Property & Site Drainage in Oregon: The Complete Guide

Drainage Is the Real Foundation of Every Oregon Property

Few places test a property's drainage like the Pacific Northwest. From the long, soaking rains of the Willamette Valley to the atmospheric rivers that roll in off the coast, Oregon ground spends much of the year saturated. When water has nowhere to go, it pools in lawns, seeps into crawlspaces, undermines foundations, and turns parking lots into shallow ponds.

This guide is the hub for everything Cojo Excavation & Asphalt covers on property and site drainage. Below you will find the core concepts every Oregon owner should understand, plus links to deeper articles on specific systems, problems, permits, and costs. Drainage is rarely one-size-fits-all, so think of this as a map rather than a checklist. Every site is different, and a proper fix starts with a site assessment.

Surface Water vs. Subsurface Water

The first thing to understand is where your water actually is. Almost every drainage problem falls into one of two categories.

Surface water runs across the ground. It comes from rain hitting roofs, driveways, patios, and lawns, then flows downhill until something stops it. Surface fixes move that water along faster and steer it away from buildings. Regrading, swales, catch basins, and area drains all manage surface water.

Subsurface water sits in the soil itself. In Oregon, this is often a high water table or a perched layer of water trapped on top of dense clay. Subsurface fixes pull water out of the ground. French drains, footing drains, drain tile, and curtain drains all manage subsurface water.

Many properties have both problems at once, which is why the right solution is usually a combination. Our guide on catch basin vs. French drain breaks down the surface-versus-subsurface decision in detail, and French drain vs. swale vs. catch basin compares the main systems side by side.

Where Your Water Should Go

Every drainage system needs a destination. Water collected by a pipe or swale has to exit somewhere lower than where it started. That exit point is called the outfall, and a system without a good one will back up and fail.

The cleanest outfall is daylighting — running a solid pipe to a spot on a slope where it can simply spill out into the open. Other options include tying into a public storm system (where allowed and permitted), routing to a dry well that lets water soak into deeper soil, or directing flow to a rain garden or bioswale that treats and absorbs it. Whatever the destination, gravity does the work, so slope matters at every step.

How Much Slope You Need

Drainage runs downhill or it does not run at all. A few baseline numbers guide nearly every project:

• Surface grading should fall at least 1 percent (about 1 foot of drop over 100 feet) so water keeps moving across a lawn or lot.
• The ground around a foundation should slope away at roughly 2 percent — a 6-inch drop within the first 10 feet — so rain sheds away from the structure rather than toward it.
• Drainage pipe generally needs a minimum fall of about 0.5 to 1 percent to carry water and self-clean.

These are general targets; soil, layout, and outfall location all affect what a site actually needs. For the full breakdown, see how much slope for drainage.

The Oregon Soil Problem: Clay and High Water Tables

Much of western Oregon sits on heavy clay or silt loam that drains slowly. Water hits that dense layer and stops, which is why a yard can stay soggy days after the rain ends. On clay, a deep French drain often underperforms because there is no fast path for water to reach it. Surface-first strategies — regrading, swales, and shallow area drains — usually do more good. Our guide on draining Oregon clay soil covers what actually works here.

In valley-floor and coastal areas, a high water table adds another layer. When groundwater sits close to the surface, a buried drain can fill from below instead of draining the yard. These sites often need curtain drains, sump-and-pump setups, or raised planting beds rather than a standard French drain.

Common Drainage Problems and Their Fixes

Most calls we get trace back to a handful of root causes. Knowing the cause points you toward the right system.

• Standing water in the lawn — usually compaction, clay, or negative grade. Start with why you have standing water.
• Water running toward the house — almost always a grading problem. See the negative grade fix.
• Wet crawlspace or basement — often solved from the outside first, with footing drains, regrading, and downspout extensions.
• A drain that stopped working — sediment, roots, or a crushed pipe. Many can be flushed; some need a rebuild.
• Ponding parking lots — a slope or sub-base issue best diagnosed by survey.

Choosing the Right System

Here is a quick orientation to the systems covered across this silo:

System	What it does	Best for
French drain	Collects subsurface water in a gravel-and-pipe trench	Soggy ground, slope seepage
Footing / drain tile	Protects the foundation perimeter	Wet basements and crawlspaces
Catch basin	Collects surface water at a low point	Lawn and lot ponding
Area drain	Point drain for hardscape low spots	Patios, driveways
Swale / bioswale	Shallow channel that conveys and treats runoff	Moving water across a site
Curtain drain	Intercepts water flowing in from uphill	Sloped and hillside lots

Pipe choice matters too. Perforated pipe collects water along its length, while solid pipe carries water without losing it — you want solid pipe for the run to your outfall. Filter fabric (a sock or a fabric-lined trench) keeps fine soil from clogging the gravel. These details are what separate a drain that lasts decades from one that silts up in a season.

Permits, Stormwater, and the DEQ

Drainage work can trigger local grading or drainage permits, especially when you disturb a lot of ground, alter where water flows onto a neighbor, or connect to a public storm system. Larger construction sites that disturb an acre or more often need an Oregon DEQ 1200-C construction stormwater permit with an erosion and sediment control plan. When in doubt, confirm with your city or county before digging.

What It Costs

Drainage pricing depends on length, depth, soil, site access, the outfall distance, and permits — so figures are best treated as industry baseline ranges, not fixed quotes. To plan a budget, start with what drives drainage cost, then dig into the specifics with our French drain cost in Oregon, yard drainage cost guide, and foundation drain installation cost guides.

When to Call a Professional

A homeowner can extend a downspout or dig a small swale. But once water is reaching a foundation, a basement is staying wet, a lot is ponding, or a drain has failed underground, the stakes get high. Misreading the slope or skipping filter fabric can mean tearing the whole thing out a year later. A contractor who walks the site, checks the grade, and finds a real outfall will give you a system that works the first time.