Iowa Soil Drainage Class GIS Data
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Author: emlemke
This is an archived story. The content, links and information may have changed since the publication date.
Natural soil drainage class describes the expected frequency and duration of wetness under undisturbed conditions. Classes range from excessively drained to very poorly drained and are assigned from soil morphology and hydrology evidence—depth and duration of seasonal water tables, redox features, organic accumulations, permeability, restrictive layers, and landscape position. In practice, class is interpreted from field descriptions in soil surveys and long-term observations; it reflects inherent wetness/aeration rather than present-day management.
Applied Relevance
Drainage class is a fast, defensible indicator of waterlogging risk, trafficability, timing of field operations, and tile-drain need. It frames nutrient-loss pathways (denitrification, runoff), guides crop and variety selection on marginal ground, and screens sites for basements, septic systems, and utilities. At watershed scales it helps target wetland restoration and flood-storage opportunities and explains persistent yield variability linked to soil–landscape position.
GIS Map Folder Download
Click the button below to access the GIS data.
GIS Map Details
Maps are derived from USDA-NRCS gSSURGO. Component-level drainage classes in NASIS were generalized to map units and rasterized statewide at 10-m resolution to match SSURGO cartographic detail. Symbology is standardized so counties and watersheds can be compared directly. The download includes a GeoTIFF with overviews for fast display, world/supplemental files, and layer files for ArcGIS Pro/Desktop along with a short README covering projection and class colors.
Metadata – Sources – Limitations
Source data: gSSURGO vector map units and tabular attributes (most recent statewide extract at time of publication); definitions follow the Soil Survey Manual. Projection: NAD83 UTM Zone 15N. The layer depicts inherent wetness at the original SSURGO mapping scale (roughly 1:12,000–1:31,680) and should not be used for site delineation without field verification. Modern alterations—tiling, ditching, grading, irrigation, and fill—are not represented, and small inclusions within map units may differ from the mapped class.
Produced by: Meyer Bohn, Joshua McDanel, and Bradley Miller January (2019)
Created with the gSSURGO mapping toolset for ArcGIS for Desktop 10.6. Available for download at:
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/geo/?cid=nrcs142p2_053628
Raster Format: 10-m resolution GeoTIFF, 32-bit floating point
Projection: NAD83 UTM Zone 15N
Extent – West: -96.801571 East: -90.007463 North: 43.644364 South: 40.302683
Soil Survey Staff. 2018. Natural Resources Conservation Service. United States Department of Agriculture. Gridded Soil Survey Geographic (gSSURGO) Database for Iowa. Accessed 27 Oct 2018.
Use limitations: See “Sources of Apparent Error on Existing Soil Maps”. Soil Survey Staff. 2018. Soil Survey Manual – Ch. 4: Soil Mapping Concepts. Natural Resources Conservation Service. United States Department of Agriculture. Available at:
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054254#quality
Scale Range: Not intended for use at scales larger than an order 2 Survey (1:12,000 to 1:31,680).