Wastewater Overflow Measurement

[Bluenoser337]

Looking for a good solution for measuring the volume of overflow from a number of good old duplex lift stations. Each station has a concrete overflow pipe, probably between 8 and 12 inches. There are a lot of ideas kicking around like using the already measured analog wet well level to know when there is an overflow. That's fine but getting an accurate volume from that seems impossible. Another option being discussed is to dig down and install a flowmeter of some sort in (or on) the overflow pipe...but I am concerned that the flow will be too low to measure accurately this way. I have seen information on mounting an ultrasonic level sensor aimed at the water "trapped" behind a weir. I was thinking that this arrangement could be mounted fairly easily in the start of the overflow pipe inside the wet well. The sensor would connect to the existing RTU/SCADA equipment and would continuously monitor the liquid level behind the weir. Levels above the overflow height would be easily calculated into overflow volumes. Has anyone seen anything like this in a lift station, or done anything similar. Any other suggestions on measuring lift station overflows would be greatly appreciated.

 

[bimr]

There are a number of options with the Marsh McBirney flow meters that are used for monitoring sewer flows.

http://www.hachflow.com/portable/Flo-tote3-FL900.cfm

 

[cvg]

there are a number of types of flumes and weirs that can be used in combination with ultrasonic level sensor to measure flow. you can buy packaged manholes to do this in as well

http://www.plasti-fab.com/wastewate...etering-manholes-fiberglass-manhole-solutions

http://www.plasti-fab.com/wastewater-products/flumes

http://www.globalw.com/products/wl705.html

 

[TexasCHe]

We have been successful at monitoring effluent from a WWTP using an ultrasonic level sensor aimed at the water "trapped" behind a weir. As you mentioned our sensor feeds signal to a SCADA system. Levels above the overflow height would be easily calculated into overflow volumes. I’d have to look at our to refresh my memory but we may use a v-noch weir for low flows and higher flows that exceed the v-noch and spread outward to the limits of a rectangular weir. It’s all the same plate but the calculations have to be programmed into SCADA. This allows sensitively on the low end while retaining the ability to measure higher flows.

 

[Openchannelflow]

What TexasChe is looking for is a compound weir:

http://www.openchannelflow.com/blog/article/compound-weirs

That works well so long as you have enough area in which to form a proper weir pool.

http://www.openchannelflow.com/blog/article/foolproof-weir-installations-in-9-easy-steps

After that, all you need to worry about is making the weir plate itself. Stainless steel or fiberglass are the materials of choice here.

 

[bimr]

Weirs will not work in this application. The poster has said that he is interested in something that will fit in a pipe. These magmeters fit in a pipe and are simple to install:

http://www.hachflow.com/portable/Flo-tote3-FL900.cfm

 

[Openchannelflow]

Actually a Thel-Mar weir would fit in a pipe and is a compound weir. You can find more at

http://thel-mar.com/

Thel-mar weirs are available from the likes of Pollard Water, USABlueBook, etc.

Keep in mind, though, that you would have to either visually read the level / flow rate or use the weir in conjunction with a bubbler type flow meter. Thel-Mar offers units with integral bubbler tubes.

Flow meter models similar to the Flo-Tote would include Teledyne-ISCO's 2150 and 4250 (

http://www.isco.com)

as well as Greyline's AVFM 5.0 and Stingray models (

http://www.greyline.com).

The one problem with any area velocity unit is going to be the need to have a minimum flow depth. The Thel-Mar weir would most like give you the ability to measure lower flow rates.

 

[bimr]

The development of the electromagnetic area / velocity sensor made the Thel-mar device obsolete.

The Thel-mar does not include an integral electronics package that is capable of integration into a SCADA system. The Thel-mar also can not measure flow in both direction. Bubbler systems are also not oommon anymore either.

The Thel-mar device seems to measure flow moving out of an open pipe. At CSO points, it is commonly necessary to measure flow going into pipes.