Flooding

[Roger BestParticipant @rogerbest89007]

Cool thread.

There are lots of lessons here, meddle and there are consequences, even to simple actions.

I also live in a glacial-clay valley in the middle of chalk downland ironically, Several properties nearby have suffered subsidence and a stream runs under my house. Fortunately my footings are under the water level, so consistently soggy, even in summer. Its the change in resistance of footings that causes subsidence as we found in our first house.

To answer the first question, yes we need to be improving rivers, even though it will be expensive. These wet winters are here to stay for a good long time, and flooding will be common. So we should seek sustainable solutions and make our environment resistant to lethal flash floods too.

[SamsarandaParticipant @samsaranda]

On the estate that I live on prior to the estate being built a spring fed stream fed the local horse pond. When the plans were approved for the estate in the mid 60’s the developer was required to culvert the stream and feed it into the surface water drain under a road that was built to serve the houses, this culvert runs under a number of gardens on the lowest part of the estate. Recently the properties where the culvert runs have experienced flooded gardens during the winter months when obviously any spring fed watercourse will have an increased flow. During the intervening years from when the estate was built, many house owners have planted trees, some of which like conifers have extremely extensive root systems that seek out any underground water, it appears that the roots of all these trees have penetrated the culvert in numerous places and blocked it so solidly that the flow no longer happens, resulting in the flooding of the gardens. There is now a bitter argument as to who is responsible for the work to remedy the situation, they will eventually have to accept that under ancient common law, ie. Riparian Rights, then keeping a watercourse free flowing rests with each freeholder, whose land the watercourse flows over or under. The moral of this story is that there can be consequences to building on low lying land particularly when it is an established watercourse. Dave W

[Nigel Graham 2Participant @nigelgraham2]

We can all agree on the folly on allowing building on flood-plains, but there are flaws in the suggestions and complaints you often hear about the flood all being the fault of no dredging and straightening of the river.

Think of the geometry of a typical river. Unless running more or less straight from hills into the sea, it is steep in its upper reaches then eases in gradient to almost flat across the coastal lowlands. On wide lowlands its long profile is almost asymptotic to the sea's surface. There are exceptions of course, and some rivers have intermediate flood-plains well inland and above sea-level, with steeper sections between them.

So dredging can only "work" if at all, in two cases:_

1) The entire course is dredged from the upper limits of the flood-plain down to meet the estuary bed level, but dredging below that level would obviously achieve nothing useful.

2) If a river has a flood-plain upstream that can be dredged to move its downstream boundary knick-point, which acts rather like a natural weir, artificially upstream to the steeper ground. These knick-points can be very subtle and shallow though, so dredging might not have much effect anyway. (Dorset's R. Frome seems to behave like that, with a slight and ill-defined steepening where it passes Dorchester.)

Merely dredging a reach that overflows, without thinking about the bed gradient profile or of any weir downstream, would clearly create only a long, deep pool that would fill to the original level pretty well as the dredging proceeds. So it would still overflow in high flood.

Widening the channel instead might have a similar effect.

'

Straightening meandering rivers was common in the 19C, as it was thought to improves the river's efficiency as a land-drain. A river is at its most efficient if left alone, meanders and all – as well as being far better for wildlife, not just looks. It will gradually modify its and intervening sediment deposits, slowly wandering from one side of its valley to the other and back, though over centuries or millennia.

'

I'm afraid we've finally twigged that Man cannot "conquer" or "control" Nature, without it turning and biting us. We even seem to have lost human wisdom of the ages, by which we either didn't live too close to rivers that generations knew would sometimes flood, or we put up with occasional floods.

[Bill PudneyParticipant @billpudney37759]

In 69 or 70 I went to inspect a house with a view to purchase. It was in one of the "Wallops" in Hampshire.  There are several Wallops, Nether, Upper, Lower etc etc. Nice very old house, thatched roof, solid stone, 4' thick walls full of character etc etc. When walking around the garden, I couldn't help but notice a fairly high bank, obviously man made running round the place. I asked the Real Estate person "What is the bank for" , "In case the river floods" (there was a small river on the other side of the road), Says I "..When did the river last flood?", says the R.E.P., without a trace of irony, humour or sarcasm, "1572".

Happy New Year, stay safe

cheers

Bill

Edited By Bill Pudney on 24/01/2021 23:31:44

[Pete.Participant @pete-2]

Posted by Calum Galleitch but we desperately need more housing and suitable sites aren't always easily found.

And all the while climate change is effectively making the ground everywhere inexorably closer to the water…

Why do we desperately need more housing? Our population is pretty stagnant, possibly slightly declining, concreting over more land really isn't the answer.

[Danny M2ZParticipant @dannym2z]

Where I live, the willow trees were ripped out a few years ago (to appease the greenies).

Unfortunately, no native trees have been planted to replace the willows and so the soil is washing into the Mitta Mitta river and the fishing is declining angling waters

A large estate has recently been built on a floodplain near the Kiewa river in Vic, Au.

The property developer is a close friend of the local mayor of Wodonga.

Make up your own minds and conclusions.

*danny *

 

Edited By Danny M2Z on 25/01/2021 05:52:06

[PackmuleParticipant @packmule]

As a boat owner, the main problem is that its the Canal & River Trust who do not dredge, do not cut back overgrowth which restricts the navigation so part of it silts up ,again making it more liable to flooding.

It was the trust who are responsible for the dam at Hebden Bridge and we all know what happened there. They charge boat owners a lot of money for a license which is charged by the ft and you can buy either a river license or river/canal. A current river/canal for 12 months on a 60ft narrow boat is over £1000 so their income is substantial. God alone knows what they spend it on.

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