Yard Drainage Learning Center: The Concepts Behind the Fixes
Every drainage fix rests on a few basics: how water moves across and through the ground, whether your soil can absorb it, why clay behaves the way it does, and how much slope water needs to move. Understand these four and you can judge any advice you're given.
Why the basics are worth ten minutes
Most yard drainage mistakes aren't installation errors — they're understanding errors. A French drain buried under surface water, a dry well dug into clay, a low spot filled in a yard that drains poorly everywhere: each is the right tool used without grasping the concept underneath.
The pages here cover the four ideas that sit beneath every drainage decision. None of them takes long, and together they let you tell whether the advice you're reading — or being quoted — actually fits your yard.
The four concepts
- How yard drainage works — surface water versus water in the soil, and why that single distinction decides almost everything.
- What is a perc test? — the septic test for land, how it differs from a soil evaluation and a DIY drainage test, and what results and costs look like.
- How to test your soil's drainage — the one-hour perc test that tells you whether your ground can absorb water at all, and what the result means.
- Clay soil and drainage — why the soil that causes most drainage problems drains so slowly, and what actually helps.
- How much slope you need for drainage — the grade numbers, how to measure them, and why "flat" is rarely as flat as it looks.
Reference tables
The numbers the calculators use, with their sources, so a figure from a quote, a spec sheet or another site can be checked against the same baseline.
- North Carolina rainfall data for drainage design — storm depths and peak intensities for 18 NC cities from NOAA Atlas 14, and which figure each calculator wants.
- Soil infiltration rates by soil type — how fast sand, loam and clay actually absorb water, in inches per hour, and what that rules in or out.
- Drainage gravel sizes and void space — #57 stone, pea gravel, crusher run: what each is for, how much water it stores, and what it weighs.
Once these make sense, what you're seeing and which fix suits it both get much easier to sort out.
FAQs
What do I need to understand before fixing yard drainage?
Four things: whether your water is on the surface or in the soil, whether your soil can absorb water (a perc test answers this), how clay changes the picture if you have it, and how much slope you have to move water. Those four decide which solutions can possibly work in your yard, before cost or preference enter into it.
Why does understanding the basics matter?
Because most drainage failures are the right tool used in the wrong situation — a French drain for surface water, a dry well in clay. Grasping a few concepts lets you avoid those expensive mistakes and judge whether a contractor's diagnosis makes sense. Ten minutes of understanding saves thousands in misapplied fixes.
All pages in this section
Clay Soil and Drainage: Why It Holds Water and What Actually Helps
Clay drains slowly because its particles are tiny and pack tightly, leaving almost no room for water to pass — often less than half an inch an hour. That's why it causes most yard drainage problems.
Does Gravel Help Yard Drainage? The Dig-a-Hole Myth, Explained
Gravel drains water through itself far better than soil — but it's a conduit, not a destination. Water still has to reach somewhere lower or soil that absorbs it.
Drainage Gravel Sizes and Void Space: #57 Stone, Pea Gravel, Crusher Run and What Each Is For
Use clean, washed, angular stone about ¾ to 1 inch — #57 in most of the US — for French drains, dry wells and behind retaining walls. It stores water in roughly 40 percent of its volume and weighs about 1.4 tons a cubic yard.
French Drain Maintenance: What It Needs, and How Long It Lasts
A French drain needs inspecting once a year and flushing every one to two years, more often under trees or in silty soil. Most of what determines its life was decided at installation — fabric, stone, and access — not by anything you do afterwards.
How Much Slope Do You Need for Drainage?
Near the house, aim for about 6 inches of fall over the first 10 feet — roughly a 5% grade. Out in the yard, 1% is enough to move water — about ⅛ inch per foot, or 1¼ inches per 10 feet.
How to Test Soil Drainage: A Free DIY Perc Test
You can test soil drainage for free with a shovel, water, a ruler, and an hour. Dig a 12-inch hole, fill it and let it drain to pre-soak the soil, then refill it and measure the drop after one hour.
How Yard Drainage Works: Surface Water vs Water in the Soil
Yard drainage manages two kinds of water: water on the surface, which runs and pools where you can see it, and water in the soil, which soaks in and saturates the ground below. Different tools handle each, and telling them apart is the one distinction that decides almost every drainage fix. .
North Carolina Rainfall Data for Drainage Design: Storm Depths and Intensities by City
Across most of North Carolina a hard day of rain that arrives every year or two drops about 3.4 to 3.8 inches in 24 hours; the once-a-decade storm drops about 5 inches, and the coast sees 4.5 and 7. For sizing pipes and grates, the 10-year peak intensity runs about 7 inches per hour in the Piedmont and 9 to 10 on the coast.
Retaining Wall Backfill and Geogrid: The Specification
Behind a retaining wall you want at least 12 inches of 3/4-inch clear gravel running the full height, filter fabric between that gravel and the native soil, and a 4-inch perforated pipe at the base falling about one inch every four feet to an outlet. Geogrid reinforcement normally enters above three to four feet. .
Soil Infiltration Rates by Soil Type: How Fast Sand, Loam and Clay Actually Drain
Sand absorbs water at 2 to 8 inches per hour or more, loam at roughly a quarter to half an inch, and clay at a twentieth of an inch or less. The line that matters for a yard is about half an inch per hour: above it, dry wells and rain gardens work; below it, water has to be moved rather than soaked in.
What Is a Perc Test? How It Works, Costs and What Failing Means
A perc test measures how fast water soaks into soil, in minutes per inch, to decide whether land can support a septic drain field. A licensed evaluator digs test holes to drain-field depth, saturates them and times the water drop.
By Under Your Home Team · Last reviewed 2026-08-09