Saturday, January 21, 2017

Semiahmoo Spit

Semiahmoo Spit reaches north across the mouth of Drayton Harbor - with a long narrow neck and a very broad bulb at its distal end. This large expanse was created when the marina was dredged and the dredge "spoil" was used to greatly increase the size and elevation of the spit.


AERIAL VIEW

The perimeter of the spit consists of an irregular pattern of modest banks eroded into the dredged material and low depositional segments likely formed by the gradual redistribution of material along the shoreline. That means much of this shoreline is constructed, yet behaves much as a natural beach. And other than at the neck of the spit itself (see below), there's been no need to armor the beach.  


After numerous delays, a new phase of development is occurring on the outer edge of the spit, south of the existing resort. Fortunately, the development maintains a public trail system along the shore and has placed the new buildings fairly far back from the edge. Rather than try to fight the chronic erosion, the designers pulled the abrupt edge landward, creating more beach-like area. I say beach-like, because it's still fairly high and steep compared to a natural upper beach.


It looks great, but bears watching. The underlying reasons some segments of this shoreline were receding have not changed by reducing the height of the bank (any more than armoring an eroding bluff prevents the ongoing erosion of the beach itself). So we may find that the new beach continues to erode, probably as a low scarp. And ironically, by reducing the height of the eroding "bluff" we may have reduced the supply of sediment to the beach, which could result in more rapid erosion.

Again, this bears watching. If erosion continues, this might be a good place to consider a localized feed source - a periodically restocked pile of gravel that can meter out sediment to adjacent shorelines as it erodes.  On the other hand, maybe this won't be necessary. And regardless, kudos to Blaine and the development and their designers for what they've done here. In another era, this would have all been riprap.

Speaking of riprap, the real problem at Semiahmoo is the neck of the spit (aside from the clever idea to build a destination resort on a sand spit). Narrow and low - armored on both sides - the roadway is increasingly a causeway. And increasingly vulnerable - even at today's sea levels. (No pictures this trip - maybe next time). There have been some efforts to rebuild a berm on the inside (low energy, marshy), but they may need to be more ambitious. And the outside may require some serious thinking - maybe a coarse gravel cobble revetment of some sort?  It probably won't be easy or cheap, though maybe throwing some coarse gravel at the south end would be a useful experiment?

Previous posts from Semiahmoo:
Tongue Point: March 2009
Semiahmoo: March 2009

Thursday, January 19, 2017

Birch Bay

The north end of Birch Bay was once a marked by a large complex of spits and marshes. Drift was eastward into the bay, carrying sediment from Birch Point to form a series of spits that terminated in an inlet at the northern corner of the bay. The spits and marshes probably recorded a wonderful chronology of sea level change, geologic events, and early first nations occupation.

AERIAL VIEW



In the late 1960s, it all became Birch Bay Village. The wetlands were dredged to create lakes and a marina. The sediment was used to create dry land for homes and golf. A new inlet to the new marina was cut at the base of the spit and the old inlet was left to drain a very small remnant of the original marsh. Drift rapidly built a broad fillet against the west jetty and the downdrift beaches were starved of their natural source of material (though sediment dredged from the inlet is now periodically bypassed to those beaches). Wolf Bauer and Maury Schwartz both used Birch Bay Village as an example of what not to do to beaches.

These pictures were taken at the inlet and near the west end, where the bluff ends and the spit begins. They show the beach west of the inlet, the jetties, the seawalls east of the inlet, and a remarkably large rock buttress on the first bluff property to the west.







Wednesday, January 18, 2017

Gulf Road


A cold, clear day at the southern end of the Strait of Georgia. The wind was blowing out of the Fraser Valley but that meant this section of southwest facing beach was remarkably calm (farther south, Mukilteo and Edmonds were getting hammered by waves).

Gulf Road ends at this wonderful little stretch of beach, just south of Cherry Point. While there are bluffs in the distance in both directions, this section is a barrier beach with a nice back-barrier wetland, fed by two small streams. An old conveyor extends across the beach, dating to some unknown (by me) operation decades ago.

The roadway is eroding - as roadways on beach berms usually do. It would be neat if they could rethink this shoreline a little - maybe remove the road prism from the berm, restore the altered parts of the wetland, and make some simple public improvements - restrooms, some interpretive signage, some trails.

