Thread: soak well installation

G'day Paul

Welcome to WA - the world's biggest sandpit! You say that one of your downpipes needs a soakwell installed. The normal position in Perth is that all of your downpipes would need a soakwell. Is this just one that has been left out when the house was built and all the others have them?

To answer some of your questions

It is that simple - yes. Dig the hole, place the soakwell in it, connect the downpipe (you can buy all the relevant fittings from hardware stores), place a paving slab on top and bury the whole lot in sand. You've probably noticed that supply of sand won't be a problem!

Plastic downpipes are normally adequate. Shop around a bit. You'll find that different outlets (even Bunnies!) offer deals on soakwell plus paving slab for around $20 -$25. (The concrete soakwells are stronger but, frankly, they're not placed under great stress, being circular and buried in sand, the plastic ones do the job).

They tend to come in a standard size. You need one for every downpipe. You're right about the roof catchment size etc. This determines the number of downpipes required. I don't have the formula immediately available but I've got it buried somewhere amongst some paperwork. If I can find it, I'll post it later on.

We do tend to get some fierce rainstorms in Perth. When they happen, your downpipes and soakwells won't cope. I've seen water spewing back out of the connection up to a foot high. In those conditions, no soakwell will cope. This means you need to be careful about the positioning. It's not a good idea to place one anywhere close to a doorway unless the door's threshold is significantly higher than the point where the downpipe disappears below ground level.

Hope this helps.

Col

Just out of interest's sake, do all downpipes go into soakwells over there? Are you not allowed to run stormwater pipes out to the road gutters? This soakwell business definitely wouldn't work here, we had over a metre of rain week before last.

Mick

Paul.
DAMHIK.
Calculate the total volume of the soakwell you need (the suppliers have info as the that) then double it.
Paddling in 50 mm of water across the verandah to get to the garage and sweeping 25 mm of water out of the workshop makes you realise that the soakwells really aren't too expensive.

Mick.
Where I live, in Albany WA, it is illegal to run water from the roof into street drains or sewers. Mind you, 1000 mm is more than the average rainfall per annum down here.

Thanks Col, Robert

The house we moved into 2 years ago has some soak wells but not on all the down pipes.

Robert excuse my ignorance but what does DAMHIK mean/stand for?

Col, My first thought was to go for concrete, but that may just be my civil engineering training, If they were pretty close to the surface and weren't too tall, plastic would be ok, but are they prone to collapsing?

Paul

Paul.
"Don't ask me how I know."

Paul

The plastic soakwells I installed in my place 16 years ago haven't collapsed and I don't expect that they will. As I said, they are circular in section and they are supported all round their perimeter by sand. This makes the completed structure pretty strong. I was trained as a structural engineer, incidentally. That explains my confidence in plastic structures - just as your training as a civil engineer explains your leaning towards concrete. (For the non-engineers I should tell you that there are a couple of really bad engineer's in-jokes in that lot!)

You know what they say - any idiot can design a bridge that works. The trick is to design one that only just works!

If you bury the soakwells so that the paving slab top is about 450mm below the surface in pedestrian-traffic only areas you really shouldn't have a problem.

Mick - what Robert says about running stormwater into roads and sewers applies all over WA. In this very dry place, the smart thing to do would be to plumb it all into rainwater storage tanks, of course. That's what happens in the bush but we spoiled townies don't do it so we let a lot of good quality water go to waste. I reckon that water restrictions are going to become a permanent feature of life in Perth sooner rather than later. That's when we'll have to seriously re-consider the issue of collecting rainwater.

Col

Paul

There can be a bit more to this topic than you probably imagined and it is right up my ally, well kinda sort of anyway.

DAMHIK either! Well okay, a townhouse I had built flooded a couple of years ago because the soak wells were inadequate! The tenant was not impressed! :mad:

So before fixing the problem I did some research. I am also in the process of replacing the slotted drain (or ag-pipe or whatever the crap is called - I WOULDN'T EVEN THINK ABOUT USING IT) that was used in my current house with concrete soak wells. There is some info from some of the councils which can be easily found by looking up "soak wells in WA" on Google.

Suppliers generally advised 1 x 600mm X 600mm soak well per downpipe. I prefer the more scientific approach (as recommended by the councils) which is 1 cubic metre of soak well per 65-80 square metres of catchment or 12.5 litres of soak well per square metre of catchment. I try to position them at least 1.5m away from the house or other structures.

All the other advice from Col and Robert is spot-on except I disagree with using plastic. Now just to add to the engineer bit, I'm a Mining Engineer so I'm used to digging holes in the ground - although not in sand! I have heard of plenty of plastic soak wells collapsing and for the slight cost saving I won't touch them. If you shop around concrete is not much more expensive.

