Mannings N from Land Use Raster Tool

Mannings N from Land Use Raster

The Mannings N from Land Use Raster tool is used to populate the spatial attributes for the Mannin's N roughness coefficient at the sea flow. A new dataset is created from NLCD, C-CAP, or other land use raster.

The tool will combine 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 center 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 Manning's N roughness value is computed taking a weighted average of all the pixel values. If a node lies outside of the extents of the specified raster object, the default value is used as the Manning's N roughness value at the node.

The tool has the following options:

Input Parameters

• Input landuse raster – This is a required input parameter. Specify which raster in the project to use when determining the Manning's N roughness values.
• 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 forC-CAP can be found here and down below.
  • "Other" – Sets the landuse raster type to use a table of values provided by the user.
• Target grid – This is a required input parameter. Specify which grid/mesh the Manning's N roughness dataset will be created for.
• Landuse to Mannings N mapping table The Select File... button allows a table file to be selected for the "Other" landuse raster type. Its full file name will appear on the box to its right. This must be a CSV file with the following columns of data Code, Description, Manning's N. See the example NLCD and CCAP tables below.
• Default Mannings N option – Set the default value to use for the Manning's N roughness values 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.
  • "Constant" – Sets a constant value to be the default for Mannings N.
    • Default Mannings N value – Sets a constant value to be the default for Mannings N.
  • "Dataset" – Sets a dataset to be the default for Mannings N.
    • Default Mannings N dataset – Select a dataset to be used as the default for Mannings N.
• Subset mask dataset (optional) – 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 Mannings N dataset – Enter the name for the new Mannings N dataset

If the landuse type is chosen as NLCD or C-CAP, the 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.

Mannings Roughness NLCD Mapping Table

Mannings Roughness NLCD Values

Code	Description	Mannings
0	Background	0.025
1	Unclassified	0.025
11	Open Water	0.02
12	Perennial Ice/Snow	0.01
21	Developed Open Space	0.02
22	Developed Low Intensity	0.05
23	Developed Medium Intensity	0.1
24	Developed High Intensity	0.15
31	Barren Land (Rock/Sand/Clay)	0.09
41	Deciduous Forest	0.1
42	Evergreen Forest	0.11
43	Mixed Forest	0.1
51	Dwarf Scrub	0.04
52	Shrub/Scrub	0.05
71	Grassland/Herbaceous	0.034
72	Sedge/Herbaceous	0.03
73	Lichens	0.027
74	Moss	0.025
81	Pasture/Hay	0.033
82	Cultivated Crops	0.037
90	Woody Wetlands	0.1
95	Emergent Herbaceous Wetlands	0.045
91	Palustrine Forested Wetland	0.1
92	Palustrine Scrub/Shrub Wetland	0.048
93	Estuarine Forested Wetland	0.1
94	Estuarine Scrub/Shrub Wetland	0.048
96	Palustrine Emergent Wetland (Persistent)	0.045
97	Estuarine Emergent Wetland	0.045
98	Palustrine Aquatic Bed	0.015
99	Estuarine Aquatic Bed	0.015

Mannings Roughness CCAP Mapping Table

Mannings Roughness CCAP Values

Code	Description	Roughness
0	Background	0.025
1	Unclassified	0.025
2	Developed High Intensity	0.15
3	Developed Medium Intensity	0.1
4	Developed Low Intensity	0.05
5	Developed Open Space	0.02
6	Cultivated Crops	0.037
7	Pasture/Hay	0.033
8	Grassland/Herbaceous	0.034
9	Deciduous Forest	0.1
10	Evergreen Forest	0.11
11	Mixed Forest	0.1
12	Scrub/Shrub	0.05
13	Palustrine Forested Wetland	0.1
14	Palustrine Scrub/Shrub Wetland	0.048
15	Palustrine Emergent Wetland (Persistent)	0.045
16	Estuarine Forested Wetland	0.1
17	Estuarine Scrub/Shrub Wetland	0.048
18	Estuarine Emergent Wetland	0.045
19	Unconsolidated Shore	0.03
20	Barren Land	0.09
21	Open Water	0.02
22	Palustrine Aquatic Bed	0.015
23	Estuarine Aquatic Bed	0.015
24	Perennial Ice/Snow	0.01
25	Tundra	0.03