What is Choteau soil and how does it affect Oklahoma foundations?
In short: Choteau is a very deep, clayey soil of eastern Oklahoma that is somewhat poorly drained, with a perched water table 2.5 to 3 feet down from December through April. Its subsoil holds about 35 to 45 percent clay. Seasonal wetness and clay that swells and shrinks with moisture are the two soil traits most relevant to foundations on Choteau.
Where does Choteau soil occur?
The USDA Natural Resources Conservation Service (NRCS) Official Series Description (OSD) describes Choteau as an extensive series in southeastern Kansas and eastern Oklahoma, mapped in Major Land Resource Areas 112, 116, 117 and 118 1. The type location is in Mayes County, and the series was established in Wagoner County 1.
Choteau forms on nearly level to gently sloping high terraces and upland footslopes in the Cherokee Prairies, on slopes of 0 to 5 percent 1. Its parent material is loamy and clayey alluvium or colluvium over Pennsylvanian shale 1. This is the landscape of the Tulsa metro and the Northeast (Ozark Plateau and Grand Lake) region, underlain by Pennsylvanian shales.
What are its key properties?
| Property | Choteau (from the OSD) 1 |
|---|---|
| Classification | Fine, mixed, active, thermic Aquic Paleudolls |
| Parent material | Loamy and clayey alluvium or colluvium over Pennsylvanian shale |
| Depth | Very deep; solum more than 60 in |
| Drainage | Somewhat poorly drained |
| Saturated hydraulic conductivity | Moderately low |
| Water table | Perched; top at 2.5-3 ft, December to April |
| Subsoil (Bt) | Silty clay loam to clay; 35-45% clay |
| Slopes | 0-5% (generally 0-3%) |
| Mean annual rainfall | About 42 in (range 37-46 in) |
"Colluvium" is soil material that has crept or washed down a slope. "Aquic" in the classification signals a soil that is wet for part of the year. Most Choteau land is cropland for small grains, sorghum or soybeans, with some tame pasture and native tallgrass prairie 1.
What do the properties mean for foundations?
A perched water table
A perched water table is a local zone of saturated soil held above the main groundwater by a slowly permeable layer, usually clay 5. In Choteau the top of this zone sits 2.5 to 3 feet below the surface and its bottom 5 to 8 feet down, from December to April 1. Related topics: groundwater and perched water, crawl space moisture and wood decay, and lateral earth, swell and hydrostatic pressure on walls.
Clay that responds to moisture
Clayey soils swell when they take on water and shrink when they dry, and uneven moisture causes more foundation damage than uniform changes 4. Choteau's subsoil holds 35 to 45 percent clay 1. NRCS rates shrink-swell by linear extensibility percent (LEP): under 3 percent low, 3 to 6 percent moderate, 6 to 9 percent high and 9 percent or more very high 3. Web Soil Survey lists the LEP for each Choteau map unit 2. Wet winters followed by dry summers are the setting for perimeter wetting heave and perimeter drying settlement.
What should you know about a Choteau lot?
- Look up the map unit, LEP and water table data in Web Soil Survey 2.
- Grade soil away from the foundation and route downspouts away from the house so roof water does not add to seasonal saturation 4.
- Keep sprinkler heads and planter beds from ponding water near the foundation 4.
- Monitor existing cracks and check drainage around the house each year 4.
Related
- Soil Series - Tulsa Metro
- Groundwater and Perched Water
- Dennis soil
- Crawl Space Encapsulation
- Soil Series Index
Common questions
Why is Choteau soil wet in winter and spring?
The official description reports a perched seasonal high water table with its top 2.5 to 3 feet below the surface from December to April. Water collects above slowly permeable clay layers instead of draining down quickly.
How much clay is in Choteau soil?
The subsoil is silty clay loam, clay loam, silty clay or clay with about 35 to 45 percent clay, and the typical pedon's subsoil is clay.
Where is Choteau soil found?
Choteau occurs in eastern Oklahoma and southeastern Kansas in the Cherokee Prairies and nearby areas. Its type location is in Mayes County and it was established in Wagoner County.
Does Choteau soil shrink and swell?
Clayey soils like Choteau can swell when wet and shrink when dry. The rated value for a map unit is published as linear extensibility in Web Soil Survey.
Sources
- Official Series Description - CHOTEAU Series USDA Natural Resources Conservation Service
- Web Soil Survey - Home USDA Natural Resources Conservation Service
- Definition: Linear Extensibility Percent (LEP) UC Davis California Soil Resource Lab (from the NRCS National Soil Survey Handbook)
- Living With Shrink/Swell Soils: A Homeowners' Guide to Maintenance of Shallow Foundations American Society of Civil Engineers, Geo-Institute
- perched water table (NAL Agricultural Thesaurus) USDA National Agricultural Library
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