River Brent catchment area
GLA Brent flood risk areas LINK
A press release from the London Mayor, Sadiq Khan, on September 23rd reported on Climate Vulnerability Mapping carried out ahead of COP26. LINK
It said:
The
boroughs at particularly high risk, meaning that the risk of both
flooding and overheating are very high, jeopardising lives and
livelihoods are:
- Hackney
- Hammersmith and Fulham
- Islington
- Brent
- Tower Hamlets
- Newham
A combination of factor contribute to flooding including over-flowing rivers; reduced permeability due to development, including reduced green space and the paving over of gardens, and drainage systems unable to cope with extreme weather events.
Aware of this, Brent Friends of the Earth last week conducted a Flood and Nature Awareness walk from Wembley Park to Stonebridge Park along the Wealdstone Brook and the River Brent. This article provides some of the background requested by the walkers.
The top image above shows the catchment area of the River Brent with Wembley at its centre. The lower image is the flood risk of all types captured in the Climate Vulnerability Mapping. Unfortunately there is no data for the immediate Wembley regeneration area but the 'High Risk' vulnerability is clear. The map is interactive so you can zoom into different areas by following the link.
The maps below whilst not so up to date gives more detail - the darker the blue the more vulnerable to flooding. Light blue is surface flooding:
Ten years ago Brent Council's Surface Water Management Plan said: LINK
Finally, a combination of poor historical planning
decisions, urban creep and infill development has had a further detrimental
impact on the ability of the Borough to hold back the rain where it falls,
Thames Water have calculated that there has been a 17% increase since 1971 in
impermeable area across North West London, as residents have added extensions
or have paved over front gardens. This results in greater volumes of surface
water for each rain event entering the system. This effect accumulates further
down the system where the increasing volumes create greater pressures on the
below ground piped assets, tending to result in overland flood flows,
increasing frequencies and levels of discharges at overflows and flooding of
peoples properties with contaminated foul and commercial wastewaters.
The amount of impermeable land in the borough must have increased greatly since then.
Wikipedia records fluvial flooding LINK:
- 1682: A very violent storm of rain, accompanied with thunder and
lightning, caused a sudden flood, which did great damage to the town of
Brentford. The whole place was overflown; boats rowed up and down the
streets, and several houses and other buildings were carried away by the
force of the waters.[53]: 39–58
- 1841: Brentford was flooded by the Brent Reservoir
becoming overfull so that the overflow cut a breach in the earth dam. A
wave of frothing and roaring water swept down the river's course taking
all before it causing fatalities. Several lives were lost.[54]
- 1976 and 1977: in the summer Britain saw drought and unusual heat
with Water Companies declaring it would take six or seven years for
empty reservoirs to recover. The following August, a rainy spell was
followed by a day and night of torrential rain that overwhelmed the
Brent reservoir — authorities decided to open the sluice gates maximally
at time of highest volume and pressure, to avoid costly overflow
flooding, having been under general pressure to keep stock water
supplies. Later, before the river below overflowed in many sections
certain local sewers overflowed, some into homes. The streets, including
arterial roads were jammed and local trains blocked. Hundreds of homes
and businesses closed for the clean-up, with widespread press coverage.[citation needed]
- 2007: August saw heavy rain cause a short bout of flash flooding in Brentford and Hanwell on roads, the Hounslow Loop Line and London Underground.
- 2009: On 30 November, the Environment Agency warned residents of a flooding along River Brent from Hendon to Brentford, after a day of notably heavy rain. Several premises were temporarily flooded in Brentford and Perivale.[55]
Local resident John Timms who has studied the 1977 flood in detail says that in fact the flow of the Wealdstone Brook had already increased significantly before the Welsh Harp sluice gates were opened and had caused flooding in Kenton and flooding followed down river with the draiage system unable to cope.
Laurie Pavitt, MP for what was then Brent South presented a petition to the House of Commons:
With your permission, Mr. Speaker, and that of the
House, I beg leave to present a petition signed by 588 of my constituents who
seek relief from the acute anxiety that arises especially among the elderly, in
my area whenever there is a heavy downpour of rain.
The petition sheweth That 71 households were
flooded with sewerage water following the heavy rainfall on 16th and 17th
August 1977. That this disaster has caused severe physical, mental and
financial distress, and that investigations reveal that these floods were not
unexpected, and according to expert engineering opinion the risk of further
flooding has been rapidly increasing due to extensive new building developments
and drainage systems. Planned and approved alleviation works have not been
implemented and the reason given for this failure has been the shortage of
finance. At a time of cuts in public expenditure which affect all citizens, the
people of Stonebridge have had the additional burden of living through a
disaster which has destroyed the contents of the ground floors of their homes,
with all the consequent hardship and suffering. Nor will they have the
wherewithal to replace their losses, as most families have a weekly wage and
live from week to week.
The petition concludes: Wherefore your petitioners
pray that your honourable House by legislation or otherwise ensure that:
(1) full compensation be paid adequately to
restore that which was lost.
