What pump would lower a lake 10 m? 1

[PEng222]

I'm not a pumping expert but need to figure out whether it would be possible to lower the level of an alpine lake by pumping so that a water intake can be installed.

Facts:

1. The lake is about 700 m long, 200 m wide.

2. The inflow is about 2 m3/s.

3. I need to lower the lake level 10 metres

4. The lake is in a high alpine, remote location where there is no power. There will be 4 wheel drive and heavy equipment road access to the site so I can bring in generators and pumps.

5. I can afford to take a couple of weeks to lower the water, so I figure I need to be able to pump out at 3 m3/s (2 m3/s to deal with inflow, and another 1 m3/s to actually lower the water level).

So any advice on how I might do this, and where I might get more info on the WEB would be appreciated.

 

[Artisi]

For a job of this nature you should look at a multiple of direct diesel drive skid mounted pumpsets.

When calculating the number of pumps required you have to include extra units to allow for any breakdowns, any units off-line for servicing as well as off-line when repositioning pumps to a lower level as the lake level falls, this is necessary to keep the suction lift to a minimum and 10 metres is beyond the maximum suction lift.

You need to plan for pumps to be staged to lower levels as the lake level falls and staged to higher levels at completion of the works as you withdraw the pump units.

Other important factors usually overlooked in jobs of this nature are, how much water is there in any surrounding water table (which needs to be included in the total amount to be pumped) and what will be the additional inflow if it should rain during the operation.

Questions

1. Where are you?
2. From your pumping position - what will be the head on the pump unit/s to the disposal point.
3. what is the elevation above sea level of the alpine lake

let's know if this is helpful or if you need any further info.

 

[TenPenny]

That's a fairly straightforward application, but you may find that as the lake level drops, you'll need to reposition the pumps so that the suction lift isn't as high.

Alternatively, put diesel driven pumps on a barge, then the change in the suction lift isn't an issue.

I would suggest you look at godwinpumps.com, they do this sort of thing all the time. Having said that, your flowrate is pretty large, depending on the head required, you may be talking 5 or 6 pumps.

 

[PEng222]

Thanks to both of you for the info- much appreciated.

We're talking about an alpine lake in southwestern British Columbia, Canada, which is located at about 1100 metres elevation.

The idea of using a pump on a barge to minimize the head is a good one. The ultimate purpose here is to construct an intake for a hydro project. So in order to allow the lake to be used for water storage, the plan is to excavate a 10 metre deep trench out into the lake. Except for some lake bottom muds, most of the excavation will be in competent rock- but we need to lower the lake in order to allow the trenching work to be carried out.

Is it possible to use electric submersible pumps mounted on a small barge, with a generator on the shore (it would only be a few metres away). Like, what kind of pump would be needed to give us the flow capacity (3 m/s or more) that we need?

 

[PEng222]

Most of the trench going from the intake to the lake would be excavated before the lake would need to be lowered- so it is only the remaining rock on the lake-end of the trench that we're thinking of removing by lowering the lake level. We have thought of drilling a lake tap or just doing a final controlled blast to remove the final plug of rock in the trench, but we're worried about the potential problems in doing this- hence the idea of lowering the lake level instead, and then finishing off the trench excavation.

It should be possible to minimize the head by continually blasting out the trench as the lake level is lowered- which would mean that the maximum head would be maybe 2-3 metres.

 

[PEng222]

Sorry, the flow withdrawal rate is 3 m3/s, not 3 m/s.

Few other points:

Water from surrounding water tables shouldn't be an issue- the lake is in a rock basin. Also, I'm not too worried about unexpected pump breakdowns or an unusual rain storm- if that happened, the lake level would rise somewhat, and we've have to backtrack a bit, but it shouldn't be a big problem.

 

[Artisi]

You could use electric submersible units with a genset/s on shore. My suggestion is to contact some of the bigger pump hire companies in Canada or the USA.

 

[MikeHalloran]

Uh, 3m^3/s is a little under 48000 usgpm. That takes a serious pump, or a bunch of big ones.

