Groundwater Flooding in Wilton

It is difficult to believe that parts of the County were still officially in a ‘Drought’ status until late Autumn. How quickly a situation can change. Met Office information tells us that October 2022 was quite a wet month for much of Wiltshire, but it was really in November and December 2022, and the first half of January 2023, when we saw the wettest weather with up to 1.5 times the usual rainfall in parts of the County. However, just over halfway through January it turned much drier again, a theme which continued through February 2023.  

The excessive rainfall was welcomed by many, especially the water companies, because it provided much needed replenishment of reservoirs after last year’s extreme heat. 

Much of South Wiltshire’s chalk geology means that there are underground aquifers. Excessive rain sees these filling quickly and water can seep up through the ground. A situation that is not easy to deal with because traditional flood defences do not work in such circumstances. Many properties have to pump water from their cellars and others can suffer from failed sewage systems. Local roads can flood for excessive periods.

January’s rainfall meant the River Wylye was becoming full. It was being dominated by groundwater coming from Salisbury Plain and this, coupled with more rain falling than was forecast, started to present authorities with a problem in Wilton.

On Monday 16th January 2023, the Environment deployed staff on the ground. Their gauges did not raise any undue alarm, but this was at odds with what their operatives were seeing on the ground. With waters rising staff were beginning to become concerned about the possibility of flooding. A combination of groundwater and heavy rain was not a good mix for the River Wylye! 

The Environment Agency has assets upstream of Wilton in the form of gates and pumping stations, however, these were unlikely to make much difference as there was little potential for pumping because there is simply nowhere for the water to go. They predicted that this situation in Wilton may deteriorate and be a prolonged event. It was possible that Wilton could experience flooding from both the Rivers Wylye and Nadder and there was little more they could do to prevent it.

Some properties in Wilton were already experiencing flooding immediately outside their premises with waters rising to a depth of between 6-8 inches. There were reports that toilets were not flushing properly, electricity outages and a request for sandbags. The latter is always problematic as Wiltshire Council only holds a limited supply of them and their deployment has previously met with limited success in the Wilton area. They are no defence against groundwater.

LRF partners held a number of multi-agency meetings during the evening. There was particular concern for one residential property containing ten dwellings with some vulnerable people living within. The real key was to get accurate information from the scene so that informed decisions could be made, and appropriate action taken. There was also concern for the Riverside area of the town. 

The problem faced by agencies was that it was one of the coldest nights of the year with black ice reported on roads across the County. Both Wiltshire Police and Dorset & Wiltshire Fire and Rescue Service reported one of their busiest evenings dealing with an unprecedented number of accidents. Wiltshire Council gritter lorries were fully deployed with the same weather event. Therefore, getting any staff to the scene of flooding at Wilton to provide accurate information was proving problematic.

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In view of the exceptional circumstances faced by agencies, the next layer of response was called upon. The voluntary sector, who are crucial in supporting the activities of statutory agencies during times of crisis, was deployed to the scene in the form of Wiltshire Search and Rescue (WILSAR). Twenty of their volunteers worked in conjunction with colleagues from Scottish and Southern Electricity Networks (SSEN). They provided photographs of the scene which helped to provide situational awareness. They undertook door knocking, sought to understand residents’ needs and provided reassurance. SSEN undertook welfare checks of their vulnerable customers in the area and determined that there were no power issues. Additionally, Wiltshire Council was able to contact providers who deliver care at the residential property. The providers raised no concerns for their clients housed in the building. The property management agency was also contacted and highlighted that the building has two entry points, and they were experiencing no issues with access. It was agreed not to call on the residents themselves at such a late hour so as not to unsettle them or cause any unnecessary distress. 

The situation had been stabilised and local residents were grateful for the welfare checks. As always, one couldn’t understand what all the fuss was about! Things were now settled as we entered a very cold and unpredictable night.

Multi-agency partners met the following morning to review the situation. No flooding issues had been reported and the utility companies were satisfied that the situation was stable. It did not rain again overnight and the weather going forward was favourable with the Met Office forecasting dry conditions for the remainder of the week and beyond. Therefore, the multi-agency response was able to stand-down and the situation would be monitored going forward.

This was one of the most significant flooding emergencies that we have faced locally since the 2013/14 flooding when more properties flooded in Wiltshire than on the Somerset Levels! Consequently, and in line with a culture of learning and continuous improvement promoted by Wiltshire & Swindon LRF, a Debrief has been held. Among other lessons, work needs to be done to further develop the local Flood Plan to include more than just technical detail. We need to ensure early engagement with the Parish Council and make better use of Flood Wardens when such circumstances arise again.

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