Excavation
French Drain for a Wet Backyard in Oregon
Cojo
April 18, 2026
10 min read
A soggy backyard is the defining Oregon homeowner complaint. Water sits on the lawn for weeks at a time in winter. Kids cannot play on the grass. Pets track mud into the house. Raised beds rot. The clothesline area smells like a swamp. By February, half the yard is unusable.
The reason this is so common in Oregon is specific: clay soil plus 40–60+ inches of rain per year in the Willamette Valley. Clay does not absorb water, so every inch of rain that does not run off as surface flow just sits in the top foot of soil until evaporation removes it months later. In winter, evaporation cannot keep up. The yard stays saturated — the same pattern you see at scale on sloped backyard properties across the valley.
A French drain is the most common, most effective, and most durable fix. It is a gravel-filled trench with a perforated pipe at the bottom, wrapped in filter fabric, that collects subsurface water and carries it to a legal discharge point. Done right, it transforms a seasonal swamp into a usable yard within one rainy season.
This article is the residential backyard-focused variant of the general French drain cost article. It goes deeper on the specifics that matter most to a homeowner looking at a wet lawn. For surface-water problems that don't need a buried pipe, also see our drainage swale grading guide.
Published industry averages are baselines, not guarantees. Backyard French drain cost depends on length, depth, discharge option, soil type, and access for equipment.
Industry Baseline Range
| Backyard Drain Scenario | Unit | Industry Baseline |
|---|---|---|
| Short drain, easy discharge (under 50 ft) | per linear foot | $15 – $80+ |
| Medium drain, typical backyard (50–150 ft) | per linear foot | $20 – $100+ |
| Long drain, sump pump required | per linear foot | $30 – $120+ |
| Drain with dry well (no legal outlet) | per linear foot | $25 – $110+ |
| Full backyard system (multiple branches) | total project | $4,000 – $22,000+ |
| Line Item | Unit | Industry Baseline |
|---|---|---|
| Drainage gravel delivered | per cubic yard | $45 – $110+ |
| 4-inch perforated pipe | per linear foot | $2 – $8+ |
| Filter fabric | per sq ft | $0.50 – $2.00+ |
| Sump pit and pump | flat | $800 – $3,500+ |
| Dry well installation | flat | $1,200 – $5,500+ |
| Dirt haul-off | per load | $250 – $750+ |
| Mobilization | flat | $250 – $800+ |
| Minimum job callout | flat | $500 – $1,500+ |
The industry baseline ranges above represent ideal conditions — easy access, workable soil, shallow depth, minimal haul-off. In practice, actual project costs frequently exceed published averages by 2 to 3 times when complications arise. Oregon's clay soils, rocky terrain, unmarked utilities, permit requirements, and disposal fees can all push costs well above baseline figures. The only reliable way to know your actual cost is through an on-site assessment.
Backyards routinely hide:
The three questions that size the job:
Typical residential sizing:
A 60-foot single-run drain handles a typical soggy backyard corner. A 120-foot branched system handles a fully saturated lawn.
Gravity daylight: Simplest and cheapest. If the yard slopes to a lower area (street, alley, creek, lower property line with easement), the drain simply empties out at grade.
Storm drain tie-in: Legal in most Oregon jurisdictions with a permit. Requires a licensed plumber for the connection in most cases.
Dry well: A gravel-filled pit (sometimes with a prefabricated infiltration chamber) that lets collected water slowly percolate into surrounding soil. Works best when there is a deeper, more permeable soil layer below the clay. Sometimes doesn't work well in pure clay. Our dry well installation cost guide goes deeper on sizing.
Sump pump: Water is collected in a sump basin, then pumped to a higher discharge point. Required when the yard has no gravity outlet. Adds ongoing power cost and the risk of pump failure — see sump pump trench excavation for trench and power specifics.
Not a legal discharge option: Your neighbor's yard, the sidewalk, or anywhere that obviously creates a nuisance for someone else.
Restoring the yard (topsoil, seed, sod) adds days after the drain is buried.
Willamette Valley clay: Clay is the reason French drains are so effective here, but also the reason the drain has to be designed properly. Clay needs clean washed drainage gravel (not pea gravel), filter fabric on all sides of the rock, and a pipe slope of at least 1% (1/8 inch per foot). Mistakes in any of these cause clay fines to migrate into the gravel and the drain clogs within 5 years. On backyards that also have standing-water problems uphill, pair the drain with a drainage swale to handle surface flow separately.
Wet-season constraints: Working saturated clay is a slog. Equipment gets stuck, trenches collapse, and the yard ends up churned. Most contractors push backyard drains to the May–September window when possible.
Lot access: Backyards are frequently fence-enclosed with narrow gates. If a mini excavator cannot fit through the gate, the job becomes hand-dig or temporary fence removal. Either option adds days — and the spoil often needs to be hauled away, which is where our backyard dirt removal costs guide comes in.
Neighbor relations: Trenching across a property line for a gravity outlet often requires a recorded easement or explicit permission. Discharge onto a neighbor's property is not legal.
Protected trees: Portland and some other Oregon jurisdictions have tree codes. Cutting structural roots of protected trees during trenching can result in violations and fines.
Stormwater rules: Some jurisdictions require on-site stormwater management. A dry well or rain garden may be required rather than a direct connection to a storm drain.
DIY-friendly:
Hire a pro for:
The most common DIY mistakes are wrong slope (water pools instead of flows), missing filter fabric (clay clogs the gravel within a few years), and no legal outlet (water ends up under the neighbor's fence).
Permit fees typically $100 – $600+ when applicable.
For the full vetting checklist, see how to hire a residential excavation contractor.
A wet Oregon backyard does not have to stay wet. A properly designed French drain converts a seasonal swamp into a usable yard with 30+ years of service life. The difference between a drain that works for decades and a drain that clogs in 3 years comes down to slope, gravel, fabric, and outlet choice — four details that a knowledgeable contractor treats as non-negotiable. On sloped lots where groundwater is moving through the yard from above, we also recommend a companion curtain drain to intercept flow before it reaches the saturated zone.
Cojo provides free on-site assessments for backyard drainage across Oregon. We diagnose the water source, identify the legal outlet options, and put the drain scope in writing.
Get a free excavation estimate, explore our services, or see our project portfolio and additional resources.
How much does a backyard French drain cost in Oregon? Industry baseline ranges run roughly $15 to $120+ per linear foot, with total backyard projects landing between $1,500 and $22,000+ depending on length, depth, discharge option, and whether a sump pump or dry well is required. Clay soil and tight access routinely push costs above baseline. On-site assessment is the only reliable way to budget.
How long does a backyard French drain last? A properly installed drain with clean washed gravel, filter fabric on all sides, and a 1%+ slope lasts 30–40 years before needing major work. Drains without filter fabric or with the wrong gravel often fail within 5–10 years as clay fines migrate into the rock.
Do I need a permit for a backyard French drain in Oregon? Simple gravity-discharge yard drains usually do not require a permit. Drains that tie into a storm sewer, drains crossing a property line, or drains involving significant grading changes often do. Permit fees generally fall in the $100 – $600+ range. Check with your local building department.
Can I run the drain to my neighbor's yard? No, not legally. Discharging collected water onto a neighbor's property is a nuisance and is generally prohibited. Legal discharge options are a public storm drain (with permit), a natural drainage course on your own property, a dry well on your property, or a sump pump discharge to an approved location.
How fast will the backyard dry out after installation? Most homeowners see dramatic improvement within the first significant rain event after installation. Fully saturated clay takes weeks to drain even with a new drain in place, so the full benefit usually shows up over the course of a single wet season rather than immediately.
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