Search

Groundwater mixing dynamics play a crucial role in the biogeochemical cycling of shallow wetlands. In this paper, we conducted groundwater simulations to investigate the combined effects of evaporation and local heterogeneity on mixing dynamics in shallow wetland sediments. The results show that evaporation causes groundwater and solutes to upwell from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology reveals that local heterogeneity generates spatially varied mixing patterns mainly along preferential flow pathways. The upwelling of groundwater induced by surface evaporation through heterogeneous sediments is likely to create distinct mixing hotspots that differ spatially from those generated by lateral preferential flows driven by large‐scale hydraulic gradients, which enhances the overall mixing in the subsurface. These findings have strong implications for biogeochemical processing in wetlands. Plain Language Summary: In shallow wetlands, groundwater mixing and exchange have been identified as critical factors affecting biogeochemical cycling and transformation in sediments. Our results for the first time demonstrate evaporation causes a significant upwelling of groundwater and solutes from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology, including the Okubo‐Weiss parameter and dilution index, reveals that evaporation and local heterogeneity generates dynamic mixing patterns along preferential flow pathways. Such mixing mechanisms would strongly affect biogeochemical conditions in near‐surface sediments of shallow wetlands, which have strong implications for wetland ecosystems. Key Points: Evaporation causes groundwater and solutes to upwell from deep sediments to the surface, resulting in near‐surface solute accumulationHeterogeneity causes strain‐dominated and vorticity‐dominated flow regions to coexist at small spatial scales along preferential flow pathsUpwelling groundwater creates distinct mixing hotspots that differ spatially from those generated by large‐scale hydraulic gradients [ABSTRACT FROM AUTHOR]

A density‐dependent, variably saturated groundwater flow and solute transport model was used to investigate the influence of swash motions on subsurface flow and moisture dynamics in beach aquifers with heterogeneous distributions of hydraulic conductivity (K) and capillarity. The numerical simulations were performed within a Monte Carlo framework using field measurements conducted in the swash zone of a sandy beach. Our results show that heterogeneous capillarity causes spatially variable capillary rise above the groundwater table. In response to swash motions, heterogeneity creates capillary barriers that result in pockets of elevated moisture content beneath the swash zone. These moisture hotspots persist within the unsaturated zone even at ebb tide when the swash motions recede seaward. Heterogeneous capillarity also results in highly tortuous preferential flow paths and alters the flow rates from the sand surface to the water table. Heterogeneous K greatly enhances the seawater infiltration into the swash zone and modulates its spatial distribution along the beach surface. Due to heterogeneous K and capillarity, complex mixing patterns emerge. Both strain‐dominated and vorticity‐dominated flow regions develop and dissipate as tides and waves move across the beach surface. Complex mixing patterns of seawater percolating from the swash zone surface to the water table, with localized areas of high and low mixing intensities, are further demonstrated by analysis of dilution index. Our findings reveal the influence of geologic heterogeneity on swash zone moisture and flow dynamics, which may have important implications for sediment transport and chemical processing in beach aquifers. Plain Language Summary: In marine coastal environments, swash zone mixing and exchange dynamics have been identified as critical factors affecting biogeochemical cycles and nutrient loads from aquifers to coastal waters. Our results for the first time demonstrate a dynamic response of moisture and subsurface flow to swash motions in the presence of aquifer heterogeneity. Heterogeneity coupled with high‐frequency wave forcing results in moisture hotspots and significant tempo‐spatial variability of strain‐dominated and vorticity‐dominated flow regions within the swash unsaturated zone, which have important implications for biogeochemical processes and local‐scale mixing rates. These results highlight the importance of considering geologic heterogeneity in both hydraulic conductivity and capillarity in studies of groundwater flow and solute transport processes in coastal beach aquifers subjected to swash motions. Key Points: Swash motion on beaches with heterogeneous sediments leads to capillary barriers and moisture hotspots beneath the beach surfaceStrain‐dominated and vorticity‐dominated flow regions coexist at small spatial scales within the swash zone due to geologic heterogeneityHeterogeneity creates both high and low mixing spots in subsurface flow percolating from the swash zone into the porous media [ABSTRACT FROM AUTHOR]

