analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers sloping coastal aquifers in reality are ubiquitous and well documented steady state sharp interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the dupuit forchheimer approximation specifically analytical solutions based on the constant flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone analytical solutions for the constant head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant flux inland boundary it is found that for the constant flux inland boundary the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types despite that the geometry of the bottom confining layer determines the location of the interface tip this is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary so the shape of the bed below the interface is irrelevant to the interface position moreover developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable density flow numerical modelling analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer this article is protected by copyright all rights reserved

a correction factor to account for mixing in ghyben herzberg and critical pumping rate approximations of seawater intrusion in coastal aquifers 1 the classic ghyben herzberg estimate of the depth of the freshwater saltwater interface together with the dupuit approximation is a useful tool for developing analytical solutions to many seawater intrusion problems on the basis of these assumptions strack 1976 developed a single potential theory to calculate critical pumping rates in a coastal pumping scenario the sharp interface assumption and in particular this analytical solution are widely used to study seawater intrusion and the sustainable management of groundwater resources in coastal aquifers the sharp interface assumption neglects mixing and implicitly assumes that salt water remains static consequently this approximation overestimates the penetration of the saltwater front and underestimates the critical pumping rates that ensure a freshwater supply we investigate the error introduced by adopting the sharp interface approximation and we include the effects of dispersion on the formulation of strack 1976 to this end we perform numerical three dimensional variable density flow simulations we find that strack s equations can be extended to the case of mixing zone if the density factor is multiplied by an empirically derived dispersion factor 1 t b 1 6 where t is transverse dispersivity and b is aquifer thickness we find that this factor can be used not only to estimate the critical pumping rate but also to correct the ghyben herzberg estimate of the interface depth its simplicity facilitates the generalization of sharp interface analytical solutions and good predictions of seawater penetration for a broad range of conditions

effect of climate change on sea water intrusion in coastal aquifers there is increasing debate these days on climate change and its possible consequences much of this debate has focused in the context of surface water systems in many arid areas of the world rainfall is scarce and so is surface runoff these areas rely heavily on groundwater the consequences of climate change on groundwater are long term and can be far reaching one of the more apparent consequences is the increased migration of salt water inland in coastal aquifers using two coastal aquifers one in egypt and the other in india this study investigates the effect of likely climate change on sea water intrusion three realistic scenarios mimicking climate change are considered under these scenarios the nile delta aquifer is found to be more vulnerable to climate change and sea level rise copyright 1999 john wiley sons ltd

tidal influence on seawater intrusion in unconfined coastal aquifers studies of seawater intrusion in unconfined coastal aquifers typically neglect oceanic oscillations such as tides and assume a static seaward boundary condition defined by the mean sea level laboratory experiments and numerical simulations were conducted to investigate the influence of tidal oscillations on the behavior of the saltwater wedge for the conditions examined the experiments showed that an upper saline plume formed in the intertidal zone due to tide induced seawater circulation the presence of the upper saline plume shifted the fresh groundwater discharge zone seaward to the low tide mark and restricted the intrusion of the saltwater wedge the overall seawater intrusion extent as indicated by the wedge toe location was reduced significantly compared with the nontidal static case results from the numerical model matched these experimental observations and further demonstrated the similar type of tidal influence on the saltwater wedge in a field scale aquifer system the glover 1959 solution for predicting the saltwater wedge was modified to account for the tidal effect by including the tide induced circulation as a recharge to the aquifer the findings highlight the significant impact of the tide in modulating the groundwater behavior and salt freshwater dynamics not only within but also landward of the intertidal zone

