Environmental Engineering Reference
In-Depth Information
21
Assessment of Infection Risks
due to Urban Flooding
LORNA FEWTRELL, KEREN SMITH
AND DAVID KAY
Introduction
been adopted to gain a 'feel' for the infection risk as
generally data are not collected to allow specific
estimation via other means.
Urban flooding can result in a number of public
health impacts, including fatalities resulting from
drowning and entrapment during the immediate
flood event, mild impacts such as stomach upsets,
and long-term effects such as increased levels of
anxiety and mental health problems (Fewtrell and
Kay 2008). This chapter focuses on the risk of
human infection presented by microbial hazards
in the flood water.
For there to be an infection risk from urban
flooding, a number of factors must coincide;
these can be thought of in terms of a Source,
Pathway and Receptor paradigm, as illustrated in
Figure 21.1.
Thus, the Source is the microbially polluted
floodwater, the Pathway is the route that the flood
water takes, and the means by which people are
exposed to its microbial contaminants, and
the Receptor is the householder (or member of the
rescue services, etc.) affected by the floods and
exposed to the constituent pathogens. The source,
pathways and receptor issues are examined in
more detail, before the presentation of an explor-
atory quantitative microbial risk assessment
(QMRA), which examines the risk of gastrointes-
tinal disease resulting from flooding and associat-
ed clean-up operations. The QMRA approach has
Source
In an urban flood there may be a number of com-
ponent flood flows that contribute to the 'quality'
of the flood water. These are illustrated in
Figure 21.2 and outlined in more detail in the
following subsection.
Component flood flows
Combined sewer overflows
Combined sewer overflows (CSOs) have been
identified as an important component ofmicrobial
discharge from urban areas, representing a mix-
ture of raw sewage, stormwater microbes and
combined sewer sediment. Ellis and Yu (1995)
identified CSOs as a primary source of microbial
contamination to urban waters in London.
Foul flow
The occurrence and concentration of microbial
contamination in raw sewage will vary, both tem-
porally and spatially, depending upon the catch-
ment and the health and size of the population.
Treated, or partially treated, wastewater may also
be a component of a flood flow after discharges
from wastewater treatment works into receiving
