Just came across a couple of issues related to this topic:
- A lake with a river mapped through it, but the river segments a) did not have a node on the perimeter of the lake, nor were they split into riverine and lacustrine segments. If we are to map rivers through lakes I would suggest a minimum is to ensure that both of these are done. Yes, they can be derived, but it broke my current workflow quite a way downstream, as the straight skeleton does not include the outflow.
- Reservoirs with multiple inflows and outflows other than the obvious streams/rivers entering and spillways etc. The one I looked at was Rutland Water: its primary outflow is a pipe to a water treatment works, but this outflow is in the same place as two overflow outflows, and pumped inflows from other catchments. (Much more complex systems exist in the Swiss Alps, e.g.Zervreilasee system)). The original river, the Gwash, which flowed through the valley is mapped on OSM, but this scarcely reflects actual flows and anyway it’s marked as historic.
These suggest that there are additional mapping nuances which need to be handled if mapping lines though lakes and reservoirs. See my current attempts to create such lines by pruning straight skeletons.