Wichita Soil, Rainfall and Frost Data: Why Slabs Move in Sedgwick County

Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.

Concrete does not sink. The ground under it moves, and the slab follows. In Wichita that movement has three published drivers - rainfall that swings by more than 40 inches between the wettest and driest years on record, clay-dominated soils that the USDA rates in the slowest-draining hydrologic class, and a building code that protects footings while saying nothing about the flatwork beside them. This page collects the primary figures behind all three, taken from the National Weather Service, USDA NRCS, the Kansas Geological Survey, the Wichita-Sedgwick County building code and the City of Wichita.

Every number here comes from a published source that is linked at the bottom of the page, and nothing on it is estimated, averaged across sources or carried over from memory. Where a figure covers Sedgwick County rather than the city, or a specific soil map unit rather than the whole county, the text says so. Journalists, appraisers, engineers and neighborhood groups are welcome to reuse any of it with attribution. If you are trying to work out why one driveway on a street has dropped and the one next door has not, the soil table below is usually the fastest place to start.

Wichita's rainfall swings 41 inches between its extremes

The single most useful number for understanding slab movement here is the spread. Wichita's wettest calendar year on record delivered 53.82 inches of precipitation in 2008. Its driest delivered 12.15 inches in 1966. That is a 41.67-inch spread between the two ends of a record that runs back to 1888, against a 1991-2020 normal of 34.31 inches. Clay soils respond to that by expanding and contracting, and a slab bearing on them rides the difference.

The short-duration numbers matter just as much for washout. Wichita recorded 14.43 inches in a single month in June 1923 and 10.31 inches in 24 hours on September 12, 2008. The Halloween Flood of 1998 produced storm totals of 12.66 inches at Wichita's Brooks Middle School and 12.30 inches at Valley Center West Elementary, and Cowskin Creek crested at a stage of 22.00 feet on October 31, 1998 at the 119th Street gauge. Rain arriving that fast does not soak in on clay. It runs, and it takes bedding material with it.

National Weather Service Wichita. Climate records begin in 1888; normals are the 1991-2020 period.

What sits under a Wichita slab, from the shale up

The Kansas Geological Survey describes Sedgwick County's bedrock as Permian. The Wellington Formation - calcareous gray and blue-gray shale containing several thin beds of impure limestone and thin beds of gypsum and anhydrite, 80 to 550 feet thick - underlies most of the county and is the principal groundwater source east of the Arkansas Valley. The western fifth of the county is Ninnescah Shale, alternating beds of brownish-red silty shale and siltstone. Buried beneath the Arkansas Valley is the Pliocene Ogallala Formation, described as calcareous gray to pink-tan silt and clay with fine to coarse sand and gravel.

Above that sits the material a driveway actually bears on. KGS describes the Pleistocene alluvium of the valley as fine to coarse sand and fine to very coarse gravel, with clayey silt through the upper section. The surface soils formed on all of this include some genuinely expansive series. The USDA official series description for Goessel classifies it as a Fine, smectitic, mesic Udic Haplusterts - a Vertisol - with low saturated hydraulic conductivity, slickensides in the profile, and gilgai features observed in native pasture. Tabler is a Fine, mixed, active, thermic Udertic Paleustolls with very slow permeability and slickensides between 27 and 107 centimeters, roughly 10 to 42 inches down.

Hydrologic group D is the rating that predicts trouble

USDA NRCS sorts soils into four hydrologic groups by how readily water moves through them. Group A has low runoff potential when thoroughly wet and transmits water freely. Group B is moderately low runoff with unimpeded transmission. Group C is moderately high runoff with somewhat restricted transmission. Group D is high runoff potential when thoroughly wet, with water movement through the soil restricted or very restricted. The NRCS hydrologic soil group reports filed with the City of Wichita for Sedgwick County add the detail that matters for concrete: Group D soils consist chiefly of clays that have a high shrink-swell potential.

Four of the county map units in those reports carry a D rating, including Tabler silty clay loam, which the report describes as having a very slow infiltration rate and high runoff potential. The practical translation for flatwork: rain does not drain vertically away from the slab, it sheets across the top of the clay and exits at the lowest edge, undercutting bedding as it goes. The same clay then shrinks when it dries. A slab over Group D ground is far more likely to develop a void beneath it than one bedded on the Pratt or Lincoln sands nearby.

Group ratings from USDA NRCS hydrologic soil group reports for Sedgwick County filed with the City of Wichita; group definitions from the NRCS National Engineering Handbook.

What the building code assumes about this ground

Wichita and Sedgwick County adopted a single Unified Building and Trade Code, built on the 2018 International Residential Code and the 2015 Uniform Plumbing Code, effective January 1, 2019. Section 2.4.115 amends IRC Table R301.2(1) with the local design criteria: a ground snow load of 15 pounds per square foot, a wind entry reading 76w/90-3 sec. gust, a frost line depth of 24 inches, a winter design temperature of -7 degrees at 97.5 percent, a mean annual temperature of 55 to 60 degrees, seismic design category A and a weathering classification of Severe.

