Upstream flow greater than downstream flow - --- is this possible?

Do you mean flow (cfs) or velocity? (fps)

Unless there are losses or diversions, the total flow (velocity x cross-section) will generally increase as you go downstream. The velocity, however, will depend on the exact stream characteristics at any given point, rather than the upstream/downstream location.


Peter Smart
HydroCAD Software

I mean flow. The pygmy meter computes the average velocity at a cross section and then multiplies the average velocity with the measured cross-sectional area to come up with the flow. Flows for some of the upstream cross sections are higher than those downstream and I am trying to figure out the reason behind this odd trend.

Thanks.

Forgive my ignorance, but how does the meter determine the cross-section? I thought it just measured velocity at a specific point in the channel, and you had to do the final calculation of flow rate based on a surveyed/measured cross section.


Peter Smart
HydroCAD Software

I'm also curious how the pygmy meter determines average velocity, since the velocity profile is going to change throughout the water column. See my response in the Storm/Flood forum for a half dozen possible sources of error.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

The device we are using is called AquaCalc 5000 and it has a USGS pygmy current meter attached to it. For more information about this device and how it works, please go to website below:


Thanks.

Would have helped to know that in the first place...

Anyway, the device still requires manual input for the position and channel width, correct? There's a lot going on in that (black) box, and it seems that you need to take a closer look at exactly what it's doing. Basically, you need to be able to replicate and verify all the calculations it's doing.

BTW: Please avoid posting the same question in two forums. It just gets confusing and wastes other people's time.


Peter Smart
HydroCAD Software

Yes the device still requires manual input for position and depth along a transect.

You are right I should not have posted the same question in two forums. What happeded was that I first posted it in the modeling forum and later made the decision to repost it in the storm/flood engineering forum since the question is more in place with this forum. My appologies. Anyway I can take of them off the forum?

I sent a request for the two threads to be merged.

Peter Smart
HydroCAD Software