For computing the SCS Curve Number, is there any guidance on what format the data fields in shapefiles for impervious, cover density, and soil groups should be? I’ve compared my attribute tables with those in Lesson 7 and see no difference. From what I see, Impervious field is in decimal format (0.05 for 5%), Cov_den is in text/string format, and Soil is a text string e.g. B Desert Brush or C45%D55% Desert Brush. Are there restrictions on what’s in the field (max and min values)? trying to determine why my shapefiles will not work.
Good question. Those values are pretty specific to Pima County so if you aren’t using the formulas exactly shown in the GDS manual, you will likely get an error. For example, if you are using a category that isn’t listed in the Pima County classifications, you’ll probably get an error. I suggest that you would be better off developing your own system using rasters or shapfiles and a field calculator to generate a shapefile that has only curve numbers.