Research

Where yards flood, and what the soil survey already knew

Name: NRCS drainage classes and hydrologic soil groups, as applied to residential yards
Creator: HyreYard Research Desk
License: https://creativecommons.org/licenses/by/4.0/

Poorly drained and somewhat poorly drained are federal soil ratings, not a mowing failure. This page reads the classes. It does not invent a national flood-yard map.

Updated September 2026 · Data as of NSSH, Soil Survey Manual and NEH Part 630 retrieved 5 September 2026

Written by HyreYard Research Desk Primary-source research and fact checking

8 NRCS drainage classes NSSH 618.18, including subaqueous

4 + 3 hydrologic soil groups and dual classes NEH 630 Ch. 7 · A/D, B/D, C/D

Not computed national poorly-drained × housing join Stated as a gap, not filled

The finding

The federal soil survey already rates every mapped soil for how long it stays wet. Somewhat poorly drained, poorly drained and very poorly drained are drainage classes in the National Soil Survey Handbook (NSSH Part 618.18) and Soil Survey Manual Chapter 3. They describe the frequency and duration of wet periods in the natural soil — not whether last Tuesday’s storm left a puddle, and not whether the builder regraded the lot. Hydrologic soil groups A through D, in National Engineering Handbook Part 630 Chapter 7, rate runoff potential when the soil is thoroughly wet. Group D is the high-runoff end: clays, a high water table, a claypan, or a shallow soil over rock. Dual classes (A/D, B/D, C/D) are group D in the undrained condition. A wet map unit is a reason the yard floods. It is not the only reason, and it is not a determination about your address. Web Soil Survey is the lookup. Compaction, downspouts, reverse grade and off-site water will pond a well-drained soil. HyreYard did not join drainage class to housing nationally for this page, and did not scrape municipal 311 complaint feeds. Those joins remain uncomputed. This is not a foundation page, not an insurance-claim page, and not a plumbing page.

Limitations — above the fold

A soil survey is not a determination about one yard. A map unit is a polygon of similar soils. The survey does not see your downspouts, your fill, or the compacted strip along the driveway. Web Soil Survey is the starting lookup. A soil scientist or a drainage contractor who walks the lot is the next one.

We did not publish a national flood-yard ranking. The contract asked to join poorly drained soils to Census housing and to check the join against 311 drainage complaints. We did not run that Soil Data Access query, and we did not scrape 311. The expansive-soils sibling on this site computed Vertisol and linear-extensibility acreage — a different property. Inventing a drainage-class choropleth would be fabrication.

Drainage class is the natural soil, not the installed drain. NSSH is explicit: infer the class from landscape position and morphology. Artificial drainage is recorded as a phase where it has changed the soil. A working drain tile does not rewrite the class on a printout you have not checked.

Stop lines. Do not excavate next to a foundation, over a septic field, or toward a utility mark. House-foundation movement is out of scope (HyreFoundation). An insured interior loss is out of scope (HyreRestore). A failed supply line is out of scope (HyrePlumber). HyreYard does not install drains.

Two federal ratings, two different questions

Source fact — drainage class. NSSH Part 618.18: drainage class “identifies the natural drainage condition of the soil. It refers to the frequency and duration of wet periods.” Eight classes, from excessively drained to subaqueous. The class descriptions used on this page are the Soil Survey Manual Chapter 3 definitions, which NSSH points to.

Source fact — hydrologic soil group. NEH Part 630 Chapter 7 assigns soils to groups A, B, C or D by infiltration when thoroughly wet, unprotected by vegetation, under a long-duration storm. The Soil Survey Manual appendix restates the four groups and the three dual classes. Dual classes are assigned only to soils that are group D in their natural condition; the first letter is the drained condition.

HyreYard analysis: homeowners search “why does my yard flood” and get aeration coupons. The survey already split the problem. Drainage class asks how long the profile stays wet. Hydrologic group asks how much of a storm runs off the surface. A somewhat-poorly-drained Group D clay is a different job from a well-drained Group B loam whose downspouts dump at the foundation. Treating them as the same “drainage problem” is how people buy the wrong fix twice.