(2) the Ministry of Agriculture, Fisheries and
Food shall, in conjunction with the Greater London Council, seek to
implement a satisfactory flood alleviation scheme as a matter of urgency.
(3) temporary works and an effective flood
warning system be put into operation immediately and that the lowering of
the 1126 water level in the reservoir known as the Welsh Harp shall have
high priority.
If you or your family were affected by these floods, and particularly if you have any photographs, John Timms is keen to hear from you for his research. Write to me at martinrfrancis@virginmedia.com and I will pass it on.
This was the background to our walk which started on the bridge over the Wealdstone Brook on Bridge Road.
Wealdstone Brook serving as a green corridor from Bridge Road (north side)
Brook Avenue, named after Wealdstone Brook which flows alongside it, is the site of planned tower blocks on the station car park (currently subject to a Public Inquiry) but has also been ear-marked in the Local Plan as a potential site for development between the avenue and the brook.
The surburban side of Brook Avenue where gardens back on to the brook
The modification to the Local Plan both suggests development of the site, including a larger Premier Inn, and enhancement of the brook area:
The
Premier Inn site provides the opportunity to provide a more defined edge to Wembley Park
Drive/Brook Avenue and introduce an active frontage containing main
town centre uses.
The site is adjacent to
a mixture of residential and commercial buildings up to ten storeys.
Within this context, development that is taller than the existing
two storey suburban dwellings will be acceptable to the eastern side of the site,
stepping down towards the residential buildings to the west of the site which
is identified as an intensification corridor along Forty Avenue.
·
A minimum of 8m setback
from Wealdstone Brook will be sought. Development will be
required to positively contribute to the biodiversity, improve
access to the waterway and provide an appropriate landscaped setback which
may include public open space.
·
The building line should
be closer towards Brook Avenue.
The brook flows beneath Bridge Road to the College of North West London on the south side. Here it emerges into a small green space with mature trees and some landscaping.
College of North West London Grounds
The College building is adjacent to a major redevelopment site called the 'Fulton Quarter' which includes the retail park, McDonalds and the former studios, currently the temporary Troubadour theatre. The College site is also due to be redeveloped.
According to John Timms in the 1977 flood this park of the brook reached a height of 11-1/2 feet.
However, the modifications to the Local Plan concentrate on surface water:
The
site is in flood zones 2 and 3a and susceptible to surface water flooding. All proposed
development will require a detailed Flood Risk Assessment (FRA).
Development must be consistent with the recommendations of the
Brent Strategic Flood Risk Assessment Level 2.
Due to
the site’s location in Flood Zone 3a, the ‘sequential approach’ at site level should be
applied to steer more vulnerable development such as residential, student
accommodation, hotels, and certain community uses towards areas of lowest
risk within the site; north west area and southern edge.
Associated
infrastructure including water attenuation tanks, and the diversion of any
utilities and services to accommodate the development.
· Green and sustainable
infrastructure should be part of the development process and the
development.
Most significantly a paragraph follows in bold that is repeated for many of the developments, including Brook Avenue, covered in the Local Plan Modifications, which really requires additional scrutiny. Who in Brent will provide it?
Waste water facilities
enhancement Thames Water has indicated the scale of development is
likely to require upgrades to the wastewater network. Thames Water will
need to be engaged at the earliest opportunity to agree a
housing and infrastructure phasing plan to ensure essential
infrastructure is delivered prior to the development creating identified
additional capacity requirements.
The Fulton Quarter (yellow) with CNWL and Wealdstone Brook bottom left. Numbers equal storeys.
The Wealdstone Brook is culverted beneath Olympic Way and emerges next to 1 Olympic Way which has recently been converted from office accommodation to housing. Previously, as with the neighbouring Michaela School building, and as planned for the Fulton Quarter, the ground floor was not occupied, presumably because of the flooding risk.
Wealdstone Brook emerges from beneath 1 Olympic Way
The brook is canalised here and very soon is out of view as a platform has been erected over it:
Now the brook meanders either side of North End Road with the attractive low rise Empire and Danes Court contrasting with the high rise developments. Soon we come across an interesting new development that was faced with the problem of potential flooding. It is on the former Amex site and as you can see from the diagram surrounded on what is almost three sides by the Wealdstone Brook.
The planners recognised the flood risk:
The NPPF requires the Exception Test to be
applied in the circumstances shown in Table 3 of the ‘Planning Practice
Guidance: Flood Risk and Coastal Change’. Paragraph 102 of the NPPF makes clear
that all elements of the test must be passed for development to be permitted.
Part 2 of the test requires the applicant to demonstrate that the development
will be safe for its lifetime taking account of the vulnerability of its users,
without increasing flood risk elsewhere, and, where possible will reduce flood
risk overall.
The flood modelling prepared by the
applicant shows that North End Road would be inundated in both the 1 in 100 35%
climate change event and the 1 in 100 70% climate change event, which appears
to be the only access/egress route. This means that safe refuge within the
development is required for future occupants as safe access and egress cannot
be achieved.
The finished floor levels of the development
have been raised above the 1 in 100 chance in any year, including an allowance
for climate change flood extent. This means that floodwater is unlikely to
enter the property during a 1 in 100 chance in any year plus climate change
flood extent.
