Sea Level Rise: Notes on the December 27, 2022 Tide Flood

Back in mid December I visited a dike on the distal Skagit River delta area near Samish Island. The dike holds back high tides from Alice Bay from inundating the low farm fields and road. My site visit took place during high tide. During low tides Alice Bay typically fully drains becoming a broad mud flat.  

Samish Island Road and the dike between the road and Alice Bay.

The road is below sea level

View of the dike looking north. Alice Bay on the right, the east end of Samish Island is in the distance and the Chuckanut Range in the far distance 

View looking south along the dike.

Grassy areas in the near distance are saltwater marsh.

Dike District 5 portion of dike. This section of dike was and lined with with rock last year.

Last February there was a tide surge that caused tidal flooding in Edison. The minimal free board and dike erosion resulted in significant dike raising by the District. However, the district boundary ends between the above shown new work and the high ground to the north at Samish Island.

On December 27, 2022 a very deep and broad area low pressure storm system combined with very high astronomical high tide. The low pressure path and associated wind pattern added to the water levels. At Port Townsend the storm tidal surge was 2.5 feet.

    The result was water overtopping the dikes shown  above. 

Sea water over topping the a low spot in the dike

Multiple over flow locations along dike and water filling the low area behind dike including the road

Tide flood water pouring across road into fields to the west.

Flooded fields viewed from the north

While the above shown flooding covered on the order of 150 acres of fields with sea water, the impact for other areas was more acute. Flooding was reported at multiple locations from this event including Olympia and Port Townsend. 

North shore of Samish Island looking east.

Note that water just reached the top of the slightly elevated area between the homes and Samish Bay.

From the same location above but looking west.

Note here that the berm between the homes and bay is lower allowing flood waters to reach the homes.

Water getting over or around the elevated shoreline berm flooded the whole low area behind the berm. I had some work to do at this area and the water over topped my rubber boots. Not particularly pleasant as the flooding included flooding all the septic systems.  

Sea level rise is pushing what in the past had been a close call tidal flood to full out flood events with a higher frequency. 

Notes on Sweet and others (2022) Seal Level Rise

Earlier this year Sweet and others(2022) updated Sweet and others (2017): Global and Regional Sea Level Rise Scenarios for the United State. Sweet and others (2017) suggested global sea level (GMSL) will rise as between 0.3 meters and 2.5 meters by 2100. Sweet and others (2022) find the high end of 2.5 m by 2100 less plausible. The bad news is that the rate of GMSL rise has been increasing and Sweet and others (2022) project that the rise in GMSL over the next 30 years will be as much as that over the past 100 years. The 2022 report notes a high level in confidence for their sea level rise scenarios over the next 30 years. Post 30 years the confidence level for sea levels is lower primarily because of uncertainty regarding some of the ice sheets in Greenland and Antarctica.  

GMSL is not simple and the sea level rise is not uniform around the planet. Some places will see greater sea level rise and others less. The 2017 report included an image of global sea level rise from 1992 to 2016 derived from satellite data measurements. 

 

Figure from Sweet and others (2017)

Global sea level has rises in an uneven manner due to currents, warm water expansion, and changes to gravity fields from more water in the oceans (the Earth's surface is flexible). The sea level also can vary due to cyclical climate patterns that move the ocean water around via wind and temperature patterns. I like to think that the ocean layer as having weather only slower and a bit less pronounced than the atmosphere. The image above also shows that on the Washington State coast the global sea level trend was near neutral for the 1992-2016 time period.

The 2022 report has an image with three plots showing global sea level rise along the coast of North America. 

Figure 2.1 from Sweet and others (2022) Regional sea level linear rates of rise (mm/year) from satellite altimetry over three different time periods: (a) 1993–2006, (b) 2007–2020, and (c) 1993–2020. Linear rates of change of relative sea level (ocean and land height changes) from tide gauges over the same time period are also shown (circles). 

For Washington State the 1993 to 2006 period the regional sea level rise was mostly neutral, but the more recent period of 2007 to 2020 shows that regional sea level on the Washington coast has increased as has the regional rates in most places around North America. 

The global and regional sea level increase is not a simple uniform rise. There is an added complexity: while regional sea level is changing, the land next to the sea is also changing in level. More on that on a future soon post.

The Two Hat Islands in Washington State

I visited Hat Island in Possession Sound west of Everett this week. The icy thick fog in the morning prevented a good picture of the island, but but I had a nice view from the island. 

View from a high bluff on Hat Island looking south to the Mukilteo Ferry and Whidbey Island coast

Just the week before I had a nice view of Hat Island in Padilla Bay east of Anacortes. 

Hat Island viewed from the west in Guemes Channel 

How can there be two Hat Islands in the same state?  

If one zooms in on the USGS National Map the Possession Sound Hat Island has two names.  

I have always thought of the island in Possession Sound as Hat Island. The community of homes and lots on the island is called Hat Island and the ferry (private) is the Hat Island Ferry. However, its official name on the USGS topographic map is Gedney Island. The name was given to the island by Wilkes following a common custom of the time of the random naming things for associates or friends that never came near the area. Waterman (2017) provides some background on Gedney and his role in the La Amistad case. Gedney's claims on the La Amistad and it cargo may explain why locals preferred using the name Hat Island. 

