Storm Bert – A reminder of our flood vulnerability
Storm Bert brought a spell of extremely wet weather on the weekend of Saturday 23rd to Sunday 24th November as a deep Atlantic low pressure system, especially across South Wales and south-west England with over 150mm falling in the wettest areas. Indeed, 23rd November was the wettest recorded day in the UK as an average since 3 October 2020.
Around three-quarters of the whole-month average rain fell in an area from South Wales to Northamptonshire. The storm also brought strong winds, although gusts did not reach the same level as Storm Darragh two weeks later and were not necessarily exceptional. It was the local severity of the rainfall totals from upland catchments funnelled into towns and villages that again caught the headlines.
A Torrent through Tenbury
Tenbury Wells is a beautiful historic market town on a flat low lying part of the southern bank of the River Teme and at the confluence of a major tributary – the Kyre Brook. It has a long history of flooding and in 1795 suffered a flood so extreme that bridges were washed away, consequently rebuilt by none other than Thomas Telford.
When the Teme reaches above 5.5m in height, it escapes the main river channel and rapidly fills the low lying high street. The swollen main river also backs up the Kyre Brook.
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This scenario played out almost exactly during Storm Bert. While the main Teme stream caused considerable damage, the media footage focused on the often overlooked Kyre Brook. At one point on a bend, a standard brick built wall had been in position for perhaps 30 years above the Brook, but it was no match for the volume of water coursing around the bend, putting huge pressure on the aging mortar. The wall inevitably gave way, sending a wave of water through the shopping streets and caught on camera . The situation was made worse by a tractor driving at speed through the floodwater breaking windows and doors of the shops in the process, adding to the damage.
The EA has projected this area to have a 20% increase in flood peaks on the Teme, so the situation will only get worse. Flood defences are the obvious answer and amply demonstrated by the inadequacies of that brick wall. Feasibility studies have been carried out over the last quarter century or so but the geography of the town has driven both cost and complexity to the point that it hasn’t been viewed as viable when placed against the number of properties safeguarded, compared to other priority locations, when the Environment Agency (EA) has a finite budget.
There has been some more recent lobbying by Harriet Baldwin MP for West Worcestershire, but some businesses are already on the move, such as Rainbow Crafts and Garlands Flowers who may be forced to close and set up pop up shops elsewhere, following with stock losses running into the tens of thousands of pounds.
Pontypridd: failure to learn lessons
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Residents in Pontypridd were dealt the same blow that was served up to them by Storm Dennis 4 years previously. Residents of Sion Street, whose properties are lined along the River Taff understand the risk of flooding from a river whose catchment is highly responsive and fed by multiple upland tributaries from the South Wales valleys and Brecon Beacons that were saturated with huge rainfall totals. Again, the existing flood defences that had been breached during Storm Dennis were overtopped, as residents were locked in a semi-futile battle with sandbags and dustbins to bail out their gardens and front rooms.
The wider management issue was again a repeat of previous failings where warnings were given out too late for local councils to coordinate the emergency response and open up shelter facilities. Senedd Members warned Wales had failed to learn lessons from devastating floods in 2020, Delyth Jewell, Plaid Cymru’s shadow climate change secretary, told the Senedd that hundreds of homes were again hit by flooding, leaving communities in crisis. Huw Irranca-Davies, Wales’ climate change secretary, said the intensity exceeded Storm Dennis, with the River Taff rising by 30cm every 15 minutes at the height of the deluge.
Better natural catchment flood management needed
The residents of Sion Street know that the Taff is highly prone to flooding that is channeled so that the water rises quickly and that has defences, but that are clearly not tall enough to face the torrent. They may not necessarily want to be looking at a 5 metre tall defence and lose that river view, but that may have to be the case.
Alternatively, consideration should be given to more cost-effective investment and co-operation with landowners on implementing more natural flood management schemes on the upland catchments, such as the re-introduction of mosses, peat and pools created by the reintroduction of beavers and naturally dammed sections. Schemes such as in Pickering, North Yorks, have proven to be a success and the residents of Caerphilly and similar vulnerable towns across the country should be given priority in a more joined up, holistic flood risk management strategy.
Culvert Calamity
Source: OpenStreetMap
Location map of the suburb of Pant near Merthyr Tydfil. Note the stream that disappears into a buried culvert to the north east that has given way on Nant Morlais and close to property.
