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Intake Design
2

Intake Design

Intake Design

(OP)
I am looking for some input on how to size a water intake.

It is for a smaller distribution system. Phase 1 max day is 882m3/day and ultimate is 3628.8m3/day. The intake has to be HDPE, and I think it will be in the 300mm diameter range.
Also, are there manufacturers in Ontario that supply pre-cast pipe anchors for sinking?

Thanks
Joe

RE: Intake Design

You don't provide much information. Is it a river? lake? Municipal?

A common method to install intakes is to install the intake pipe with a directional drill out to the intake location. Then you come up to the surface and install a well screen intake.

A riverbank filtration intake may also be an attractive option.

http://publications.usace.army.mil/publications/en...

The water flow velocity objective in the intake pipe should be to achieve an approximate velocity minimum of 0.9 m/s to a maximum of 1.2 m/s (3-4 ft/sec). The minimum flow is to prevent the deposition of solids.

https://www.google.com/webhp?hl=en&tab=ww#hl=e...


RE: Intake Design

I beleieve the Keswick Water Treatment Plant in Keswick Ontario had a HDPE pipe and they used concrete anchors to wiegh down the pipe. Did you try to ask your HDPE pipe manufacturer for a design of the concrete anchor? They should have one and they will tell you how to space them

RE: Intake Design

(OP)
Bimr,

The intake is into a lake, about 250m. We will require the first 100m or so to be dredged or directional drilled to obtain sufficient cover over the intake since it is shallow before the water drops off.

If you directional drill, how can you ensure the pipe wont float in the future? I expect you cannot install concrete pipe anchors on the portion of pipe that is directionally drilled?

RE: Intake Design

flood the pipe then ballast. If the pipe is full of water, it will not float.
ACB mattress is often used.

RE: Intake Design

I was thinking that you would directionally drill the entire pipe length out to the intake.

RE: Intake Design

cvg, I beg to differ, HDPE has a density of .97 to .93g/cm3 so it will float
although 'just' floating when full of water

RE: Intake Design

Specific Gravity 1.68 ASTM D792

dont belive everything you see on wikipedia

RE: Intake Design

Most expect HDPE to have a lower specific gravity. CVG, what is your reference?

Q: Will HDPE pipe float in water?

A: Yes, HDPE pipe has a specific gravity of about 0.95, so it will float. For underwater anchored pipeline installation, it is important to specify the proper weights and spacing of the weights. Screw-anchors are a practical alternative. Whenever possible, an underwater pipeline should be installed in a trench with protective crushed rock cover.

http://iusco.com/FAQs


RE: Intake Design

An my reference was taking a piece of HDPE and placing it in water,
guess what, it floated

RE: Intake Design

The 300 mm is ok, however 8" gives 1.23 m/sec velocity which is aceptable.
The water intake in a lake shall be type floating supported by a floating pontoon with a screen basket for the intake. This is to have the intake always under the surface level but far from the lake bottom where sediments will clog the pipe.
Drilling is ok if having a gravity pipe to the storage/treatment tank.But having a pump you do not need to drill. In case the water drops down bellow the dam level and you discharge is still bellow the water level, a vaccum pump is good idea: it works a siphon.

RE: Intake Design

You dont need afloating pontoon. Aslong asthe inlet is kept aove the mud level there is no need. The useof a "mussel" on the intake allows for very low approach velocity andthus themud will not be etrained. h "mussel" is used to get intake from very low water levels. http://www.irrigationwarehouse.com.au/category304_...

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

RE: Intake Design

The poster says he is from Ontario Canada. One would have to assume that the lake is ice covered at least part of the time. How would the floating pontoons or mussels work on an ice covered lake? Don't really think they are an option.

RE: Intake Design

Mussels are below the water and ice. Pipe is on the bottom of the lake and upturns to an inverted mussel above the mud line. Even if the PE line were allowed to float the pipe would turn down below the ice to the mussel.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

RE: Intake Design

(OP)
I also have another problem.

At the shoreline, I only have about 3 feet of depth from the water surface to bedrock. Has anyone ever installed a shallow raw water intake. My fear is it getting hit by boat traffic and of course freezing.

Any thoughts?

RE: Intake Design


When in doubt, call the blasters. And it is fun to watch. You can have them blast you a trench till you get to a grade you like.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Intake Design

Is the water elevation in the lake at a constant height?

What about a riverbank filtration system?

RE: Intake Design

If anyone has ever designed an intake pipe for a water plant from a lake or river and studied the hydraulics what the water level would be in the low lift wet well at maximum plant flow you would know right away that you have to cut into the bedrock. There is something wrong with your thinking, the wetwell design or how you are doing your hydraulic calculations if you think that you can get away with leaving the pipe close to the surface of the lake bed near the shoreline.

From a pipe protection point of view definetly the pipe should be trenched into the bedrock

I think you need more senior help.

RE: Intake Design

I would like to add the following:

1. You need to determine what the historical high water level (HWL) and the historical low water level (LWL) is where your intake is located. There are government publications that can tell you that. That gives you your design envelope.

2. You then figure out the head loss in the intake piping to determine what the HGL is in the low lift wetwell at HWL and LWL conditions. At LWL you will need to ensure the pump is flooded with adequate submergence to prevent vortexing. This will set depth of your wet well.

3. Always check that on power failure, the oscillating surging water in the wetwill will be contained by the walls of the wetwell or there is an overflow pipe set at the proper elevation.

4. For a small system like yours, it may very well be that there is not much head loss in the HGL and the wetwell may not be required to be very deep. Therefore protecting the intake pipe close to the shoreline becomes the governing factor and that in turn forces the wetwell to be deeper in order to have the pipe trenched into the bedrock.


RE: Intake Design

(OP)
thanks gents

RE: Intake Design

You aslo need to check that at HWL the differential head of the pump is not such that it runs off the curve or even at BEP >115%. You may need to have a flow control valve to protect the pump.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

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