The core of the program is an efficient second-order numerical solution of the depth-averaged equations of motion (the shallow water equations) for granular flows. Flow heights and velocities are calculated on three-dimensional digital terrain models. Single or multiple block-release (initiation) areas are easily specified using GIS-type drawing tools; alternatively an input hydrograph can be used to specify the discharge as a function of time. Users are provided with useful overview information related to simulations, such as release area (mean slope, total volume), flow behavior (max. flow velocities and heights) and stopping behaviour (mass flux). Maps and remote-sensing imagery can be superimposed on the terrain models to aid the specification of input conditions and facilitate the calibration of the model with historical event data.
The numerical model uses the two-parameter Voellmy relation to describe the frictional behaviour of the flowing debris. This relation has been shown by others to be useful for modeling the runout of debris flows and other flowing landslides. To calibrate the RAMMS Voellmy model, users generally simulate well-documented historical events and determine the best-fit parameter sets which can be used in subsequent analyses. Additional features include the ability to export the results to GIS as well as the ability to modify the topography to include deposits from a previously-modelled surge or to include constructional migitation measures (e.g. retention or deflection dams), thereby allowing users to evaluate the influence of previous flows or mitigation measures, respectively, on the runout of future debris flows.