Geoscience Reference
In-Depth Information
Contaminant sources
Sediment sources
Mixing
Deposition
Road-deposited sediment
(RDS)
Accumulation
Differential
transport by
particle size
Further
mixing
Changing
environmental
conditions
Attrition
Removal of
fines
Chemical
changes
Physical
changes
Removal via
storm sewers
Deposition in
gully pots
Remains as
RDS
Input into
rivers
Chemical changes
Floodplain
accumulation
Cleaning and removal
from system
Transport as
suspended sediment
Physical and chemical changes during
transport
Deposition in canals,
docks or lakes.
Early diagenesis
Fig. 6.4
The urban sediment cascade,
showing the pathways of, and changes in,
urban sediment particulates from sources
to sinks. (Modified and extended from
Charlesworth & Lees 1999.)
Dissolution of grains and
Fe/Mn oxides
Growth of authgenic
minerals (e.g. phosphates,
carbonates, sulfides).
Sink for contaminants.
Contaminant release to
water column
sewage system. Once within rivers, sediment
transport takes place via channel transport pro-
cesses typical for rivers in general (see Chapter 3).
The temporal and volumetric scales of this pro-
cess, however, contrast with rivers from non-
urbanized environments (see section 6.3).
Street surfaces are subaerial and during dry
periods resuspension of fine sediment particulates
by wind can readily take place. The suspension
of sediment particulates has major impacts on
urban air quality. Miguel et al. (1999) attributed
5-10% of the allergenicity of atmospheric sus-
pended particle matter in California to road dust
emissions. Particles less than 10
μ
m (PM
10
) and
less than 2.5
m (PM
2.5
) have been measured
extensively in urban air, and a major component
of these particles, especially those above 2.5
μ
m
in size, can be derived from road-deposited sedi-
ments (e.g. Hosiokangas et al. 1999; Harrison
et al. 2001).
μ
