Huge River Paradox

[waldronate]

The reason that you did not get the expected river flow is that there is an outlet to the sea that is lower than the ridge between the bottom and top areas of the map. The attached file shows the the too-high area in red and the too-low area in yellow. If you lower the ridge area and/or raise the low area then your river will flow as desired.

Another thing you can try is to paint in the desired river channel in Wilbur using a small brush at a fairly low level. Wilbur uses an algorithm that always follows the path of steepest descent and so will always generate plausible river channels by following the terrain. If you give it a desired channel that's lower than the surrounding terrain and connects to your sink (the lowest points or edges of your map) then the river network will follow that path.