Modelling coastal ground‐ and surface‐water interactions using an integrated approach

Beach water table fluctuations have an impact on the transport of beach sediments and the exchange of solute and mass between coastal aquifer and nearby water bodies. Details are given of the refinement of a dynamically integrated ground‐ and surface‐water model, and its application to study ground‐ and surface‐water interactions in coastal regions. The depth‐integrated shallow‐water equations are used to represent the surface‐water flow, and the extended Darcy's equation is used to represent the groundwater flow, with a hydrostatic pressure distribution being assumed to apply for both these two types of flows. At the intertidal region, the model has two layers, with the surface‐water layer being located on the top of the groundwater layer. The governing equations for these two types of flows are discretized in a similar manner and they are combined to give one set of linear algebraic equations that can be solved efficiently. The model is used to predict water level distributions across sloping beaches, where the water table in the aquifer may or may not decouple from the free water surface. Five cases are used to test the model for simulating beach water table fluctuations induced by tides, with the model predictions being compared with existing analytical solutions and laboratory and field data published in the literature. The numerical model results show that the integrated model is capable of simulating the combined ground‐ and surface‐water flows in coastal areas. Detailed analysis is undertaken to investigate the capability of the model. Copyright © 2009 John Wiley & Sons, Ltd.     

Modelling groundwater/surface water interaction in a managed riparian chalk valley wetland

Understanding hydrological processes in wetlands may be complicated by management practices and complex groundwater/surface water interactions. This is especially true for wetlands underlain by permeable geology, such as chalk. In this study, the physically based, distributed model MIKE SHE is used to simulate hydrological processes at the Centre for Ecology and Hydrology River Lambourn Observatory, Boxford, Berkshire, UK. This comprises a 10‐ha lowland, chalk valley bottom, riparian wetland designated for its conservation value and scientific interest. Channel management and a compound geology exert important, but to date not completely understood, influences upon hydrological conditions. Model calibration and validation were based upon comparisons of observed and simulated groundwater heads and channel stages over an equally split 20‐month period. Model results are generally consistent with field observations and include short‐term responses to events as well as longer‐term seasonal trends. An intrinsic difficulty in representing compressible, anisotropic soils limited otherwise excellent performance in some areas. Hydrological processes in the wetland are dominated by the interaction between groundwater and surface water. Channel stage provides head boundaries for broad water levels across the wetland, whilst areas of groundwater upwelling control discrete head elevations. A relic surface drainage network confines flooding extents and routes seepage to the main channels. In‐channel macrophyte growth and its management have an acute effect on water levels and the proportional contribution of groundwater and surface water. The implications of model results for management of conservation species and their associated habitats are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluating the interactions between surface water and groundwater in the arid mid-eastern Yanqi Basin,northwestern China

The environment of Bosten Lake in the Mid-Eastern Yanqi Basin (MEYB), an arid inland area in northwest China, has deteriorated greatly due to increasing groundwater exploitation and changes in the interactions between groundwater and surface water. This study intended to simulate the spatio-temporal variability of groundwater and surface water across the entire MEYB over the period 2000–2013. The applicable groundwater flow model and mass balance calculation method for river water were constructed to evaluate the change in groundwater recharged by and discharged to different segments of the Kaidu River. Simulation results show that the entire river seepage in the MEYB increased from 1.05 to 6.17 × 10⁸ m³/year between 2000 and 2013. The increasing river seepage, induced by increasing groundwater exploitation, plays the most important role in the water level decline in the downstream reaches of the Kaidu River and in Bosten Lake. This implies that the current utilization of groundwater resources in the MEYB is unsustainable.     

Effects of intensive aquifers exploitation on groundwater salinity in coastal wetlands

The coastal plain of the Río de la Plata constitutes a large wetland which develops on the right margin of the river estuary. Anthropic activities such as intensive exploitation of groundwater carried out in the vicinity of the wetland can modify the natural hydrological regime. The aim of this work is to asses the effects of intensive aquifer exploitation in coastal wetlands using hydrogeological models. Such models allow to evaluate changes in the environmental conditions of wetland at regional level. The hydrogeological model exposed in this work shows how the intensive groundwater exploitation affects the wetland area, generating important variations both in the groundwater flows and in the salinity of the groundwater. Identification of these modifications to the environment is important to generate guidelines leading to minimize these affectations.     

