No abstract

In recent decades, rapid urbanization has resulted in a growing urban population, transformed into regions of exceptional socio-economic value. By removing vegetation and soil, grading the land surface and saturating soil air content, urban developments are more likely to be flooded, which will be further exacerbated by an anticipated increase in the number of intense rainfall events, due to climate change. To date, data collected show that urban pluvial flood events are on the rise for both the UK and China. This paper presents a critical review of existing sustainable approaches to urban flood management, by comparing UK practice with that in China and critically assessing whether lessons can be learnt from the Sponge City initiative. The authors have identified a strategic research plan to ensure that the sponge city initiative can successfully respond to extreme climatic events and tackle pluvial flooding. Hence, this review suggests that future research should focus on (1) the development of a more localized rainfall model for the Chinese climate; (2) the role of retrofit SuDS (Sustainable Drainage Systems) in challenging water environments; (3) the development of a robust SuDS selection tool, ensuring that the most effective devices are installed, based on local factors; and (4) dissemination of current information, and increased understanding of maintenance and whole life-costing, alongside monitoring the success of sponge cities to increase the confidence of decision makers (5) the community engagement and education about sponge cities.

Sustainable Drainage (SuDS) improves water quality, reduces runoff water quantity, increases amenity and biodiversity benefits, and can also mitigate and adapt to climate change. However, an optimal solution has to be designed to be fit for purpose. Most research concentrates on individual devices, but the focus of this paper is on a full management train, showing the scale-related decision-making process in its design with reference to the city of Coventry, a local government authority in central England. It illustrates this with a large scale site-specific model which identifies the SuDS devices suitable for the area and also at the smaller scale, in order to achieve greenfield runoff rates. A method to create a series of maps using geographical information is shown, to indicate feasible locations for SuDS devices across the local government authority area. Applying the larger scale maps, a management train was designed for a smaller-scale regeneration site using MicroDrainage ® software to control runoff at greenfield rates. The generated maps were constructed to provide initial guidance to local government on suitable SuDS at individual sites in a planning area. At all scales, the decision about which device to select was complex and influenced by a range of factors, with slightly different problems encountered. There was overall agreement between large and small scale models.

This paper reviews the devices suitable for building scale application and then outlines three case studies, two from Coventry, UK and one from Valencia, Spain. The first assesses the potential to retrofit an extensive green roof to the Frederick Lanchester Library, Coventry University. Costings are given, the structural strength of the building is investigated and various benefits of its installation, including potential to sequester and store carbon, are assessed. The second reports part of the AQUAVAL Project, Spain, whereby an extensive green roof was retrofitted to half of a school roof and porous concrete retrofitted to a pavement. Preliminary monitoring results show expected benefits, including attenuation of the storm peak and increased time to peak. The third case study using WinDes ® software compared a conventionally drained new-build housing estate with a Sustainable Drainage Systems train of porous paving, bioretention and swales. Stormwater volume was reduced by ∼20% and peak flow by >250 L s -1 . Addition of extensive green roofs to all buildings increased these differences and delayed return to baseflow conditions reflecting water stored in the management train components.

This novel research models the impact that commonly used sustainable drainage systems (SuDS) have on runoff, and compare this to their land take. As land take is consistently cited as a key barrier to the wider implementation of SuDS, it is essential to understand the possible runoff reduction in relation to the area they take up. SuDS management trains consisting of different combinations of detention basins, green roofs, porous pavement and swales were designed in MicroDrainage. In this study, this is modelled against the 1% Annual Exceedance Potential storm (over 30, 60, 90, 120, 360 and 720 min, under different infiltration scenarios), to determine the possible runoff reduction of each device. Detention basins were consistently the most effective regarding maximum runoff reduction for the land they take (0.419 L/s/m2), with porous pavement the second most effective, achieving 0.145 L/s/m2. As both green roofs (20.34%) and porous pavement (6.76%) account for land that would traditionally be impermeable, there is no net-loss of land compared to a traditional drainage approach. Consequently, although the modelled SuDS management train accounts for 34.86% of the total site, just 7.76% of the land is lost to SuDS, whilst managing flooding for all modelled rainfall and infiltration scenarios.