I've been playing for a very long time. Shorelines are most easily handled with the Mayor Mode levelling tool using the various options to control the effect. Here is a review:
CTRL cuts the effect circle for the brush in half
SHIFT double it
SHIFT+n (1 <= n <= 0) controls the diameter of the brush
SHIFT+n+Fm (1 <= m <= 10) controls the weight of the brush
The lower the number the less the effect.
Hitting shift alone resets everything.
Historic Harbor Addon