SDS installs Scotland's largest stormwater attenuation system.
Edinburgh Airport’s expansion to accommodate increases in passenger numbers, increased freight traffic and long-haul air routes, is continuing as part of the airport’s 2040 development masterplan. The Edinburgh Airport Stands Development is being overseen by main contractor Careys Civil Engineering and will create thirteen new aircraft parking places and associated taxiways.
During heavy rainfall, it is essential that stormwater drains as quickly as possible from the new 75,000m2 concrete pavement area created as part of the Stands Development. Due to their location away from the main airport terminal, passengers will be transported by bus to and from the stands. With aircraft operations, service vehicles and passengers on foot, effective flood-free drainage across the entire pavement area is essential to ensure the airport can continue to operate efficiently and without interruption.
SDS was tasked to effect the fast and efficient removal of surface water from the site and to ensure its safe dispersal to natural water receptors. As well as mitigating anticipated flooding issues as a consequence of the Airport’s expansion, this involved minimising the Airport’s impact on the environment whilst satisfying the environmental demands of the West Edinburgh Strategic Design Framework (WESSDF).
How it works
Surface water, predicted to run off the newly-created impermeable surface at flows of up to 3,000 l/s, must not be allowed to discharge into receiving natural water bodies surrounding the airport at a rate that could cause environmental damage or flooding. It is, therefore, collected via a gravity network of heavy-duty slot drains and a 660m-long run of 1,500mm diameter pipes, before being fed, via a single 1500mm pipe, to the SDS GEOlight® attenuation system.
Installed approximately 20 metres to the south of the new stands area, the GEOlight® tank, measuring 72 metres long, 32m wide and 3.25m deep, is designed to hold back almost 7,000m3 of surface water during heavy storms. A number of oil interceptors are positioned along the gravity network to clean the water before it enters the GEOlight® tank.
The amount of water leaving the tank is carefully controlled by a pumping station, so that discharge into the Gogar Burn, that runs along the airport perimeter and eventually into the River Almond, is limited to 110 l/s, the maximum flow rate permitted by the Scottish Environmental Protection Agency (SEPA).
In time for Winter 2019 and any freezing weather conditions, Careys will construct a system to hold surface water collected in the SDS GEOlight® tank if a sensor detects that it is contaminated with Glycol anti-freeze. The polluted water will then be diverted into specially-designed storage tanks, where it will be collected and correctly disposed of.
Selecting the right design for a tank of such large proportions was the first challenge to overcome. Given the size, the only potential solutions were either a concrete tank or modular crate storage. Installing a concrete tank would, however, have posed significant civil engineering challenges; with a tight programme, specifying SDS modular storage offered the advantage of both buildability and speed. SDS worked on the tank design with consulting engineers Amey to optimise the strength and durability of the tank during its design life.
With good ground conditions of sandy clay, Careys was able to prepare the excavation, measuring nearly 100m x 50m at ground level, ready for SDS to install the tank. Allan Crozier, Senior Project Manager at P.J. Careys: “We only needed to prepare the groundworks for the tank to be installed, and then provided backfilling as required, as SDS constructed the tank in stages. The SDS guys were very engaging and cooperative and worked just as if they were part of our team. They met daily with the project engineer for that section and co-ordinated whatever they needed between them.”
“The SDS team know their business and know better than anyone how to install the tanks. SDS have a good safe system of work, so we had comfort in that as well. Deliveries were scheduled to be just-in-time, almost to the day’s work, sometimes involving several deliveries a day. So, the amount of space needed for storage of crates on site was minimal and SDS planned deliveries according to the capability of the team to install the blocks on site that day.”
Allan Crozier, Senior Project Manager at P.J. Careys: “Although on smaller schemes we do sometimes install storage crates ourselves, working with SDS meant we could hand over the installation of the tank to them. The SDS team were totally self-sufficient and extremely slick. They are the experts and were able to complete the installation within 7 weeks, with both speed and skill.”