Historic Discharge Measurements in Three Rhine Branches

Flow velocity measurements on several Rhine branches near the Dutch-German border were carried out in 1790 and 1792. Original description of the velocity instrument and original measurement techniques were evaluated to assess the reliability of the instrument and data. The operation of the instrument is based on a dynamic balance between drag force on a submerged vertical plate and gravitational force on a weight above the water surface. Uncertainty in measured velocities caused by friction of the instrument is negligible. Consequently, velocities measured with this instrument are realistic and can be used for detailed analysis of river flow parameters. The original aim of the 1790-1792 campaign was to determine the new discharge distribution of the Rhine branches after construction of groynes at the bifurcations in 1784. The measurements showed that discharge distribution had improved. The analysis herein of instrument operation and accuracy justifies this conclusion.