Guest post by Philip Grant
The Welsh Harp
Reservoir – a warning from Whaley Bridge
We know that Global Warming is causing more frequent extreme weather
conditions, such as record heat waves in summer, and more intense storms. In
the past few days, we have been watching (from a safe distance) the news about
a threatened dam collapse at Whaley Bridge, caused by the volume of water
flowing into the reservoir above the town after prolonged torrential rain. I
don’t want to cause alarm, but this should be a wake-up call about a reservoir
much closer to us.
The Toddbrook Reservoir in Derbyshire was built in the 1830’s, to
supply water along a “feeder” to the High Peak Canal. The embankment dam was
constructed of earth, around a central core of puddled clay.
The Kingsbury, or Brent, Reservoir (now better known as the Welsh
Harp) was built in 1834/35, to supply water along The Feeder (which still runs
through Neasden and Stonebridge) to the Paddington Branch of the Grand Junction
Canal. Its dam, using the same method of construction, was the work of a
Hammersmith contractor, William Hoof. The price for the work, which he agreed
with the Regent’s Canal Company, was £2,747 and six shillings!
William Hoof’s
letter of 18th October 1834, agreeing to build the reservoir and
embankment dam at Kingsbury.
Heavy rain, and a rapid thaw of snow, caused a partial collapse of the dam in January 1841.
A
newspaper illustration of the flooding in Brentford, 1841.
The water
swept down the Brent valley, which was then just open farmland, and caused
major flood damage at the canal port of Brentford, where the river met the
Thames. Several people were drowned, and more than 100 boats were wrecked.
The dam had been repaired by 1843, and was enlarged ten years later as
the Regent’s Canal Company needed more water for its operations. A spillway was
added to the dam, allowing excess water to escape into the river below when the
reservoir was full. By late Victorian times, this had become a tourist
attraction for people visiting the local countryside from the crowded city.
The Kingsbury
“waterfall”, in a postcard from c.1900. [Brent
Archives online image 1341]
The land downstream of the reservoir remained as farmland until 1880,
when the Metropolitan Railway built a large engineering works at Neasden, on
the line they were building out from Baker Street. They also had to build homes
for the many people needed to run the works, and the first 100 houses in “A”
and “B” (now Quainton and Verney) Streets were occupied by 1882. If you want to
learn more about Neasden’s Railway Village, there is an illustrated article on
the Brent Archives website LINK .
Across Neasden Lane (North), suburban development in the 1930’s saw
new roads such as Braemar Avenue built right up to the foot of the dam, and a
new junior school, Wykeham Primary in Aboyne Road, to serve the area’s growing
population. Two more schools, Neasden High and St. Margaret Clitherow R.C.
Primary, were built in the early 1970’s, on the site of the former Neasden Power
Station, between the River Brent and The Feeder. When the High School closed,
as part of Brent’s cull of secondary schools in 1989, its site was redeveloped
as the Quainton Village housing scheme.
More housing developments were built near the reservoir in the late 20th
century. Runbury Circle nestles under the north-west edge of the dam, while
Harp Island Close lies between the river and The Feeder, near to where the
Brent emerges below the dam. This estate of 128 flats was built by Laings in
the 1980’s, and the view here is from its gardens (in 2009).
What had been the dam’s Victorian spillway was replaced in 1936 by
five siphons, designed to take water out of the reservoir if its level becomes
too high. These were installed as a safety measure, under changes introduced by
the Reservoir (Safety Provisions) Act in 1930. That law was introduced after 16
people were drowned in Dolgarrog, North Wales, in 1925, when floods coming down
a valley in the hills caused an embankment dam above the village to collapse.
Toddbrook Reservoir had been inspected, both by its owners and an
independent engineer, under the provisions of the current (1975!) Reservoirs
Act, as recently as November 2018, and found to be “safe”. In the light of the
near collapse of its dam, less than nine months later, and what we know about
more extreme weather events, as a result of Global Warming, we need to think
again about the safety of all of the country’s Canal Age dams, including the
one at the Welsh Harp.
Brent Council needs to work with the Canal and River Trust, and the
Environment Agency, to review all aspects of our local dam’s safety, both to
minimise the risk of a similar event to Whaley Bridge happening here, and to
ensure that plans are in place on how any such emergency would be dealt with.
