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Sea Level Rise Risk Assessment
Pacific County Department of Community Development
This StoryMap provides an introduction to sea level rise and how projections and scenarios are developed and mapped. It also provides the results of the mapping projections, including some of the maps created for the assessment. Recommendations for next steps and examples of adaptation strategies used in other coastal communities are also included.
"Sea Level Rise Projections" is the amount of sea level rise that might be seen by a certain time frame with a certain probability.
"Sea Level Rise Mapping Scenarios" use sea level rise projections and other considerations, like land surfaces and storm frequencies, to estimate how far landward sea water might reach by a certain time frame under certain conditions and visualize the result with maps.
"Sea Level Rise Assessments" use scenarios to create maps and assess potential impacts to man-made structures, landscape features and wildlife habitats.
The Pacific County Department of Community Development's Sea Level Rise Risk Assessment project includes an assessment report with details on the projections used, the scenarios developed, the maps created and the assessment that was done, along with recommendations for future actions. The project also includes this storymap that summarizes the information from the report. The storymap also lets readers explore the maps in more detail.
For more details behind the information found here, please see the companion report " Planning Sea Level Rise Risk Assessment - Pacific County, June 2023 " available from Pacific County Department of Community Development.
When reading this storymap, readers can use the navigation bar above these paragraphs to jump to different sections. Maps showing how far future high tides and extreme floods may reach upland and what that might impact are included in the sections "Mapping Scenarios for Pacific County" and "Vulnerability & Risk Assessment".
Residence in North Cove, Pacific County, Washington
Intro to Sea Level Rise
Coastal communities, like Pacific County (Washington State) are facing rising seas and increasing storm impacts to various degrees, largely dependent on location. Several factors affect how much seas will rise and how far inland the water will reach and at what frequency.
"Sea level rise" (SLR) is the overall increase in the level of the world’s oceans. It is primarily caused by two factors: added water from melting ice sheets and glaciers caused by a warming climate, and the expansion of ocean water as it warms.
Due to the potential effects of rising sea levels, coastal communities are expected to face significant challenges. To address this, communities, like Pacific County, use the latest research and public input to identify areas that are most vulnerable to sea level rise. By understanding these vulnerabilities, adaptation and risk mitigation strategies can be developed and potentially implemented, to help ensure the long-term safety and resilience of coastal communities.
Long Beach, WA - Photo Credit: Pacific County Tourism Bureau
What is Pacific County doing to address SLR?
Pacific County Department of Community Development received a grant from the Washington State Department of Ecology to complete a sea level rise vulnerability and risk assessment to map different projections of sea level rise and identify what the impacts to critical infrastructure, residences, and wetlands might be.
"Critical Infrastructure" are structures that the community is dependent on for safety and well-being, such as roads, fire stations, police stations, hospitals, wastewater treatment plants and airports.
Pacific County's Department of Community Development will use this assessment as a guide to develop more detailed, site-specific scale plans and to inform regulations for mitigating sea level rise and climate change impacts. This assessment is intended to assist the County and community in their planning efforts to protect and preserve critical facilities through identifying potential adaptation strategies to reduce loss and impacts to existing development and infrastructure.
Driving Forces of Changing Tidal Heights
As levels of daily average tides are expected to increase, so are the tidal heights reached during storm-driven flood events when atmospheric pressure is low and wave energy is high. A second element that drives higher-than-average tides are “King tides.”
"King Tides" are very high tides when the moon is at its closest point to the Earth and the sun aligns with the moon. This results in a gravitational pull from both the sun and the moon, in the same direction, which increases the height of the high tide.
Mapping Sea Level Rise
The purpose of mapping sea level rise is to show residents, County planning staff and Planning Commissioners the possible extent of flooding due to sea level rise specific to Pacific County.
"Relative Sea Level Rise" (RSLR) is sea level rise in relation to how the land is moving, either up or down, as a result of plate techtonics or rebound after glaciers recede.
Recently, projections for Relative Sea Level Rise (RSLR) above mean higher high water (MHHW) levels, by a given year, were developed with associated probabilities (Miller I. M., 2018). For example, planners can select specific scenarios to assess the impacts of sea level rise by 2050 for a given probability (1% to 99%).
These probabilities are intended to communicate the likelihood that sea level rise will reach or exceed a particular amount by a certain time; therefore the higher the probability (i.e. 99%), the more conservative (lower) the amount of sea level rise expected.
Pacific County chose to assess sea level rise for 2050 and 2100 at the 17%, 50% and 83% probability levels, and mapped scenarios specifically focused on the sea level rise assessed at the 83% probability level. In other words, maps were created for sea level rise scenarios that are very likely (83% chance) to be reached or exceeded by 2050 and 2100.
