## 5 Discussion
While errors in depth measurements and RTK-GPS positioning contribute to errors in estimated bed elevations, the interpolation step to create the DEMs is considered to be the dominant source of error [54]. Nonetheless, the presented study intended to test a simpler, cheaper and easier approach to evaluate the capability to estimate bedload transport using a modified ISSDOTv2 method. The ADCP application (with HydroSurveyor capabilities activated to measure bathymetry) shows great potential, despite the spatial resolution constraints. However, since the bathymetry interpolation applied to create DEMs increases noise and uncertainties in the longitudinal profiles, the application of mISSDOTv2, although promising, must be carried out with caution. During the field campaign, it was not possible to repeat the bathymetric survey more than once, preventing the establishment of a linear relationship between lost area and time interval to evaluate the computed corrected values [15] in the modified ISSDOTv2 method. During the second bathymetry, the pilot of the boat tried to follow the original track lines, maintaining the boat speed as constant as possible, but in general it was not possible to cover the same exact paths. Then, the visual inspection of longitudinal profile pairs (before interpolation) and the recognition of equivalent dunes at different times were hampered by the limited time-spatial resolution of the ADCP bathymetric surveys. Two pieces of evidence were considered to evaluate if bedforms traveled less than 50% of their wavelength in the time interval between the consecutive surveys (24 h). The first evidence was based on dune-tracking measurements performed with an ADCP in the Parana River [55], where bed material and flow velocities are similar to those found at the Taquari River, which resulted in dune velocities of approximately 1 m/day. The second piece of evidence was based on the results of a computational morphological modeling of the study site with the Delft3D software [25]. Simulations were performed, testing different sediment transport formulations and providing longitudinal bed profiles that pointed out that dunes traveled less than 50% of their wavelength in 24 h (Figure 17). Despite these efforts, it was not possible to guarantee that dunes did not travel more than their wavelength in the 24-h interval between the ADCP surveys. This is the main uncertainty related to the application of the mISSODTv2 in the presented research. Nevertheless, the authors considered it useful to present the results to illustrate the potential of the methodology, and to warn about the necessary precautions. A major piece of advice is to perform several transects along a fixed longitudinal path before the bathymetric surveys, with the aim of recognizing bedform features at different time steps. From the analysis of the distance traveled by these bedforms, the proper time interval between the bathymetric surveys should be chosen, considering the equipment used, the extension of the area, and the local sand wave velocities for a specific hydrologic condition. It is worth mentioning that the bedload empirical formulations applied in this paper (Table 2) predict the maximum bedload transport rate that a flow in equilibrium can produce, given the local hydraulic and sedimentological conditions. This transport capacity may not be equal to the actual transport if the channel is undergoing aggradation or degradation processes. Since it is not trivial to determine when this capacity is reached, the use of field-measured data to check the validity of bedload transport equations (and vice versa) should be carried out carefully. Table 4 summarizes the main advantages and disadvantages of the methods analyzed in this paper. As seen, it is not possible to choose one method as the most efficient and recommended of all.