i.e. is there one catastrophic event where everything is immediately flooded? (Similar to Katrina).
Or is the area just slowly flooded over decades? In which case, no one does anything? (i.e. the Sacramento scenario is hard to fathom in this scenario)
Maybe look into whatever it is they do in the Netherlands. A very large fraction of the entire country is just barely above sea level (or even below it in places).
For example, if the sea were to spill over onto all below-sea-level land, Amsterdam would be an island, some 15 km off the new coastline. The Port of Rotterdam would still be there (25km offshore), but the rest of the city would disappear.