Assessment of Sea-level Rise for King County Wastewater Facilities

John Phillips, Cathie Scott, Shaun O’Neil
Posted on: 7/18/2022 - Updated on: 11/08/2023

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Sea-level rise poses a direct and measureable threat to low-lying infrastructure in tidally influenced areas. For the last half of the 20th century, the mean sea level in Puget Sound has increased 4.24 inches. In the most likely sea-level rise scenario, it is predicted to rise an additional 6 inches by 2030 and 13 inches by 2100 as the result of climate change. Storm surges are expected to increase tide heights even more. King County’s regional wastewater system serves 1.5 million people in the greater Seattle area. Salt water is entering the system during high tides.

To determine the potential for greater amounts of saltwater inflow, the county assessed the vulnerability of its facilities using combinations of predicted sea-level rise and historical storm surges. The methodology relied on in situ data collection, observations, facility inspections, and geographic information system (GIS) analytical techniques applied to spatial data. Half of the facilities (20 of 40 surveyed) were identified as at risk of saltwater intrusion. The resulting inventory of vulnerable facilities provides a tool for decision-makers to use in determining the acceptable risk of sea-level rise when allocating future capital expenditures.


Phillips, J., Scott, C., O’Neil, S. (2015). Assessment of Sea-level Rise for King County Wastewater Facilities. Michigan Journal of Sustainability, vol. 3: DOI:

Affiliated Organizations

King County Department of Natural Resources and Parks