Shropshire Permo-Triassic Sandstone: Regional Groundwater Model

Case Study

ESI was commissioned by the Environment Agency initially in 2005 to develop a regional groundwater model of the East Shropshire Permo-Triassic sandstone aquifer, since then ESI has subsequently worked on expanding and improving the model over the last 10 years.

Background

60101Q_6103C East Shrops GW Model_1The Permo-Triassic sandstone aquifer of Shropshire forms a regionally significant water resource which is exploited for both public water supply and for river regulation (the Shropshire Groundwater Scheme). However, water resources in parts of the area are under pressure.

The Project

Initial Stages
During 2001 – 2005 ESI constructed a regional numerical model of the East Shropshire Permo-Triassic Sandstone for the Environment Agency’s Midlands Region. This model provided a detailed technical tool to assist with the management of water resources in the area.

 

However, with a large study area (over 1000 km2) and complex hydrogeology in places, it was not clear at the start of the programme whether it would be technically feasible to develop a groundwater model of sufficient robustness and reliability to fulfil requirements.

 

The Agency therefore decided to carry out a preliminary scoping study. To assist ESI provided an experienced hydrogeologist on secondment for a three month period and outline conceptual models of hydrogeological processes occurring in eleven sub areas were developed.

 

The output was a report which assessed the technical issues that would need to be addressed in developing a groundwater model of all or part of the area. The report also identified additional data that could help in constraining uncertainties where these occur.

 

We were subsequently instructed to carry out work on the implementation of the groundwater model, including a review of existing literature and pumping test data and the calculation of detailed water balances for the study area.

2008
60101Q_6103C East Shrops GW Model_2In 2008 ESI was commissioned to update the East Shropshire groundwater model to include the period April 2002 to March 2007.

 

The model was also extended to incorporate the Merrington Groundwater Management Unit (GWMU) to encompass Phases 3 and 5 of the Shropshire Groundwater Scheme (SGS).

2013
In August 2013, the Environment Agency commissioned ESI to update the ESM to include the period April 2007 to March 2013. ESI updated the relevant model datasets and developed a new recharge model using the 4R code. This then required some refinement of the MODFLOW model due to minor changes to the recharge being applied.

 

The resultant combined recharge and groundwater model simulated flows and groundwater levels at key target locations to match performance of the previous model and also showed some marked improvements in several places.

 

This latest model has now been extensively used to assess the effect of groundwater abstractions on groundwater levels and stream flows.

The Outcome

Key uses of the East Shropshire model have been for groundwater assessment in the Environment Agency’s Catchment Abstraction Management Strategy (CAMS) and for the management of existing and future phases of the SGS on groundwater levels and stream flow.

 

Whilst these requirements remain, a further use of the ESM is in relation to the Water Framework Directive (WFD). The East Shropshire groundwater body (GB40901G300100) has poor WFD status as it fails the WFD resource balance and some observation boreholes have shown declining groundwater levels in some areas.

 

It also fails the dependent surface water status test due to apparent low flow issues in the River Strine and Pipe Strine watercourse. These issues are being addressed through Severn Trent Water’s Low Flows Investigation programme, find out more about our work on this project here.