Arc8.1 ArcMap Commands for Computing USPED using GIS



Given data 


grid:

	elevation
	Kfac
	Cfac
	(P)


constant: R=120, resolution=10


Computation

1. Enable Spatial Analyst Under View... Toolbars select Spatial Analyst
2. Calculate Slope and Aspect From the Spatial Analyst toolbar, select Surface Analysis... Slope Enter the elevation layer, select Degree, and enter output information.
Give the new theme name slope
From the Spatial Analyst toolbar, select Surface Analysis... Aspect Give the new theme name aspect
3. Raster Calculator From the Spatial Analyst toolbar, select Raster Calculator Build an expression: FlowAccumulation(FlowDirection([elevation])) Evaluate Make the new theme permanent and change the name to flowacc
Build an expression in the Raster Calculator Note: to get contributing area per unit width we multiply by cell area and divide by resolution leading to mult. by resolution below. The width unit [m] cancels out in steps 4-6 by computing the directional derivative leading to final erdep rate per cell in ton/acre.year, for 10m cell divide by 4046 to get ton/year eroded from a grid cell (!!! skip conversion to radians - multiplication by 0.01745 - in ArcGIS9.2 in all expressions below): (for prevailing rill erosion): Pow([flowacc] * resolution , 1.6) * Pow(Sin([slope] * 0.01745) , 1.3) Evaluate Make the new theme permanent and change the name to sflowtopo
(for prevailing sheet erosion): [flowacc] * resolution * Sin([slope] * 0.01745) Evaluate Make the new theme permanent and change the name to sflowtopo
Build an expression in the Raster Calculator: note: R changed from the original 280 to R=120 (Oct 28, 2008) [sflowtopo] * [kfac] * [cfac] * 120 * Cos((([aspect] * (-1)) + 450) * .01745) Evaluate Make the new theme permanent and change the name to qsx
Build an expression in the Raster Calculator: [sflowtopo] * [kfac] * [cfac] * 120 * Sin((([aspect] * (-1)) + 450) * .01745) Evaluate Make the new theme permanent and change the name to qsy
4. Select qsx in the Spatial Analysis Toolbar Select Surface Analysis... Slope Give the new theme name qsx_slope Select Surface Analysis... Aspect Give the new theme name qsx_aspect
5. Select qsy in the Spatial Analysis Toolbar Select Surface Analysis... Slope Give the new theme name qsy_slope Select Surface Analysis... Aspect Give the new theme name qsy_aspect
6. Raster Calculator Build an expression Cos((([qsx_aspect] * (-1)) + 450) * .01745) * Tan([qsx_slope] * .01745) Give the new theme name qsx_dx Build an expression Sin((([qsy_aspect] * (-1)) + 450) * .01745) * Tan([qsy_slope] * .01745) Give the new theme name qsy_dy Build an expression [qsx_dx] + [qsy_dy] for prevailing rill erosion Give the new theme name erdep
([qsx_dx] + [qsy_dy]) * 10. for prevailing sheet erosion Give the new theme name erdep


Using Soil Erosion Modeling for Improved Conservation Planning: A GIS-based Tutorial

ArcGIS 8.1, ArcMap