Tilshead Borehole Levels: 8th March 2020

Another week of intermittent rain and showers.  This has led to the Tilshead borehole level returning to it 99.58m AOD and exceeding that briefly yesterday to achieve an annual high of 99.59m AOD.  Today, it has fallen slightly back to 99.58 m AOD.

In its latest Flood Warning update issued on Friday at 14:30, the Environment Agency said:

“The groundwater level at the Tillshead borehole is currently artesian at 99.5 m AOD. Groundwater levels on the Salisbury plain are forecast to rise after recent heavy rainfall. We believe a possibility of flooding still exists for Tilshead, Orcheston, Shrewton, Winterborne Stoke, Berwick Saint James and Stapleford. Residents are advised to ensure property resilience measures are put in place and that pumps are working where they have been installed. Residents may experience problems flushing toilets and have issues with septic tanks. Further rainfall over the weekend and into the early parts of next week are forecast by the met office, with this rainfall we anticipate groundwater levels to continue to rise.”

For the first time in the last 7 years, the Environment agency is talking about the borehole being “artesian at 99.5 m AOD.”  This is where the level of precision matters, but if we take the Environment Agency data at face value by way of example, this is what it suggests.  If the borehole is artesian at 99.50m AOD then when the borehole level reaches 99.50m, the water would be at ground level.  As the water level is now 99.58m AOD, then you would expect a column of water 8cm high to be emerging from the Tilshead borehole.  However, due to the lack of precision in the Flood Warning,  99.5m might, with rounding up or down, be any measurement between 99.45m and 99.54m – so the water column at Tilshead could be anywhere from 4cm to 13cm tall – that’s a big range when it comes to flooding.

Next week is going to be much the same as last week with more periods of rain and showers, so the water level is unlikely to fall a great deal.  In the longer term, from mid-month onwards, the weather is expected to become increasingly settled.  Add that to the coming of Spring and the water levels should start to stabilise.

Winterbourne Stoke Parish Council