Future Climate Effects on Columbia and Willamette River Levees

Science Center Objects

USGS research directly helps local public agencies that are responsible for the design and maintenance of the levees that surround the northern Portland metropolitan area with the goal of protecting life and property in the event of flooding from the Columbia and Willamette Rivers that surround the city.

The Multnomah County Drainage District is in the process of accrediting levees that it manages in Portland to protect lands from flooding on the Columbia and Willamette Rivers. They MCDD have requested assistance in determining design criteria that incorporate the effects of a changing climate on the water levels in the two rivers. The USGS is modeling peak flows in the Columbia and Willamette Rivers in a future climate and projected sea level change at the mouth of the Columbia River, both of which affect river levels in Portland.

Specificially, the main objective of this study is to provide management agencies with an estimate of the Columbia and Willamette River flood stage on levees surrounding North Portland during extreme high-flow events in the future, using:

  • State-of-the-art hydraulic models
  • Boundary condition hydrographs describing future climate scenarios at warmer and wetter extremes
  • Sea level change scenarios describing intermediate and high scenarios of sea level rise based on moderate to maximum ice sheet loss
  • Two different hydraulic models that provide some assessment of the uncertainty inherent in hydraulic model selection

Climate projections predict that the Pacific Northwest will experience a decline in spring snowpack, earlier snowmelt, and earlier peaking streams. This is particularly true for mixed-rain-and-snow type basins. Projections also indicate that some basins may experience higher peaks, as well. The Willamette and Columbia Rivers are expected to share these trends.