Template:Chezy Friction

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Chezy Friction

The Chezy Friction tool creates a new scalar dataset that represents the spatially varying Chezy friction coefficient at the sea floor. The tool is built to specifically support NLCD and C-CAP rasters with built in mapping values, but can be applied with custom rasters or custom mapping as well. Tables containing the default parameter values for these raster types are included below.

The tool combines values from the pixels of the raster object specified as a parameter for the tool. For each node in the geometry, the "area of influence" is computed for the node. The area of influence is a square with the node at the centroid of the square. The size of the square is the average length of the edges connected to the node in the target grid. All of the raster values within the area of influence are extracted from the specified raster object. A composite Chezy friction value is computed taking a weighted average of all the pixel values. I a node lies outside of the extents of the specified raster object, the default value is used as the Chezy friction coefficient at the node.

Input Parameters

  • Input landuse raster – This is a required input parameter. Specify which raster in the project to use when determining the Chezy friction coefficients.
  • Landuse raster type – This is a required parameter. Specify what type of landuse raster to use.
    • "NLCD" – Sets the landuse raster type to National Land Cover Dataset (NLCD). A mapping table file for NLCD can be found here and down below.
    • "C-CAP" – Sets the landuse raster type to Coastal Change Analysis Program (C-CAP). A mapping table file for C-CAP can be found here and down below.
    • "Other" – Sets the landuse raster type to be set by the user. This adds an option to the dialog.
      • Landuse to Chezy friction mapping table – The Select File... button will allow a table file to be selected. The entire file name will be displayed in the text box to its right.
  • Target grid – This is a required input parameter. Specify which grid/mesh the canopy coefficient dataset will be created for.
  • Default Chezy friction option – Set the default value to use for the Chezy friction coefficient for nodes not lying inside the specified raster object. This can be set to "Constant" to use a constant value or set "Dataset" to select a dataset to use.
    • Default Chezy friction value – Enter the constant value to use as a default value.
    • Default Chezy friction dataset – Select a dataset to use as a default value.
  • Subset mask dataset – This optional option allows using a dataset as a subset mask. Nodes not marked as active in this dataset are assigned the default value.

Output Parameters

  • Output Chezy friction dataset – Enter the name for the new Chezy friction dataset.

If the landuse type is chosen as NLCD or C-CAP, the following default values below are used in the calculation. If there are different landuse raster types, or wishing to use values that differ from the defaults, specify the raster type as Custom and provide in CSV file with the desired values.

Chezy Friction NLCD Mapping Table

Chezy Friction NLCD Values
Code Description Friction
0 Background 60
1 Unclassified 60
11 Open Water 110
12 Perennial Ice/Snow 220
21 Developed Open Space 110
22 Developed Low Intensity 44
23 Developed Medium Intensity 22
24 Developed High Intensity 15
31 Barren Land (Rock/Sand/Clay) 24
41 Deciduous Forest 22
42 Evergreen Forest 20
43 Mixed Forest 22
51 Dwarf Scrub 55
52 Shrub/Scrub 44
71 Grassland/Herbaceous 64
72 Sedge/Herbaceous 73
73 Lichens 81
74 Moss 87
81 Pasture/Hay 66
82 Cultivated Crops 59
90 Woody Wetlands 22
95 Emergent Herbaceous Wetlands 48
91 Palustrine Forested Wetland 22
92 Palustrine Scrub/Shrub Wetland 45
93 Estuarine Forested Wetland 22
94 Estuarine Scrub/Shrub Wetland 45
96 Palustrine Emergent Wetland (Persistent) 48
97 Estuarine Emergent Wetland 48
98 Palustrine Aquatic Bed 150
99 Estuarine Aquatic Bed 150

Chezy Friction CCAP Mapping Table

Chezy Friction CCAP Values
Code Description Friction
0 Background 60
1 Unclassified 60
2 Developed High Intensity 15
3 Developed Medium Intensity 22
4 Developed Low Intensity 44
5 Developed Open Space 110
6 Cultivated Crops 59
7 Pasture/Hay 66
8 Grassland/Herbaceous 64
9 Deciduous Forest 22
10 Evergreen Forest 20
11 Mixed Forest 22
12 Scrub/Shrub 44
13 Palustrine Forested Wetland 22
14 Palustrine Scrub/Shrub Wetland 45
15 Palustrine Emergent Wetland (Persistent) 48
16 Estuarine Forested Wetland 22
17 Estuarine Scrub/Shrub Wetland 45
18 Estuarine Emergent Wetland 48
19 Unconsolidated Shore 60
20 Barren Land 24
21 Open Water 110
22 Palustrine Aquatic Bed 150
23 Estuarine Aquatic Bed 150
24 Perennial Ice/Snow 220
25 Tundra 60

Current Location in Toolbox

Datasets/Chezy Friction

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