There’s been a lot of weather lately, so we sent our lagoons correspondent Angus Young to report on how our city avoids (another) disaster.
If you happened to be in Hull or the surrounding area on 25 June 2007 you will almost certainly remember what you were doing that day. It was when exceptionally heavy and prolonged rainfall led to around 10,000 homes and businesses being flooded. Instead of the threat coming from swollen rivers or a Humber tidal surge, the low-lying city and its suburbs were flooded because the drains and various pumping stations couldn’t cope. As a member of a panel set up to investigate the causes of the flooding and make recommendations put it: “Hull lies on the bottom of a sink and no-one managed to pull the plug out that day.”
Building a bigger drainage system to prevent future similar surface water flooding was ruled out on cost grounds. After all, Yorkshire Water had only recently spent £200m constructing a new 10km long combined sewer and storm drainage tunnel under Hull which had taken over four years to complete. Big enough for a Mini to be driven along a section for a publicity stunt but seemingly not big enough to handle a month’s worth of rain which fell in less than 24 hours.
Instead, the idea of keeping as much surface water out of the drains as possible during a storm has been gradually turned into reality via a new series of huge storage lagoons ringing the city designed to hold rain falling on slightly higher ground from entering Hull’s drains. Once the worst of the weather is past, the stored water is slowly discharged into the system.
The first lagoons were built along Eppleworth Road near Cottingham. They can hold 30,000 cubic metres of water.
The Willerby and Derringham Flood Alleviation Scheme came next with four storage lagoons created immediately to the west of the A164 at Willerby and on land off Wold Road in West Hull. The total capacity here is 233,000 cubic metres.
The Cottingham and Orchard Park Flood Alleviation Scheme is even bigger. Featuring more storage sites in Eppleworth Road and a lagoon on land between the village and Orchard Park, it can hold 478,000 cubic metres of water.
Then there’s the Anlaby and East Ella Flood Alleviation Scheme which even boasts its own tunnel to funnel surface water from the hills above Tranby Croft and a new storage lagoon created at the site of the former Sydney Smith School in Hull which was demolished after being flooded in 2007. Here the capacity is 150,000 cubic metres.
Overall, the schemes to the west and north of Hull now provide added protection from flooding to over 16,000 homes and businesses. They have recently been joined by the Castlehill Aquagreen project to the east of the city which has been designed to reduce the risk of flooding to another 800 properties in Bransholme and Sutton. This scheme is capable of storing 15,000 cubic metres of water and also includes a fully automated pumping station to manage water levels on the flood-prone Holderness Drain.
Overall, the new storage capacity for surface water run-off around the edge of Hull is now 906,000 cubic metres. We’ve done our maths and concluded that’s the equivalent of 350 open air Olympic-sized swimming pools. (That’s nearly 6 million bathtubs full – Ed.)
Brexit fans might also want to note that all the schemes with the exception of Castle Hill received 50 per cent funding from the European Union worth around £30m. Lucky we got flooded before the 2016 referendum and not after it!