Parking Lot Drainage in Gladstone, Oregon: Stop the Ponding

Stop Parking Lot Ponding in Gladstone

A ponding parking lot in Gladstone usually comes back to the high water table. This Clackamas County city sits on low, flat river-bottom land at the confluence of the Clackamas and Willamette, so commercial lots have little natural slope to shed water and a saturated sub-base underneath. When water can't drain off the surface or soak away below, the result is puddles, birdbaths, and sheet flow across drive aisles that customers wade through — and that quietly destroys the asphalt. Standing water breaks down the surface and undermines the base, which softens fast on saturated river-bottom ground. Good parking lot drainage gets water off the surface and into a managed outlet before it does damage.

This guide covers why Gladstone lots pond, how proper drainage design fixes it, and what the work typically costs.

Why Gladstone Lots Pond

Most ponding traces back to one or more of these.

A high water table. With two rivers nearby, the water table keeps the sub-base saturated, so surface water has nowhere to soak away and the base stays soft — accelerating settling and ponding. This is the defining factor on Gladstone river-bottom sites.

Flat river-bottom grade. Asphalt needs a consistent slope — commonly around 1 to 2 percent — toward inlets to keep water moving. On flat ground, that slope is hard to establish and easy to lose as the base settles, leaving low spots that pond.

Settling and a soft base. Over time the base compacts unevenly and sections sink. On saturated river-bottom soil, the base softens and settles faster, creating birdbaths.

Heavy wet-season rainfall. The long, steady Oregon rainy season delivers more water than an undersized or settled system can handle, especially during peak storms.

How Proper Lot Drainage Works

Fixing ponding is about getting water to a collection point and then to a managed outlet.

Slope to inlets. The surface is graded so every area sheds toward a catch basin. Where settling has created low spots, a mill-and-overlay or targeted patching restores the correct slope. Adding an inlet at a stubborn low spot is sometimes the cleanest fix.

Catch basins and a piped network. Grated catch basins collect surface water and feed an underground pipe network that carries it to the outlet. Proper basin spacing keeps any single storm from overwhelming the system.

Trench drains at problem lines. Where water crosses an entrance or drive aisle, a trench drain — a continuous grated channel — intercepts sheet flow before it spreads.

A managed outlet and DEQ compliance. Commercial lot runoff in Oregon often has to be treated and metered before discharge, which can mean an oil-water separator, a detention feature, or a connection to an approved storm system. Sites near the rivers face particular scrutiny, and a high water table can complicate where collected water can go — sometimes requiring a pumped outlet.

For the full design framework, see our guide on commercial parking lot drainage design in Oregon.

What Parking Lot Drainage Costs in Gladstone

Industry baseline ranges. Actual costs depend on lot size, scope, the number of inlets, outlet requirements, and DEQ obligations. Flat, high-water-table sites run higher.

Scope	Industry Baseline Range
New catch basin (each, installed)	$1,500–$4,000
Trench drain (per linear foot)	$100–$300
Targeted regrade / patch of a low spot	$2,000–$8,000
Mill-and-overlay to restore slope (per sq ft)	$2–$6
Full lot drainage design + install	quote-based, varies widely

These are commonly reported starting figures, not quotes. Outlet requirements, oil-water separators, a pumped outlet where the water table is high, and DEQ stormwater obligations can change the total substantially. A site assessment is essential for commercial work.

Why a Site Assessment Is Essential

Commercial parking lot drainage on flat, high-water-table ground is engineering, not guesswork. Catch-basin spacing, the slope to each inlet, outlet capacity, and stormwater treatment all have to be right — and a high water table can dictate whether a gravity outlet is even possible or whether a pump is needed. A site assessment that maps the existing grade, finds the low spots, checks the water table, and confirms the outlet and DEQ requirements is the foundation of a lot that drains in the worst storms — and stays compliant. We strongly recommend one before any commercial drainage work.

Protect the Asphalt You Already Have

Ponding doesn't just inconvenience customers — it destroys pavement, and a high water table makes it worse by keeping the base soft. Water that sits on the surface and saturates the base shortens the life of the whole lot, turning a drainage problem into a repaving bill. Fixing drainage early protects the much larger investment in the asphalt. Cojo Excavation & Asphalt helps Gladstone property owners and managers stop ponding with drainage built for river-bottom conditions. Learn more about our excavation services and the full property drainage solutions in Oregon.