This shoreline reach extends from Point Whitehorn at the north, south to Sandy Point, a large, heavily developed spit that extends south into Lummi Bay. Sediment transport (beach transport, at least, I can't speak for finer grained sediment farther offshore) has always been a little controversial here. South winds are common, but the influence of a very large fetch to the north is significant and may be more important for drift.  I mentioned this in a previous post from Point Whitehorn (March 2015).

AERIAL VIEW

There are three major industries along this shoreline -- a refinery (BP) to the north and another refinery (Phillips) and an aluminum plant (Intalco) to the south. The recently proposed Gateway Pacific Terminal, which was set back by the Corps last spring, would have extended offshore just north, between this site and the BP pier in the distance.

Previous post from here:
Gulf Road: March 2010


Sunday, January 08, 2017

Seahurst Park



Last Monday, I dropped M at the airport early, lingered over coffee at the Burien Press, and then drove down the hill to Seahurst Park. Burien got more snow than the rest of us on New Year's, so the road was still pretty icy. The sun wouldn't come over the bluff for an hour or two, so it was dark. The tide was pretty high, so not a lot of beach was showing. And it was cold. I guess it wasn't surprising that it was so quiet.

The beach appears to have naturalized nicely since the project was wrapped up in 2014 (wow - it's already been more than 2 years!). A more distinct berm has built up in front of the wetland in the central portion of the north beach. The logs have distributed themselves more naturally across the berm. The northern stream mouth has continued to rearrange itself, much as the larger stream to the south has always done. The plantings have taken off. And it looks like there's been some sliding on the bluff at the north end of the park.

Previous Post:  Spring 2015

AERIAL VIEW

Speaking of the larger stream - the main one that comes down the ravine with the road - the water level in the small wetland/lagoon at it's mouth was very high and was overflowing across the berm in several locations (the stream mouth in the lead photo is the smaller, northern one, not this one). Some of this looked like it might be the function of some human modifications at the primary outlet, where amateur engineers had been practicing building dams. 

Cultural artifact at the north end


Tuesday, October 25, 2016

Bray Strand



This entry is a significant geographic break from the previous ones. After working our way down the Wild Atlantic Way on Ireland's west coast, we're now back on the Irish Sea on Ireland's east coast. This will also be the last post from Ireland --- not because we ran out of beaches, but because we ran out of time.

Bray seems like a classic beach town from an earlier era. A string of old hotels, a small amusement arcade, and an aquarium line the main drag across from the beach.  Bray is on the main railroad line less than an hour south of Dublin, so was an easy weekend escape for the city crowd.


AERIAL VIEW


The beach is gravel - or at least mainly gravel. My cursory internet research hasn't shed much light on the history, but it sounds like gravel was added as nourishment here back around 2000, and maybe again more recently, but I'm not sure. Beaches often have complex backstories and I wish I knew this one.


Longshore transport is generally south to north along this coast. You get a sense of this looking at the jetties at Bray Harbor in the distance. The beach is stacked up against the south jetty. And the narrow beach farther north is backed by eroding bluffs, suggesting a sediment deficit.

A similar situation apparently exists at Greystones (AERIAL VIEW), a few miles south, where structures that cross the foreshore (a marina) have led to beach problems on the downdrift (northern) side.

I added 33 beaches to my collection during our three weeks in Ireland. And this was the 804th post on Gravel Beach. It began back in late 2005 with a beach northwest of Port Townsend, a shot from Cama Beach, and a few pictures from California (Gravel Beach: December 2005).




Monday, October 24, 2016

Derrynane


This white sandy beach seems like a bit of an anomaly on the southwestern coast of the Ring of Kerry. Aerial images don't show much in the way of beaches, even small ones, along this section of rocky coastline, yet this bay has a really nice one. Typically, beaches need both a source of sand and a place for it to accumulate. No sediment, or a coast so steep that sand is lost offshore, prevents beaches from forming.

The sediment here may have been delivered by the stream at the head of the bay. This assumes that the stream valley yields a reasonable amount of sand, perhaps from glacial deposits. Another option, not necessarily exclusive of the first, is that glacial drift was deposited in the lower valley or the bay and waves have redistributed it directly.

AERIAL VIEW

In either case, a broad, relatively shallow bay would have fairly little accommodation space, and a modest amount of sand would accumulate fairly rapidly. And wave action would tend to trap the sand within the bay.

