Monday, October 14, 2013

Whiffen Spit

Barrier beaches, in their simplest conception, are sort of a dynamic balance between loose sediment and wave action. One consequence of this is that they typically have smooth curves with few inflections. When there are sharp bends and discontinuities, it usually suggests that something else is going on. This may be some localized bedrock control or an underlying boulder lag, it may be related to a historic breach or an uneven supply of sediment, or it may be due to a human intervention such as an old revetment, the foundation of an old mill, or a groin.

Whiffen Spit stretches, somewhat crookedly, across the mouth of Sooke Harbor. It must be more than a kilometer in length, with a navigation marker at the tip. It's a wonderful park and on a pleasant October Sunday morning, half the dogs on Vancouver Island were out for walks on it.  I suspect that the footpath began as a road, perhaps access to whatever was built on the old concrete foundations farther out on the spit.

Google Maps: AERIAL VIEW

The neck of the spit is heavily armored with riprap and there is also a large groin, which together segment the base of the spit into small pocket beaches.  I don't know the story at Whiffen Spit, but typically the necks of these features are the narrowest parts and are often most susceptible to erosion. This portion of a spit is often actively migrating landward, aided by large storms that cause overwash, while the end of the spit remains more stable and may actually accrete.

When a road is built on this narrow part of the spit, it is inevitably damaged by big storms and the response is to armor and elevate the road. Over time, the base of the landform becomes less a spit and increasingly a causeway. This seems like it may have happened here. The groin would have been a logical, but short-sighted, fix to ongoing erosion, reducing updrift erosion, but aggravating erosion farther down the spit.

These things alone would help explain the irregular shape of Whiffen Spit, but as much as the human imprint on is obvious, I couldn't help but wonder if the shape of this spit also reflects some more fundamental geologic factors - an irregular glacial deposit, some underlying bedrock.  Even a small ledge of bedrock in the location now marked by the large groin might have led to a spit with this general configuration.  Another possibility is limited sediment supply, which can cause a barrier to begin to break down, scavenging itself to form shorter, more swash-aligned beaches - certainly a possibility for a spit like this without an obvious source of new sediment. An historic map of the spit would be a great resource right about now!

Whiffen Spit is a fascinating feature and one I'd love to know more about.  Much of the above is speculation, but it's a good opportunity to discuss some common aspects of spits, some of which may apply better here than others.  The scale and the history are different, but this place reminded me a lot of Ala Spit on Whidbey Island. There are definitely some similarities:

Gravel Beach: posts on Ala Spit (not necessarily in order)

When I put nine photos in a post, you know it's a pretty neat place. One of the more famous small inns in the Pacific Northwest is located right above the base of the spit -- seems like a good excuse to come back for a weekend to explore.

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