Constant charge in Stormwater line.

I have to build a waterfeature -creek bed in a playground and will be fitting a 3000 lt tank to collect SW off the extensive roof. the tank will be an above ground type that you are only supposed to bury up to one third
The tank will have a submersible pump in it to feed the creekbed.

Anyway if we follow the manufacturers instruction the inlet to the tank will be higher than the existing SWL - but well lower than the roofs gutter inlet. This means that there will be a constant charge of water in the line.

This worries me a tad...should it?

One way to alleviate this is to sink the tank deeper into the ground which ofcourse isn't what the manufactures want you to do.... but by cement stabilizing the backfill soil we haven't had problems in the past.. we have done a few of these.

Trouble is you are never going to stop the stormwater line having a charge unless the top of the tank is below the entire run of the SW line which is a bit impracticle in this (and a lot of) cases.
So is it best to sink the tank lower and minimise the charge or follow the manufacturers instruction and have several metres of water sitting in the line?

The other consideration is the reticulation system for the creek. It would also have a charge in the outlet unless the tank is sunk deeper.

Oh and I know I could have specified an underground tank but the budget wouldn't stretch on this job.

Sorry BT, I don't quite follow.
SW off the roof into the tank.
Water pumped from tank to head of creek bed.
Are you trying to recycle the creek water back into the tank?
If so, how far from creek end to tank inlet and approx height of inlet above creek bed end? Is there a sump or similar at end of creek bed?
I love water features and i really like the sound of this one.
Some photos of the finished job would be great.

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Anyway if we follow the manufacturers instruction the inlet to the tank will be higher than the existing SWL - but well lower than the roofs gutter inlet. This means that there will be a constant charge of water in the line.

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Those damn manufacturer's instructions again.

However, this is how my tank is set up. The lines are constantly charged. It's not a problem, you just have to make sure your downpipes are watertight to the height of the tank inlet.

Like Silent C has said, it's not that unusual and it's certainly accepted practice. You need to make sure that vehicle traffic can't damage the buried pipes (if there are any) as this may cause groundwater to contaminate the pipeline. This would probably not be as big a problem in youir application as it's not for drinking water.

Mick

Hi NC, Yes the submersible pump takes the water to the head of the creek about 2m higher than the pump and about 12 metres away. the water goes down the creek into a sump and returns to the tank.
The stormwater inlet is the only watersupply to the tank - no mains top up.

Strickly speaking this does not meet certain health codes that govern public contact with water.. If I was to follow one of the codes...there are a few It would cost another $10K for water scrubbers, direct chemical injectors and various controllers not to mention the plant room to fit all this crap.
As an example I build 2 small water features either side of an entrance road to a subdivision a couple of years ago, very small not much bigger than a bath tub with a small wall behind - $120K each!
With this one we will provide a $20 floating pad that you put chlorine tablets in.
Another way to keep water quality up is to run an irrigation system out of the tank to water the gardens and then provide mains water topup its a bit hard with water restrictions at present and we cant get a rebate on the tank if we go that way.

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Originally Posted by silentC

you just have to make sure your downpipes are watertight to the height of the tank inlet.

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Even if they weren't OK you would lose the water charge back to the soil which wouldn't be a great deal of water - less than any irrigation system would supply or is the worry what Mick mentioned the water entering the system?

I have a feeling that even though all the pipe we have uncovered so far are PVC I think that it enters earthenware down where this feature is located.:roll:
All the digging has revealed dry sand loam so I don't think we'll have a problem but I may have to raise the level of the pump to allow for sediment buildup in the tank

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is the worry what Mick mentioned the water entering the system

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In our case, both. We don't want to lose the water, there would more than a couple of hundred litres in the network of storm water pipes and we would lose that after every rain if it leaked. We also get a lot of water in the tank just from condensation. You can hear it dripping from the gutters into the downpipes every morning and also on cold nights after a warm day. Probably covers us cleaning our teeth each day :)

We also definitely don't want run off or ground water getting in.

Much clearer now thanks BT. My thoughts:-
Charge in the return line shouldn't be a problem. The only consideration is availability of water and potential losses through normal operation. Pipework good and tight. No leaks. Restrict losses to creek bed seepage and evaporation.
A float switch to cut the pump out once the water level drops. Avoid burning the pump out.
The pump can be mounted on a stainless plinth to keep it out of the silt.
Some sort of grate or sieve in creek bed sump to keep leaves, plastic bags etc out of the tank (and the pump).

Good luck with the project.

I'm glad this job isn't to capture drinking water...I'd hate having to throw this cowboy hat away!

Actually how do you control the quality of your drinking water in your tank besides keeping dead possums out etc...:rolleyes:

I am supposedly governed by the regulations that dictate what I have to do to keep water up to a standard if the public come into physical contact with it.

These standards are heaps more stringent than swimming pool water quality standard and unbeleivable if you think of water sitting stagnant in your tank for drinking!(and your pipes)

Is it only me or does there seem to be something wrong here! It seems that things are the wrong way around.:?

When Ive done similar set ups if possible i run the water lines at grade ( 1%). This way any sediment build up - trust me it will happen over time- can be delt with. On the inlet pipework i run no less than 100 pvc DWV grade. I use I.O junctions raised to surface at either end and a buried scewed cap at the low end.

This means at the very worst you only have to dig up the low end and push any rubbish through with a drain rod.

A First flush diverter at the roof outlet might help too, or a sealed bucket trap somewhere in the system.

As Bricks said, they will collect silt and plenty of it over time, Ive set up a few like this on a few properties, with the wind and the dust and crap blowing around they get quite grotty, 1st flush diverter is the way to go.

I had considered them but I thought that it would be a waste of time considering all the stuff that will collected by the creek and not to mention what the little buggers will be floating down there when they play.... it makes what comes of the roof a wee bit trifle.

We just put IOs at the bottom of the run just before it runs up the side of the tank to the inlets. Periodically (and I would say that would be once in a blue moon) we can open them and the water that is in the line will flush it out. No leaf matter gets in because we have leaf guard on all the gutters.