For those of you with Amazon Prime, it is worth watching the Brit show called Time Team. Not only is it a fascinating show, but they frequently in their digging uncover harbors and estuaries where there is today a field many meters above current sea level.
Season 6 Episodes 11 is amazing in the discovery of an "island" which now contains the remnants of medieval and older era habilitations.
In another episode, they found a venue where massive ships were once built for the transportation of goods but which today is not even close to the remaining stream.
"Viva le niveau de la mer monte"