Incorporating Sustainable Urban Drainage Systems into landscape design

Looking out of the window this morning on to a rainy Birmingham, I think that the subject of this blog article is pretty apt. What happens to rain water once it reaches the ground can have a huge impact not only on where it falls, but further downhill, or downstream. Flash floods can be caused when runoff from surfaces and buildings overwhelms the sewers and drains. One solution is to integrate SUDS into the design of new schemes.

To those unfamiliar with the term, Sustainable Urban Drainage Systems (SUDS) look to deal with rainwater on site as far as possible. The principles are:

• Attenuation (hang on to lots of water and drain into the land)
• Infiltration (let the water drain into the land)
• Conveyance (take the water away and then let it drain)

We are working with Shropshire Housing Group to deliver a scheme of 12 units available as social housing in Much Wenlock. The scheme is exciting not only in terms of a positive social impact, but in the focus that has been given to high environmental standards. The site is on the rural edge of the town at the bottom of a sloping site with arable fields at a higher level. The two biggest issues to address were to deal with water coming on to the site, and water within the site. SUDS plans were integrated into the design from concept stage, where we worked closely with the architects and engineer to position houses, SUDS, roads, and driveways sympathetically.

A central retaining basin has been designed to be a feature of the site. It provides an open, green space for residents. In addition to allowing space for play and reflecting the rural nature of the area, it will perform the attenuation role within the system by taking water from swales across the site in the event of very heavy rain.

Swales (shallow ditches) will hold the water draining off houses, driveways and gardens. Generally, the intention is to let water drain into the swales and be held there to infiltrate into the land. As the site slopes, swales on the steeper parts of the site will be used to collect and convey water to the main retention basin.

The last part of the SUDS strategy is the design of rain gardens in several locations over the site. These gardens are designed to retain and allow water to slowly drain after a storm. They will look like typical areas of planting, planted with species tolerant to extended periods of wet conditions.

The rain gardens will be the final part of the system to ensure that water flowing onto the site, and falling onto the site, does not simply drain onto roads or adjoining properties: rather it is dealt with in an environmentally minded way that also creates a beautiful and positive environment for residents.