Southwest Washington

Overview

Southwest Washington is home to some of the most marine dependent communities in the nation. The local economy relies on healthy waters and intact coastal habitats that support fishing and shellfish aquaculture activities. Fortunately, Washington’s outer coast has avoided many of the negative impacts associated with population growth and urbanization and still contains vast expanses of natural shoreline. In the estuaries and mudflats, shellfish and eelgrass beds provide food and shelter for young Pacific salmon, Dungeness crab, and migratory birds. On land, coastal dunes and forests are a source of high quality habitat for flora and fauna alike. This collection of habitats also buffers the shoreline from storms and flooding, protecting people, property, and infrastructure.

As populations grow, development pressure on coastal habitats may increase along the outer coast. Concurrently, the effects of climate change– sea level rise, flooding, increasing storms, and coastal erosion– cause the shoreline to retreat landward. In a changing environment, habitat conservation is essential so that coastal habitats can continue to deliver their steady stream of benefits. We must create a vision for our shoreline that balances the needs of the community with the needs of the environment so that both can thrive.

Salt marsh on Willapa Bay, Washington. Photo Credit: Keith Lazelle.

 

Coastal Hazards

The southwest Washington Coast is subject to inundation and erosional hazards that pose a threat to coastal communities. The sandy beaches and bluffs of Pacific County and Grays Harbor County are particularly vulnerable to erosion due to indirect effects of human activities and natural weather patterns. For example, construction of dams on the Columbia River and jetties at its mouth has altered sediment flow and hydrology of the Columbia River littoral cell. The result is a lack of sediment to replenish beaches as they erode. Erosion of bluffs and shorelines is further intensified during El Niño periods and large storms, when sea levels are higher and wave action is stronger. These impacts can result in significant economic losses to property owners and communities charged to protect the shoreline through mitigation (e.g. installment of geotubes, sandbags, and hardening structures).

Unlike sandy beaches and bluffs that undergo rapid change, estuaries are a transitional buffer between land and sea.  Protected estuaries like Grays Harbor and Willapa Bay (Pacific County) receive sediment inputs from surrounding rivers and streams. Eelgrass and other intact shoreline habitats play an essential role in maintaining accretion within estuaries to prevent shoreline erosion by trapping sediments. However, storm events that bring surge, waves, and high river flows can still lead to inundation and erosion in both the Grays Harbor Estuary and Willapa Bay.

As the global climate changes, rising sea levels on top of storm surges and high tides will intensify flooding and erosion in coastal regions. The National Oceanographic and Atmospheric Administration (NOAA)’s mid-level  sea level rise projections for the southwest Washington Coast range from 4-27 cm by 2030, 8-73cm by 2050, and 19-289 cm by 2100 based on a series of future greenhouse gas emission scenarios. An increase in sea level may cause declines in coastal habitats like eelgrass beds that depend on a narrow optimal depth range and saltmarshes that need room to migrate inland. A decline in these protective habitats may further exacerbate the impacts of erosion and inundation.

Table 1. The National Oceanographic and Atmospheric Administration (NOAA)’s mid-level (50th percentile) sea level rise projections for the southwest Washington Coast based on the “Toke Point” tidal gauge location.  Projections are presented from low to extreme are based on a range of greenhouse gas emissions scenarios.

Scenario 2030 (cm) 2050 (cm) 2100 (cm)
Low 4 8 19
Intermediate-low 7 12 31
Intermediate 11 25 83
Intermediate- high 16 40 151
High 22 59 229
Extreme 27 73 289

Shoreline Armoring

Armoring techniques (e.g. sea walls, jetties, breakwaters, and groins) are sometimes used as a solution to control coastal flooding and erosion. These methods can have negative ramifications on ecosystems by degrading surrounding vegetation and ecological functions, as well as altering sediment transport, hydrology, and channel movement (WAC 173-26-231). Additionally, armored shorelines can prevent the natural shoreline from retreating inland as sea levels rise, leading to loss of important coastal habitats (Figure 1).

Now, more than ever, communities should consider their vulnerability to flooding and erosion, protect or restore important buffering habitats that be cost effective and reliable solution to hardening a shoreline.


Figure 1. Certain ecosystems (e.g., wetlands) can move landward as sea levels rise. The ability of a habitat to move landward depends on several factors including the presence of physical obstacles preventing the subtidal or intertidal habitat from migrating.

Natural Infrastructure

Coastal communities are increasingly interested in using natural habitats and soft stabilization methods to maintain coastal resiliency in the face of a changing environment. Coastal habitats such as eelgrass beds, shellfish beds, saltmarshes (wetlands), sand dunes, and coastal vegetation (e.g the marine riparian) are valuable natural resources that can dissipate wave energy, slow water transfer, and stabilize sediments. In the long run, investing in natural habitats (through protection, enhancement, or restoration) is more cost effective than shoreline armoring as natural systems grow stronger with time, adapt as sea level rise, and self-recover after a storm.

Natural habitats also provide other co-benefits that serve the community continually over time.  In addition to their ability to buffer shorelines, they can serve as nursery grounds for economically important species, improve water quality, and provide recreation opportunities.

Development in vulnerable areas poses a risk to property and habitats, which can have a cascading effect on coastal communities. To increase coastal resiliency, communities can encourage developers to implement setbacks and buffers along the shoreline to reduce risks to infrastructure and the need for shoreline armoring in the future.

To learn more about the role that natural habitats play in protecting infrastructure visit NOAA’s Green Infrastructure website.

Photo Credit: David Ryan

Modeling Tools

Spatial modeling tools can help communities see risks of coastal hazards both now and in the future. The The Integrated Valuation of Environmental Services and Tradeoffs (InVEST) Coastal Vulnerability model is one tool that can help communities understand how their shorelines are vulnerable to storms and the role that habitat plays in buffering shorelines from the impacts of erosion and inundation. The model was run for Pacific County and Grays Harbor and the results are located on the Coastal Resilience Mapping Portal under the “Regional Planning” application for the Outer Coast.  This tool will allow communities to:

  1. Identify coastlines currently vulnerable to erosion and flooding due to storm surge and waves (called exposure), and
  2. Highlight the areas where vulnerability is reduced due to the presence of natural habitats (called habitat role).

The model estimates how vulnerable different areas of the shoreline are to erosion and inundation during coastal storms. Shorelines considered highly vulnerable are those that are most likely to experience erosion and inundation.  That vulnerability is a based on five characteristics of the shoreline – 1) Its geomorphology, 2) Surrounding coastal habitats that may or may not buffer the shoreline, 3) Its exposure to wind and waves, 4) The surge potential, 5) And the surrounding relief.  Each of these characteristics are ranked for the shoreline segment, and those ranks are then combined and rescaled to produce an index of vulnerability (called exposure) from low to high.

The results can be used to inform the creation of policies and regulations on buffers for local development plans, educate developers and homeowners on the importance of coastal habitats for shoreline protection, and guide restoration activities. By preserving the ecological functions of county shorelines, southwest Washington has the opportunity to work towards resiliency in the face of a changing coastline.

A full report on the InVEST Coastal Vulnerability model is available here.