While acknowledging that erosion is also caused by many other factors, Bruun (1962) showed that as sea level rises, the upper part of the beach is eroded and deposited just offshore in a fashion that restores the shape of the beach profile with respect to sea level.
A rise in sea level immediately results in shoreline retreat due to inundation. However, a 1 m rise in sea level implies that the offshore bottom must also rise 1 m. The sand required to raise the bottom can be supplied by beach nourishment. Otherwise waves will erode the necessary sand from the upper part of the beach.
Sea level rise would generally enable saltwater to advance inland in both aquifers and estuaries. In estuaries, the gradual flow of freshwater toward the oceans is the only factor preventing the estuary from having the same salinity as the ocean.
A rise in sea level would increase salinity in open bays because the increased the cross-sectional area would slow the average speed at which freshwater flows to the ocean.
The impact of sea level rise on groundwater salinity could make some areas uninhabitable even before they were actually inundated, particularly those that rely on unconfined aquifers just above sea level. Generally, these aquifers have a freshwater "lens" floating on top of the heavier saltwater.
As sea level rises, the depth of the freshwater lens in the coastal zone is greatly reduced, leading to salinization of water supplies. In extreme cases exacerbated by over-pumping, the aquifer may rapidly become unsuitable for drinking and even for irrigation.
Changing the resonance frequencies of tidal basins.
Greater tidal currents would tend to form larger ebb tidal deltas, providing a sink for sand washing along the shore and thereby causing additional erosion. Some of the bathymetric changes that might amplify tides would have the same impact on storm surges. Finally, higher tidal ranges would further increase the salinity in estuaries due to increased tidal mixing.