A study of interaction between surface water and groundwater using environmental isotope in Huaisha River basin

The surface water and groundwater are important components of water cycle, and the interaction between surface water and groundwater is the important part in water cycle research. As the effective tracers in water cycle research, environmental isotope and hydrochemistry can reveal the interrelationships between surface water and groundwater effectively. The study area is the Huaisha River basin, which is located in Huairou district, Beijing. The field surveying and sampling for spring, river and well water were finished in 2002 and 2003. The hydrogen and oxygen isotopes and water quality were measured at the laboratory. The spatial characteristics in isotope and evolution of water quality along river lines at the different area were analyzed. The altitude effect of oxygen isotope in springs was revealed, and then using this equation, theory foundation for deducing recharge source of spring was estimated. By applying the mass balance method, the annual mean groundwater recharge rate at the catchment was estimated. Based on the groundwater recharge analysis, combining the hydrogeological condition analysis, and comparing the rainfall-runoff coefficients from the 1960s to 1990s in the Huaisha River basin and those in the Chaobai River basin, part of the runoff in the Huaisha River basin is recharged outside of this basin, in other words, this basin is an un-enclosed basin. On the basis of synthetically analyses, combining the compositions of hydrogen and oxygen isotopes and hydrochemistry, geomorphology, geology, and watershed systems characteristics, the relative contributions between surface water and groundwater flow at the different areas at the catchments were evaluated, and the interaction between surface water and groundwater was re- vealed lastly.     

A coupled physical-biochemical lake model for forecasting water quality

A new one-dimensional numerical model that includes physical and biochemical processes has been developed. The biochemical processes, influenced by the lake dynamics, are required for forecasting water quality. The model is used to investigate the effects of different internal restoration measures, such as artificial mixing, input of oxygen and drainage of deep water.The model is applied to the Northern Basin of Lake Lugano, a Swiss-Italian border lake. The lake is highly eutrophic and chemically stratified throughout the year. The model was calibrated over one year and validated over a period of several years. The results agree well with the measured data. The coupled model reproduces the observed depth dependency of conductivity even during long simulation times. Due to the predominant mixing, decoupled physical models cannot maintain such gradients. The forecasting capabilities of the model are demonstrated for different case studies. The impact of restoration measures on water quality is rather small. Best results are achieved by reducing the external nutrient loading. Caution is recommended for internal measures as these have to be studied in greater detail.     

Geomorphologic control on pollutant retardation at the groundwater–surface water interface

The results of research on the pollutant retardation potential of permeable riverbed sediments in catchments with significant groundwater–surface water (GW-SW) interaction are presented. The fraction of organic carbon and cation exchange capacity of fluvial sediments in various geomorphologic environments have been quantified. Sediments in selected reaches of the rivers Tern and Leith (UK), from the underlying Permian sandstone aquifers, and from along the length of the rivers Severn and Eden into which the Tern and Leith discharge have been investigated. Statistical analyses show significant variation in the geochemistry and pollutant retardation potential of sediments from different geomorphologic features, and between upland and lowland rivers. The sorption potential of fine-grained sediments deposited in pools was greater than sand in runs and coarser deposits in riffles. Similarly, sediments in lowland rivers were found to have a greater retardation potential than those in upland rivers. There was generally greater retardation potential in fluvial sediments of all types than in the underlying aquifers, and in lowland rivers the fluvial sediment retardation potential greatly dominated that of the aquifer. The findings demonstrate the potential for pollutant retardation processes in riverbed sediments of sandstone catchments, and suggest that consideration of retardation processes at the groundwater–surface water interface should be included into environmental risk-assessment studies, in order to better assess and manage the effects of contaminated groundwater discharges to rivers, particularly in lowland catchments. Copyright © 2008 John Wiley & Sons, Ltd.     

