Sunday, April 24, 2011

The construction of the south breakwater

I've previously believed that the south and west breakwaters at the Conner Recovery Site were built to protect that wildlife refuge from wave erosion.  I've since learned that the breakwaters were built in 1931 when there was no tidal flat present -- where Conner was found was then an open water environment.  I've borrowed this topographic map from pg. 45 of the "Western Stege Marsh Restoration Project Year 5 Hydrologic Monitoring Report" prepared by the Kamman Hydrology and Engineering, Inc., and annotated it to indicate Conner's recovery location and to label open water environments.

To get a better perspective on how the area has changed in appearance, I've annotated a Google Earth map to show the previous layout.  The West set of breakwaters consists of A, B, C, and D.  The East section consists of E and F.  A is no longer visible; it was either removed or has been totally covered with landfill.  B is less than half as long as it used to be.

I've not been able to find literature that specifically identifies how these breakwaters were constructed, but during this last trip I did catch a good look at the west end of E, which continues to protrude into the open water environment.  It was obvious that this is a rubble mound structure, and the assumption is that the sections of the West breakwaters were built the same way.  

You can see how the land fill has covered up the rest of the northern side of the breakwater.  That is exactly what has happened with the south breakwater (C) on the Conner Site.  I did a little experiment on this visit.  At one point on the north side of the breakwater, I tried to drive a scredriver into the ground, and could not penetrate more than a couple of inches.  It wasn't just hard to penetrate, it was impossible. It definitely is rock under the mud.  

I borrowed a diagram of a rubble mound structure from 2-17-00, Breakwaters and Rubble Mound Structure Design, and annotated it to show the amount of land fill on the northern side.  The "sea side" is the southern slope of the breakwater. 

On this last trip, I tried to measure the "crest width," but was unable to do so because it is too short a distance for the range finder.  Instead I had to measure out to one of the rocks on the southern slope.  

This next photo shows the same rocks, but from the backside (or the southern, seaward slope).  In this photo, the black arrow points to the rock I was standing in front of to take the measurement, and the yellow arrow to the point of the rock point that I measured to.  That rock is 3'6" across at its longest point, and 1"10" tall.  The rock above it is 4'5" across its longest point.

In a few days I will post a YouTube video of numerous photos of the southern side of the breakwater, to give you a perspective of what the waves caused by gusty winds would be beating up against.

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