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Project Summary / Overview
The relatively low elevation of downtown Olympia, Washington, makes it prone to flooding due to sea level rise. To assess the city’s vulnerability, flooding maps were produced for a variety of sea level rise scenarios. Olympia’s propensity and duration of flooding vary with the amount of sea level rise projected. As a result of the sea level rise flooding maps, city planners have brainstormed a variety of strategies that could reduce the vulnerability of downtown Olympia.
Lower downtown Olympia sits on reclaimed land created with hydraulic fill that abuts Budd Inlet, a tidally-influenced southern arm of Puget Sound. On average, downtown Olympia is 18 to 20 ft above sea level but, Budd Inlet can have tides that reach a maximum height of 18 ft, which can make the water’s edge mere feet from downtown buildings at times. Due to its tenuous location, Olympia considered the potential effects of sea level rise initially in 1993 and released the "Preliminary Assessment of Sea Level Rise in Olympia, Washington: Technical and Policy Implications." The report covers sea level rise predictions as they were known at the time, potential impacts to Olympia, and presents some strategies and policy options. However, because sea level rise was not a recurrent cause of flooding in downtown Olympia, little action was taken after the publication of the report.
In 2007, there was a renewed drive by the City Council to plan for the effects of sea level rise after they realized the site selected for the new City Hall could be prone to flooding if sea level rose. In 2009, the Climate Impacts Group released “The Washington Climate Change Impacts Assessment,” which provided updated regional sea level rise predictions varying from 2 to 50 inches by 2100.
To assess the impacts sea level rise could have on downtown Olympia, the city invested in high resolution LIDAR elevation data and used the LIDAR maps to run flooding simulations during high tides and storms at 0.5 ft incremental increases in sea level relative to its current level. Maps were produced to assess areas flooded, duration of flooding, damage and interference with existing infrastructure, and interactions with piped streams/large stormwater culverts. The city also invested in geological monitoring equipment to monitor land subsidence or uplifting and plans to install local tide gauges.
Olympia has multiple stormwater outfalls designed to transport precipitation from the streets of downtown Olympia into Budd Inlet. If a 0.5 ft increase in sea level rise were to occur, marine waters could infiltrate existing stormwater pipes during the two highest tides of the year. The marine waters could be transported in the stormwater pipes and discharged onto the streets of Olympia, resulting in ponding on some streets and temporary flooding of low-lying structures. With a 1 ft increase in sea level, some stormwater pipes are projected to be inundated with marine waters and unable to transport waters from the streets of downtown to Budd Inlet, causing an increase in flooding area and duration in downtown Olympia. A 2.5 ft increase in sea level could cause Budd Inlet to overtop its banks and flood most of downtown Olympia. In parts of downtown Olympia the wastewater system is combined with the stormwater system. Higher sea levels could compromise the integrity of the system when marine waters flood the pipes, potentially causing wastewater contamination and exceeding the capacity of Olympia’s wastewater treatment facility.
A piped stream bisects downtown Olympia and discharges into Budd Inlet. The pipe frequently runs at capacity during winter storms. Simulations indicate that the existing system can handle a 0.5 ft increase in sea level rise during an average tide and average storm. However, if there is a 1 to 2 ft increase in sea level, an extremely high tide and heavy rainfall, the volume of water in the pipe could exceed capacity, causing prolonged flooding in parts of downtown Olympia.
Project Outcomes and Conclusions
Using the results of the sea level rise inundation models of downtown Olympia, the Department of Public Works is brainstorming a variety of ways to help reduce their vulnerability to flooding. The City of Olympia is considering both short-term and long-term adaptation strategies to enhance their resilience to sea level rise; some of which are:
- A shorefront park is being modified to consolidate the number of stormwater outfalls by half to ease future management
- The town is being sub-divided into 8 sub-basins for further detailed analysis using sea level rise simulations
- Enact a new SEPA requirement to raise floor elevations that house critical resources in all new buildings
- Install underground water pumps at critical points
- Raise the shoreline height
- Continue to monitor changes in land elevation
- Update the city’s comprehensive plans to address the impacts of climate change including sea level rise
- Support state and federal officials in developing guidelines/regulations to assist the adaptation of local communities
- Create an institutional structure/framework to work on the problems climate change poses
The City of Olympia is proactively considering the impacts of sea level rise by using models to simulate downtown flooding. Results indicate that the amount of damage will vary with the amount of sea level rise. However, it is difficult for city planners to incorporate the modeled simulations into future city plans without a probability being assigned to various rates and maximum amounts of sea level rise. To help local jurisdictions adapt to sea level rise, risk needs to be associated with probability.
Currently there are no plans to abandon or relocate downtown Olympia to an area that is less prone to flooding due to sea level rise. In fact, a city ordinance was passed calling for the rejuvenation of downtown Olympia, the heart of the city. Thus, city planners are focused on strategies that will reduce the vulnerability of downtown Olympia to sea level rise. This process could be advanced and simplified if state or federal guidelines/regulations existed.
Feifel, K. (2010). Planning for Sea Level Rise in Olympia, Washington [Case study on a project of the City of Olympia's Public Works Department]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE: www.cakex.org/case-studies/planning-sea-level-rise-olympia-washington (Last updated March 2010)