For average velocity, please refer to the attached file.

Regards

Thanks Sir

But i need information about velocity data measurements for natural rivers not calculation procedure.

The USGS and perhaps others including companies that develop current meters have developed guidance on stream gauging. Most scientific research in the past used type AA or pigmy meters depending on the water depth. A few decades ago, Doppler meters were developed to more quickly and accurately take channel dimension, velocity and calculate flow measurements. Other methods have used such things as floating multiple oranges to estimate velocity through a section of river, with the fastest oranges perhaps a measure of the fastest waters, and average of the oranges reaching a downstream point perhaps the average value. If you are into fluorescent dyes, a known concentration can be introduced at a constant rate over time, and using a fluorometer detect concentration changes to estimate discharge or as desired, velocity between two points. Velocity meters and pitot tubes can be used for at point velocities if desired. The maximum velocity might or might not be at the extreme flow discharge, as the mean velocity reduces above bankfull flow as the water level expands across the floodplain. If you have the channel morphology measurements, perhaps the HEC RAS or Rivermorph software might help. If you have a discharge reading, and channel cross section at the desired time, you can divide the discharge by the cross section to get mean velocity at that location and time. As you probably know, there are primary velocity vectors and secondary vectors as flow continues downstream in a double helical pattern. Finding that extreme value in velocity may take some playing to get the meter in the right point and height in the cross section. Generally high quality flow measurements might still have 10-20% error. Channel gradient is one of the main factors, but there are considerations as whether above or below critical flow, turbulence, etc. probably the Doppler meter or specifically designed and monitored dye tracing set up might give best results if you want accuracy. For stations with a well developed stage discharge relationship, the calculations using discharge divided by cross section would produce the mean velocity changes at that location as water stage increases or falls. Some channel types tend to have slow velocities such as braided streams. So there may be a substantial number of factors to consider as water flows from headwaters to points downstream.

Sorry Sir,

Please refer to the following links and the attached files.

Regards

https://www.researchgate.net/publication/289552305_Water_Surface_and_Velocity_Measurement-River_and_Flume

https://www.usgs.gov/special-topic/water-science-school/science/how-streamflow-measured?qt-science_center_objects=0#qt-science_center_objects

https://www.hydrol-earth-syst-sci-discuss.net/hess-2019-289/hess-2019-289.pdf

Bachir Achour William F. Hansen

thanks for valuable information

Bachir Achour William F. Hansen

USGS is providing discharge data for many streams but I require maximum velocity data as average velocity can be calculated from USGS data as they are providing bathymetry details also as illustrated in the attached file.

Please let me know if there's any agency or portal from which I can get maximum velocity data.

As in the excel file, average velocity Q/A = V mean, for a specific reading. If you go to the stream measurement, and then the USGS stream gauging paper that Dr. Achour provided, you will see there are measurement point in cross section. These measurement sites are typically at some combination of 0.8, 0.6, and 0.2 depth, and not intended to obtain max V. The Doppler may have that capability, but as you move the cross section, the max V will change. Some of the highest velocities for a stream system will be in high gradient sections that in some instances can roll or move boulders. The max V possible for any cross section is most likely a very localized point or relatively small area. As a rule of thumb when wading, depth (ft) x velocity (ft/sec) should not exceed 10, so if 2 feet deep and 5 feet/sec velocity is an example of what not to exceed, and if the bottom is slippery or unstable, that could add safety problems. PPE as life jacket and tethered rope may help. The dye method may help identify the fastest water in a reach. In many instances, the fastest water possible is nearly impossible to locate, and then measure. The highest mean velocity may be at bankfull on streams with flood plains, because the mean velocity slows as water expands across the floodplain. At a specific discharge rate, the section with smallest cross section area would have the highest mean velocity, but not necessarily containing the at point max V, which may be very localized. The pitot tube is one device that can measure a very localized velocity, and they make velocity meters. But how much time and effort would a person devote to finding that maximum V in a stream or river system? And if you thought you found it, how could you be certain it won’t be exceeded at some other time or location? You might look up some of the papers that deal with erosion and bank stress. I seem to remember a flume study that might be of some interest, if I can locate it.

William F. Hansen thanks sir for explaining in depth. I should be grateful if you can locate and share the flume study as I am familier with flume studies due to past experience.

This is flume study paper by Kean et al, 2009 I was thinking about.

Basically we have a different techniques to measure the velocity of flow in the river for example from the continuity equation we can calculate once if we know the flow passing through that river. But in real-life situations, permissible velocity is required to avoid silting and Scouring.

Acoustic Doppler current profiler (ADCP) has been widely used by hydrologists all around the world to measure velocity and discharge in rivers and streams. ADCP can measure the velocity profiles (i.e. velocity distribution in water column) along the ship's track. The ADCP software usually displays velocity contour plots from which you can identify the maximum velocity.