The water levels in the Tilshead borehole have fallen excruciatingly slowly over the last week from a peak of 99.59m AOD to today’s low of 99.54m AOD; the lowest it has fallen since the 20th of February.  Of course, we’ve now had a few days with a fair bit of rain, so we might see the levels drop for 2 or 3 days before they level off or even rise again.

The Flood Warning for the Till is the only one in the area still in force. The Environment Agency is currently saying:

“The groundwater level at the Tilshead borehole is currently 99.56 mAOD and stable. 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 flood resilience measures are in place and that pumps are working where they have been installed. Residents may experience problems flushing toilets and have issues with septic tanks. The Met Office forecast is for intermittent showers over the weekend until Sunday evening 15/03/20, but with a drier spell expected next week any rise in levels will be limited.”

The forecast is for the rain to ease this evening then we should have dry weather until Wednesday when things break down again and we can expect rain continuing into Thursday.  This should clear and we may get a week or more of predominantly dry weather.  As we head into April the dry trend should continue, so the flood season may be coming to an end.

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.

A fascinating week in which to watch the water levels in the River Till and the Tilshead borehole.  At the start of the week, the Environment Agency was suggesting that the borehole level had peaked and was falling.  The reality, from their own borehole data, was quite the opposite and the level peaked at around 99.58m AOD overnight on Tuesday but never exceeded 99.57m at my fixed measuring time of 04:00.  The borehole level started to fall slowly on Thursday morning and now stands at 99.55m AOD.  With the heavy rain towards the end of the week, the borehole level may start to rise again in the next couple of days as the rain works through the system.  By contrast, the river continued to drop steadily throughout the week but shot up again to pretty close to its peak levels again yesterday.  The speed of the river’s response is another indication that the ground is pretty much saturated and additional rainwater is simply running off directly into watercourses.   The sharp-eyed amongst you may have spotted that the 29/02/2020 data isn’t shown on the graph, nor is data for earlier leap years.  That was a conscious decision taken when the records were started to avoid a data gap in three out of four years.

We are expecting some further rain overnight and into tomorrow; perhaps getting heavier in the afternoon.  The good news is that the forecast, that had been suggesting another week of moderate rain, is now much more optimistic with a few showers during the working week, but with further rain coming in for the weekend.   As we move further into March, it is possible that we will have a spell of more heavy rain or even snow before things settle down a little.  The second half of March may finally give us some relief from the rain and, at least for the moment, it looks like a period of dry, settled, and even warm weather.

The Environment Agency updated the ongoing Flood Warning yesterday (29/02/2020):