The main feature is a broad spit, backed by dunes, but the beach is strung out along the northern shore behind a series of rocky ledges. And there is a tombolo at the west end linking the beach to Abbey Island.





Friday, October 21, 2016

Waterville



Maybe it was just the nice light at the end of the day (the same day we weren't able to visit Skellig Michael due to the morning's bad weather), but this beach turned out to be a very pleasant surprise. Which meant I took a lot of pictures.


The town faces out across Ballinskelligs Bay toward the open Atlantic and I suspect it can get pretty exciting sometimes. The community is oriented toward the beach, with a nice park, and is protected from those nasty storms by either a high gravel berm or by some very impressive stacks of riprap (much of it red sandstone).


AERIAL VIEW


The beach has the red tone I saw on a lot of these local beaches and that I suspect reflects the oxidized Devonian source for much of this material. There were steep eroding bluffs in both directions, exposing what appeared to be glacial drift (it doesn't look much like the drift we see on Puget Sound).




Northeast of Waterville, beyond the short stretch of bluffs, lies Inny Strand. Unlike Waterville, Inny is a spit with a well-developed set of dunes (and therefore a well-developed golf course). The golf course is protected from the sea by more riprap.



Valentia Island



This post captures several different shorelines, none of them beaches, from around Valentia Island. Valentia lies at the west end of the Iveragh Peninsula and the Ring of Kerry, across a narrow channel from Portmagee - see photo below. The island's southern side consists of green slopes that gently rise to a ridge along the crest of the island. From the south, you don't get much sense of the drama on the other side.

AERIAL VIEW

Bray Head forms the western end of the island. Geokaun Mountain, in the central part, is the highest part of the island. The mountain's north side drops sharply - the Fogher Cliffs - and looks suspiciously like a very large landslide. There's a great view east from the top of Geokaun, looking over bays and islands towards Cahersiveen and beyond that, the higher interior of the peninsula. There's an old, but still active, slate quarry below the northeastern side of Geokaun Mountain. And on the low seacliffs nearby, there are apparently footprints left by Devonian Tetrapods (we didn't visit either the quarry or the trackway).



Thursday, October 20, 2016

Kerry Cliffs


Beaches are actually the anomaly along most of the Kerry coastline -- rocky shores are far more common. But not all rocky shores are equal. Some sea cliffs are simply higher and more spectacular than others. Here, west of Portmagee, the land rises steeply, then just plunges hundreds of feet into the Atlantic.





AERIAL VIEW

I believe most of the Iveragh Peninsula is composed of Devonian Old Red Sandstone, even if it isn't all red and doesn't all consist of sandstone. But it was all deposited in rivers and desert conditions a very long time ago.


We could see Skellig Michael offshore. We had booked a trip out a day or two before, but gale force winds jinxed those plans. The 700' high rocky spire was the site of a small monastic community between 700 and 1200AD and their stone huts can still be visited, perched high on the rock. This year, tourism to this site (already a UNESCO World Heritage site), went through the roof, since it was featured in the last two minutes of last year's Star Wars: The Force Awakens (it's where Rey finds Luke).



St. Finian's Bay


This was a wonderful little pocket beach nestled among an exceptionally ragged rocky coastline. You can see from both the photos and the aerial view that the sedimentary rocks here have a distinct grain that runs out to sea. Of course, if you think about it, both the Dingle and the Iveragh Peninsulas (that's this one) are just large-scale manifestations of the same thing. Thus the role of structural geology in shaping coastlines at multiple levels.

AERIAL VIEW


We passed it several times and each time, conditions were different.

St. Finians Bay lies below an area of west Kerry called the Glen. It offers great views towards Skellig Michael, 6 miles out in the Atlantic.

Two notable aspects of this beach:


1. The strand line was marked by an enormous amount of plastic - something I simply hadn't noticed to this extent on other beaches. Besides the plastic in the wrack, piles of plastic debris had been collected and piled up at the parking lot. I have no idea whether I just wasn't paying attention at other beaches, whether other beaches get cleaned more regularly, or whether this particular beach is simply a plastic magnet. Plastic, like other flotsam, is highly subject to currents and wind and seems to accumulate in places where subtle aspects of the configuration of the shoreline conspire to trap material.

2. There is a small chocolate factory five minutes away, which makes this remote beach almost as good as one with its own coffee roaster or its own brewpub.