Environmental Engineering Reference
In-Depth Information
2000
). It is an organisation composed of representatives from local authorities,
local development corporations, North West Water (now United Utilities) and
the Environment Agency (e.g., Webb
1993
). The objective is to upgrade all
watercourses in the region to at least an Environment Agency Class 2 classifi-
cation by 2010 with the aim of supporting a diverse fish community, meeting
European targets under the Water Framework Directive and encouraging
waterside regeneration (MBC
2000
). A 25-year programme was devised at an
estimated total cost of £4 billion; £2 billion of United Utilities investment to
improve the aesthetic and chemical quality of the waterways and £2 billion of
further investment to develop the region's watersides (MBC
2000
). Following a
detailed water quality monitoring programme, a series of recommendations
were proposed as part of an integrated management framework (Struthers
1993
). However it was recognised that a 25-year regeneration programme is
outside the generic development timescale and pressure from the local author-
ities resulted in short-term ameliorative measures to improve water quality
(Hendry et al.
1993
). Improving conditions adjacent to potential development
sites between Woden Street Footbridge (subsequently altered to Trafford Road
Bridge) and Mode Wheel Locks on the MSC was of particular interest to the MBC
(APEM
2000
)(
Fig. 14.2
). In this area of the MSC, the short-term measures were
based around satisfying the oxygen requirements of the sediments and the
water column (Rees & White
1993
).
In a baseline study carried out by APEM in 1989, a semi-quantitative scale
(0 to 3) was used to quantify the observed degree of bubbling caused by low DO.
Regression analysis found a negative correlation with bottomwater DO concen-
tration (p
0.05; Webb
1993
). Reference to recorded DO concentrations for
locations at which slight, moderate or severe gassing was noted indicated that
severe gas generation was less likely to occur when DO concentrations were
4mgL
1
or higher; a minimum bottom water quality objective of 4mg L
1
was
thus set (APEM
1989
). However the elevated SOD and BOD combined with
summer stratification created such a high oxygen demand that a mixing
system (as in Salford Quays) would not be capable of raising the oxygen levels
sufficiently to prevent bottom water anoxia. In addition, the canal's drainage
and navigational functions prevent isolation as was possible with Salford
Quays (Rees & White
1993
). As a result of these factors, it was considered
necessary to artificially oxygenate the water using pure oxygen.
A 3-month trial using a venturi oxygen injection (VITOX) device (
Fig. 14.7
)
was undertaken during the summer of 1990 (APEM
1990b
). Oxygen is injected
via a venturi system into water drawn into each unit through mechanical
screens. Fine bubbles are formed which readily dissolve under pressure and
the oxygen-rich liquor is returned to the water body via a twin nozzle sparge
system. The system was successful in elevating DO concentrations in the MSC,
in common with other polluted waterbodies such as the River Thames
<
