Chezy Friction Tool

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

Related Tools

• Chezy Friction
• Directional Roughness
• Landuse Raster to Mannings N
• Quadratic Friction