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St. Tammany Parish, Louisiana

A shallow water table limits basements on 67% of St. Tammany Parish's mapped land, a higher share than 79% of US counties. Shrink-swell clay limits houses without basements on 4%.

0.9% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 4,416 flood losses here since 2016, under 1% of them in buildings with basements. 21% of homes were built before 1980, against 50% nationally; the median home dates from 1995.

Data as of October 13, 2026 · sources

4%

expansive clay: shrink-swell limits slab homes

67%

high water table: limits basements

1%

in drought, October 13, 2026

21%

of homes built before 1980

Soil under St. Tammany Parish

Expansive clay (limits slab homes)4.0%
High water table (limits basements)67.0%
Septic fields very limited70.1%
Clay swell (LEP, by area)2.4%
High-swell land (LEP 6%+)4.4%
Mapped soil721,800 acres
Soil seriesShare hereSeries nationally: high water table
Myatt14%n/a
Stough12%n/a
Savannah9%n/a
Prentiss6%n/a
Guyton4%n/a
Arkabutla4%n/a
Orleans Parish: 37%Hancock County: 90%Tangipahoa Parish: 73%Washington Parish: 51%Pearl River County: 59%St. John the Baptist Parish: 61%St. Charles Parish: 63%Livingston Parish: 86%St. Tammany Parish OrleansHancockTangipahoaWashingtonPearl RiverSt. John the BaptistSt. CharlesLivingstonSt. Tammany
St. Tammany Parish (heavy outline) and nearby counties, shaded by high water table share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas LA103 (2025-08-29)

What the numbers mean here

On 67% of St. Tammany Parish's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.

Rain over the 12 months to August 2026: 57.28 in, 7.09 in below the 1991-2020 average year of 64.37 in.

USDA rates 70% of the land very limited for septic absorption fields.

Drought

0.9% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 31 of the last 52 weeks; the most was 100% of its area, in 8 weeks, most recently on the May 5, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse99.8%
D1 moderate drought or worse0.9%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

4,416 flood losses since 2016, $153.8 million paid. The worst year was 2021, with 2,608. Foundations of the buildings, where recorded: under 1% basements, 56% slabs, 4% crawl spaces, 40% elevated. Median water depth outside the building: 15 in.

YearFlood losses
2016960
201758
201870
201955
2020240
20212,608
202226
202323
2024269
202513
2026 to date94

Rain

Average year, 1991-202064.37 in
12 months to August 202657.28 in (-7.09)
202548.34 in (-16.03)
Wettest year since 18952021: 92.38 in
Driest year since 18951924: 36.71 in
Days with 1 inch or more, normal at ABITA SPRINGS FIRE TWR (6 mi away)21.8

Homes

Housing units113,911
Median year built1995
Built before 198021%
Built 2000 or later41%
Owner-occupied79%
Median value, owner-occupied$284,000
Single-family detached77%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Basement waterproofing, US $3,000 to $10,000 Fixr, February 6, 2026
Sump pump installation, US $800 to $2,000 Fixr, January 31, 2025
Crawl space encapsulation, US $2,000 to $8,000 Fixr, August 29, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Orleans Parish, LA 25 mi 29% 37%
Hancock County, MS 28 mi 2% 90%
Tangipahoa Parish, LA 31 mi 2% 73%
Washington Parish, LA 31 mi under 1% 51%
Pearl River County, MS 33 mi 3% 59%
St. John the Baptist Parish, LA 37 mi 43% 61%
St. Charles Parish, LA 42 mi 44% 63%
Livingston Parish, LA 46 mi 27% 86%

Sources: USDA SSURGO (August 29, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status