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Del Mar stretches from Solana Beach and the San Dieguito Estuary on the north to Torrey Pines on the south. The northern portion of the community, north of Powerhouse Park, is built on the beach, but the southern portion lies on the bluffs. One unique aspect of this stretch is that the railroad follows the beach and was cut directly into the bluffs.
AERIAL VIEW
I spent 48 hours of my own time - three weeks ago - on the San Diego coast. Three weeks later, I'm finally wrapping up my little beach debrief. Technically, Black's Beach in Torrey Pines was my last stop before heading for the airport, but I ended up posting those photos out of order.
Three trips to California during the past year have been a windfall for my beach collection - which now has 40+ posts from the state.
Gravel Beach: California
Neptune Avenue in Encinitas (or Leucadia, to be a bit more precise) has three places you can access the beach, Stone Steps, Beacons, and Grandview. Beacons is the only one where you aren't squeezed into a street end or narrow path between bluff top homes. Apparently, it got its name from a World War II vintage beacon at the north end that is now long gone (Beacon's Beach)
. The apostrophe may date to a restaurant named Beacon's that was reported to have been here in the 50s and 60s.
The park has a switchback trail down the bluff. The whole segment looks like an old slide scar, which sort if fits with the geology of this whole stretch.
AERIAL VIEW
This segment of beach and bluffs is an interesting contrast to the section at Stone Steps. Both are cut into the 80' sandstone face of the marine terrace. But at Stone Steps, the bluffs are steeper and appear to be subject to shallow failures, but the bluffs at Beacon's seem to fail as deeper slumps, several hundred feet long. There was a lot more water seeping out of the lower bluff and some indication of an impermeable zone - older fine-grained sediments nearer beach level - that might explain the different slope behavior.
Of course, this is all based on brief superficial observations and virtually no knowledge of the local geology, so no one should even consider basing any serious geotechnical decisions on my speculative rambles!
At Stone Steps, erosion control was largely achieved with seawalls, but here folks have resorted to an amazing variety of much more complex slope engineering measures - at the top, bottom, and middle of the slope. But just as at Stone Steps, what has really saved these properties - and probably been largely subsidized by everyone else - is beach nourishment.
At the north end of Beacons, the armored toe of the slope extends much farther seaward than elsewhere along here and seriously impacts beach walking at higher tides. It was probably much worse before the 2012 nourishment. My first guess is that this is an old slide and the property owners simply armored the toe where it pushed out across the beach, creating a bottleneck for posterity. A private toll house on a public highway.
More photos of Encinitas over at hshipman.
This is the first of two posts from this part of the Encinitas shoreline - the next one will be from Beacons, a short distance north. Stone Steps marks the dead end of South El Portal Street, just west of Neptune Ave, where an elegant public stairway leads to the beach.
This coastline is largely built on an old marine terrace, lifted above modern sea level by the chronic uplift of the California coast. The shore is cut into the seaward edge of the terrace, forming a steep 80' bluff that exposes layers of sediment, mainly sandstone. Erosion patterns are cyclical, driven by climate and water levels and variations in the amount of sediment passing by on the beach.
AERIAL VIEW
Building along here encroached right to the bluff's edge (see the aerial view), perhaps during a period in the post-war era when erosion rates were low -- but most likely when opportunities in southern California land development were high. High water levels and storms during the 1983 El Nino hammered these bluffs, as have a number of subsequent events. There were numerous places where it was clear the bluff had slid in the past and many more where property owners had installed seawalls of some sort to counter the waves. Most were built almost flush with the steep bluff and many were camouflaged (this is afterall, the land of Disneyland and artificial landscapes) to blend with the tawny sandstone.
The need to protect these bluff top homes may make perfect sense to the relatively small number of folks who live here, but it isn't sustainable in the long-term and in the meantime it represents a significant public subsidy. The naturalized seawalls may reduce the direct impacts on the beach, but they prevent the erosion of the bluff without addressing the erosion of the beach itself, so in the absence of other miracles the beach itself would eventually go away.
The miracle in this case is beach nourishment. In its absence, waves would increasingly pound the toes of these bluffs. In a future El Nino, there would be landslides and lost homes, emergency declarations, huge damage estimates, and sad stories of residents returning to condemned homes. Local communities would seek state and federal funds to manage the disaster. The coastline would be increasingly engineered (see next post). The public beach would be lost. The shoreline would begin to look more look like Pacifica.
