Soil series profile

Coteau soil series

Coteau is a somewhat poorly drained soil with a silt loam surface, mapped on 110,628 acres in 15 counties in LA. Hydrologic group C.

#3247 by mapped area fine-silty Glossaquic Hapludalfs (Alfisols)

Drainage class: Somewhat poorly drained
Hydrologic group: C
Typical topsoil pH: 5.5
Mapped area: 111k

Typical Coteau profile

Texture and pH by depth

Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).

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Typical Coteau horizons (representative values)
Depth	Texture	pH	Clay	Sand	Organic matter
0–5 in (Ap)	Silt loam	5.5	14%	5%	2.25%
5–12 in (Bt)	Silty clay loam	5.5	28%	4%	0.25%
12–22 in (Bt/E)	Silty clay loam	5.5	28%	7%	0.25%
22–43 in (B't)	Silty clay loam	5.5	28%	4%	0.25%
43–100 in (BC)	Silt loam	6.2	19%	5%	0.25%

Representative values from the most extensive Coteau map unit (Coteau silt loam, 0 to 1 percent slopes, survey area LA055). Other map units of this series vary within the series range.

Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Coteau soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Coteau soils is strongly acidic: pH 5.5. Most vegetables and lawn grasses do best around 6.0 to 7.0, so lime is often needed; blueberries, azaleas and rhododendrons like it as it is.

Loamy topsoil (loam, silt loam and similar) covers 92% of mapped Coteau acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (91% of mapped Coteau acres).

98% of mapped Coteau acres is somewhat poorly to very poorly drained, so soil stays soggy for long spells after rain and in wet seasons. Raised beds, plants that tolerate wet feet, and not working the soil while wet all help.

For lawns and yards

On 92% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.

For a septic system

For conventional septic absorption fields, NRCS rates 92% of the acres in mapped Coteau soils very limited, 0% somewhat limited and 0% not limited (8% not rated, such as urban land, pits or water).

Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.

Where Coteau soil is found

Mapped acres

Coteau is mapped in Louisiana.

Counties with the most mapped Coteau soil
County	Acres	Share of county land
St. Landry Parish, LA	31,559	5.3%
Lafayette Parish, LA	30,726	18.0%
Avoyelles Parish, LA	17,453	3.3%
Vermilion Parish, LA	12,738	1.8%
Iberia Parish, LA	8,396	2.4%
Evangeline Parish, LA	2,718	0.6%
St. Martin Parish, LA	2,328	0.5%
East Baton Rouge Parish, LA	1,706	0.6%
Acadia Parish, LA	1,200	0.3%
St. Mary Parish, LA	987	0.2%
Ascension Parish, LA	551	0.3%
Livingston Parish, LA	115	0.0%
East Feliciana Parish, LA	94	0.0%
St. Helena Parish, LA	42	0.0%
West Feliciana Parish, LA	15	0.0%

Septic absorption fields

NRCS rating, share of Coteau acres

Not limited 0%

Somewhat limited 0%

Very limited 92%

Not rated 8%

Septic tank absorption field rating across mapped Coteau acres. Scale 0 to 100% of mapped land.

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Septic tank absorption field rating across mapped Coteau acres.
Category	Share of acres
Not limited	0.0%
Somewhat limited	0.0%
Very limited	91.9%
Not rated	8.1%

Drainage, water table and flooding

Share of Coteau acres

Depth to seasonal high water table: About 2.2 feet (26 in) (median where reported).
Flooding: Not mapped as flooding on most acres.
Slope: Typically 0–2% (median 0%).
Topsoil organic matter: Median 2.2%.

Drainage class

Excessively drained 0%

Somewhat excessively drained 0%

Well drained 0%

Moderately well drained 0%

Somewhat poorly drained 98%

Poorly drained 0%

Very poorly drained 0%

Not rated 3%

Drainage class across mapped Coteau acres. Scale 0 to 100% of mapped land.

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Drainage class across mapped Coteau acres.
Category	Share of acres
Excessively drained	0.0%
Somewhat excessively drained	0.0%
Well drained	0.0%
Moderately well drained	0.0%
Somewhat poorly drained	97.5%
Poorly drained	0.0%
Very poorly drained	0.0%
Not rated	2.5%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%

B: moderate infiltration 0%

C: slow infiltration 52%

D: very slow infiltration (clayey, shallow or wet) 0%

A/D: D as is, A if drained 0%

B/D: D as is, B if drained 0%

C/D: D as is, C if drained 40%

Not rated 8%

Hydrologic soil group across mapped Coteau acres. Scale 0 to 100% of mapped land.

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Hydrologic soil group across mapped Coteau acres.
Category	Share of acres
A: fast infiltration (mostly sandy or gravelly)	0.0%
B: moderate infiltration	0.0%
C: slow infiltration	52.3%
D: very slow infiltration (clayey, shallow or wet)	0.0%
A/D: D as is, A if drained	0.0%
B/D: D as is, B if drained	0.0%
C/D: D as is, C if drained	39.7%
Not rated	8.1%

Sources & data dates

Source: USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
Data date: SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
Scope: All map unit components named Coteau (component kind "Series") in SSURGO: 110,628 acres.
Method: Shares are by mapped acres of Coteau components. The profile comes from the single largest Coteau component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Coteau.