SAGA-GIS Tool Library Documentation (v7.7.0)

Tool Gravitational Process Path Model

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.


References


Parameters

 NameTypeIdentifierDescriptionConstraints
InputDEMGrid, inputDEMDigital elevation model [m].-
Release AreasGrid, inputRELEASE_AREASRelease areas encoded by unique integer IDs, all other cells NoData [-].-
Material (*)Grid, input, optionalMATERIALHeight of material available in each start cell [m].-
Friction Angle (*)Grid, input, optionalFRICTION_ANGLE_GRIDSpatially distributed friction angles [degree]. Optionally used with the Geometric Gradient, Fahrboeschung's angle or Shadow Angle friction model.-
Slope Impact Areas (*)Grid, input, optionalSLOPE_IMPACT_GRIDSlope 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, optionalFRICTION_MU_GRIDSpatially distributed friction parameter mu [-], optionally used with the 1-parameter friction model or the PCM Model.-
Mass to Drag Ratio (*)Grid, input, optionalFRICTION_MASS_TO_DRAG_GRIDSpatially distributed mass to drag ratio [m], optionally used with the PCM Model.-
OutputProcess AreaGrid, outputPROCESS_AREADelineated process area with encoded transition frequencies [count].-
Deposition (*)Grid, output, optionalDEPOSITIONHeight of material deposited in each cell [m]. Optional output in case a grid with material amounts is provided as input.-
Maximum Velocity (*)Grid, output, optionalMAX_VELOCITYMaximum velocity observed in each cell [m/s]. Optional output of the 1-parameter friction model and the PCM Model.-
Stopping Positions (*)Grid, output, optionalSTOP_POSITIONSStopping positions, showing cells in which the run-out length has been reached [count].-
OptionsGrid SystemGrid systemPARAMETERS_GRID_SYSTEM--
ModelChoicePROCESS_PATH_MODELChoose a process path model.Available Choices:
[0] Maximum Slope
[1] Random Walk
Default: 1
Slope ThresholdFloating pointRW_SLOPE_THRESIn case the local slope is greater as this threshold [degree], no lateral spreading is modeled.Minimum: 0.001000
Maximum: 90.000000
Default: 40.000000
ExponentFloating pointRW_EXPONENTThe 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 FactorFloating pointRW_PERSISTENCEFactor [-] used as weight for the current flow direction. A higher factor reduces abrupt changes in flow direction.Minimum: 1.000000
Default: 1.500000
IterationsIntegerGPP_ITERATIONSThe number of model runs from each start cell [-].Minimum: 1
Default: 1000
Processing OrderChoiceGPP_PROCESSING_ORDERChoose the processing order.Available Choices:
[0] RAs in Sequence
[1] RAs in Sequence per Iteration
[2] RAs in Parallel per Iteration
Default: 2
Seed ValueIntegerGPP_SEEDThe 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
ModelChoiceFRICTION_MODELChoose 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 FallFloating pointFRICTION_THRES_FREE_FALLThe 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 ImpactChoiceFRICTION_METHOD_IMPACTChoose 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
ReductionFloating pointFRICTION_IMPACT_REDUCTIONThe energy reduction [%] on slope impact with the 1-parameter friction model.Minimum: 0.000000
Maximum: 100.000000
Default: 75.000000
Friction AngleFloating pointFRICTION_ANGLEFriction angle [degree] used as Geometric Gradient, Fahrboeschung's angle or Shadow Angle.Minimum: 0.000000
Maximum: 90.000000
Default: 30.000000
MuFloating pointFRICTION_MUThe (constant) friction parameter mu [-] used with the 1-parameter friction model or the PCM Model.Minimum: 0.000000
Default: 0.250000
Mode of MotionChoiceFRICTION_MODE_OF_MOTIONChoose the mode of motion on hillslope with the 1-parameter friction model.Available Choices:
[0] Sliding
[1] Rolling
Default: 0
Mass to Drag RatioFloating pointFRICTION_MASS_TO_DRAGThe (constant) mass to drag ratio [m] used with the PCM Model.Minimum: 0.000000
Default: 200.000000
Initial VelocityFloating pointFRICTION_INIT_VELOCITYThe initial velocity [m/s] used with the PCM Model.Minimum: 0.000000
Default: 1.000000
ModelChoiceDEPOSITION_MODELChoose 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 StopFloating pointDEPOSITION_INITIALThe percentage of available material (per run) initially deposited at the stopping position [%].Minimum: 0.000000
Maximum: 100.000000
Default: 20.000000
Slope ThresholdFloating pointDEPOSITION_SLOPE_THRESThe slope angle below which the deposition of material is starting [degree].Minimum: 0.000000
Maximum: 90.000000
Default: 20.000000
Velocity ThresholdFloating pointDEPOSITION_VELOCITY_THRESThe velocity below which the deposition of material is starting [m/s].Minimum: 0.000000
Default: 15.000000
Maximum Deposition along PathFloating pointDEPOSITION_MAXThe 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 LengthFloating pointDEPOSITION_MIN_PATHThe minimum path length which has to be reached before material deposition is enabled [m].Minimum: 0.000000
Default: 100.000000
Minimum SlopeFloating pointSINK_MIN_SLOPEThe minimum slope to preserve on sink filling [degree].Minimum: 0.000000
Maximum: 90.000000
Default: 2.500000
(*) optional