groundwater pumping in head controlled coastal systems the role of lateral boundaries in quantifying the interface toe location and maximum pumping rate summary the current study explores quantitatively the impact of lateral impermeable boundaries on groundwater pumping in head controlled coastal systems based on the potential theory and the image well superposition method we compare the interface toe location and maximum pumping rate among three scenarios that assume s1 an infinite domain width and a finite domain length s2 a finite domain width and length and ss an infinite domain width and length focusing exclusively on boundary effects the upstream freshwater discharge is assumed the same for all scenarios regardless of the variation in domain size it is found that the impact from both inland and lateral boundaries could play a significant role on the interface toe location and maximum pumping rate defined as the maximum allowable pumping rate that will not lead to pumping saltwater depending on sizes of domain length and width since the impacts of inland fixed head boundary and lateral impermeable boundaries are contrary on the maximum interface toe location defined as the farthest inland point of the interface toe under pumping condition and maximum pumping rate they can be offset under certain critical conditions such that the results of the two quantitative indictors i e the maximum interface toe location and maximum pumping rate in s2 are close to those in ss in particular a linear equation is derived to reflect the relationship between the domain width and length under such critical conditions and expressed as l 0 87 w 0 62 w 1 or l 1 5 in which w and l are the domain width and length normalized by the distance between the coastline and pumping well when l 0 87 w 0 62 the impact from lateral overcomes that from inland producing a larger maximum interface toe location and a lower maximum pumping rate than those in ss when l w 0 62 by contrast the impact from inland exceeds that from lateral and hence resulting in a smaller maximum interface toe location and a higher maximum pumping rate it is expected that the results developed in the current study could support the design of numerical models and 3d laboratory experiments as well as the assessment of domain size impact on pumping in head controlled coastal groundwater systems

analytical single potential sharp interface solutions for regional seawater intrusion in sloping unconfined coastal aquifers with pumping and recharge summary contamination of groundwater by intruding seawater is a major problem in many parts of the world this work derives novel analytical solutions for addressing this problem by extending the girinskii strack concept of discharge potential to represent regional steady state sharp interface seawater intrusion in a sloping unconfined coastal aquifer the aquifer has hydraulic conductivity k is recharged uniformly at the rate r receives an inflow at its land boundary and has a collector trough or well gallery idealised as line sink located at the distance lw from the coastline that penetrates the aquifer and draws groundwater at the rate qw the theory rests on the approximation of a linearised gravity part of the hydraulic potential analytical solutions for the discharge potential are derived through which the hydraulic head the flow depth and the sharp interface and particularly the location of the interface toe lt are also determined these solutions simplify to known results for the horizontal aquifer case the utility and robustness to uncertainty regarding the base slope of the results in applications is demonstrated in the regional example of the akrotiri coastal aquifer cyprus recasting the problem in non dimensional form provides a relationship for the dependence of the relative interface toe location lt lw on the appropriately normalised difference between the groundwater flow just up gradient of the collector trough qo and the pumping rate qw given values of the base slope r k and hsea lw where hsea is the sea surface elevation above the aquifer base at the coastline that relationship frames a common groundwater management problem in coastal aquifers subject to a certain exploitation scheme with lt as decision variable in an exploratory demonstration study non dimensional sets of performance curves are calculated for the regional akrotiri aquifer in general the derived analytical solutions can be used for first order assessments of seawater intrusion vulnerability and management possibilities across a wide range of current regional coastal aquifer conditions and or projected water demand groundwater management and climatic change scenarios

crustal architecture and tectonic evolution of the gulf of cadiz sw iberian margin at the convergence of the eurasian and african plates 1 the gulf of cadiz located at the southwestern iberian margin is characterized by widespread seismicity compressional and strike slip fault plane solutions and by a large elongated positive free air gravity anomaly the gulf of cadiz gravity high gcgh multichannel seismic profiles across and along gcgh together with bathymetric and gravity data allow us to study in detail the tectonic architecture and crustal structure of the gulf of cadiz the upper shelf and slope of the gulf of cadiz includes the main structural domains of the betic fold and thrust belt in the middle part of the gulf the paleozoic basement crops out on the shallow guadalquivir bank and is associated with the largest signature of the gcgh whereas toward the outer part of the gulf the basement deepens progressively a large nw se normal fault and conjugate ne sw faults define a prominent basement high associated with the gcgh modeling of the gcgh suggests localized crustal thinning of 10 km along the central part of the gulf of cadiz probably generated during the mesozoic rifting episode between the iberian and african plates concentric wedges of fold and thrust belts and large allochthonous masses were emplaced in the gulf of cadiz during the neogene compressional phase the final emplacement of these units becomes progressively young from the se pre early langhian toward the foreland in the nw late tortonian seafloor surface ruptures pockmarks and submarine landslides provide evidence of active faulting in the gulf of cadiz to accommodate the present day convergence between the african and eurasian plates previously extensional faults have probably been reactivated and inverted at depth as suggested by the intermediate depth seismicity

