B. Adams

An early warning system for groundwater flooding in the Chalk

Abstract An early warning system has been developed for groundwater flooding and trialled in the Patcham area of Brighton. It provides a fit-for-purpose approach for forecasting groundwater flood events in the Chalk and is capable of operating across longer time scales than had previously been possible. The method involves a set of nested steps or tasks. Initially, the catchments response to recharge is determined and, using a representative hydrograph, a simple regression model that relates annual groundwater level minima and autumn and winter rainfall to subsequent annual maxima is developed. The regression model is then applied at the end of each summer recession using the observed annual minimum and estimates of winter rainfall to predict the following groundwater level maximum. Based on the results of this prediction a variety of steps may then be appropriate. Where the model predicts potentially high groundwater levels the frequency of groundwater level monitoring observations can be increased. A novel element of the method developed is the monitoring of changes in the matric potential of the unsaturated zone. Specific trigger levels to initiate either the next step of the method or promulgation of warnings of varying severity will be developed through experience of use of the system.

Thermal energy storage studies in the Lower Greensand aquifer in Cambridgeshire

Summary A field experiment has been carried out in the Lower Greensand near Cambridge to test the feasibility of injecting, storing and recovering heat in this formation. Approximately 1500 m3 of water at about 60°C were injected into the Lower Greensand over a period of 78 days. After storage for 105 days, the heat was abstracted over a period of 97 days. Over this single cycle of operation 33% of the injected energy was recovered. This proportion is likely to increase significantly with further injection/abstraction cycles. Increasing the amount of heat injected was also thought likely to reduce losses and increase the proportion of heat recovered. A digital model of the Aquifer Thermal Energy Storage (ATES) system was set up and calibrated on the Cray IS system at the University of London Computer Centre. It was then used to predict the behaviour of larger ATES systems both on inter-seasonal and diurnal bases. Energy recovery factors of over 66% appear to be feasible.

Aquifer susceptibility to side-effects of groundwater exploitation

Abstract Aquifer vulnerability has become a ‘cornerstone’ of groundwater protection policies, taking into account, as it does, aspects of pollution resulting from applied contaminant load. However, this is not the whole story and groundwater resource degradation can also result from other impacts of development such as piezometric level decline, saline intrusion and subsidence. It is generally the case that such impacts are normally diagnosed after they have occurred. Nevertheless, it is evident that certain aquifers are more susceptible to these impacts (often referred to as ‘over-exploitation’) than others. As a first step towards a method to determine aquifer susceptibility to such impacts, a diagnostic method is introduced as a means to provide managers and planners with an additional method of evaluating potential aquifer degradation as a result of development. The method, as presented, is at an early stage of development and cannot yet be used for inter- regional comparisons. Used critically, however, the authors believe it provides a useful tool for giving a first estimate of aquifer susceptibility. Planned future developments of the methodology are also presented.