Rufus I do know that, at the least, the Environment Agency advise local authorities on planning decision concerning the flood plains of rivers.
However, it tends to go along the lines of
Environment Agency - we recommend not building houses on the flood plain due to the increased risks of flooding
Local Authority - thank you for your advice
Local Authority - application approved (while rubbing hands thinking of all the council tax revenue they will received once the new homes are occupied)
I would very much like to see the owners of the houses so affected win a class action against the local authority who granted planning permission against the expert advice.
Even if rivers were dredged, when river levels are high and they're in spate, this causes tremendous pollution and there will be a loss of wildlife as a result.
Everyone that takes down their front garden wall, and replaces it with a concrete or tarmac driveway increases the risk of flooding - it's not just Tesco with their massive carparks. Years and years ago, Charlie Dimmock was talking about green driveways helping to reduce flooding.
If all the front gardens are concreted to provide off-street parking, after heavy rainfall, the water won't have anywhere else to go, except into people's homes.
We were nearly flooded in 1980 when 2 out of 3 road bridges in Preston over the Ribble were under water. The houses at the end of our road were flooded, and some lost the supporting brick pillars under the downstairs floorboards. The water came within less than a foot of our back door, but fortunately the wind didn't increase, else we would have been flooded.