Ravensbourne Valley Residents

• How often would you expect to flood the new catchment area?
  
• For how long would the water be retained?
  
• What damage would be caused by the retention of floodwater?
  
• How long would it take the grass etc. to recover?
  

We can now publish their answers to these questions:

From: KSL PSO SE London & North Kent [mailto:PSO.SELondon&NKent@environment-agency.gov.uk]
Sent: 24 July 2014 18:48
To: chairman.rvps@outlook.com
Subject: RE: Material for Beckenham Place Park

Dear Mr Lees,

Thank you for your interest in our proposal. In answer to your questions:

How often would we expect Beckenham Place Park to store flood water?
Based on our current work, if the proposed works are built then flood water would be temporarily stored in Beckenham Place Park only during infrequent large storm incidents. Under our current climate we would expect there to be a 5 percent chance each year that a large enough storm would occur which would result in flood water storage at the park. This means that we might expect a storm of this magnitude to happen perhaps once every 20 years.

We estimate that in the future the potential impacts of climate change could make large storms more frequent. This could mean more frequent use of the flood storage area. We estimate that in the future there may be a 10 percent chance each year that a large enough storm would occur which would result in flood water storage at the park. This means further in the future we might expect a storm of this magnitude to happen perhaps once every 10 years.

How long would the water be retained within the park?
The River Ravensbourne has a relatively small urban catchment. This means that floods tend to occur over a matter of hours. We would expect water to be safely stored within the park approximately for less than one day. 

What damage would be caused by the retention of floodwater / How long would it take the grass etc. to recover?
Some silt and debris may be deposited in parts of the park by the flood water. Prior to completion of flood alleviation schemes we agree and set up arrangements with land owners as to who and how clearance of this is managed. Ground levels would be amended where necessary to enable free draining of the water back into the river channel once the flood has passed, preventing longer term ponding. Following a flood, access to affected areas may have to be temporarily restricted until the ground has drained and debris has been removed. The water should not have long term impacts on vegetation. The time it takes vegetation to recover can depend upon the specific plant species and the time of year. Careful selection of grass and plant species and, where appropriate, the application of fertiliser post flood can reduce the impacts.

I hope this addresses your questions. If you have any further questions please contact us on pso.selondon&nkent@environment-agency.gov.uk or 01252 729541.

Kind regards,

Rich

Richard Peddie
Flood and Coastal Risk Management Advisor
Partnerships and Strategic Overview
South East London and North Kent
Tel: 01252 729541