THREE-DIMENSIONAL COMPUTER SIMULATION OF DRAINAGE NETWORK DEVELOPMENT

We have developed a Java encoded finite-difference model of drainage network development that operates in a web environment. The model uses simple assumptions for material removal by both slope and stream processes, and a geometrical definition for streams. The starting conditions assume base level is defined along one edge of the array. The introduction of a certain (adjustable) amount of randomness to the erodibility at each node is critical to the development of drainage networks by headward erosion. A small number of adjustable parameters may be set by the user to examine their effect on network development. After each cycle of sediment redistribution (which results in a new array of elevations) the stream network is extended by examination of the geometric conditions at each point in the array, and a new erosion cycle is calculated. The program also determines stream order number for the links in the drainage network during each iteration and the results of elevation; stream position and stream order are displayed in a three-dimensional graphic. The graphic can be examined from various positions and magnifications using simple mouse commands. It is possible to introduce both geologic and tectonic elements (structures, erodibility differences for rock units and uplift, etc.) by setting initial conditions for erodibility as a function of z(x,y) and adjusting z along structural elements to simulate (for example) uplift along a fault. However, if geologic conditions vary temporally then the stream network must adjust through stream piracy, which is accommodated by an algorithm that reroutes drainages along the steepest course and abandons channels as appropriate. The speed of calculation for a 200x200 array is fast enough that the graphical output is movie-like on a GHz level computer.