Intertidal aquifers are hotspots of biogeochemical cycling where nutrients and contaminants are processed prior to discharge to the ocean. The nature of the dynamic subsurface mixing zone is a critical control on mitigating reactions. Simulation of density‐dependent, variably saturated flow and salt transport incorporating realistic representations of aquifer heterogeneity was conducted within a Monte Carlo framework to investigate influence of nonuniform permeability on intertidal groundwater flow and salt transport dynamics. Results show that heterogeneity coupled with tides creates transient preferential flow paths within the intertidal zone, evolving multiple circulation cells and fingering‐type salinity distributions. Due to heterogeneity, strain‐dominated (intense mixing) and vorticity‐dominated (low mixing) flow regions coexist at small spatial scales, and their spatial extent reaches peaks at high tide and low tide. Such topological characteristics reveal complex tempo‐spatial mixing patterns for intertidal flow with localized areas of high and low mixing intensities, which have implications for intertidal biogeochemical processing. Plain Language Summary: In marine coastal environments, groundwater‐seawater mixing and exchange have been identified as critical factors affecting biogeochemical cycles and nutrient loads from aquifers to coastal waters. Our results for the first time demonstrate a dynamic response of intertidal flow topology and preferential flow paths to tides in the presence of aquifer heterogeneity. Heterogeneity coupled with tides results in different types of mixing than homogeneous or nontidal systems, which is important for geochemical reactions in the beach. These results highlight the importance of considering geologic heterogeneity in studies of groundwater flow and solute transport processes in tidally influenced beach aquifers. Key Points: Heterogeneity coupled with tides creates transient preferential flows within the intertidal zone, altering salinity distributionStrain‐dominated and vorticity‐dominated intertidal flow regions coexist at small spatial scales due to geologic heterogeneityHeterogeneity increases spatial variability of mixing of pore water flowing through the intertidal zone [ABSTRACT FROM AUTHOR]

Jets and plumes have been the focus of quantitative investigations since the mid-1950s. These investigations intensified following the Deepwater Horizon oil spill, in which thousands of tons of oil and natural gas were released into the Gulf of Mexico. This review focuses on plume dynamics that apply to both single-phase and multiphase liquid-in-liquid and liquid plus gas into liquid plumes, including bubble and droplet formation, and heat and mass transfer. Broadly, our work highlights several previously unknown or overlooked aspects of multiphase flow in the deep oceans. Upstream of the jet release, multiphase hydraulics can significantly affect the turbulence, for instance, through churn flow that enhances the turbulence in the free jet, affecting the conditions where bubbles and droplets are formed. Droplet formation was a major focus recently, with experiments covering a range of scales and flow rates of oil and gas at low and high pressure. Detailed observations of droplet formation at the jet-water boundary reveal the formation of compound droplets, which are emulsions of oil and water with implications for mass conservation and mass transfer. At the plume scale, integral models have been adapted to include the complex thermodynamics and chemistry of oil and gas plumes. In parallel, significant advances were made in numerical simulations of multiphase plumes through large eddy simulations by treating the oil and gas either a continuous or discrete phase. Through this work, a vivid picture of the complex droplet, chemical, and hydrodynamic behavior of multiphase plumes in the ocean is emerging. [ABSTRACT FROM AUTHOR]

A numerical study, based on a variably saturated groundwater flow model within a Monto Carlo framework, was conducted to investigate flow and solute transport in a heterogeneous beach aquifer subjected to tides. The numerical simulations were conducted based on our previous tracer experiments performed in a laboratory beach. Heterogeneity is assumed to be multifractal generated using the Universal Multifractal model. Our results show that heterogeneity greatly alters temporal and spatial evolution of the tracer plume migrating in the beach. The spreading coefficient of the plume shows very dynamic response to tides; it increases as the tidally driven recirculation cell overlaps with the plume and decreases as the recirculation cell moves far from the plume with tides. Descriptive statistics suggests that heterogeneity enhances spreading of the plume in the beach in an ensemble sense along with significant spatial and temporal variation. Due to heterogeneity, high spots of the pore water velocity are formed within the recirculation cell, creating transient preferential flow paths in the beach in response to tides. Contours of the Okubo-Weiss (OW) parameter show that coupling with tides, heterogeneity creates vorticity-dominated flow regions and also expands strain-dominated flow regions more downward, indicating complex local-scale mixing in the beach, compared to corresponding homogeneous case. Geologic heterogeneity also alters the spatial extent of the recirculating cell and induces highly variable transit time along the recirculating flow paths. The results provide insights into effects of geologic heterogeneity on seawater-groundwater mixing and associated solute transport processes in tidally influenced coastal aquifers. [ABSTRACT FROM AUTHOR]

