Groundwater flooding

Published Friday, 2 May 2014

Although the level of water has declined in recent weeks, Sparrows Den continues to be affected by groundwater flooding. This is as a direct result of record high levels of groundwater which is ultimately explained by the record winter rainfall. Whilst springs continue to ‘issue’ on Sparrows Den, the rate of issue has decreased and continues to reduce.

On Thursday, 1 May, the council started an additional pumping operation from the standing lake to a road gully on Corkscrew Hill which connects to the culverted (piped) River Ravensbourne.  There is now sufficient capacity in that culvert to allow for an around the clock pumped drain down from the Sparrows Den rugby pitches.  This is an experimental operation to see if the existing drainage by infiltration will then be sufficient to cope with the reduced and reducing groundwater levels.

This pumping is in addition to the 10 week pumping operation in Courtfield Rise to protect homes from internal flooding.

Sparrows Den remains open to members of the public but visitors are advised to proceed with caution near the water, particularly if in charge of children or dogs. The water has been tested and is not a threat to public health but it is not advisable to swim in the water.

Sparrows Den and Addington Road are situated in a valley and therefore it is natural that water will collect in the valley.  The council is continuing with its around the clock pumping operation to protect actual homes from being flooded, with water being pumped into a culverted river.  The groundwater flooding has occurred naturally because of the valley’s geological characteristics and the low ground level and this is true both for Sparrows Den and properties and gardens in Courtfield Rise and Addington Road too.

Ground levels are actually lower further along Addington Road, away from Sparrows Den and this helps to explain why groundwater flooding is not confined to Sparrows Den and this flooding will continue for at least as long as the groundwater flooding in Sparrows Den.  The Environment Agency have advised that groundwater levels remain at extremely high levels albeit that they are receding slowly over time.  Groundwater levels locally will probably remain high, even going into the summer months, albeit that they will recede and levels of water on the surface will disappear but it is not clear exactly when this will be.

The water which has collected in Sparrows Den is making its way under Corkscrew Hill and Glebe Way, along the culvert which runs parallel with Addington Road going towards Hayes, where there is an open section of water course and forms part of the River Ravensbourne.  There is not a direct causal link between the groundwater flooding and river.  It is also important to note that Sparrows Den has not been flooded deliberately (and nor is the water being held on the site) but it is a naturally occurring groundwater flooding event.

Whilst residents have some responsibilities with reference to the river, the Environment Agency have been working to improve flow and capacity in the river and culvert and a lot of this work is complete.  In the very early stages of this groundwater flooding incident, the Army assisted in some of the clearance work but more recently, Environment Agency contractors have carried out works.  The council supported this work (which was planned) by ‘jetting’ the culvert, primarily in and around the Glebe Way section.

It has been said that that the work undertaken by Thames Water on Sparrows Den a few years ago should have ‘solved the problem’ but the Thames Water work was never designed to tackle groundwater, but was instead about their foul sewage systems.

The heavy duty sand bags which were initially placed along Corkscrew Hill to protect the road and homes directly opposite Sparrows Den will be removed shortly as there is no longer a risk of water flowing over the road from Sparrows Den.