Author(s): F. Zunic; K. Fiedler; P. Rutschmann
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Abstract: Exact determination of flood discharges in rivers is of high importance for many hydrologic tasks. They are crucial data for statistics and all hydrodynamic-numerical models. Besides traditional gauging by flow meters, the ADCP-technique (Acoustic Doppler Current Profiler) has become generally accepted for velocity gauging in rivers. Nevertheless there are still many unsolved problems to deal with: 1) In rivers with high sediment transport, ADCP-gauging of velocities is inadequate and sometimes even impossible to be carried out satisfactorily. 2) Rivers with bed-load make it difficult to validate the measured data, if the position of the ADCP is fixed by the so-called bottom-tracking-method. 3) Sediment transport is also responsible for inconsistencies at some gauging stations. Due to streambed erosion during floods, the supposed rating curve is not valid during peak discharge, and has to be adjusted according to the measurements of the actual velocity and the current shape and depth of the riverbed. 4) Gauging during floods is quite a challenge, because the carrier boats face extreme waves and a lot of driftwood during high waters. Common hull shapes do not work satisfactorily. In a two-year research project, the mentioned were investigated in detail on two typical rivers in Southern Bavaria: 1) the major river Inn with a lot of sediment transport and considerable erosion during floods, and 2) the much smaller river Tiroler Achen, which is flowing into Lake Chiemsee. Although no erosion occurs here, considerable bed-load requires additional measurement techniques for satisfactory results. This article shows results of the investigations and presents solutions to overcome the problems described. The project was funded by the energy company E. ON and by the Bavarian government. This clearly shows the general importance of the investigations.
Year: 2009