The Gravitational Process Path (GPP) model can be used to simulate the process path and run-out area of gravitational processes based on a digital terrain model (DTM). The conceptual model combines several components (process path, run-out length, sink filling and material deposition) to simulate the movement of a mass point from an initiation site to the deposition area. For each component several modeling approaches are provided, which makes the tool configurable for different processes such as rockfall, debris flows or snow avalanches.
The tool can be applied to regional-scale studies such as natural hazard susceptibility mapping but also contains components for scenario-based modeling of single events. Both the modeling approaches and precursor implementations of the tool have proven their applicability in numerous studies, also including geomorphological research questions such as the delineation of sediment cascades or the study of process connectivity.
Please provide the reference cited below in your work if you are using the GPP model.
Addendum:
The article is not clear about the way the impact on the slope is exactly modelled when the 'Shadow Angle' or '1-parameter' friction model is used. Besides the 'Threshold Angle Free Fall' criterion to determine the location of the first impact, it is also assumed that the particle must leave its own release area (given by its ID) in order to impact. This is actually a conceptual design, taking into account that free fall usually occurs in steep rock faces (release areas), and the fact, that such rockfaces are not characterised very well in a 2.5D elevation model. You can work around that conceptual design by providing a grid describing the 'slope impact areas' as input. Using such a grid disables the 'Threshold Angle Free Fall' parameter.
New in version 1.1:
Since version 1.1 the model supports the monitoring of potentially endangered objects like infrastructure and reports from which process paths and release areas objects might be hit. In order to enable this backtracking, the user must provide an 'Objects' grid as input. The grid can be used to store different types or classes of objects, using one-hot categorical data encoding for each object class, i.e. powers of ten: 1, 10, 100, 1000, etc. (all other cells NoData). The 'Endangered Objects' output grid will contain combinations of these numbers if several different classes were hit from a grid cell, allowing to analyse which object classes might be hit from which location.
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | DEM | Grid, input | DEM | Digital elevation model [m]. | - |
| Release Areas | Grid, input | RELEASE_AREAS | Release areas encoded by unique integer IDs, all other cells NoData [-]. | - |
| Material (*) | Grid, input, optional | MATERIAL | Height of material available in each start cell [m]. | - |
| Friction Angle (*) | Grid, input, optional | FRICTION_ANGLE_GRID | Spatially distributed friction angles [degree]. Optionally used with the Geometric Gradient, Fahrboeschung's angle or Shadow Angle friction model. | - |
| Slope Impact Areas (*) | Grid, input, optional | SLOPE_IMPACT_GRID | Slope impact grid, impact areas encoded with valid values, all other NoData. Optionally used with the Shadow Angle or the 1-parameter friction model. | - |
| Friction Parameter Mu (*) | Grid, input, optional | FRICTION_MU_GRID | Spatially distributed friction parameter mu [-], optionally used with the 1-parameter friction model or the PCM Model. | - |
| Mass to Drag Ratio (*) | Grid, input, optional | FRICTION_MASS_TO_DRAG_GRID | Spatially distributed mass to drag ratio [m], optionally used with the PCM Model. | - |
| Objects (*) | Grid, input, optional | OBJECTS | Potentially endangered objects (like infrastructure) to monitor, using one-hot categorical data encoding for each object class [1, 10, 100, 1000, ...]. | - |
| Output | Process Area | Grid, output | PROCESS_AREA | Delineated process area with encoded transition frequencies [count]. | - |
| Deposition (*) | Grid, output, optional | DEPOSITION | Height of material deposited in each cell [m]. Optional output in case a grid with material amounts is provided as input. | - |
| Maximum Velocity (*) | Grid, output, optional | MAX_VELOCITY | Maximum velocity observed in each cell [m/s]. Optional output of the 1-parameter friction model and the PCM Model. | - |
| Stopping Positions (*) | Grid, output, optional | STOP_POSITIONS | Stopping positions, showing cells in which the run-out length has been reached [count]. | - |
| Endangered Objects (*) | Grid, output, optional | ENDANGERED | Endangered objects, showing cells from which objects were hit. Cell values indicate which object classes were hit [combination of object classes]. Optional output in case a grid with potentially endangered objects is provided as input. | - |
