streams. We compare the effect of different vertical and horizontal discretization within MODFLOW and also compare MODFLOW simulations with those produced by HydroGeoSphere. HydroGeoSphere is able to simulate both saturated and unsaturated flow, as well as surface water, groundwater and the full coupling between them in a physical way, and so is used as a reference code to quantify the influence of some of the simplifying assumptions of MODFLOW. In particular, we show that (1) the inability to simulate negative pressures beneath disconnected streams in MODFLOW results in an underestimation of the infiltration flux; (2) a river in MODFLOW is either fully connected or fully disconnected, while in reality transitional stages between the two flow regimes exist; (3) limitations in the horizontal discretization of the river can cause a mismatch between river width and cell width, resulting in an error in the water table position under the river; and (4) because coarse vertical discretization of the aquifer is often used to avoid the drying out of cells, this may result in an error in simulating the height of the groundwater mound. Conditions under which these errors are significant are investigated.

Formation and Control of Self-Sealing High Permeability Groundwater Mounds in Impermeable Sediment: Implications for SUDS and Sustainable Pressure Mound Management

A groundwater mound (or pressure mound) is defined as a volume of fluid dominated by viscous flow contained within a sediment volume where the dominant fluid flow is by Knudsen Diffusion. High permeability self-sealing groundwater mounds can be created as part of a sustainable urban drainage scheme (SUDS) using infiltration devices. This study considers how they form, and models their expansion and growth as a function of infiltration device recharge. The mounds grow through lateral macropore propagation within a Dupuit envelope. Excess pressure relief is through propagating vertical surge shafts. These surge shafts can, when they intersect the ground surface result, in high volume overland flow. The study considers that the creation of self-sealing groundwater mounds in matrix supported (clayey) sediments (intrinsic permeability = 10–8 to 10–30 m3 m–2 s–1 Pa–1) is a low cost, sustainable method which can be used to dispose of large volumes of storm runoff (

Soakage testing: modelling the effect of antecedent hydrology

Current design methods for sustainable drainage system infiltration devices such as soakaways, permeable pavements and infiltration basins require knowledge of the empirical soil infiltration coefficient, which is determined using a soakage test procedure. However, the control that seasonal antecedent hydrological conditions, specifically unsaturated zone soil moisture and water table position, have on the infiltration coefficient is uncertain. This paper uses exploratory numerical modelling to investigate this uncertainty. The results show that antecedent water table position has a significant effect on the infiltration coefficient, while for a properly conducted test the seasonal antecedent soil moisture is less important. To avoid overestimating the infiltration coefficient, soakage testing should ideally be performed under the most onerous hydrological conditions and three successive drain downs must be used. Model outputs such as those presented can be used to reduce the design infiltration coefficient to account for tests made during periods of lower groundwater level and higher design water table positions. Additionally, the current infiltration coefficient calculation is shown to be biased towards the initial, more rapid, infiltration rate. Therefore, an alternative full-depth infiltration coefficient calculation is proposed. Finally, a potential detrimental feedback is hypothesised between infiltration device performance and groundwater mounding. Significant design implications are discussed.

A particular analytical solution of a steady-state flow of a groundwater mound

Semi-inverse method with successive conformal mapping are used to obtain a particular solution of the problem of steady-state flow of a groundwater mound. Groundwater flow parameters are evaluated, and examples of calculations are given. The obtained solutions coincide with available exact solutions in particular cases.

Spatial and temporal aspects of the transition from connection to disconnection between rivers, lakes and groundwater

A changing groundwater table can affect the flow regime between surface water and groundwater. Quantitative approaches are required to understand how such changes influence the flow regime. While in a fully connected regime changes in the groundwater table are related linearly to changes of the infiltration rate, in a disconnected regime the infiltration rate is essentially independent of such changes. However, transitional regimes between connected and disconnected regimes also exist and we identify different transitional pathways. We illustrate how hydrological parameters determine the pathway of transition and show that spatial variations of the infiltration flux through a surface water body strongly depends on these different pathways of transition. Moreover, the spatial distribution of seepage through a surface water body is shown to depend on the state of connection. We also show that the transition from a connected to disconnected flow regime may require a significant drop of the groundwater table. The study demonstrates that the transition zone may be of greater importance than is usually acknowledged. A comparison of lakes and rivers reveals that the latter are less likely to disconnect in response to a decrease of the regional groundwater table. We relate this behavior to differences in the build-up of a groundwater mound in 2D and 3D. Finally, we carry out some simple transient simulations for 3D systems to analyse the transient behavior of surface water groundwater interaction in the context of disconnection. We show that the state of connection is a critical variable in the dynamics of infiltration in a non-steady system.

