Background
In the last 24 hours we have received two communications from the Environment Agency and Wiltshire Council regarding the grounwater situation across Wiltshire. Clearly, these have direct relevance for all of us living alongside the River Till.
The bottom line of both these documents is to urge town parish councils to be aware of the current situation and to adopt such measures as they can. In turn, we are now asking parishioners, particularly those of you owning/living in properties known to be susceptible to groundwater flooding, to be aware of the situation and take appropriate measures for your own properties; for instance by checking that water pumps are functioning and that other measures you have adopted in the past, sandbags, moving furniture and carpets to higher parts of the property, etc., can be initiated at short notice and carried out quickly.
The Current Regional Situation
“We have noticed the recharge (the aquifer starts to refill) season started earlier this year due to the wetter autumn that we have experienced, in fact bore hole levels across Dorset and Wiltshire are recording levels considerably above average for this time of year.
Below is a graph of the Groundwater level at Woodyates (on the Dorset / Wiltshire / Hampshire border) the dotted blue line is the mean October 31st level. This site is used as a national indicator for groundwater levels as it is fairly central and has a long period of recorded data.
As you can see, we ended the first month of the traditional re-charge period in October at around 91.0 mAOD (Ordnance datum (mAOD) is based on the mean sea level at Newlyn in Cornwall) compared to a twenty year mean of 76.0 mAOD. It is the second highest level on record after 2012 which was a bit of an anomaly as there was almost no recession that summer due to a Groundwater flooding event. As you can see we are at a level that is already higher than average for this time of year.
The Flood Alert level at this site is 98m mAOD and we would consider issuing a Flood Warning at 102 mAOD.
The Current Local Situation
As of 9:15 this morning, the water level in the Tilshead borehole stands at 90.24m mAOD. Levels have been rising for the last three weeks, but it is fair to say that the rate of increase over the last few days, with less rain, has begun to slow. The graph looks as follows:
The red arrow indicates the level this morning. We are only 4 metres below the 6-year average MAXIMUM winter level and in a credible worst-case scenario, less than two weeks/9 metres from possible groundwater flooding. If that looks scary, don’t forget that the average winter maximum is 94m. The good news is that we should have several days of dry weather over the next week and the rate of increase should fall and may even reverse. That said, the Environment Agency make the following point: “With Groundwater levels currently higher than average for this time of year, if we continue to have heavy rainfall events across Dorset and Wiltshire we anticipate issuing Groundwater Flood Alerts across Dorset and Wiltshire before Christmas”. Even then, it is far from certain we will have flooding here.
Winterbourne Stoke Parish Council will continue to monitor groundwater levels in the aquifer and publish weekly updates with the first due to appear on Sunday 8th December showing data collected for the first week. Keep an eye-out here for any interim bulletins or on the village Facebook page.
Please let the Parish Clerk (or any Councillor) know if you have concerns about specific properties, are seeking further help, or believe that a flooding event is imminent or underway.
Further Information
The Environment Agency and Wiltshire Council are holding two drop in sessions to enable town and parish councils and residents an opportunity to discuss groundwater issues in your area, share flood maps that maybe helpful for you to identify areas at risk of flooding and share knowledge on what to look for in your area. We can also give you more information on the Groundwater flood warning service available for your community.
We would also like to hear about your observations and feedback
If you have not made or updated your flood or emergency plan it’s not to late! If you need assistance, help or advice contact: drainage@wiltshire.gov.uk
Drop-in Sessions
Tuesday 10th December 2019 – Amesbury
Shears Dr, Amesbury, Salisbury SP4 7XT
10 – 6
Tuesday 17th December 2019 – Wilton
Castle Meadow Pavilion
SP2 0HG
To sign up for flood and groundwater warnings, click here https://www.gov.uk/sign-up-for-flood-warnings
or
FloodlineTelephone: 0345 988 1188 24-hour service