Attenuation ponds

GBR78

One of our potential purchases (as long as our sale happens in time) is a new build, which following a quick drive-by yesterday, appears to be sited directly opposite an attenuation pond. Currently it is bone dry, but it appears it's there for the '1-in-100 year' storm events from what I can find in the planning application.

A small brook runs through the middle of the estate which is fed from a local pond network that we have known for many years. This pond network has never flooded, and to my knowledge nor has the small brook that is now sited through the middle of this land. This brook intersects two attenuation ponds (but doesn't look to actually directly connect with them). I believe these ponds are for surface water run off rather than extra stream capacity.

Having never lived anywhere near one of these before, does anyone have any experience of the impact? Does it affect house prices at all? Are they a worry or is the fact that they are there (and really quite large) eliminate that worry of flooding?

Might be a difficult one to answer but I'd appreciate any help!

davidmcn

They should be designed to overflow into "normal" drainage rather than cause flooding. I expect the risk is fairly small as they should only be dealing with e.g. the surface water from your development, not all the other rainwater from further upstream (which is the sort of thing which causes normal waterways to burst their banks).

G_M

GBR78 wrote: »

Having never lived anywhere near one of these before, does anyone have any experience of the impact? Does it affect house prices at all? Are they a worry
well the fact that you are asking suggests that some buyers might be worried, and that might affect the price
or is the fact that they are there (and really quite large) eliminate that worry of flooding?
It almost certainly reduces the risk of flooding.
whether it reduces the worry is a different question!

Might be a difficult one to answer but I'd appreciate any help!

This certainky suggests the site is in a flood plain of some kind. Whether there is adequate protection you'll find out in 22 years when a flood occurs.

Davesnave

I don't think these usually worry people like, say, power lines do, although I know of one instance where the water from such a pond bubbled-up in someone's garden in wet conditions and it took them some time to prove it, before expensive rectification by the builders.

You have the advantage of knowing the area first hand, so you are far better placed than we are to judge whether this might be a 'worrying' feature.

What I would say is that you can show people on here any house and we'll find a down-side to it, so be careful you're not doing the same! Every decision to buy involves compromises.

marksoton

Chances are it's a SUDS scheme...

http://www.bgs.ac.uk/suds/

A lot of authorities now require them as part of their planning permission.

They're actually nothing to do with flood events.

Davesnave

marksoton wrote: »

Chances are it's a SUDS scheme...


They're actually nothing to do with flood events.

Isn't the whole point of SUDS that the measures are intended to hold back and control run-off to prevent sudden, overwhelming influxes into river systems?

Most people would see that as part of flood prevention and therefore linked to flood events, though in a positive way.

marksoton

Davesnave wrote: »

Isn't the whole point of SUDS that the measures are intended to hold back and control run-off to prevent sudden, overwhelming influxes into river systems?

Most people would see that as part of flood prevention and therefore linked to flood events, though in a positive way.

That's a benefit of them but not their sole intention. More and more they're being installed for non storm events.

Water companies love them because quite often someone else is paying, it alleviates pressure on their network and it saves them costly sewer up-sizing.

Fuzzyness

G_M wrote: »

This certainky suggests the site is in a flood plain of some kind. Whether there is adequate protection you'll find out in 22 years when a flood occurs.

an attenutation pond wouldnt have been put in to try and stop river flooding. they are there primarily to deal with surface water runoff. when it rains, the runoff congregates in the ponds and either infiltrates into the ground or is discharged into the brook (that the OP refers to) at a controlled rate so as to avoid mass runoff that causes the problems.

Fuzzyness

marksoton wrote: »

Chances are it's a SUDS scheme...

http://www.bgs.ac.uk/suds/

A lot of authorities now require them as part of their planning permission.

They're actually nothing to do with flood events.

really? might not relate to river flooding but are specifically there to address surface water runoff which occurs when it rains. a flood event by another name??

marksoton

Fuzzyness wrote: »

really? might not relate to river flooding but are specifically there to address surface water runoff which occurs when it rains. a flood event by another name??

No, just because it rains doesn't make it a flood event.

SUDS are increasingly being used as a general drainage solution.

That's very different to flood alleviation schemes.

GBR78

Thanks all.

From what I can see in the planning information this is a SUDS scheme, but my understanding was for a flood event - mainly due to the concentration of the data on the '1-in-100' and '1-in-1000' year storm events that is in the documentation.

I believe that these ponds are being put in place as one of the restrictions on the site was that surface water run-off cannot be increased compared to the current land (which is/was all farm land). Alledgedly the local existing estate has had issues with surface water flooding on one road (which hasn't affected housing) during some major storm events in 2007, which has highlighted to the planners that the foul water network cannot cope with large additional flows. I believe the attenuation ponds are then pumped at a controlled rate into the existing network rather than into the existing brook.

I would hope that the developers/consultants have done their work properly meaning that they would never reach full capacity - and the documentation points towards that as their simulated data looks to show maximum water depths of less than 1 meter through all their examples. I believe the closest pond has a maximum depth capacity over 1.7 meters.