The Effect of Sea Level Rise on Estuarine Morphology Of Natural and Dredged Estuaries in Experimental Setup

Abstract

Many estuaries are of great economic importance as they are home to large harbours and provide passage to large container ships when extensively dredged. Estuaries are also typically rich in mudflats and marshes that provide flood protection and are home to biodiverse ecosystems. The impact of Sea Level Rise (SLR) on these estuaries and the functions they provide may be large. Therefore, it is important to understand how all the different morphological features of estuaries (e.g., channels, tidal zonation) form and interact in natural and dredged systems and how they will respond to future SLR in order to develop sustainable management strategies. To research the effect of future SLR, two experiments were conducted in the Metronome tidal flume, one with a natural estuary and SLR and one with a dredged estuary and SLR. The results show that the natural system is better able to keep up with SLR than the dredged system. In the upstream regions of the natural system, channel mobility decreased and bank stability increased relative to natural estuaries without SLR, and thus SLR stabilises upstream estuarine morphology. In the upstream regions of the dredged system, the channel mobility significantly increased due to a strongly meandering channel that eroded the banks in the outer bends. As a result, the bank stability decreased in the dredged system with SLR relative to natural and dredged systems without SLR. While dredging on its own stabilises estuarine morphology, it destabilises estuarine morphology in combination with SLR. In the downstream regions of the estuary, bank stability decreases under influence of SLR for both the natural and dredged system. In dredged systems like the Western Scheldt, the results show that current dredging strategy is not sustainable with SLR, because total dredging volumes will increase as SLR and dredging continue and the most heavily dredged areas move upstream due to transgression.