Guest post by David Walton
This review https://londonfloodreview.co.uk/ published in May 2022 states that:
"New sewer systems are typically designed such that all flows are contained within the sewer (no flooding at ground level) up to a 1-in 30 year return period. Older sewer systems do not have the same requirements and often have a capacity much less than the current 1-in-30 year standard. While the Victorian sewer system for London had ample capacity at the time of its construction, the evolution of the cityscape has had an effect on the ability of the sewer system to cope with the current flows which drain to it. This results in areas of London with sewers which cannot cope with a 1-in-5 year event, despite Thames Water’s continuous upgrade in the sewer network where performance issues are identified".
See London Flooding Review Maida Vale Study Area. Its red line includes the South Kilburn Growth Area Tall Building Zone.
"We confirm that the scale of the events experienced in July far exceeds any design standards for sewer systems and acknowledge it may not be economical or practicable to implement schemes to eliminate risk for a similar event. Whilst we report specifically on the performance of Thames Water’s assets, due to the scale of the events in July 2021, and the flooding mechanisms, multiple organisations had a duty of care and responsibility to their customers, so the responsibility does not lie wholly with Thames Water."
"Typically, Thames Water uses a 1-in-30 year return period design standard for new flood protection schemes; with a range of duration storm events….it is recommended to apply climate change factors to design rainfall, increasing the intensity of the rainfall event."
The question, is can South Kilburn Growth Area Tall Building Zone re-development ongoing for 21 years thus far, in legal terms be classified as 'new'? Maida Vale Flooding Review Study Area includes South Kilburn Growth Area Tall Building Zone a low bowl with hills around in the stage 3 report.
"Analysis of the current network identifies that some drainage systems can be predicted to flood in less than a 1-in-5 year return period rainfall, with properties being affected by frequent flooding. This is true of all major cities in the UK and is not specific to London."
"Maida Vale is situated in a low spot, and has the Ranelagh trunk sewer (River Westbourne), Mid Level No. 2 sewer and the North Western Storm Relief sewer running through it. When the Ranelagh sewer is surcharged, flows can back up into connected basements."
"Cambridge Gardens (Brent) consists of a new Flooding Local Improvement Project (installation of package pumping stations for individual properties with non-return valves) to isolate individual properties from the sewer network."
5 homes in South Kilburn fitted so far by Thames Water.
"The Maida Vale Study Area was defined using LiDAR (Light Detection and Ranging topographic) data to identify the topographic area where surface flows could contribute to the tank, which is located in a low spot. The extent of the (low spot) study area can be seen in Figure 5.5."
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Page 55 of the London Flooding Review pictures Chippenham Gardens, Brent, that in July 2021 become a sewage lake.
"We confirm that the scale of the events experienced in July (2021) far exceeds any current design standards for sewer systems and it may not be economical or practicable to implement schemes to eliminate risk for a similar event. We will also look at more holistic recommendations, such as ways of Thames Water responding to similar incidents in the future, increased monitoring and warning systems, engagement with customers, and how TW, and possibly the wider industry, could consider setting out their modelling approach and design criteria for flood alleviation schemes in the future. Due to the scale of the events in July 2021, multiple organisations had a duty of care and responsibility to their customers, so the responsibility does not lie wholly with Thames Water. We will look at how data and communications are shared across organisations, what community groups and individuals can do to improve their own resilience and how planning policy can be changed to reduce flood risk and the impact of flooding."
Brent the Lead Local Flood Authority should protect and invest in what remains of South Kilburns public owned modern natural parks and bowls flood defence system built in the 1960's and 70's.
David Walton
FLASK (Flood Local Action South Kilburn)
