Summary
This project is a new-build affordable housing development of 92 houses on a site of 1.1 hectares. Almost all of the site lies within a flood plain (see plan below), and this - together with the fact that the site is relatively flat, and the water table lies no deeper than 400mm below the surface - meant that water management was crucial to the success of the project.

Background
The main feature of the drainage of the project was the linking of hard and soft drainage systems. A narrow shallow combined kerb drainage system was used in combination with attenuation devices such as swales. There were a number of severe design issues:

• Discharge from the site was limited to 9.5 litres/second
• Generated site discharge was calculated to be 154 litres/second
• Existing ground levels were to be maintained, on a virtually flat site
• No raised traffic calming measures were permitted The final solution brings together both 'hard' and sustainable drainage techniques within an overall site strategy.

Implementation:
The site was considered as a whole entity

• all adoptable areas
• all non-adoptable areas Drainage was possible no deeper than 400mm, and on-line storage of 130m3 was required. The SUDS had to be easily maintainable. Discharge from the site was strictly restricted because of the potential for impact on other sites downstream.

Results:

• Traditional drainage and SUDS solutions were used and linked together. A proprietary kerb drainage system kept outfall invert levels sufficiently high to enable practical use of sustainable urban drainage systems (SUDS); the SUDS requirement for "quantity and quality" were achieved at site level through the use of proprietary attenuation systems and swales.

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