The possible extent of extreme flooding was also assessed. For more information on the science behind how the projected sea level increase amounts were developed, please refer to the two following documents produced by the University of Washington Sea Grant (linked below):
Technical reports utilized in developing the Pacific County Sea Level Rise Risk Assessment
Resilience Resource Library
Relative Sea Level Rise (RSLR) is calculated using tide gauge levels, projected sea level rise and how the fast the land is rising or dropping - known as 'vertical land movement'.
Depiction of How RSLR is Estimated
Vertical land movement is estimated to be approximately 10 inches +/- 5 inches /century of uplift along the outer coast of Washington and along the Columbia River to 1 inch +/- 1 inch/century of uplift in the Willapa River area (University of Washington Climate Impacts Group, 2018).
The RSLR projections do not take into consideration a sudden drop in elevation ("subsidence") as result of a subduction zone earthquake. Coastal subsidence would result in a drop in elevation relative to sea levels, of –4 feet to -5 feet, 2 inches along the outer coast to -2 feet to -5 feet, 11 inches in the Willapa River area (University of Washington Climate Impacts Group, 2018).
RSLR is referred to as "sea level rise" in this storymap.
Cape Disappointment, Long Beach; Photo Credit: Pacific County Tourism Bureau
Mapping Scenarios for Pacific County
"Mapping scenarios" were used to represent the extent of flooding that might be seen with a +1 foot tidal increase and the extent of extreme flooding on top of sea level rise by 2050 and 2100.
It is projected with 83% probability that sea level will rise between 0 inches to 5 inches by 2050 and between 6 inches to 1 foot, 4 inches by 2100. This will be an increase in the average daily high tide.
When extreme flooding that we see today is added to increased average high tide in Willapa Bay, it is projected that flood levels may be between 3 feet, 5 inches to 4 feet, 1 inch by 2050 and between 4 feet to 5 feet and 2 inches by 2100.
Because the outer coast is not as sheltered as Willapa Bay, flooding is usually more extreme. For those areas facing directly west, extreme flood levels are projected to be about 13 feet above average daily high tide levels by 2050 and 14 feet by 2100.
Map of Areas of Pacific County corresponding to Area IDs in the table above.
Levels close to these extreme flood projections are likely experienced by the community already. It is expected that they will become more frequent and/or longer in duration in the future.
As new research that includes how wind-driven waves and river inputs affect these sea levels and flood extents are developed, these projected levels may need to be reviewed and refined.
Ocean, coastal and climate experts are developing a tool, named the Coastal Storm Modeling System (CoSMoS), that will improve projections of sea level rise and extreme flooding because it will also include additional factors, like wind-driven wave runup. Once the tool has been calibrated for the Olympic Peninsula, the sea level rise projections used in this assessment should be compared to the CoSMoS results.
Visit the CoSMoS Web Site here for more information.
How the different scenarios were mapped
Seeing differences of a few inches in sea levels on maps that show large areas of the County is not possible. Using the more precise projections listed in the table above is recommended for site-specific planning purposes. However, for this County-wide planning exercise, levels to the nearest +1-foot increments were used for the mapping projections.
The benefit of mapping the increase of the average daily high tide at a +1-foot level is that, because it is higher than the 2050 projections for average daily high tides, it provides a planning buffer in case sea levels rise faster than projected. The extreme flooding extents by 2050 and 2100 and the average daily high tides levels by 2100 are mapped closer to the currently projected amounts.
Mapping layers from NOAA's Office of Coastal Mangement were used in Pacific County's assessment. The maximum level available from NOAA is +10 feet. This underestimates the projected potential height for the outer coast and planning efforts should take this into consideration.
NOAA offers a Sea Level Rise Viewer tool (below) to allow users to visualize different levels of sea level rise in their areas. This is an embedded interactive map, you can zoom "+" and "-" in the lower right corner for a closer look of how your community may be impacted.
NOAA Sea Level Rise Viewer
Pacific County Mapped Impacts
Several maps were created for Pacific County to visualize where the rising sea waters and the extreme floods may reach and where those tides or floods may impact critical infrastructure, residences, and wetlands.
Most of the maps can be scrolled into for a closer look using the zoom "+" and "-" in the lower right corner. The map can be moved by holding the right mouse button down while moving the cursor. To make the map full-screen, click on the 2 diagonal arrows in the white box in the upper right corner.
The following map shows the difference between the latest average daily high tide layer from NOAA (2017) and the 2050 Mapping Scenario. Use the swipe tool to see the difference between the two maps.
Current Sea Levels on the left. 2050 Mapping Scenario on the right. Yellow indicates +1 ft increase. Pink indicates +4 ft increase in Willapa Bay and +10 ft increase on the outer coast.
Current Sea Levels on the left. 2100 Mapping Scenario on the right. Yellow indicates +1 ft increase. Pink indicates +5 ft increase in Willapa Bay and +10 ft increase on the outer coast.