Impact of water transfer on interaction between surface water and groundwater in the lowland area of North China Plain

The contradiction between the freshwater shortage and the large demand of freshwater by irrigation was the key point in cultivated lowland area of North China Plain. Water transfer project brings fresh water from water resource‐rich area to water shortage area, which can in turn change the hydrological cycle in this region. Major ions and stable isotopes were used to study the temporal variations of interaction between surface water and groundwater in a hydrological year after a water transfer event in November 2014. Irrigation canal received transferred Yellow River, with 2.9% loss by evaporation during water transfer process. The effect of transferred water on shallow groundwater decreased with increasing distance from the irrigation canal. Pit pond without water transfer receives groundwater discharge. During dry season after water transfer event, shallow groundwater near the irrigation canal was recharged by lateral seepage and deep percolation of irrigation, whereas shallow groundwater far from irrigation canal was recharged by deep percolation of deep groundwater irrigation. Canal water lost by evaporation was 2.7–17.4%. Influence of water transfer gradually disappeared until March as the water usage of agricultural irrigation increased. In the dry season, groundwater discharged to irrigation canal and pond; 2.2–31.6% canal water and 11.3–20.0% pond water were lost by evaporation. In the rainy season (June to September), surface water was fed mainly by precipitation and surface run‐off, whereas groundwater was recharged by infiltration of precipitation. The two‐end member mix model showed that the mixing ratio of precipitation in pond and irrigation canal were 73–83.4% (except one pond with 28.1%) and 77.3–99.9%, respectively. Transferred water and precipitation were the important recharge sources for shallow groundwater, which decreased groundwater salinity in cultivated lowland area of North China Plain. With the temporary and spatial limitation of water transfer effects, increased water transfer amounts and frequency may be an effective way of mitigating regional water shortage. In addition, reducing the evaporation of surface water is also an important way to increase the utilization of transfer water.     

Understanding the extent of interactions between groundwater and surface water through major ion chemistry and multivariate statistical techniques

The present work examines the possible use of major ion chemistry and multivariate statistical techniques as a rapid and relatively cost‐effective method of identifying the extent of groundwater and surface water (GW–SW) interaction in an urban setting. The original hydrogeochemical dataset consists of groundwater (n = 114), stream water (n = 42) and drain water (n = 24) samples, collected twice in a year for the pre‐ and post‐monsoon seasons, for three successive years along an 8 km reach of the Delhi segment of River Yamuna, India. The dynamic and similar seasonal changes of hydro‐geochemical facies and major ion trends of river, drain and groundwater samples indicate the existence of an empirical relationship between GW and SW. Results of both R‐ and Q‐mode factor and cluster analyses highlight multi‐scale control of the fluid exchange distributions, with distinct seasonal alteration in mode and extent of GW–SW interaction, namely, the influence of the mixing zones between urban river and groundwater and the pattern of groundwater flow through the river bed. Hierarchical cluster analysis (HCA) of sampling locations efficiently illustrates different groups that comprise samples severely influenced by contaminated surface water downstream and the upstream fresh water samples. These results substantiate the strong exchange processes between GW and SW all along the stretch. The study shows that the combination of an empirical and statistical relationship between different ionic species and sampling locations can provide greater confidence in identifying the extent of GW–SW interaction/exchange processes. Copyright © 2008 John Wiley & Sons, Ltd.     

Mapping groundwater discharge to a coastal lagoon using combined spatial airborne thermal imaging,radon (222Rn) and multiple physicochemical variables

Coastal lagoons are significant wetland environments found on coastlines throughout the world. Groundwater seepage may be a key component of lagoon water balances, though only a few studies have investigated large (>100 km²) coastal lagoons. In this study, we combined airborne thermal infrared imagery with continuous measurements of radon (²²²Rn—a natural groundwater tracer), conductivity, water temperature and dissolved oxygen to map groundwater seepage to a large coastal lagoon in New Zealand. We found evidence of seepage along the margins of the lagoon but not away from the margins. Our findings confirmed previously known seepage zones and identified new potential locations of groundwater inflow. Both point source and diffuse seepage occurred on the western and northwestern margins of the lagoon and parallel to the barrier between the lagoon and sea. These observations imply geologic controls on seepage. The combination of remote sensing and in-situ radon measurements allowed us to effectively map groundwater discharge areas across the entire lagoon. Combined, broad-scale qualitative methods built confidence in our interpretation of groundwater discharge locations in a large, dynamic coastal lagoon.     