Subsurface heterogeneity could influence groundwater flow with implications on structure and productivity of aquifer ecosystems. Here we investigate effects of multifractal heterogeneity on topology of groundwater flow through MODFLOW simulations within a Monte Carlo framework. The results show that heterogeneity leads to focused groundwater advection and the creation of hotspots of bending‐type vortex flow in the fields. We demonstrate for the first time that the vortex structures characterized by Q criterion are 3‐D distributed and greatly deform surrounding pore‐water flow. The structures exhibit scale‐invariant features in multifractal fields and in stationary fields below the correlation scale, indicating that such vortex flow might be widely present with no characteristic scale. Complex spatial patterns of kinetic energy dissipation rate are identified for pore water flowing through heterogeneous porous media and correlate strongly with preferential flows. These findings are important for understanding solute fate and transport in aquifer systems. Plain Language Summary: The findings of this study provide insight into influences of heterogeneity on groundwater flow and solute transport processes in aquifers. Our results reveal that multifractal heterogeneity leads to focused regions of groundwater advection and creates hotspots of bending‐type vortex flow that are 3‐D and greatly deform surrounding pore water. It has strong implications for groundwater contamination and associated implementation of effective bioremediation strategies. This is because solutes/contaminants would be spun around these structures and therefore have less interaction with the soil matrix in the inner part of the vortices. We also demonstrate that the structures of the vortex flow are scale invariant in multifractal K fields and below the correlation scale of stationary K fields. It indicates that these vortex flow structures may be widely present in the field with no characteristic scale. Substantial energy dissipation along the high‐velocity zones also has strong implications for understanding activity, diversity, and the distribution of subterranean microorganisms. Key Points: Deformation and rotation of pore‐water flow occur near high vorticity zones, formed as blobs and correlated strongly to preferential flowsVorticity‐dominated blobs exhibit scale invariance in both multifractal K fields and up to the correlation scale in variogram K fieldsHeterogeneity dissipates substantial kinetic energy within large pore‐water velocity zones [ABSTRACT FROM AUTHOR]

Most existing numerical research on tide‐induced groundwater dynamics assumes a constant surface water salinity on the seaward boundary (constant salinity case). Few studies have investigated the influence of tidally varying salinity on shallow groundwater dynamics in coastal aquifers (tidal salinity case). We compiled field observations of tidally varying salinity in multiple estuaries across the eastern coast of China and a tidal creek in North Inlet‐Winyah Bay, United States. Numerical simulations were then conducted to explore the effect of tidally varying salinity on groundwater flow and salt transport in an idealized creek marsh aquifer. Results showed that the upper saline plume and classical saltwater wedge appeared in all cases, but the salinity in the saltwater wedge was diluted in the tidal salinity cases. Notably, groundwater transit times were shorter in the tidal salinity case than in the constant salinity case, especially under the creek bottom. Quantitative analyses indicated that tidally varying salinity significantly enhanced surface water‐groundwater exchange, increasing submarine groundwater discharge by 10% and the total inflow of surface water across the water‐sediment interface by 7%. As the density of groundwater differs from that of the overlying surface water, fingered saltwater flow formed in sediments under the creek bottom, leading to some small local water circulation cells. These small cells reduced groundwater transit times and almost doubled the water exchange rate. Coupling the density‐dependent flow to a simplified nitrogen reaction network revealed that the tidally varying salinity may have the potential to influence nitrogen biogeochemical transformations that modify nitrogen loads prior to discharge. Key Points: A large salinity gradient causes unstable density fingering in sediments under the creek bottomUnstable flow enhances local water circulation and reduces groundwater transit timesTidally varying salinity enhances surface water‐groundwater exchange and has the potential to modify nitrogen loads prior to discharge [ABSTRACT FROM AUTHOR]

