The planning application for the development of garages at Lidding Road in the north of Brent was deferred last December after councillors heard representations from the Friends of Woodcock Park on sewer capacity and flooding in the area of the development which is close to the Wealdstone Brook. LINK
The application was for demolition
of the existing garages and redevelopment to provide 3 self-contained
flats and 5 dwelling houses; with
associated car parking, cycle storage, refuse
storage, amenity space and
landscaping
The application is back at Planning Committee on April 20th with a detailed response from Thames Water. Officers continue to recoemmend approval of the application.
Officers' Report extracts:
Members will be aware that the application was
first reported to Committee at the meeting on 15 December 2021 where the
committee agreed to defer a decision on the application in order to:
Impact of the proposed development on drainage and the maintenance of the
sewerage infrastructure and how these would be mitigated
In the Committee members raised concerns regarding flood risk impacts on the site. Specific concerns were raised regarding the potential for the voids under the houses to be blocked by residents; the ability for Thames Water to access and service the pipes where necessary. Additionally members raised concerns over the potential impact of the development on pollution in the Wealdstone Brook and further details were requested regarding any projects to clean the Brook.
Since the application was deferred, further comments were received from Thames
Water regarding impacts of the development. It should be noted that these
comments relate only to flooding that may rise from foul or surface water
flooding. Flooding from other sources (such as the Brook) fall outside the
statutory responsibility of Thames Water.
They consider that there is sufficient capacity and that the flow expected from
the development would be exceptionally small. They have specified that they
have no concerns over the risk of foul water flooding as part of the
development. Additionally, they consider that the development would not result
in an increase to the pollution of the Wealdstone Brook.
With regard to the concerns raised by residents about the sewers, Thames Water
have specified the following:
We acknowledge concerns raised by residents about the performance of the foul
sewers in this area. These have not been caused by the capacity of the sewers
but by sewer blockages. Sewers are only designed to take water from toilets,
sinks, baths and showers along with human waste and toilet tissue. Everything
else should be put in the bin.
Sewer blockages in this area are predominantly due to fats, oils and grease
being inappropriately put down the sewer. This then clogs the pipes, which
causes the foul water to back up and eventually flood out of the sewer.
Sewer capacity is when the pipe is too small to accommodate flow and it can
eventually back up and eventually cause flooding. Increased flow to the foul
sewer from new developments has the potential to increase the risk of flooding due to sewer capacity. From our knowledge of the
current flow in the sewer in question and the expected increase due to this
development we are confident that the receiving sewer has sufficient capacity
to accommodate the proposed flows. If we had concerns that capacity did not
exist to serve this development, it would initiate Thames Water funded
modelling investigations. Our initial assessment of this site shows this is not
necessary.
They also note that with regards to surface water flooding there would be an
overall reduction in flood risk due to the increased flow rates identified in
the drainage strategy.
With regards to access to the sewers, Thames Water have confirmed that the
applicants have engaged with them during the course of the development and a
build-over agreement has been proposed. Thames Water raise no objections or
concerns in regards to this and note that such matters are usually dealt with post-approval
via Building Regulations.
The applicant has also advised that they already have details of the existing
line, level and condition of the existing sewers within the development
boundary prior to development, from undertaking drainage CCTV condition and
utilities surveys in 2020. The flood risk consultant has therefore suggested
that a post-construction drainage CCTV and conditions survey is undertaken of
the Thames Water assets within the redline boundary to confirm that there has
been no damage to the existing sewers during construction. Any damaged and/or
blocked pipes could then be reported to Thames Water for repair. Such details
could be conditioned to any forthcoming consent.
With regards to pollution in the Wealdstone Brook, colleagues in the Parks team
have provided further information on the existing circumstances. They note that
most of the pollutants in the water would have originated upstream and flowed
down into Brent towards the River Brent.
Brent Parks Service are working on an early-stage scheme to improve the structural and wildlife diversity and amenity section of the Brook through woodcock Park. Additionally, the catchment area of the brook is mainly located in Harrow and Harrow Council has ongoing projects to improve the brook.
Thames Water have an on-going programme looking at addressing the issues with
water quality in the Wealdstone Brook, and have specified the following:
We recognise that there is a significant issue with water quality in the Wealdstone Brook. We host a “Friends of the Wealdstone Brook” quarterly meeting where residents, the Environment Agency, Lead Local Flooding Authorities are other interested stakeholders can meet and engage on the issue. This allows us to share water quality data for the watercourse, our operational activity and longer-term investment plans with interested stakeholders. The group is attended by the NERC funded CAMELLIA project (Community Water Management for a Liveable London) consisting of many academic partners including Imperial College, British Geological Survey, and Oxford University. We completed an extensive Catchment Study on the Wealdstone Brook in 2016/17 that assessed the root cause of poor water quality and flood risk in the area. Following that study, we have a long-term list of improvements we propose to make to the sewer system. As water quality and flood risk are intrinsically linked, we have to start by creating capacity in the river system. We are in discussions with Harrow Council about a potential scheme to do that.
Once details
are available, we will share them. We hope to promote a similar scheme with
Brent Council in the future. Thames Water conclude their further advice by
confirming that they have adequately assessed the impact that the proposed development will have on
the sewer system and that they are confident that the development will not cause a deterioration to the level of service residents
receive at present.
Location of the flooding incidents identified within the Flood Risk Assessment
In the committee members noted that the flood risk assessment identified 66
flooding events at postcode ‘HA3 0’. It should be noted that this postcode zone
encompasses a larger area stretching from Kingsbury to Northwick Park and
including the area between Kenton Road and Preston Road.
In response to the above, the applicants have requested a Sewer Flooding
History Enquiry from Thames Water. This has selected 1 Lidding Road as the
centre point but encompasses a wider area around this address. The report notes
that there have been no recorded flooding events in the area as a result of surcharging
public sewers.
With regards to the potential for the voids to be blocked, the applicants have
agreed that a planning condition can be attached requiring a verification
report to confirm that the relevant measures have been implemented on site.
This is intended to include a drainage maintenance schedule which can
incorporate checks to the void structure.
Notwithstanding that, the voids are closed in by ‘hit-and-miss’ brickwork leaving several small gaps for water to escape. The gaps are considered small enough to avoid large objects from being inserted into the void space. Additionally, these voids would be located under all plots 1-6. As such, officers consider that the likelihood of the voids to be fully blocked and therefore resulting in undue flooding impacts is low and suitably addressed by the suggested condition
