Effects of Sea Level Rise: Beach Erosion, Nourishment, and… Much More

By Hansi Hals

The sand spit and office buildings in Sequim Bay.

There is a small, unnamed sand spit that I can see from my office window overlooking Sequim Bay. It is rare for high tides to reach across it, even partially, but now the entire spit is submerged. A few tufts of vegetation and a curved line on the water surface show me the spit is still there— it’s just underwater because our recent winter weather has created a storm surge. The snow and storms, severe enough to close I-90 because of avalanche hazard, have everybody talking— even the tide is reacting! And they’re providing a picture of how higher sea levels and the storm surges that come with them may change our shoreline.

With this picture in mind, I ask myself: will the spit become submerged more often as sea levels rise, or will high water events and future new tide elevations deliver sediment so that the spit maintains its general shape relative to the new ordinary high sea water elevation? It’s a rhetorical question, mostly, because I think the answer is that it depends on the sediment supply. The water can only deliver what it has, and if it is starved of sediment, then it’s likely to do some eating rather than delivering. I believe it will do both— some delivering (since we have a fairly intact feeder bluff complex) and some eating because water does that— it erodes.

I’ve observed the power of storms and waves to build upon or eat away at beaches over many years. Years ago, I drove out to Rialto Beach in Olympic National Park on the Pacific Coast. I’d been there many times and was aghast when the entire parking lot was consumed by sand and beach logs. Parking for maybe 40 cars was entirely displaced by deep sand that had arrived during one storm. It was stunning.

Then, just last week, I visited a shoreline in Dungeness Bay where several adjacent landowners are responding to a December 2015 storm where the opposite occurred: up to two feet of the beach had receded overnight. The beach has since generally returned to the same elevation, but the memory of that event persists and the landowners are now planning a shoreline protection project. Thankfully soft shore techniques appeal to them, and as I walked along the project site, where they will lay down up to two feet of sand, gravel, and logs, I wondered again about the dynamics of beach nourishment and sea level rise. I wondered if the landowners are doing what the system would otherwise do, but I understand their reasons for wanting a head start. To those of you who study these dynamics: can we predict which storms will deliver the earthen cargo and which will pick it up?

Dungeness Bay, WA soft shoreline protection project site.

That proposed project appears to be a smart choice for the landowners and avoids the negative consequences of hard armoring projects. But it’s a stop-gap measure, and it’s limited. Besides shoreline changes like erosion and sediment deposit, what about the effects of sea level rise on the groundwater table and the shoreline septic systems? Spoiler alert: it won’t be good. Saturated septic systems don’t function properly; elevated fecal coliform can downgrade shellfish beds and nutrient loading can promote harmful algae blooms. So now, when I watch how weather-related rising waters affect the sand spit outside my office, I am also asking: what do you think happens when septics get wet?