Thanks for the replies. I've tried all the scenary height tools, with different settings. The best results so far have been to use the level tool, set with a brush width of 80, height of -7.1, and follow a marker path down the middle of the channel. I'm going to try to create a cross-section of the channel in Sketchup, and see if I can get a loft object created. The channel is key to the project, as there is a large amount of yard trackage parallel to the channel, along with numerous rail and highway bridges that cross it.