| Options | Grid System | Grid system | PARAMETERS_GRID_SYSTEM | - | - |
| Model | Choice | PROCESS_PATH_MODEL | Choose a process path model. | Available Choices:
[0] Maximum Slope
[1] Random Walk
Default: 1 |
| Slope Threshold | Floating point | RW_SLOPE_THRES | In case the local slope is greater as this threshold [degree], no lateral spreading is modeled. | Minimum: 0.001000
Maximum: 90.000000
Default: 40.000000 |
| Exponent | Floating point | RW_EXPONENT | The exponent [-] is controlling the amount of lateral spreading in case the local slope is in between zero and the slope threshold. | Minimum: 1.000000
Default: 2.000000 |
| Persistence Factor | Floating point | RW_PERSISTENCE | Factor [-] used as weight for the current flow direction. A higher factor reduces abrupt changes in flow direction. | Minimum: 1.000000
Default: 1.500000 |
| Iterations | Integer | GPP_ITERATIONS | The number of model runs from each start cell [-]. | Minimum: 1
Default: 1000 |
| Processing Order | Choice | GPP_PROCESSING_ORDER | Choose the processing order. | Available Choices:
[0] RAs in Sequence
[1] RAs in Sequence per Iteration
[2] RAs in Parallel per Iteration
Default: 2 |
| Seed Value | Integer | GPP_SEED | The seed value used to initialize the pseudo-random number generator. A value of 1 will initialize the generator with the current time, higher numbers will always produce the same succession of values for each seed value [-]. | Minimum: 1
Default: 1 |
| Model | Choice | FRICTION_MODEL | Choose a friction model. | Available Choices:
[0] None
[1] Geometric Gradient (Heim 1932)
[2] Fahrboeschung Principle (Heim 1932)
[3] Shadow Angle (Evans & Hungr 1988)
[4] 1-parameter friction model (Scheidegger 1975)
[5] PCM Model (Perla et al. 1980)
Default: 0 |
| Threshold Angle Free Fall | Floating point | FRICTION_THRES_FREE_FALL | The minimum slope angle [degree] between start cell and current cell for modeling free fall with the Shadow Angle or the 1-parameter friction model. | Minimum: 0.000000
Default: 60.000000 |
| Method Impact | Choice | FRICTION_METHOD_IMPACT | Choose the velocity calculation on slope impact with the 1-parameter friction model. | Available Choices:
[0] Energy Reduction (Scheidegger 1975)
[1] Preserved Component of Velocity (Kirkby & Statham 1975)
Default: 0 |
| Reduction | Floating point | FRICTION_IMPACT_REDUCTION | The energy reduction [%] on slope impact with the 1-parameter friction model. | Minimum: 0.000000
Maximum: 100.000000
Default: 75.000000 |
| Friction Angle | Floating point | FRICTION_ANGLE | Friction angle [degree] used as Geometric Gradient, Fahrboeschung's angle or Shadow Angle. | Minimum: 0.000000
Maximum: 90.000000
Default: 30.000000 |
| Mu | Floating point | FRICTION_MU | The (constant) friction parameter mu [-] used with the 1-parameter friction model or the PCM Model. | Minimum: 0.000000
Default: 0.250000 |
| Mode of Motion | Choice | FRICTION_MODE_OF_MOTION | Choose the mode of motion on hillslope with the 1-parameter friction model. | Available Choices:
[0] Sliding
[1] Rolling
Default: 0 |
| Mass to Drag Ratio | Floating point | FRICTION_MASS_TO_DRAG | The (constant) mass to drag ratio [m] used with the PCM Model. | Minimum: 0.000000
Default: 200.000000 |
| Initial Velocity | Floating point | FRICTION_INIT_VELOCITY | The initial velocity [m/s] used with the PCM Model. | Minimum: 0.000000
Default: 1.000000 |
| Model | Choice | DEPOSITION_MODEL | Choose a deposition model. | Available Choices:
[0] None
[1] On Stop
[2] Slope & On Stop
[3] Velocity & On Stop
[4] min(Slope,Velocity) & On Stop
Default: 0 |
| Initial Deposition on Stop | Floating point | DEPOSITION_INITIAL | The percentage of available material (per run) initially deposited at the stopping position [%]. | Minimum: 0.000000
Maximum: 100.000000
Default: 20.000000 |
| Slope Threshold | Floating point | DEPOSITION_SLOPE_THRES | The slope angle below which the deposition of material is starting [degree]. | Minimum: 0.000000
Maximum: 90.000000
Default: 20.000000 |
| Velocity Threshold | Floating point | DEPOSITION_VELOCITY_THRES | The velocity below which the deposition of material is starting [m/s]. | Minimum: 0.000000
Default: 15.000000 |
| Maximum Deposition along Path | Floating point | DEPOSITION_MAX | The percentage of available material (per run) which is deposited at most (slope or velocity equal zero) [%]. | Minimum: 0.000000
Maximum: 100.000000
Default: 20.000000 |
| Minimum Path Length | Floating point | DEPOSITION_MIN_PATH | The minimum path length which has to be reached before material deposition is enabled [m]. | Minimum: 0.000000
Default: 100.000000 |
| Minimum Slope | Floating point | SINK_MIN_SLOPE | The minimum slope to preserve on sink filling [degree]. | Minimum: 0.000000
Maximum: 90.000000
Default: 2.500000 |
| (*) optional |