Streams don’t have to be visible to cause even greater peril. Further upstream on the Taff Merthry Tydfil lies close to the Heads of the Valleys. But it wasn’t the river that hit the headlines but a hidden masonry culvert under houses on the Nant Morlais estate. Successive extreme rainfall events over recent years have caused damage to the Pant Culvert and collapse of the supporting brickwork.
A void then opened up towards the surface as the unconsolidated fill sank. The volume of water coursing through the old culvert forced material out and for many days continued to wash and erode the sides of a rapidly widening sinkhole threatening a number of houses around it and forcing the evacuation of the street. Without intervention the sides would widen before it found stable rock.
Emergency and geotechnical crews scrambled to infill the void to prevent further erosion and widening, but have been hampered by the high winds of Storm Darragh that followed two weeks after. Additional future studies will also look at the role of groundwater passing through and around the culvert.
Contains OS data © Crown copyright and database rights 2024© Mapbox© OpenStreetMap© Maxar
A map showing the local geology in the area of Pant, Merthyr Tydfil. The yellow band is mudstone, on which Nant Morlais. On either side, the pink band is coal and the pale brown is sandstone.
Given the area’s past coal mining legacy, it was initially thought that an old adit, shaft or loose spoil could have been to blame. But the estate is sat on a bedrock of mudstone, with superficial till deposits and it looks like it’s another case of infrastructure inadequacy and/or neglect.
The Pant Culvert had experienced damage in 2009 as reported in Council records that had exposed the foundations of the arch itself. The report identified that any subsequent storms could affect dwellings and infrastructure and works were carried out in 2010 and again in 2015. But these patch repairs mask how beyond serviceable use many of such Victorian culverts are and simply aren’t designed to cope with the surge and volume of water from climate driven rainfall events like Storm Bert.
Our Vulnerability
The media usually has a short term memory when it comes to flooding and moves on quickly after the episode passes. We saw the usual human stories of businesses and homes affected, or bailing out water, possessions ruined, lengthy insurance claims or costs where no insurance has been available.
But the wider question remains ever more pressing – the UK is ill equipped to cope with climate change. And this is only going to get worse unless we are serious about prioritising investment in our nation’s resilience at the local level. Tenbury is a good example of the kind of place that even now has to get overlooked year after year for effective flood defences. Yes, the Environment Agency has a finite budget and it has to be viable, but it cant just be focused on how many chimney pots would be protected for the cost. There needs to be root and branch identification of next level streams and culverts that have little or no defence, are frequently blocked and poorly maintained or aged beyond the point of use.
We can’t expect councils or the EA to dish out unending money to protect us so there also has to be property level protection. Homebuyers and owners need to think about mitigating local flood risks through investing in better flood resistance measures – non-return sewer values to avoid flooding into the home from utilities, air brick covers, flood barriers, raising electricity points, installing impermeable, washable membranes on ground floor level. Etc. This places expense on the homeowner and at the point of purchase may lead to future renegotiation between parties on cost or retention by the lender until effective insurance cover can be placed.
Otherwise, estates could be blighted and residents as “stuck climate refugees” – perhaps it would be more cost effective for the Government to incentivise flood resistance in the same way as they encourage energy efficiency to start to shift the needle?
We help conveyancers and homebuyers identify flood risks from all sources as part of transactional due diligence. This includes the effect of flood defences and their failure. Our consultants can also review local ground conditions and topography to consider highly localised differential impacts to the main house, outbuildings or gardens.
For more information on flood risks in our residential environmental reports contact us on 01273 257 755 or email info@groundsure.com
References
https://www.business-live.co.uk/retail-consumer/how-flooding-changed-face-shropshire-6539642
https://www.harriettbaldwin.com/news/mp-repeats-funding-plea-tenbury-flood-scheme
https://www.walesonline.co.uk/news/wales-news/people-could-been-warned-earlier-30467884
https://www.westerntelegraph.co.uk/news/24754192.anger-fear-delayed-flood-warnings-wales
https://democracy.merthyr.gov.uk/documents/s5887/Extra%20Item%20Pant%20Culvert%20GR.pdf?LLL=0
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Date:
Dec 13, 2024
Author:
David Kempster