Clogged French Drain? Signs, Causes & Fixes

When a French Drain Quietly Gives Up

A French drain is supposed to be a set-it-and-forget-it system. When one stops working, it rarely announces itself. The water just starts pooling again where it used to drain, and you're left wondering whether the drain was ever any good. Most of the time it was — it simply clogged. And in Oregon's fine, silty soils, clogging is the number one reason French drains fail.

The good news: a clogged drain is diagnosable, and many can be fixed without tearing the whole thing out. This guide covers the signs, the causes, and the choice between flushing and rebuilding. For the full system context, see our Oregon drainage guide.

Signs Your French Drain Is Clogged

• Water pools where it used to drain. The clearest signal — the drain isn't moving water anymore.
• Slow drainage after rain. Areas stay wet far longer than they should.
• Nothing comes out of the outfall. If water enters the system but the daylight point or pop-up stays dry during rain, flow is blocked somewhere.
• Soggy ground over the drain line. Water backing up in the pipe saturates the soil above it.
• The drain worked for a few years, then declined. Gradual decline points to sediment slowly filling the system.

What Causes French Drains to Clog

Sediment (The Big One)

Fine soil — silt and clay — washes into the gravel and pipe, fills the void spaces, and eventually blocks the slots. This is the most common failure in Oregon, and it almost always traces back to one thing: missing or inadequate filter fabric. A drain built without geotextile around the gravel envelope has no defense against the fine particles in Willamette Valley soil. It silts up from the inside, sometimes within just a few years. Our perforated vs solid drain pipe guide explains the fabric-and-gravel system that prevents this.

Root Intrusion

Tree and shrub roots seek water, and a French drain is a buffet. Roots work into the pipe through slots and joints, forming a mat that catches sediment and chokes flow. Drains run near established trees are especially vulnerable.

Crushed or Collapsed Pipe

Thin corrugated pipe under a driveway, or any pipe that wasn't bedded properly, can crush under load or settle and collapse. This is a silent failure — the surface looks fine while the pipe is pinched shut underground.

A Failed or Buried Outfall

Sometimes the drain itself is fine and the outfall is the problem — buried under landscaping, crushed, blocked by debris, or grown over. Water has nowhere to exit, so the whole line backs up.

Jet, Snake, or Rebuild?

The right fix depends on the cause.

Jetting or snaking can clear a drain when the pipe is intact but blocked by sediment or roots. A high-pressure water jet flushes out accumulated silt and can cut through fine root masses, restoring flow. This is the least invasive option and worth trying first when the pipe is sound. Our drainage maintenance and cleaning guide covers routine flushing.

Rebuilding becomes necessary when:

• The pipe is crushed or collapsed — no amount of jetting fixes a flattened pipe.
• The drain was built without filter fabric and the gravel itself is fully silted — flushing the pipe doesn't restore a clogged gravel envelope.
• Roots have grown through so thoroughly that clearing them just opens the door to regrowth.
• The original design was flawed — wrong slope, no real outfall, perforated pipe used where solid belonged.

A rebuild is more work, but it's also the chance to fix the original mistake so the new drain lasts decades instead of years. Our French drain cost in Oregon guide covers both repair and replacement budgeting.

Diagnosing the Real Problem

Before deciding, a contractor traces the issue. A camera scope down the pipe reveals whether it's sediment, roots, or a crush. Checking the outfall confirms whether water has anywhere to go. Knowing the slope and whether fabric was used tells you whether jetting will hold or just buy a season before the silt returns. Diagnosis first, fix second — otherwise you risk jetting a drain that needed a rebuild and watching it clog again within the year.

Preventing the Next Clog

A French drain built right rarely clogs: filter fabric around the gravel, the correct slope, solid pipe to a clear outfall, and pipe placed away from aggressive tree roots where possible. Periodic flushing and an outfall check before the heavy winter rains keep a good drain working. The drains that fail early are almost always the ones built without fabric — fix that and clogging becomes a rare event.