SEQUIM — Port Townsend faces the possibility of more flooding by 2030 while Port Angeles and Neah Bay are so far keeping pace with sea level rise, but that could change within the next 85 years, according to a climate change study that will be discussed at a free seminar this week.

Ian Miller, a coastal hazards specialist with Washington Sea Grant, and Cindy Jayne of the North Olympic Development Council, will discuss the impacts of sea level rising over the next several decades on communities on the North Olympic Peninsula at the Thursday seminar.

The preliminary results of the nearly completed study will be presented from 6 p.m. to 7:30 p.m. at the Dungeness River Audubon Center, 2151 W. Hendrickson Road, Sequim.

The climate change vulnerability assessment and adaptation planning study is being conducted by Washington Sea Grant, an extension of the University of Washington.

During the seminar, Miller will speak about sea level rise, ocean acidification, marine debris, tsunamis, beach erosion, Washington coastal ecology, coastal sediment transport and geomorphology — the study of the physical features of the surface of the earth and their relation to its geological structures.

Rates to accelerate

The assessment suggests “that rates of sea level rise are almost certain to accelerate in the coming decades and that sea level rise will almost certainly lead to shoreline impacts for all three communities by 2100, and probably much sooner — especially for Port Townsend and Port Angeles,” Miller said.

“Our projections suggest, for example, that there is a reasonable chance that there will be a noticeable increase in the flooded areas in downtown Port Townsend during winter storm events by 2030,” Miller said.

A rise in sea level can be a normal geological development depending on how you look at it, Miller said.

“Certainly sea level has changed over the geologic record, but modern development is largely premised on the idea of stable sea level. So, from that standpoint, it’s not normal.”

Causes of rising seas

Globally much of rising sea level can be attributed to two factors, Miller said.

These are increases in the amount of heat stored in the ocean, which causes the water to expand, and the addition of new water volume to the oceans as land-grounded ice in Greenland and Antarctica melts.

“Once you narrow your focus to the regional, things get much more complicated, as complex patterns of heat distribution in the ocean or patterns of large-scale winds and pressure over the ocean can alter sea level patterns,” Miller said.

Changing land elevations

Analysis of the study suggests that “eustatic” sea level — the level of the sea irrespective of a change of land elevation due to tectonic events — has risen at a rate of 3 to 4 inches per century since about 1940.

“However, the land is also moving at different rates in the different communities on the Olympic Peninsula,” Miller said.

The Olympic Peninsula sits on the North American Plate.

To the west lies the Juan de Fuca Plate, which is subducting, or slipping beneath, the northerly portion of the western side of the North America Plate at the Cascadia subduction zone, according to geologists.

The subduction zone includes a large western portion of the Olympic Peninsula.

As the Juan de Fuca Plate slowly slips beneath the North American Plate, it causes the land to rise.

Because of the rising land mass, “we also need to consider ‘relative’ sea level, which is the level of the sea relative to the land,” Miller said.

“There, the story is a bit more complicated.”

In Neah Bay, for example, “the land is rising rapidly and has outpaced sea level rise,” Miller noted.

“As a result, relative sea level has fallen in Neah Bay at a rate of approximately 7 inches per century.”

In Port Townsend “the land appears to be subsiding, and therefore relative sea level has risen faster than the eustatic rate, at about 6 inches per century,” Miller said.

In Port Angeles “it appears that the land is rising, but at a much slower rate than in Neah Bay, and [has] largely kept pace with rising sea levels over the past 40 years or so.”

However, that is expected to change over the next 85 years, with sea levels creeping up in the Port Angeles area, he said.

It remains to be seen how sea level rise will ultimately impact communities in Jefferson and Clallam counties, Miller said.

Variety of vulnerabilities

“There are a variety of sea level rise vulnerabilities in Jefferson and Clallam counties, typically associated with development in low-lying areas — residential development on the Dungeness River delta for example — and on coastal bluffs, the erosion of which is likely to accelerate with increased rates of sea level rise,” Miller said.

Risk, though, “is a function of both the hazard — in this case erosion and flooding of the shoreline — and vulnerability, i.e. development along the shoreline that puts people and infrastructure in harm’s way.”

Local communities can mitigate their “vulnerability by modifying the ways that we use and develop the shoreline,” Miller said.

“Such actions will reduce our risk to sea level rise.”

Stemming the tide

When asked if anything could be done to prevent increasing sea levels, Miller replied, “over the short term, not really.”

But, “in thinking about sea level rise projections for the coming century, the answer is yes,” he said.

“The magnitude of sea level rise over the coming century is governed to a large extent by how much greenhouse gases are added to the atmosphere.”

Miller works out of Peninsula College in Port Angeles as well as the University of Washington’s Olympic Natural Resources Center in Forks.

His work is to help Olympic Peninsula coastal communities increase their ability to plan for and manage coastal hazards, including tsunami, chronic erosion, coastal flooding and hazards associated with climate change.

He has a blog at http://coastnerd.blogspot.com.

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Sequim-Dungeness Valley Editor Chris McDaniel can be reached at 360-681-2390, ext. 5052, or cmcdaniel@peninsuladailynews.com.