Thursday, December 15, 2011
Waves are introduced early in oceanography and coastal geomorphology books, since they are a fundamental way by which energy moves through water and by which water moves sediment. One of the most important aspects of waves is their behavior as they reach shore - and terms like reflection, refraction, and diffraction are important concepts, but often misapplied words. There were some nice examples in the little tiny waves at Ala Spit in Monday's low early morning light.
Reflection is the simplest notion, in part because we can all relate to other examples in day to day life - like billiard balls, canyon echoes, and shiny countertops. Here, waves are striking a vertical wall at about 45 degrees. The reflected waves leave the wall at the same angle, creating a mesh of intersecting waves. Where the wave peaks cross, their heights add, doubling the height of the individual waves. This photo also shows how the small waves steepen and grow in height as they arrive in shallow water. One of the most dramatic examples of wave reflection here in the Sound is the havoc on the south side of the Hood Canal Bridge during a strong south wind (Shine, January 2007).
This second picture illustrates both diffraction and refraction (though tough to separate here), as waves wrap around the small bar (and diffract from its ends). Diffraction seems to be the hardest concept to pin down and takes me back to college physics labs, the diffraction of microwaves through narrow slits, and the relevance to the wave-particle character of electromagnetic energy. Refraction is the bending of waves that occurs as waves slow down in shallower water and is an incredibly important concept to coastal geomorphologists and to surfers (these avocations frequently overlap). Reflection also reappears in this photo, since there are a series of waves reaching the far side of the bar that have reflected off of the log in the distance.
Tuesday, December 13, 2011
A lesson in overwash. The frost on this chilly morning highlighted the beautiful overwash fans from past storms, when waves and high tides spilled gravel over the top of the berm and into the backshore. Some of these probably go back many years or decades; others are brand new.
Since my visit last month (November 11) waves have washed over the newly constructed berm, depositing much of the sand and gravel on the back side of the narrow neck of the spit. The crest of the berm through this area is now only slightly above Mean Higher High Water so this winter's spring highs will continue to flood over the top. The beach face is flat and littered with scattered large cobbles and small boulders and occasional chunks of concrete that were left from the old riprap. The large wood that was placed along the temporary berm has largely washed out.
There are some good photos of the tide washing across the spit in the December 5th Whidbey News-Times.
Restoring nature isn't just about removing man made structures and replanting native vegetation; it's also about restoring the physical conditions that created and maintained the landscape in the first place. This means allowing storms and erosion and natural disturbances back into the picture - the very things we often go to such great lengths to control. The trouble is that these dynamic processes are difficult to predict and a site that has been altered for a long period of time will only return to its original condition slowly, and even then, is not likely to return in its original position.
Recovery of the berm will take time and it will take sediment. The first will require patience. The latter will be a challenge, as the neck of this spit is short on sand (and particularly gravel, since this is what best builds robust berms). The foreshore appears to have been starved of sand and gravel due to the development of a bar or proto-spit just to the south. There are also human modifications, including an updrift groin, that complicate the picture. In an ideal world, these other structures might have been removed and perhaps more gravel might have been added to the foreshore to help jump-start a new berm.
I look forward to watching what happens. Meanwhile, I trust that folks walking on the spit will take care to head back to their cars before high tide - lest their feet or their dog gets wet.
Saturday, November 12, 2011
Unfortunately, my Canon was filled with salt water, the normal backup camera I keep in the car wasn't in the car, and all I had left was the camera on my cellphone, which just didn't do the late afternoon light much justice. I stopped at Libbey Beach, Ebey's Landing, Camp Casey, and Keystone Spit to watch the waves rolling southward down Admiralty Inlet (I've included a couple of cell phone pictures at the bottom of this post).
Bush Point was my last stop before the light ran out and I had to head for the Clinton ferry. The wind was howling from the north and locals were pulling up and letting their children and their dogs out to stand in the spray. Waves were crashing into the old restaurant/inn, launching themselves up through the decking of the wharf, and blowing over the two-story structure in big sheets.
Bush Point - one month ago
The tide was scheduled to peak a bit higher than 10' MLLW around 4PM (when I arrived), but the surge added more than a foot (here's the Seattle record), so the the water was right around MHHW. Imagine if this storm had arrived on a 2' higher tide!
Friday, November 11, 2011
The strong westerly winds were coming out of a big hole in the clouds over the Strait, so I actually had some late afternoon sun. Hastie Lake is a little farther south on West Beach and is the site of a small boat ramp and a row of homes built on an old barrier beach. This would have been amazing to watch on a really high tide!
Tonight I'll try posting some of the videos I took this afternoon, including the one from here - my camera's last valiant effort before swallowing salt water and dying in a frenzy of small electronic gasps.
It's nice when storms come on weekends and state holidays - that way I don't sit in the office wishing I were on the beach. I just go. I headed for Whidbey via the northern route, figuring I could follow the afternoon's high tide and the shifting winds down the island. Deception Pass was quiet, as was Ala Spit on the northeast side of the island, and I was tempted to question the wisdom of the forecasts, but I arrived at West Beach to find the wind coming out of the west - furiously.
Cliff Mass's discussion of today's windstorm
SMITH ISLAND WINDSPEED
(located just west of this beach, I was there just before the peak)
The tide wasn't terribly high. If the water had been 1-2 feet higher, which it could easily have been, this storm would have caused a lot more damage. As it was, the wave runup only occasionally reached the bluff toe and we weren't even close to having logs washed over the road.
