Research
Where yards flood, and what the soil survey already knew
The NRCS drainage classes and hydrologic soil groups, read for a residential yard, plus the causes a soil map cannot see.
Written by HyreYard Research Desk Primary-source research and fact checking
The finding
Some yards flood because of the soil itself. NRCS rates every mapped soil in eight drainage classes (NSSH Part 618.18). Somewhat poorly, poorly and very poorly drained soils stay wet near the surface for long periods.
Hydrologic group D (NEH Part 630, Chapter 7) marks the highest runoff. Downspouts, reverse grade and compaction can pond a well-drained soil too. Web Soil Survey shows your map unit; walking the lot after rain shows which cause you have.
Read these limits first
Call 811 before any digging. Do not excavate next to a foundation, over a septic field or toward a utility mark. HyreYard does not install drains.
A soil survey is not a determination about one yard. A map unit is a polygon of similar soils. It does not see your downspouts, your fill or the compacted strip along the driveway. Web Soil Survey is the first lookup; a soil scientist or drainage contractor who walks the lot is the next.
We publish no national flood-yard ranking. We set out to join poorly drained soils to Census housing and check the join against city 311 drainage complaints. We did not run that Soil Data Access query or collect 311 data, so no such map appears here.
Drainage class describes the natural soil, not the installed drain. NSSH infers the class from landscape position and soil morphology. Artificial drainage is recorded as a phase only where it has changed the soil.
Out of scope. House-foundation movement belongs to HyreFoundation, water inside the home to HyreRestore, and a failed supply line to HyrePlumber.
What do the two federal soil ratings measure?
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.” There are eight classes, from excessively drained to subaqueous. The class descriptions below are the Soil Survey Manual Chapter 3 definitions, which NSSH points to.
Hydrologic soil group. NEH Part 630 Chapter 7 sorts soils into groups A, B, C or D by infiltration when thoroughly wet, bare, under a long storm.
The Soil Survey Manual appendix restates the four groups and three dual classes. Dual classes go only to soils that are group D in their natural state; the first letter is the drained condition.
HyreYard analysis. Drainage class asks how long the soil 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 with downspouts dumping at the foundation. Calling both “a drainage problem” can mean paying for the wrong fix.
The eight NRCS drainage classes, read for a yard
| Class | What NRCS means | Yard reading |
|---|---|---|
| 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 limit. If the yard still ponds, check 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 limit. If the yard still ponds, check 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 limit. If the yard still ponds, check 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 are possible; a chronic pond can 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 reason standing water returns. Confirm the map unit before adding fertilizer or seed. |
| 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 reason standing water returns. Confirm the map unit before adding fertilizer or seed. |
| 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 reason standing water returns. Confirm the map unit before adding fertilizer or seed. |
| 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 September 5, 2026. The “yard reading” column is HyreYard analysis, not an NRCS interpretation.
Hydrologic soil groups A to D
| Group | Runoff when wet | Definition (NRCS) |
|---|---|---|
| A | Low | High infiltration when thoroughly wet. Deep, well drained to excessively drained sands or gravelly sands. High rate of water transmission. |
| B | Moderately low | Moderate infiltration when thoroughly wet. Moderately deep or deep, moderately well drained or well drained, moderately fine to moderately coarse texture. |
| C | Moderately high | Slow infiltration when thoroughly wet. A layer that impedes downward movement, or moderately fine / fine texture. |
| 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 when undrained.
Group D includes high shrink-swell clays. That is a runoff rating, not the NSSH linear-extensibility class used on the expansive-soils page. A soil can be both, but the ratings are not interchangeable.
How do I look up the soil under my yard?
Web Soil Survey is the free public NRCS soil map.
Set the area of interest around the house, not the county. Read drainage class and hydrologic group for the main soil component. A polygon covering the street and the back lawn is not a point sample.
Where does water stand, and for how many hours? Does it track the downspouts, the low corner the builder left, or a mapped wet inclusion? The survey cannot see the downspouts.
A French drain in the wrong place, next to a footing or over a utility line creates a new problem. Our drainage diagnostic asks where and when water stands. It does not design a drain.
Causes of standing water that are not the soil
Roof water concentrated at two or four points will pond a well-drained soil. That is a conveyance problem, not a map-unit problem.
Cut-and-fill around a new house can leave a bowl, a reverse slope toward the foundation, or compacted fill that no longer matches the survey map unit.
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.
Off-site water is a grading or drainage-easement question. The soil survey describes the soil, not the neighbor.
Standing water the morning after a scheduled watering is not a drainage class.
What this page covers, 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 or compaction failure.
Yards, lawns, beds and surface water that never enters the house.
Not this page
Shrink-swell soils breaking pavers and freestanding walls: expansive soils and hardscape.
A wall that retains soil against the house: HyreFoundation, not a landscape drain.
Water in the living space: HyreRestore. A failed supply line: HyrePlumber.
How we built this page, and what we did not compute
NSSH Part 618.18; Soil Survey Manual Chapter 3 and appendix; NEH Part 630 Chapter 7. Retrieved September 5, 2026.
We did not query Soil Data Access for drainage-class acres by state. The expansive-soils study queried Vertisols and linear extensibility, a different property, so those acres do not belong here.
Some cities publish drainage-complaint feeds. We did not retrieve them. A later pass can test mapped wet soils against complaints where a feed is public.
Map units are updated as surveys are maintained. Look up the parcel; this page is a key to reading it, not a substitute.
Questions
Why does my yard flood?
What is poorly drained soil?
What is hydrologic soil group D?
Can I look this up for my house?
Is standing water after rain always a soil problem?
Should I install a French drain?
Is this the same as expansive clay?
Written and audited by
HyreYard Research Desk
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.
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Data as of NSSH, Soil Survey Manual and NEH Part 630 retrieved September 5, 2026. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold.
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Sources & retrieval dates
Diagnose before you dig
HyreYard does not install drains. The diagnostic asks where water stands and when. Web Soil Survey tells you whether the ground was mapped wet. Neither one is a design.
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.