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Dikes

Labor Day Hurricane 1935

Page 2:  Dikes

Historically, transportation in the Florida Keys was by boat. After construction of the Panama Canal, a railroad was built from the Florida mainland to Key West, to try to capitalize on possible future trade through Panama. The railroad was not cost-effective, and after the 1935 Hurricane it was converted to the present highway for automobiles.

Before the railroad was converted to the present day Overseas Highway, a highway for automobiles was under construction parallel to the railroad. At the time, the highway extended from Miami to the Upper Keys, and from Key West toward the rest of the Keys. Automobiles had to traverse the intervening Middle Keys by ferry (Coch, Fig. 8.1).


Figure 2.1:  A Florida Keys ferry.


Figure 2.2:  Automobiles queuing to board a ferry in the Keys.


The Florida Keys once had abundant creeks and streams across each island to facilitate water flow between the gulf and ocean sides of the Keys. However, cut and fill construction was used to flatten the otherwise stream-laden islands to accomodate railroad and road construction (Coch, Fig. 8.3b), reducing tidal flow between Florida Bay and the Atlantic Ocean.

Further constricting the estuary, long jetties and viaducts for the railroad (and later highway) blocked otherwise open ocean/bay water flow by a minimum of 65 percent (Coch, p. 215). The jetties were long strips of land fill (earth and rock fill) that we refer to as dikes, because they block water flow.

The gaps between islands were very long, and to cheat (build less bridges) these dikes (earth and rock fill embankments) were built and still stand today, continuing to block water flow between Florida Bay and the Atlantic Ocean.


Figure 2.3:  Dike connecting to Long Key before 1935.


Fig. 2.3 shows such a dike (earth and rock fill jetty), connecting to Long Key in the background. The Atlantic Ocean is on the left, and Florida Bay / Gulf of Mexico on the right.

These dikes are referred to as causeways, and are used with gaps to let some water through, for example culverts or short span bridges, as recently constructed by the military government in the estuaries of northern Cuba.

“Cuban tourism authorities have constructed causeways (or stone embankments) bridging barrier islands to the mainland and to one another called pedraplenes (see Map 10.1). These pedraplenes block the movement of water in the intracoastal waters, exacerbating contamination and destroying coastal and marine habitats… several colonies of flamingos that used to nest in the Sabana-Camaguey sub-archipelago have left this area because of the destruction of their habitat resulting from tourism facilities and pedraplenes and settled in the Bahamas”
— 
Sergio Diaz-Briquets and Jorge Perez-Lopez, Conquering Nature, University of Pittsburgh Press, 2000 (online book), p. 264, 274

The following photographs show this type of construction in the Florida Keys, where Florida Bay is much larger than the bays in northern Cuba that have pedraplenes.


Figure 2.4: Dike with culvert in the Middle Keys before 1935.


Fig. 2.4 shows a dike in the Middle Keys before the 1935 Hurricane, with a culvert consisting of two concrete walls and a short bridge spanning between the tops of the concrete walls and holding up the rail bed.

Water flows between the concrete walls, to allow some (but not enough) tidal exchange of water between the bay and ocean. Fig. 2.4 above shows water flowing from left to right, with turbulent water discharge to the right of the concrete walls. The direction of flow changes every few hours depending on the tide.

The next photograph shows such a dike washed out to sea by the 1935 Hurricane, leaving only the culvert behind.


Figure 2.5: Washed out dike at Snake Creek, 1935.


Fig. 2.5 shows what remained of the dike at Snake Creek after the ebb current of the 1935 Hurricane washed the dike out to sea. Only the concrete walls of the culvert remained. The photo shows a person standing on top of one of those concrete walls.

A temporary suspension bridge was hung, to connect the two Keys across Snake Creek. Under the suspension bridge, water is flowing again where the dike had been before the ebb current from Florida Bay pushed the dike into the Atlantic Ocean.

“Fluid pressure built up on the gulf side of the fills and eventually they failed quickly and violently.”
— 
Coch, in Coastal Hazards, p. 223

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