If a similar spell of very wet weather hit North West London, as it
did North West England last week, the wide catchment areas of the Dollis Brook
/ River Brent and the Silk Stream would bring huge volumes of water into the
Welsh Harp. Not only the safety of the dam structure in such conditions needs
to be properly assessed, but also the ability of the siphons to cope with such
volumes.
If the reservoir had to shed large volumes of water, could the river
below the dam take that water away safely, without flooding low lying
residential areas and roads for several miles downstream. There have been
times, in living memory, when debris restricting the culvert which channels the
river under the Harrow Road has caused flooding in the Monks Park and St
Raphael’s Estate areas.
Are Brent’s own maps of areas at risk from flooding, if there were to
be a partial (or worse) failure of the dam up to date? Does the Council know
how many people currently live, work or go to school in these areas, and how it
would manage their evacuation if there were to be an emergency of the type
experienced at Whaley Bridge. The recent events there have been a warning which
must not be ignored.
Despite this warning, the Welsh Harp Reservoir is still a place to be
treasured and enjoyed, rather than to be feared, as long as its potential
dangers are properly considered, and the necessary action taken. If you want to
discover more about its history there is an article online LINK t, or for more of its fascinating story, beautifully illustrated, borrow a copy
of Geoffrey Hewlett’s “Welsh Harp Reservoir Through Time” from one of Brent’s
libraries. Better still, take a stroll beside it yourself!
Philip Grant.
Note from Editor: I am awaiting a response from the Canals and River Trust to a request made for a comment on the above piece.
Carolyn Downs, Brent Council CEO, has sent thos response to Philip Grant:
Dear Mr Grant,
Thank you for your email and attachment, on behalf of Carolyn Downs I acknowledge receipt.
Please
be assured that the matter is being discussed by the relevant teams
internally and we will seek to engage with the relevant external
partners on this to provide you with a further response.
In the meantime, the council’s Flood Risk Management Strategy is publically available on the website*.
Kind regards,
Tom Welsh
Head of the Chief Executive’s Office'
* THIS IS A LINK TO BRENT'S FLOOD RISK MANAGEMENT STRATEGY document:
https://www.brent.gov.uk/media/16406897/flood-risk-strategy-sept-2015.pdf
Roger Wilson has sent in this comment:
Phil, I support your proposal to Brent Council that it take heed of the
'warning from Whaley Bridge' and review its emergency flood planning
and the maintenance schedules of the Welsh Harp/ Brent reservoir Dam
Wall and spillways have not slipped.
But as a regular user of
this leisure facility, both as a sailor and for the enjoyment its
wildlife, I'd be more than upset to see an overly cautious kneejerk
response to your blog, such as dropping water levels in the reservoir.
Your Blog would be a more worthy if it reported some of the some of
the measures that HAVE been carried out in the more recent past along
side the sensationalist historic events of the past.
So to redress the balance ...
A quick online search 'Brent Reservoir repairs/ upgrades' reveals that:
i)
that the spillway was redesigned in the 1930's (at the same time as
the expansion of Housing below the reservoir) and is of a more
sophisticated design than that of Toddbrook Reservoir impacting Whaley
Bridge.
ii) That Brent's residents are fortunate that the Brent
reservoir Dam and Brent River rainfall catchment basin have been the
subject of a number of academic specific case studies (published
between 1990 and 2000. These case studies included reviews of
mathematical modelling methods used to predict floods, and of the
capacity and design of the of the Brent Reservoir spillways to safely
disperse flood water.
iii) Possibly as a result of these studies,
between 2005 and 2007, e.g. only 12 years ago, the height of the Brent
reservoir Dam Wall was raised with a new Concrete Cap and earth bunds
and concrete walls added to the north and south side of the Dam wall.
This I believe was to meet revised estimates of flood water levels in
the event of a 1 in 10,000 year extreme rainfall.
Yes Brent
Council , the Canal and Riverboat Trust who manage the reservoir , and
the Environment Agency should review, publicly report and act on any
short comings in their Flood prevention and Emergency planning
provisions but in the meantime I hope this response lets anyone
concerned sleep a little more easily in their bed!
Roger Wilson
