Abstract
Flow velocity measurements using point-velocity meters are normally obtained by sampling one, two or three velocity points per vertical profile. During high floods their use is inhibited due to the difficulty of sampling in lower portions of the flow area. Nevertheless, the application of standard methods allows estimation of a parameter, α, which depends on the energy slope and the Manning roughness coefficient. During high floods, monitoring of velocity can be accomplished by sampling the maximum velocity, umax, only, which can be used to estimate the mean flow velocity, um, by applying the linear entropy relationship depending on the parameter, M, estimated on the basis of historical observed pairs (um, umax). In this context, this work attempts to analyze if a correlation between α and M holds, so that the monitoring for high flows can be addressed by exploiting information from standard methods. A methodology is proposed to estimate M from α, by coupling the “historical” information derived by standard methods, and “new” information from the measurement of umax surmised at later times. Results from four gauged river sites of different hydraulic and geometric characteristics have shown the robust estimation of M based on α.
Highlights
A reliable rating curve at a river site is of fundamental importance in hydrological practice, as accurate discharge values are fundamental in addressing water resources management and rainfall-runoff model calibration as well as hydraulic risk assessment
This is due to the difficulty and dangers that operators have to face to sample velocity points in the lower portion of the flow area during high floods in particular when classical propeller current meters are used
The linear relationship is reliable even when Φ is estimated for gauged river sites where a sample of historical standard velocity measurements is available and which are updated, at a later time, by the sampling of umax
Summary
A reliable rating curve at a river site is of fundamental importance in hydrological practice, as accurate discharge values are fundamental in addressing water resources management and rainfall-runoff model calibration as well as hydraulic risk assessment. These topics might be seriously affected by uncertainty if the stage-discharge relationship is poorly estimated at river gauging sites. At gauged river sections flow data needed for rating curve estimation are often limited to low flow stages This is due to the difficulty and dangers that operators have to face to sample velocity points in the lower portion of the flow area during high floods in particular when classical propeller current meters are used.
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