Swantown, April 2006 (earlier post on Gravel Beach)
The last time I visited Ala Spit, in early October, the park was closed and there were three excavators on the beach removing the old concrete rubble and repositioning rocks and logs (below). Today, the crews were gone, and nature was busy editing their final project. The neck of the spit had been eroding for a long time - for a bunch of reasons - and the junk that had been dumped on the beach to protect it wasn't helping. It may have been making it worse (Ala Spit, 2007-2008).
The project involved pulling out all the hard parts that were keeping the spit from responding constructively to wave action and adding sand and gravel in the form of a new higher berm. The berm is a bit higher than the natural berm would have been and the waves are already cutting a scarp into it, but that's okay. And this winter, I suspect waves will cut through the new berm, creating a lower and slightly broader feature. That will also allow the logs to distribute themselves more evenly - right now they are packed into a narrow band on the steep upper beachface. Some of the eroded sediment will be added to the beachface; some will get washed over and down the backside. The salicornia (pickle weed) will object initially, but will soon remember that this is how it always used to happen before the spit was buried in big rock and concrete.
Here's what it looked like a month ago.
Sunday, October 30, 2011
We're back to False Creek, this time along the north side, where the last two decades have seen an incredible transformation to park space and dense residential development. The shoreline is severely hardened - most of this edge is old fill that extends out into the historic False Creek estuary - but the seawall also provides another link in Vancouver's wonderful waterfront trail system. Variations in the height and design of the wall provide access and outlooks and interest. There have also been numerous attempts to provide some habitat, including intertidal benches, gravel and softer substrate, and even some shoreline vegetation.
I may have seen this beach from the Lion's Gate Bridge earlier, but the first time it really registered with me was 20 years ago when I heard Wolf Bauer talk about it. But this week was the first time I've actually walked it - or watched the sun set from it!
The exposure to waves from the west must drive any loose sediment on the West Vancouver shoreline eastward and historically it probably wound up incorporated into the protruding delta of the Capilano River, which emerges into Burrard Inlet just east of the bridge. Groins (groynes, in Canadian) now organize West Vancouver's sand and gravel into pocket beaches - including the large one at Ambleside Park. The beach curves out to meet a large groyne, on the end of which stands a Squamish figure welcoming visitors to Vancouver and the Squamish's historic land.
Saturday, October 29, 2011
There is a public promenade along the shoreline all the way from Dundarave to Ambleside (2-3 kms), most of it heavily armored to protect it from storm waves. The high tide prevented me from getting much of a sense of the intertidal, but it appears that the orientation, and perhaps severely limited sediment availability, results in little opportunity for real beaches except where projecting structures act as groins.
The West Vancouver Shoreline Preservation Society has been experimenting with using strategically placed rock to act as reefs to enhance habitat and to help trap sediment in the intertidal. They have also been working to improve stream mouths and stormwater outfalls along this heavily urbanized shoreline. I'll have to come back at a low tide sometime and take a closer look.
I was originally just going to do a single "West Vancouver" post, but I couldn't decide what to leave out, so I've split it into three.
It was a quick late afternoon bus trip across the Lion's Gate Bridge to West Vancouver. I got off at 25th Avenue in the Dundarave neighborhood and walked down to the beach. The beach here is limited to a beautiful little fillet on the west side of the pier (a groin/jetty, actually), swash aligned with the significant fetch from the west across the Strait of Georgia.
There was a small, lower beach against a stepped seawall in the lee of the pier, but it was mainly under the relatively high tide.
West Vancouver Shoreline Preservation Society
(I'm adding this because sometimes the location feature below links to a view that is zoomed much too far out)
The last time I visited this site was on a dreary August morning two summers ago. Today's October sunshine was a great improvement.
This is the Olympic Village site at the southeast corner of False Creek, Vancouver's urban ex-estuary. The mud flats, fringing salt marsh, and small streams have all given way to a heavily developed, and redeveloped, landscape with a steep, hardened edge. There is a longer discussion of this site in the earlier post:
False Creek: August 2010
Several of us got a great tour of the area on the eve of the Salish Sea Conference. The upland development is a world class green development with sophisticated water re-use, energy efficiencies, stormwater systems, and careful choices of buildings materials. The shoreline is a little less green than the buildings, but there are still many ecological enhancements, including the habitat island and the stream/wetland in the park that manages stormwater.
And of course, like so much of Vancouver's shoreline, the edge is a very public and a very accessible one.
I last visited this site in January 2010, only a few months after the seawall and the fill were removed and the stream mouth estuary was re-excavated. Now the site has had enough time for the vegetation to really begin to take hold. The stream has deposited a significant volume of sediment in the upper portion of the lagoon and this area is now high enough for alder to establish. The lower portions of the estuary are giving rise to various salt marsh plants. The mouth of the estuary is probably still trying to figure out how to balance the stream and the daily ebbing and flooding of the tides. On the other hand, I guess the mouths of estuaries are always trying to sort this out.
The spit itself is a pretty uneven feature. The beachface is marked by two distinct humps, perhaps an artifact of the original shoreline shape or perhaps the coarse-grained fans of earlier stream mouths. The restored spit has a low point in the berm that has been overtopped. Eventually, I expect the spit will even out a little bit, but there's not a lot of beach sediment and not a lot of wave action to move it around, so this process will be slow.