There are several mods adding terrains in the game, but none of them will have water as an edge to the map, edges have to be moutains, with the exception of the river ends.

The biggest "map options" standalone mod I can think of is the "CC terrains[blackliquidsoftware.com]" mod on the Black Liquid site.
I haven't looked in a while, but I bet you can also find some good terrain mods on WorldOfBanished.com (RedKetchup's site).
And finally you also have a few map mods on BanishedInfo.com, although I don't think there was a lot of choice in that category there.

Only one terrain/map mod can be active at the time: They all affect the same files, so only the one on top in your modlist will be loaded.

ty very much im looking right up