Flash flooding - August 2020

Since the evening of Monday 24 August, Liberal Democrat councillors have been speaking to residents about the flash flooding in parts of Raynes Park and Motspur Park.

They've also been in discussions with Merton Council and Thames Water about taking action to solve the problems and clean up the affected areas.

West Barnes councillors would like to thank all the residents for sending photos and video footage of the of flooding which has been shared with Merton Council and Thames Water. Several roads were affected, including Grand Drive, Greenway and West Barnes Lane. The extreme rainfall caused damage to the corner shop and parked cars on Seaforth Avenue in particular. Concerns have been raised for some time about blocked drains and gullies and the need for immediate action in this area is needed. With the increase of non-porous materials being used on drives and front gardens and the likelihood of more unpredictable weather due to climate change a long term solution needs to be discussed by Merton Council.

There have been flooding problems on Abbott Avenue in Dundonald ward for years - Lib Dem councillors successfully pushed for some action to be taken by Thames Water in 2018, and we hoped this had improved things. More info here.


As of Tuesday 25 August, Council told us the following:

"The intensity and volume of rainfall experienced across [South West] London yesterday was exceptional and exceed the capacity of the receiving drainage network in a few locations across the borough. This rainfall occurred in a very short time period and floodwaters have receded since the rains have stopped. Sewers are designed to accommodate storms up to the 1 in 30 year event and this localised storm have likely exceeded that probability.

We are speaking with Thames Water regarding all of the sites which have been affected, with particular focus with Thames Water asset manager on the Abbott Avenue pump station.

Flood Warnings were also issued by the Environment Agency due to very high river levels on the River Wandle, Beverley Brook and Pyl Brook. These Environment Agency warnings are now no longer in force.

The high risk gully cleansing programme has targeted deep cleaning of the highway drainage in areas at risk of flooding and this has ensured that in the majority of locations, road gullies have been clear in advance of these summer storms. West Barnes Lane, Seaforth Avenue along with all of Raynes Park town centre was covered in this programme of works early this summer. Similarly, Merton Park, Cannon Hill and Dundonald are all areas included in this works programme, due to historic flooding issues.

Furthermore, we had an emergency gully crew dispatched last night who worked through the night and are continuing to attend all reported sites today on a priority basis.

Where flooding has occurred or on street debris or detritus has been left by the flooding, we have organised a clean and sweep of the road by our term waste contractor."

On Wednesday 26th August, there was a response from Thames Water:

"A comprehensive response will need to come from our Government Liaison Team regarding this matter. 

I’m aware on Monday 24th we had received a significant amount of rainfall, whilst our sewers are designed to cope with most storms, the flooding that had occurred at Abbott Avenue was down to the amount of rainfall, this can overwhelm the system and cause it to overflow.

I understand that once the rain had stopped the water drained away, suggesting there are no blockages in the sewer network, and we had quickly sent a team to clean down the affected road.

As previously stated, I would like to assure you that our team will send a detailed response to you regarding this matter."

The latest from the Council on Thursday 27 August is:

"A meeting [was held] yesterday with the Thames Water asset planner which went well and on reporting the flooding sites and roads they having dispatched operational crews to undertake detailed investigations and CCTV surveys of their assets in these areas in West Barnes/Motspur Park and Raynes Park.

In the Seaforth, West Barnes Lane, Linkway areas (which are all roads shown to be at high or medium risk of Surface Water flooding), the [Thames Water] surface water sewers discharge via a relatively small sewer into the Pyl Brook culvert. In my view, during times of very high river levels, these outfalls are likely to be surcharged which would restrict flows and could have been the cause of the flooding we saw due to the intensity and volume of the storm.

Abbott Avenue pump station will be of the upmost priority location for Thames Water given its history and due to the fact this is foul water flooding.

We have aldo issued a works order to FM Conway to attend all of the flooded roads and clean a further 769 road gullies and report back on siltation or any defects they may find.

Veolia’s gully crew have also worked through all reported ponding locations and we have called them out for a further night shift tonight, given the forecast and they are on call."