Potential consequences of sea level rise in Olympia

Greater risk of flooding

Since many parts of Olympia’s downtown are only a few feet above the current high-tide water level already, a rise in sea level could cause flooding in parts of the city like the Port of Olympia and the waterfront business district, as well as Capitol Lake. Higher water levels would also increase the risk of high-tide flooding and a greater risk for storm damage. 50 or 100-year storms could increase in frequency, causing greater damage to coastal areas [1]. Olympia already has experience with these events, such as the 17.6 foot (5.4 m) tide on December 17, 2012 (pictured at left) [2].

Inundations of the sewer and storm water system

In many areas of downtown Olympia, the wastewater and stormwater systems are combined. Higher sea levels  could result in sea flow into wastewater pipes through drains. Stormwater pipes would be inundated during storms,  not allowing stormwater to drain. At higher water levels, water flow could reverse and come out of drains and into  the streets (pictured at right) [3].

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Higher water table

In much of downtown Olympia, the water table is only about a foot beneath the ground surface in winter months. Sea level rise could cause the water table to rise, possibly to the point where during extreme storm events the water table could reach ground level. This could exacerbate flooding as flood waters would recede more slowly with nowhere to drain. A higher water table could also negatively affect building foundations and pavements, as well as pose a danger to underground storage tanks storing hazardous  material, dozens of which are located in the vulnerable Port of Olympia and downtown areas [4].


Shoreline erosion and habitat loss

Sea level rise will increase the amount and speed of erosion along the shoreline of Budd Inlet as well as the risk of landslides. In low-lying areas, there will be more frequent flooding and damage to infrastructure. Marshy shorelines will experience increased flooding and erosion, and loss of salt marsh and similar habitat will depend on constraints of surrounding development. Construction of protective structures like seawalls and dikes in vulnerable areas will also lead to beach and marsh habitat loss, which will affect many species within those habitats. Sea level rise could also disturb other coastal ecosystems by moving tidal inlets, stream mouths, estuaries and wetlands [5].

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Salinization of water supplies

McAllister Springs, Olympia’s main drinking water source, is vulnerable to saltwater intrusion with rising sea levels. Olympia has planned to shift this supply to the McAllister Wellfield, a few miles upgradient and less vulnerable to saltwater intrusion by 2014, however other natural freshwater systems are at risk for salinization, endangering habitat and the species that live within them [6].

[1] Washington Dept of Ecology. Shoreline Master Program Guidebook. Pg. 3.

[2] Haub, A. (2013). Community Update on Sea Level Rise. Powerpoint presentation. City of Olympia.

[3] McGowen, V. (2007). Climate Change – Olympia is Concerned. City of Olympia.

[4] Craig, D. (1993) Preliminary Assessment of Sea Level Rise in Olympia, Washington: Technical and Policy Implications. City of Olympia. Pg. 16.

[5] Craig, D. (1993) Preliminary Assessment of Sea Level Rise in Olympia, Washington: Technical and Policy Implications. City of Olympia. Pg. 4.

[6] McGowen, V. (2007). Climate change – Olympia is concerned. City of Olympia.

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Contact: peter (at) stat.washington.edu