Continuous electrical imaging for mapping aquifer recharge along reaches of the Namoi River in Australia

ABSTRACTIn this study the capacity of towed floating electrical imaging for mapping a known aquifer recharge zone in more detail is investigated. A 50 km reach of the Namoi River, Australia, was surveyed. The river is perched up to 16 m above an unconfined aquifer that extends to 30 m below the ground surface. The unconfined aquifer overlies a semi‐confined aquifer system. The electrical array consists of two current electrodes near the boat, followed by nine potential electrodes. The sequence of 1D electrical sounding curves generated was automatically inverted to obtain a layered earth electrical model along the river to a depth of approximately 40 m. There was weak correlation between the water conductivity measured in boreholes and the layered earth electrical model. Lithological logs from boreholes near the river indicate that the major layers seen in the electrical conductivity cross‐section correspond to the major sedimentary units. Groundwater mounding in the vicinity of the river has been monitored after flooding. The groundwater flood mounds coincide with the location of the predominantly low electrically conductive sediments mapped beneath the river. This suggests that aquifer recharging waters migrate via the sands and gravels, then pool at the water table before dissipating. This survey demonstrates that mapping intervals of low electrically conductive sediments beneath the river maps potential aquifer recharge pathways.

Slumping of groundwater mounds: revisiting the Polubarinova-Kochina theory

Decay or rise of the water table from a disturbed (mound or trough) position to a quiescent flat state is studied by a linear potential theory that does not rely on the Dupuit-Forchheimer vertical averaging but is a solution to the full Laplace equation. We consider an unconfined aquifer of high (infinite) thickness disturbed by a linear or point hydrodynamic dipole and assemblies of dipoles, which generate two- and three-dimensional seepage. Hydrologically, the dipoles mimic a channel (or circular-recharge basin), which generates the mound. The dipole ascends (descends) and the corresponding free surface, on which the isobaricity and kinematic conditions hold, slumps. A solvability condition, which stipulates no singularities in the seepage domain, is explicitly presented. The mound signal is defined as the time peak of the water table at any piezometer located away from the original recharge area. The flow net and isotachs prove the Bouwer caveat that the Dupuit-Forchheimer theory is specious if applied to high-thickness aquifers accommodating mounds originating from short infiltration events. The analytical value of the water table peak and the time of its arrival are compared with piezometric observations in recharge experiments conducted in a coastal aquifer of the United Arab Emirates, where the hydraulic conductivity is assessed from hydrographs. The inversely determined hydraulic conductivity fits well with those found from infiltration double-ring experiments and MODFLOW simulation.

Macroinvertebrate cycles of decline and recovery in Swan Coastal Plain (Western Australia) wetlands affected by drought-induced acidification

Management of wetlands influenced by the Gnangara groundwater mound, Western Australia, is becoming increasingly challenging due to an ongoing decline in the regional groundwater table. A number of these groundwater-dependent wetlands have acidified (with adverse effects on the extant macroinvertebrate fauna) due to the oxidation of pyritic sediments. One management option in such cases is artificial augmentation of surface water in order to maintain or reinstate anaerobia in the sediments. This paper documents cycles of macroinvertebrate decline and recovery over 12 years of monitoring in three Gnangara mound wetlands affected by drought-induced acidification, one of which is being artificially augmented. Acidification did not result in a reduction of the total number of macroinvertebrate families present, however, there were clearly identifiable groups of acid-sensitive taxa (amphipods and isopods, ostracods, chydorid and daphnid cladocerans, mayflies, oligochaetes, clams and snails) and acid-tolerant taxa (sandfly larvae, macrothricid cladocerans and water boatmen). In the artificially augmented wetland, the effects of acidification were reversed: acid-sensitive taxa reappeared and acid-tolerant taxa decreased in numbers. Moreover, there were a number of taxa that appeared for the first time since augmentation, and summer family richness increased markedly. This study has shown that artificial augmentation of wetland water levels can be a successful recovery strategy for recently acidified systems, but this will depend on a number of factors, and the ‘recovered’ state will be at least slightly different from the original state.

