Carneros Watershed: Erosivity

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  • [[Media:|PDF file - for printing]]
  • [[Media:|JPG file]]


  • Data Source: USGS, 1/3 arc second, Digital Elevation Model: See Carneros Watershed: Map of Elevation
  • Data analysis: ArcMap
  • Map produced by: Kathy
  • Coordinate system: UTM Zone 10
  • Datum: NAD 83

Processing Steps

1.Download SSURGO data (fastest is from USDA GSG)

2.Receive zip file of zip files, each one like

3.Extract, and open basic shapefile of map-units (MU): soilmu_a_ca069.shp in Arc 4.Can't read tables in this zip, because need special MS Access Template

5.Download Access template from

6.Open template in Access; Enable Macros; and it should prompt for location of your tables

7.Wait a few minutes while Access imports your tables

8.Create some custom queries in Access to extract some kind of Kf for each map unit

8a. Review the SSURGO data model:

8b. Each MapUnit contains several Components, each containing several Horizons.

8c. First query selects the surface horizons: 8c1 - it joins tables muaggatt+component+chorizon, 8c2 - joining on keys mukey and cokey 8c3 - selecting only horizons whose hzdept_r is 0 (i.e. surface horizons) 8c4 - includes the kffact (Kf-factor) and comppct_r (Percentage of map-unit occupied by Component) fields that will be used below

8d. Second query takes first as input, and is a MakeTable query, making the table that will be used in Arc 8d1 - computes an expression 'fredkf: Sum([comppct_r]*[kffact]/100)' 8d2 - it is a Summation query, and the Summation is done on the fredkf field (above) 8d3 - the other two fields are musym and mukey, and they are GroupBy fields

8e. RUn the second query; it will make a table

8f. Export the table to DBF format (one way of getting it to Arc)

9.Back in Arc, add the DBF table as a layer

10.Join the soilmu_a_ca069.shp layer to the DBF layer, using the mukey

11.Change the soilmu_a_ca069.shp symbology to display quantitative based on the fredkf field