An update post by David Walton of FLASK
Brent used to have more River
Westbourne flood defences but still has some, publicly owned natural
parkland flood defences throughout South Kilburn Vale, that were built in the 1950's and
1960's. These flood defences have been incrementally built on since 2000 and
the impacts are already being felt. The new
intention is to establish this as a tall building zone as set out in the Brent
Local Plan to 2041 which awaits final approval. Population growth is planned to rise from
6,000 in 2000 to 36,000 by 2041. Brent has no plan to mitigate growing flood
risk which is exacerbated yet further by excavating giant underground car parks.
A mainline electrified railway luckily severs South Kilburn Vale from the rest
of Brent.
For its River Westbourne flood
defences, the City of Westminster uses complex and expensively engineered
solutions built inside its borough boundary, but it also ( cf July 2021 major
Incident) clearly relies on Brent playing its full part in the flood defence of the City of Westminster upstream
of the River Westbourne.
Westminster has the Carlton Hill natural
hill (pending new developments area) which drains down onto the Brent
floodplain vale, with Kilburn Park Road on the east bank of the River
Westbourne (Westminster) relying on Brent's depleting natural parkland flood
defences for safety. Then at the main borough boundary at Shirland Road, Westminster
engineered flood defences start and which though of considerable scale failed in
July 2021 and will with certainty fail again unless Westminster and agencies
look at the bigger River Westbourne flood attenuation cross borough boundary
picture. (See key Kilburn Park Road flood defences already removed like the 40
veteran trees roundabout flood defence or the Granville Road park flood defence
three-quarters removed).
New map fragments recently obtained
from Thames Water show how the culvert straightened high speed River Westbourne
takes a dramatic giant sweeping curve from Kilburn Park Road into Shirland Road,
and at this point (underneath the zebra crossing) also connects to the North
West Storm Relief Sewer which heads west down to the River Thames at
Hammersmith, while the Mid Level 2 Interceptor Sewer which heads east to Beckon
Sewage Works connects to the River Westbourne nearby at the south east end of
Shirland Road. Flood protection support is also supplied by two new large flood
storage reservoirs underneath Tiverton Gardens and Westbourne Green. Both are rivers
connected and were built in 2016 at a cost of £22 million. To quote from this new
project’s 2012 description:
"The Sewer
Flooding History Database (SFHD) lists 105 properties that have a flooding category of either AI or
BI; however, it is known that the
flooding issues affect many more properties in the area. Optimise (the
contractor) are targeted with removing 177
properties from the SFHD flooding register and
contracted to remove a minimum of 147 properties.
Primarily, the
identified flooding areas are located around Formosa Street and Shirland Road. Prior to 2005
the problem was much smaller with far fewer
properties affected; however there have been severe flooding events in 2005, 2007, 2008 and 2009. In both areas the
flooding occurs incommercial and residential property basements.
Having considered a
number of options, the preferred option proposed by Optimise is to construct a
20m dia, 20m deep storage shaft in Westbourne Green. From this a 3m dia tunnel will be driven to a
7.5m dia reception shaft in Formosa
Street. In conjunction with managing flows at the Kings Scholar’s Pond and at a
number of bifurcations in the Formosa Street area this will effectively resolve the flooding issues at
Formosa Street. Flows from the shaft in Westbourne Green will be
returned to the Ranelagh sewer (River Westbourne) by means of a pumping station with a return pump rate
of 400 l/s. The Shirland Road flooding
will be resolved by diverting more flow to the Mid-Level 2 sewer and constructing a 20m dia, 20m deep storage shaft in Chippenham Gardens.
In order to remove
properties from the SFHD it has also to be proven thatthe properties flood due
sewer surcharge / local incapacity. This information was collated through existing databases
already connected to the properties, and
via interviews with current residents in the area. There was an initial reluctance to complete the survey by
residents and this was for a number of
reasons, including many residents were not living at the properties at the time of the flooding events
and property owners do not want their
property on a flooding register. As such, the verified model has and will continue to be used to validate the
number of properties that suffer from
flooding".
The sheer scale of the City of
Westminster's engineered flood defences that are place and being rapidly extended indicate that the wild River Westbourne is a
major environmental risk to lives and property for this entire area of London.
Yet this river is deregulated from Environment Agency responsibility and often
commercially driven boroughs so Thames Water must work out what to do in an ad
hoc and uncoordinated way instead.
The City of Westminster does seem at least to
be trying seriously to take mitigating actions to protect its own residents and
businesses on a borough boundary frontline siege basis, but these actions have clearly
failed to accept this area’s wider geography and factor in the housing
infrastructure in Brent’s urban growth zone. Brent seems to think that leaseholders and
tenants in Brent and City of Westminster should 'learn to live with' traumatic flood
risk escalation and then pay the costs created by its tall buildings growth
area, built on a flood plain.
Liability is being cleverly being passed
entirely to leaseholders and tenants for the moment, as this area’s big
freeholder housing block owners will just make sure that flood repairs are
actioned in a timely manner and that costs are then fully recovered from block
leaseholders and tenants. They will be paying literally forever for the extreme over development
of this floodplain. This, when natural
parkland flood defences (that Brent is destroying) had proved excellent in protecting
South Kilburn and North Westminster for decades.
David Walton
FLASK (Flood Local Action South
Kilburn)
