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The principles of SuDS and WSUD may be more widely appreciated now than they were, but actually carrying out the work requires skills of both analysis and detail, and involvement at an early a stage as possible. Illman Young, which is based in Cheltenham, has built up expertise in this area of work over eight years, including carrying out a 30-month research study in association with the University of Gloucestershire. As a result it developed an in-house training scheme to ensure that all staff are as knowledgeable as possible. The knowledge gained has helped inform Sue Illman’s decision, as president of the Landscape Institute, to make water one of the main themes of her presidency.

Illman gives popular CPD presentations on SuDS and WSUD. The drawings shown on these pages appear in her presentations. Here there is an opportunity to study them in more detail, with descriptions provided by her colleague Judith Puckmayr.

Cribbs Urban Village
The site for the new Cribbs Urban Village is on the edge of North Bristol, between the boundary set by the M5 motorway, and the A4018 (Cribbs Causeway). It is 51 hectares and will accommodate approximately 1250 dwellings. The main objectives for the SuDS at Cribbs Urban Village is the immediate containment of surface water runoff on site preventing any increased and rapid runoff from impermeable areas affecting the downstream environment which already experiences flood problems.

The early design work considered how and where water would be conveyed and stored on site, considering the topography, existing landscape features, and the available discharge points to the local watercourse.  The potential to discharge is highly restricted to a small part of the site, and is itself within flood zone 2. This early planning was essential to ensure that appropriate space was allocated within the scheme in the right places.

Drainage features will be used in series, starting with prevention and dealing with the runoff as close to source as possible, followed by site and regional control measures, such as the use of basins, ponds and wetland features. Most SuDS features used will be above ground and will take advantage of opportunities to enhance the landscape and biodiversity. They will allow easy access as they will be part of the overall landscape maintenance strategy, with any blockages or pollution becoming visible very quickly. The aim is that the SuDS will become an integral part of the landscape and urban design and give the development a
distinct identity.

Middlemore
These three drawings show Middlemore, a small site in Daventry, Northamptonshire that illustrates how a single-phase development of approximately 50 residential units could be developed in a new local community. The site chosen has an area of 2.72 ha in total, with a target density of approximately 36 dwellings per hectare.

As the site is currently a green field that slopes down in one direction, it was important to begin the masterplanning process by understanding the existing drainage characteristics. The initial study showed that water will naturally collect along the access road at the bottom of the site and the approach was to allow the direction of water flow to occur in a natural way, with controls at source, site and regional levels. An intial SuDS strategy was then developed which showed how the site can be divided into two ‘sub-catchments’, each with a system of source control – e.g. permeable paving and green roofs;  site control, – e.g. ponds, basins and swales; and regional controls – e.g. ponds, basins and wetlands.

There will be a discharge from the regional control features to storm sewers after the larger or longer storms. The SuDS features are positioned so that the larger controls are at the bottom of the site (in this case, the south-east), allowing as many natural features as possible and to minimise the use of underground pipes and pumps.

For cost comparison purposes not only was a fully integrated SuDS solution developed, but also a traditional layout as well as a semi-engineered ‘end of pipe’ solution.

The cost comparison showed that the lowest capital cost was for the full SuDS scheme which is fully integrated within the site layout, and which uses the least number of hard features. This did not include the added benefit of a ‘pond premium’ that SuDS schemes can offer – i.e. the extra capital value on the price of the housing units due to the attractive green environment.

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