Geomorphic controls of perched groundwater interaction with natural ridge-top depressional wetlands

Geographically isolated wetlands (GIWs) are commonly reported as having hardpan or low hydraulic conductivity units underneath that produce perched groundwater, which can sustain surface water levels independently of regional aquifer fluctuations. Despite the potential of GIW-perched aquifer systems to provide important hydrological and ecological functions such as groundwater storage and native amphibian habitat, little research has studied the hydrologic controls and dynamics of these systems. We compared several ridge-top depressional GIW-perched groundwater systems to investigate the role of watershed morphology on hydroregime and groundwater-surface water interaction. Ridge-top depressional wetlands in the Daniel Boone National Forest, Kentucky were chosen because they offer natural controls such as lack of apparent connection to surface water bodies, similar climate, and similar soils. Three wetlands with different topographic slopes and hillslope structures were mapped to distinguish key geomorphic parameters and monitored to characterize groundwater-surface water interaction. Wetlands with soil hummocks and low upland slopes transitioned from infiltration to groundwater discharge conditions in the spring and during storm events. The magnitude and duration of this transition fell along a continuum, where higher topographic slopes and steeper uplands produced comparably smaller and shorter head reversals. This demonstrates that ridge-top GIW-perched groundwater systems are largely sensitive to the runoff-recharge relationship in the upland area which can produce significant groundwater storage on a small-scale.     

A regional coupled approach to water cycle prediction during winter 2013/14 in the United Kingdom

A regional coupled approach to water cycle prediction is demonstrated for the 4-month period from November 2013 to February 2014. This provides the first multi-component analysis of precipitation, soil moisture, river flow and coastal ocean simulations produced by an atmosphere-land-ocean coupled system focussed on the United Kingdom (UK), running with horizontal grid spacing of around 1.5 km across all components. The Unified Model atmosphere component, in which convection is explicitly simulated, reproduces the observed UK rainfall accumulation (r² of 0.95 for water day accumulation), but there is a notable bias in its spatial distribution—too dry over western upland areas and too wet further east. The JULES land surface model soil moisture state is shown to be in broad agreement with a limited number of cosmic-ray neutron probe observations. A comparison of observed and simulated river flow shows the coupled system is useful for predicting broad scale features, such as distinguishing high and low flow regions and times during the period of interest but are less accurate than optimized hydrological models. The impact of simulated river discharge on NEMO model simulations of coastal ocean state is explored in the coupled modelling framework, with comparisons provided relative to experiments using climatological river input and no river input around the UK coasts. Results show that the freshwater flux around the UK contributes of order 0.2 psu to the mean surface salinity, and comparisons to profile observations give evidence of an improved vertical structure when applying simulated flows. This study represents the first assessment of the coupled system performance from a hydrological perspective, with priorities for future model developments and challenges for evaluation of such systems discussed.     

First‐order exchange coefficient coupling for simulating surface water–groundwater interactions: parameter sensitivity and consistency with a physics‐based approach

Distributed hydrologic models capable of simulating fully‐coupled surface water and groundwater flow are increasingly used to examine problems in the hydrologic sciences. Several techniques are currently available to couple the surface and subsurface; the two most frequently employed approaches are first‐order exchange coefficients (a.k.a., the surface conductance method) and enforced continuity of pressure and flux at the surface‐subsurface boundary condition. The effort reported here examines the parameter sensitivity of simulated hydrologic response for the first‐order exchange coefficients at a well‐characterized field site using the fully coupled Integrated Hydrology Model (InHM). This investigation demonstrates that the first‐order exchange coefficients can be selected such that the simulated hydrologic response is insensitive to the parameter choice, while simulation time is considerably reduced. Alternatively, the ability to choose a first‐order exchange coefficient that intentionally decouples the surface and subsurface facilitates concept‐development simulations to examine real‐world situations where the surface‐subsurface exchange is impaired. While the parameters comprising the first‐order exchange coefficient cannot be directly estimated or measured, the insensitivity of the simulated flow system to these parameters (when chosen appropriately) combined with the ability to mimic actual physical processes suggests that the first‐order exchange coefficient approach can be consistent with a physics‐based framework. Copyright © 2009 John Wiley & Sons, Ltd.     

