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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Europe
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Western Europe
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United Kingdom
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Great Britain
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England
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Cumbria England
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Sellafield England (1)
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Scotland (1)
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Wales (1)
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commodities
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water resources (1)
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geologic age
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Cenozoic
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Quaternary (1)
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Mesozoic
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Triassic
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Sherwood Sandstone (1)
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Primary terms
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Cenozoic
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Quaternary (1)
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data processing (1)
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Europe
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Western Europe
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United Kingdom
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Great Britain
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England
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Cumbria England
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Sellafield England (1)
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Scotland (1)
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Wales (1)
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government agencies (1)
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ground water (2)
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hydrology (1)
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Mesozoic
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Triassic
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Sherwood Sandstone (1)
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sediments
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clastic sediments
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diamicton (1)
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structural analysis (1)
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water resources (1)
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sediments
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sediments
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clastic sediments
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diamicton (1)
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Front Matter
Abstract Groundwater has been used in the UK as a source of drinking water for centuries. For example, certain springs have been used to supply small urban areas for more than a thousand years. However, extensive use of groundwater began during the industrial revolution that started in the eighteenth century. The technology from the industrial revolution provided the means to access greater quantities of groundwater. Nevertheless, probably the more important factor was the increasing urbanization, with industrial cities such as Birmingham, Liverpool and Nottingham expanding at a phenomenal rate. With the higher population came an increased demand for water, which could be provided from local aquifers. The trigger for extensive exploitation was the 1848 Public Health Act that required local authorities to ensure a source of clean drinking water. From 1850 onwards, large red-brick Victorian pumping stations (Figs 1 & 2 ) started to appear on the outcrops of the principal aquifers in England, and abstraction steadily increased until the 1990s. In 2003, the use of groundwater in England and Wales was c. 6400 Ml/day (6 400 000 m 3 /day), of which c. 5000 Ml/day was for public supply ( Environment Agency 2006 ), comprising about a third of the total drinking water supply in England and Wales. The abstraction is predominantly from the Chalk and Permo-Triassic Sandstone (Fig. 3 ), which account for 60 and 25% of total groundwater abstraction, respectively ( Downing 1998 ). Outcrops of these two aquifers are located mainly in the SE and Midlands
A national approach to groundwater modelling: developing a programme and establishing technical standards
Abstract In the 1970s regional groundwater modelling began to be used in support of many hydrogeological investigations in the UK. A number of the studies were concerned with groundwater development at a regional scale in conjunctive use schemes; elsewhere the effect of pumping from aquifers on river flows or the ingress of saline water was considered. Due to the limited power of digital computers at that time, special numerical codes were often prepared for individual projects, with consequent inefficiency and inconsistency of practice. However, by the mid 1990s the need to formalize and standardize groundwater modelling projects was recognized. The Environment Agency of England and Wales prepared a strategy to manage and monitor the projects. A Template Project Brief was prepared to define the many tasks involved in groundwater studies and to clarify the roles of contractor and client (Environment Agency). In addition Guidance Notes were prepared to disseminate procedures and techniques that had resulted in successful outcomes. This paper summarizes some of the earlier studies, provides information about the Project Brief and Guidance Notes and illustrates some critical issues in groundwater modelling by reference to two case studies.
Abstract Over the last 10 years there has been a unique regulator-led programme involving extensive development of regional groundwater models across England and Wales for water resources purposes by the Environment Agency for England and Wales. Eight regionally managed programmes are underpinned by a framework, which has allowed a coordinated national approach. The main uses of the models are for catchment abstraction management and licensing. Models have also assisted in monitoring network design, investigating groundwater quality and implementing groundwater source protection zones. A five-yearly review of the programmes recognized the importance of benefit realization and stakeholder involvement as well as technical good practice. The programme already delivered provides a solid foundation for supporting the management decisions required in areas such as climate change mitigation and integrated catchment management using appropriate tools at a time of rapid organization change and financial uncertainty.
