Pre-settlement Water Regimes of Iowa Wetlands GIS Data
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Author: Bradley Miller
This raster estimates pre-settlement (pre-drainage) wetland water regimes across Iowa—the natural, undrained condition before widespread tiling and channelization. Soil map units from gSSURGO were linked to regime classes described in Official Soil Series Descriptions (OSD) and harmonized to National Wetland Inventory (NWI) definitions. Because hydromorphic soil indicators persist for decades and much Iowa mapping occurred roughly 100–150 years after drainage expansion, OSD wetness notes provide a reasonable proxy for historic hydrology. Use this layer as baseline context rather than a depiction of current conditions.
Applied Relevance
The map supports restoration targeting by highlighting landscapes likely to have supported wetlands prior to drainage; informs conservation planning by pointing to places with high potential for flood storage, nutrient removal, and habitat; adds historical context for mitigation and permitting; frames watershed assessments of drainage legacies on peak flow, denitrification, and baseflow; and serves education and historical-ecology uses by showing how soils record long-term wetness across landforms.
Water-regime classes
Classes follow NWI conventions. Areas may be saturated at or near the surface without persistent standing water, temporarily flooded for brief periods during the growing season, seasonally flooded for extended periods in most years, semipermanently flooded through much of the growing season, or permanently flooded/open water in most years. See the map legend for the exact codes applied.
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GIS Map Details
Inputs include gSSURGO polygons and OSD hydrology notes, aligned to NWI regime definitions. Series were assigned to a historic water-regime class, dissolved to map units, and rasterized to a statewide grid with modest generalization to avoid over-precision near boundaries. Deliverables are a GeoTIFF raster of integer class values with a legend/readme. The intended use is regional to watershed-scale screening; site-level decisions should be field-verified.
Metadata – Sources – Limitations
The layer reflects historic potential, not present-day hydrology. OSD text varies in detail through time, and some series were mapped long after drainage changes. Modern alterations—ditches, ponds, tiles, fill—are not represented. Interpret comparatively to identify areas likely or unlikely to have supported wetland regimes rather than as precise site delineations.
Miller, B.A., W.G. Crumpton, and A.G. van der Valk, 2009. Spatial distribution of historical wetland classes on the Des Moines Lobe, Iowa. Wetlands 29:1146-1152. doi: 10.1672/08-158.
Soil Survey Staff. 2014. Official Soil Series Descriptions (OSD). United States Department of Agriculture, Natural Resources Conservation Service. https://soilseries.sc.egov.usda.gov/osdname.asp
Soil Survey Staff. 2014. Gridded Soil Survey Geographic (gSSURGO). United States Department of Agriculture, Natural Resources Conservation Service. http://datagateway.nrcs.usda.gov