Maybe you can find a dozen or so trailerable dredges and wrestle them up there.










Mike Halloran
Pembroke Pines, FL, USA

 

[PEng222]

Yep- serious pumping efforts would be needed- I figure I need at least four, 10,000 gpm electric submersibles. Electric pumps would be desirable because they reduce the possibility of a fuel spill (even though the lake has no fish).

But I'd like to have a better idea from some of you experienced hands whether there is something better, and how difficult (and expensive!) the present system I'm contemplating would be.

 

[GregLamberson]

PEng222

May be off the wall, but have you looked at a cofferdam?

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[PEng222]

Yeh- a cofferdam definitely wouldn't work- the water gets too deep too quickly as one moves offshore- we need to work from the shore out; or more specifically, from the existing outlet channel out.

It's possible that we may be able to advance the trench to the lake edge, and then slowly remove the remaining "plug" of granitic rock- basically, remove it one blast at a time, let the water drain out, then do the next blast, etc. until we get to the required depth.

 

[Artisi]

You need to give us the discharge head so we understand what size pumps we are looking at.

 

[PEng222]

Assume a two metre discharge head- that is, I think I can keep cutting the outlet trench down so that the lake level is never more than two metres below the level of the outlet trench as it is being excavated.

BTW, thanks for all the help; this is great. If you can provide me with any rental pump suppliers in the Vancouver area, please do so.

 

[Artisi]

Head shouldn't be any problem although it will be round 12 -13 metres when you are at the lowest level whether you are using submersibles or diesel driven units.

Sorry, can't help with a rental company as I'm on the otherside of the world but can't see that you should have any problems sourcing this equipment.
However, I would be interested in putting a hire package together but logistics would be a problem

 

[dickon17]

What about using a syphon pipe. Two x 60 inch should do it. Each end could capped with thin steel plate and primed with a diesel driven pump. Explosive charges could be used to open both pipe ends at the same time (assuming no fish in the lake). Just a wild suggestion.

 

[macmil]

Try Canadian Dewatering. They are into large pumps on skids

 

[PEng222]

We've thought about siphoning- that is definitely a possibility. We'd have to have a valve on at least one end so we can fill the pipe, and limit the head to probably somewhere less than 7 metres, which shouldn't be a problem.

I had forgotten about Canadian Dewatering- I've used them in the city, but never in a remote site like this before. Fortunately, I designed the access road (under construction) for bringing in heavy equipment, so we do have reasonably good access. It is steep, and will soon be vulnerable to snow avalanche activity, but we weren't planning on doing too much more until next spring.

Artis: the stream coming out of the lake drops steeply after about 75 m (this is a pretty rugged mountain environment), so I'm planning on first diverting the stream into a bypass channel, and then cutting out a trench at the existing channel as I lower the lake level- that way, there should never be more than a couple of metres between the lake level and the ultimate intake trench, which will be entirely in rock.

 

[dickon17]

Re: syphoning. With such large pipe sizes you would need a valve on each end to prime the pipe. Such large valves would open too slowly to prevent loosing the prime. You would need instant opening of both valves simultaneously. This is why I suggested using explosives. This would also be visually entertaining, any TV crew would love to film the action. Restricted access combined with large size equipment requirements severly restricts your choices.

 

[MikeHalloran]

For siphoning, I'd try a _bunch_ of PVC drain pipes with rubber couplings, which should be easier to manhandle from one side of the cut to the other as it goes deeper. Once you got one started, you could use a crude eductor to prime the rest.

OR,
You could make productive use of the winter, by harvesting the ice and sliding it down the road...




Mike Halloran
Pembroke Pines, FL, USA

 

[TenPenny]

\With the big Godwin CD400, you'll probably be able to get in the order of 9000 gpm, so you'll only need to rent 5 or 6 of these things. You might want to rent a diesel tanker, too, as these things have 275 hp diesel engines, which you'll need to keep fed for the duration.