Abstract The usage of modelling results by their intended audience is an important aspect of undertaking any project. However, providing the appropriate results in the correct way to key stakeholders is not a straightforward task. Fortunately, there is a growing body of work about approaching the engagement of stakeholders in a way to maximize the impact of modelling results. Using the lessons learnt from a number of recent workshops, including those conducted for the benefits realization process undertaken for the Environment Agency of England and Wales, suggestions for best practice are presented and their relative merits discussed. Best practice for getting groundwater modelling results used by their intended audience is proposed.
The National Groundwater Modelling System: providing wider access to groundwater models
Abstract The National Groundwater Modelling System (NGMS) is a map-based, client–server system for holding groundwater models and supporting documentation. Models can be run, new ‘what-if’ scenarios created, and time series and spatial data rapidly viewed and exported. Use of the system will result in greater standardization of data formats, model codes and methods used by the Environment Agency without stifling technological progress. NGMS enables a wider audience of water resource staff to access groundwater models. The system is being used to improve representation of groundwater in Catchment Abstraction Management Strategies and to forecast the potential impacts of climate change upon water resources. However, the day-to-day, operational use of groundwater models by the Environment Agency remains a challenge that requires engagement with other specialists (e.g. hydrologists and IT systems specialists). Considerable effort is required to roll out the system, train people and adapt operational decision-making processes to bring NGMS into regular and safe use.
Abstract Recharge calculations based on daily soil moisture balance models define the resource available for most regional-scale groundwater models used by the environmental regulator in England and Wales. A switch in recent years from the Penman–Grindley methodology to the Food and Agricultural Organization approach has improved the representation of soil properties in these calculations. A new Meteorological Office algorithm for calculating potential evapotranspiration inputs has also been adopted and rain-gauge data processing on individual models are currently being streamlined towards the use of nationally derived grids. A range of infiltration, bypass and runoff–recharge mechanisms have been conceptualized and modelled incorporating simple representation of unsaturated zone storage and flow processes. This paper reviews the recent changes adopted and considers future challenges.
The role of numerical modelling in understanding groundwater flow in Scottish alluvial aquifers
Abstract Groundwater in Scotland has been, until recently, an under-rated resource given the abundance of surface water resources. In the last decade, a number of new abstractions have been developed and existing ones enhanced. Implementing groundwater abstraction licensing through the Scottish Water Environment (Controlled Activities) Regulations (2005) has accelerated the need to understand such schemes. Simulating the groundwater systems, which are generally small in area, with an immature understanding and where subsurface data are often sparse, is a challenge. This challenge is amplified when groundwater abstraction is proposed from previously unexploited gravel valley deposits in close proximity to large rivers. Examples of recent work undertaken for Scottish Water illustrate the important role that groundwater models have in testing and refining conceptual understanding as well as convincing regulators of the suitability of the groundwater abstraction.
Abstract In London, groundwater abstractions for public supply are predominantly from the Chalk aquifer. However, water resource pressures put existing abstractions at risk and often require complex analysis to support new source development. Thames Water develops and uses regional groundwater models for such analysis to support communication with stakeholders such as the Environment Agency, the environmental regulator of England and Wales. Using two case studies, the importance of regional models as Thames Water assets is demonstrated. While Thames Water has developed regional models as a context for sub-catchment scale analysis of groundwater source development, they are subsequently used to address other issues. As a result, the models are updated regularly, enhancing both conceptual understanding and calibration. These models cost less than 1% of the capital cost of new water source schemes. However, as they are enhanced and applied more widely, the models accrue further value as active decision support tools. Regional model usage to investigate a range of local systems and interactions is of particular value to Thames Water. In this regard, it is important to appreciate and promote the clarity and consistency generated when stakeholder-specific issues can be analysed within an agreed regional model framework.
