Thursday 2 December 2021

The River Westbourne, a tale of two boroughs: Kilburn major flood incidents update

 Guest Post by David Walton

Previous posts have discussed the River Westbourne and its tributary the Malvern, which together form the borough boundary between City of Westminster and Brent in Kilburn  and which have a tendency to flood impact lives and homes both sides of this administrative, social and political divide.


City of Westminster's Finance, Smart City and City Management Policy Scrutiny Committee 30th September 2021 published its Lead Local Flood Authority Section 19 Interim Flood Investigation Report findings. LINK This is based on what Westminster knows and disclaims any error in or omission from this report.


Report summary


The nearest rainfall gauge is at Putney Heath 8.5 km away and so it proved impossible to establish exactly how heavy the rainfall was on 12th July, but it is estimated by Thames Water that more than the entire month's average rainfall fell in 1 hour*. Local sewers/rivers in this area were unable to cope. In Westminster approximately 230 properties were internal flood impacted with Kilburn Park Road (shared with Brent) needing to be evacuated. Underground lines closed due to flooding as was one primary school, three libraries and three community centres.


Thames Water reported that the rainfall on 12th July was equivalent to a 1 in 300 year event. The second flooding on 25th July in this same cross borough boundary area (this time a month's rainfall in 2 hours and another 1 in 300 year's event) is now subject to a second separate Section 19 Flood Investigation by the City of Westminster. The report states that the Environment Agency is not the responsible risk management authority for the 12th July flood event.


The River Westbourne is report named as a combined sewer and it is described how in heavy rain it sewage discharges into the River Thames. The Kilburn sewer rivers were likely already at full capacity when heavy rains* started and tried to enter the network. The £22 million Maida Vale Flood Alleviation Defence is meant to deal only with a 1 in 30 year storm event/ not a 1 in 300 year one? The report states that the entire cross borough boundary flood area is Flood Zone 1 having an annual flooding probability of 0.1% from fluvial and tidal sources. There is however High Surface Water Flood Risk throughout this floods prone area.


Westminster is in 2021 trialling gully sensors to give real time information on silt level build-up in gullies, the aim being to clean gullies before surface water events. In the flood area these gullies were cleaned within 3 months of the event and were in effective condition for July 12th event. (For the 25th event many would have likely had blockages?)


Westminster Lead local Flood Authority interim recommendations are for


a) an increase in reliable rain gauges on site b) The LLFA to keep better records of past flood events for future reference c) to further optimise drainage maintenance d) wider catchment considerations (South Kilburn destroying all of its natural parkland flood defences) will be investigated by flood responsible agencies where the Regional Flood and Coastal Committee may be involved. e) Thames Water is organising meetings with LLFA's and its own Independent Review and these findings will inform the final S19 report. This process could take 6 months!


Thames Water reported that the July 12th rainfall was more than the drainage "network was ever designed to cope with. To the best of our knowledge, our sewers and pumping stations performed as designed….." No system blockages were found either. The Northwest storm relief sewer was overloaded and a River Thames high tide prevented overflow flaps from opening.


"Where there is uncertainty over the cause of the incident and therefore responsibility for it, Thames Water needs to take action to support customers without concerns that in taking action we are wrongly accepting liability."


An Independent Flood Review has been commissioned by Thames Water, in a time scale which can meaningfully inform Thames Waters and other parties' plans (such as South Kilburns natural park flood defences all being destroyed upstream). Thames Water also now supports the Mayors 'Grow Back Greener' scheme to make sure that every Londoner lives within 10 minutes of a green space. So, extra funding for South Kilburn Public Open Space and Chippenham Gardens natural flood defence parks major upgrade works?


Westminster LLFA is attempting to be open about its struggles with its rivers and vales environment and climate change in this London boundary area and I would now expect Brent to follow this lead and to also seriously engage the issues to proactively protect Kilburn major Town lives and properties from escalating flood risk.


David Walton, FLASK (Flood Local Action South Kilburn


Thames Water Interim Report on July 12th events   LINK

London Fire Brigade Briefing on 'Major Incident' July 12th LINK


David Walton said...

Just to add.....

The report states that the Environment Agency is not the responsible risk management authority for the 12th July flood event. So, the River Westbourne, an at times dramatic riverscape in this part of London is de-regulated from fluvial floods risk to surface water floods risk only, this loophole for the EA to responsibility disappear along with all of its extensive river floods historical memory and predecessor agency environmental protective actions data….

Why the South Kilburn Estates parkland natural flood defences for protecting homes?

Why were social housing blocks of that time raised above this rivers level by 1970's architects (Gloucester, Hereford, Bronte and Fielding Houses for example) with no ground floor or basement homes being allowed and ramped drawbridge-like main entrances with for flood event large ponding basins built underneath?

Brent needs to urgent action a Section 19 flood investigation ( its first ever)to study and to re-learn harsh river environmental lessons from the past and to appreciate real world climate change flood risks to lives and properties old and new in Kilburn.

Unity Place, fully Brent owned is newly built below river level. How can this design be considered building Gloucester House (demolished) back better? Better for who?

David Walton said...

Brent Lead Local Flood Authority according to latest information is to-

a) scope model for a potential flood alleviation scheme in Woodcock Park (Wealdstone Brook with vulnerable Wembley City sited downstream)

b) Borough wide scope flood alleviation schemes (hopefully already existing natural flood alleviation schemes such as the one in South Kilburn protecting vulnerable Central London sited downstream will no longer continue to be for developer colonialism denied and environment cancelled?)

c) Update its Local Flood Risk Management Strategy (to now include the rivers and springs of South Kilburn)

d) To finally action (after 5 months delay) a section 19 Investigation into the July 2021 floods in South Kilburn (better late than never, this S19 investigation will be a Brent first).

Thanks to Wembley Matters