Sunday, August 16, 2009


Saltspring is a pretty rocky island and beaches are scarce. This year I tried to get to the tombolo at Walker's Hook, but gave up in the face of mud and private property (yes, these Canadians are just as proprietary about their beaches as us Americans). Clearly, I need a boat.

Fernwood is on the northwest shore of the island, not far from St. Mary Lake where we stay every year and across the road from the Raven Street Market where we occasionally come for pizza. And now there' a coffee place, too, so I have another excuse to come down to the beach early in the morning before everyone else gets up.

The beach is a thin gravel one, anchored by outcrops of steeply dipping metamorphosed sediments and scattered glacial boulders.

Beach Grove

The beach at Centennial Park runs out of steam as it heads north and is eventually replaced by a dike. But where the dike turns west (at 12th Avenue), a spit has formed and created a small lagoon and marsh. North of the lagoon, behind the houses on Beach Grove Road, seawalls line the narrow beach. Maybe next year I'll come back with more time and my bike - there's a trail that follows the dike eastward along Boundary Bay.

Centennial Beach

Lily Point, at the southeast corner of Point Roberts, has been feeding sediment to the beach for millenia and waves have been sending it north to form the beaches that extend from Maple Beach
on the American side into Beach Grove on the Canadian side. Yes, several thousand cubic yards of American dirt going to Canada every year -- no charge, no duty, no intention to return. The sediment has accumulated in a series of prograding spits in the northwest corner of Boundary Bay, where they created the large marsh behind and beneath Beach Grove - now diked and managed to accommodate the growth of suburban Vancouver (this is all part of Tssawwassen).

The long history of accretion means there's a broad sandy backshore, and even some semblance of low dunes. The upper foreshore is a narrow band of gravelly sand, running along the edge of the broad flats of Boundary Bay. The transition between the upper foreshore and the flats occurs at mid-tide or above. The lower beach appeared to be a lag surface of small gravel.

What I found intiriguing was the strong southeast-northwest fabric to the lower beach - a pattern seen both in gravel ridges (amplitude of ten cms or so and wavelength of several meters) and in the sand between them (amplitude of mms and wavelength of several cms). Strange. These did not look like ripples or cusps or any sort of depositional feature - they looked more like erosional features (I'm not sure why I felt that). And their orientation was parallel to the large fetch from the southeast - where I might have expected just the opposite. It looked like a surface that had been scoured by strong southeast winds and waves. As with every beach, there is a story here. I just don't have much clue as to what it is.

Wednesday, August 05, 2009


The story of the beach between the mouth of the Elwha River and Port Angeles is well known – or at least often told. Dams, riprap, and a spit starved of sediment. Simple stories are easy to tell. There’s a longer, more complicated story, and one that I won’t try to tell here, in part because there are others working hard on figuring it out, but here’s snippet.

Years ago, I noticed in older aerial photos that the character of the beach between the delta and Dry Creek
seemed to change significantly on a decadal scale. Photos from the 1970s show a wide gravel berm and a heavily vegetated bluff, while photos from the 1990s showed a narrow berm and a bare, eroding bluff. By the beginning of this decade, the beach was widening again in locations and the bluff seemed to be responding by growing trees. When I walked this stretch in 2005, the beach showed evidence of the building seaward in sections, but for the most part the berm farther east was relatively narrow (beach level photos).

Last week, I flew over this stretch of shoreline and took this aerial of the same stretch. Wow! Whatever the mechanics – longshore drift, onshore transport – that’s a lot of gravel!

In the spirit of multiple working hypotheses…. The Elwha probably releases sediment to the beach in pulses, maybe associated with avulsion of the spits that regluarly form across its mouth, and one would expect these to travel downdrift in a somewhat coherent fashion. Or alternatively, there are oceanographic or meteorological factors that lead to long-term cycles of accretion and erosion. Or maybe, longshore gravel transport in highly oblique wave environments is influenced by nonlinearities that give rise to emergent landforms (I’ve probably butchered the jargon). Or maybe all three.