Advances in modelling groundwater behaviour in Chalk catchments
Abstract Groundwater in Chalk catchments is a major resource that also helps support internationally important habitats and ecosystems. Its dual porosity and dual permeability properties, coupled with large-scale structural features (such as hard rock layers and marls), produce a highly complex hydrogeological system. Recent impacts from groundwater flooding as well as vulnerability to drought have raised questions over the ability of traditional approaches to model these aquifers. Current work on near-surface hydrological processes has highlighted the importance of the soil and weathered zone for controlling recharge rates. In addition, karst-like features, sedimentary deposits and valley bottom processes govern stream–aquifer interaction and present a challenge in their representation in any modelling system. Methods that have, and are being, developed to incorporate these features, and their use in modelling Chalk catchments, are described. These are required in order to address major challenges, such as groundwater flooding and drought impacts, both of which could become more frequent and intense as a result of climate change.
Modelling the hydrogeology and managed aquifer system of the Chalk across southern England
Abstract Six regional recharge and groundwater models have been recently developed of the Chalk and Upper Greensand from Dorset to Kent. Updated Chalk stratigraphy and mapping have improved understanding of geological structure and the development of preferential groundwater flow pathways along hardground horizons. Where shallow dipping folds bring these into the zone of active groundwater flow, extensive ‘underdrainage’ may result in marked differences between surface and groundwater catchments. Hardgrounds and marls are also associated with spring discharges, as are some faults and the clay formations that underlie or confine the aquifer system. Higher specific yield within the Upper Greensand helps support summer baseflow, as do local groundwater discharges from augmentation schemes, watercress and fish farm operations. The aquifer system has been successfully modelled using the ‘variable hydraulic conductivity with depth’ version of MODFLOW. Depths of secondary permeability development have been distributed according to ground and groundwater level data. Interfluve–valley contrasts overlie a base hydraulic conductivity set according to the formation saturated at the water table and enhanced by active hardgrounds. Local parameter overrides may also be needed. The Wessex Basin conceptual and numerical model is described before summarizing similarities and contrasts from the other five regional model areas.
Crossing boundaries, the influence of groundwater model boundaries and a method to join and split MODFLOW models
Abstract Neighbouring groundwater models often have large areas of overlap to avoid boundary issues in hydrogeological assessments and such overlap or artificial boundaries can lead to inconsistent representations of aquifers and processes. This paper presents the aggregation of six adjacent models spanning East Anglia, England, into one model without internal boundaries. This study principally discusses the effect of, and difficulties arising from model edge boundaries. In addition, a review of conceptual and numerical discontinuities at model boundaries is included and a more consistent and robust modelling approach over the whole area is demonstrated. The large, joined model is used to delineate groundwater divides, assess their transient migration, review edge boundary implications for water balances and investigate abstraction impacts without the influence of internal static boundaries. Computer codes developed in conjunction with this study facilitate joining adjacent models and, conversely, splitting of the joined model back into models at the scale of the original component models using simulated groundwater divides, or to smaller submodels incorporating edge boundary conditions calculated from the parent model.
Abstract The Lincolnshire Chalk aquifer on the east coast of England is used regionally for water supply. However, groundwater abstraction can exceed recharge during times of drought, resulting in saline intrusion. Following hydrogeological investigations in the 1970s and 1980s, a regional groundwater model was developed to underpin the tactical management of the aquifer. Although it is a coarse, single-layer, constant-density model, routine regulatory use of the model since 1988 has enabled a sustainable level of groundwater abstraction to be reached and brought saline intrusion under control. Abstraction rates have been proactively adjusted to suit prevailing conditions using model forecasts. Forecasts are evaluated against model-based thresholds, set by comparing model output (e.g. aquifer–estuary flux) with observed data (e.g. groundwater salinity). The success of the model in managing groundwater resources is attributed to: field-based hydrogeological investigations informing the model design; collaboration between regulators and abstractors, which has built confidence in the model results; commitment to updating the model; and flexibility in the supply network through conjunctive use of ground and surface water. The model has also been applied for purposes not considered during development and has therefore provided value for money for the UK water industry over a 30 year period.
