Beach dynamics make the West End Natural Resources News

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.

The broad sandy beach at Kalaloch, one of two study sites for this project.  Photo from April 2018

 My study focuses on two beaches – Rialto and Kalaloch – though it is likely that the lessons I’ve learned are the same up and down the stretch of the Olympic Coast from Pt. Grenville to the south to Cape Flattery in the north.  The beaches along this stretch of coast are alive and dynamic, molding themselves each day to the changing behavior of the unruly North Pacific Ocean, and the geologically-tortured lands of the western fringe of the Olympic Peninsula.  Sandwiched between these two restless bodies, Olympic Coast shorelines literally shape-shift in an effort to hold a line.

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. 

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. 

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.

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. 

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.