Oil droplets transport in a deep‐water plunging breaker of height 0.18 m was simulated by coupling computational fluid dynamics with Lagrangian particle tracking. The Reynolds‐averaged Navier‐Stokes equations were solved in a two‐dimensional vertical slice within the computational fluid dynamics code Fluent to reproduce the movement of breaking waves in the absence of wind stress and large‐scale turbulence. The generated plunging breaker generated two additional (residual) breakers, consistent with experimental observations from the literature. The hydrodynamics of the breaker was subsequently used as input to the Lagrangian particle tracking code, NEMO3D, where the equation of motion was solved for each droplet by incorporating the major local forces including those due to the mass of the droplet. The droplet sizes were selected to vary from 100 to 600 μm. It was found that the droplet plume split into three clouds, one below and upstream of the first breaker, one below the second breaker, and one downstream of the third breaker. The largest penetration depth was within the second cloud. The largest entrainment (fraction of surface mass in the water column) occurred for the 100‐μm droplets, while the smallest entrainment occurred for the 600 μm. However, the 300 μm exhibited smaller entrainment than smaller droplets, which is due to the vortical nature of the breaker, which advected the 300 μm horizontally and then upward. This has implications on the biodegradation and dissolution of droplets of various sizes, and on the application of countermeasures such as dispersant. Plain Language Summary: Oil droplets transport in a deep‐water plunging breaker was simulated by coupling computational fluid dynamics with Lagrangian particle tracking. Based on the authors' knowledge, this is the first time to study the transport of oil droplets under an isolated breaker by coupling the computational fluid dynamics with Lagrangian particle tracking. Key Points: A deep‐water plunging breaker is reproduced with Reynold average Navier‐Stokes (RANS) approachDroplet transport was simulated while accounting for major forces (inertia, added mass, and lift)Accounting for droplet inertia results in larger droplets (300 microns), penetrating less than smaller droplets [ABSTRACT FROM AUTHOR]

Abstract: Improved understanding of the character of an uncontrolled pipeline flow is critical for the estimation of the oil discharge and droplet size distribution both essential for evaluating oil spill impact. Measured oil and gas properties at the wellhead of the Macondo255 and detailed numerical modeling suggested that the flow within the pipe could have been “churn,” whereby oil and gas tumble violently within the pipe and is different from the bubbly flow commonly assumed for that release. The churn flow would have produced 5 times the energy loss in the pipe compared to bubbly flow, and its plume would have entrained 35% more water than that of the bubbly flow. Both findings suggest that the oil discharge in Deepwater Horizon could have been overestimated, by up to 200%. The resulting oil droplet size distribution of churn flow is likely smaller than that of bubbly flow. [ABSTRACT FROM AUTHOR]

Abstract: A combined field and numerical study was conducted to investigate dynamics of subsurface flow and moisture response to waves in the swash zone of a sandy beach located on Cape Henlopen, DE. A density‐dependent variably saturated flow model MARUN was used to simulate subsurface flow beneath the swash zone. Values of hydraulic conductivity (K) and characteristic pore size (α, a capillary fringe property) were varied to evaluate their effects on subsurface flow and moisture dynamics in response to swash motions in beach aquifers. The site‐specific modeling results were validated against spatiotemporal measurements of moisture and pore pressure in the beach. Sensitivity analyses indicated that the hydraulic conductivity and capillary fringe thickness of the beach greatly influenced groundwater flow pathways and associated transit times in the swash zone. A higher value of K enhanced swash‐induced seawater infiltration into the beach, thereby resulting in a faster expansion of a wedge of high moisture content induced by swash cycles, and a flatter water table mound beneath the swash zone. In contrast, a thicker capillary fringe retained higher moisture content near the beach surface, and thus, significantly reduced the available pore space for infiltration of seawater. This attenuated wave effects on pore water flow in the unsaturated zone of the beach. Also, a thicker capillary fringe enhanced horizontal flow driven by the larger‐scale hydraulic gradient caused by tides. [ABSTRACT FROM AUTHOR]

