The City of Anacortes, Washington recognized that its water treatment plant, located along the Skagit River and serving 56,000 people, was vulnerable to current floods and future climate risks. In 2003, the City recognized the need to update the facility from 21.4 million gallons of water per day (mgd) to a stated capacity of 31.5 mgd. Moving the facility out of the floodplain was deemed cost prohibitive in 2008, so officials decided to rebuild on the existing site. Such a strategy can be risky unless climate projections are taken into account and adaptation strategies implemented to reduce future vulnerability.
To determine the plant’s vulnerability, Anacortes officials worked with non-profit organizations to determine the best available climate science and the associated impacts to the plant siting. A variety of climate risks were taken into account including:
- more frequent and intense storms
- saltwater intrusion
- increased sedimentation levels
Climate change impacts were projected through the 2080s and downscaled for the Skagit River area. These vulnerabilities included an expanded 100-year floodplain, an estimated 350% increase in peak suspended sediment load in winter and anticipated upstream migration of the salt water wedge due to the effects of sea level rise.
In design and construction of this plant, officials sought to protect against higher risk of flooding by:
- minimizing penetration below current 100 year flood elevation
- raising critical electrical equipment out of the 100 year flood level
- utilizing water proofing techniques below 40 foot elevation
- designing ring dikes for flood protection
This plant was rebuilt on site at an expected cost of $56 million dollars and improvements to this design better prepare the facility to meet increased service demand as well as projected changes in climate.