How do Oklahoma river floodplain and terrace soils affect homes?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: Along every major Oklahoma river, the youngest ground is alluvium, sediment the river laid down on its floodplain, with older terraces standing higher on the valley sides. These deposits range from soft, wet floodplain clay to sandy dune ground to dense, expansive claypan soils. The soil series matters more than the river name for predicting how a foundation will behave.

How do floodplains and terraces differ?

Alluvium is sediment deposited by flowing water. The present floodplain is the low, flat land a river still floods. A terrace (or paleoterrace) is an older floodplain surface left higher than today's river as it cut downward.

Alluvium can be thick. In Oklahoma County, the North Canadian River alluvial aquifer generally averages about 50 feet thick and may be up to 150 feet thick in the river channel itself, and productive alluvial aquifers are generally within about a mile of either side of the river ⁷. Alluvium along Deer Creek can be up to 50 feet thick ⁷.

What soils form on floodplains?

Series	Material	Drainage	Water and flooding
Osage	Thick clayey alluvium; smectitic ¹	Poorly drained; very slow permeability ¹	Seasonal high water table 6–18 in, Nov–May ¹
Port	Calcareous loamy alluvium ²	Well drained ²	Occasionally or frequently flooded, Mar–Oct ²
Verdigris	Silty alluvium ³	Well drained ³	Subject to flooding ³

Osage is a Vertisol, a clay soil defined by shrink-swell, with intersecting slickensides from about 13 to 60 inches deep ¹. It occurs on floodplains along major streams in eastern Oklahoma, southeastern Kansas and southwestern Missouri ¹.
Port occurs on floodplains in the eastern Central Rolling Red Plains and the Central Rolling Red Prairies of Oklahoma, Kansas and Texas ².
Verdigris occurs on floodplains in northeastern Oklahoma, southeastern Kansas and southwestern Missouri ³.

What soils form on terraces?

Series	Material	Key trait
Kirkland	Clayey sediments over Permian shale, on paleoterraces ⁵	Slow permeability; intersecting slickensides ⁵
Tabler	Calcareous loamy or clayey alluvium on paleoterraces ⁴	Very slow permeability; slickensides ⁴
Dougherty	Sandy and loamy sediments on Pleistocene terraces ⁶	Stabilized dunes; about 20–40 in of sandy surface ⁶

An Oklahoma State University study of five western Oklahoma soils found Kirkland had the greatest total shrink-swell across its profile, with a coefficient of linear extensibility up to about 0.090, and found Norge, on uplands of old alluvial origin, reached about 0.066 ⁸. The authors linked these values to smectite clay and severe limitations for many engineering projects ⁸.

What does this mean for foundations?

Soft, wet floodplain clay

A thick clay floodplain soil with a water table within 6 to 18 inches for half the year ¹ can compress under load and stay wet beneath crawl spaces. See soft soil consolidation and crawl space moisture.

Flooding and scour

Port and Verdigris are subject to flooding ²³. Floodwater can scour soil from around footings. See creeks and flood history and erosion, undermining and washout voids.

Expansive terrace clay

Kirkland and Tabler subsoils have slickensides ⁴⁵, and lab tests show high shrink-swell in Kirkland-type soil ⁸. These lots behave like other expansive clay sites. See perimeter drying settlement.

Sandy terraces

Dougherty's thick sandy surface ⁶ swells little but can wash out under leaks or concentrated runoff.

Common questions

What is the difference between alluvium and a terrace?

Alluvium is sediment laid down by a river, usually on the present floodplain. A terrace is an older, higher floodplain left behind as the river cut down, so terrace soils are older, better developed and usually above normal flood levels.

Are floodplain soils bad for foundations?

It depends on the soil. Some, like Osage, are thick, poorly drained smectite clay with a water table within 6 to 18 inches in winter and spring. Others, like Port and Verdigris, are well-drained silty or loamy soils that still flood at times.

Can terrace soils be expansive?

Yes. Kirkland and Tabler formed on old terraces and have clay subsoils with slickensides, a sign of repeated shrink and swell. Others, like Dougherty, are sandy.

How thick is alluvium along Oklahoma rivers?

It varies. In Oklahoma County, the North Canadian River alluvium generally averages about 50 feet thick and may be up to 150 feet thick in the river channel itself.

Sources

Official Soil Series Description: OSAGE Series USDA Natural Resources Conservation Service
Official Soil Series Description: PORT Series USDA Natural Resources Conservation Service
Official Soil Series Description: VERDIGRIS Series USDA Natural Resources Conservation Service
Official Soil Series Description: TABLER Series USDA Natural Resources Conservation Service
Official Soil Series Description: KIRKLAND Series USDA Natural Resources Conservation Service
Official Soil Series Description: DOUGHERTY Series USDA Natural Resources Conservation Service
OK County Groundwater Model (Project 174601) Association of Central Oklahoma Governments
Shrink-Swell and Other Characteristics of Five Benchmark Soils of Western Oklahoma (Technical Bulletin T-150) Oklahoma State University Agricultural Experiment Station

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