Estimating specific yield and storage change in an unconfined aquifer using temporal gravity surveys

Two high‐precision gravity surveys were conducted to determine groundwater mass changes at a managed groundwater recharge site in northeastern Colorado. Gravity data were collected during pumping and two months after pumping ceased. During pumping, gravity was lower by as much as 46 μGal near the pumping wells and higher by as much as 90 μGal near the recharge ponds in comparison to data collected after pumping had ceased. These differences are attributed to changes in groundwater mass associated with drawdown and infiltration. Inverse modeling of the gravity data indicates a 5.1 × 105 m3 decrease in storage beneath the recharge ponds between the two surveys, which we attribute to dissipation of the groundwater mound created by recharge during pumping. This estimate of the change in groundwater storage is made independently of assumptions of physical properties of the aquifer. Dividing the change in water volume per unit area determined from the gravity modeling by the change in water level measured in wells provides an estimate of specific yield (Sy) of 0.21 ± 0.03, which is within the range of specific yield estimates derived from aquifer tests at the site. Water level changes predicted from the gravity data agree on average to within ±0.45 m of those measured, which we take to be an estimate of the uncertainty in water table depth predictions that can be obtained from gravimetric data in unconfined aquifers. The study covers a 3.2 km2 area, providing a prototype for similar studies at larger scales.

Hydrogeologic controls on disconnection between surface water and groundwater

Understanding how changes in the groundwater table affect surface water resources is of fundamental importance in quantitative hydrology. If the groundwater table below a stream is sufficiently deep, changes in the groundwater table position effectively do not alter the infiltration rate. This is referred to as a disconnected system. Previous authors noted that a low‐conductivity layer below the surface water body is a necessary but not sufficient criterion for disconnection to occur. We develop a precise criterion that allows an assessment of whether surface water–groundwater systems can disconnect or not. We further demonstrate that a disconnected system can be conceptualized by a saturated groundwater mound and the development of a capillary zone above this mound. This conceptualization is used to determine the critical water table position at the point where full disconnection is reached. A comparison of this calculated critical water table position with a measurement of the water table depth in a borehole allows the assessment of the disconnection status. A sensitivity analysis of this critical water table showed that for a given aquifer thickness and river width, the depth to groundwater where the system disconnects is approximately proportional to the stream depth and the hydraulic conductivity of the streambed sediments and inversely proportional to the thickness of these sediments and the hydraulic conductivity of the aquifer. The conceptualization also allows the disconnection problem to be analyzed using both variably saturated and fully saturated groundwater models and provides guidance for numerical and analytical approaches.

Implications of bioretention basin spatial arrangements on stormwater recharge and groundwater mounding

Stormwater bioretention basin recharge has the potential to raise the watertable and adversely impact subsurface infrastructure, undermining the benefits of naturalizing the urban water cycle. This research examined how groundwater mounding responded to three spatial arrangements of bioretention basins, from separated units to clustered units to single units, and changes in hydraulic conductivity, storm intensity, and antecedent recharge, for 28 sub-watersheds in an 8-ha Syracuse, New York, sewershed with 43% impervious cover. Bioretention basin volumetric capacities were designed for a 24-h duration 2-yr return interval rainfall event. MODFLOW simulations with hydraulic conductivity at 1 cm h −1 predicted an increase in median groundwater mounding from 0.28 m to 0.72 m when separation distances were reduced from equally distributed to single units. In sag points, however mounding exceeded 1 m. By setting hydraulic conductivity to 0.01 cm h −1, a worst case scenario, median mounding was greater than 1 m for all spatial designs, in all locations. Groundwater mound overlap was identified for spatial arrangements where intersecting streets created superposition, and greater mounding was observed at corner-situated bioretention basins. After 30 years of recharge, the steady state watertable had risen by 1.1 m, and subsequent storm event mounding could interfere with subsurface infrastructure in approximately 20% of the watershed, localized in the floodplain. This study recommends an expanded investigation of long-term watertable adjustment, possibly followed by removal of some floodplain infrastructure or designs to enhance watertable tolerance.