Parking Lot Drainage in Happy Valley, Oregon: Stop the Ponding

Why Happy Valley Parking Lots Pond

Happy Valley sits on the rising ground east of the Willamette, where Clackamas County's hills, heavy clay subsoil, and long wet season combine to make parking lot drainage a recurring headache. Lots along Sunnyside Road, Misty Drive, and the newer retail centers off 172nd Avenue catch runoff from above and hold it on a surface that clay refuses to let drain downward. When a Pacific atmospheric river parks over the metro for three straight days, the water has nowhere to go but across your asphalt.

Ponding is not just a nuisance. Standing water seeps through hairline cracks, softens the gravel base beneath the pavement, and accelerates the freeze-thaw cycle that breaks asphalt apart over a Happy Valley winter. A lot that ponds today becomes a lot with alligator cracking and potholes within a few seasons. The fix is almost never more sealcoat — it is correcting where the water goes.

If you manage a retail strip, church, medical office, or apartment complex in Happy Valley, this guide explains why your lot ponds and what a real drainage correction involves. For the broader picture, start with our guide to property and site drainage in Oregon.

How Parking Lot Drainage Actually Works

A well-drained parking lot moves water in a deliberate sequence: the surface is sloped so every square foot drains toward a low point, inlets (catch basins) collect that water at the low points, underground pipe carries it away, and an outfall releases it to a storm system, swale, or approved discharge point. Break any link in that chain and water backs up onto the surface.

In Happy Valley, the most common failure is the surface slope itself. Many older lots were paved with too little fall, or have settled over the years so that what was once a gentle 1.5 percent slope toward an inlet is now a dead-flat or even reverse-graded birdbath. Clackamas County's clay base compresses unevenly, and heavy delivery traffic accelerates the settling.

Typical components of a corrected lot

• Surface grading — A minimum of roughly 1 to 2 percent slope toward inlets so water sheets off rather than puddles
• Catch basins — Set at the low points, spaced so no single basin is overwhelmed in a downpour
• Underground conveyance pipe — Sized to the lot's drainage area and the region's rainfall intensity
• Oil-water separator or water-quality treatment — Often required for commercial lots under Oregon DEQ stormwater rules
• A positive outfall — Where the water legally and physically exits the property

Our detailed commercial parking lot drainage design guide walks through inlet spacing and slope targets in depth.

What Drives the Cost in Happy Valley

Every lot is different, so any honest answer starts with a site assessment rather than a flat price. That said, the factors below drive what a Happy Valley drainage correction costs. Industry baseline ranges are a starting reference only — actual project cost depends on your lot's condition.

• How much of the surface needs regrading — A localized birdbath repair (mill, fill, and re-slope a single low spot) is far cheaper than re-establishing slope across an entire lot
• Number and depth of catch basins — Clay digs slow and wet; deeper inlets and longer pipe runs raise excavation cost
• Distance to a legal outfall — Lots far from a storm main or approved discharge point need longer conveyance runs
• DEQ water-quality requirements — Commercial sites disturbing enough area may need treatment and permitting
• Surface restoration — New asphalt patching, an overlay, or full resurfacing over the corrected base

Because clay holds water and Happy Valley's terrain often slopes toward, not away from, the buildings it serves, drainage corrections here tend to run more involved than on a flat, sandy lot east of the Cascades.

Signs Your Lot Needs Drainage Work

• Puddles that linger more than a day or two after rain stops
• "Birdbath" depressions that hold water in the middle of drive aisles or stalls
• Cracking and potholes clustered around the low spots
• Catch basin grates that overflow or stay submerged during storms
• Water sheeting toward the building entrance instead of away from it
• Ice patches forming in the same spots every winter

Any one of these is worth a professional look before the damage spreads into the base layer, where repairs get dramatically more expensive.

The Clackamas County Clay Factor

The single biggest reason Happy Valley lots behave differently from, say, a lot in Central Oregon is the soil. The valley's silty clay loam drains slowly and swells when saturated. That means you cannot rely on water simply soaking into the ground beneath the pavement — it has to be collected and conveyed. Dry wells and infiltration trenches that work in sandy soil often fail in Happy Valley clay because the surrounding ground won't accept the water fast enough.

This is why a surface-and-conveyance approach — proper slope, catch basins, and piped outfall — is usually the right answer here, and why a contractor who knows local soils matters. A solution copied from a high-desert lot will pond by the first real storm.

How a Drainage Correction Project Runs

A typical Happy Valley parking lot drainage project follows these stages:

1. Site assessment — We measure existing grades, identify low points, locate the legal outfall, and check soil and base condition
2. Design — Slope targets, inlet locations, pipe sizing, and any required DEQ treatment are laid out
3. Permitting — City of Happy Valley or Clackamas County grading and stormwater approvals where required
4. Excavation and installation — Catch basins set, pipe trenched and laid to grade, base corrected
5. Surface restoration — Patch, overlay, or resurface, then re-stripe
6. Verification — We confirm the lot drains as designed, ideally observed during or after a rain event

Skipping the assessment is how lots end up with a brand-new catch basin sitting at the wrong elevation, still surrounded by standing water.

Why a Professional Assessment Matters

No price chart can tell you what your lot needs, because the answer lives underground and in the grades. A contractor who measures your slopes, locates your outfall, and evaluates your base will give you a real scope and an accurate quote — not a guess. For Happy Valley commercial properties, that assessment also catches DEQ obligations early, before they become a permitting surprise.

Cojo Excavation & Asphalt provides drainage assessments and corrections across Happy Valley and the wider Clackamas County area. Learn more about our excavation services or request a free quote and we'll come measure your lot.