The Effects of Sea-Level Rise on Estuary Morphology In Dredged and Undredged Systems

Urbanized estuaries and deltas are increasingly dredged and deepened for navigation purposes. However, how sea-level rise (SLR) will affect dredged systems in terms of their morphology and sediment transport is not yet well understood. Here, we compare scale experiments ofdredged and undredged estuaries, performed in a tilting tidal flume, to isolate the effects of SLR on estuarine morphology. We focus on response of channels, intertidal area, and estuary mouth (depth and width). Our results indicate that both dredged and undredged systems will see a significant loss of intertidal area due to SLR, mostly in the middle and upper parts of the estuary, nearthe limits oftidal influence. Moreover, dredged channels will suffer from bank instability and collapse (lateral changes) caused by SLR, particularly in the middle and upstream parts of the estuary. The channels in natural system have more space to laterally adapt and instead mainly respond in terms of bed level (vertical change). SLR causes widening i.e. lateral expansion of estuary mouth in all experiments. In the dredged system channels in the mouth remain deep under various SLR conditions, while increased sediment export causes overall shallowing of channels in the estuary mouth in the undredged system under SLR. The implications are that channels, which tend to be fixed and embanked in urbanized systems, have many flood protection measures placed at risk by increased water levels and flow velocities as tides penetrate further into the system. Meanwhile, intertidal areas that act as flood storage areas and valuable nature areas will be placed at serious risk mainly around the tidal limit.