what if the gauge is in an eddy ? Nm
some calcs
Suiram is right, estimate area and divide that into the CFS reading, then divide by about 1.5 (or 1.466667 exactly) to convert feet/sec to mi/hr.
Estimating area is pretty easy if the river is in its banks, but it gets more difficult when it spills over. I see from the gages online that the Lumber is just dropping below flood level.
JackL, were you trying to estimate a speed at flood levels? If not, what’s your estimate for normal river width? And which gage are you using, Lumberton, West 5th or Boardman?
Just to illustrate the math and the assumptions needed, let me make up some numbers for the Lumberton USGS gage, and estimate the speed when the gage is 12 feet and the CFS is 1500. Say the river is 50 feet wide. We need to know a little about the shape of the channel, so, looking at the gage history, it looks like 8 feet is a normal low water mark, so lets assume the river bottom is V-shaped below this point (i.e., the average depth is 4 feet when the gage reads 8), and has vertical banks between 8 and 12 feet. Thus, at 12 feet, the area is 400 SF, 50 feet wide by 8 feet average depth. Flow of 1500/400 = 3.75/1.4667 = 2.56 MPH.
Now, this is the average MPH for the whole body of water. The fastest part, where you travel in a canoe (top center of channel) will be somewhat faster. As a SWAG, a factor of 1.5 seems reasonable, so the fastest part would be 3.84 MPH.
Now let’s consider it at flood. Looks like it peaked at 16.4 feet and 4500 CFS. Now the next questions are: how far out of its banks did it spill, and what’s the shape of the bank there? To illustrate, let’s say it spread out to 200 feet wide, and the banks are a consistent, even slope above 12 feet.
So, the new area is 400 (the part below 12 feet is the same) plus 4.4 feet height times 125 feet average width, for a total new area number of 950 SF. So, speed here = 4500/950/1.466667 = 3.23 MPH average, x1.5 (if the same SWAG number is applicable at flood)= 4.85 MPH peak speed in the middle of the channel.
It was Boardman.
yes it was at flood, (way into the woods)
Flow was 3960 and the gage was 8.07.
We were guessing that the flow was between 4 and 5 MPH
At Fair Bluff where it came to a weir under the bridge, we were guessing between 5 and 6 MPH.
Jack L