I live in the Fens in England and noticed the same thing. You can set it back 1000 years and not only is the Fens still drained, there are artificial drainage channels that weren't dug out for another 600 years. It seems an assumption has been made that rivers and coastlines don't change over time but it's so far from true! For me it's one of the most interesting, and scary, things when looking at old maps. Does the data model support changing natural features like rivers and coastlines?
Yes any feature as far as I'm aware can have a start date and end date so can show the changes over time. As can be seen in London (https://www.openhistoricalmap.org/#map=16/51.5108/-0.1086&la...) where the shape of the river changed when the Embankment was built in 1869. As far as I'm aware there is no reason why changing coastlines couldn't be mapped, though it is a lot of work to draw in a long length of coastline.
