Soil Drainage Class GIS Data
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Author: Bradley Miller
Drainage class describes the natural frequency and duration of wet periods in soil, based on the conditions under which the soil formed. It reflects long-term hydrologic behavior without considering artificial drainage or irrigation unless those changes have altered the soil’s morphology. Drainage classes range from excessively drained to very poorly drained and are determined through indicators like soil color, redox features, horizon development, and landscape position.
Applied Relevance
Drainage class is critical for land management, agriculture, engineering, and environmental planning. It informs crop selection, conservation practice design, septic system placement, and wetland identification. Poorly or very poorly drained soils may require artificial drainage to be productive, while excessively drained soils may need irrigation support or erosion control measures.
Available Depths
This is a profile-level classification and does not vary with depth. It represents the overall drainage behavior of the soil as a single mapped attribute.
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Drainage Class Definitions
- Excessively Drained – Water is removed very rapidly. The occurrence of internal free water is commonly very rare or very deep. The soils are commonly coarse-textured and have very high hydraulic conductivity or are very shallow.
- Somewhat Excessively Drained – Water is removed from the soil rapidly. Internal free water occurrence is commonly very rare or very deep. The soils are commonly coarse-textured and have high saturated hydraulic conductivity or are very shallow.
- Well Drained – Water is removed from the soil readily but not rapidly. Internal free water occurrence commonly is deep or very deep; annual duration is not specified. Water is available to plants throughout most of the growing season in humid regions. Wetness does not inhibit the growth of roots for significant periods during most growing seasons. The soils are mainly free of features that are related to wetness.
- Moderately Well Drained – Water is removed from the soil somewhat slowly during some periods of the year. Internal free water occurrence commonly is moderately deep and transitory through permanent. The soils are wet for only a short time within the rooting depth during the growing season, but long enough that most mesophytic crops are affected. They commonly have a moderately low or lower saturated hydraulic conductivity in a layer within the upper 1 m, periodically receive high rainfall, or both.
- Somewhat Poorly Drained – Water is removed slowly so that the soil is wet at a shallow depth for significant periods during the growing season. The occurrence of internal free water is commonly shallow to moderately deep and transitory to permanent. Wetness markedly restricts the growth of mesophytic crops, unless artificial drainage is provided. The soils commonly have one or more of the following characteristics: low or very low saturated hydraulic conductivity, a high water table, additional water from seepage, or nearly continuous rainfall.
- Poorly Drained – Water is removed so slowly that the soil is wet at shallow depths periodically during the growing season or remains wet for long periods. The occurrence of internal free water is shallow or very shallow and common or persistent. Free water is commonly at or near the surface long enough during the growing season so that most mesophytic crops cannot be grown, unless the soil is artificially drained. The soil, however, is not continuously wet directly below plow-depth. Free water at shallow depth is usually present. This water table is commonly the result of low or very low saturated hydraulic conductivity of nearly continuous rainfall, or of a combination of these.
- Very Poorly Drained – Water is removed from the soil so slowly that free water remains at or very near the ground surface during much of the growing season. The occurrence of internal free water is very shallow and persistent or permanent. Unless the soil is artificially drained, most mesophytic crops cannot be grown. The soils are commonly level or depressed and frequently ponded. If rainfall is high or nearly continuous, slope gradients may be greater.
GIS Map Details
The rasters originate from the Gridded SSURGO (gSSURGO) database, a National Cooperative Soil Survey (NCSS) SSURGO product in the format of an Environmental Systems Research Institute, Inc. (ESRI®) file geodatabase. Both SSURGO and gSSURGO are considered products of the NCSS partnership. SSURGO generally has the most detailed level of soil geographic data developed by the NCSS in accordance with NCSS mapping standards (1:15,840 scale) and is stored in a vector format which display soil map unit delineations. The gSSURGO product was generated by creating a 10-m resolution raster of the original SSURGO vector data. The soil property tabular data are stored in the National Soil Information System (NASIS) database.
Metadata – Sources – Limitations
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).