Upper Colne groundwater model update

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Courtesy of ESI Ltd - Environment Specialists

Client: Environment Agency

Location: Hertfordshire

Services: Groundwater Modelling , Low Flow Studies and Hydroecology

Issues: Identification of management options for low flows in the River Gade

Summary: ESI developed a groundwater model of the Upper Colne Catchment capable of simulating groundwater heads and surface water flows that provided a high level of confidence in subsequent model predictions. Five future scenarios accounting for potential future variation in precipitation and potential evapotranspiration allowed the Environment Agency to assess the resulting potential variation in future river flows.

The River Gade was identified as suffering from low flows and in 2001 the Environment Agency appointed a joint team of ESI and JacobsGibb Ltd to carry out a major study into the causes of and potential solutions to this problem. An integral part of the study, and the principal responsibility of ESI within the project team, was the development and use of a numerical groundwater model of the Upper Colne Catchment. The groundwater model developed proved capable of simulating groundwater heads and flows to a degree of accuracy that provided a high level of confidence in the subsequent predictive scenarios.

Low precipitation and consequently low recharge conditions in recent years since the model was developed have resulted in concern for the low flows that may potentially be observed in the River Gade during 2006 and in future years. ESI was appointed in 2006 by the Environment Agency to extend the original numerical groundwater model to allow the comparison of model predictions with observed data from January 2000 to May 2006.

Results indicate that the model developed reproduces observed river flows and groundwater levels well, justifying the extension to the year 2008 for drought forecasting. Five future scenarios that take into account the potential future variation in precipitation and potential evapotranspiration were developed by the Environment Agency to observe the potential resulting variation in future river flows. Model results indicated that low flows may be expected in late summer 2006, with potential recovery in April 2007, allowing the Environment Agency to consider the options available for alleviation of this problem.

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