Under natural conditions, most of the sediment washing down rivers is deposited in the estuary due to settling and flocculation. Settling occurs downstream from the head-of-tide because the slowly moving water characterized by estuaries can not carry as much sediment as a flowing river.
Flocculation is a process by which salty water induces easily entrained fine-grained sediment to coalesce into larger globs that settle out. A rise in sea level would cause both of these processes to migrate upstream, and thereby assist the ability of wetlands in the upper parts of estuaries to keep pace with sea level, while hindering their ability in the lower parts.
If sea levels were to rise at a pace faster than corals could build their reefs upward, eventually light conditions would be too low for the zooxanthellae to continue photosynthesis.
Losses of coral reefs would mean losses in the high biodiversity of these systems as well as the fisheries and recreational opportunities they provide.
Increase in the heights of waves
A rise in sea level would also increase the size of waves. In shallow areas, the depth of the water itself limits the size of waves, which could be the most important impact of sea level rise along shallow tidal embayments with steep, muddy shores.
The steep slopes imply that inundation would not be a problem. However, with water depths one meter deeper, waves could form large enough to significantly erode the muddy shores.
Bigger waves could also increase the vulnerability of lands protected by coral reefs. In many areas, these reefs protect mangrove swamps or sandy islands from the direct attach by ocean waves; but deeper water would reduce the reef’s ability to act as a breakwater.
The extent to which this will happen would depend on the ability of the corals to keep pace with sea level rise.