Couple of other points:
I have a big block with vehicle access all round so I use heavy duty (or traffic) concrete lids in any position they are likely to have vehicles run over them.
Also, I backfill around the soak well with blue metal - which increases their capacity and helps stop sand washing back in to them.

Probably more than you wanted to know - but I have been burnt once so now I do them properly.

Good luck
Geoff

Just wondering what the reasoning is behind the use of soak wells rather than discharging to the gutters which eventually feed into stormwater drains/creeks/rivers/ocean. Urban development tends to stuff up the environment pretty big time but I think that having stormwater take as natural a path as possible would be better for the environment. I release that this may not have been in the forefront of people's minds when these laws were written. I'm also guessing that perhaps over there there aren't too may natural watercourses and that when it rains (which isn't that often by the sounds of things) water just tends to lie where it falls before soaking into the ground. But surely there must be some areas that have soil types that are not so well drained. If you are situated right next to a natural watercourse are you still not allowed to discharge stormwater into it, even though that's where the water would end up if your house roof was not there to catch it? And wouldn't it make more sense to have a single large rubble drain fed by all the downpipes (not thinking for one moment that laws always have to make sense).

Puzzled:confused: :confused:
Mick

Mick.

You have asked a question that derives from logic and common sense. That is entirely the wrong way to approach matters of government in WA.

The answer to the question is, probably, that it was the way things were 150 years ago and one must not make hasty changes.

Having said that, why would anyone live anywhere else than in WA?

Mick,

I would have thought that a soakwell would be a more natural path given the reasons you stated yourself.

If the house were not there, the water would soak directly into the ground. Surely the next best approximation with a house would be to distribute the water about the house dumping into soak wells spread about it?

Using stormwater pipes, ultimately feeding directly into creeks is definately not natural. I take witness to the storms in Melbourne before Christmas where usual calm creeks were turned into raging torrents, rising some 6+ metres simply due to the direct feed of storm water into these creeks. The evidence of these flood waters is still present along parts of the Merri Creek bicycle path around Bell Street area.

But Perth is so sandy that yes it is hard to believe there is any natural water courses as water literally just disappears from the surface directly down!

These soak wells are simply a sandy bottom which the water soaks into, not a massive bore directly into the water table, which is another thing over on Perth where the water is lifted up through bores for gardens - now that causes problems as the water table becomes depleted...

Mick

Reckon also, as with most things, it probably comes down largely to a cost thing.

As mentioned Perth tends to be sandy and has little in the way of natural watercourses etc. Local councils already have to take care of the stormwater runoff from roads etc for which they generally build ugly big surface soaks. So, when it comes to private land the easiest and cheapest thing is - "all stormwater must be contained within that land". How easy and cheap is that!

Oh, don't worry about the fact that they created a high density housing area zoned R60 where up to 75% of the block can be covered by buildings. I reckon it is almost physically impossible to dispose of 100% of your stormwater in less than 25% of the land area during some of the heavy storms we get. Net result - someone gets wet! :mad:

Geoff

Ray,
Actually round here discharging to a watercourse is more natural but then it's a matter of soil types and rainfall. I'm right near the river and on the only bit of non clay soil for miles around (alluvial silt) but up here almost everywhere is clay. Even after months of rain you can dig down a few inches and it's bone dry. So when you get 150mm of rainfall in two hours it just finds the most direct path to the nearest watercourse. During a recent deluge (over 1M in a week) I had a stream of water over a metre wide and about 200mm deep running down the middle of my yard. So it looks like our respective local legislators are perhaps not that silly and are tailoring laws to suit conditions.

Mick

Originally posted by PaulS
Hi as you can see i am in Perth. Didn't know what a soak well was until I moved here.

One of my downpipes needs a soak well installed. (I think) Is it as simple as just digging a hole and placing the soak well in the hole and connecting the down pipe to it?

More or less javascript:smilie('')

Anyone got any tips?

Yes dig the hole at least 200mm larger in diameter than the soakwell. Place the soakwell in the middle of the hole and fill the surrounding 100mm space with bluemetal. This improves the efficiency of the soakwell and helps prevent any sand from being "washed in" by the water leeching out. Place at least 50mm of bluemetal in the bottom of the soakwell again for efficiency, it helps soak the water over a larger area instead of it just forming a dip in the path of the water flow.

What is better plastic of Conrete?

I prefer concrete - partly just a psychological thing - though a necessity if the area is to be driven over.

How do you work out the size needed? (this must depend on rainfall, roof catchment size, & ???)

There probably is a formula but in general you can't really go too big. I'd start with a 900mm unit myself, though your circumstances may justify more and smaller units.


thanks
paul

Regards

Peter

Thanks for all your help
Now comes the hard work or digging the hole, lucky its just sand! Although there are sewer pipes (and other services, phone, electricity... now that i think about it) going past where it must go which may complicate things a little.