Command-line

Usage: saga_cmd sim_geomorphology 0 [-DEM <str>] [-RELEASE_AREAS <str>] [-MATERIAL <str>] [-FRICTION_ANGLE_GRID <str>] [-SLOPE_IMPACT_GRID <str>] [-FRICTION_MU_GRID <str>] [-FRICTION_MASS_TO_DRAG_GRID <str>] [-PROCESS_AREA <str>] [-DEPOSITION <str>] [-MAX_VELOCITY <str>] [-STOP_POSITIONS <str>] [-PROCESS_PATH_MODEL <str>] [-RW_SLOPE_THRES <double>] [-RW_EXPONENT <double>] [-RW_PERSISTENCE <double>] [-GPP_ITERATIONS <num>] [-GPP_PROCESSING_ORDER <str>] [-GPP_SEED <num>] [-FRICTION_MODEL <str>] [-FRICTION_THRES_FREE_FALL <double>] [-FRICTION_METHOD_IMPACT <str>] [-FRICTION_IMPACT_REDUCTION <double>] [-FRICTION_ANGLE <double>] [-FRICTION_MU <double>] [-FRICTION_MODE_OF_MOTION <str>] [-FRICTION_MASS_TO_DRAG <double>] [-FRICTION_INIT_VELOCITY <double>] [-DEPOSITION_MODEL <str>] [-DEPOSITION_INITIAL <double>] [-DEPOSITION_SLOPE_THRES <double>] [-DEPOSITION_VELOCITY_THRES <double>] [-DEPOSITION_MAX <double>] [-DEPOSITION_MIN_PATH <double>] [-SINK_MIN_SLOPE <double>]
  -DEM:<str>                         	DEM
	Grid, input
  -RELEASE_AREAS:<str>               	Release Areas
	Grid, input
  -MATERIAL:<str>                    	Material
	Grid, input, optional
  -FRICTION_ANGLE_GRID:<str>         	Friction Angle
	Grid, input, optional
  -SLOPE_IMPACT_GRID:<str>           	Slope Impact Areas
	Grid, input, optional
  -FRICTION_MU_GRID:<str>            	Friction Parameter Mu
	Grid, input, optional
  -FRICTION_MASS_TO_DRAG_GRID:<str>  	Mass to Drag Ratio
	Grid, input, optional
  -PROCESS_AREA:<str>                	Process Area
	Grid, output
  -DEPOSITION:<str>                  	Deposition
	Grid, output, optional
  -MAX_VELOCITY:<str>                	Maximum Velocity
	Grid, output, optional
  -STOP_POSITIONS:<str>              	Stopping Positions
	Grid, output, optional
  -PROCESS_PATH_MODEL:<str>          	Model
	Choice
	Available Choices:
	[0] Maximum Slope
	[1] Random Walk
	Default: 1
  -RW_SLOPE_THRES:<double>           	Slope Threshold
	Floating point
	Minimum: 0.001000
	Maximum: 90.000000
	Default: 40.000000
  -RW_EXPONENT:<double>              	Exponent
	Floating point
	Minimum: 1.000000
	Default: 2.000000
  -RW_PERSISTENCE:<double>           	Persistence Factor
	Floating point
	Minimum: 1.000000
	Default: 1.500000
  -GPP_ITERATIONS:<num>              	Iterations
	Integer
	Minimum: 1
	Default: 1000
