Lower Mersey Basin Groundwater Model

Case Study

The Environment Agency commissioned ESI to develop a conceptual and numerical groundwater model of the Lower Mersey Basin.

Background

6438b Lower Mersey_2The Permo-Triassic Sandstones of the Liverpool & Ormskirk and Lower Mersey Basin aquifer units are a significant groundwater resource for both industrial and public water supply.

 

Historic over-abstraction in some parts of the aquifer has resulted in falling groundwater levels and the upflow of saline water from depth and intrusion from the adjacent Mersey Estuary.

The Project

The Environment Agency commissioned ESI to carry out a scoping study to identify the key issues in the area and to develop an appropriate approach to tackle them.

 

As part of the discussions with key stakeholders, it was apparent that the project area should be expanded significantly from the Lower Mersey to include the North Liverpool area.

 

The project delivered an updated conceptual model of the area, a detailed terms of reference for the main project and a detailed cost benefit analysis of the different possible approaches, then used to support a bid for funding for the main project.

 

ESI was then appointed to carry out the main study, working with BV under the NEECA contract. The overall objective of the project was to carry out a phased water resource assessment to deliver a significantly improved technical basis for groundwater abstraction licensing decisions in the study area.

 

In Phase 1 of the project, ESI reviewed the data for the study area and developed an improved conceptual model. We then developed a regional groundwater model to implement this understanding of the aquifer.

 

The conceptual understanding from the water resources model was then developed further to examine the potential for saline intrusion to occur along the estuary. This phase of work involved complex variable density modelling and from the results of this a draft licensing policy was developed for the Environment Agency to help them to manage the risk of saline intrusion in the area.

The Outcome

6438b Lower Mersey_3The process of model refinement led to further improvements in understanding, particularly regarding the role of faults in compartmentalising the aquifer.

 

The model is now being used as a water management tool to assist the Environment Agency and United Utilities to determine the most appropriate way of managing groundwater levels.