using raise land will turn cliff tiles on the coast into beach tiles. best result for beachs are when there are at least two passable land tiles adjacent to where you cast raise land. with only one adjacent tiles water tiles may be created
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thought not related to transport ships another use of beach tiles is to dam up a river that dumps into a lake or sea. this may cause one or more of your cities to get an error that claims it is no longer contiguous with capital city and hence suffers a new 15% city unrest penalty
I have found no general rule of what triggers this bug. in some cases after a few turns the bug disappears one or more of the bugged cities (and hence the unjustified 15% city unrest penalty for those unbugged cities)