Parking Lot Drainage in Sandy, Oregon: Stop the Ponding

Parking Lot Drainage in Sandy, Oregon

A ponding parking lot is a problem no Sandy business can afford, and the Mt. Hood foothills make it more likely than almost anywhere in the metro region. Sandy catches heavier rainfall than the valley below, and storms here can dump water faster than a marginal lot can shed it. For the businesses along the highway corridor that serve travelers heading to and from the mountain, standing water means slip-and-fall liability, accelerated pavement failure, and a poor first impression. A lot built for valley rainfall can be overwhelmed by a Sandy storm.

Parking lot drainage is a solvable engineering problem. Water has to travel from where it lands to a controlled outlet, and the pavement must be shaped and equipped to handle the volume. When a Sandy lot ponds, it usually means the slope settled or was never adequate for the rainfall, the drainage structures are undersized or clogged, or runoff is entering from higher ground.

Why Sandy Lots Pond

The foothill setting drives several local factors:

• Heavy rainfall. Sandy's elevation means more precipitation and more intense storms, overwhelming lots without enough slope or inlet capacity.
• Runoff from above. On sloped sites, sheet flow from adjacent hillsides can pour onto the lot, adding to the volume it must handle.
• Settlement. Asphalt sections settle over time, creating birdbaths that hold water — and Sandy's heavy rain fills them fast.
• Undersized structures. Inlets and pipe sized for lowland rainfall may not keep up with foothill storms.

Our overview of property and site drainage in Oregon covers how these surface and subsurface factors interact across the region.

How Sandy Parking Lot Drainage Is Designed

A well-drained lot in Sandy relies on coordinated elements, sized for the rainfall:

• Positive slope to inlets — The pavement is graded so every part of the lot sheds water toward a catch basin or trench drain, on a slope that can move heavy storm volume without pooling.
• Adequately sized catch basins and area drains — Set at the low points and spaced for the rainfall, feeding collected water into the underground network. In Sandy, capacity matters more than in the lowlands.
• Trench drains — Channel drains across drive aisles and entrances where sheet flow needs interception in a line.
• Perimeter interception — On sloped sites, a curtain drain or perimeter swale keeps hillside runoff out of the lot.
• A piped conveyance system — Underground pipe carrying water to an approved outlet or storm connection, sized for peak flow.
• Water quality treatment — Larger or newer sites may need an oil-water separator, a bioswale, or other treatment before discharge, depending on DEQ requirements.

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

Fixing an Existing Ponding Problem

For an existing Sandy lot that ponds, the fix depends on the cause:

• Localized birdbaths from settlement can be corrected with a mill-and-overlay or infrared patch that restores proper slope.
• Insufficient capacity — common when a lot was built for lowland rainfall — may call for adding or upsizing catch basins and trench drains.
• Runoff from above may require adding perimeter interception to keep that water out of the lot.
• Clogged structures sometimes just need cleaning and renewed maintenance.
• Widespread slope failure may require regrading and resurfacing larger sections.

A contractor evaluates the lot during or right after one of Sandy's heavy rains — when the problem is most visible — then matches the fix to the cause.

What Parking Lot Drainage Costs in Sandy

Cost varies with lot size, the extent of the problem, the number of structures, whether capacity needs upsizing for the rainfall, and whether stormwater treatment is required. A single catch basin addition or targeted patch sits at the low end. A full regrade with upsized conveyance and treatment for a large lot sits much higher.

Local factors in Sandy:

• Heavy rainfall may require upsized inlets and pipe.
• Runoff from adjacent slopes may require perimeter interception.
• DEQ and stormwater requirements can add treatment costs for larger sites.

Published ranges are a reference only. A site assessment that observes the actual ponding during a storm gives the accurate number.

Get Your Sandy Parking Lot Drainage Quote

Cojo Excavation & Asphalt provides free, no-obligation parking lot drainage assessments for Sandy and Mt. Hood corridor businesses and property managers. We evaluate the slope, inspect the drainage structures, account for foothill rainfall, identify the cause of ponding, and deliver a clear plan to fix it.

Learn about our excavation services, or request a free quote and we will respond within 24 hours.