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Tracing Future Shorelines

posted Sep 7, 2014, 4:12 PM by Dean Hardy   [ updated Sep 7, 2014, 7:38 PM ]
I had a great idea last spring to cycle the Georgia coast while recording the areas of the coastal landscape that are susceptible to sea-level rise. Some of the video footage would later be incorporated into a short educational outreach film. I decided that the most efficient way to go about this would be on a bicycle - moving not too fast, nor too slow - tracing the 3' contour line.

Well, measuring elevation can be a bit confusing if you're not familiar with it, because it has to be referenced to something called an elevation datum, so really I was planning to cycle along the contour line that's 3' above the current mean higher high water (MHHW) mark; i.e. 3' above the average high tide as it flows in currently, but for now let's just say the plan was to ride along the area where the sea might be at the end of this century, based on the latest scientific assessment of sea-level rise projections and assuming no shoreline armoring or modifications that would alter current topography. I'll stop there with that side track. Perhaps I'll write a post in the coming weeks/months about datums and the technical aspects of measuring tides and sea-levels (and their changes). If you're really excited about datums and just can't wait on me to post about them, you can learn more about them over at NOAA's website.

Anyway, much of this line falls on people's private property, sometimes in their back yards, sometimes in their front yards. Needless to say, I wasn't going to trespass, so I mapped out a route along roads that followed the 3' contour above high tide as close as the roads permitted. This ended up being just a little over 20 miles on Tybee, so not too far at all on the bike. You can see the extent of the current mean high tide (green shades), the extent of high tide if sea-levels were 3' higher (blue shades), and my cycle route in the map below.
Note that there are two routes. The lighter shaded one was a ride without the video
camera and preceded the day I rode with the camera mounted on the handlebars.

Tybee's a great place to start out such a ride too, as everyone - tourists, recreational cyclists from Savannah, and locals - all ride here. 

The plan had been to cycle the whole coast this way (which would have been a few hundred miles), but I got caught up in the ethnographic parts of my research interviewing local residents and government officials and staff on Tybee Island and in Chatham County. I spent the majority of my limited time (and budget!) interviewing instead of cycling and filming the landscape. I still hope to get to it, but I only cycled around Tybee for a couple of  days in July, and then later in mid-August I cycled 70 miles along the ocean front area of the mainland in McIntosh County. I'll post some details about McIntosh later.

Tybee lies just to the south of the Savannah River and is one of many sea islands stretching from northern Florida into North Carolina, backed by a vast swath of salt marsh wetlands. Georgia has 13 barrier islands all formed between 30,000-40,000 years ago. Most who know Tybee Island (at least everyone I've met that does) really love it, as do I. It's an eclectic small island community of around 3000 people on the outer edge of Georgia (the most eastern point, as a matter of fact). Much of the island is covered with little cottages and beach businesses, but this has changed some in the past couple of decades as interest in living on the coast has increased across the U.S. And on that note, I'm going to stop chatting at you and share some clips of my ride that capture the residential zones of Tybee vulnerable to sea-level rise.