Modeling the movement of oil released underwater is a challenging task due to limitations in measuring the hydrodynamics in an oil-water system. In this work, we conducted an experiment of horizontal release of oil without and with dispersant. The model VDROP-J was used and compared to the model JETLAG, a miscible plume trajectory model. Both models were found to reproduce the oil jet hydrodynamics for oil without and with dispersant. The predicted DSD from VDROP-J matched closely observation for untreated oil. For oil with dispersant, experimental results have shown evidence that tip streaming occurred. For this purpose, a new conceptual module was developed in VDROP-J to capture the tip streaming phenomenon and an excellent match was achieved with observation. This study is the first to report tip streaming occurring in underwater oil jets, which should have consequences on predicting the DSD when dispersant are used on an underwater oil release. © 2017 American Institute of Chemical Engineers AIChE J, 2017 [ABSTRACT FROM AUTHOR]

Evaporation has been recognized as a major driving force affecting coastal aquifer systems. However, its effects on subsurface flow and salinity structure have not been investigated in sufficient detail. This paper presents field measurements and numerical simulations of pore water flow and subsurface salinity structure in the supratidal zone of a sandy beach subjected to evaporation as well as rainfall. It was found that evaporation significantly increased pore water salinity, up to 85 g/L, within a shallow layer, approximately 10 cm below the beach surface. The induced density gradient generated salt fingers near the beach surface, which caused local groundwater circulation (i.e., fingering flow). However, unlike inland aquifers, the salt fingering was significantly diminished by tidal action that prompted the horizontal mixing of salt in the beach. The subsequent precipitation (e.g., rainfall) diluted the evaporation-induced high saline plume near the beach surface and drove the plume to migrate downward; the plume gradually dispersed and was diluted along the groundwater pathways. The simulation results indicated that evaporation as well as precipitation at the beach surface induced complex driving mechanisms for supratidal groundwater flow. Depending on the intensity at the beach surface, evaporation and rainfall significantly altered the pore water flow and associate solute transport processes in the supratidal zone of the beach. [ABSTRACT FROM AUTHOR]

We coupled a mass-transfer formulation of evaporation to the density-dependent variably saturated finite element model MARUN to predict the salinity under realistic conditions in a beach in the Gulf of Mexico. The results showed that evaporation almost doubled the pore water salt concentration in the intertidal zone in comparison to the case with no evaporation. The results also showed that for the relatively wet atmospheric conditions, the maximum evaporation did not occur from the supratidal zone, rather from the intertidal zone, and it was due to the difference in moisture between pore water and atmosphere. The highest salinity occurred during the spring tide period, and extended into the neap tide period. When the atmospheric condition was assumed to be constant and conducive to large evaporation (high temperature and low air humidity), the maximum salinity region shifted to the supratidal zone and persisted there due to low mixing. The maximum salinity value in the intertidal zone for this case was not larger than that of the variable atmospheric condition case. However, the maximum was more landward than the (more realistic) variable atmospheric condition case, which suggests that accurate characterization of pore water salinity in tidally influenced beaches requires accurate knowledge of atmospheric conditions in addition to beach and hydraulic properties. The constant atmospheric condition simulations suggest that antecedent extreme conditions greatly affect the salinity in the supratidal zone but they are dampened in the intertidal zone. [ABSTRACT FROM AUTHOR]

