Flash floods: drains and water courses may not be able to take the volume of water predicted to fall in rain storms in the next 48 hours
No sooner has the amber heatwave warning in south London faded away in some light rain than the Environment Agency has put the area on alert for flash flooding.
With heavy rain forecast to hit the capital today and tomorrow, flood alerts have been issued in Croydon, Sutton, Merton, Lambeth and six other south London boroughs.
The flood alert covers the entire course of the River Wandle, which rises in South Croydon and wends its largely underground way until it surfaces in Wandle Park before heading off towards Sutton and Merton and on to Wandsworth, with its Norbury Brook tributary also running into parts of Lambeth.
Another warning area impacts parts of Lewisham, Bromley and Greenwich around the Ravensbourne.
A third covers the Beverley Brook area including Richmond and Kingston.
Warning: the flood risk map for today and tomorrow, as issued by the Environment Agency
The EA said heavy rain and thunderstorms had been forecast for the next 48-hour period and there was a possibility of “flooding to low lying land, roads and riverside gardens”.
With the ground bone-dry after weeks of drought, heavy downpours risk overwhelming the watercourses, as little of the water will be quickly absorbed.
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I want to know what weather forecast is the Environment Agency using?
I looked yesterday (Tuesday 16th) at the Meteorological Office forecast for Wednesday August 17th/Thursday 18th and it predicts LIGHT rain all day on 17th, and completely dry on 18th. I have looked at the forecast again today (Wednesday 17th) and it remains exactly the same.
Clearly the EA are not using that forecast. We shall see who is right!
Floods on the Wandle?.
If only the remaining flat sections of the Beddington marshes could be made into a series of lakes to hold storm water–and then (pie in an eco-fantasy sky) treated to remove the silt and nasties– before feeding the water in a controlled way into the Wandle.
I have just been thinking about the culverted section of the Bourne from Purley to Wandle Park . Assuming that this is concrete channel with a large capacity, does this have flood gates installed inside the channel, to store water as a temporary flood control measure?
Or is it full to capacity when a storm happens?
The lesson of water management is that when it is spread out, and infiltrates into the ground, it is not a problem. When concentrated, above ground, it is.
We really need major interception in the form of permeable pavings in front gardens, plus bigger soakways and more road gullies. Plus a separate storm water sewer to keep these surges of dirty water out of the sewage works.
The Chief Exec of Thames’ pay packet would cover quite a few new soakways.