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studied extensively (see Chapter 3), very limited
study has been made of river sediment sources
in urban catchments. A recent exception is that
of Carter et al. (2003) for the Aire-Calder river
basin in eastern England (see Case Study 6.2).
Through the application of well-developed stat-
istical fingerprinting techniques (see Collins &
Walling 2002) they showed that the sediment
in the urban river sections was sourced from
channel bank erosion (18 -33%), uncultivated
topsoil (4 -7%), cultivated topsoil (20 - 45%),
road-deposited sediment (19 -22%) and sewage
input (14 -18%). The high contribution of urban
sources (up to 40% sewage and RDS) illustrates
the marked contrast of urban sediments to those
in non-urbanized catchments. This is in general
Case study 6.2 Sources and dynamics of urban river sediments: Rivers Aire and Calder,
West Yorkshire, UK
Limited information is available on the specific sources of sediment to urban rivers, in direct
contrast to that of other river systems (Chapter 3). Exceptions are the Rivers Aire and Calder
in West Yorkshire (eastern England; Case Fig. 6.2a), which has seen recent detailed analysis
through research programmes directed at understanding fluvial and urban environments
(The Land-Ocean Interaction Study (LOIS) and the Urban Regeneration in the Environment
(URGENT) programmes of the UK Natural Environment Research Council). These rivers are
part of a catchment that in its upper parts is predominantly rural in nature, but which in its
lower parts runs through heavily urbanized catchments.
Sediment sources in the Aire and Calder have been shown to vary between the upstream
rural-dominated and the downstream urban-dominated parts (Carter et al. 2003). Suspended
sediment in the upper reaches is predominantly sourced from channel-bank material (43 - 84%)
and from uncultivated topsoil (16 -57%). This is in contrast to the lower, urbanized reaches,
where road-deposited sediment (19 -22%) and sewage treatment works (14 -18%) acted as
significant sources of suspended sediment (see Case Fig. 6.2a). Carter et al. (2003) also found that
the proportions of sediment sources to the urbanized reaches varied over individual storm events.
Road-deposited sediment sources were highest at the end of high-flow events (Case Fig. 6.2b)
as a result of the time lag to flush sediment from road surfaces.
The quality of urban river water is commonly poor and the role of sediments, and sediment-
borne contaminants, on water quality and contaminant fluxes is poorly understood. Goodwin
et al. (2003) and Old et al. (2003) have quantified the nature of suspended sediment fluxes
through the Bradford Beck, a tributary of the River Aire, which runs through the heavily urban-
ized city of Bradford. Goodwin et al. (2003) carried out continuous monitoring of the urban
segments of the river, both for discharge and suspended sediment loads. The hydrographs
show that the river responds rapidly to rainfall events and suspended sediment concentrations
are also high during these events (up to a maximum of 1200 mg L −1 ). They proposed that in
the urban segments sediment was derived from road runoff and combined sewer outflows. As
can be seen from Case Fig. 6.2c, suspended sediment loads were several orders of magnitude
higher during storm events than during low flow times. Although Goodwin et al. (2003) do
not publish compositional data for suspended sediments, as well as the physical impact of
the suspended sediment, the flux of contaminants on these sediments is likely to be highly
significant also.
For the same river, Old et al. (2003) studied the sediment dynamics for a single, large con-
vectional summer rainfall event (Case Fig. 6.2c). They found that during this event, over a
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