Sustainability: Drainage systems | Features

The following are indicative costs for commercial schemes located in south-east England, current in first quarter 2006.
Infiltration systems
Standard pavings, 150 mm thick sub-base (not SUDS, comparison only)	£35-40/m2
Permeable pavings, 250 mm crushed rock sub-base, disposal of spoil on site	£40-45/m2
Permeable pavings, 350 mm crushed rock sub-base, disposal of spoil off site	£50-55/m2
Land drainage, perforated pipes in trenches, granular fill	£30-45/m
Soakaways, crushed rock soakaway, cover and cover slab, geotextile membrane and granular surround, excavation and disposal of soil off-site	£150-275/m3
Swales; excavation and formation of swale channel to fall, 1m wide by 750 mm average deep; geo-textile membrane; vegetation	£75-100/m
Retention systems
Geocellular storage system; 500 mm thick storage blocks, perforated land drains in granular surround; sub-base; impermeable membrane; excavation and disposal of spoil off site (surface costs excluded)	£100-140/m2
Vortex control valves
Supply cost of valve and chamber ring only	£200
Total cost of valve and inspection chamber	£2,000-2,700
Control systems
Bypass separator, about 7,000-litre capacity	£9,000-10,000
Full retention separator, about 7,000-litre capacity	£15,000