Calculating Water Flow in Scotland

I'd have thaught a rainwater tank (the bigger the better) with an overflow into the sewer of a suitable bore to restrict the flow (worked out by some arithmetic or experimentation) A second overflow say a foot above the first will limit the head (and hence flow) from the first one. This second overflow can lead to a soakaway of some sort...or a nice pond.

This may of course be completely bonkers.

Thats about the rain fall you would get from a heavy fog. If you figure total rain fall over the entire roof. I would question the specs. The .5 litres per second could be for a rain fall over a given area not the whole roof.

Swirl it.

The public utilities companies use things sometimes called "hydrobrakes" to slow down the flow of water in municipal drainage systems.

The concept involves passing the incoming water into a cylindrical chamber off-centre, so that significant swirl is developed within the chamber before the water is discharged. The water passing around the swirl chamber forms a resistance to the tater trying to flow into it, so that it backs up. When the level of water in the chamber falls, more water is introduced from the backed-up storage.

Talk to them about appropriately-sized swirl chambers and sizing and call their bluff! They may even have a design in a drawer that they can pass to you. It ain't gonna be very big.

Hey that's cool...not sure where the taters fit into this tho' .

Of course if you provide a resistance to the incoming water then it will need to be able to overflow somewhere if the inlet flow is greater than the outlet flow....pond?Tank? Black hole?
Del

thanks.

OK, I'm in the U.S.A. so I had to do some math to figure out what we are talking about here, .5 litres is about 16.9 oz. that's more than a standard can of beer. And you can allow one per second to pass.

Seems like a lot to me. If you take a bottle of water, (The one on my desk hold 20 oz. close enough for who it's for) and I poured it out into the sink. It took 5 seconds to empty. But there the water flow and to stop to allow air to pass back into the bottle. So I estimate it would have taken 3 seconds if it had air flow. The opening measures 1" dia.

My rough estimate is if you use a 2 1/2" dia. (or 63.5 mm) pipe, you will be at or below .5 liters per second.

if you have the pipe draining from the bottom of your rain barrel, then you should be all set.

Did you put a hole in the bottom of you're water bottle before draining into sink? Or does your water tank have an obstructed vent?

I think the problem is where to put the excess water during heavy rains. This might overwhelm a swirl chamber unless it is large enough, which would depend on estimated maximum input. That kind of information should be available from the local council authorities. Until you get that information you really can't pick a solution.

Of course I can't resist the pun of turning the water into whisky. The local council couldn't possibly object to that!

I think the problem is where to put the excess water during heavy rains.

See #1 & #4

I'm sure between us we have given a solution....

You could consider using a restriction in the tank such as an oriface plate sized to give you the required flow rate when the tank full.

Why not construct a nice pond and install a small pump, with the flow rate you are allowed (if that has been cleared up?) and when the water goes over a certain level, this excess is pumped away into the main sewage.

The pump could even be very small and mechanical and run by a windmill/solar cells/Donkey to save money most of the time.....

With a wind driven pump (Scotlands best resource is wind and rain!!), it could run day and night!!

Yup that's far too sensible suggestion. I think you should incorporate a hydo plant too .

I think you've got the best bits of all the ideas... I dun mark it as good.

Del

Thanks Mr Cat!

And a second 'GA' from me - the only caveat being whether there's space for a pond of any size, and if there's a restriction on constructing one. Was the distance not a mere 9 meters to the sewer connection? So some 28 feet -4 feet from the curb = 24 -4 feet from the house = 20 -2 feet on each side for margin of error = 16 foot diameter space for a pond presuming there doesn't need to be extra room for a driveway or a bed of hollyhocks. Probably IS space available, then, but does the Great Faceless Voice of Authority allow one?

I'd guess if he's constructing a building in Scotland he probably has room for a small Loch . It's not very crowded up there... (ok it may be in the middle of Glasgow...what do I know...?)
Mind, I've been saying pond way back at post #1 ... no GA for me...dunno why I bother ... <sobs into dish of cat food>

Del

Do you like salty Cat food then, better not to do that I feel.....

If that is a problem, then an underground cistern is best.

I personally prefer the concrete ones as:-

a) you don't have to fill them up with expensive drinking water when back filling as you do with plastic, to stop it being crushed, nor do they suddenly float up, when empty in wet soil either!.

b) they are cheaper

c) You can drive over them with a car or truck if they need to be in a driveway.

d) you always have plenty of water for the garden. We in Germany also install a pump and filter system, that turns rainwater into perfect soft drinking water!!!

But it is "illegal" to drink it (should I have written "illogical"?) in Germany as they want you to pay for the fresh water from the normal tap!!! But you are allowed to use it for the toilets and washing clothes......we only use it for the toilets and garden. All our water is metered, in the UK it is mixed I believe....

The only drawback is that you need a crane to install/deliver it.......the plastic ones can be handled by 2 or 3 men......bulky but light.

If you are on metered water, you could earn a few bucks back over the next 20 years or so with a cistern.....

You will need to start emptying it when it goes say over half full to stay within the allowed tolerances......and it will need to be big, a 10,000 liter tank being a good bet.....that will give you a 5,000 liter tolerance for rain and 5,000 for your usage.....

The sizing of the piping and orifices to control the runoff from the property to 0.5 liter/sec is a straightforward engineering calculation. The issue is what is the likely maximum rate of rainfall to be encountered in order to define the required size (volume) of a holding tank for the rain. This information should be available from the nearest meteorlogical station to your building.

Thanks for your response. The local authority have not asked for a holding tank to be installed although I appreciate the principal of such. I'm aware that most of these attenuation systems are designed taking maximum recorded rainfall over a differing number of years and specifying a holding vessel to suit. My development is off very small scale (110msq. off roof collection). If you could point me in the right direction for the engineering calculation of an orifice plate then this would solve my immediate problem.

Many Thanks again

Shaun Kerr

Till a couple of leaves block it I would guess......

So true... the little 'top pond' in my garden is fed from a pump from the main pond...this autumn, the waterfall (returning the water to the main pond) got partially blocked with leaves. Result, raised water-level in top pond which overflowed into the garden and the main pond was almost pumped dry .
I am the king of the pond and my loyal subjects the froggies and fish were near rebellion .

Del (king of pond town.....it's the only thing Mrs Cat will let me have sovereignty over)

In Surrey British Columbia, Canada we are in a temperate rain forest (lots of rain).

For residential buildings (houses) we are not allowed to have water from the roof directly connected to storm or sanitary. It has to be spread over the lawns and gardens. If that floods then the runoff can go across the curb and into the storm.

I don't know the restrictions on commercial buildings, but the emphasis is on storm water retention.

Collect it bottle it and sell it...

I can see the adverts now:

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Let me know Shaun, EM-ER NA Productions ™ stands ready to market this product on a world-wide basis!