Estimating water intake from a canal 1

[springtide]

We are designing a water intake from a canal and need to estimate discharge. One suggestion is to have a manifold installed above the bottom of the canal such that intake pipe is parallel to water flow before it bends and connect to the lateral. Then water velocity inside the pipe can be estimated by relating the canal velocity (which is known) to pipe velocity.
Second suggestion to only install a lateral pipe perpendicular to canal flow and then estimate the flow by the water level in the canal (which is also known).
Which one makes sense.

 

[GeoPaveTraffic]

Irrigation canals that i've observed usually contain a weir for measuring the flow. The turnouts, as they are called, are usually perpendicular to the canal.

Mike Lambert

 

[cvg]

suggest getting a copy of USBR publication "Design of Small Canal Structures", see chapter 3

 

[JedClampett]

Doesn't the entity that "owns" the canal have a method they require or at least a preference? Parshall flume, in line meter, weir, etc?

 

[bimr]

Parshall flumes are usually used for that application.

http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/chap08_10.html

 

[CivilTom]

Derive the cross section of the canal lengthxheight and measure the velocity of the water... Time a floating object traveling a certain distance. Use Darcy equation flow = discharge = area * velocity

 

[BenJohnson]

Parshall Flumes have the advantage of allowing most large floating objects in the canal to pass through a flow meter without getting hung up on the edge of a weir or pipe.

I've use electronic height gauges above the flume to get a continuous flow readout that can be connected to a recording device, etc.

 

[WRIRR]

Another reference to consider is: USBR Water Measurement Manual

http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/

The most common irrigation turnout I have seen is the constant head orifice (Chapter 9-10 in USBR Water Measurement Manual). This provides control and measurment. However other options (partial flume, weirs, ramped flume, other flow meter) need to be considered based on flow measurment accuracy required, control required, debris in the canal, and of course cost.

I've come across the Rubicon slip flow meter for irrigation turnouts but I have no experience with it and I think it may be costly. See details at the followin link:

http://www.rubicon.com.au/EN/products/slipmeter.html