Author Topic: How does a soakaway drain work?  (Read 1123 times)

How does a soakaway drain work?
« on: November 10, 2018, 03:38:10 pm »
As above.
I have the fluid contents of a roof, gutter and drainpipe directed towards a soakaway which is located a couple of feet in from the edge what passes as my lawn.
Does it literally just soak into the surrounding soil, or is it linked in any way to the drainage/sewage  system?
I ask because I've been running a garden hose for a while (in order to wet sweep-up excess cement left behind by the guys who've just installed a fence) and there doesn't appear to be too much soaking away going on.
Can it be that the volume of water the hose has delivered is more than the soak away can cope with.
I've had a drain spring down there, and ladled out some rocks from the drain cover in the lawn, but the water level doesn't appear to be receding.
Drains.
Saturday afternoon.
That's how I like to spend my time.

TIA

hellymedic

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Re: How does a soakaway drain work?
« Reply #1 on: November 10, 2018, 03:45:58 pm »
London Clay?
Soakaway?
Heavy rain?

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Re: How does a soakaway drain work?
« Reply #2 on: November 10, 2018, 03:47:52 pm »
Just soaks into the soil. Should have loose stony material in the bottom but this tends to silt up eventually, making it somewhat ineffective.

Re: How does a soakaway drain work?
« Reply #3 on: November 10, 2018, 03:59:23 pm »
London Clay -Check
It's what I have to live with.
Is removal of the stony material desirable?
Or should I put it back?

Re: How does a soakaway drain work?
« Reply #4 on: November 10, 2018, 04:16:40 pm »
A old soakaway typically consists of an excavation with some clean hardcore or stone aggregate filled in and then covered over with a sheet of something impervious to stop the material silting up immediately with backfilled earth.  (Anything from old carpet to plastic sheet). Occationally they will be properly constructed complete with inspection covers and be of masonry/concrete construction. They should be several metres away from any property but were often not placed sufficiently far away from buildings.

Nowadays purpose made plastic 'baskets' are used in sustainable separate drainage systems which can interlock with each other so as to increase their capacity where required and which have knock out holes for drainage runs to enter in multiple locations. They are then wrapped in a permeable material allowing water to escape but which prevents silting. The  drainage capacity of these soakways is very high due to their ability to store volume togther with their specific surface and they are also very strong hence good at load bearing without crushing

The old soakaways are not so efficient but do work. They however have a tendency to silt up over time and become less efficient hence your observation. As above, the nature of the sub soils is also a factor affecting the rate of dispersion.

Tree roots are another issue.

https://job-prices.co.uk/soakaway-questions/
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Basil

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Re: How does a soakaway drain work?
« Reply #5 on: November 10, 2018, 05:56:54 pm »
We have one soak away that deals with roof draining plus one of the upstairs sinks.
It is it is 123 years old. It is not very efficient.
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Re: How does a soakaway drain work?
« Reply #6 on: November 10, 2018, 06:20:15 pm »
When planning a soakaway, there's a test you have to do that involves digging a 1'x1'x2' deep hole, and timing how long it takes for a certain volume of water to drain away. I'm betting London Clay is going to be an issue, but when I did one, it was in Breckland, Norfolk. There, if you dig down 2', it's like digging on the beach - it's just sand, and getting ANY water to hang around was a challenge; it just disappeared instantly.

LittleWheelsandBig

  • Whimsy Rider
Re: How does a soakaway drain work?
« Reply #7 on: November 10, 2018, 06:20:29 pm »
Soakaways work very well in granular soils (sandy gravels and suchlike), if they are done well. They can be close to useless in clay soils. The average inflow has to be less than the average outflow with the storage capacity of the soakaway smoothing out peak inflows.
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Re: How does a soakaway drain work?
« Reply #8 on: November 10, 2018, 06:38:30 pm »
Soakaways work very well in granular soil (sandy gravels and suchlike), if they are done well. They can be close to useless in clay soils. The average inflow has to be less than the average outflow with the storage capacity of the soakaway smoothing out peak inflows.
I'm close to sunk . Aren't I?

Re: How does a soakaway drain work?
« Reply #9 on: November 10, 2018, 06:59:12 pm »
There’s a soakaway drain in the road at the back of our garden, which is the highest bit of our garden. Occasionally someone puts paint down the drain and it comes out on our garden steps.

LittleWheelsandBig

  • Whimsy Rider
Re: How does a soakaway drain work?
« Reply #10 on: November 10, 2018, 07:07:14 pm »
I think soakaways may be used 'optimistically' in this country because they can be cheaper and easier to install than piped drainage. Residential construction is quite different to my normal line of work though, so pinch of salt and all that.
Wheel meet again, don't know where, don't know when...

Re: How does a soakaway drain work?
« Reply #11 on: November 10, 2018, 07:09:02 pm »
I think soakaways are often used 'optimistically' in this country because they can be cheaper and easier to install than piped drainage.
That was my feeling.
ETA - Shit inna clay soil environment.

hellymedic

  • Just do it!
Re: How does a soakaway drain work?
« Reply #12 on: November 10, 2018, 07:20:30 pm »
I have a Facebook friend at the north face of the London conurbation.

He moans about his septic tank/soakaway approximately fortnightly.

Quite why piped sewerage has not yet reached this affluent suburban outpost seems ridiculous to me!