The eight drainage classes

Class	What NRCS means	Yard reading (HyreYard analysis)
Excessively drained	Water is removed very rapidly. Internal free water is commonly very rare or very deep. Coarse textures, very high hydraulic conductivity, or very shallow soils.	Wetness is not the mapped limitation. If the yard still ponds, look at grade, compaction and roof water first.
Somewhat excessively drained	Water is removed rapidly. Internal free water is very rare or very deep.	Wetness is not the mapped limitation. If the yard still ponds, look at grade, compaction and roof water first.
Well drained	Water is removed readily but not rapidly. Internal free water is commonly deep or very deep; wetness does not inhibit growth of mesophytic crops during the growing season.	Wetness is not the mapped limitation. If the yard still ponds, look at grade, compaction and roof water first.
Moderately well drained	Water is removed somewhat slowly during some periods. Internal free water is moderately deep and transitory to permanent. The soil is wet for only a short time within the rooting depth during the growing season.	Wet for a short time in the root zone. Seasonal puddles possible; chronic ponds usually have another cause.
Somewhat poorly drained	Water is removed slowly so that the soil is wet at a shallow depth for significant periods during the growing season. Wetness markedly restricts mesophytic crops unless the soil is artificially drained.	A soil-property reason standing water returns. Confirm the map unit. Do not start with more fertiliser.
Poorly drained	Water is removed so slowly that the soil is wet at shallow depths periodically during the growing season or remains wet for long periods. Most mesophytic crops cannot be grown unless the soil is artificially drained. The soil is not continuously wet directly below plow depth.	A soil-property reason standing water returns. Confirm the map unit. Do not start with more fertiliser.
Very poorly drained	Water is removed so slowly that free water remains at or very near the surface during much of the growing season. Level or depressed sites, frequently ponded.	A soil-property reason standing water returns. Confirm the map unit. Do not start with more fertiliser.
Subaqueous	Free water is above the soil surface. Positive water potential at the surface for more than 21 hours each day.	Not a residential yard class in ordinary use.

Class names and definitions: NSSH 618.18 and Soil Survey Manual Chapter 3, retrieved 5 September 2026. The “yard reading” column is HyreYard analysis, not an NRCS interpretation rating.

Hydrologic soil groups

Group	Runoff when wet	Definition (NRCS)
Group A	Low	High infiltration when thoroughly wet. Deep, well drained to excessively drained sands or gravelly sands. High rate of water transmission.
Group B	Moderately low	Moderate infiltration when thoroughly wet. Moderately deep or deep, moderately well drained or well drained, moderately fine to moderately coarse texture.
Group C	Moderately high	Slow infiltration when thoroughly wet. A layer that impedes downward movement, or moderately fine / fine texture.
Group D	High	Very slow infiltration when thoroughly wet. Clays with high shrink-swell, a high water table, a claypan near the surface, or soils shallow over nearly impervious material.

NEH Part 630 Chapter 7 (January 2009), restated in the Soil Survey Manual appendix. Dual classes A/D, B/D, C/D are group D undrained.

Group D includes high shrink-swell clays. That is a hydrologic rating, not the NSSH linear-extensibility class used on the expansive-soils page. A soil can be both. They are not interchangeable.

How to look up a parcel without pretending we already did

1
Open Web Soil Survey
Web Soil Survey is NRCS’s public map. It is free. It is not a contractor.
2
Define the area, then look at the map unit
AOI around the house, not the county. Read drainage class and hydrologic group for the dominant component. A polygon that covers the street and the back lawn is not a point sample.
3
Then walk the lot
Where does water stand, after how many hours, after what kind of rain? Does it track the downspouts? The low corner the builder left? The mapped poorly drained inclusion? The survey cannot see the downspouts.
4
Do not excavate first
A French drain in the wrong place, next to a footing, or over a utility is an expensive new problem. The diagnostic tool on this site asks where and when. It will not draw a drain from a dropdown.

Causes that are not a drainage class

Downspouts discharging onto the lawn
Roof water concentrated at two or four points will pond a well-drained soil. That is a conveyance problem, not a map-unit problem.
The lot was regraded for the slab
Cut-and-fill around a new house often leaves a bowl, a reverse slope toward the foundation, or compacted fill that no longer matches the survey map unit.
Compaction from construction or traffic
A well-drained map unit can still perch water in the top six inches if the structure was destroyed. Aeration treats compaction; a French drain does not.
A neighbour’s yard, a sidewalk, or a street that sheds onto you
Off-site water is a grading / drainage-easement question. The soil survey describes the soil, not the neighbour.
An irrigation clock that runs after rain
Standing water the morning after a scheduled watering is not a drainage class.

What this page owns, and what it does not

Covered here

Natural drainage class and hydrologic soil group as NRCS publishes them.

The difference between a wet map unit and a grading / roof-water / compaction failure.

Yards, lawns, beds, surface water that never enters the house.

Not this page

Shrink-swell / linear extensibility breaking pavers and freestanding walls — expansive soils and hardscape.

A wall that retains or bears on the house — HyreFoundation, not a landscape drain.

Water in the living space — HyreRestore. A failed supply line — HyrePlumber.

Method and what we did not compute

Sources
NSSH Part 618.18; Soil Survey Manual Chapter 3 and appendix; NEH Part 630 Chapter 7. Retrieved 5 September 2026.
No acreage table
We did not query Soil Data Access for drainage-class acres by state. The expansive-soils study on this site queried Vertisols and linear extensibility. Copying those acres into a flooding page would be the wrong property.
No 311 table
Municipal drainage-complaint feeds exist in some cities. We did not retrieve them for this launch. A later pass can validate mapped wet soils against complaints where the feed is public.
Web Soil Survey is current; this page is a key
Map units are updated as surveys are maintained. Look up the parcel. Do not treat this page as a substitute for the survey.

