D-Infinity Avalanche Runout

Title  D-Infinity Avalanche Runout

Summary

Identifies an avalanche's affected area and the flow path length to each cell in that affacted area. All cells downslope from each source area cell, up to the point where the slope from the source to the affected area is less than a threshold angle called the Alpha Angle can be in the affected area. This tool uses the D-infinity multiple flow direction method for determining flow direction. This will likely cause very small amounts of flow to be dispersed to some downslope cells that might overstate the affected area, so a threshold proportion can be set to avoid this excess dispersion. The flow path length is the distance from the cell in question to the source cell that has the highest angle.

All points downslope from the source area are potentially in the affected area, but not beyond a point where the slope from the source to the affected area is less than a threshold angle called the Alpha Angle.


Usage

Command Prompt Syntax:

mpiexec -n <number of processes> DinfAvalanche -ang <angfile> -fel <felfile> -ass <assfile> -rz <rzfile> -dfs <dfsfile> [ -thresh ] [ -alpha ] [ -direct]

angfile: Input Dinf flow direction grid

felfile: Input pit filled elevation grid

assfile: Input avalanche source site grid

rzfile: Output avalanche runout zone grid. The values output are actually the alpha angles from the

source zone to each grid cell. All will be greater than the input alpha threshold angle.

dfsfile: Output distance down (path distance) grid

thresh: Input proportion threshold

alpha: Input angle threshold

direct: Flag to indicate whether distance is measured along flow path (default) or as a straight line

from source to grid cell (if direct is given). Distances are horizontal distances in both cases.


Syntax

DInfAvalancheRunout (Input_Pit_Filled_Elevation_Grid, Input_D-Infinity_Flow_Direction_Grid, Input_Avalanche_Source_Site_Grid, Input_Proportion_Threshold, Input_Alpha_Angle_Threshold, Path_Distance_Method, Input_Number_of_Processes, Output_Runout_Zone_Grid, Output_Path_Distance_Grid)

Parameter Explanation Data Type
Input_Pit_Filled_Elevation_Grid Dialog Reference

A grid of elevation values. This is usually the output of the "Fill Pits" tool, in which case it is elevations with pits removed. Pits are low elevation areas in digital elevation models (DEMs) that are completely surrounded by higher terrain. They are generally taken to be artifacts that interfere with the processing of flow across DEMs, so are removed by raising their elevation to the point where they just drain. This step is not essential if you have reason to believe that the pits in your DEM are real.

 Raster Layer
Input_D-Infinity_Flow_Direction_Grid Dialog Reference

A grid giving flow directions by the D-Infinity method. This is usually the output of the D-Infinity Flow Directions tool. Flow direction is measured in radians, counter clockwise from east. The algorithm is described in Tarboton, D. G., (1997), "A New Method for the Determination of Flow Directions and Contributing Areas in Grid Digital Elevation Models," Water Resources Research, 33(2): 309-319

 Raster Layer
Input_Avalanche_Source_Site_Grid Dialog Reference

This is a grid of source areas for snow avalanches that are commonly identified manually using a mix of experience and visual interpretation of maps. Avalanche source sites are to be input as a short integer grid (name suffix *ass, e.g. demass) comprised of positive values where avalanches may be triggered and 0 values elsewhere.

 Raster Layer
Input_Proportion_Threshold Dialog Reference

This value is a threshold proportion that is used to limit the disperson of flow caused by using the D-infinity multiple flow direction method for determining flow direction. The D-infinity multiple flow direction method often causes very small amounts of flow to be dispersed to some downslope cells that might overstate the affected area, so a threshold proportion can be set to avoid this excess dispersion.

 Double
Input_Alpha_Angle_Threshold Dialog Reference

This value is the threshold angle, called the Alpha Angle, that is used to determine which of the cells downslope from the source cells are in the affected area. Only the cells downslope from each source area cell, up to the point where the slope from the source to the affected area is less than a threshold angle are in the affected area.

 Double
Path_Distance_Method Dialog Reference

This option selects the method used to measure the distance used to calculate the slope angle. The Flow Path option measures it along the flow path, where the Straight Line option causes the slope to be measure along the straight line distance from the source cell to the evaluation cell.

 String
Input_Number_of_Processes Dialog Reference

This input indicates the number of stripes that the domain will be divided into and the number of MPI parallel processes that will be spawned to evaluate each piece of the domain.

 Long
Output_Runout_Zone_Grid Dialog Reference

This grid Identifies the avalanche's runout zone (affected area) using a runout zone indicator with value 0 to indicate that this grid cell is not in the runout zone and value > 0 to indicate that this grid cell is in the runout zone. Since there may be information in the angle to the associated source site, this variable will be assigned the angle to the source site (in degrees).

 Raster Dataset
Output_Path_Distance_Grid Dialog Reference

This is a grid of the flow distance from the source site that has the highest angle to each cell.

 Raster Dataset

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