To make the coastline slightly less generic slash tolkienian, I'm trying out different patterns. Using the line-to-pattern or whatever it was called in Inkscape (same as the one used for the tapering river trick, except this time with Repeating (Stretched) and the original figure orthogonal to the orientation in river tapering), etc. then doing lots of selection-to-pattern-to-selection stuff in GIMP, I got this. Still a few glitches I'll fix later, but I think it looks quite ok when it's toned down with a colour instead of using heavy black.