Five hundred and eighty-one cubic discharges were measured under very
varied conditions. The process adopted contained three steps: (1)
Sounding along about fifteen float courses, scattered across the site in
eight cross sections; time, say four hours. (2) Measurement of the mean
velocities through the full depths in those float courses, each thrice
repeated; time, say four hours. (3) Computation, say two hours. This
process was direct and wholly experimental; each step was done in a time
which gave some chance of a constant state of water. From an extended
comparison of all results under similar conditions, it appeared that the
above process yielded, under favorable circumstances, results not likely
to differ more than 5 per cent. The sequel showed that in a channel with
variable regimen, a discharge table for a given site must be of at least
double entry, as dependent on the local gauge-reading, and on the
velocity or surface-slope.
Special attention was paid to rapid approximations to mean sectional
velocity. The mean velocity past the central vertical, the central
surface velocity, and Chezy's quasi-velocity--i.e.,
100 x Sqrt (R x S)
where R = the hydraulic mean depth, and S = surface slope--were tried in
detail; thus 100, 76, and 83 average values thereof respectively were
taken from 581, 313, and 363 detail values. The ratios of these three
velocities to the mean velocity were taken out, and compared in detail
with Bazin's and Cutter's coefficients.
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