If you’ve ever said, “Sometimes it works… and sometimes it doesn’t,” you’re describing one of the most common and most misunderstood drainage problems I see across Maryland.
These are the toughest water issues for homeowners because they create doubt. After a light rain, everything looks fine. After a heavy storm, the yard floods again. One season the system seems to do its job. The next season, the same wet spots return.
Homeowners often tell me, “Bob, we already have drainage. Why is this still happening?”
After more than four decades diagnosing drainage problems, I can tell you this with confidence: a drainage system that works sometimes is almost always telling you something very specific about the water problem — and it’s rarely random.
This article is written in my AskBobCarr educator voice, the way Marcus Sheridan teaches us to communicate. I’m going to walk you through exactly what I check when a drainage system works part of the time but not all of the time, using real homeowner stories, real Maryland conditions, and the diagnostic framework we use at TLC before recommending any changes.
WHY “SOMETIMES” IS THE MOST IMPORTANT CLUE
When a drainage system fails all the time, the cause is usually obvious: no discharge, collapsed pipe, clogged system, or completely wrong design.
But when it works sometimes, that’s a clue.
It means the system can handle certain conditions but not others. That narrows the list of causes dramatically.
Most intermittent drainage problems come down to capacity, discharge, water source, or timing — not total failure.
The key is identifying which variable changes when the system stops working.
STEP ONE: I LISTEN TO THE HOMEOWNER’S STORY FIRST
Before I look at the yard, I listen.
I ask questions like:
When does it work well?
When does it fail?
Is it worse after heavy rain, long rain, or snow melt?
Does it fail in spring but not summer?
Did anything change before the problem started?
Have you noticed water backing up from a discharge point?
Do downspouts tie into the drainage system?
These questions matter because intermittent drainage problems are usually triggered by specific conditions.
A homeowner in Columbia once told me, “It only floods after long rains, not quick storms.” That immediately pointed me toward capacity and discharge issues instead of clogs.
STEP TWO: I IDENTIFY THE TYPE OF WATER INVOLVED
The next thing I determine is what kind of water the system is dealing with.
Surface water shows up quickly and moves fast. Subsurface water builds slowly and lingers. Roof runoff is high volume and concentrated. Groundwater is slower and persistent.
A system that works sometimes is often being asked to manage more than one type of water.
A homeowner in Severna Park said, “It worked fine until we tied the downspouts into it.” That one change turned a groundwater drain into a roof-water drain — and the system was never designed for that volume.
When roof water overwhelms a system designed for groundwater, intermittent failure is almost guaranteed.
STEP THREE: I CHECK DISCHARGE FIRST — NOT THE PIPE
One of the biggest mistakes homeowners make is assuming the pipe is clogged.
In reality, many systems fail intermittently because the discharge point becomes compromised.
I physically locate where the water exits and look at:
Is it lower than the collection area?
Does it stay open during heavy rain?
Does it empty into an area that floods itself?
Does it get buried by mulch, leaves, or sediment?
Does water ever back up toward the house?
A homeowner in Gambrills told me, “It used to work, but now it doesn’t.” The pipe was fine. The outlet had been buried over time.
Clearing and protecting the discharge restored full function.
STEP FOUR: I EVALUATE CAPACITY VS. DEMAND
Drainage systems are designed for certain volumes of water.
If demand exceeds capacity, the system will work sometimes and fail during peak events.
This happens when:
Rain events exceed design assumptions
Additional water sources are added
The yard changes and sheds more water
Soil compacts and reduces infiltration
I look at pipe size, number of inlets, spacing, and how much area the system is being asked to serve.
A homeowner in Odenton once said, “It works unless we get a really heavy storm.” That’s a classic capacity issue.
STEP FIVE: I CHECK SLOPE AND PIPE ALIGNMENT
Drainage relies on gravity. If slope is marginal, small changes can have big effects.
Pipes that are too flat, have bellies, or settle unevenly may move water during light events but stall during heavy ones.
Signs include:
Slow drainage long after rain stops
Water bubbling at inlets
Wet stripes along trench lines
In many cases, correcting slope in a single section restores reliability.
STEP SIX: I LOOK FOR SOIL AND FABRIC ISSUES
In Maryland clay soils, fabric and stone choice matters.
Over time, fine particles migrate and clog poorly designed systems.
A system may work early in its life, then slowly lose effectiveness.
A homeowner in Arnold told me, “It worked great for a couple of years, then gradually stopped.” Diagnosis revealed fabric that clogged like a filter.
STEP SEVEN: I CHECK SEASONAL PATTERNS
Seasonal clues are critical.
If a system fails mainly in spring, shallow groundwater and saturated soils are often involved.
If it fails during summer storms, roof runoff and surface flow are usually the culprits.
If it fails after snow melt, frozen ground and poor surface drainage are often at play.
Matching the fix to the season prevents overbuilding.
CASE STUDY: THE ‘IT WORKS MOST OF THE TIME’ YARD
A homeowner in Pasadena said, “Most of the time it’s fine. Then once or twice a year, it’s a mess.”
Diagnosis showed the system handled normal rain but failed when roof runoff and groundwater combined during long storms.
The solution wasn’t replacing the system — it was separating roof water and improving discharge.
STEP EIGHT: I LOOK FOR ‘HELPFUL’ PAST FIXES THAT CREATED NEW PROBLEMS
Over the years, homeowners and contractors add fixes that seem logical but cause new issues.
Adding heads to a drain
Tying more downspouts into an existing line
Covering outlets with mulch
Changing grading without adjusting drainage
These changes often create intermittent failure.
STEP NINE: I DECIDE WHETHER THE SYSTEM IS UNDERBUILT, OVERBUILT, OR MISUSED
Intermittent performance usually points to one of three things.
The system is underbuilt for current conditions.
The system is overbuilt but discharges poorly.
The system is being used for a problem it wasn’t designed to solve.
That distinction guides the solution.
FAQS HOMEOWNERS ASK ABOUT INTERMITTENT DRAINAGE
Why does it only fail during heavy rain? Because demand exceeds capacity or discharge during peak events.
Is intermittent failure worse than constant failure? It’s harder to diagnose, but usually easier to fix once understood.
Do I need to replace the whole system? Often no. Targeted corrections are usually enough.
Can maintenance fix intermittent problems? Sometimes. Clearing outlets and inlets can restore function.
How long should diagnosis take? Long enough to observe patterns — not a five-minute walk.
FINAL THOUGHTS FROM BOB CARR
When a drainage system works sometimes but not always, it’s not random. It’s giving you clues.
The key is understanding which conditions overwhelm the system and why.
At AskBobCarr.com, my goal is to help homeowners stop guessing and start understanding.
Diagnosis first. Explanation second. Solutions that actually work.
That’s how we’ve helped Maryland homeowners for more than four decades — and it’s how I’d want someone to help my own family.