effects of kinetic mass transfer and transient flow conditions on widening mixing zones in coastal aquifers 1 the width of a mixing zone between freshwater and seawater is important primarily because it directly reflects the extent of mixing and the growth and decay of the mixing zone indicates changes of the flow regime and water exchange between freshwater and coastal seawater wide mixing zones have been found in many coastal aquifers all over the world however the mechanisms responsible for wide mixing zones are not well understood this work examines the hypothesis that kinetic mass transfer coupled with transient conditions which create the movement of the mixing zone may widen mixing zones in coastal aquifers the hypothesis is tested by conducting two dimensional numerical simulations based on a variable density groundwater model for a scaled tank model and a field scale model periodic water levels representing periodic tidal motion and freshwater table fluctuations are imposed at the seaward and landward boundary respectively which cause the movement of the mixing zone both the scaled tank model and the field model show that the combination of the moving mixing zone and kinetic mass transfer may significantly enhance the extent of mixing and create a wider mixing zone than the models without kinetic mass transfer in addition sensitivity analyses indicate that a larger capacity ratio immobile porosity mobile porosity of mass transfer leads to a wider mixing zone and the maximum width of the mixing zone may be reached for a given capacity ratio when the mean retention time scale in the immobile domain the reciprocal of mass transfer rate and the period of water level fluctuations are comparable

a formulation for vertically integrated groundwater flow in a stratified coastal aquifer we present the comprehensive discharge potential for steady three dimensional flow in horizontally stratified coastal aquifers with a horizontal base and a vertical coastline the gradient of this comprehensive potential gives the vertically integrated discharge throughout the aquifer i e the specific discharge vector as a function of three dimensional space integrated over the saturated portion of the aquifer the boundary values of the comprehensive potential along the coast can be computed precisely given the geometry of the aquifer the hydraulic conductivities of the strata the elevations of the horizontal planes that separate the strata and the elevation of the impermeable base of the aquifer relative to sea level boundary conditions of the comprehensive potential may either be given in terms of its gradient or computed from given heads along the boundaries the governing equation of the comprehensive potential is the poisson equation in areas of infiltration and the laplace equation elsewhere the computation of interface elevations piezometric heads and the vertical distribution of flow requires that an assumption be made regarding the relation between the comprehensive potential and piezometric heads we adopt the dupuit forchheimer approximation for this purpose and make use of the ghyben herzberg equation we present several applications of the approach and find that the stratification may have a significant effect on the boundary value of the comprehensive potential and thus on the flow rates in the aquifer this article is protected by copyright all rights reserved

theoretical and conceptual models of subsurface hillslope flows 1 theoretical and conceptual models for predicting the subsurface flow in a sloping aquifer are presented one category of models is of the lumped conceptual type that is based on combining the continuity equation with discharge storage relationships derived from the steady state solutions of the linearized boussinesq equation the second categories of models are derived from the linearized unsteady boussinesq equation using the method of green s function the green s function solution determines the water table profile and the aquifer outflow for nonuniform and nonsteady recharge distribution arbitrary initial water table profile and time varying stream level at the downstream end the latter theoretical models pertain to a finite domain and to a semi infinite domain and are of two types depending on the linearization approach the conceptual and theoretical models are used to derive the outflow and the cumulative outflow expressions for a particular set of conditions and a comparative analysis is carried out semi infinite aquifer models generate almost the same results as the more complicated finite aquifer models and the quasi steady state models perform as well as the nonsteady ones for long recharge events the kinematic wave model is also shown to provide a good approximation of boussinesq models for steep slopes and high hydraulic conductivity the application of the various models is also illustrated for three published experimental data the present models can be easily incorporated in catchments models and can provide a suitable framework for aquifer parameter estimation base flow separation and recession analysis and analysis of drainage in landfills

