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  • 1 Oct 2014

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Survey of Bull Run Watershed landslide risks proposed

Less than a week after a massive landslide damaged homes on Whidbey Island near Seattle, the Portland City Council will consider contracting with the Oregon Department of Geology to survey landslide risks in the Bull Run Watershed.

Although negotiations over the proposed contract began long before the landslide in Washington, widely reported images of the devastation it caused suggests the threat that landslides pose in the watershed, which is the primary source of water for approximately 935,000 people living in the metropolitan area.

The water is collected behind a dam and transported to the city through large pipes in the watershed, which is federally protected against development.

“Landslides are a concern for the watershed because of their potential impact on water quality, infrastructure, and fish habitat. Landslides have the potential to create turbidity events that negatively impact water quality for both people and fish; they also have the potential to damage portions of the Water Bureau's conduits and segments of the Bull Run road system that run through landslide terrain,” reads the ordinance to authorize the $114,600 contract.

City officials have long been aware of the risk of landslides in the watershed. It was last surveyed for landslide risks in 1980. According to the ordinance, the technology for detecting landslide risks has improved tremendously over the past 30 years, justifying a new survey at this time.

“Oregon Department of Geology and Mineral Industries, the State expert in landslide mapping, proposes to use highly accurate surface-terrain maps derived from existing Light Detection and Ranging (LiDAR) data to create maps of landslide hazards in the Bull Run watershed,” the ordinance reads.

According to the ordinance, “Increased understanding of the landslide hazards in the Bull Run watershed will allow the Water Bureau to actively plan for the risk of landslide impacts to water quality, existing and proposed infrastructure, and the environment.”

A fiscal analysis submitted with the ordinance says the Water Bureau has sufficient funds for the survey in its current budget and will not be required to raise water rates to pay for it.

The ordinance and a more detailed description of the work is available on the city’s website at www.portlandonline.com/auditor/index.cfm?c=50265&a=441339