Existing Flooding Conditions
When community members were consulted, it was confirmed that much of flooding shown on the maps is already being experienced. What climate science tells us is that these storm flooding events, while temporary, will likely occur more frequently and for longer periods of time.
Scroll through each photo using the arrow. To the right of the photo, you will see the corresponding mapped location of each flood event.
01 / 06
1
Raymond
Willapa Place Way, Raymond, WA 98577
2
South Bend
W. Robert Bush Drive, South Bend, WA 98586
3
South Bend
Central Ave, South Bend, 98586
4
Naselle
State Route 401, Naselle, WA 98638
In addition to the sea water flooding shown in the map, Naselle also experiences freshwater flooding, which is not shown in the map.
5
Naselle
S. Valley Rd, Naselle, WA, 98638
6
Chinook
Port of Chinook - 743 Water St., Chinook, WA 98614
Vulnerability & Risk Assessment
This vulnerability rating is intended to be broad in nature to help prioritize facilities that will have the greatest likelihood of impacts from sea level rise and/or extreme flooding. Where vulnerability rank is noted with “potentially”, these ratings are based on the general proximity of these types of facilities to locations with an increased flooding risk but that are not mapped with the specificity to have a high certainty of rating accuracy.
It is important to note that these vulnerability ratings do not include the additional consideration of erosion or subsidence that is potentially exacerbated by sea level rise and extreme coastal flooding. This rating system only considers the exposure of facilities to the interaction of sea water on ground surface as it inundates inland areas with increased frequencies and to greater extents.
Vulnerability Ranking Key
Table of Vulnerability Ranking
01 / 04
1
Roads
Roads that may become flooded during extreme floods were reviewed. Are there alternate routes in and out? Will the bridges be tall enough?
2
Critical Infrastructure
Airports, police and fire stations, hospitals, libraries, schools, waste water treatment centers and electrical substations were checked. Would they be inundated by everyday high tides? Or will they only be flooded during extreme flood events?
3
Residences
How many homes and buildings will be flooded by daily high tides? How many will be flooded by extreme tides? Where are those homes? Which are historical buildings?
4
Wetlands
Where are the wetlands that will be flooded by daily high tide? How will that impact the food web?
Roads
State Route 4, Naselle; Photo Credit: Longview Daily News
The length of roads that are likely to be impacted by each of the scenarios was calculated and mapped below. This assessment assumes that existing bridges and culverts have clearance to pass these water levels if, on the map, the roads immediately before and after do not appear to be inundated.
Roads_2
Photo Credit: Chinook Observer
Airports
All of the airports and airstrips in Pacific County are likely to be impacted by extreme floods.
Yellow = +1-foot Sea Level Rise(SLR), Light Pink = +4-feet SLR, Dark Pink = +5-feet SLR
Critical Infrastructure
Willapa Regional Wastewater Treatment Facility
For this assessment, hospitals, airports, police and fire stations, schools, public libraries, septic systems, and wastewater treatment centers (WWTC) were considered critical infrastructure. Any impacts to these could compromise the health and safety of the community by reducing public services or critical functions.
Critical_Infrastructure
Coastal Residences
Coastal residences have varying degrees of vulnerability based on the how close they are to the shoreline and the existing elevation. Several historic structures, as identified by the Department of Archaeology and Historic Preservation (DAHP)’s online mapping tool, WISAARD , are rated/identified as having a "high" vulnerability rating. Adaptation strategies can be implemented for many existing and future coastal residences to prevent or reduce damage from sea level rise or extreme flooding over time.
North Cove
Buildings
South Bend - Photo Credit: Chinook Observer
Commercial Areas
Pacific County is heavily reliant on the marine and agricultural industries as the primary sources of economic viability. Pacific County is known for its cranberry and shellfish production, as well as crabbing and fishing industries. With rising sea levels and increased extreme flood events, these industries are vulnerable to the expected climate change impacts. Maintaining drainage systems, tidegates and dikes that keep the tidal saltwater out of cranberry bogs and other facilities should be considered as a priority. Adapting the buildings that store and process seafood and cranberries to increase their resilience to more frequent flooding should also be prioritized.
Habitats
Willapa Bay - Photo Credit: Chinook Observer
Sea level rise will likely have significant impacts on freshwater wetlands in low-lying coastal areas due to the increased exposure to saltwater. Many plant and animal species found near coastlines can tolerate different levels of saltwater. However, some species, especially plants, that are not salt-tolerant will die off and be replaced by those that are salt-tolerant. As a result, some freshwater wetlands will become saltwater marshes. Even if some animal species may not be affected by this change, their food source could be impacted and cause disruptions in the ecosystem and overall food web functions.
Wetlands_Impacted
Planning for the Future (Adaption Strategies)
"Adaptation Strategies" are plans and techniques that can be used to reduce or eliminate impacts from increasing sea level rise and changing storm patterns.