active deformation in old oceanic lithosphere and significance for earthquake hazard seismic imaging of the coral patch ridge area and neighboring abyssal plains sw iberian margin recently acquired high resolution multichannel seismic profiles together with bathymetric and sub bottom profiler data from the external part of the gulf of cadiz iberia africa plate boundary reveal active deformation involving old mesozoic oceanic lithosphere this area is located 180 km offshore the sw iberian peninsula and embraces the prominent ne sw trending coral patch ridge and part of the surrounding deep horseshoe and seine abyssal plains e w trending dextral strike slip faults showing surface deformation of flower like structures predominate in the horseshoe abyssal plain whereas ne sw trending compressive structures prevail in the coral patch ridge and seine hills although the coral patch ridge region is characterized by subdued seismic activity the area is not free from seismic hazard most of the newly mapped faults correspond to active blind thrusts and strike slip faults that are able to generate large magnitude earthquakes mw 7 2 8 4 this may represent a significant earthquake and tsunami hazard that has been overlooked so far

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

assessment of the impact of sea level rise on seawater intrusion in sloping confined coastal aquifers abstract previous studies of the impact of sea level rise on seawater intrusion slr swi are mostly based on horizontal coastal aquifers despite that most coastal aquifers are sloping a recent study has shown that the effect of aquifer slope can not be neglected when assessing slr swi in unconfined coastal aquifers however the effect of slope in confined aquifers has not been evaluated in this study we apply existing analytical solutions to quantify the effect of the slope of both upper and lower confining layers on slr swi the results show that for flux controlled sloping confined coastal aquifer systems slr does not change the steady state interface location consistent with previous findings for horizontal aquifers therefore our analysis focuses on head controlled sloping confined coastal aquifer systems for which we find the assumption of horizontal confining units causes significant errors we demonstrate this by assessing the sensitivities of the seawater toe location and seawater volume to slr for various combinations of sloping confining layers the results indicate that the influence of the slope on slr swi is small in thin confined aquifers however the slope is an important factor in thick confined aquifers the influence of the slope in the lower confining layer on slr swi is much greater than that of the upper confining layer aquifers that thin towards the sea are most susceptible to slr swi whereas those that thin towards inland are least susceptible the assessment of slr swi in sloping confined coastal aquifers in the current study demonstrates application of a rapid first order assessment tool that can be applied to a wide range of other sloping coastal confined aquifer problems

focal mechanisms for sub crustal earthquakes in the gulf of cadiz from a dense obs deployment 1 an eleven month deployment of 25 ocean bottom seismometers provides an unprecedented opportunity to study low magnitude local earthquakes in the complex transpressive plate boundary setting of the gulf of cadiz known for the 1755 lisbon earthquake and tsunami 36 relocated earthquakes ml 2 2 to 4 8 concentrate at 40 60 km depth near the base of the seismogenic layer in 140 ma old oceanic mantle lithosphere and roughly align along two perpendicular nne ssw and wnw ese striking structures first motion focal mechanisms indicate compressive stress for the cluster close to the northern horseshoe fault termination which trends perpendicular to plate convergence focal mechanisms for the second cluster near the southern termination of the horseshoe fault indicate a strike slip regime providing evidence for present day activity of a dextral shear zone proposed to represent the eurasia africa plate contact we hypothesize that regional tectonics is characterized by slip partitioning

