Colloquium

Thesis Colloquium Merel Verbeek

This study analyses the tidal dynamics and salt dispersion at a channel junction in the Rhine-Meuse Delta in the Netherlands, using a 13-h survey of Acoustic Doppler Current Profiler (ADCP) and Conductivity Temperature Depth (CTD) data. The results imply that salt intrusion is largely controlled by the character of the barotropic tidal motion.

Organisator Hydrology and Quantitative Water Management
Datum

vr 1 mei 2015 11:00 tot 11:30

Locatie Lumen, building number 100
Droevendaalsesteeg 3a
100
6708 PB Wageningen
+31 317 481 700
Zaal/kamer Lumen 2
Tidal motion and salt dispersion at a channel junction

On a global scale, freshwater availability in low-lying coastal areas is threatened by salt water intrusion. There is a need to better understand the processes governing salt intrusion, especially in densely populated deltas. In delta channel networks, channel junctions may play a key role in salt dispersal. This study analyses the tidal dynamics and salt dispersion at a channel junction in the Rhine-Meuse Delta in the Netherlands, using a 13-h survey of Acoustic Doppler Current Profiler (ADCP) and Conductivity Temperature Depth (CTD) data. The study includes a unique set of five salinity profiles in each of the three cross-sections bounding the junction, once every hour. The observations capture the 3D character of the flow and salt fluxes at the junction. The flow at the junction is dominated by the semi-diurnal tide, which shows to be highly spatially variable. The tidal phase differs 1 to 2 hours between the junction branches, and locally phase lags of up to 4 hours are found. The residual salt transport was decomposed into contributions representing (1) the advective transport due to water discharge and change in storage during the tidal cycle, (2) a sloshing effect, i.e. tidal dispersion via triple correlation between tidal depth change, tidal current, and tidal salinity, (3) the cross-correlation between tide and salinity, (4) Stokes’ drift dispersion and (5) salt dispersion due to mean shear produced by gravitational circulation. Advective transport and the sloshing effect dominate the salt balance. This implies that salt intrusion is largely controlled by the character of the barotropic tidal motion.