The applicant has overcome the EA’s previous
objection by submitting an acceptable emergency flood plan framework to the
local planning authority that deals with matters of evacuation and refuge to
demonstrate that people will not be exposed to flood hazards.
Since the development was completed North End Road has been reconnected with Bridge Road at a very steep junction which in extreme torrential rain could see a flood of water coming down the road.
This development also raises a continuing problem - that of the pastekl drawings of the development versus the harsh reality. The long term plan to utilise and enhance the Wealdstone Brook as a feature was addressed in the application's depiction of a waterside walk. At the time it was unclear whether this would be open to the public - another long-term plan. It was festooned with Private notices when we dropped by. Compare the artists's impression with the reality.
The brook now runs past industrial buildings and another ptential development site named rather anonymously 'Central Place' -. It is between Fulton Road and Fifth Way with Wealdstone Brook to the north. There is a big warehouse and car park occupying the site.
The Local Plan Modification states (NB items in bold:
North of the site is
the SINC Grade II Wealdstone brook. The site is recognised
as a waterside development,
as such, developers will be required
to contribute towards restoration and naturalisation of the
Brook, improve
access to the
waterway, provide appropriate landscaped setback, enhance water
quality and biodiversity.
· Small sections of the
site is susceptible to surface water flooding. The site is
also adjacent to flood zone 3a (fluvial and tidal) so an appropriate buffer
zone along
the brook will remove the developable area of the site of
any major risks.
A critical trunk sewer
runs through this site which would need to be considered.
A buffer strip of at
least 10m wide should be retained for a publicly accessible
brook side park to allow for a cycle way/footpath, associated landscaping,
tree planting and street furniture as agreed in consultation with
the Environment Agency and Brent Council.
Infrastructure
Requirements
· Developers would be
required to contribute towards restoration and naturalisation
of the SINC Grade II Wealdstone
brook.
· Further master planning
work will provide additional requirements.
· Green and sustainable
infrastructure should be part of the development process
and the development.
· Thames Water has indicated
the local water network capacity in this area
may be unable
to support the demand anticipated from this development. Upgrades to the
wastewater network are likely to be required. Thames Water will need to
be engaged at the earliest opportunity to agree a housing and
infrastructure phasing plan to ensure essential infrastructure is delivered prior to the
development creating identified additional capacity requirements. Public
sewers cross or are close to the site. The risk of damage
during construction must be minimised. It must be ensured that development doesn't inhibit
access for maintenance or the services in any other way.
There is quite a lot of vagueness in all this and as we have seen pretty plans sometime turn into something much less and there does not seem to be a reliable process, with staff availability low after government cuts,to make sure promises are delivered.
As a result over concerns over potential flood danger as a result of climate change and severe weather events, now with the addition of Sadiq Khan's warning, I have put two questions to November's Full Council meeting:
In the light of the
increased prevalence of extreme weather events as a result of climate change
and recent flooding in the borough, as well as a large number of new
developments and increasing numbers of paved over gardens, does Brent Council:
Intend to work with
partners including the Environment Agency and Thames Water to review and revise
Brent Council’s
1) Flood Risk Management Strategy
2) Surface Water Management Plan
and advise property owners and developers on mitigation measures?
Look out for Part 2 where we walk from Brent River Park to the North Circular at Stonebridge
NOTE
In case you feel you need to know more about how to react in a flood as a reesult of reading this article this is the guidance from Brent Council:
Be Aware. Be Prepared. The time to think is now
don't wait until it happens.
See how putting a grab bag may will help you to
respond see the preparing
for an emergency page.
If your house is potentially at risk from flooding
here are some key things to remember.
If you are in a flood risk area find out if you can
sign up to the Environment Agency's free 24 hour Floodline Warnings Direct
service by calling Floodline on 0345 988 1188 (or Type Talk: 0345 602 6340).
You can select to receive warnings by phone, text or email.
Keep details of your insurance policy and the emergency contact numbers for
your local council, emergency services and Floodline quick dial number
somewhere safe - preferably as part of your emergency flood kit.
Know how to turn off your gas, electricity and
water mains supplies.
If a flood is forecasted, take valuable items
upstairs and take photos for insurance purposes.
Leave internal doors open, or ideally, remove them
and store them upstairs.
Outside
the house
Move anything not fixed down into a safer location,
e.g. dustbins, garden chemicals car oil and similar.
Move your car to higher ground to avoid damage.
Weigh down manhole covers outside the house to
prevent them floating away and leaving a hazardous hole.
See our
page about who to call regarding drains and gullies for more advice.
For more information on preparing for a flood and
other publications visit the Environment
Agency's website
Sandbags
We do not supply sandbags or flood protection products directly to the public.
Builder's Merchants and DIY Stores may have
sandbags available.
If you can't obtain sandbags, you can make them
yourself by filling things like compost bags, old pillowcases or carrier bags
filled with earth or sand.
https://www.brent.gov.uk/emergencies/severe-weather/flooding/
