New Water Policy and Practice Issue 4, Number 1, Fall 2017 | Page 37

Sustainable Drainage in Challenging Environments
SuDS design under these circumstances cannot be overstated. Devices therefore
have to have the capacity to cope with tropical storms, but must also ensure water
is kept underground to prevent mosquitoes from breeding. Such devices have been
designed in Malaysia by Sidek et al., (2002) and Zakaria et al., (2003). Called BioE-
cods, they are based on swales, but water is kept below the surface (Charlesworth
and Mezue, 2017) in an aggregate-filled modular box. The vegetated surface of the
swale is native Cow grass (Axonopus compressus), and it is important that native
vegetation is utilised when considering green SuDS devices.
3.2 Informal settlements
Fig 2 illustrates the proportion of people living in slums globally from 1990 to 2014
for Nigeria, Brazil, South Africa and Iraq, and whilst populations are decreasing
for the first 3 countries, by 65, 60 and 50% respectively, generally the population
has stabilised between 2007 and 2014 at more than 20% for South Africa and Bra-
zil and more than 50% for Nigeria. In the case of Iraq, however, populations have
increased by nearly three times, probably due to the influx of refugees and the
setting up of refugee camps. Problems here are around the lack of infrastructure
and hence problems with surface water flooding and greywater management. Ex-
acerbating these problems are a lack of services, as waste is not collected and thus
it accumulates, blocking existing drainage infrastructure (Armitage et al., 1998).
Fig 3a show a slum, or informal settlement in Lagos, Nigeria, with accumulated
waste on the lower slopes and Figs 3b and c illustrate the lack of maintenance of
any existing drainage infrastructure with vegetation overgrowth and the accumu-
lation of waste blocking the passage of water.
Figure 2 Proportion of individual country’s urban population living in slums (UN-Hab-
itat definition) from: World Bank, United Nation’s Millennium Development Goals da-
tabase. Available from: (https://data.worldbank.org/indicator/EN.POP.SLUM.UR.ZS?end
=2014&start=2014&view=map) .
35