The aerobic biodegradation of oil in tidally influenced beaches was investigated numerically in this work using realistic beach and tide conditions. A numerical model BIOMARUN, coupling a multiple-Monod kinetic model BIOB to a density-dependent variably saturated groundwater flow model 2-D MARUN, was used to simulate the biodegradation of low-solubility hydrocarbon and transport processes of associated solute species (i.e., oxygen and nitrogen) in a tidally influenced beach environment. It was found that different limiting factors affect different portions of the beach. In the upper intertidal zone, where the inland incoming nutrient concentration was large (1.2 mg N/L), oil biodegradation occurred deeper in the beach (i.e., 0.3 m below the surface). In the midintertidal zone, a reversal was noted where the biodegradation was fast at shallow locations (i.e., 0.1 m below the surface), and it was due to the decrease of oxygen with depth due to consumption, which made oxygen the limiting factor for biodegradation. Oxygen concentration in the midintertidal zone exhibited two peaks as a function of time. One peak was associated with the high tide, when dissolved oxygen laden seawater filled the beach and a second oxygen peak was observed during low tides, and it was due to pore oxygen replenishment from the atmosphere. The effect of the capillary fringe (CF) height was investigated, and it was found that there is an optimal CF for the maximum biodegradation of oil in the beach. Too large a CF (i.e., very fine material) would attenuate oxygen replenishment (either from seawater or the atmosphere), while too small a CF (i.e., very coarse material) would reduce the interaction between microorganisms and oil in the upper intertidal zone due to rapid reduction in the soil moisture at low tide. [ABSTRACT FROM AUTHOR]

Delivery of dissolved chemicals to potentially bioremediate oil from the Exxon Valdez oil spill was investigated at Smith Island, Prince William Sound, Alaska. Two transects for tracer application were installed: one at a clean area and another at an oiled area. Tracer delivery occurred under ambient pressure through manifolds. Lithium in LiBr/sea water solution was the inert tracer, and the solution (82.6 mg/L of lithium) was released at a flow rate of 0.23 L/min for 58.5 h. While maintaining the flow rate, the solution was switched to sea water (i.e., 0.0 mg/L of lithium) for 16 h. The results show that the tracer moved landward with rising tides and seaward with falling tides. The plume got deeper moving landward and shallower moving seaward of the manifold. Thus, in situations where oil biodegradation is limited by the availability of nutrients or oxygen, applying these chemicals by this technique would allow them to reach entrapped oil seaward of the manifold from below. The seaward plume traveling speed (around 2.0 m/d) suggests that this technique is logistically feasible from a hydraulic point of view. [ABSTRACT FROM AUTHOR]

Delivery of dissolved chemicals to bioremediate oil from the Exxon Valdez oil spill was investigated at Beach EL056C of Eleanor Island, Prince William Sound, Alaska. The delivery technique was high pressure injection (HPI) of an inert tracer, lithium, at the approximate depth of 1.0 m into the beach near the mid-tide line. The results revealed that the maximum injection flow rate was 3.0 L/min and the associated pressure was around 196 kPa. Therefore, exceeding any of these values would probably cause failure of the injection system. The injected tracer was monitored at multiple depths of four surrounding observation wells, and the results showed that the tracer plume occupied an area of 12 m within 24 h. The tracer plume traveled at the average speeds of 10 m/d in the seaward direction and 1.7 m/d in other directions. The rapid movement under HPI and the large diameter of influence (3.0 m) indicated that bioremediation of the Exxon Valdez oil on this beach via injection of chemicals is logistically feasible. [ABSTRACT FROM AUTHOR]

