Soakaway alternatives

[welshsonic]

Hi! Been reading PavingExpert for about 1 year now & have been quite impressed with the amount of knowledge / info on the site. That said & having read the main site & some of the forum posts, I have some questions about soakaway alternatives for our garden.

We are on clay soil but there is no combined or rainwater drainage in the road. The property was built in 1960 & has rainwater downpipes going to a TBD location. We are about to embark on a major renovation project, as the house really hasn't been touched since it was built -- one of the items to fix/change is new gutters, downpipes, etc.

Our garden is in effect on 2 levels; the house sits on the higher of the 2 & there is about a 6 ft drop between the levels. The backgarden is 30m wide and 20m from farthest edge of house to back boundary, so in theory plenty of room for a soakaway. The area to be drained is approx 250 metres squared.

We dug a trial hole this weekend: The main hole is 700mm wide by 1500mm long by 1000mm deep. We then excavated a 300mm square hole 250mm deep at the bottom of the 1000mm deep hole. The soil is a very dry, compacted and extremely hard clay in this 300x300x250 hole. Left it overnight in case water decided to fill it, but still bone dry, so not an issue with the water table.

Put the 25% & 75% pegs in as suggested by BRE Digest 365. Filled the hole with water and began to time how long for the water to seep away. Been waiting for 3 hours and I think it has dropped 1-2mm total -- nowhere close to the 75% mark, let alone the 25%. Since our first trial isn't even completed yet, it makes me think that a soakaway just won't be feasible.

I've looked at Part H of the Building Regs & it says that to dispose of rainwater it needs to go to 1) soakaway, 2) watercourse 3) sewer, in that order of preference. Now, like I said, I think the soakaway will be not feasible based on our trial and there is no watercourse near by. However, there is a 'sometimes stream/ditch' about 100m down the road, it's culverted in places & it floods the road when it rains. The only way of channelling rainwater from our house into that is to either dump it on the road, which is against the Highways Act, or to dig up the road & put in a new rainwater drain & connecting into it. According to the water search we had performed by our solicitors when we bought the property, the only pipe in the road is Foul (no combined or rainwater).

So, based on that info, is there anything else I could try to see if a soakaway would work? Obviously the current rainwater for the house has to go somewhere, and I know it isn't going into our Foul sewer. How would you suggest I approach Building Control with this info? And if the only answer is to practically put the rainwater into the sewer, would you have any advice on how to approach the water company to make them amenable to this? (As an aside, I know for a fact that at least 1 resident in the road has his rainwater going into the sewer, but it was put there by a previous occupier and probably wasn't officially approved by the water company). Would the water company tell me I would have to pay to dig up the road to divert the rainwater into the ditch I mentioned above?

The only other option I thought we might have is to put in some perforated pipe connecting our drains & running them down the garden & 'lighting' them on the boundary. This is a Parish Council owned field at the back of our property which is used by the local residents for playground, walking of pets, etc. However, I don't know if the council would consent to such a practice as it means possibly quite soggy patches at times.

Any advice or other options would be greatly appreciated.

???

[sqidd1g]

Hi, welshsonic
a question for you --- are you extending the property, and is your existing rainwater drainage working without any problem.

The reason I ask is if you are just replacing downpipes etc, why not just join to your existing underground drainage.

sqidd1g

[welshsonic]

Thanks sqidd1g for the speedy reply. In answer to your question:

Yes we are extending the property -- building a new detatched 2x garage as well as gabling both ends of the hipped roof. Some downpipe positions would be changing, others would remain in the same location. However, where downpipes enter the ground, all seem to back up / overflow. There is a small square grille near each but it's difficult to get a rod in at 90 degree angles (ie no rodding points).

Surveys of the house have indicated that the drains are blocked/silted up and the soakaway is also likely to be silted up.

After heavy rain parts of the garden appear soggy, however, that could also be due to poor lawn maintenance (ie needs spiking, new lawn, digging over).

Hence, the reason we dug a trial pit as we thought we would need to replace the soakaway. ???

[Tony McC]

I reckon an attenuation system is what you'll have to use. Have you seen the bit on the mian website about installing a simple two-crate system to drain a small patio - well, like that only much bigger; big enough to take all the run off from the building - maybe 8-10 'crates'.

Have you mentioned the magic word "SUDS" to the BCO? If s/he goes pale, you might need to speak to someone else, but if they are anywhere near up-to-date with their CPD, they should be able to advise.

[welshsonic]

Tony McC - Thanks for the info. Yes I had seen the page on attentuation -- before we dug the trial pit we were considering using cells instead of filling a soakaway trench with gravel. However -- I still don't see how this will work with our situation and here's why (but please feel free to prove me wrong):

* There is an example soakaway calculation in BRE digest 365. I took the infiltration rate from the example & plugged it into my spreadsheet just to see how big of a soakaway we would need if the infiltration rate was the same. Based on 250m2 roof area & in the Bristol area & needing to cater for a 1 in 10 year storm & the example infiltration rate, there were 2 ways of creating a soakaway:

1) 15m long, 0.5m wide, 1.5m effective depth trench with 30% free granular fill

2) 13m long 0.5m wide, 0.8m effective depth trench using AquaCell Lite system (for a total of 26 units).

