Swishwash Island was not always an island, but has for ages past been a tidal marsh. A combination of human industry and later environmental actions has resulted in the creation of an island that now functions as a key ecological ground in Metro Vancouver. From your current location, you are standing on Sea Island, looking across Moray Channel at Swishwash Island.
This Earthcache is designed to introduce you to the area, and gain an understanding of how both human and natural actions have combined to create this island. Further, you should be able to identify similar salt-water marsh islands elsewhere in your travels and have an appreciation of how they came to be and their importance to the geology and ecology of the area.
Parking and observation are both at the same coordinates; a large, safe pull-off along a public road on Sea Island.
QUESTIONS:
Please send your answers to these questions before logging your find on this Earthcache. Answers are required for logging per Geocaching.com guidelines. Also, information in the Earthcache description below paired with observations from ground zero will be essential for successful answers.
1. According to the sign at GZ, how many acres is Swishwash Island?
2. Estimate the width of Moray Channel between Swishwash Island and Sea Island.
3. Assume the length of this channel is approximately 1.5 kms, and the depth is estimated at an average of 10m. What is the approximate volume of water in this section of Moray Channel?
4. If 5% of the total sediment carried by the Fraser River were deposited in this channel, assuming no other natural or human forces were to act upon it, how long might it take to become a Palaeochannel?
5. Did you observe any wild animals in the area during your visit? Do you think they would have been here without the rewilding process?
“What If…”
The Fraser River is the longest river in British Columbia, and it winds it’s way 1,375kms through the amazing geology of our province before it deposits water into the Salish Sea at a rate of 3550 cubic metres per second. Along with this comes 20 million tons of sediment each year collected along the 1,375 kms.
The heavier sediment settles to river bottom as the current slows once the Fraser becomes intertidal from approximately the Mission Bridge. In fact, Sediment deposit is significant from the area of Hope to the Pacific Ocean.
As this sediment settles it fills the river, resulting in further slowing the current and increasing the sediment deposition. This process has resulted in the creation of much of the intertidal marshland and small islands in the Fraser River Delta.
This very process created an extensive intertidal marsh area and series of islands which have subsequently been dyked, drained, and converted to agricultural, industrial, and urban land including the Vancouver International Airport behind you right now.
Swishwash Island itself was used in the late 1800s to early 1900s as the location for a cannery and homes for those who worked the salmon fishery. Today, you can still see the pilings from the cannery on the far west end of the island, but not from this location.
Years after the cannery had burned down and people had moved away from Swishwash, in the 1940s and 50s the island was used as a dumping location for the dredged spoils resulting from trying to keep the river channels passable for commercial sea traffic. The lower river reaches of the Fraser River accumulate nearly 3 million cubic metres of sediment annually, requiring repeated dredging operations; the mechanical human intervention of the natural sediment deposits.
But what if the area hadn’t been touched by human hands?
When a river or stream channel is filled in by younger sediment and no longer has an active pathway of water coursing through it, it is referred to as a Palaeochannel. In simplest terms, think of this as a river that has been completely filled in by it’s own sediment.
Imagine that in the late 1800s the islands and shores of the Fraser River had not been dyked. Imagine that this area remained untouched by significant agriculture or industry, nor homesteading. Imagine the river had never been dredged.
“What is…”
Today, human intervention has tried to address our “What if...” questions by granting the island and intertidal marshes of Swishwash Island to the Nature Conservancy of Canada to recreate important disappearing habitat for animal and plant life native to the area.
The process underway is called “rewilding” and constitutes two important actions - invasive species are removed by trained and diligent volunteers, and the public is prohibited from recreational access to the area.
With Swishwash in the process of rewilding, native plant and tree species are taking hold, creating more “catch” area for Fraser River sediments as the river slows around the island and it’s marshes. This is resulting in Swishwash Island and its intertidal marshes in Moray Channel towards Sea Island slowly filling in with sediment again, recreating natural habitat for salmon, steelhead, flounder, beavers, otters, coyotes, eagles, herons, and many different migratory birds.
Thanks to the efforts of the Nature Conservancy of Canada Swishwash Island is slowly returning to the geological state it was in the late 1800s, almost 150 years ago.
Sources:
Nature Conservancy of Canada interpretive sign
https://events.natureconservancy.ca/al-location/swishwash-island/
Wikipedia - Fraser River
https://en.wikipedia.org/wiki/Fraser_River
The Richmond Archives
https://richmondarchives.ca/2017/05/04/island-city-by-nature-richmonds-islands/
GZ and the interpretive sign are along a public roadway; no need for landowner permission to stop and make necessary observations.