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adjustable stand pipes / low flow pipes - detention pond

adjustable stand pipes / low flow pipes - detention pond

adjustable stand pipes / low flow pipes - detention pond

(OP)
i oringally posted this under the general forum but it may get more hits here..........thanks

a local municipality has requested that we design an adjustable stand pipe for an existing detention pond.  the stand pipe would act as a low flow pipe in order to recharge a downstream detention pond.  since the site is not developed yet and relatively large, the stand pipe needs to be adjustable (i.e. standpipe's inlet would need to be raised in the future such that the head would be reduced).  anyone have any experience with tsomething like this or recommend a typical detail to start out with? (don't want to reinvent the wheel).  the calcs will be a challenge since we need to accomdate this flow in the pipe to the pond's release rate...but trying to start with a detail

first response by slideruleera:
 
The standpipe material, diameter and unsupported length (intitial & final) will have a lot to do with the detail. Have you make any decisions on these factors? Also, does the standpipe need to have variable length, or would a few discrete steps be acceptable?


 
 
zzmarkzz (Civil/Environme) Oct 5, 2004
the low flow pipe would likely consist of 6" diameter PVC, the stand pipe would be 6" PVC with a 2" restrictor inside of it.  we would need standpipe to have a variable length....currently the site is undeveloped so the standpipe would be relatively short (±0-1' high).  once the site is developed, there will be more flow into the ponds and the elevation of the standpipe will need to be increased (±2-4' high) in order to decrease the flow of the low flow pipe (by lowering head).  again, its a unique design requested by the municipality and their thought is that this low flow pipe will recharge an existing downstream retention pond which has recently dried up.
 

RE: adjustable stand pipes / low flow pipes - detention pond

Have you considered leaving the standpipe alone and installing a valve or gate instead? Then you could adjust the valve or gate as required.

I've seen something similar here with a weir gate that would be raised and lowered throughout the year in order to control the water level in the pond. Something similar should work for you since you could just raise the "weir" as required instead of trying to adjust a standpipe.

David

RE: adjustable stand pipes / low flow pipes - detention pond

(OP)
I believe a valve/gate was an option, but the municipality didn't want the valve easily accessible for anyone to adjust the release from the pond (a locking valve may be an option though)  i need to double check this though as i didn't sit in on the meeting with the local municip.

the adjustable weir is a good option, however, the municiaplity wouldn't likely allow it (concrete lined weirs are required)

RE: adjustable stand pipes / low flow pipes - detention pond

zzmarkzz - Found you again - Could you consider this approach:
1. Construct the standpipe full heigth but put a 6" PVC union in the horizontal line, just before the 90 deg. elbow to the standpipe.
2. Then you could rotate the standpipe (roll it over to one side) to make the vertical height component any value desired.
3. When your project is fully developed, the stand pipe would be positioned "permanently" vertical.

Six inch PVC unions appear to be available, here is a link to a typical source:
http://12.107.25.236/smcweb/eINM022.pgm?Book=80-1&...

RE: adjustable stand pipes / low flow pipes - detention pond

(OP)
that's a good idea s.r.era....do you know if a union could be locked in place in some sort such that once its vertical or at a certain elevation, it doesn't start tottering over?

RE: adjustable stand pipes / low flow pipes - detention pond

You certainly have a valid concern. I'm not familiar with PVC unions that large. It certainly would not be as strong as the pipe. However you may be able to compensate by using temporary pipe supports during the early phase of your project (when the standpipe is rolled to one side) - then forming & placing a neat concrete "block" to encase the 90 degree elbow and lower part of the standpipe when it is in the final, vertical position.

RE: adjustable stand pipes / low flow pipes - detention pond

I have a client that uses something similar to what you describe to control the level in one of their feedlot runoff ponds.  Basically what they have is a series of 10 inch pvc fittings that will slide into each other.  When the pond needs to be drained, they remove the top fitting.  The pond will drain down to the next fitting.  This fitting is removed to drain the pond further.  The process continues until the pond is back to the desired level.  The fittings are put back in place to await the next rainfall event, where the process then starts again.  It works pretty well, and is a cost effective way to drain the pond.

RE: adjustable stand pipes / low flow pipes - detention pond

A simple adjustable weir using boards seems the cheapest. You can use bolts and inset five corner nuts for the security you want.

RE: adjustable stand pipes / low flow pipes - detention pond

The PA Erosion and Sediment Pollution Control Manual available here:

http://www.dep.state.pa.us/dep/deputate/watermgt/w...

on pages 43-44 describes methods to size orifices on a Basin Skimmer.  Note it is intended to be a temporary E&S control design, but with some affordable peripherals (guide rails, etc.), it could possibly be made permanent.  Use a smaller orifce during initial conditions.  Later, pull it in from the bank by hand, and using hand tools, drill a bigger orifice.

Use care, the Skimmer is PVC which is notorious for embrittlement after prolonged sunlight exposure.

RE: adjustable stand pipes / low flow pipes - detention pond

After rereading the problem statement and the the comments from others it seems to me that rather than looking for an adjustable standpipe you are looking for an adjustable orifice of some kind so that as the expected water level under storm conditions increases you end up with the same outlet rate.

Because you are considering a 6" PVC with a 2" orifice I would recommend just installing a ditch inlet catch basin with a mounting for a steel plate with an orifice cut into it over the outlet pipe. Then you could replace the steel plate with one with a smaller orifice anytime you wanted.

David

RE: adjustable stand pipes / low flow pipes - detention pond

(OP)
an adjustable orifice (i.e. valve) would be great if we could use it at this site...unfortunately and mainly for political reasons we need to go with the standpipe for (trying to limit people's control of the release rate but still addressing their needs)...the low flow pipe to consist of a 6" stand pipe with a 2" restrictor inside of it?  sheeeesh the main restrictor for this pond is >18" pipe.
 how the 2" pipe in standpipe will really work without getting easily clogged, that's the challenging design i'm trying to come up with (i.e. a 2" pipe with a couple 90 degree bends coming out of the 6" standpipe and likely having to drain the pond in the future (or union idea) to raise the stand pipe??)

RE: adjustable stand pipes / low flow pipes - detention pond

I would still recommend either the adjustable weir with stoplogs or the orifice plate.  The 6 inch pipe with restrictor will likely be a maintenance headache as it may plug easily.  Without significant encasement, the pipe can easily be broken.  Adjustable weirs are very commonly used in irrigation applications and are maintenance free.

RE: adjustable stand pipes / low flow pipes - detention pond

(OP)
anyone know where (i.e. website) i could find a typical standpipe detail?

RE: adjustable stand pipes / low flow pipes - detention pond

In this neck of the woods we typically use a flow restrictor standpipe that has removable elbows, each with a restrictor plate (see link to detail drawing, below).  This provides flexibility to reconfigure the outlet in the future to alter the release rate by swapping out orifice restrictor plates.  It would not enable you to change the outlet elevation, but you can control the release rates in this manner.  If you anticipate needing to change the actual elevation of an orifice/outlet, you could provide the initial installation with "blind elbows", e.g. no orifice drilled into the restrictor plate.  You could then open these up in the future as needed.  

This design addresses clogging by positioning the orifices on a downturned elbow.  Floatables/oil/grease can collect above the orifice, and a sump collects grit.

Orifices provide tighter flow control (for more a greater range of events) than a weir, but a weir can usually handle high flow rates with less head.

http://www.wsdot.wa.gov/EESC/Design/designstandard...

RE: adjustable stand pipes / low flow pipes - detention pond

(OP)
thanks blt!

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