How do I measure water volume flow rate in a trench drain?

Question

The flow varies a lot throughout the day, so I'm guessing I'll need to use some sort of flow meter.

Answer 1

The depth will give you a good approximation.

Flow = constant x (depth)^2 thats depth squared

the value of the constant depends on the design of your trench. I'm assuming its rectangular. If so the the depth at a know flowrate is measured the constant can be calculated.


ISCO company has many open channel flow meters mainly for waste water applications.

Answer 2

You could put a dam (a piece of plywood) across the trench with a rectangular notch in it. (Don't restrict the flow too much) Knowing how wide the notch is and measuring how "deep" the water is goinig through the notch, you can get a good cross sectional area of the water. A paddle wheel or some such device at that point could tell you how fast the water is going. Just multiply the area of the water times the velocity and you get flow rate. Later, when you have some data on the device, you might be able to measure flow from the depth of the water through the notch alone.

Answer 3

we used a meter that converted the depth of the water to a volumetric flow rate as they were proportional, v = proportionality constant x depth. I don't know the how throwing a leaf in the water will give you a volume. volumetric flow rate is equal to volume per given time.

Answer 4

short of fancy flowmeters, measure or closely estimate the cross section area of the water, then have somebody throw in a leaf, etc upstream and time how long it takes to travel a known distance.

velocity x area = volume flow rate

Answer 5

flow=3.33 (width of trench (in feet)-0.2xdepth of water (in feet))((depth of water) to 1.5 power) This assumes a rectangular cross section.