  -GPP_PROCESSING_ORDER:<str>        	Processing Order
	Choice
	Available Choices:
	[0] RAs in Sequence
	[1] RAs in Sequence per Iteration
	[2] RAs in Parallel per Iteration
	Default: 2
  -GPP_SEED:<num>                    	Seed Value
	Integer
	Minimum: 1
	Default: 1
  -FRICTION_MODEL:<str>              	Model
	Choice
	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
  -FRICTION_THRES_FREE_FALL:<double> 	Threshold Angle Free Fall
	Floating point
	Minimum: 0.000000
	Default: 60.000000
  -FRICTION_METHOD_IMPACT:<str>      	Method Impact
	Choice
	Available Choices:
	[0] Energy Reduction (Scheidegger 1975)
	[1] Preserved Component of Velocity (Kirkby & Statham 1975)
	Default: 0
  -FRICTION_IMPACT_REDUCTION:<double>	Reduction
	Floating point
	Minimum: 0.000000
	Maximum: 100.000000
	Default: 75.000000
  -FRICTION_ANGLE:<double>           	Friction Angle
	Floating point
	Minimum: 0.000000
	Maximum: 90.000000
	Default: 30.000000
  -FRICTION_MU:<double>              	Mu
	Floating point
	Minimum: 0.000000
	Default: 0.250000
  -FRICTION_MODE_OF_MOTION:<str>     	Mode of Motion
	Choice
	Available Choices:
	[0] Sliding
	[1] Rolling
	Default: 0
  -FRICTION_MASS_TO_DRAG:<double>    	Mass to Drag Ratio
	Floating point
	Minimum: 0.000000
	Default: 200.000000
  -FRICTION_INIT_VELOCITY:<double>   	Initial Velocity
	Floating point
	Minimum: 0.000000
	Default: 1.000000
  -DEPOSITION_MODEL:<str>            	Model
	Choice
	Available Choices:
	[0] None
	[1] On Stop
	[2] Slope & On Stop
	[3] Velocity & On Stop
	[4] min(Slope,Velocity) & On Stop
	Default: 0
  -DEPOSITION_INITIAL:<double>       	Initial Deposition on Stop
	Floating point
	Minimum: 0.000000
	Maximum: 100.000000
	Default: 20.000000
  -DEPOSITION_SLOPE_THRES:<double>   	Slope Threshold
	Floating point
	Minimum: 0.000000
	Maximum: 90.000000
	Default: 20.000000
  -DEPOSITION_VELOCITY_THRES:<double>	Velocity Threshold
	Floating point
	Minimum: 0.000000
	Default: 15.000000
  -DEPOSITION_MAX:<double>           	Maximum Deposition along Path
	Floating point
	Minimum: 0.000000
	Maximum: 100.000000
	Default: 20.000000
  -DEPOSITION_MIN_PATH:<double>      	Minimum Path Length
	Floating point
	Minimum: 0.000000
	Default: 100.000000
  -SINK_MIN_SLOPE:<double>           	Minimum Slope
	Floating point
	Minimum: 0.000000
	Maximum: 90.000000
	Default: 2.500000