National Land Cover Data (NLCD)
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Step 1: Curve Number Generator method
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- Load the **Curve Number Generator** from the **Processing** toolbox.

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- Set the Extent to **Watershed** Layer.
- Set the name and path.
- Uncheck the other items.
- Click Run

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Step 2: Download the USGS data
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- Connect to the NLCD Land Cover data.

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- Repair the data Source

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- Select the layer and click OK.

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- Right click the Land Cover layer and click Export.

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- Fill the form and click OK.

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- Move the Land Cover layers to the **Manning's** group.

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- Copy the Style from the NLCD Layer.

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- Paste the Style to the Downloaded Layer.

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- Note the difference between the Curve Number Generator 2021 and the Land Cover NLCD Server 2024 data.

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Step 3: Review look-up tables
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Land cover lookup table.
The full table is in the Excel Spreadsheet.

- Modify these table per local **Flood Control Specifications.**

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- Manning's roughness for shallow overland flow developed for FLO-2D. (source: FCDMC)

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Step 4: Run NLCD Land Cover Roughness processor 
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- Open the **Processing Toolbox**.

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- Open the Existing Processor Model.

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- Double click the Reclassify module.

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- This table may be modified to reflect local Manning’s n value standards. 

.. note:: Every raster value must be explicitly assigned a corresponding Manning’s n value. 
  If one value is omitted, the processor may fail during roughness surface generation.

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.. hint:: Processor models are script-based. Editing the table in a plain text editor is often 
  faster than using the graphical interface.

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- Run the processor model to reclassify the land cover data as roughness data.

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Step 5: Interpolate Manning's n to the Grid 
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- Run the Roughness Raster processor.

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- Move the Land Cover and Roughness layers to the Manning's n group.

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