Abstract The Cam and Ely Ouse Chalk aquifer has been an important source of public water supply for over 100 years. In response to growing demand for water in the area in the 1970s and 1980 s, the National Rivers Authority developed the Lodes–Granta scheme to provide augmentation water to key rivers, subject to low flows. However, during the droughts in the late 1990s, the River Granta, which derives baseflow from the Chalk aquifer, was dry in some locations for several months. In response, the Environment Agency and Cambridge Water carried out investigations into the impacts of abstraction on the flow and ecology of the Granta and agreed to restrict abstraction from two operational groundwater sources during low flow periods. However, these abstraction restrictions could potentially result in a shortfall within the relevant public water supply zone under some climatic conditions and so Cambridge Water was considering increasing abstraction from an alternative source of groundwater within the catchment to retain the level of resilience of its supply. The Environment Agency was concerned that use of this abstraction could pose a risk of deterioration of the ecological status of the water body under the EU Water Framework Directive. This paper describes the investigations undertaken to assess the risk of deterioration and shows how these are being used to manage this risk going forward.

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 We briefly outline the progressive development of approaches to both the characterization and simulation of the hydrogeology of northern European chalk aquifers, which were some of the first in the world to be studied. The volume's scope includes work on water resources and quality, chalk streams and wetland ecosystems, chalks as heat reservoirs for building temperature regulation, sources of groundwater flood risk and impacts of engineering on the subsurface, and diffuse and point-source pollution affecting these aquifers. It excludes hydrocarbon-related studies and those focused on offshore chalk sequences. We briefly outline the current state of knowledge of hydrogeological processes, characterization, assessment and modelling, and the increasingly recognized importance of karst features. The latter were little discussed 20 years ago and are still often neglected. There follows a brief quantitative analysis of publication topics relating to chalk hydrogeology in the scientific literature over the past three decades, which highlights key trends including both the purposes of studies and the methods employed. We present a summary of the topics and contributions within this volume, and conclude by identifying the key issues that need to be addressed in order to ensure the sustainability of our chalk aquifers for the future.

Abstract Construction excavations and tunnels in chalk can encounter groundwater challenges, including high water flow rates, instability of excavations in weathered chalk and basal instability in overlying aquitards caused by high groundwater pressures in deeper chalk aquifers. In hydrogeological settings where the chalk has been exposed to periglacial weathering during the Quaternary Period the upper zones may be degraded to structureless chalk which can potentially be of very low hydraulic conductivity (putty chalk) or very high hydraulic conductivity (chalk bearings). In deeper, structured chalk groundwater flow tends to be concentrated along fissures associated with pre-existing geological structures such as bedding planes, flint beds or faults. A range of groundwater control strategies can be deployed, including open pumping, pre-drainage pumping, shallow and deep cut-off walls, ground treatment and, for tunnels and shafts, application of fluid counter pressures to exclude groundwater. The strategy appropriate to a given site must be selected based on a thorough understanding of the hydrogeological setting and chalk weathering profile. This requires a ground investigation of appropriate scope, using suitable techniques to characterize the chalk. Borehole geophysics can play a key role in identifying discrete zones of inflow.

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.