Abstract The development of the Vale of St Albans groundwater model made use of two techniques not commonly used in UK regional modelling studies: parameter estimation (using PEST) and representation of dual storage. Parameter estimation techniques can significantly improve model calibration and can be used to inform model development. Because parameter estimation typically involves running a groundwater model many hundreds of times, using a steady-state version of the model can help to keep run times short. Care must be taken to ensure that the parameter distributions produced through these techniques are conceptually defensible, and they must be checked against the conceptual model and modified where necessary. Simulation of extreme conditions such as floods and droughts can be problematic for Chalk aquifers. Previous studies have shown that the Chalk can be resistant to drought, with higher flows recorded in rivers than can be accounted for from releases from fissure storage alone. An approach has been developed that simulates a weak hydraulic connection between fissures and a proportion of matrix storage within the Chalk, providing a delayed yield of significant additional volumes of water during droughts. The application of this approach results in a significant improvement in the simulation of extreme events.
Abstract Catchment-scale (>40 km 2 ) contamination of the Chalk aquifer of Hertfordshire by bromate, emanating from a disused industrial site north of St Albans, represents the largest occurrence of point-source groundwater contamination in the UK. The influences of ‘double porosity’ diffusive exchange and rapid transport along solution-enhanced conduits complicate predictive modelling of contaminant transport to threatened public supply wells. Tracer testing indicates that solution-enhanced flow routes exist beyond the surface distribution of dissolution features in Hertfordshire, more extensively than previously thought. A quantitative conceptual understanding of this flow system has been incorporated into a spatially distributed equivalent porous media representation in MODFLOW and MT3D-MS. The calibrated model reproduces essential features of the aquifer system, including heads and flows, seasonal responses, and the timing and spatial distribution of observed tracer breakthroughs in the solution-enhanced aquifer, but does not fully capture the magnitude and form of tracer and bromate advance. Due to the influence of local solution enhancement and matrix effects, detailed breakthroughs at receptors cannot be resolved at the coarse grid scale. However, the model is able to simulate general trends.
Abstract The first numerical model of solute transport to incorporate Fickian diffusive exchange between mobile fracture water and immobile porewater for an actual case of groundwater contamination at catchment scale was applied to the Chalk aquifer at Tilmanstone in SE England by Bibby ( Water Resources Research , 1981, 17 , 1075–1081). The unconfined aquifer at Tilmanstone had been contaminated by coalfield brine leaking from disposal lagoons operating throughout much of the twentieth century. Recent observations show that the Bibby model underestimates dual-porosity diffusive retardation, and hence underestimates the persistence of contamination, probably by several decades. 2D representation of the aquifer in plan ignored the hydrostratigraphy, and model calibration was limited by the lack of time-variant paired profiles of fracture water and porewater. Vertical profiles through the Chalk determined by packer testing, borehole dilution testing and geophysical logging, together with a new depth profile of chloride concentration in Chalk matrix porewater, are described. The hydrostratigraphy is interpreted in relation to the Chalk lithostratigraphy of SE England, and incorporated into a vertical-section model of chloride transport along the axis of the valley, consistent with the new and historical profiles of fracture water and porewater chloride concentrations. New predictions of the longevity of the chloride contamination at Tilmanstone are presented.
