A very informative talk was given by Kevin Voyce ( Hydrogeologist, Environment Agency) on the strategic water resource management of the River Severn catchment.

The upper River Severn catchment, here in Mid-Wales, is underlain by Ordovician and Silurian mudstones, shales and grits. These rocks have a low permeability and therefore do not store water, so that most of the water stored is above ground. The Clywedog dam was built in the 1960's to regulate the flow in the River Severn. If flow in the river is low, a release valve can be opened to release water from the reservoir and into the river to provide flow. The ground water storage in Mid-Wales contrasts sharply with that found across the border in Shropshire. Here the rocks consist of Permo-Triassic sediments of sandstones and mudstones. The sandstones have large pore spaces and therefore large storage capacity and high transmissivity. A scheme for supplementing the River Severn flow via use of the ground water has been set up. This required the drilling of a line of boreholes which draw water from the groundwater reserves and pump the water into the river to enhance flow.

Thus the hydrogeologist needs to understand the properties of the rock, how much water it can store and its transmissivity. Also knowledge the presence of joints and faults in the rock is necessary as this can markedly affect storage and flow within the aquifer. Abstracting water from the aquifer may also lead to problems in nearby areas, for example with a wildlife reserve or a private borehole. Therefore safeguards must be put in place to protect other water users and monitoring must be undertaken. This includes checks on water levels, chemical analysis and monitoring of wildlife populations. The aim of the agency is to have a minimal environmental impact.

With growing population and therefore increasing requirements for water and the challenge of climate change the Environment Agency must work to be able to balance the growing needs with that of a dwindling resource. This will require water resource planning for the longer term and to secure the preservation of surface and ground water reserves.

The next meeting will be on Wednesday 15th April when club member Roy McGurn will give a talk entitled “ The Geology Of War”

On Sunday 26th April there will be a field trip to Hendre Quarry, near Ysbyty Ystwyth. Leader will be Prof. David James.