USDA Soil Area Download

This command downloads soil group index and soil boundary lines from USDA website for the area-of-interest, then draws soil polylines and index labels in the plan view. These soil lines and labels are then used in watershed analysis to calculate weighted curve numbers when using the SCS Method.

The program requires the user to define the dwg grid projection in order to convert the local area to Latitude/Longitudinal values used on USDA website. Run command Settings > Drawing Setup to set up the local projection, zone and Lat/Lon datum.

The USDA classifies soil into four soil types, A, B, C, or D, based on the soil's ability to infiltrate water during a storm event.  This classification is used in conjunction with ground cover types, which are broken into the broad categories of Fully Developed Urban Areas, Developing Urban Areas, Cultivated Agricultural Lands, Other Agricultural Lands, and Arid and Semi-Arid Rangelands.  These Cover Types are then broken into as many as three subcategories based on their hydrologic condition, Good, Fair or Poor.  For example, you might draw a polygon around a wooded area on your surface and determine that this should be categorized as Other Agricultural Lands, Woods, Good.  The USDA issued data show that the Curve Numbers, depending on the underlying soil type, would be 30, 55, 70, or 77.  Downloading the Soil Areas might show that the woods has several soil types within it.  If the woods was 25% A, 25% B, 25% C and 25% D, it would have a weighted Curve Number of 58.  The ground cover type, the hydrologic condition of this cover and the soil type underneath determine the Curve Number.


In order to draw soil lines and labels on the drawing for watershed analysis purposes, it's required to set up the layers for soil lines and labels. Run command > Watershed > Define Watershed Layers to set up layers for soil lines and labels.


Run Watershed > USDA Soil Area Download, then either pick bounding box or specify a surface file in order to download soil lines in side the watershed perimeter.


Pulldown Menu Location: Watershed > USDA Soil Area Download
Keyboard Command: usgs_soil
Prerequisite: Run Watershed > Define Watershed Layers command to set soil layers