Swansea needs more Car Parks

Swansea is Wales' second city and has been described as the “gateway to West Wales”. It occupies a strategic position in the historical, political and economic development of Wales.The city is a mixture of outstanding natural beauty, commerce and industrial activity. In order to maintain sustainable development of the city and provide the city with more car parking facilities, an out-of-town park and ride scheme was constructed off Fabian Way in 2002, as one of four new proposed car parks out of the city centre. This route is the main eastern access into the city from the M4 motorway. The City and County of Swansea's Local Transport Plan (LTP) recognised the need for park and ride schemes to cut city centre congestion and the project was completed in December 2002 in time for the run up to Christmas. The total cost of the project was £4.3m, £2m of which was required for land acquisition, and the project came in on time and to budget. The success of this project has led to the model being used as a template for future schemes.

Sustainable Development

Swansea is currently experiencing a commercial boom with heavy investment and the regeneration of its docks into the SA1 Waterfront Development expected to raise the profile of Swansea significantly. The need to provide sustainable development in an area that offers so much more than commerce was imperative to Swansea's future. Not only does the Fabian Way scheme reduce congestion and pollution in the city centre by making it more attractive to pedestrians and cyclists, it also uses a Sustainable Drainage System (SuDS) to manage surface water effectively.

Constraints to Construction

The main constraint for the developing the site at Fabian Way was the lack of a suitable outfall for surface water disposal. Three options were considered:

• Construction of a new outfall under Fabian Way into Swansea Docks to the south of the site;
• Construction of a new outfall to the east of the site into the Port Tennant Marsh (SSSI);
• Discharge to existing combined system, with on-site storage to limit discharge to allowable rates, which were low.

Why SuDS?

None of these options were particularly attractive, and it was recognised at this stage that a SuDS would be the best solution. The relatively flat nature of the site meant that a permeable surface could be used, providing flow attenuation in a stone media beneath the paving system. Two manufacturers were considered for the construction of the system, with Formpave being the selected contractor.

Porous Car Park

The Formpave Aquaflow system employs a system of blocks and slabs, manufactured from C49 concrete. The blocks and slabs provide drainage through vertical channels created by bevelled sides forming a V section. The system is designed to allow water to penetrate through the surface at a rate of 9000 litres per square metre per hour. The water is passed into the underlying upper and lower sub-base layers (approximately 350mm thick), which are separated by an intergrid mesh. A permeable geotextile at the base of the lower sub-base layer facilitates controlled infiltration into the underlying strata and the trapping of solid particles. The sub-base layers, with their inherent system of voids allow the surface water passing through the paved surface to be attenuated and the stone layers also provide filtration, reducing solids and hydrocarbon content to acceptable levels prior to infiltration.

The site was designed using the following materials:

• Parking Bays – SuDS blocks;
• Roundabout Area – Heavy Duty SuDS Blocks;
• Access Aisles – Lightweight Flexible Construction;
• Pedestrian Areas – Traditional Block Paviours.

Assessment of Ground Conditions

Prior to construction of the scheme, a site investigation was carried out to confirm the permeability of the underlying strata, to assess the suitability of the ground for an infiltration solution. The results of this investigation showed that the ground was suitable, with porosity tests carried out in accordance with BRE Digest 365. Approval for the system was also sought from the Environment Agency Wales (EAW). The main advantages of providing this Sustainable Drainage System at this site were:

• No new outfall required, reducing costs and minimising disruption;
• Reduced earthworks scope as falls did not have to be created to drain the area.

Adoption

The City and County of Swansea have adopted the site and are responsible for its maintenance. The recommended maintenance routine is twice yearly suction cleaning, and it is envisaged that the replacement of the 50mm clean stone layer directly beneath the blocks will be required in 20 years. The main access road has been adopted as a public highway, so maintenance responsibilities do not extend beyond the car park. The site maintenance will be monitored over the next twenty years and this analysis should provide valuable input into whole life costing of similar SuDS.