Hydrodynamics of the Rhine Rofi near IJmuiden

Abstract

The paper will focus on hydrodynamics of the Rhine ROFI in its most northerly extent near IJmuiden. A bottom-mounted ADCP was deployed near IJmuiden and measured for almost 6 months. Observations show that the largest difference in ellipticity between surface and bottom mostly occurred during neap tide, suggesting that the water column was stratified, leading to a cross-shore circulation. However, for 3 out of the 11 neap tides no ellipticity difference was observed and during 1 out of the 10 spring tides a strong ellipticity difference occurred. To understand the causes of these irregularities a model was set up with GOTM. Based on the depth-averaged currents the barotropic pressure gradient is determined. Using a simple advection equation the salinity profile was estimated at the measurement location and used as input for the model. We were able to simulate the overall characteristics of the observed flow patterns. Model results show a strong link between wind stress magnitude and direction and reduced stratification during low energetic neap tides. An increased fresh water discharge was the cause for the strong ellipticity difference during spring tide. The strong effect of wind speed and direction on the onset of stratification of the Rhine ROFI has never been shown before. Furthermore, the results show that during the 150 days of observations the plume always reached IJmuiden.