Lidding Road planning application near Wealdstone Brook, returns to Planning Committee after Thames Water commentary

 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:

1. seek further details and assurance from Thames Water in relation to the impact of the proposed development on drainage and the maintenance of the sewerage infrastructure and how these would be mitigated;
 

2. seek further details on the location of the flooding incidents identified within the Flood Risk Assessment; 

 

3. seek further details on the proposals to alleviate concerns regarding the access of construction traffic to the site via Gooseacre Lane as part of the Construction Method Statement and Logistics Plan to be secured via condition.

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