In 2012, SANDAG completed the most recent round of nourishment. This is a huge public expenditure, and one with some adverse environmental impacts and much controversy. It benefits the public by rebuilding and maintaining an accessible beach, but the only reason the nourishment is necessary is because of the need to protect these homes. If the bluffs could erode on their own, the beach would do just fine. The result is that private property benefits from a large public investment. I wonder if these folks see themselves as living in subsidized housing?
I'm a big fan of nourishment - in the right place and with adequate forethought to its geologic, ecologic, and economic implications. It's been a great boon to this coastline. But as the rate of sea level rise increases and the beach system gets farther out of equilibrium, the frequency and volume of nourishment will have to increase, along with its price.
From the Smith River in the north to the Tijuana River in the south, California's beaches are broken by dozens of small stream mouths that flow out through shifting sand spits to the oceans. Or at least used to. Or at least used to some of the time.
There is always competition between streams and tides trying to keep an inlet open and waves and sediment trying to close it off. Bigger rivers and large estuaries always have enough water moving in and out to stay open. But small streams, particularly when subject to low seasonal flow and emptying into estuaries with small tidal prisms, may periodically close off. This is especially likely if an energetic wave environment and abundant sediment lead to active beach transport and rapid rebuilding of the berm.
The shifting nature of the inlets, frequent flooding on the margins of the estuary, and the desire to enhance the lagoon for boats and recreation, leads to dikes, dredging, reclamation (filling) to create dry land, and structural measures to maintain the inlet. The result is a static, somewhat more predictable system. Development potential goes up and the native ecosystems decline as the messy geologic processes that maintained them are gradually brought under control.
AERIAL VIEW
Agua Hedionda lies just south of Carlsbad and the modern lagoon is a miracle of multi-use management (Agua Hedionda) - with railroad and highway crossings, swimming and boating, bird and wildlife habitat, aquaculture, a power station, a planned desalination plant, all at the receiving end of a heavily developed watershed. But this is probably a long way from what it originally looked like - marsh, salt pan, mud flat, and that darned shifting inlet. It is just one of a number of estuarine case studies in San Diego County - each of which has a different natural character and a different 20th century development trajectory (Batiquitos, the next one south, has also received much attention in the last two decades).
I'll admit right now that I don't know the specifics of Agua Hedionda. Its name translates loosely to "icky, foul-smelling water" and that sort of goes along with the notion of a stagnant system trapped behind a stream mouth barrier. So I suspect it occasionally closed off historically. But whether it did or not, it has been dredged and its inlet has been channeled between rock jetties, assuring that flow is maintained and the inlet doesn't shift up and down the beach.
The jetties interrupt longshore sediment transport. Drift along this coastline is north to south, so the beach is built up on the north side, and narrow on the south side (and heavily armored). The beach here is further confused by the rock jetties farther south that protect the outflow from the generating station.
At this month's estuaries conference (CERF), there were a neat series of talks about the history and ecological function of small bar-built estuaries (sometimes called intermittently open/closed inlets), with many examples from California, but also others from South Africa and elsewhere. Our historic inclination is to see periodic closure of these lagoons as a problem to be solved. Closure meant stagnant water and flooding and when the inlet reopened, it didn't always reopen where people wanted it to. But these are ecosystems that were adapted to this type of cyclical closure. Flooding when the lagoon is closed off inundates high marshes and may increase productivity and fish habitat within the lagoon, often at times when water levels would otherwise be very low. And the consequences of "managing" these systems are not without their own adverse impacts on the environment - jetties, dredging, dikes and levees, increased development of the fringing wetlands, and so forth.
Here are a couple of other examples from my brief excursion to California's central coast in July:
Pescadero Creek
Sequel Creek in Capitola
The Klamath River in northern California is a nice example of a bar-built estuary, but the river is much larger and probably never closes off.
Black's Beach, named for the family that once ranched above the bluffs where the over-the-top mansions of La Jolla Farms now perch, and sometimes referred to as Torrey Pines City Beach, lies below the high bluffs described in the previous two posts. Unlike much of the San Diego coastline, where natural sediment sources (particularly from bluffs) have largely dried up (or been entombed), these bluffs are still dumping large amounts of sand onto the beach (those landslides in the Torrey Pines photos). This material gets transported south toward La Jolla where it is lost into the offshore canyons.
