A catch basin, also called a yard drain or area drain, is a surface inlet that collects water and sends it through pipe to an outlet. When it overflows, water comes up out of the grate instead of going down.
Overflow usually means the pipe downstream is blocked, too small, too flat, or has no outlet.
What you may be seeing
- Water bubbling up out of the grate
- Water standing around the basin
- Silt and debris in the basin
- The grate covered with grass or mulch
- The basin works in light rain but overflows in storms
First question: is the basin full of debris, or is the problem downstream?
Lift the grate. If the box is full of silt or leaves, clean it and test it. If it's clean but still backs up, the pipe or the outlet is the problem.
If the basin is full of debris
The sump and pipe entrance are blocked.
Possible causes:
- Leaves and grass clippings
- Silt from bare soil
- Mulch washing in
If the basin is clean but backs up
The pipe or the outlet is blocked or undersized.
Possible causes:
- Clogged or crushed pipe
- Buried outlet
- Roots in the line
If it only overflows in heavy rain
The system can't carry the volume.
Possible causes:
- Undersized pipe
- Several downspouts on one line
- Flat pipe slope
What you can check yourself
Only check these safely and after rain has stopped. Do not dig near marked utilities, and do not go near electrical equipment that is standing in water.
- Lift the grate and clean the basin
- Hose test and watch the outlet
- Find whether downspouts connect to the same line
- Keep grates clear of grass and mulch
Answer 20 quick questions → to get a preliminary drainage assessment.
What a drainage professional may evaluate
- Camera inspection
- Jetting
- Pipe size and slope check
- Outlet capacity check
Most common causes
Debris
Leaves, clippings and silt.
Pipe blockage
Silt, roots or crushing.
Outlet problems
Buried, blocked or too high.
Undersized or overloaded line
Too much water for one pipe.
Possible solutions
The right fix depends on where the water comes from, where it collects and where it can legally and physically go. These are the solutions most often considered:
Clean the basin and pipe
Restore flow.
Outlet repair
Open or rebuild the discharge.
Resize or add lines
Separate downspouts or increase pipe size.
Sediment control
Stabilize nearby bare soil.
When to call a drainage professional
- The basin backs up after cleaning
- It floods near the house
- You can't find the outlet
- It overflows in most storms
Frequently asked questions
How often should catch basins be cleaned?
Check them a few times a year and after storms, more often near trees.
Why is my yard drain overflowing?
It's usually blocked downstream, has a buried outlet, or carries more water than the pipe can handle.
Bottom line
An overflowing catch basin is a symptom of what's downstream. Clean it, test it and fix the pipe or the outlet.
This page is educational and does not replace an onsite evaluation. Conditions, codes and HOA rules vary by property.