Extreme Weather Test for New Leaky Dams on Kent’s Alder Stream Catchment
A natural flood management scheme which was only installed in Tudeley Woods near Tunbridge Wells in January has functioned effectively during the extreme weather conditions in Kent caused by Storms Ciara and Dennis, according to the South East Rivers Trust (SERT).
Just a few weeks after the completion of 50 “leaky dams” on the Alder Stream catchment, located within a 900-acre woodland RSPB reserve owned by the Hadlow Estate, the scheme was put to the test with heavy rainfall, amounting to peaks of 28mm in just one hour, recorded at Paddock Wood.
Although some properties in Five Oak Green and Capel were flooded after sudden torrential rainfall on February 9th during Storm Ciara, the cause was hillside run-off, rather than flooding from the Alder Stream.
Dean Morrison, SERT’s Natural Flood Management Project Officer, explained: “Properties in Five Oak Green were flooded as well as a row of properties including the Dovecote pub at Alders Road, Capel. While these cottages missed flooding from the Alder Stream, they were hit by water flowing off the hillsides and into the ditch network behind the village.
“Whilst it’s too early to claim that the number of leaky woody structures we’ve put in have had a significant impact yet, we checked on them during the storms and they’re functioning as they’re designed to,” added Dean.
The streams in Tudeley Woods near Tunbridge Wells have been blocked by a set of 50 intricately-constructed dams, which were built over the winter of 2019-2020.
“The project aims to add fallen timber to the streams to slow the flow of water,” explained Harry Teacher, whose family has owned the 900-acre Tudeley Woods for 170 years. Harry and his wife Kate head up the Hadlow Estate in the Weald of Kent. “It will even out the flow of water and the aim is to prevent flooding further downstream.”
The Natural Flood Management Project has been carried out by the Hadlow Estate in partnership with the South East Rivers Trust (SERT) – a local environmental charity bringing rivers back to life across the South East of England.
Dean explained: “What we have found is that, in heavy rain, water rushes down from the headwaters and rapidly increases the flow in rivers downstream. Within a short period of time, this huge increase in water volume can pose a serious flood threat to property and people.”
To this end, the steep-sided streams in Tudeley Woods – or ghylls, as they are known locally – now have logs jammed across them. Over time, these will catch sticks and leaves to become what are known in the conservation world as “leaky wooden structures”.
The project was carried out in December 2019 and January 2020, with financial support from SERT and The Environment Agency as part of the Medway Flood Action Plan.
The streams in Tudeley Woods stem from natural springs within the woods and feed into the Alder Stream, a tributary of the River Medway with a history of flooding. The Natural Flood Management Project aims to help protect over 50 residential properties at risk from flooding from the Alder Stream in the village of Five Oak Green.
The benefits of the project will also be felt within the woods themselves, says Harry’s wife Kate, who has been working on the scheme for some time. “The idea of using our upland woodland for natural flood management has been under consideration for a couple of years. We first commissioned a survey of the woods, including the streams and a large central pond, to see exactly what was happening. We discovered that despite the wet winters, the warmer summers have meant that the woods are drying out year-on-year, which can have serious consequences for biodiversity.
“Tudeley Woods are a remnant of ancient woodland that once covered most of South East England. The woods are home to nearly 1200 varieties of fungi as well as rare birds and plants. There’s the nationally-rare Marsh Valerian flower as well as many butterflies and orchids. And in terms of birds you’ll see tree pipits, nightjars, woodlarks and Britain’s most rare woodpecker, the Lesser Spotted Woodpecker.”
The retention of water in the woods, preventing it from rushing away downstream, is very important for preserving habitats, said Harry. “We are using natural methods to increase resilience to climate change. Leaky dams are an effective way of preventing flooding further downstream but we are also working to prevent the woods from drying out, preserving the biodiversity of the flora and fauna here. It’s a win-win situation.”
Much of the timber used for the dams had fallen naturally within the woods, with other logs being felled as part of routine tree management.Until now, the image of flood prevention has been one of expensive engineering work, pumps and interventions near the site of a flood risk. Now, thanks to this timely project in Tudeley Woods, it seems that fallen trees, sticks and leaves can also make a contribution to protecting property.
“It’s a scheme that, if successful, could have implications for woodland management both nationally and further afield,” said Harry. “We look forward to monitoring the project in the months and years ahead.”