Parking Lot Drainage in Gresham, Oregon: Stop the Ponding

Why Gresham Parking Lots Pond

Gresham's commercial corridors along Powell Boulevard, Division Street, and Burnside Road carry a lot of traffic, and the lots that serve them take a beating from the Pacific Northwest wet season. The eastern Portland metro gets months of steady rain, and Gresham's heavy clay soil makes the job harder: water that should drain away through the sub-base instead sits in saturated clay, weakening the base from below while the rain ponds on top.

A ponding parking lot is more than an eyesore for a property manager. Standing water accelerates asphalt failure, undermines the base, breeds potholes, washes out striping, and creates a liability hazard. In Gresham's climate and soil, the problem compounds fast. The causes are finite and the fixes are known — but they have to account for the clay and the relentless rain. This guide walks through both.

For the wider picture, see our guide to property and site drainage in Oregon. For lot grading engineering, see parking lot drainage design in Oregon.

What Causes Lot Ponding in Multnomah County

Flat or Settled Slope

A lot needs roughly a 1 to 2 percent slope to drain. Years of traffic loading settle Gresham asphalt unevenly, and on clay sub-base the surface can sink into low spots that hold water. Once a birdbath forms, the standing water softens the asphalt beneath it and the low spot grows.

Saturated Clay Sub-base

This is Gresham's signature problem. When the clay base under the asphalt stays saturated through the wet months, it loses load-bearing strength. The surface sinks, new low spots appear, and the whole lot becomes more prone to ponding and potholing.

Clogged or Undersized Catch Basins

Months of rain wash silt, leaves, and debris into the catch basins and storm lines. A basin that worked in summer backs up once it is half-full, and undersized systems simply cannot move Gresham's peak winter flows.

Crushed or Disconnected Storm Lines

Older lots along Gresham's established commercial streets often have storm pipe that has shifted or cracked over decades, so water enters the inlet and has nowhere to go.

How Parking Lot Drainage Gets Fixed in Gresham

The repair depends on the cause, so an assessment comes first. Common solutions include:

• Regrading and an asphalt overlay — Milling and overlaying to re-establish positive slope is the most durable fix for widespread ponding, especially over a settled clay sub-base.
• Adding or relocating catch basins — A new inlet tied into the storm system gives water somewhere to go where it currently collects.
• Trench drains — Across entrances and drive aisles, linear trench drains capture sheet flow before it crosses the lot.
• Storm line repair or replacement — Cracked or undersized pipe gets excavated and replaced, often with larger line to handle Gresham's wet-season flows.
• Sub-base repair — Where saturated clay has failed the base, the affected area is excavated and rebuilt before resurfacing.

Our excavation services cover the grading, trenching, and catch-basin work involved.

What Parking Lot Drainage Costs in Gresham

Drainage corrections are priced by the foot, by the structure, and by the volume of excavation — never a flat rate. Industry baseline ranges commonly referenced include:

Work	Industry Baseline Range
Catch basin installation (each)	$1,200–$3,500
Trench drain (per linear foot)	$50–$150
Storm line run (per linear foot)	$25–$60
Asphalt overlay for regrading (per sq ft)	$2–$5

In Gresham, cost drivers are excavation depth, whether the clay sub-base needs rebuilding, the distance to a storm tie-in, and how much asphalt has to be removed. A new catch basin and short pipe run sits at the low end; a full regrade with sub-base repair and new storm infrastructure runs well above it. A site assessment is the only way to budget accurately.

Why a Site Assessment Matters in Gresham

Two Gresham lots with identical ponding can need completely different repairs. One may have a flat slope correctable with an overlay; the next may have a saturated, failing clay sub-base that no resurfacing alone will fix, or a collapsed storm line under the asphalt. A proper assessment measures the slope, inspects and flushes the catch basins and lines, and evaluates the sub-base. Skipping it is how property owners pay twice — first for a cosmetic patch, then for the real repair after it ponds again the next winter.

Get Your Gresham Parking Lot Drainage Quote

Cojo Excavation & Asphalt helps Gresham and Multnomah County property managers stop ponding for good, with solutions designed for clay sub-base and the long PNW wet season. We assess your slope, inspect your drainage, and recommend the most cost-effective fix for your actual conditions.

Request a free drainage assessment and we will respond within 24 hours. Learn more about our excavation services for Gresham-area commercial properties.