The promontory that marks the south end of the beach (and separates it from Scripps and La Jolla Shores) is associated with a volcanic dike on the platform that is more resistant to erosion than the surrounding sedimentary rocks. It is also marked by the old NMFS buildling described in an earlier post (Scripps) and a crazy guest house (called the mushroom house) at the bottom of a steep tramway.
AERIAL VIEW
The sand on this beach contains a lot more than just quartz. Heavier dark minerals and shiny golden ones (muscovite?) are abundant and each swash erases the previous pattern and creates a new one. The dark grains form little cusps that open seaward during the backwash. The light ones tend to spread out more evenly. A study in density and subtle differences in fine-scale transport characteristics. If it is muscovite, I suspect that suggests that the beach is composed of pretty fresh bluff - I doubt the muscovite would persist long in this setting. Interestingly, some accounts of Black's Beach describe it as Black Beach and credit this to the dark sands.
Beach wrack, mainly torn up kelp, was distributed in small and large piles across the beach and was crawling (hopping, actually) with small critters and attracting birds. I suppose as it breaks down, some of material and nutrients get washed back out into the nearshore. These are probably far more complex ecosystems than sandy beaches are normally given credit for.
I watched dolphins follow a stand-up paddle boarder (couldn't get photos) - maybe if the waves had been bigger they would have been surfing (check this out on YouTube).
Black's Beach is best known for surfing - I guess the break is enhanced by the head of the Scripps submarine canyon lying just offshore - and as a clothing-optional beach, although that portion lies a little farther north. I guess that's good thing, since it might be a little awkward to be a middle-aged guy taking a ton of pictures in the midst of the sunbathers and volleyball games.
I'm going to proceed with my San Diego posts as if I'm systematically marching northward up the coast, but my actual itinerary was a bit more complicated. After La Jolla on Friday afternoon, I made it to Torrey Pines for a wonderful sunset from the top of the bluffs, but then headed north to Carlsbad for the night. The next morning was spent working my way south through Carlsbad, Encinitas, and Del Mar, before I ended up back at Torrey Pines and Black's Beach for a few hours before hightailing it to the airport. So some of these shots are from late Friday afternoon, some from Saturday afternoon.
AERIAL VIEW
Torrey Pines lies just north of La Jolla and includes a spectacular stretch of bluffs and one of the least developed stretches of coastline in the county. Above the bluffs are trails, a golf course, and a dedicated gliderport for folks inclined to thrown themselves off the cliffs with artificial wings.
The distinction between sea cliffs and bluffs is fuzzy, but I tend to reserve cliffs for bedrock coastlines that plunge into deeper water or to an eroded rocky platform. And I use bluffs for steep slopes of more erodible material, usually with a real beach at the bottom. Sunset Cliffs and La Jolla were sea cliffs. Torrey Pines and the rest of northern San Diego County (subsequent posts) are bluffs.
And impressive bluffs they are, with enormous landslides, some a hundred years old, some much more recent. The beach below these bluffs, which we'll visit in the next post, is Black's Beach. As usual, there are (or will soon be) more pictures of all of these places on my other blog: hshipman.
Just a mile or two north of the last posting and we're back to sand beaches - but still pockets and patchy beaches controlled by the complex shape of the rocky coastline.
AERIAL VIEW
The photo of the homes was taken farther south, but the other shots were taken from different places along Neptune Place and Coast Boulevard - near the center of the modest little village of La Jolla.
Beaches are subsidy-based ecosystems (a term I learned at this week's conference), with much of the organic input to the system coming from elsewhere (therefore allochthonous) - sometimes in large amounts and with significant ecological importance. The beach wrack is a good example. I suppose the mansions and the village are, too!
This is the first of two posts from La Jolla (now two weeks ago) and probably the only serious gravel beach of my San Diego trip. There are others in the area, but this is the only one I found in my two days of drive-by sampling.
AERIAL VIEW
La Jolla juts out from the coastline and this probably makes the transport of sediment along the shore difficult and discontinuous. Sand may be easily lost offshore and what beaches there are appear to be relatively isolated pockets that form where platform, orientation, and available sediment conspire to create a beach. I suspect this gravel is locally derived - the sedimentary cliffs had plenty to offer.
This shoreline is heavily developed with fancy homes perched on the edge, many with large rock armor at the toe of the cliff, but the cliffs here at Calumet Park were protected only by the high, steep gravel berm (unless there is riprap hiding underneath).
