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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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Why do we still have drainage and flooding problems after building the big pipes?

storm drainMany things cause drainage and flooding problems, including:

  • Storm drains clogged with leaves or other debris - city maintenance crews clean storm drain inlets, but residents can help by clearing leaves from storm drains and gutters before rainstorms
  • Development in or near floodplains
  • Culverts that are too small to carry streams swollen during heavy rains
  • Heavy rain that creates enough stormwater runoff to overwhelm the city’s network of drainage pipes

The city designs new roads and pipes to carry all stormwater from 96% of all storm, but the 4% of storms that are larger may create more runoff than some pipes can handle. The city designs the system this way to reduce the costs of building huge pipes that are only rarely used. Cities all over the U.S. build roads and pipes to similar standards.

Older roads and drainage systems not built to today’s standards
Drainage and flooding problems may be more frequent in parts of Portland that developed without proper drainage systems.

Many Environmental Services construction projects help reduce drainage and flooding problems. But the bureau needs to balance the amount of money available each year between those projects and maintaining and repairing aging sewer pipes and treatment systems, and meeting water quality permit requirements.