[agracier]

have a problem with my rivers.
the map I'm working on is very mountainous and i need my rivers to start above sea level then come down.
Is this possible?

This is certainly possible. First off when making a DEM and using the elevation tables, especially for the gray elevation table, do not use the 'lake check' option. Or rather, make 2 dems, one with and one without 'lake check' option turned on.

Then with the gray DEM without the lake check, you should make a multi-layered file to work on. This should ideally be your map_C.

Create a new layer and on that layer you should manually draw in rivers in RGB 0, at least 3 pixels wide, though of course near river mouths, these can become very wide.

This hand editing can take some time to accomplish, especially if the terrain contains intricate rivers and run-offs and what not. Just be certain to create the rivers and lakes and any other type of inland water on a separate layer, as afterwards it will save time and effort.

When that is all done, you can then create a map_h, by importing the downsized river layer into a multi-layered file for map_h, then by merging the layers and doing what is described in the tutorial. But don't forget to turn off the river layer of RGB 0 when merging. Otherwise you will end up getting the grand canyons of all Grand Canyons since RGB 0 corresponds to sea level. Try out the map and see how the rivers look.

In mountainous terrain they will probably creep up along mountain sides and show pyramid like forms ... to correct this you can for instance go back to the multi-layered file with the river layer. Select all the rivers on their own layer and expand the selection by at least 1, 2 or 3 pixels, then keeping this selection active, go to the background layer, the gray dem, and then either soften or blur the selection a few times. You can soften or blur by hand if you wish, but generally a blanket command works just as well.

By doing this, you'll be eliminating much of the sharply elevated terrain around river borders into more gentle slopes. Canyons will become less steep as a result and less dramatic looking, but the upside is that the river course will be more or less level and not show any more pyramids along the slopes.

Then you merge layers and create a new map_h (again not forgetting to turn off the river layer RGB 0)... and of course take a look and see how it looks in-map.

Bear in mind that this works fairly well, but in terrain that descends very swiftly, there will always be some deformation of rivers. For instance if you approach a river from down-valley and it drops very swiftly, you will probably always be able to see 'under' it in some way or another. Especially if you are flying low.

Viewing from a higher altitude gives much better views ...