Lichfield Groundwater Model Development

Case Study

LichfieldIn 2007 the Environment Agency commissioned ESI to develop a groundwater model to address new water resource issues in the Lichfield area, following this the model has since been redeveloped to address new resource issues.

 

Background

 

The Lichfield Permo-Triassic sandstone aquifer is a strategic groundwater resource for the West Midlands. However, several vulnerable low-flow streams arise from it. The catchment of one of these, the Leamonsley Brook, is under-drained by a 5 km long Victorian water transfer tunnel, known as the Hanch Tunnel. The Hanch Tunnel was excavated below the water table for its entire length and is only partly lined.

 

The Project

 

In 2007 the Environment Agency engaged ESI to develop a numerical groundwater model of the Lichfield aquifer. This model would significantly improve the Environment Agency’s ability to make technically robust abstraction licensing decisions, in the Leamonsley Brook catchment and elsewhere in the aquifer.

 

ESI developed the numerical model with MODFLOW. The effects of the Hanch Tunnel were reproduced with an adapted version of the MODBRNCH code that allows simulation of open channel and pressurised pipe flow systems. This was the first time this sophisticated modelling approach was used on an operational model in the UK. Model results were used to demonstrate that the Hanch tunnel gains, and removes, a considerable amount of groundwater from the Leamonsley Brook catchment that would otherwise flow into the brook.

 

Several scenarios for augmentation of flows of the Leamonsley Brook were tested using the groundwater model. It was shown that compensation from the Hanch Tunnel will have lower impact on the existing flows in the brook than from an existing borehole, constructed for that purpose. This recommendation has been taken forward for economic consideration by the stakeholders.

 

In 2011-12 the Environment Agency commissioned ESI to update and recalibrate the existing model to address new water resource issues in the area. The update project included conversion of the recharge model to the 4R code. This made it more consistent with national standards and simplified the way in which the Hanch Tunnel was simulated in order to make the model easier to use. These changes also required other aspects of the model to be re-calibrated.

 

The Outcome

 

The groundwater model provided a useful and technically robust tool to aid decision making concerning two location-specific water resources issues;

      • Low flows in the Leamonsley Brook catchment, specifically the role of the Hanch Tunnel
      • Potential impacts of groundwater abstraction on Plants Brook following the renewal of time limited licences

 

ESI loaded the updated and refined model to the Environment Agency’s NGMS to allow access to Environment Agency staff managing water resources in this area.