Human Impacts on Tides Overwhelm the Effect of Sea Level Risee on Extreme Water Levels in the Rhine-Meuse Delta

Abstract:

Mean sea level rise receives ample attention in the literature. However, peak water levels, which are most important for flood vulnerability and salinity intrusion in tidal river networks, may not be linearly related with mean surface levels. To quantify tidal and subtidal water level changes and to link these changes to human intervention, 70 years of water level data for the Rhine–Meuse tidal river network is analysed using a variety of statistical methods. Using a novel parameterization of probability density functions, mean high and low water levels are examined, and extreme water levels are investigated by applying the combined Mann–Kendall and Pettitt tests to find trends and trend changes. Tidal water levels are studied based on harmonic analysis. Results show that the mean water levels throughout the system rise with the same pace as the mean sea level. However, high and low water levels do not show the same increase, and the spatial variability in decadal trends in high- and low water levels is high. High water and low water extremes generally decrease. Both the extreme water level analysis and the harmonic analysis display significant trend breaks in 1970, 1981 and 1997. These breaks can be attributed to the closure of the Haringvliet estuary, the removal of sluices and the removal of a dam, respectively, which radically alter the tidal motion. These results demonstrate that the direct human influence on the tidal motion can overwhelm the effect of mean sea level rise on water level extremes.