The Effects of a Storm Surge Event on Salt Intrusion

Abstract

The Rhine-Meuse Delta is a low-lying delta in the Netherlands that is subject to both salt intrusion events and storm surges. Typically, storm surges only temporarily cause increased salt intrusion and do not cause severe problems for freshwater availability. However, during the storm surge of December 2013, salt reached the closed southern branch of the delta and higher salinities were observed for weeks after the storm surge. The purpose of this study is to examine the mechanisms controlling salt intrusion in the Rhine-Meuse Delta during and after a severe storm surge event. A three-dimensional hydrodynamic model (Delft3D-FM) of the Rhine-Meuse Delta was developed that successfully reproduces salt intrusion for both normal and storm surge conditions. During the storm, high water levels in the northern branch caused a salt flux toward the southern branch. The southern branch of the Rhine-Meuse Delta is closed off by an estuarine dam, consequently salt was retained landward of the dam. Local stratification in the southern branch caused salt to remain in the deeper parts, limiting the effectiveness of flushing after the storm surge. In the post-storm period, salt was gradually released from the southern branch, raising salinity levels in an adjacent channel. The river discharge was only just below the yearly average, showing prolonged salt intrusion can also occur outside of dry periods.