A conceptual hydrologic model for a forested Carolina bay depressional wetland on the Coastal Plain of South Carolina,USA

This paper describes how climate influences the hydrology of an ephemeral depressional wetland. Surface water and groundwater elevation data were collected for 7 years in a Coastal Plain watershed in South Carolina USA containing depressional wetlands, known as Carolina bays. Rainfall and temperature data were compared with water‐table well and piezometer data in and around one wetland. Using these data a conceptual model was created that describes the hydrology of the system under wet, dry, and drought conditions. The data suggest this wetland operates as a focal point for groundwater recharge under most climate conditions. During years of below‐normal to normal rainfall the hydraulic gradient indicated the potential for groundwater recharge from the depression, whereas during years of above‐normal rainfall, the hydraulic gradient between the adjacent upland, the wetland margin, and the wetland centre showed the potential for groundwater discharge into the wetland. Using high‐resolution water‐level measurements, this groundwater discharge condition was found to hold true even during individual rainfall events, especially under wet antecedent soil conditions. The dynamic nature of the hydrology in this Carolina bay clearly indicates it is not an isolated system as previously believed, and our groundwater data expand upon previous hydrologic investigations at similar sites which do not account for the role of groundwater in estimating the water budget of such systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Groundwater–surface water interactions in a lowland watershed: source contribution to stream flow

The lower coastal plain of the Southeast USA is undergoing rapid urbanisation as a result of population growth. Land use change has been shown to affect watershed hydrology by altering stream flow and, ultimately, impairing water quality and ecologic health. However, because few long‐term studies have focused on groundwater–surface water interactions in lowland watersheds, it is difficult to establish what the effect of development might be in the coastal plain region. The objective of this study was to use an innovative improvement to end‐member mixing analysis (EMMA) to identify time sequences of hydrologic processes affecting storm flow. Hydrologic and major ion chemical data from groundwater, soil water, precipitation and stream sites were collected over a 2‐year period at a watershed located in USDA Forest Service's Santee Experimental Forest near Charleston, South Carolina, USA. Stream flow was ephemeral and highly dependent on evapotranspiration rates and rainfall amount and intensity. Hydrograph separation for a series of storm events using EMMA allowed us to identify precipitation, riparian groundwater and streambed groundwater as main sources to stream flow, although source contribution varied as a function of antecedent soil moisture condition. Precipitation, as runoff, dominated stream flow during all storm events while riparian and streambed groundwater contributions varied and were mainly dependent on antecedent soil moisture condition. Sensitivity analyses examined the influence of 10% and 50% increases in analyte concentration on EMMA calculations and found that contribution estimates were very sensitive to changes in chemistry. This study has implications on the type of methodology used in traditional forms of EMMA research, particularly in the recognition and use of median end‐member water chemistry in hydrograph separation techniques. Potential effects of urban development on important hydrologic processes (groundwater recharge, interflow, runoff, etc.) that influence stream flow in these lowland watersheds were qualitatively examined. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of groundwater flow-through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns

A numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes, wetlands and ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and stable isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake. Many different possible flow regimes are identified, however, in this paper attention is focused on flow-through water bodies, as these are the flow regimes observed in field validation. Two shallow lakes on the Swan Coastal Plain of south-west Western Australia are the subject of field studies where hydrogeochemical and stable isotopes are used to validate the flow-through groundwater flow regime predicted by the modelling confirming the validity of the approach. The flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices Cl_L/Cl₊ and (1000+δ_L)/(1000+δ₊). These ratios are introduced as an additional two of nine non-dimensional ratios that are necessary to analyse the problem. The ratios represent the chloride and isotopic composition (Cl_L and δ_L), respectively, in the groundwater release zones of the lakes, relative to these parameters in the groundwater capture zone (Cl₊ and δ₊) for the lake. Field data from the case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modelling approach and its underlying assumptions. It is concluded that isotopic and hydrogeochemical data are invaluable in interpreting the interaction between lakes or wetlands and regional aquifers as it is very difficult to make physical or hydraulic measurements in the field that allow an understanding of lake–aquifer interaction. The tools and concepts developed that are summarized in the presented transition diagrams are invaluable starting points for the consideration and analysis of other case-specific examples of groundwater–surface water interaction and will improve the scientific basis of decision-making concerning lake and wetland management and groundwater interaction by water resource and environmental managers.     

Tracing contamination sources through phenotypic characterization of Escherichia coli isolates from surface water and groundwater in an agro-ecosystem

The objective of this research was to evaluate the groundwater chemical and bacteriological quality in the Barranquita-Knutzen basin (Córdoba, Argentina). The main purpose was to trace contamination through the examination of bacteriological parameters and antibiotic resistance of Escherichia coli, relating them to surface water, hydrogeological features and land use. Thus, 40 water samples were collected. The major chemical components and bacterial indicators were determined and antibiotic resistance was analysed using standard methods. Multivariate factorial analysis showed that the first principal component (PC) reveals the process of water mineralization, while the second and the third PCs explain a low percentage of variance, but collect chemical constituents and total and faecal coliform bacteria, respectively, revealing specific contamination situations. The observed antibiotic resistance profiles of E. coli and their relation with the land uses revealed that the source of faecal contamination in water is mainly from animal residues.     

