What is Kiomatia soil and how does it affect Oklahoma foundations?

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

In short: Kiomatia is a deep, sandy soil that forms in Red River alluvium (river-laid sediment) on floodplains and natural levees. It is well drained but floods frequently where unprotected and has a water table about 42 to 60 inches down for part of the year. Its low clay content means flooding and water, not clay swelling, drive most foundation concerns.

What is Kiomatia soil?

Kiomatia is a soil series described by the USDA Natural Resources Conservation Service (NRCS). Its taxonomic class is "Sandy, mixed, thermic Typic Udifluvents" ¹. "Sandy" describes the texture of its control section ¹. The "fluv" in its name marks it as a Fluvent; the USDA soil glossary lists flood plains among the landscapes where soils grading toward Fluvents occur ⁴.

The series forms in sandy alluvial sediments with thin finer layers, washed down from Permian red beds ¹. It occurs in the Red River alluvium of Texas, Oklahoma, Arkansas and Louisiana and is rated as extensive ¹. The series was established in Haskell County, Oklahoma, in 1972, although its type location (the reference profile) is in Red River County, Texas ¹.

In Oklahoma, Red River floodplain soils fall within the Southeast (Ouachitas and Red River) and South-Central (Arbuckles and Texoma) regions, on the Quaternary alluvium and terraces geologic unit.

What is the typical soil profile?

The official description gives this typical profile ¹:

Key properties from the same description ¹:

• Clay content: 5 to 18 percent clay and 60 to 92 percent sand in the control section ¹.
• Drainage: well drained, with rapid permeability (water moves through quickly) ¹.
• Slopes: 0 to 5 percent, usually under 2 percent ¹.
• Water table: fluctuates between 42 and 60 inches below the surface, typically January through July ¹.
• Flooding: frequently flooded for brief periods in most years where unprotected ¹.
• Climate: mean annual precipitation about 44 inches (range 40 to 48) ¹.
• Use: mostly bermudagrass pasture; native trees are cottonwood and willow ¹.

What does it mean for foundations?

Shrink-swell is not the main driver

Shrink-swell soils are clays that grow and shrink as their moisture changes. Soil scientists measure this as linear extensibility, the linear expression of the change in volume between moist and oven-dry soil, with less than 3 percent rated "low" ⁵. Kiomatia's sandy, low-clay profile ¹ does not fit the clay-rich pattern behind most seasonal foundation movement. The exact rating for a mapped unit is listed in Web Soil Survey ².

Flooding and a seasonal water table

The bigger factors on Kiomatia are water-related. The soil floods frequently where it is not protected, and its water table fluctuates between 42 and 60 inches below the surface, typically January through July ¹. For any lot on a floodplain soil, the official flood zone comes from FEMA's flood maps, which can be searched by address ³.

Layered sandy and loamy floodplain sediments can behave differently from layer to layer. For how loose or wet alluvium can compress under a house, see soft soil consolidation. For how flowing water can carry sandy soil from beneath footings, see erosion, undermining and washout voids. Filled or built-up lots on floodplains are covered under fill consolidation settlement.

How is the soil at a property confirmed?

• Web Soil Survey shows the mapped soil units for an area and lets users judge soil suitability for a particular use ².
• Check the FEMA Flood Map Service Center for the Flood Insurance Rate Map panel covering the address ³.
• A site-specific soil boring is the way to confirm actual layers and water levels; see soil testing and lab values.

Related

• Groundwater and perched water
• Erosion, creeks and slopes
• Soft soil consolidation (alluvium and wet clays)
• Creeks and flood history data
• Soil series index