Bed-roughness investigation for a 2-D model calibration: the San Martìn case study at Lower Paranà

This paper illustrates how the acoustic Doppler current profiler (ADCP) and single-beam echo-sounder (SBES) recordings can be used for the calibration of existing software to assist in generalizing the morphodynamic processes in large rivers at key sites such as bifurcations and confluences. Calibration of the MIKE21C numerical model by the Danish Hydraulic Institute at the 25-km-long reach of Lower Paranà near Rosario (Argentina) is presented. This reach includes two downstream confluences and two bifurcations. The model simulates the depth-averaged (2-D) streamflow velocity and the related sediment fluxes to predict the bifurcation morphodynamics that affects the Paranà waterway. To investigate the river channel bathymetry, roughness, flow discharge allocation at bifurcations, suspended sediment concentration and grain size distributions, several instruments were used. These instruments included two ADCPs by Teledyne RDI working at frequencies of 600 and 1200 kHz, a Sontek ADCP working at a frequency of 1000 kHz and a SBES. The method to assess suspended sediment concentration and grain size distributions has been previously described. This paper focuses primarily on investigating dune morphology (by means of SBES depth measurements) and friction velocity (by means of ADCP profiling) to determine the river channel bed-roughness. The 2-D model results agree with observed values of bed-roughness, flow velocity and bed sediment concentration distributions at the investigated sections, known data of water slope and total load of bed sediment are in good agreement with model results.