Two of those deserve attention from anyone with a settled slab. Section 2.4.420 requires that all exterior footings be placed at least 24 inches below the undisturbed ground surface - the code's answer to frost heave, and the reason houses here generally stay put. A driveway, sidewalk or patio has no footing at all. It bears directly on whatever fill or subgrade was under it the day it was poured, which is why the flatwork moves while the structure does not. The Severe weathering classification is the freeze-thaw durability rating, and it is the reason surface scaling shows up on concrete that was never air-entrained properly.

Drought stages, watering days, and the second half of the cycle

The dry half of the cycle is documented too. The City of Wichita's Drought Response Plan is codified at municipal code Section 17.14.020, and it sets triggers against the Cheney Reservoir conservation pool. Stage 1 is declared when the 12-month average drops to between 70 and 89 percent of the conservation pool; Stage 2 at 50 to 69 percent. Wichita entered Stage 1 in January 2023, moved to Stage 2 in August 2024, and returned to Stage 1 in September 2025. The city's current update reports the conservation pool 100 percent full and 0.8 feet above normal, with a 12-month average of 90 percent.

Alongside those stages Wichita runs a permanent outdoor watering schedule: no watering between 10 a.m. and 6 p.m. on any day, odd-numbered addresses on Wednesday, Friday and Sunday, even-numbered addresses on Tuesday, Thursday and Saturday, and no watering on Monday. That schedule is a water-supply measure, but it has a side effect worth understanding. Clay soils shrink as they dry, and shrinkage under a slab opens a void the slab cannot bridge. When the rain returns the clay swells again - but the void the dry spell created does not close itself, and the slab has already dropped into it.

Sources & Methodology

Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.

1. National Weather Service Wichita: Climate Records and Extremes — Wettest year 53.82 inches in 2008, driest year 12.15 inches in 1966, wettest month 14.43 inches in June 1923, wettest 24 hours 10.31 inches on September 12 2008, greatest seasonal snowfall 39.7 inches in 1911-12, record high 114 degrees on August 12 1936 and record low -22 degrees on February 12 1899. Records begin in 1888.
2. National Weather Service Wichita: Annual Climate Normals — Normal annual precipitation of 34.31 inches and normal annual snowfall of 12.7 inches for the 1991-2020 period.
3. National Weather Service Wichita: The Halloween Flood of 1998 — Storm totals of 12.66 inches at Brooks Middle School in Wichita and 12.30 inches at Valley Center West Elementary, and the Cowskin Creek crest of 22.00 feet on October 31 1998 at the 119th Street gauge.
4. Wichita-Sedgwick County Unified Building and Trade Code — Adoption of the 2018 International Residential Code and 2015 Uniform Plumbing Code effective January 1 2019, the Section 2.4.115 amendments to Table R301.2(1) including the 24-inch frost line depth and 15 psf ground snow load, and Section 2.4.420 requiring exterior footings at least 24 inches below undisturbed ground.
5. USDA NRCS Hydrologic Group Rating for Sedgwick County, Kansas — Group ratings for Tabler silty clay loam, Waldeck sandy loam, Pratt loamy fine sand, Lincoln soils and Canadian fine sandy loam, the very slow infiltration and high runoff description of Tabler, and the statement that Group D soils consist chiefly of clays with high shrink-swell potential.
6. USDA NRCS Hydrologic Soil Group Report, Sedgwick County: Goessel and Rosehill map units — Group D ratings for Goessel silty clay and Rosehill silty clay on 1 to 3 percent slopes.
7. USDA NRCS Hydrologic Soil Group Report, Sedgwick County: Carwile, Elandco and Shellabarger map units — Group D rating for Carwile fine sandy loam on 0 to 1 percent slopes and Group B ratings for Elandco silt loam and Shellabarger sandy loam.
8. USDA NRCS National Engineering Handbook, Title 210 Part 650 Chapter 2 — Definitions of hydrologic soil groups A through D, including Group D as high runoff potential when thoroughly wet with water movement restricted or very restricted.
9. USDA NRCS Official Series Description: Goessel — Taxonomic class Fine, smectitic, mesic Udic Haplusterts, low saturated hydraulic conductivity, slickensides, and gilgai features observed in native pasture.
10. USDA NRCS Official Series Description: Tabler — Taxonomic class Fine, mixed, active, thermic Udertic Paleustolls, very slow permeability, and slickensides from 27 to 107 centimeters.
11. Kansas Geological Survey: Geologic Formations of Sedgwick County — Descriptions and thicknesses of the Wellington Formation and Ninnescah Shale, the buried Ogallala Formation, and the Pleistocene alluvium of the Arkansas Valley.
12. City of Wichita Drought Update and Response Plan — Drought Response Plan codified at municipal code Section 17.14.020, the Stage 1 and Stage 2 Cheney conservation pool triggers, the January 2023 to September 2025 stage timeline, and the permanent outdoor watering schedule.