If you haven't done so, I recommend reading the "Fun With Wilbur" things (
https://www.cartographersguild.com/s...ad.php?t=29412 ). The Eriond tutorial was written before a few features common use in Wilbur, namely the finding rivers feature and the morphological erode feature.
Note that many of the terms are just as mysterious to cartographers as they are to artists. I blame the software people.
The river density is controlled by the "Flow Exponent" item on the "Incise Flow Process" dialog. A value of 0.2 will give you a high density of rivers, a value of 0.6 will give you a "reasonable" amount of rivers, a value of 3 will give you probably just one or two major stems, and larger values will continue to give you shorter and shorter rivers.
For you particular case, I recommend doing the following from your Wilbur map (assuming that you still have the original height data):
1) Select altitudes above 0 to preserve your existing coastlines.
2) One pass of Filter>>Erosion>>Precipiton-Based to break down the excessive hard-edged tributaries.
3) Filter>>Noise>>Absolute Magnitude Noise with a value of about 5% of your total height range to break up any flat spots. Note that this is NOT the same as the "percentage noise", which adds a different amount of noise to each pixel.
4) Filter>>Fill>>Fill Basins to reconnect all of the river basins.
5) Filter>>Erosion>>Incise Flow with a flow exponent value of about 0.6 to get a few rivers. You can adjust the exponent value and click Preview to see what the results will be.
6) Filter>>Fill>>Fill Basins to reconnect all of the river basins. This step isn't required if you aren't going to use Wilbur's river finding feature.
The Eriond tutorial relies on deep river canyons to give the impression of rivers. Since those days, Wilbur has sprouted a feature where it can calculate rivers directly without having to chop deep canyons into the landscape. Texture>>Other Maps>>River Flow gives you a dialog that uses a process similar to Incise Flow except that it doesn't use the computed information to modify the terrain, but just to color some pixels. The slider gives you control over the equivalent of the Flow Exponent value, and you can have the rivers colored differently at mouth as compared to source. Producing a white river mask (or one fading from black to white) on a black background offers you many options for masking and coloring tricks once in your image editing software.
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