The following paragraphs highlight some case studies outside of the UK that demonstrate International applications of retrofit SUDS. The first two - Malmö and Portland - are well-established and well-publicised success stories (by-and-large); though Tokyo probably has higher density development to contend with, this application is less well publicised. The Emscher Drainage Basin rehabilitation plans provide an ambitious and extensive programme of planned retrofit in a high-density industrialised European context.
Augustenborg is a highly populated inner-city suburb in Malmö, southern Sweden. Stormwater from the area was originally drained via a combined sewer system (pipe diameters between 225 and 750 mm). During heavy rain storms, CSO and flooding in basements and garages occurred. In an effort to solve these problems, it was proposed that Augustenborg be disconnected from the existing combined sewer and drained by means of an open stormwater system. The open system has been operational since 2001. Stormwater is now led through a complex arrangement of green roofs, swales, channels, ponds and small wetlands. Villarreal et al. (2004) suggest that the green roofs are effective at lowering the total runoff, and that the ponds should successfully attenuate storm peak flows for even the 10-year rainfall.
A detention basin in a school yard also acts as an auditorium
The Augustenborg project focused on an area of 'tired' public/private apartment blocks and council offices. Community participation was an important factor in the implementation of stormwater disconnection, amongst a range of other eco-friendly measures.
Portland has a long-established (10 years) downspout disconnection programme - More than 42,000 homeowners have disconnected downspouts, removing more than 942 million gallons of stormwater per year from the combined sewer system.
Fujita 1984, (3ICUSD) described the 'Experimental Sewer System' (ESS) which had been installed in about 249 ha of dense urbanized area in Tokyo since 1980. Fujita, 1994, claims that all footpath pavements in Tokyo have been changed to permeable pavement. Some of the porous concrete blocks now are made from incinerated sewage sludge or slag of melted sewage sludge. Residents cooperate to construct soakaways in their own housing areas at their own expense. The infiltration trench is so effective that it is used in various locations such as housing sites, housing complexes, streets, school grounds, public gardens. Storage tanks have been constructed in a housing complex, thus stored stormwater can be effectively used for toilets, sprinkling, car wash, and for a recreational pond.
Fujita, 1997, claims that 'the ESS (Experimental Sewer System) incorporating infiltration and storage systems in the sewerage network has proved highly effective to control the storm runoff. During the past 12 years (from April 1983 to March 1995), the Tokyo Metropolitan Government has built the ESS over an area of more that 1,423 ha with 33,294 infiltration pits, 285 km of infiltration trenches and 484,00 m2 of permeable pavement'. Fujita, 1997, reports that in Koganei City in Tokyo 19,199 soakaways were installed across the city during the 10 years to March 1995, at no cost to the public budget, apparently due mainly to the enthusiastic public engagement activities of one council worker.
Presumably a considerable portion of this represents retrofit into a dense urban area. Tokyo also implements RTC.
Emscher (865 km2) is an industrial conurbation, which - due historically to subsidence - is drained using surface water channels that act as combined sewers. The plan over the next 15 years is to replace this system with sanitary sewers and to retrofit source-based stormwater management systems where feasible. Their aim is to reduce the total amount of stormwater carried by the combined system by 15% over 15 years. They have established a GIS-based planning tool (with all the usual elements) that highlights and prioritises the feasible level of disconnection in each area. Institutional buildings are being prioritised for detailed design. Becker et al's Table 1 illustrates land use types that might be matched to typical UK urban layouts.
Focusing on Vancouver, Graham and Kim (2003) suggested that 'modeling results for 50-year watershed retrofit scenarios show that re-development of existing buildings with green roofs could effectively counteract the anticipated effects of climate change and land use densification, and also help to restore watershed health over time. Green roofs combined with infiltration facilities was shown to be one of the most effective overall source control strategies for the region'. Similar approach proposed for New York City by Cheney and Rosenzweig (2003).