Abstract Groundwater models are used to manage water resources in carbonate aquifers throughout the UK. These models often utilize non-linear modifications of equivalent porous media (EPM) assumptions to simulate the observed head-flow relationships. This paper describes the application of similar principles to time-variant water balance modelling of a karstified aquifer: the Carboniferous Limestone in SW England. The non-linear model successfully simulates the large changes in bulk hydraulic conductivity required to adequately model flows from two karstic spring catchments. Model results illustrate that the rate of drainage from the vadose zone is affected by the extent and thickness of soil cover. In a catchment with mixed soil cover, vadose zone drainage is shown not to be significant in sustaining summer low flows at the spring. The performance of the model is limited in some cases: summer storm flows in particular are poorly simulated. The limitations suggest that the true response of the system is dependent on recharge intensity (rate) as well as antecedent water levels and that the EPM assumption of good connection between conduits and the diffuse flow zone is not always valid in this aquifer. This may have implications for groundwater model design in other carbonate aquifers.
Groundwater abstraction impacts on river flows: predictions from regional groundwater models
Abstract Regional groundwater resource models are often built to improve confidence in predicted groundwater abstraction impacts on river flows and groundwater levels. By explicitly representing the aquifer system geometry, properties and boundaries, together with transient recharge and abstraction pressures, such models provide a robust platform to support abstraction impact assessment, alongside evidence from field data and investigations. Regulatory drivers include the European Union Habitats and Water Framework Directives and other abstraction licensing decisions. This paper presents examples of the spatial and temporal patterns of groundwater abstraction impacts predicted by several models. A variety of presentation formats are used to illustrate the simulated flow impacts of abstractions both individually, and in combination with other surface water abstractions and discharges. Model predictions from a range of abstraction, aquifer, and river settings are often more complex than would be suggested by simpler tools and approaches. In many cases, absolute low-flow impacts are less than long-term groundwater abstraction rates. The ‘real world’ hydrogeological mechanisms behind these impact patterns are discussed. The paper also recommends a protocol for using regional models to assess individual licensed groundwater abstraction impacts across the full range of historic climate conditions (typically, as monitored since 1970) and in the context of other operational artificial influences.
A rapid model for estimating the depletion in river flows due to groundwater abstraction
Abstract The Environment Agency of England and Wales uses its calibrated regional models to estimate the reduction in river flows resulting from proposed groundwater abstractions. Where there is no regional model, analytical equations can produce quick initial estimates of river flow depletion. However, users often want more confidence in their estimates by representing more faithfully their understanding of the real river–aquifer system. This paper shows that, when using a numerical model designed to predict river flow depletion, it is important to include adjacent catchments and intermittent streams and less important to include river elevations and variations in transmissivity with groundwater head. Recharge does not usually need to be included unless part of the river becomes disconnected or dry. Therefore, for rivers where stream length is constant and transmissivity variations are small, it is valid to use a ‘no-recharge’ depletion model, which can be built quickly (within a month). A case study on the River Leith in NW England illustrates the use of such a model to assess the ecological impact of two groundwater abstraction licences under the European Union Habitats Directive.
The use of groundwater levels and numerical models for the management of a layered, moderate-diffusivity aquifer
Abstract The predictions from a numerical time-variant distributed groundwater model are used to assess the spatial and temporal impacts of groundwater abstraction for an unconfined and layered, moderate diffusivity aquifer; the West Midlands–Worfe Permo-Triassic Sandstone in the UK. These impacts have been determined by comparing a recent actual baseline predictive simulation with simulations where groundwater abstractions are switched off, including a ‘naturalized’ simulation. By reference to the historic simulation, the predictive model results are compared against observed groundwater levels. The predictive simulations demonstrate that observed groundwater levels could be an indicator of groundwater abstraction impacts on surface water flows where widespread stream disconnection has occurred due to high rates of abstraction. This relationship also depends on the aquifer hydraulic characteristics, the interaction between groundwater levels and the surface drainage network and other artificial flow influences. Abstraction impacts on groundwater levels are large for the West Midlands–Worfe aquifer, but can be obscured by the climatic recharge signal in observed groundwater level records. This is a consequence of the moderate diffusivity and the main groundwater abstraction development preceding systematic monitoring. The groundwater model can be used to identify which observation boreholes have negligible abstraction impacts; this may be valuable for identifying groundwater level records that are useful for climate change analysis.