Discharge Measurements in Lowland Rivers: Field Comparison Between an Electromagnetic Open Channel Flow Meter (EOCFM) and an Acoustic Doppler Current Profiler (ADCP)

Abstract

Field tests were carried out on two lowland rivers in Poland, namely Narew and Wilga, both being right tributaries of the Vistula River, in order to compare the results of flow velocity and discharge measurements. Both measurements were completed with the use of an acoustic Doppler current profiler (ADCP RiverSurveyor S5) manufactured by SonTek and an electromagnetic open channel flow meter (model 801) manufactured by Valeport. Narew is one of Europe’s few anastomosing and vegetated rivers. The field measurements were done in the central part of the Narew National Park. By contrast, Wilga is mostly a sandy and meandering river, and the measurements were carried out on the regulated channel that is part of the river. In both cases, field tests in each cross-section were made using both methods. The chapter mostly focuses on the potential errors and differences in the measurements of flow velocity and discharge resulting from: (1) the existence of vegetation on the river bottom; (2) the influence of obstacles such as islands or large fluvial dunes above the measuring cross-section; and (3) the quantity of measuring profiles and measuring execution time for the method using the electromagnetic flow meter. For the latter method a simple but accurate procedure, which is also briefly presented in the chapter, was applied to obtain the flow discharge. It is shown that the differences in the measured values of the flow discharge are from 12 to 35 %, depending on the method of measurement, the nature of the river and flow conditions. The findings of this study may be a suitable tutorial material for education in hydrology, civil engineering and environmental hydraulics.