Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 222

water accumulation. In some cities, due to a lack of maintenance, more than 40% of the
water supply is lost due to leaking pipes.
In many cities, groundwater abstraction for consumption can be excessive, particularly
in regions where available surface water is dificult to access and transport, in arid regions,
and in regions where the quality of surface water supply is deemed unsafe for consump-
tion. Examples cited by Fauchon (2012) show that the water table in Greater Beijing, China,
is falling between 4 and 8 m each year and that in Chennai, India, 300,000 m 3 more water
per day are consumed than available, This will lead to severe problems of ground subsid-
ence, soil erosion, aridiication, and salinization. In coastal regions particularly, high rates
of groundwater abstraction can lead to land subsidence and looding during high rainfall
periods. Seawater intrusion into the aquifers can also occur as a result of groundwater
abstraction from the aquifers, resulting in contamination of shallow aquifers. If vertical
communication exists between shallow and deeper aquifers, contamination of the deeper
aquifers will eventually occur (Yong et al., 1994, 1995). Land subsidence will also result in
damage to structures with foundations affected by differential settlement (Figure 7.2). This
problem has been discussed in detail in the previous chapter in respect to the impact of
high rates of groundwater abstraction in regions where cities are founded on Quaternary
sediments.
Urban discharges can substantially degrade groundwater quality. For example, in China,
phenols, cyanides, mercury, chromium, and arsenides and luorine have been found in
more than 50 urban regions. Urban efluent iniltration can also increase levels of nitrates,
sulfates, and chlorine up to 90 m in depth (Chamley, 2003). Groundwater contamination
causes many health problems and restricts human use.
Salinity is also increasing in the urban environment from discharges of domestic waste-
water, seawater intrusion into aquifers, and contamination from road salt. Detergents,
Evidence
of subsidence
Foundation crack
FIGURE 7.2
Subsidence and foundation impairment resulting from excessive groundwater abstraction.