Derry Hill Residential Development, Calne, Wiltshire

The development comprises fifty house units and garages with associated access roads and car parking contributing to hard run-off areas. All run-off is managed using infiltration systems via a combination of Charcon Infilta pervious pavements underlain with either DrainAgg 20 open-graded aggregate or Permavoid modular sub-base replacement, and narrow linear Permavoid soakaways for collection of a limited number of roofs. The run-off from external pavements is managed in localised sub-catchments to attenuate/infiltrate up to a 1 in 10 year storm event. Roof run-off is managed up to a 1 in 100 year storm event using a combination of either Permavoid modular sub-base replacement or narrow linear Permavoid soakaways. The vertical soakaways, encapsulated in filter geotextile, are laid as discrete linear systems, each with a uniform invert level to maximise capacity and to maximise the infiltration contact area, which has the effect of averaging out any variability in soil permeability that exists.

Client: CG Fry Ltd

Contractor: Tithegrove Building and Civil Engineering

Design Engineer: Peter Brett Associates

Permavoid distributor: Aggregate Industries

Date: 2007

Key design aspects: The SUDS design is based on the following parameters:

Roofs and garages: Total 3347 m²

Main Car Park: 1622 m²

Driveways: Total 2220 m²

Soil Infiltration rate: 3.00 x 10-6m/s (0.0108m/hr)

Storm Return period:
(1) External areas 10 years stored below ground*, with 100 year event contained within overland features;
(2) Roofs and garages 100 years below ground.