The Hat Island in Padilla Bay is a Washington State Natural Resource Conservation Area. Perhaps an official name change is in order for one or both of the Hats.      

Mary McCaslin - Prairie In The Sky

Mary McCaslin died earlier this month (nytimes./music/mary-mccaslin). Mary McCaslin wrote and sang a number of songs that always stuck with me - enough so that I could sing them through myself years after. Prairie in the Sky still resonates. I believe Mary and I shared a similar romantic view of the West. In elementary school I would always pick 'Home on the Range' whenever it was my turn to pick a song. Prairie in the Sky better captures that childhood longing to be out on the open range and essentially replaced that older song in my music list.    

Former Placer Mining on the Columbia River

A gold rush in the Cariboo District of British Columbia resulted in an influx of miners passing through Washington Territory in the late 1850s and 1860s. Some of the miners traveling along the Columbia and Okanogan River took to placer mining at the gravel bars along the rivers. Splawn (1917) described 50 miners working the gravel bar at the south side of the Columbia River at the confluence with the Okanogan River in the early 1860s. Much of the placer mining working river bars on the Columbia River was undertaken by Chinese miners.  

Much of those placer mine workings have been submerged as the result of dams on the Columbia River. During a recent project I came across some old trenches on a terrace above the Columbia River well upstream of the Okanogan-Columbia confluence. The 1860s and 1870s placer mines were not documented operations and the archeological record is a bit thin.

I took a look at lidar bare earth imagery and found two obvious placer mine sites -- both partially submerged on gravel bars along the river between Grande Coulee Dam and Chief Joseph Dam.    

The Chinese operated placer miners primarily operated in the 1860s through the 1870s (Evenson, 2016). There are references to troubles with First Nations with one description of a massacre of the miners south of Chelan. Some of the placer sites were further worked in the early 1900s and I suspect that was the case at the two sites shown above. 

Reference:

Evenson, Lindsey M., "Pre-1900s Chinese placer mining in northeastern Washington State: an archaeological investigation" (2016). EWU Masters Thesis Collection. 358.   

Splawn, A.J., "Ka-Mi-Akin, the Last Hero of the Yakimas", (1917)

My First Pronghorn Spotting in Washington State

Antilocapra americana (pronghorn antelope) have been reintroduced to Washington State first by the Yakama Nation in south central Washington and a few years ago by the Colville Confederated Tribes in north central Washington. I finally saw my first Washington State pronghorn last week.   

These two are from the Colville introduction. I had been told that that some of the pronghorns from Colville had crossed the Columbia River and these two were south of the river in northern Douglas County. This area of Douglas has a fair bit of scrub steppe land. The area was glaciated and has large areas of very thin soils over bedrock or thin glacial soils. As such cultivation has been very limited with grazing operations being the main historic land use and very few humans. All and all good wildlife habitat with pronghorns being new entrant after a period of absence.

The Yakama pronghorns have expanded their range as well and the herd numbers have held up post reintroduction (https://wdfw.wa.gov/publications/02288).  

Shuksan Greenschist

I had a work venture up the Skagit Valley near Marblemount. A major tectonic structure is located near Marblemout, the Straight Creek-Fraser River Fault. The fault is a strike slip fault with the west side having moved about 60 miles to the north. Movement took place about during the Eocene. The fault divides the Northwest Cascades to the west from the Cascade Crystalline Core to the east. Near Marblemount the rocks on the west side of the fault consist of the Shuksan Greenschist.

Shuksan Greenschist near Marblmount, Washington

The Shuksan Greenschist is named for the famous mountain, Mount Shuksan. 

Mount Shuksan

There is a good chance that you have seen pictures of Mount Shuksan as viewed from Picture Lake. Ned Brown noted in his book Mountain Building Geology in the Pacific Northwest that he saw a mural of Mount Shuksan in a coffee house in Japan. The back of my 4th grade class located nearly 1,000 miles from Shuksan had a mural of Mount Shuksan and Picture Lake and I saw the same mural image in a taverna in Greece.

   

The Shuksan Greenschist is metamorphosed ocean floor basalt and is part of the Easton Metamorphic Suite, one of the many accreted terranes in Washington State. The Easton Terrane is an ocean floor terrane that includes thick ocean floor basalt and gabbro and deep ocean floor sediments. The age of the original terrane is between 170 and 130 million years old. The basalts and gabbro have undergone multiple metamorphic events. The initial metamorphism of some of the areas of the Shuksan ocean floor was from hot fluids post eruption of the basalts and crystallization of the gabbros (Haugerud, 1980). The primary metamorphic event was during accretion to the margin of North America when the basalt and gabbro were metamorphosed into greenschist and in some areas blueschist from high pressures during deep burial in the accretion zone along the edge of North America. Further low grade metamorphism took place during post accretion emplacement tectonic events. 

Shuksan Greenschist has a high density and in places where the joint sets in the rock are widely spaced, the rock breaks into large heavy blocks that make for good ocean jetty rocks, in particular at the mouth of the Columbia River (skagit-county-greenschist). This possible use has generated some interest in mining into a mountain side a bit west of Marblemount. My venture took me past the potential mine site. 

Cliffs of Shuksan Greenschist west of Marblemount

Site of on again off again proposed rock quarry

Last winter I visited the south jetty at the Columbia River. 

Jetty at the Mouth of the Columbia River

Blocks of greenschist at jetty construction site