Why Dallas–Fort Worth yards hold water — North Texas clay soil explained
Most of Dallas–Fort Worth is built on clay that soaks up water fast when it's dry, then swells shut when it's wet. That's why water sits in DFW yards after a storm.
The soil under DFW
Eastern Dallas County and Collin County sit on the Blackland Prairie, a band of dark, heavy clay that runs from north of Dallas south toward San Antonio. Parts of western Dallas County are on different soil. Its best-known soil, Houston Black, is the official state soil of Texas. In one USDA profile it's about 55% clay.
These are expansive clays, which means they change volume as they get wet and dry:
- When dry, they shrink and crack. The USDA describes cracks from half an inch to 4 inches wide, a foot down. Water pours into those cracks, so a dry yard soaks up a light rain quickly.
- When wet, the clay swells and the cracks close. Water then moves through it very slowly.
That second state is the problem. After a long rain, or a heavy one on already-wet ground, the soil is effectively sealed. Anything that can't run off the surface stays put.
Why it shows up in some yards and not others
- Flat lots, or low spots where water collects and can't run off
- Downspouts that dump a whole roof's worth of water in one place
- Ground that slopes toward the house, often after landscaping or settling
- Neighboring yards that drain across yours
Why it matters for your house
The same swelling and shrinking that seals the soil can move a foundation. Big swings between soaked and dry soil right next to a slab are what you want to avoid. Water pooling against the house during wet months, then the ground baking dry in summer, is the worst pattern.
What actually helps
- Move the water, don't try to make the clay absorb it. Regrading, French drains and buried downspout lines all carry water away instead of waiting for it to soak in.
- Slope the ground away from the house. For new construction, the International Residential Code (as cities adopt it) requires the ground to fall at least 6 inches in the first 10 feet from the foundation. Where there isn't room, it calls for a drain or swale instead. It's a good target for an existing yard too.
- Extend downspouts well away from the foundation, or pipe them underground in solid pipe to their own outlet.
- Don't count on amendments. Compost and sand help lawns and beds, but they don't drain the clay below.
Next: what a fix costs, or whether you can do it yourself.
Common questions
Why does water stand in my yard for days after rain?
The clay under most DFW yards absorbs water quickly when it's dry and cracked, but very slowly once it's wet and swollen. After a long or heavy rain, water that can't run off the surface has nowhere to go.
Does standing water hurt my foundation?
It can. Clay swells when it's wet and shrinks when it dries, and big swings in moisture near the house can move a slab foundation. Keeping water moving away from the house helps keep the soil moisture around the foundation more even.
Will adding sand or compost fix clay drainage?
Not for a real standing-water problem. Amending the top few inches helps lawns and beds, but the clay below still won't drain. Moving the water with grading or a drain is what fixes pooling.
Sources
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