Doubling up

(Work related)

I need to measure the flow in my channel two cases -

1. 50% of the flow this way, 50% down the other channel
2. 25% of the flow this way, 75% down the other channel

Of course the Bristish standard flume that works for case 1 is too wide for case 2.
Of course the Bristish standard flume that works for case 2 is too narrow for case 1.  And also the associated huting penstock would create supercritical flow and a hydraulic jump just at the point where you need a smooth water surface to take your measurement.

My solution:

Subdivide the channel into two, each with a flume and hunting pesntock designed for 25%.  Then for case 1 you use both and for case 2 you close one and use the other.