Monday, April 11, 2011

Rocky Point's Mysterious Past

A mystery has plagued the marsh ever since ecologist Patricia Rafferty visited last fall: what did Rocky Point used to look like?

The answer would have profound implications for the site's potential restoration. The historical quandary goes as follows. There are two groins (low seawalls built perpendicular to the shore) framing the marsh. Did their construction form the dune that separates the marsh from the bay? If so, it would suggest that prior to the groin construction, the marsh flooded daily, not monthly, as it does now. In order to restore the daily influx, the dune would need to be removed using heavy machinery. Patricia suggested that historical aerial photos might shed light on what happened. She provided images from 1951, 1974 and 1996. Using Google Earth's historical imagery tool, I captured satellite photos dating from 1994 to present. After patching them together, we're a bit closer to solving this mystery. Watch this:

Ever since the groin (upper left) was installed, sometime before 1951, the shoreline has remained fairly consistent. Note that some 100 houses, an entire marsh-front neighborhood, disappeared sometime after 1951. Were they vacation homes or residences? Why were they moved? Where did the people go? click image to expand

The road was removed sometime between 1974 and 1994. The crumbled remains now serve as my wheelbarrow highway.

Sometime between 1951 and 1974, an additional groin was built immediately to the west of the marsh. The creek mouth initially bordered the eastern edge of the groin. But sometime between 1974 and 1994, it migrated to it's present location, and has remained stable for at least a decade.

In conclusion, Patricia wrote, "It looks like the bayward edge of the marsh has had a dune feature. Thus throughout the 1951 to 2008 time period it seems to me that the creek has been the sole source of hydrologic exchange with the bay (except perhaps during extreme storms when the dune would be overtopped or overwashed.)"

So what did Rocky Point used to look like? Despite all the changes to the surrounding area, we discovered it looked very much like does today. But before we can abandon any dune-busting plans, we need to see the marsh before 1951, before the 'big groin' was built. Patricia says the NPS has recently acquired and is currently georectifying imagery from around 1924. An image from that time period could potentially close the case on Rocky Point.

Special thanks to Patricia Rafferty for providing the imagery.

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