We report a field study and numerical modeling of multicomponent flow in a tidal gravel beach in Knight Island, Prince William Sound, Alaska, where oil from the 1989 Exxon Valdez oil spill persisted. Field measurements of water table, salinity, and tracer (lithium) concentration were obtained for around a week during the summer of 2008. The numerical model MARUN was used to simulate the field observations. On the basis of field experiments and numerical simulations, the beach was identified to have a two-layered hydraulic structure: a high-permeability surface layer underlain by a low-permeability lower layer. The hydraulic conductivity was found to be 5 × 10−2 m s−1 for the surface layer and 7 × 10−6 m s−1 for the lower layer. The simulations reproduced the observed water table, salinity, and lithium concentrations accurately. The small flow entering the beach from the land side resulted in a beach water table dropping below the interface of the two layers. This seems to be the major reason for the presence of oil in the lower layer. The exchange flow between the beach and the sea due to tidal influence was ∼2.12 m3 d−1 m−1. The patterns of inflow and outflow rates showed that the maximum seawater-groundwater exchange occurred in the middle to high intertidal zone, which explains the persistence of oil in the lower intertidal zone. To explore bioremediation of the beach with nutrient amendment, a numerical simulation of nutrient application on the beach surface was conducted, where the applied nutrient concentration was 5,000 mg L−1. The results showed that the nutrient concentration remaining in oiled areas after a week was larger than 50 mg L−1, which is larger than that needed for maximum microbial growth (2-10 mg L−1). This implies that the bioremediation via nutrient application on the beach surface could be adopted if nutrients were the only limiting factor. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution of groundwater head response to dual-tide fluctuation in the transect of an island leaky aquifer system comprising a confined aquifer and its overlying semipermeable confining layer. Both layers terminate at the coastlines on two sides of the island. Solution analysis indicates that the tidal waves from the two sides of the island transect interfere at the middle of the island and the interference decreases to zero as the horizontal length of the aquifer increases to infinity. The leakage of the overlying confining layer enhances the landward attenuation of the tidal head fluctuation and shortens the time lag between the head and tide fluctuations. The solution agreed well with the observations in eight piezometers in Garden Island on the continental shelf of Western Australia reported by Trefry and Bekele (2004). [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to quantify bank storage in a variably saturated, homogenous, and anisotropic aquifer abutting a stream during rising stream stage. Seepage faces and bank slopes ranging from 1/3 to 100/3 were simulated. The initial conditions were assumed steady-state flow with water draining toward the stream. Then, the stream level rose at a constant rate to the specified elevation of the water table given by the landward boundary condition and stayed there until the system reached a new steady state. This represents a highly simplified version of a real world hydrograph. For the specific examples considered, the following conclusions can be made. The volume of surface water entering the bank increased with the rate of stream level rise, became negligible when the rate of rise was slow, and approached a positive constant when the rate was large. Also, the volume decreased with the dimensionless parameter M (the product of the anisotropy ratio and the square of the domain’s aspect ratio). When M was large (>10), bank storage was small because most pore space was initially saturated with ground water due to the presence of a significant seepage face. When M was small, the seepage face became insignificant and capillarity began to play a role. The weaker the capillary effect, the easier for surface water to enter the bank. The effect of the capillary forces on the volume of surface water entering the bank was significant and could not be neglected. [ABSTRACT FROM AUTHOR]

A confined coastal aquifer usually extends under the sea for some distance with its submarine outlet covered by a thin layer of sediment with properties dissimilar from the aquifer. Previous theoretical studies neglected this outlet capping. In this paper an analytical solution is derived for a confined aquifer subject to tidal fluctuations with a leaky boundary condition at the outlet capping. For the cases that offshore length of the aquifer and/or the leakance of the outlet capping are either zero or infinity, existing solutions in literature are obtained. It is shown that our analytical solution can also be used to describe the tidal wave propagation in a confined aquifer extending infinitely under a tidal river. The full solution agreed well with the observations in a piezometer in the Jahe River Basin in China, 200 m inland from the coastline where the tide-induced head fluctuations without delay were observed but cannot be explained using previous analytical and numerical solutions ignoring the effect of the outlet capping. The sensitivity analysis showed that the combined actions of the tidal loading and outlet capping lead to complex dependency of the head fluctuation on the outlet capping's leakance. When the offshore confined aquifer is short, the inland head fluctuation increases with the outlet capping's leakance. In this case significant negative phase shift occurs if the leakance is small. For offshore aquifer length greater than a threshold value the inland head fluctuations are independent of this length and the outlet capping's leakance. [ABSTRACT FROM AUTHOR]

We analyzed the scaling properties of the hydraulic conductivity K at three sites in Northern America: MADE, Borden, and Cape Cod. We found that K at all sites exhibits multifractality (fractal and multiscaling) in both the vertical and horizontal directions, though the multiscaling was within a range smaller than that of the maximum distance between measurements. In the vertical direction, the K data for MADE, Borden, and Cape Cod were multiscaling from 0.15 to 1.35 m, 0.05 to 0.5 m, and 0.15 to 0.9 m, respectively. They were multiscaling in the horizontal direction from 9 to 45 m, 1 to 10 m, and 1 to 17 m, respectively. The multiscaling was also anisotropic. Evidence of scaling was poorest for the horizontal direction of the MADE site, and it spanned half an order of magnitude. Such results compel one to treat multifractality in the horizontal direction of MADE as supported by heuristic arguments, rather than by pure statistical evaluation. We fitted a multifractal model to the data and estimated its parameters. We found the underlying statistics of all data to be non-Gaussian, and the model capable of reproducing the probability distribution of K data, especially the negative skewness of log K. We also generated two-dimensional isotropic multifractal fields illustrating the role of the parameters of the selected multifractal model. [ABSTRACT FROM AUTHOR]

Focuses on the role of capillarity in transient seepage situations. Equations for water flow in variably saturated media in dimensionless form; Information on soil moisture and hydraulic conductivity; Definition of seepage face.

