When constructing a new car park, a stormwater management system should be considered to prevent localised flooding. As one of the UK’s leading stormwater specialists, we are experts in this field.
Here is a recent example of a stormwater attenuation system we supplied and installed for construction company, Henry Williams and Son (Roads) Ltd, when they built a new car parking facility at a North West NHS Hospital
The stormwater management challenge
The North West based NHS hospital decided it needed to extend its car parking facilities after patients, staff and visitors were struggling to find somewhere to park at the busiest times. They decided to buy a patch of land near the hospital to manage the overflow of traffic and create an additional 338 parking bays.
With the introduction of a new car parking facility, there was a concern over potential future flooding. The car park’s hard impermeable surface would lead to an increase in surface water runoff which local sewers would struggle to cope with during periods of heavy rainfall.
A sustainable surface water management system was therefore deemed a key requirement for the 7,000 sq.m. car park. Henry Williams and Son (Roads) Ltd, the construction contractor working on the car park contacted the team at Cotterill Civils.
We supplied and installed a stormwater attenuation system to ensure the car park met with Defra’s Sustainable Drainage Systems (SuDS) regulations. SuDS is a natural approach to managing drainage in and around properties and other developments.
The system was created using stormwater attenuation crates, which offer an economical and versatile solution to stormwater management. The individual crates were lowered into the excavated area and then interconnected to form one huge below ground holding tank, measuring 355.2m3 and 12m x 37m x 0.8m.
Then to prevent water discharge to the substrate, as well as prevent any soil or sand particles from going through, the crates were wrapped in a geotextile protective fleece and an impermeable membrane, with heat-welded joints.
The below-ground tank is designed to fill up and hold the resulting stormwater when heavy rainfall occurs. The collected stormwater is then released back to the main sewers via a hydrobrake over a more sustained period of time, preventing localised flooding.
Sean Martin, MD of Henry Williams and Son (Roads) Ltd, commented: “We were really pleased with the stormwater attenuation tank installation Cotterill Civils did for us. Despite the timescales being tight, they completed all works one day ahead of programme. The offsite support was great and the attitude of the installation gang was very good on-site, with high standards of health, safety and quality shown throughout the installation. We would definitely use Cotterill Civils again. ”