Yard Drainage in Tualatin, Oregon: Fixing a Soggy Lawn

Why Tualatin Lawns Pond

Few places in the Portland metro stay as wet as Tualatin. The city sits low in the Tualatin River valley on flat, heavy clay, with a high winter water table and very little natural fall to carry water away. When the Pacific Northwest wet season settles in, a lawn here can pond for weeks at a time. Water that lands simply has nowhere to go: the clay won't absorb it, the flat ground won't move it, and the high water table means there's no dry soil below to soak it up. If your Tualatin lawn turns into a shallow lake every January, the terrain is working against you, not your lawn care.

This combination — flat grade, water-holding clay, and a high water table — is the defining drainage challenge of Tualatin and the surrounding Washington County flats. The good news is that it's a well-understood problem with proven fixes. The catch is that those fixes have to work around the lack of slope, which is what makes a thoughtful approach matter here.

What's Causing the Wet Spot in Tualatin

Flat grade with nowhere to go. With little natural fall, water that lands just sits. This is the root of most Tualatin ponding.

Clay holding water at the surface. Once the top layer of clay saturates, rainfall pools rather than soaking in.

High winter water table. When groundwater is near the surface, there's no dry soil below to absorb water, so even subsurface drains have limited room to work.

Downspouts at the foundation. Roof water concentrated near the house saturates a lot of lawn and adds to the pooling.

Compacted soil. Construction traffic and foot traffic pack the clay until it sheds water like pavement.

Drainage Solutions That Work in Tualatin

Regrading and Swales

Because Tualatin's clay sheds water at the surface and the ground is flat, the most effective move is often to create gentle slope where there isn't any — a regrade or a shallow grassed swale that carries water toward a usable outlet, a rain garden, or a detention area. On flat lots, building in that fall is frequently the whole solution.

French Drains

A French drain — perforated pipe in a gravel-filled trench — collects subsurface water and conveys it to an outlet. On Tualatin's flat ground the challenge is finding a low-enough outlet, sometimes requiring a longer run or a sump. It works best shallower and combined with grading. For pricing, see our yard drainage cost guide for Oregon.

Catch Basins and Area Drains

For a persistent low spot, a catch basin set at the dip with a buried line to an outlet removes standing water at its source. On flat lots these often pair with a pump if gravity can't carry the water far enough.

Downspout Control and Rain Gardens

Carrying roof water away on solid pipe, and directing it to a rain garden where it can soak in, keeps gutter water from adding to the lawn problem. Keep clean roof water on solid pipe, separate from any perforated French drain.

What Yard Drainage Costs in Tualatin

Pricing depends on length, depth, soil, access, and — most of all on flat ground — where the water can exit. Industry baseline ranges are a reference, not a quote. A short downspout line or a rain garden sits at the low end; a French drain that needs a long run or a sump to reach an outlet runs higher. Tualatin's clay digs harder than sandy soil, and the lack of a nearby gravity outlet is the factor most likely to push cost up.

Rather than budget from a chart, the reliable path is a site visit. We establish your grade, find where water can go, and quote the actual work. Our yard drainage cost guide for Oregon details the cost drivers.

When to Call a Drainage Contractor

Extending a downspout is a weekend job. Establishing slope on flat ground, finding a legal outlet, installing a sump, working near a foundation, or regrading a lot is not. If water is reaching your crawlspace, if you share a drainage easement — common on Tualatin's planned lots — or if the wet area keeps returning after DIY attempts, it's time for a professional look. A good contractor diagnoses the cause and, crucially on flat ground, identifies where the water can actually go before recommending a fix. For the bigger picture, see our guide to property & site drainage in Oregon.