We consider an archetypical problem relevant to a confined aquifer in contact with a stream. The model problem consists of an idealized one-dimensional region 0 ≤ x ≤ L, where the left boundary at x = 0 is held at a fixed piezometric head h0, and the right boundary's piezometric head at x = L is increased from h L to h0 at a constant rate. Exact solutions for all times, all points in the aquifer, and for any possible constant rate of change of the right boundary piezometric head are presented for the piezometric head and the instantaneous flow rate. An exact expression for the exchange volume at the groundwater/stream interface for an arbitrary time is also provided. This expression shows that there is a specific critical rising rate of the stream level above which the net exchange volume is into the aquifer and below which it is out of the aquifer. The solution shows that regardless of the rise rate, a certain water volume, inversely proportional to the rise rate, enters the aquifer. [ABSTRACT FROM AUTHOR]

BSTRACT: Twenty storm events were used to select design values of the HEC1 loss parameters STRTL and CNSTL in order to route the probable maximum flood, PMF, through the Englewood watershed, Ohio. The parameter STRTL represents the initial volume of water lost due to interception and incomplete saturation of the soil prior to the storm. The parameter CNSTL represents a continuous loss rate and depends only on the watershed. When optimized from each storm event, STRTL varied between 0.0 and 3.4 inches with an average of 1.0 inch; CNSTL varied between 0.02 and 0.26 inch/hour, and it followed a normal probability distribution with a mean of about 0.1 inch/hour. The absence of correlation between optimum CNSTL values and each of total rainfall, total loss, and runoff duration supported the selection of the mean CNSTL as a design value. PMF routing through the Englewood watershed revealed that the PMF at the outlet is not sensitive to STRTL, but highly affected by CNSTL variations. The insensitivity to STRTL was due to the presence of a dam at the outlet of the watershed that caused the buildup of water in the watershed, thereby masking the storage effect of STRTL. The peak PMF increased by about 27 percent when the design CNSTL was decreased to 0.05 inch! hour, and decreased by about 18 percent when the design CNSTL was increased to 0.15 inch/hour. [ABSTRACT FROM AUTHOR]

Existing fractal studies dealing with subsurface heterogeneity treat the logarithm of the permeability K as the variable of concern. We treat K as a multifractal and investigate its scaling and fractality using measured horizontal K data from two locations in the United States. The first data set was from a shoreline sandstone near Coalinga, California, and the second was from an eolian sandstone [ Goggin, 1988]. By applying spectral analyses and computing the scaling of moments of various orders (using the double trace moment method [ Lavallee, 1991; Lavallee et al., 1992]), we found that K is multiscaling (i.e., scaling and multifractal). We also found that the so-called universal multifractal (UM) [ Schertzer and Lovejoy, 1987] model (essentially a log-Levy multifractal), was able to reproduce the multiscaling behavior reasonably well. The UM model has three parameters: α, σ, and H, representing the multifractality index, the codimension of the mean field, and the 'distance' to stationary multifractal, respectively. We found (α = 1.7, σ = 0.23, H = 0.22) and (α = 1.6, σ = 0.11, H = 0.075) for the shoreline and eolian data sets, respectively. The fact that α values were less than 2 indicates that the underlying statistics are non-Gaussian. We generated stationary and nonstationary multifractals and illustrated the role of the UM parameters on simulated fields. Studies that treated Log K as the variable of concern have pointed out the necessity for large data records, especially when the underlying distribution is Levy-stable. Our investigation revealed that even larger data records are required when treating K as a multifractal, because Log K is less intermittent (or irregular) than K. [ABSTRACT FROM AUTHOR]