Based on this vulnerability and risk assessment, the following adaptation strategies, which have been used successfully by other jurisdictions, have been identified as potentially useful to Pacific County. This list includes some, but not all, of the adaptation strategies that could be considered to mitigate impacts from sea level rise and climate change.
- Require sea-level rise projections for development plans of potentially impacted properties.
- Review and revise development and building setbacks where appropriate.
- Consider including adjustments for future change impacts in habitat restoration efforts.
- Consider a more in-depth evaluation of potential impacts to commercial water-dependent industries.
- Consider development regulations for new or replaced on-site septic systems and public water systems in vulnerable areas.
- Limit redevelopment or expansion of existing legal non-conforming structures in vulnerable locations.
- Require special considerations when permitting critical infrastructure and facilities.
- Consider incentivizing Passive Management Strategies.
- Encourage alternatives to hard shoreline stabilization measures.
- Prioritize transportation connectivity and resiliency.
- Evaluate existing stormwater infrastructure and conduct maintenance, where needed.
- Develop a repetitive loss program to address structures that are repeatedly impacted.
Photo Credit: Chinook Observer
"Passive Management Strategies" are actions that can be taken to protect, or reduce impacts to, areas from erosion and flood events, while letting the coastline adapt to the changing environment.
Photo Credit: Jackson Blaylock
Conclusions and Next Steps
Assessing the impacts of sea level rise is an evolving science. The further out projections are cast, the lower the confidence is in those results. Also, since coastal scientists have been providing sea level rise and storm frequency projections, the amounts of predicted rise and increased storm magnitude have always increased, not decreased. Therefore, it is prudent these projections be considered a "best case scenario".
Areas most at risk to sea level rise and extreme flood impacts include:
- The Port of Ilwaco (roads, buildings, airport and wetland conversion),
- City of Raymond (roads, critical infrastructure, residences),
- South Bend (residences), and
- Tokeland (roads, residences, historic buildings).
The take-aways from this assessment include:
- Most critical infrastructure is unlikely to be threatened by sea level rise during the lifespan of the current structures. Temporary inundation during extreme flooding is limited to a few locations but will impact several buildings considered "critical infrastructure". Some roads may become impassable, and impact areas that lack an alternative route.
- Both airports are potentially impacted by extreme flood events and are at risk of inundation under the 2050 mapping scenario.
- Most residences are not at risk from a +1 foot of sea level rise above MHHW. However, this assessment does not include potential erosion that may result from increased storm activity. Additional analyses may be needed to determine if existing drinking water wells and on-site septic systems will be impacted by saltwater intrusion.
Recommended next steps:
- Additional future assessments should include a more in-depth analysis of flooding interactions with rivers.
- Review of existing drainage problems that are anticipated to become exacerbated by rising seas and heavier rains. These drainage impacts, as well as saltwater intrusion, could have significant impacts on coastal on-site septic systems and wells. It is recommended to consult with a hydrogeologist to evaluate groundwater interactions with saltwater for these facilities.
- Develop improved maps for public and private drinking water sources, on-site septic systems and other wastewater treatment plants, and other electrical and communication infrastructure (such as transmission substations and buried cables).
- Ensure the review and evaluation of the Flood Control District No. 1 Ordinances consider impacts such as rising average daily high tides and increased extreme flooding. Specifically, the County could consider evaluating the existing Ordinances for consistency with the 2019 Stormwater Management Manual for Western Washington (SWMMWW) prepared by the Washington State Department of Ecology.
- Develop emergency access plans to ensure public safety and accessibility of public services for areas with no alternative routes, such as East Tokeland.
- Examine water-crossing structures, including bridges and culverts, to ensure that conveyance of higher volumes of water at higher velocities can be maintained.
- Periodically review updated and new coastal resiliency modeling and adaptation strategies. In particular, review the CoSMOS model as it is developed for Washington’s outer coast and review new knowledge about how rivers respond to climate changes and interact with the marine environment. The findings should be applied in areas such as Raymond, Naselle and along the Columbia River.
Following this assessment, Pacific County Department of Community Development intends to apply for additional Washington State Department of Ecology Shoreline Planning grant funding to continue this assessment at a more detailed scale and develop policies and regulations to address sea level rise and climate change impacts. Additional studies around hydrodynamic modeling could be conducted to develop a more site-specific evaluation of the interactions of existing conditions with future sea level rise projections. These interactions could be used to inform regulatory language that incorporates sea level rise projections into development standards, particularly within the Shoreline Master Program (SMP). The mutually agreed upon sea level rise mapping projections could also be used in environmental assessments prepared by qualified consultants that would be required for development applications to ensure public health and safety is protected to the extent practicable.
Willapa Bay; Photo Credit: Chinook Observer