steady state phreatic surfaces in sloping aquifers 1 steady state groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented using the dupuit approximation by an ordinary differential equation of the abel type y x y x a y x x 0 whose analytical solution is derived in this work this article first investigates the case of zero saturated thickness at the upstream boundary a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary a variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary this variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer the latter being on sloping terrain in this instance analytical solutions for the phreatic surface s steady state geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface these solutions are of practical interest in drainage studies slope stability and runoff formation investigations it is shown that the flow factor a tan where k n and tan are the hydraulic conductivity vertical recharge and aquifer slope respectively has a commanding role on the phreatic surface s solutions two computational examples illustrate the implementation of this article s results

groundwater flow to a pumping well in a sloping fault zone unconfined aquifer this study develops a mathematical model for simulating the hydraulic head distribution in response to pumping in a sloping fault zone aquifer under a water table boundary condition a two dimensional equation with a sink term representing the pumping is used for describing the head distribution in the aquifer in addition a first order free surface equation is adopted to represent the change in water table at the outcrop the analytical solution of the model derived by the laplace and finite fourier cosine transforms is expressed in terms of a double series a finite difference solution within a deformable grid framework is developed to assess the solution obtained by specifying the free surface equation at the outcrop based on the analytical solution we have found that the model s prediction tends to overestimate drawdown in a late pumping period the temporal head distribution is independent of the aquifer slope if the water table change is small and exhibits a double humped shape due to the effect of the free surface the temporal drawdown predicted from the analytical solution is further compared with those measured from a pumping test conducted in northern portugal

pumping optimization in saltwater intruded coastal aquifers this paper investigates the hydraulic issues of pumping well optimization in saltwater intruded coastal aquifers the well field includes freshwater outflow pumping wells and a recharge canal the objective is to maximize the total pumping rate subject to the constraint of no intrusion of the saltwater front into the wells analytical solutions are presented for one well two well and one well with recharge canal problems for problems involving multiple pumping wells a structured messy genetic algorithm is used to search for the optimal solution

some analytical solutions of the linearized boussinesq equation with recharge for a sloping aquifer subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the boussinesq equation several attempts have been made to solve this partial differential equation and exact solutions have been found for specific situations in the case of a sloping aquifer brutsaert 1994 suggested linearizing the equation to calculate the unit response of the hillslope in this paper we first apply the work of brutsaert by assuming a constant recharge to the groundwater table the solution describes the groundwater table levels and the outflow in function of time then an analytical expression is derived for the steady state solution by allowing time to approach infinity this steady state water table is used as an initial condition to derive another analytical solution of the boussinesq equation this can then be used in a quasi steady state approach to compute outflow under changing recharge conditions subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the boussinesq equation several attempts have been made to solve this partial differential equation and exact solutions have been found for specific situations in the case of a sloping aquifer brutsaert 1994 suggested linearizing the equation to calculate the unit response of the hillslope in this paper we first apply the work of brutsaert by assuming a constant recharge to the groundwater table the solution describes the groundwater table levels and the outflow in function of time then an analytical expression is derived for the steady state solution by allowing time to approach infinity this steady state water table is used as an initial condition to derive another analytical solution of the boussinesq equation this can then be used in a quasi steady state approach to compute outflow under changing recharge conditions

deep water seamounts a potential source of tsunami generated by landslides the hirondelle seamount ne atlantic abstract submarine mass failures represent one of the most significant marine geo hazards their importance as a major contributor to tsunami generation and hazard has been recognized over the last 20 30 years this study investigates a newly mapped submarine landslide the south hirondelle landslide shl and its potential to generate a tsunami and to threat the surrounding coasts the shl is located 150 km offshore south west iberia along the southern flank of the hirondelle seamount here available swath bathymetry and one multichannel seismic profile show the presence of large geometrically well constrained deep water landslide deposit of about 500 km 3 and its associated scar the failure likely occurred in one single event and according to a detailed numerical modelling of the landslide dynamics and of the resulting water propagation the mass failure generated a mega tsunami with significant impact along the surrounding coastal areas of iberia and morocco this result strongly supports the inclusion of tsunami induced by deep water submarine landslides in the marine geo hazard assessment of the north east atlantic region