Questions

Why does my yard flood?

Sometimes because the soil is mapped somewhat poorly drained, poorly drained or very poorly drained, or because it is hydrologic group D. Sometimes because downspouts, reverse grade, compaction or a neighbour’s runoff pond a well-drained soil. Web Soil Survey tells you the mapped class. Walking the lot after rain tells you which story you are in. This is not a determination about one address.

What is poorly drained soil?

NRCS: water is removed so slowly that the soil is wet at shallow depths periodically during the growing season or remains wet for long periods. Most mesophytic crops cannot be grown unless the soil is artificially drained. It is a natural-drainage class, not a moral judgement on the lawn.

What is hydrologic soil group D?

The high-runoff group in NEH Part 630 Chapter 7: very slow infiltration when thoroughly wet. Clays with high shrink-swell, a high water table, a claypan, or a shallow soil over nearly impervious material. Dual classes such as B/D are group D until drained.

Can I look this up for my house?

Yes. Web Soil Survey (https://websoilsurvey.nrcs.usda.gov/app/) is the public NRCS map. Draw an area of interest around the house and read drainage class and hydrologic group for the map unit. Then walk the yard. The survey does not see your downspouts.

Is standing water after rain always a soil problem?

No. A well-drained map unit with downspouts dumping on the lawn, a reverse slope to the house, or compacted construction fill will pond. Those are grading and conveyance. Fertiliser and seed will not fix them, and neither will a drain in the wrong place.

Should I install a French drain?

Not from this page, and not from a dropdown. A drain is a designed conveyance. Excavation next to a foundation, over utilities or on a septic field is out of scope here. HyreYard does not install drains. The drainage diagnostic on this site asks where and when. It will not specify a pipe.

Is this the same as expansive clay?

No. Shrink-swell is linear extensibility (NSSH Part 618). Drainage class is wetness duration. Hydrologic group D includes some high shrink-swell clays, but the ratings are not the same number. The expansive-soils page on this site owns patios and freestanding walls. This page owns standing water.

Written and audited by

HyreYard Research

Primary-source research, data analysis and fact checking

We are a research desk, not a landscaping company. We read the statute, the municipal code, the water-district rule or the federal soil file ourselves, and we publish the figure with the document it came from and the date we retrieved it. Where a number cannot be traced to a primary source, we publish the shorter page and say what we could not verify. This programme is new. The counts below are what we can already stand behind — a seven-state roster and a rule that we will not make a national claim from it.

10: studies published
50: states in the licensing and HOA tables
7: states the contractor roster is titled to
0: national claims drawn from our own store

How this desk works

Primary sources only. A rule comes from the statute, ordinance, board or agency that issued it, cited by section, with the URL and the retrieval date. We do not cite a blog that cites a code.
Coverage is a number, not a vibe. A table titled to fifty states has fifty sourced rows. A table of cities is titled to the cities we actually read. Gaps are published as gaps.
Store-based facts stay inside the seven states. Texas, Arizona, Washington, California, Oregon, Florida and North Carolina. Texas is the largest roster on the weakest evidence — a self-reported NAICS sales-tax permit — because Texas licenses no landscaper. National claims rest on federal or state agency data, never on our counts.
Fact, calculation, analysis and recommendation stay labelled. "According to…" is a source. "HyreYard analysed… and calculated…" is ours. "This suggests…" is interpretation. We do not present our reading as something the source stated.
We do not landscape, irrigate, treat pests or pull permits, and we take no payment for placement, ranking or a favourable mention. Nobody buys a position on this site.

Data as of NSSH, Soil Survey Manual and NEH Part 630 retrieved 5 September 2026. Authorship on this site is organisational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold. Our editorial policy sets out how we source, date and correct what we publish.

Sources & retrieval dates

USDA NRCS — National Soil Survey Handbook, Part 618.18 Drainage Class , Eight natural drainage classes. Class descriptions live in Soil Survey Manual Chapter 3. Retrieved 5 September 2026.
USDA NRCS — Soil Survey Manual , Chapter 3 drainage-class descriptions; appendix hydrologic soil groups and dual classes. Retrieved 5 September 2026.
USDA NRCS — National Engineering Handbook Part 630, Chapter 7, Hydrologic Soil Groups , January 2009. Groups A–D and dual classes. Retrieved 5 September 2026.
USDA NRCS — Web Soil Survey , Public map-unit lookup for drainage class and hydrologic group at a user-defined area of interest. Retrieved 5 September 2026.

Diagnose before you dig

HyreYard does not install drains. The diagnostic asks where the water stands and when. Web Soil Survey tells you whether the map unit was already wet. Neither is a design.

Drainage diagnostic Find a Landscaping Company

This page is general information about NRCS soil ratings, retrieved on the dates shown. It is not a geotechnical report, not a drainage design, and not a determination about a named lot. HyreYard does not perform landscaping or drainage work. Foundation-bearing conditions, insured interior losses and failed supply lines are out of scope.