Discharge estimation in open channels using dimensionless isovel contours and one fixed-point velocity measurement at least

A procedure for estimating discharge in a river cross-section based on the combined use of dimensionless isovel contours and one or more point velocity measurements is presented. The procedure is derived from the Biot Savart law; in particular a specific formulation of the relationship characterizing the “effect” of the wetted perimeter on the range of velocities in a cross-section which depends on roughness, expressed by means of Manning’s coefficient is proposed. Once appropriately nondimensionalized, the “isoeffect” contours can be read as dimensionless isovel contours. At this point, assuming that a number of velocity measurements are available, it is possible to estimate discharge. The proposed procedure was applied to two cross sections and the results showed that it enables a very accurate estimation of discharge, even when it is based on a limited number of velocity measurements or even on the measurement of maximum surface velocity alone.