Module 6 - Process Infiltration Data

Choose one method: Green-Ampt or SCS.

Green-Ampt Method

These agencies use Green-Ampt infiltration data with FLO-2D.

FCDMC, AZDOT, NVDOT, PCRFCD

Step 1: Run the Green Ampt Processor

  • Open the Infiltration Global button and check Green-Ampt and SCS CN.

  • Click OK

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  • Click Calculate Green Ampt button and set the radio buttons to SSURGO and OSM and use the Calculate buttons to get data.

  • Cancel the final process.

  • The data QC is performed in the next step.

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Step 2: Review the LandUse data

  • Open the attribute table of the LandUse layer.

  • Some polygons are categorized as Medium Density Residential with a 30 RTIMP.

  • Change these areas to Desert Landscape with 0 RTIMP.

  • Select the polygons with the polygon selector.

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  • Open the attribute table of the Soil layer.

  • Sort all of the pertinent columns by high low to verify that the values are within a reasonable range.

  • Spot checking polygons is also recommended to determine if the data is valid.

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  • Save the two layers to Module 6 folder and add them to the Infiltration Group.

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SCS Curve Number Method

Many agencies and clients use the SCS Curve Number (CN) method for rainfall-runoff modeling. In the Southwestern United States, Pima County Regional Flood Control District has developed a well-documented and regionally calibrated CN methodology that reflects desert hydrology and local soil conditions.

For reference, see the Pima County guidance:

PCHydro User Guide

Warning

This workshop demonstrates use of the Curve Number Generator tool in QGIS in combination with the Desert Curve Number lookup table from TR-55 to represent arid watershed conditions.

This workflow is provided for instructional purposes and does not reflect the recommended methodology for Pima County.

A more comprehensive QGIS-based procedure, incorporating updates to the FLO-2D Plugin, will be provided in a future tutorial.

Step 1: Run the Curve Number Generator

  • Load the Curve Number Generator from the Processing Toolbox.

  • Download the data only.

  • The final process will be completed after modifying the lookup table.

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Step 2: Review the CN lookup table

  • Modify the lookup table to apply the TR-55 Desert CN values.

  • The table may also be adjusted to reflect local agency standards where required.

  • The processing model can be adapted to connect to local servers if needed.

  • The plugin developer is responsive to enhancement requests.

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