NOTE: On paper, option 1) appears to drain faster due to science of soakaways being more effective the deeper & longer they are.

But from my brief trial, our infiltration rate is nowhere near the one in the example. It is much slower. In fact, I just went to check on the hole we dug over the weekend & filled with water on Sunday. After 72 hours, the 300mm x 300mm x 250mm hole is still 70% full. Now extrapolate that perceived rate with the entire rainfall from a roof & we are talking possibly weeks to drain the soakaway. And according again to BRE 365, if a soakaway takes more than a few days to get to 1/2 empty, then performance is unsuitable.

So that would mean scaling up the size of the system from my 2 possible solutions. I can only imagine the size required -- probably the entire lower area of the garden (20m x 30m)-- which I really can't see BC saying is feasible (nor can our financial pockets), right? And BTW - the Parish Council owned playing field bordering this lower area of the garden is lower still -- so all the water from the soakaway would eventually find its way to that.

In this case, is dumping the rainwater into the foul sewer the only correct option?

So any additional advice/help you can supply is greatly appreciated.

[TheRobster]

Have you no idea at all where the current surface water goes to?

And if the only answer is to practically put the rainwater into the sewer, would you have any advice on how to approach the water company to make them amenable to this?

If they let you connect to the existing sewer, they will almost certainly give you a maximum discharge rate, meaning that some sort of attenuation system will be required. However, if the sewer is foul only then it's highly unlikely they will let you connect to it at all.

So that would mean scaling up the size of the system from my 2 possible solutions. I can only imagine the size required -- probably the entire lower area of the garden (20m x 30m)-- which I really can't see BC saying is feasible (nor can our financial pockets), right? And BTW - the Parish Council owned playing field bordering this lower area of the garden is lower still -- so all the water from the soakaway would eventually find its way to that.

Another option would be to make your garden part of the attenuation system. This depends to a large extent on the topography.....but assuming your garden is flat then it could be made to work. You could have a smaller underground storage/attenuation system for say a 1 in 1 year storm, then allow some of your garden to flood for any storms in excess of this. Effectively a part of your garden would become a temporary above-ground storage area, which would only flood occasionally (say a couple of times a year). You'd have to make sure you bunded the storage area properly though.

[sqidd1g]

welshsonic,

the chances of your water company allowing you to use the mains sewer are slim, but they do look at things on a case by case basis --- it is definitely worth putting it in writing to them to see how helpful they might be.

good luck

sqidd1g

[Sporange]

I have a similar situation going on. We are extending and the current downpipes either go to water butts or just to the ground (and by that I mean they have small collector with a grate on and no pipes connected to the outlet). The only difference here is that I have over an acre to play with. With this in mind I was thinking of a pond or a balance pond or something similar. Any suggestions? We do have a ditch along one side of the garden into which I do have consent to discharge from my Klargester. Could I discharge the rainwater into this drain to under that consent? I do like the idea of a pond as we have a bit of a slug problem and I understand frogs love slugs. Any comments or suggestions?

[Dave_L]

Surely rainwater is classed as 'surface water' and where it ends up, is where it ends up, that's it! If it ends up in your balance pond, then so be it! :p

[Sporange]

Not when it comes off a roof. Then it comes under the influence of Part H3 of building regs.

The yanks have things called rainwater gardens that we don't seem to do here. It is this type of thing I would like to do.

[dig dug dan]

we have heavy clay soil here, not blue clay though, and we find that although the trial holes fill up with water, they do drian, albeit slowly.
I think you have three options
1. Dig as deep as you can and install some stormwater storage cells. I have used these and they are brilliant for maximising the hole size, rather than filling it with rubble. Whats more , installed correctly, the ground doesn't sink after installation
2. get a drilling company to drill as far down into the soakaway until you hit chalk, or gravel.This way your soakway will drain faster.
3. Dig your drains into the stream as you suggest. Rather than dig the road up, you could have iot "moled" underneath.

regards

Dan

[lutonlagerlout]

AFAIK the building control round here,will not allow rainwater into sewers-- its a hanging ofence
when i asked the bco what happens with clay soil he said that eventually the water seeps through fissures in the clay
personally if the garden slopes away from the house a pond or a tank to store water seems a good idea,when the summer comes its handy having free water to water the garden with,plus its more ecologicaly sound
cheers LLL

[TheRobster]

When i asked the bco what happens with clay soil he said that eventually the water seeps through fissures in the clay...

LoL that's the funniest thing I've ever read on here...

[lutonlagerlout]

well in a way robster he must be partially right because i have dug loads of soakaways in luton in clay and they work,in that,the rainwater gets away
where and how it goes i dont give a flying f*** as long as it goes and stays gone IYKWIM
its one of those things that shouldnt happen but do
cheers LLL

[TheRobster]

Well clay can (and does) conduct water, it's just usually very bad at it. I took what you posted to mean that the bco was implying that soakaways in clay soil are okay (generally they are not).

IYKWIM

What does that stand for?