Untitled

Abstract

Direct measurement of water levels and velocities can provide fundamental insight into the hydrodynamics of tidal rivers and estuaries. They represent a reliable source of data for the verification and calibration of numerical models. Such knowledge is also crucial for navigation, environmental assessments, and coastal protection and development. To reach a high level of description, measured data must cover a wide range of spatial and temporal variability. Long-term monitoring stations provide high-frequency records, but they are usually limited in number, thereby limiting their ability to represent spatial features of the flow. Conversely, satellitebased measurements provide synoptic snapshots of a region, but they are limited in their temporal resolution and interpretation of the velocity field. Boat surveys remain the best compromise between fixed measurements and remote sensing observations for the characterization of nonstationary hydrodynamic fields. They can ensure both spatial and temporal coverage, provided that the sampling strategy and resolution is adapted to the size and rate of evolution of the structures measured (e.g., Rixen et al. 2001).In the field, meeting these requirements is often a challenge, as both the instrumentation and survey strategy must meet the criteria and constraints set by the users (e.g., sampling requirements, finite measurement time, and resources) and by the environment (e.g., presence of tides, size of the river). This has been facilitated in part by the development of new technologies over the last decades, including acoustic Doppler current profilers (ADCP) for water velocity meaQuantifying lateral and intratidal variability in water level and velocity in a tide-dominated river using combined RTK GPS and ADCP measurements AbstractCross-sectional gradients in water levels and velocities play a determining role in the circulation dynamics of tidal rivers and estuaries. Documenting and analyzing their variability throughout a tidal cycle require observations with high spatial and temporal resolution. A survey strategy and a data analysis procedure have been designed to obtain continuous and synoptic water level and velocity fields over a tidal cycle, along 13 cross-sections of the St. Lawrence fluvial estuary dominated by large tidal ranges. The method combines both RTK GPS and ADCP technologies for the simultaneous measurement of water levels and velocities along repeated boat transects, allowing fast data acquisition over wide river sections and under rapidly changing conditions. The reconstruction of continuous and synoptic fields is made by interpolation. Simplifying assumptions about data stationarity and/or homogeneity are avoided by adapting the interpolation procedures to the shape and distribution of the underlying data in a space-time reference frame, thus minimizing distortion in the reconstructed quantities. The capabilities and limitations of the method are assessed through error computations and comparisons with alternate data analysis methods and complement...