Abstract
Salt dilution is a well-established streamflow measurement method in
creeks, which works particularly well downstream of turbulent flow
sections as mixing of the salt tracer is enhanced. Usually salt dilution
measurements are performed manually, which considerably limits the
observations of rare peak flow events. However, these events are
particularly important for constructing robust rating curves and
avoiding large uncertainties in the extrapolation of river discharge
values. An additional challenge is the variability of the river
cross-section, especially after larger discharge events, leading to
non-stationary rating curves. Therefore, discharge measurements well
distributed over time are needed to both construct a reliable
streamflow-water level relationship and to detect changes caused by
erosion and deposition processes. To overcome these two issues, we used
an automated streamflow measuring systems at three different sites in
the Alps for event-based discharge measurements. This system allowed us
to measure close to the highest peak flows at all three sites in the
observation period (2020-2021) and to detect abrupt changes in the
rating curve. Based on a very large data set of almost 300 measurements,
we were able to evaluate the reliability of the system and to identify
the main sources of uncertainty in the experimental setup. One key
aspect was the site selection for the downstream electrical conductivity
sensors as measurement location strongly controls the signal-to-noise
ratio (SNR) in the recorded breakthrough curves.