There is something wrong in your rivulets bitmap. Start again from scratch. Open Vue, create a terrain, give it a better resolution. Don't add any thing else. Create the rivulets bitmap in your paint program, at least in 512x512 but better in 1024x1024 or highter. Use a middle gray background and less or more light grey to white for the rivulets. When you paint the rivulets, consider the altitude of your terrain. best is you have a copy of it beside to see where you paint. When you apply this function in the material distribution, do NOT scale it there, but in the Distribution Function window under "PICTURE SCALE" (x and y). Do not use Influence of environment, uncheck it. Do not use a "Peak" for the material distribution, but some softer function. Does it work now? You will to have try several times before you get it right. Guitta