Interesting paper showing how velocity varies with depth in the columba below Grand Coulee Dam
i.e. velocity is not constant across the channel
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LoginABOUT COLUMBIA RIVER VELOCITY-DEPTH
Current velocities were measured on a number of transects across the Columbia River in Washington State, to understand how velocity varies within a channel. The velocity at any point in a river is controlled by a number of factors, including the river's slope or gradient, roughness of the channel bed, turbulence of the flow, depth of the river, etc. Typically, water moves faster away from the bed of the river, where obstacles create drag and turbulence. The highest velocity overall is usually in the deepest part of the channel, just below the surface. Knowing the average velocity in a channel is extremely important when calculating river discharge, the volume of water flowing past in a given amount of time.
The data on velocity versus depth in the channel were acquired at a station below Grand Coulee Dam at a distance of 13 feet from the edge of the river. The depth of the Columbia River at this spot was about 12 feet at the time of measurement. Velocities were measured at various heights in the water column.
These data show a regular decrease of velocity with increasing depth in the river, as might be expected. The data are fairly linear, with a high correlation coefficient.
Other locales show a similar decrease in velocity with depth, though often with much more scatter, and without the fairly monotonic behavior exhibited by this example.
Reference: Savini, J. and Bodhaine, G. L. (1971), Analysis of current meter data at Columbia River gaging stations, Washington and Oregon; USGS Water Supply Paper 1869-F.
also see:
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LoginABOUT COLUMBIA RIVER VELOCITY HISTOGRAMS
Current velocities were measured on a number of transects across the Columbia River in Washington State, to understand how velocity varies within a channel. The velocity at any point in a river is controlled by a number of factors, including the river's slope or gradient, roughness of the channel bed, turbulence of the flow, depth of the river, etc. Typically, water moves faster away from the bed of the river, where obstacles create drag and turbulence. The highest velocity overall is usually in the deepest part of the channel, just below the surface.
Data on the variation of velocity with time at 3 different depths were obtained along a transect below Priest Rapids Dam on the Columbia River in Washington State. Velocities were measured every minute for 66 minutes. Even though all other variables are fixed, velocity still varies with time as the current surges and wanes. Knowing the mean velocity in a channel is extremely important when calculating river discharge, the volume of water flowing past in a given amount of time. The data emphasize the importance of thorough measurement.
The histograms and accompanying statistical parameters show some interesting patterns. Mean velocity decreases with depth, as expected. Roughness of the bed has a strong influence on velocity, due to both drag and turbulence. The standard deviation increases with increasing depth, perhaps reflecting this increasing turbulence.
Reference: Savini, J. and Bodhaine, G. L. (1971), Analysis of current meter data at Columbia River gaging stations, Washington and Oregon; USGS Water Supply Paper 1869-F.
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