The Environment Agency
confirmed today that it has agreed that
dredging in the bed of the River Tyne for
the second Tyne Tunnel can start on 26 September.
The dredging has to
be carried out with care to avoid causing
problems to the environment, particularly
migrating salmon on their way to breed in
the upper Tyne catchment. The Tyne is one
of the best salmon rivers in England and
studies have shown that each rod-caught
salmon can generate as much as £4,600
for the local economy.
Previously the government
had made it a condition that the dredging
should take place in the winter months to
avoid the salmon migration season – however
new methods of both dredging and disposal
mean this important operation can now be
brought forward.
The improved system
uses a suction-cutting dredger, which will
suck sediment and water up and reduce the
amount of silt that would be disturbed by
the more usual bucket or ‘back-hoe’ dredger.
The silt will then be
transferred 1.5 km downstream via an enclosed
pipe system, and used to fill the now redundant
Tyne Dock. Once the dock has been filled
it will be commercially developed by the
Port of Tyne Authority. This disposal will
avoid an estimated 4,600 lorry journeys
through built-up areas, and also means there
will be no dumping at sea.
John Hogger, the Environment
Agency’s area environment manager, said:
“This scheme for dredging the tunnel trench
will have a significantly lower risk to
the environment overall than the previous
proposals. However we still have to ensure
that impacts are minimised, especially for
the salmon stocks.
“We have set the start
date to avoid the summer period when existing
water quality can cause problems for salmon
migrating through the estuary. There should
be no need for extra releases from Kielder
Reservoir, as the water quality should have
improved by that time. However this is always
an option in extreme circumstances.
“We have also imposed
minimum water quality thresholds to protect
the ecology of the estuary. We’ll be monitoring
the water quality continuously during the
operation at several key points around the
dredge site and the Tyne Dock to measure
the level of waterborne sediment and dissolved
oxygen in the river and help ensure water
quality stays above these preset thresholds.
“If the water quality drops below our thresholds
then work has to stop until the dredging
activity can be modified.
“We’ll also be monitoring
the numbers of fish passing the fish counters
at our Riding Mill site to control any impact
from dredging. Should the numbers fall below
a preset minimum level over a five day period
then dredging will be suspended.”
Once the tunnel sections
have been placed in the dredged trench ‘clean’
material will be used to fill the trench.
This will be inert sand taken from the navigation
channel in the mouth of the Tyne, an area
regularly dredged by the Port Of Tyne Authority.
Although the six week dredging period could
start in late September, it is expected
that the bulk of the work will happen in
late October and November, with dredging
actually taking place for around half of
the six weeks.
The Environment Agency
believes the risks to fish stocks will be
very low, and has stringent controls in
place should this change.
+ More
Environment Agency uses
barges to build flood banks
Engineers are taking
to the water as they start work to improve
flood defences near Goole. - The Environment
Agency is using barges on the River Ouse
during the first stages of work on the £11.9
million flood defence scheme at Swinefleet.
A crane and piling machine
upon the 30 metre long barge - called the
Maverick - will be used to carry out the
works that will better protect 9,400 homes
and 1,200 commercial properties from flooding
when complete.
Once anchored, the Maverick
and its 80 tonne crane move up and down
with the water level, which enables engineers
to work through the changing tides.
The 24 metre long crane
that sits on the Maverick is used to work
sheet piles up to 15.5 metres long into
the bank that will form the new flood embankment.
The improvements will raise and widen the
embankment as well as improving its stability.
Will Benedikz, project
manager for the Environment Agency, said:
”At this stage of the scheme we are working
in people’s back gardens.
“Using the river instead
of the land allows us to cause the least
disruption to the community. It also prevents
us damaging the existing banks with construction
traffic.”
The Environment Agency
will also be using the Humber Estuary to
bring materials into the site. Four barges
will bring steel piles onto the site via
the estuary, saving 85 wagon journeys through
Swinefleet.
The scheme is one of
the first to be built following the publication
last year of the Humber Strategy, a 100
year plan for flood risk management around
the estuary, through a partnership the Environment
Agency has set up with specialist engineering
firm Birse Civils, with design consultants
Halcrow and Black & Veatch.
The partnership will
be investing £36 million in flood
alleviation schemes for Swinefleet and Brough
on the north bank of the Humber, and Stallingborough
and Halton Marshes in North Lincolnshire.
