Another week with quite a bit of rain and the water level in the aquifer rose steadily throughout the period. The Environment Agency has kept the Flood Warning in place, even though the borehole level has only just exceeded the level we reached on 1st January 2020, when we only had a Flood Alert. The reason for the Flood Warning this month was the short period in which the bulk of the rain fell and the subsequent rapid rise in the borehole level. The Environment Agency has created a bit of a conundrum though. I monitor the raw data output by the instrumentation at Tilshead which measures to two decimal places. In its latest Flood Warning update yesterday at 16:03, the Environment Agency said: “The groundwater level in the Tilshead borehole now appears to have peaked at 99.6m AOD.”
My initial reaction was that the Environment Agency had simply rounded up yesterday’s measurement of 99.56m AOD to 99.6m AOD. A little odd, but understandable perhaps. But reading on, it then claims that: “It is currently at 99.5 and slowly falling.” If they have been rounding up and down, then the actual reading should have dropped below 99.50m AOD. The borehole instrumentation at Tilshead shows the water level rose to 99.56m AOD by 04:00 on 21st February and stayed there until the level rose again to 99.57m at 06:30 yesterday and again at 19:15 to its highest level, so far, of 99.58m AOD. Since then, its wobbled up and down a bit over the last few hours and currently stands at 99.57m AOD. So the level may be falling, or it may rise again. Although this small difference of 1.0cm may look like splitting hairs, it is very important for those whose homes may suffer flooding. The Environment Agency has been asked to explain the anomaly.
What does the weather have in store for next week? Well, if you are hoping for dry weather, Wednesday might be the only day without rain. We are expecting drizzle today, with perhaps a clearer period this afternoon before more rain arrives later. Another weather system will track in overnight, but clear by morning and a second bout of rain will hit later on Monday. This picture carries on towards the end of the week. There are suggestions that a very low-pressure system will hit the country in the following week, but it is too early to say where. The good news is that as we move into March, the weather in the south of the country looks increasingly settled and dry!
You may be surprised to see that despite an awful lot of rain over the last two weeks, the level of water in the Tilshead borehole has fallen steadily until the last day or so. If you’ve been rash enough top pop out into your garden you might realise why. The ridiculously warm winter has meant that the deciduous shrubs and trees barely went dormant and many are now coming into bud. Even the grass in your lawn has started sprouting. That takes an awful lot of water and no doubt this has increased the rate at which the water level fell.
Earlier in the week, there were a couple of false alarms when the level seemed to settle for a few hours then continued downwards. 24 hours ago, the level started to rise at much the same rate it has fallen for the last two weeks – so the present level of rainfall is overcoming the level of plant transpiration; at least for the moment. It’s hard to tell how long the rise will continue, but certainly until the middle of next week, even if the rain stopped now.
The Environment Agency has maintained its groundwater Flood Alert for the Salisbury Plain area and on Thursday last were saying:
“Groundwater levels in the Salisbury Plain remain high but have steadied over the last few days. Storm Dennis is forecast to bring heavy rainfall over the weekend. From Saturday, we will see some high rainfall totals falling over the Salisbury Plain. Levels will continue to rise into next week. We will be monitoring the situation. Residents are advised to ensure that pumps are working where they have been installed and property resilience measures are in place.”
Yesterday, they issued new Flood Alerts for the Upper Avon and its Tributaries (Upavon to Amesbury) and the River Naddder and its tributaries between Donhead St Mary and Salisbury, and for the Wylye and its tributaries including the River Till.
Storm Dennis is not doing us any favours and heavy rain is due today (Sunday), although on the plus side the wind is dropping. The rain is likely to continue overnight with heavy showers all day on Monday, easing a bit on Tuesday. Wednesday may be fine, but it looks as though the rain will kick off again on Thursday. This wet and unsettled weather seems set to continue to the end of the month when we might begin to see some more settled weather.
The water levels in the Tilshead borehole have fallen steadily throughout the week, initially at about 8cm per day and latterly at 6cm. That said, there is some evidence today that we may be close to the equilibrium state for the aquifer; the next day or two will make it obvious if this is the case or not. It’s also worth noting that the Environment Agency Flood Alert is still in force, although it has not been updated since Monday 3rd February.
All the weather news at the moment is in relation to Storm Ciara, which is a few hours away from reaching its peak (expected at around midday) here in Winterbourne Stoke. Hopefully, there will not be too much damage to properties around the village. The movement of some of the larger trees on Church Street, down towards the Church, is really quite terrifying to watch; it must be very concerning for those who live immediately adjacent to them. As of 10:00, the maximum wind speed is 41.8mph and the maximum wind gust is 52.3mph. Take a look at Janet Abbot’s weather site if you want to keep an eye on things for yourself.
Rain is forecast for the rest of the weekend and continuing for much of the rest of next week. Some forecasts suggest a fine weekend, others suggest the rain may continue for a further week before things settle down again for the end of the month.