Effect of deepening versus sea level rise on tidal range in the Elbe estuary

Abstract

Increasing tidal range in the Elbe estuary constitutes a problem for shipping and the ecosystem. The increase in tidal range over the last century has been suggested to be caused by deepening activities. Besides, rising mean sea level leads to changed tidal characteristics in the North Sea, and is thus also expected to influence tidal range in the estuary. In this thesis, the effects of both deepening and sea level rise on tidal range in the Elbe estuary were investigated and compared. Tidal range was simulated using an analytical model with solutions to the width-averaged shallow water equations, and tidal forcing including the principal semi-diurnal lunar tide and its first overtide. This was done for three different depth configurations. The model was found to reasonably represent current tidal range in the estuary. The results suggest that deepening of the estuary up to Hamburg will result in a further increase of tidal range, especially in the region around Hamburg. Global sea level rise, as estimated by the IPCC for 2100, was found to lead to an increase in M2 and M4 amplitudes at Cuxhaven, resulting in an along-estuary increase in tidal range. The maximum increase of tidal range due to deepening and expected sea level rise was comparable in size. The research shows that the combined long-term effects of both deepening and sea level rise should be studied before new dredging activities are carried out in the Elbe estuary. Lastly, possible improvements to the model are discussed.