This applet displays fractal drainage patterns. Begin exploring by using the "Preset" choice at the bottom - and the "Restart" button below it - to see some of the possible configurations. Configurable parameters include a number of manual colour-map controls (on the left) - and six main parameters of the fractal drainage system (on the right). Take care if using the other controls on the right. They are usually very sensitive. The model is a cellular automaton, based on the [Moore neighbourhood]. Toroidial boundary constraints are appled, so the images will tesselate seamlessly. Optionally, a bumpmap technique is employed to give the images a sense of depth. The controls on the right are described - using the metaphor of erosion of landscape caused by rain - as follows: Add rate: rate of rain fall on high ground; Seep rate: rate at which liquid seeps into the land; Flow rate: speed of liquid flow; Log resistance: quantifies the resistance the land puts up to the corrosive force of the liquid; Ground rising: the ground constantly rises to replace material lost through erosion; Upper threshold: height above which rain falls; Lower threshold: height below which water is removed. There's an introduction to fractal drainage patterns here, and an explanation of the modelling technique used in this applet here.