Building on flood plains

[Jameshow]

800 litres of water! Wow. That will do it.

I appreciate they are trying but that’s less than 1 cubic metre of water.

I built half a dozen of them years ago, felt like a token effort tbh!

 

[Jameshow]

Flood management on the Today programme here on the Avon at Bristol, from 1:41:32. (8 mins)

In essence, they're saying that the solution is to blot up the water high in the catchment area so that it's released slowly, at a manageable rate, rather than in one short sharp surge.

But when they build on the flood plane higher up in the aire valley for instance, it's no surprise that kirkstall / Leeds gets flooded.

 

[classic33]

But when they build on the flood plane higher up in the aire valley for instance, it's no surprise that kirkstall / Leeds gets flooded.

Have a gander around Water Lane, south of the railway station. The Halifax building has had its ground floor flooded a few times in its lifetime.

I've cycled along it, from Wellington Road, with it under half a foot of water when I worked there.

The road name is a giveaway.

 

[Drago]

I wonder why it's called Water Lane?

 

[presta]

But when they build on the flood plane higher up in the aire valley for instance, it's no surprise that kirkstall / Leeds gets flooded.

Flood water always comes from somewhere higher, the catchment area for the Aire is up in the dales. Slow the flow at source, before it forms into a flood, or before it's in a place that can be damaged by flood. As the guy on the radio says: floods occur when lots of raindrops amalgamate all at once, so the answer is to stop them from amalgamating too quickly.

When you switch on the shower the water runs down the plughole immediately, but if you lay a blanket in the bath it will absorb water for a long while, and then release it in a slow trickle.

 

[ColinJ]

When you switch on the shower the water runs down the plughole immediately, but if you lay a blanket in the bath it will absorb water for a long while, and then release it in a slow trickle.

But if your shower is above a shower tray and you put a blanket in that, you will flood your bathroom!

(The previous owners of this house had evidently done something like that because there was water damage to the kitchen ceiling below, and signs of arcing around the wiring of the kitchen light.)

It is very obvious round here that rainwater comes down off the moors far too quickly after storms. I read that the historic reason is that landowners were more interested in land management that allowed more pheasants to be shot on the hills than fewer peasants to be flooded out of their homes in the valley!

 

[classic33]

But if your shower is above a shower tray and you put a blanket in that, you will flood your bathroom!

(The previous owners of this house had evidently done something like that because there was water damage to the kitchen ceiling below, and signs of arcing around the wiring of the kitchen light.)

It is very obvious round here that rainwater comes down off the moors far too quickly after storms. I read that the historic reason is that landowners were more interested in land management that allowed more pheasants to be shot on the hills than fewer peasants to be flooded out of their homes in the valley!

Nearly all the mills were in The Valley as well. In their early days powered by water. Goods shipped in and out via the canal.

 

[presta]

But if your shower is above a shower tray and you put a blanket in that, you will flood your bathroom!

Nobody's talking about damming a valley all the way to the top so that it overflows into a neighbouring valley, are they. It follows from the fact that forecasters warn of a higher flood risk when the ground is saturated and can't hold any more water that the flood risk is lower when the ground is absorbent. Slowing the release of water from the catchment area reduces flood risk.

 

[MontyVeda]

...
It is very obvious round here that rainwater comes down off the moors far too quickly after storms. I read that the historic reason is that landowners were more interested in land management that allowed more pheasants to be shot on the hills than fewer peasants to be flooded out of their homes in the valley!

Planting lots of trees in the mid-high upland regions of any rivers' catchment area would help a lot, i reckon.

 

[ColinJ]

Planting lots of trees in the mid-high upland regions of any rivers' catchment area would help a lot, i reckon.

Yes - the problem was landowners chopping the trees down in the first place, and digging ditches to drain the moors.

Hmm, interesting... I just did a search for information and found this: Natural Flood Management in Calderdale.

 

[classic33]

Nobody's talking about damming a valley all the way to the top so that it overflows into a neighbouring valley, are they. It follows from the fact that forecasters warn of a higher flood risk when the ground is saturated and can't hold any more water that the flood risk is lower when the ground is absorbent. Slowing the release of water from the catchment area reduces flood risk.

Baitings Dam, alongside the A58.

Areas of peatland, also known as bogs in some parts, are natural reservoirs. They work at their best, for wildlife, when wet. When dry, they're a fire hazard.

But they can only hold a certain amount of water. After which any excess will just be running off.

 

[oldwheels]

Not really relevant to flooding.
At Littlemill Distillery we had a private dam in Auchentorlie Estate higher up above the distillery. A problem developed with water shortage for no apparent reason so I took a walk up the hillside [ Kilpatrick Hills] for a look at the source.
It was fairly obvious that the water board had been diverting the burns to run down the other side of the watershed to their dam which was the local public water supply.
A couple of blokes with spades were taken up and we sorted that problem and we never heard any complaints from the water board.
I suspect that what they had done was illegal and they thought it best to just accept the status quo rather than face legal action.

 

[Slick]

There's also lots of examples of using this resource by way of hydro schemes.

I've worked on a number of these small projects for one particular contractor, and I thought they were amazing projects. They turned a number of sites that you couldn't even graze sheep on and turned them into productive money making sites that were due to break even after 5 years. Every single one of them did it in just over a year, mostly because of the increased rain fall coming off the hill.

 

[presta]

But they can only hold a certain amount of water. After which any excess will just be running off.

Any scheme that can be conceived will have limited capacity, but a whole catchment area has far more scope for blotting up water and/or harmless flooding than a levee through the centre of a big city ever will.

 

[Time Waster]

It's cumulative. Tree planting, wood dams in streams slowing flow, rain collectors of various forms that slow release into drains and rivers, etc.

It's like that 800l one at the hospital. On its own it's negligible effect but what if this was copied around the country in many large organisations and buildings? It takes one organisation to do it, the idea gets out and more take similar steps available to them. Get that into development standards and the industry gets involved. Perhaps then you're getting into joined up thinking territory?