Re: How does a soakaway drain work?
« Reply #13 on: November 10, 2018, 07:23:16 pm »
As a (now retired) professional engineering geologist, I did a significant number of assessments and designs for these.  LWB, Chris S and Canardly (above) are spot on.

London Clay makes a really good liner for landfills, when dug up, spread and compacted appropriately.  That just about says it all really.

You will get some exfiltration into LC, but not much.  And after a long period of time, what you may have had will decrease as a result of siltation.  It will be a particularly poor soakaway after prolonged wet weather.

Don't feel too put upon though.  Much of England to the SE of a line from the Wash to Bristol has the same problem:  Oxford Clay, Kimmeridge Clay, the Lias Clays of Northamptonshire, I could go on......



Re: How does a soakaway drain work?
« Reply #14 on: November 10, 2018, 07:31:40 pm »
Piped drainage isn't allowed for new houses.  Look up SUDS.
Never tell me the odds.

Re: How does a soakaway drain work?
« Reply #15 on: November 10, 2018, 07:38:10 pm »
Shhhh.... yer elf and safety haven't discovered drainage ponds and reed beds yet.
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hellymedic

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Re: How does a soakaway drain work?
« Reply #16 on: November 10, 2018, 07:41:05 pm »
I don't think Hadley Highstone is new build...

Re: How does a soakaway drain work?
« Reply #17 on: November 10, 2018, 08:22:46 pm »
My parents' house, on low-lying London clay, had a soakaway somewhere where the gardens met.  Everything that wasn't actual sewage went there.  It worked until everyone got washing machines (and presumably as age and silt worked its anti-magic). Then there was the occasional foamy back-up.

By contrast, this Victorian house, sunk into Devon clay, sends storm-water and everything into the sewers.

hellymedic

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Re: How does a soakaway drain work?
« Reply #18 on: November 10, 2018, 08:50:05 pm »
Everything goes into the sewers here in 1930's built HA8. My plumber checked!

Kim

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Re: How does a soakaway drain work?
« Reply #19 on: November 10, 2018, 08:53:40 pm »
Victorians' rudimentary approach to sewage treatment (flush it out to sea and try not to swim too close to the outfall) generally benefited from it being mixed with rainwater.  Modern processes, not so much.

I recall builders molishing a soak-away when my parents had an extension built.  They dug a substantial (maybe 2m wide) hole in the clay and kept going until they reached the underlying chalk, filled it with the rubble from the patio and walls they'd un-molished, and I'm not sure what happened between that and covering it with topsoil.  Anyway, it seemed to do the job.

(Unlike the foul sewer, which had a chronic case of tree roots, and would occasionally back up and cause nasty drain smells to permeate into my brother's ensuite shower cubicle.  Eventually the pong concentration would overwhelm the prevailing Lynx Nevada and mum would lift an inspection cover, observe it to be full of nasty, and promptly GAMI.)
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Re: How does a soakaway drain work?
« Reply #20 on: November 10, 2018, 09:02:48 pm »
Victorians' rudimentary approach to sewage treatment (flush it out to sea and try not to swim too close to the outfall) generally benefited from it being mixed with rainwater.  Modern processes, not so much.

Is that why Skegness was so bracing?

Re: How does a soakaway drain work?
« Reply #21 on: November 10, 2018, 09:31:58 pm »
We had a similar problem in a new house.

Regulations state that non sewage water should not enter the drains and should utilise soak always.

We had to do the 1x 1 x 1 hole, fill it with water and then let the building inspector see it fail to empty. We then got permission to drain our roof rain runoff into the sewer.

I also diverted some of it into a very large tank in my lawn to irrigate the garden.

Wowbagger

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Re: How does a soakaway drain work?
« Reply #22 on: November 10, 2018, 09:33:58 pm »
Prior to our extention being built (2000) all our roof water went into the sewers. For the new bit, a soakaway was dug and it seems to work OK. Our soil has quite a bit of clay in it, but I think there is also some sand. WE get very little rain by UK national standards (Great Wakering, the driest place in Britain according to some measures, is about 5 miles away) but in the past 10 years or so we have had some very wet days - in two or three cases upwards of 30mm in an hour.
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LittleWheelsandBig

  • Whimsy Rider
Re: How does a soakaway drain work?
« Reply #23 on: November 11, 2018, 11:10:50 am »
Piped drainage isn't allowed for new houses.  Look up SUDS.

And there are good reasons for that approach. Piped drainage minimises groundwater recharge, exacerbates downstream flooding and transfers more pollutants into rivers but clay soils can be very problematic.

Our house is on a combined sewer. The whole combined sewer for rainwater and sewage seems an almost mediaeval approach to me but it is too late to change it in many parts of the country. I prefer separate blackwater and greywater recycling systems but that is only taking hold in small-scale developments or in some other countries. Path dependence is a real thing.
Wheel meet again, don't know where, don't know when...

Wombat

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Re: How does a soakaway drain work?
« Reply #24 on: November 12, 2018, 02:52:35 pm »
What are these "sewers" of which you speak? 

Wombat towers (all of one storey high) doesn't have any truck with any of that nonsense, being equipped with a septic tank, allegedly a soakaway, in clayish muck, and doesn't even have a mains water supply.  Nearly all my electricity comes from the sky, but there is a mains connection.  We have got fibre broadband to the house, though!

I hasten to add we do have piped water, it comes from our private borehole (150ft deep), and is absolutely lovely!  Beautiful clear, softish, water with no muck added to it.
Wombat