Product / system manufacture
Product / system supply
Southwark Council / Thames Water Utilities Ltd
Stormcell ® and Stormbloc ® modular block storage systems
A £4.28m award-winning flood defence project, led by Southwark Council, has been created to provide much-needed protection for two sensitive and historic parks.
Herne Hill and Dulwich are prone to flooding as a result of being in a low-lying catchment of the culverted Effra River. Overland surface water flow from surrounding hills and large open fields, coupled with extensive hard surfaces such as roads, car parks and other structures, combine with the impervious underlying London clay to create a significant flood risk.
The design involved the construction of above- and below-ground temporary flood storage to capture overland flow during periods of heavy rainfall. Above ground, a mixture of natural earth bunding and dwarf brick retaining wall structures was constructed in Dulwich, while in Belair Park a combination of earth bund and detention basin was installed to control peak surface water flows.
A key element of the flood defences was underground geocellular block storage from Hydro International. Engineer Mouchel’s sensitive design proposed using Hydro International’s Stormcell® and Stormbloc® modular block storage systems to store excess water.
By specifying attenuation tanks using Hydro’s Stormcell® and Stormbloc® modular block geocellular storage systems, several different concerns were satisfied. The block systems are load-bearing and could be landscaped back to their original grassed appearance, and significant money and time was saved during installation with less heavy plant on site.
Due to the modular block format, each tank is only 1m in depth, which limited the amount of excavation required. Wrapped in geotextiles, the tanks are covered with topsoil to a minimum depth of 0.5m, which means they are effectively invisible.
The innovative scheme won the 2015 Environment Agency (EA) award for Partnership Project Excellence for its integrated partnership working and community engagement. Community groups had initially objected to flood relief measures involving the use of overground pond storage in the Grade II listed park areas. Engineer Mouchel’s sensitive design proposed using Hydro International’s Stormcell® and Stormbloc® modular block storage systems.
“The public concern over retaining the parks’ appearance was very strong,” says Mouchel Project Engineer James Armitage. “Even though they realised the flooding problem, they did not want to lose significant areas of the parks to large ponds and swales.” By specifying attenuation tanks using Hydro’s Stormcell® and Stormbloc® modular block geocellular storage systems, several different concerns were satisfied.