In a unique position, the city of Hull is settled on flat land adjacent to the sea, with several surrounding valleys that drain their rain water into the basin in which Hull city centre sits.
In 2007, over 8,500 properties were affected by flooding in Hull City. The flooding also saw numerous main roads through Willerby, Derringham, Cottingham, and Orchard Park become rivers without any alternative natural water course.
The disaster affected other regions as well as Hull, leading to a partnership between Hull City Council and East Riding of Yorkshire Council. Additionally, this also led to the support from the Environment Agency, and Humber Local Enterprise Partnership as a joint venture to find solutions to reduce the threat of repeat flooding.
The Willerby and Derringham Flood Alleviation Scheme (WaDFAS) is one of two projects created through the partnership between Hull City Council and East Riding of Yorkshire Council.
Having taken the project over at the detailed design stage, Pell Frischmann set out to reduce fluvial flood risk to 8000 homes and 200 businesses, and provide economic stability within the area. Additionally, the project also seeks to maintain transport routes during severe rainfall to ensure people and deliveries get to their destinations without delays.
To identify flood storage reservoirs in the catchment area, a 3D computer model was created. The model also enabled engineers to modify existing reservoirs to catch the water flowing down into Hull city centre and release it at a predetermined rate slowly into the system to prevent flooding. This was one of the largest uses of the computer model at the time.
For ground water protection, we were required by the Environment Agency to line the reservoirs. As flood alleviation experts, we were able to access a large amount of needed clay for the lining from a chalk bedrock by a glacial till nearby. After testing the material as suitable for use, we adjusted the configurations of the reservoir to maximised the volume of clay while minimising the amount required to cut into the chalk on the reservoir. With this strategy not considered within the preliminary design, time and money was saved for our clients.
Both Willerby and Derringham, Cottingham and Orchard Park alleviation schemes will enable the great protection of residents, their homes, and businesses within the area. Pell Frischmann have been able to deliver sufficient benefits with minimum cost.
- 8,000 - homes protected
- 200 - work places protected
- 1 in 75 - year flood event