Michelle Dolphin - 10-Oct-2007
- Environment Agency workmen began work
on Wednesday 10 October 2007 to remove trees
and overgrown bushes growing in the River
Severn under Shrewsbury’s bridges.
The bushes have established themselves
in the river channel under the English and
Welsh Bridges. They are now causing blockages
under the bridge arches which, if not dealt
with, have the potential to raise river
levels upstream during a flood and put properties
at risk.
Operations Delivery Team will be removing
and cutting back the vegetation as necessary
to keep the river channel clear and the
water flowing freely.
We will not be de-silting the channel itself,
because this will not help to reduce flood
risk. Removing the silt makes no difference
to river levels and is unsustainable because
the river will always try to maintain its
natural balance, depositing more silt in
place of what has been removed. Within a
few months, silt levels are back to where
they started.
During flood events, more than an Olympic
swimming pool full of water passes every
second. To provide a deep enough river channel
to contain this enormous amount of water
would require much more than removing a
metre or two of silt. The riverbed itself
would have to be rock-blasted and excavated
by several metres.
Bridges and buildings next to the river
would have to be rebuilt with their foundations
at a depth where the deepened channel would
not cause undercutting. The cost of this
work would be substantial and would mean
demolishing a large number of structures
both up and down stream, ruining the beauty
of the river and of Shrewsbury itself.
Operations Delivery Engineer, Christian
Wilcox, says “People often think removing
silt will help reduce flood risk, but, in
reality, it makes no difference because
of the huge quantity of water that flows
through in a flood. To remove enough material
to have any impact on flooding would destroy
the beauty of Shrewsbury’s riverside and
ruin its historic buildings and bridges.
“But trees and shrubs in the river do cause
a flood risk. They form a blockage and hold
water back, especially if debris floating
downstream gets caught behind them. This
raises river levels upstream, potentially
putting properties at risk, so we need to
remove them before the winter weather sets
in, allowing the water to flow freely and
drain away quickly.”
Silk Stream project committed to a sustainable
future
Tim Abbott - 10-Oct-2007 - The Institute
of Civil Engineers (ICE) has commended the
final stages of the Environment Agency’s
Silk Stream Flood Alleviation Scheme at
a London award ceremony.
The project, which consists of six flood
storage areas, will reduce the risk of flooding
to 746 homes and businesses across the north
London boroughs of Harrow and Barnet.
At the Constructing Excellence London and
South East Awards on Friday 30 September,
the final two storage areas at Egwarebury
Farm and Bury Farm, were ‘Highly Commended’
in the Legacy Award for Sustainability.
Organised jointly by the South East Centre
for the Built Environment (SECBE) and Constructing
Excellence in London, the awards were given
to organisations that demonstrate a commitment
to delivering a sustainable built environment
through best practice, innovation and leadership.
John Laverty, Regional Manager for the
Institution of Civil Engineers in South
East England, was delighted to see the Environment
Agency’s work on flood alleviation being
recognized within the sustainability awards.
He said: “The summer floods across the
UK highlight the ongoing need to manage
and mitigate flood risk. The Silk Stream
project demonstrates the value of the Environment
Agency’s work protecting homes and livelihoods
from these risks.”
The Silk Stream catchment has suffered
from frequent flooding and the project was
started in 1992 after 293 properties were
flooded in Edgware. The construction of
the last two flood storage areas, which
will hold 34,000m3 and 14,000m3 of flood
water respectively, has been completed and
we are now carrying out extensive landscaping
to enhance the environment in the area.
The original project was approved by Defra
in March 2003 and four of the six proposed
flood storage areas have been completed.
These have protected 613 properties along
the Edgware Brook, Deans Brook and Silk
Stream within the Edgware area.
Environment Agency asset systems technical
specialist Dak Gor said: "This project
is great news for many homes and businesses
in Edgware and I’m delighted it has been
recognised by the Institute of Civil Engineers.
“Of course, if you live in the floodplain
you will never be without risk. However,
when the scheme is finished the Environment
Agency’s work will have given an improved
standard of protection to 746 properties
and enhanced the environment for the local
wildlife and people."
The scheme was praised for it sustainable
and environmentally friendly construction
techniques, including:
Clay for the embankments was taken from
adjacent land, avoiding bringing materials
from off-site. These areas provided more
flood storage and a range of new habitats
for wildlife
Recycled material was used where possible.
For example the access tracks reused recycled
material.
The structure and materials were designed
to integrate with the surrounding rural
landscape. This was done by working with
nearby landowners and tenants.
Liaison with local RSPB and bat groups
identified that the local habitat had deteriorated
over the years. Their input has helped the
scheme to improve the habitat and fauna
of the area.
The landscaping works at the sites will
create a range of habitats including seasonal
ponds and areas for wet woodland and scrub
planting. Areas of different grassland were
proposed to create and enhance the existing
vegetation. Improvements to the existing
river channel were also undertaken creating
marginal shelves with a range of plants.
Solar power was used to power the automated
telemetry – which will gauge if the river
needs clearing of debris.
The flood storage areas are designed to
hold floodwaters in times of heavy rain
to prevent the rivers bursting their banks
and flooding homes and businesses. The standard
of flood protection will be improved to
a minimum of 1 in 25 year chance (or 4 per
cent chance of flooding in a year) of flooding.
Most areas will now be protected to an improved
1 in 100 year (or 1 per cent chance in a
year) of flooding.
To find out the flood risk in your area
log on to the Environment Agency’s website
at www.environment-agency.gov.uk or call
Floodline on 0845 988 1188 for advice on
to find out how to prepare for flooding.