seawater intrusion in response to sea level rise in a coastal aquifer with a general head inland boundary seawater intrusion in response to sea level rise has been studied extensively in recent years by assuming largely a constant head or constant flux inland boundary condition however these two types of boundary conditions are not sufficient when the inland edge of the model domain is neither natural groundwater nor known hydraulic boundaries under these circumstances a general head inland boundary condition capable of characterizing the hydraulic response of model boundaries is needed previous studies adopting the general head inland boundary condition to assess coastal aquifer vulnerability to sea level rise are limited and all based on numerical modeling in this study we derive analytical solutions of the interface toe location in both confined and unconfined coastal systems with a general head inland boundary condition comparison among the performances of the three different types of inland boundary conditions in evaluating the sea level rise impact on aquifer salinization is carried out by assuming the same initial system condition it is found that the displacement of the interface toe predicted using a general head inland boundary is between those of using a constant head upper bound and constant flux lower bound inland boundary depending on the values of two general head boundary parameters i e hydraulic conductance and reference head more importantly analytical solutions developed could serve as a tool for calibrating the two boundary parameters defined in the general head boundary condition for site specific assessments

research on the tunnel excavated in urumqi glacier no 1 tianshan glaciological station china a tunnel was excavated in urumqi glacier no 1 at the tianshan glaciological station ice temperature ice displacement deformation and basal sliding etc were observed at regular intervals it is shown that the temperature near the glacier bed is close to the melting point and that the largest proportion of the overall glacier motion is within the lowermost ice layers the glacier ice is in a state of compression the maximum shear strain increases towards the entrance of the tunnel corresponding to the change in slope of the ice surface and also towards the bedrock

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

pumping management of coastal aquifers using analytical models of saltwater intrusion 1 analytical models of saltwater intrusion in coastal aquifers of finite size are developed and utilized in an optimization methodology for determining the optimal pumping rates the models are based on the sharp interface approximation and the ghyben herzberg relation the governing equations are expressed in terms of a single potential and are solved analytically using the method of images to account for the aquifer boundaries the analytical models consider ambient flow and surface recharge the results are compared to numerical simulations indicating a good match as the number of images is increased the objective of optimization is to maximize the total pumping from the aquifer and a set of constraints protect the wells from saltwater intrusion the constraints are expressed using the analytical saltwater intrusion models two different constraint formulations are investigated the toe constraint formulation protects the wells from saltwater intrusion by not allowing the toe of the interface to reach the wells this formulation results in a nonlinear optimization problem which is solved using sequential quadratic programming sqp the potential constraint formulation on the other hand protects the wells by maintaining a potential at the wells larger than the toe potential this formulation results in a linear optimization problem which is solved using the simplex method several simulation runs indicate that the optimal solution is very sensitive to variations of recharge rates hydraulic conductivity heterogeneities etc the linear programming formulation besides being computationally simpler provides a safer solution than the nonlinear formulation

a correction for dupuit forchheimer interface flow models of seawater intrusion in unconfined coastal aquifers interface flow models that use the dupuit forchheimer df approximation for assessing the freshwater lens and the seawater intrusion in coastal aquifers lack representation of the gap through whic

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

exact versus dupuit interface flow in anisotropic coastal aquifers the dupuit solution for interface flow toward the coast in a confined aquifer is compared to a new exact solution which is obtained with the hodograph method and conformal mapping the position of the toe of the interface is a function of two dimensionless parameters the ratio of the hydraulic gradient upstream of the interface where flow is one dimensional over the dimensionless density difference and the ratio of the horizontal hydraulic conductivity over the vertical hydraulic conductivity the dupuit interface which neglects resistance to vertical flow is a very accurate approximation of the exact interface for isotropic aquifers the difference in the position of the toe between the exact and dupuit solutions increases when the vertical anisotropy increases for highly anistropic aquifers it is proposed to add an effective resistance layer along the bottom of the sea in dupuit models the resistance of the layer is chosen such that the head in the dupuit model is equal to the head in the exact solution upstream of the interface where flow is one dimensional