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Yard Drainage & Erosion Control in Portland, OR

Quick answer

Portland drainage problems usually come from months of steady rain on slow-draining silt and clay, poor grading, and roof water released near the house. Fixes include regrading, downspout extensions or safe disconnection, French drains, swales and rain gardens. On steep lots, water management also affects slope stability, so get qualified help.

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Drainage is the Portland yard problem. Rain here is less about cloudbursts and more about persistence: weeks of steady rain from fall through spring that keep the ground saturated. Silty and clay soils on much of the west side drain slowly, many lots slope toward the house, and older homes often have downspouts that were tied into sewer pipes or simply dump next to the foundation. The result is lawns that squish from November to April, standing water, wet crawlspaces, and, on hillsides, soil that starts to move.

Signs you have a drainage problem

  • Standing water or a spongy lawn that lasts for days after rain
  • Moss, rushes or bare mud in the same low spots every winter
  • Water in the crawlspace or basement, or against the foundation
  • Soil, bark or gravel washing onto paths and driveways
  • On slopes: cracks in the soil, tilting fences or trees, or bulging walls

Common solutions

  • Regrading: reshaping soil so it falls away from the house toward a safe outlet.
  • Downspout management: extensions, buried solid pipe, or properly sited disconnection. Roof water is often the biggest single source of yard water.
  • French drains and curtain drains: gravel trenches with perforated pipe that intercept groundwater and carry it to an outlet.
  • Swales and dry creek beds: shallow channels that guide surface water across the yard.
  • Rain gardens: planted basins that hold runoff and let it soak in, when the soil drains well enough to support one.
  • Soil improvement: aeration and compost help over time but rarely fix a grading problem alone.

Portland's downspout rules of thumb

The City of Portland's Bureau of Environmental Services publishes safety guidance for disconnecting downspouts on existing homes. Among its points: don't disconnect on slopes steeper than 10 percent, discharge at least 6 feet from a basement and 2 feet from a crawlspace or slab, keep the outlet at least 5 feet from the neighbor's property line, and don't send water within 10 feet of a retaining wall or onto a septic system. The landscaped area receiving the water should be at least 10 percent of the roof area draining to it. Properties that manage stormwater on site may qualify for a discount on the city stormwater charge through Clean River Rewards. If you're unsure whether disconnection is safe on your lot, the city has a private property drainage line you can call.

Slopes and landslides

The USGS notes that a major storm in February 1996 triggered hundreds of landslides in Portland's West Hills, and smaller numbers occur during long rainy spells every few years. Water soaking into a slope is a common trigger. If you live on a steep lot, where roof and drain water goes is a safety question, and the fix may call for a geotechnical engineer rather than just a landscaper. Never concentrate water at the top of a slope.

Erosion control

Bare soil on a slope erodes fast in a Portland winter. Keep soil covered with mulch, erosion-control blankets and deep-rooted plants, and slow water down rather than speeding it up. Removing ivy or blackberry from a slope helps long term, but replant quickly so the ground isn't left bare through the wet season.

Rules before you dig

  • Request locates through Oregon 811 before trenching. Drain lines often cross gas, water and communication lines.
  • Don't push water onto a neighbor's property.
  • Work near streams or wetlands can need city or Clean Water Services review in Washington County, and Portland has environmental overlay zones. Check first.

Our guide to fixing a soggy Portland yard goes deeper. If water is reaching your foundation or a slope is moving, mark your request urgent and request a drainage company.

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How a French drain carries water away from a yard. Press the buttons to run each step and see what happens inside. Made with Colorfigures ·
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Frequently asked questions

Can I disconnect my downspouts in Portland?

Often, if your lot meets the city's safety guidance. Portland's Bureau of Environmental Services says not to disconnect on slopes over 10 percent and sets minimum distances from basements, property lines and retaining walls. Qualifying projects may earn a Clean River Rewards discount.

Why is my yard soggy all winter but dry in summer?

Portland gets most of its rain from fall through spring, and silty or clay soils drain slowly, so the ground stays saturated for months. In summer there is little rain, so the same spot can dry and crack.

Is my hillside at risk of a landslide?

Parts of the metro, including the West Hills, have a history of landslides during long wet spells. Cracks, tilting trees or fences, or bulging soil are warning signs. Keep roof water off the slope and talk to a geotechnical engineer if you see movement.

Sources and further reading

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