Following up from an earlier question, I am tracing a street map for a town using a bitmap from OpenStreetMap. I am using bezier curves for the roads. Different roads have different colors and sizes, shown in the figure by the green and yellow lines. I have also created a bounding box for the map, shown in graphic as a rectangle with a black stroke and a gray fill.
There is also a river crossed by a road bridge at the top of the map - only part of the river is shown. The shoreline is drawn in blue. I want to shade the river between the shorelines in light blue. I have realised that I can use the bucket tool to fill that area, but that feels like the wrong approach. Given that the area of water is bounded by the shorelines and the bounding box, I had expected to be able to use that to create an object.
Thinking that the fact that the boundary box is a shape might be the issue, I also tried adding paths to use to combine with the shorelines into one closed path, like this (new lines in red):
This didn't work as I could not fill the resulting shape:
Any suggestions as to how I could create an object from the bounding box and blue shorelines?