生态补水对白洋淀流域地表水和地下水水化学特征的影响

生态补水是维持和改善白洋淀生态环境的重要途径.为研究生态补水对白洋淀水环境的影响,分别在补水前与补水后采集淀水、河水及地下水样品,分析区域地表水和地下水水化学特征.结果表明：（1）白洋淀补水前、后地表水与地下水的水化学组成中Na⁺为主要阳离子,补水后阴离子以HCO₃^-为主,淀区南部地表水电导率高;补水后地表水与地下水Ca²⁺、Mg²⁺和HCO₃^-浓度显著增加,水体电导率降低.（2）补水前地下水为Na-HCO₃型水,地表水主要为Na-Cl·SO₄及Na-Cl·HCO₃类型;补水后地表水与浅层地下水向Ca·Mg-HCO₃型演化,深层地下水水化学类型基本保持不变.（3）生态补水使白洋淀水位升高,淀区水面积增大,缓解了水资源短缺的问题;同时也使浅层地下水水化学组成发生改变,而深层地下水暂未受到影响.生态补水后,受稀释和混合作用的影响,水体Na⁺、Cl^-和SO₄^2-浓度显著下降,Ca²⁺、Mg²⁺及HCO₃^-浓度增加.在白洋淀生态补水中应"先治污,后补水",以减少补水过程中污染物向淀区的运移,还应注意区域地下水位上升过程中的阳离子交换及水岩相互作用,为合理调配生态补水及改善白洋淀生态环境提供科学依据.     

Using selected pharmaceutical compounds as indicators for surface water and groundwater interaction in the hyporheic zone of a low permeability riverbank

This study investigates the applicability of selected pharmaceutical compounds (e.g. sulfamethoxazole, carbamazepine, ibuprofen) as anthropogenic indicators for the interaction of surface water and groundwater in the hyporheic zone of an alluvial stream. Differences in transport behaviour and the resulting distribution of the pharmaceuticals in the riverine groundwater were evaluated. The investigated field site in the Grand Duchy of Luxembourg, Europe is represented by low permeable sediments and confined aquifer conditions. Water samples from single‐screen and multilevel observation wells installed in the riverbank at the field site were taken and analysed for selected pharmaceuticals and major ions for a period of 6 months. Surface water and groundwater levels were recorded to detect effluent and influent aquifer conditions. Nearly all pharmaceuticals that were detected in the stream were also found in the riverine groundwater. However, concentrations were significantly lower in groundwater than in surface water. A classification into mobile and sorbing/degradable pharmaceuticals based on their transport relevant properties was made and verified by the field data. Gradients with depth for some of these pharmaceuticals were documented and a more detailed understanding of the system stream/riverbank was obtained. It was demonstrated that the selected pharmaceutical compounds can be used as anthropogenic indicators at the investigated field site. However, not all compounds seem to be suitable indicators as their transport behaviour is not fully understood. Copyright © 2012 John Wiley & Sons, Ltd.     

Development and verification of a 3-D integrated surface water–groundwater model

Coupled modelling of surface and subsurface systems is a valuable tool for quantifying surface water–groundwater interactions. In the present paper, the 3-D non-steady state Navier–Stokes equations, after Reynolds averaging and with the assumption of a hydrostatic pressure distribution, are for the first time coupled to the 3-D saturated groundwater flow equations in an Integrated suRface watEr–grouNdwater modEl (IRENE). A finite-difference method is used for the solution of the governing equations of IRENE. A semi-implicit scheme is used for the discretisation of the surface water flow equations and a fully implicit scheme for the discretisation of the groundwater flow equations. The two sets of equations are coupled at the common interface of the surface water and groundwater bodies, where water exchange takes place, using Darcy’s law. A new approach is proposed for the solution of the coupled surface water and groundwater equations in a simultaneous manner, in such a fashion that gives computational efficiency at low computational cost. IRENE is verified against three analytical solutions of surface water–groundwater interaction, which are chosen so that different components of the model can be tested. The model closely reproduces the results of the analytical solutions and can therefore be used for analysing and predicting surface water–groundwater interactions in real-world cases.