The Adelman's photography provides what is referred to as an "oblique" aerial view - that is, an aerial image taken at an angle to the shoreline. By flying just offshore at an elevation of approximately 500 ft, they are able to capture a side view of features such as cliffs, bluffs, seawalls, etc., that are difficult to interpret from a typical aerial image alone. For reference, here's a typical aerial image from Google Earth, taken of San Francisco's Great Highway just south of Sloat Boulevard:
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| A typical aerial photograph showing an area of the San Francisco shoreline at Sloat Blvd. |
When you examine this stretch of coastline in the aerial, you can easily identify that the parking lot appears to be quite close to the shoreline and that the beach just west of the parking area looks to be at least partially armored with rock. You can also see a more substantial revetment to the south of the parking lot and a spot in between the two armored sections that appears to have experienced more substantial erosion. Certainly, zooming in helps resolve these features in finer detail (see below), but you have limited sense of the topographic relief in the image. For example, is the parking lot on high ground? Is it vulnerable to flooding or wave overtopping? It's hard to tell exactly what's going on here - especially if you don't have the benefit of a site visit or familiarity with the area.
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| Note that even after zooming in, it is still difficult to fully interpret the photograph and the topography of the shoreline. |
This is where the benefit of an oblique aerial can really help. Here's what the view looks like from the oblique aerial shot from the CCRP:
Oh my gosh! What a mess! With the benefit of the oblique aerial you can truly tell what is going on here. We see that the parking lot is elevated on a low bluff along the back of the beach and that there is all sorts of rubble and debris on the beach at the base of the bluff. This is certainly San Francisco's most troubled stretch of shoreline. (Note this is within the area of sand nourishment from Fall 2012 - see my time comparison photos here. The good news is that the City has partnered with SPUR to help develop solutions to the shoreline erosion occurring here and develop a master plan and vision for the future of Ocean Beach).
I'll leave it to you to explore the Coastal Records website, but let me give a few pointers. First, here's a screenshot of the main navigation page:
Each photograph is georeferenced with latitude/longitude coordinates so it can be placed on a map. The navigation panel shows you the oblique aerial along with its location. You also get a preview of the adjacent upcoast and downcoast photos.
What's really neat about this site is that you can essentially "fly" along the coast and see any stretch of coastline you want to look at! Use the "Northwest" and "Southeast" buttons to jump either 1 or 10 photos in either direction, depending if you want to head to the north or south. You can also click on the map for a specific location or search for a place name from the main page - both are useful tools.
In addition to viewing the most current oblique aerial imagery, you can also view historical images, some of which dates back to the 1970s. This can be really interesting to see how the coastline has changed over time. For example, I have compared images over time to identify locations of bluff failure and to help understand rates of bluff retreat at the Daly City outfall at Fort Funston.
Here are a few neat locations you might want to check out:
Monterey Bay Aquarium
San Francisco's Cliff House
Golden Gate Bridge
Pigeon Point Lighthouse
Point Reyes Lighthouse
Certainly, an aerial tour of the California coast would inspire anyone and the variety of coastal features is impressive, to say the least. That said, I have been repeatedly shocked and appalled by some of what I have discovered through this photographic database because it reveals much of the destruction of our coastline that is often hidden from view. Here are few culprits that really get me going!
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| Hey, are you going to pick that up? (Failed bluff stabilization, Gleason's Beach, Sonoma County) |
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| Sometimes you just have to let it go... (Condemned apartment building, Pacifica, CA) |
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| Seriously, Ritz Carlton? What IS that, anyway? (Ritz Carlton, Half Moon Bay, San Mateo County) |
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| Hey, do you guys mind if I put this huge pile of rocks here? The neighbors can fend for themselves! (Malibu, Los Angeles County) |
I highly recommend browsing this great resource and see what you can find for yourself! Maybe you can find a new beach to explore or do a little aerial reconnaissance before your next hike. Enjoy!
Photos copyright © 2002-2012 Kenneth & Gabrielle Adelman - Adelman@Adelman.COM
Very interesting!
ReplyDeleteCool shots! How long do you think the Ritz has??
ReplyDeleteA - Really hard to say. Erosion rates are typically determined in terms of distance per year based on long-term comparison of shoreline positions, whereas bluff failure events are typically rare and catastrophic. So even if an area has relatively low long-term annual rates of erosion, the bluff can retreat significantly in high wave/high rainfall storm years (such as El Nino years), interspersed with little to no retreat in calm years. For example, the USGS estimates long-term erosion rates in this area of around 0.6 ft/yr. Many scientists believe that we will see increased rates of erosion in the future due to accelerated sea level rise, so for argument let's just say we might see 1.0 ft/yr in this area over the next century. The Ritz looks like it would be in serious trouble with, say, 50-60 ft of retreat. So without any further armoring of the bluff, maybe 50 years or so? But don't quote me on that - I don't want to get any calls from the Ritz!
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