Geoscience Reference
In-Depth Information
As a consequence of this the water quality of the Salford Quays was improved through increased
mixing of air into the water column (Boult & Rebbeck 1999).
The nature of sedimentation in the Quays has markedly changed in response to this water
column clean-up (Case Fig. 6.3b). Pre-remediation sediments are composed of a range of natural
detrital grains, predominantly quartz and clay, and anthropogenic detrital material dominated
by industrial furnace-derived metal-rich slag grains. Post-remediation sediments are composed
of predominantly autochthonous material, including siliceous algal remains and clays. At the
top of the pre-remediation sediments and immediately beneath the post-remediation sediments
is a layer significantly enriched in furnace-derived slag grains, input into the basin as a result of
site clearance prior to water-column remediation. These grains contain a high level of metals,
resulting in a significantly enhanced metal concentration in the sediments at this depth (Case
Fig. 6.3b). Significant porewater peaks in Fe, Mn and Zn in the sediment (Case Fig. 6.3c) are
most probably the result of dissolution of these furnace-derived grains in the sediments, possibly
mediated by iron and manganese oxide-reducing bacteria. These species have subsequently
diffused into porewater above and below the metal enriched layer, indicating the important
control of diagenesis on the long-term fate of contaminants in urban sediments.
Relevant reading
Boult, S. & Rebbeck, J. (1999) The effects of eight years aeration and isolation from polluting discharges on
sewage- and metal-contaminated sediments.
Hydrological Processes
13
, 531- 47.
Taylor, K.G., Boyd, N.A. & Boult, S. (2003) Sediments, porewaters and diagenesis in an urban water body,
Salford, UK: impacts of remediation.
Hydrological Processes
17
, 2049 - 61.
White, K., Bellinger, E.G., Saul, M., et al. (Eds) (1993)
Urban Waterside Regeneration: Problems and Prospects
.
Ellis Horwood, Chichester.
6.6
MANAGEMENT AND REMEDIATION OF
URBAN SEDIMENTS
environments, and the potential for high levels
of contaminants associated with the sediment.
It is, therefore, a key element of urban pollu-
tion management that levels and composition of
RDS are both monitored and actively managed
to minimize their impact. Management practices
attempt to address these issues in two ways. First,
target levels for contaminant concentrations can
be set, above which sediment removal is required.
Second, routine physical removal of RDS can be
undertaken. Although there have been studies
on contaminant levels in RDS (see section 6.3.1)
there have been no systematic studies on accept-
able levels of contamination in RDS, and no
guidelines or criteria exist for impacts of con-
taminants on urban runoff and water courses.
Therefore, the first of these approaches is not
currently utilized as a management strategy
(Case Study 6.4).
As discussed throughout this chapter the impacts
of urban sediment particulates on the environ-
ment are wide-ranging and include: impacts upon
water quality of runoff and receiving water
bodies, reduction of capacity in drainage systems,
an increase in atmospheric particulate concen-
trations and a reduction in depth of navigable
waterways. All this means that the active man-
agement of sediments is a key requirement in the
sustainable urban environment.
6.6.1 Management of road-deposited sediment
As has been described previously, RDS can have
a major impact upon waterways, both through
the volume of sediment transported from these
