The North Pacific Coast Marine Resources Committee publishes a great annual newsletter highlighting natural resources issues and projects in the "West End" of the Olympic Peninsula. I was given the opportunity to write up a little summary of my year-long shoreline dynamics study that I pulled off with MRC funding (along with support from Olympic National Park and Peninsula College), which is available here in the July 2019 edition. But I'm going to reproduce the article here...enjoy:
The Olympic Coast is an extraordinary place - one needs to
only try to find a trailhead parking spot on a summer weekend to find visceral
proof of that. People travel from around the world to visit. Drill down further though, and focus only on
the narrow boundary between the land and sea, and the shoreline of the Olympic
Coast becomes even more extraordinary still.
Most people who visit the coast with this sort of focus tend to dwell on
the diverse and colorful intertidal marine community of the rocky
shorelines. But, through the support of
the North Pacific Coast MRC and my employer, Washington Sea Grant, I’ve had the
opportunity to study the dynamics and behavior of Olympic Coast beaches for the
last year, and will describe a bit of what I’ve found.
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| The broad sandy beach at Kalaloch, one of two study sites for this project. Photo from April 2018 |
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| Map of the Olympic Coast, which I define as stretching from Cape Flattery to the north, and Point Grenville to the south. My two study sites, Rialto and Kalaloch Beaches, are marked on the map. |
Let me start first by describing what I do on the
beach. I use survey equipment to
measure, with great accuracy, location and elevation on the beach. Collected along transects that cut across the
beach, the raw GPS data can be converted into what are called beach profiles. The figure below is an example from a single
transect at Rialto Beach. You learn something
from a profile from a single day – you can easily calculate, for example, the
slope of the beach, the width of the beach, or the elevation of the berm at the
top of the beach. All are useful for
understanding what sort of habitat a shoreline may provide.
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| Three beach profiles, from three different days, collected at Rialto Beach, Olympic National Park. Beach profiles represent a slice through the intertidal beach |
But for me, the really interesting stories emerge by looking
at these profiles over time, which is exactly what this project focused
on. I visited Rialto and Kalaloch every
other month, developing a picture of the seasonal behavior of both beaches over
the course of a year, and was able to calculate and plot a time-series of the
position of the beach. My
take-away? Both beaches are alive, never
standing still. Rialto over that time
period moved almost 60 feet seaward between March 2018 and January 2019, and
then promptly retreated 45 feet back in just the two months following January
2019. Kalalaloch followed a similar
pattern, except its back and forth movement, first landward and then seaward,
exceeded 150 feet, and it ended the year with a final yo-yo back seaward of
over 100 feet.
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| Time-series of beach position at both Rialto and Kalaloch beaches from approximately Spring 2018 to Spring 2019. Where the slope of the time-series line is positive the beach is accreting. Where the slope is negative the beach is eroding. |
What makes beaches dance this way? If we imagine these beaches dancing to music, it is a complex composition. Different factors like the range of tides, the source and supply of beach-building sediment, the presence or absence of large wood, and even the movement of groundwater certainly play a role in the behavior of beaches. From a sediment stand-point, for example, both of these beaches are quite different; Kalaloch is a broad sandy beach along a relatively straight stretch of coast, while Rialto is a narrow mixed sand and gravel beach, positioned near a large river mouth. If I had to guess, though, these beaches are mostly moving according to the seasonal tempo set by ocean waves. At a basic level, beaches are controlled by the energy delivered to the shoreline by waves, which indeed does vary dramatically over a typical season on the Olympic Coast.
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| Surveying Rialto Beach during a winter storm, February 2018 |
I was also able to fit the beach profiles collected over the
year into a larger study focused on long-term trends at both beaches; in
essence I’m trying to determine if the beaches of the Olympic Coast are eroding
over many years, accreting, or just staying put. The reasons for doing this may not be
obvious, but they are important. Beaches
often serve as barriers that protect human infrastructure from the astonishing
energy of the ocean. Indeed, both
Kalaloch and Rialto serve this function for things that we’ve built behind
them. Erosion of beaches in and of
itself is a natural process, but if that erosion compromises things that we
value it becomes a hazard. The outlook
for damaging erosion of shorelines all over the globe isn’t great; a rising
average sea level can prompt beach erosion, as can a change in the energy
carried by waves across the ocean’s surface, and both are observed to be
happening all over the world.
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| Example summer profiles from Kalaloch Beach from 2014 and 2018, and a time-series of summer beach position (bottom panel), also from Kalaloch Beach. |
Profiles collected every year in the summer, limited though
they are to the last 5-6 years, start to paint a picture of a possible
long-term erosion trend at both beaches.
It is difficult to conclude too much from the erosion trends that are
emerging from my data…it is simply too short of a record to evince a great deal
of confidence. But perhaps these data
are a reminder that we live in a time of change, and these beaches that we
enjoy may be increasingly stressed by changes in the North Pacific Ocean. We, as a society, may have some hard
decisions to make regarding how to respond to that in the future.
