Appendix D. Field Guide to the Beaches of Dade County
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Appendix D. Field guide to the beaches of Dade County The islands of Miami Beach, Virginia Key, and Key Biscayne you pedalin from the causewayentrance or rent bicyclesat some are the most southerly of the sand barrier islands along the east of the stops. The park areas have bicycle paths and numerous coast of the United States fig. D-r!. The material making up beachaccesses, Once the new bridge is completed, bicycle access theseislands is a mixture of quartz sand, which hastraveled south from the mainland will be much safer. by longshoredrift from northern Florida and Georgia,and more The tour next examines the sediment-starved shoreline of Vir- locally derived calcium carbonate grains from the breakdown of ginia Key, after which you will then return to the mainland, drive mollusk shells and other marine skeletal remains. In addition, north through Miami, and headout to the southtip of Miami recent beachnourishment projects haveadded sandsfrom various Beachvia the MacArthur Causeway,The massivenew renourish- sources that were not naturally part of the beach system. ment beach of Miami Beach is accessible at numerous points. As this guide wasgoing to press,a numberof changeswere Three stops are recommended,including one at Government Cut taking place in Dade County. The drawbridge on Rickenbacker jetty at the south end. Causewaywas being replaced by a new high bridge designedto The final stop on the tour is at Bakers Haulover Beach,an area make storm evacuationsafer!. The city of Miami was in the begin- that has received renourishment several times but which still has ning stagesof developing northern Virginia Key as a recreational sandgenerally similar to that originallyfound on Miami Beach. park facility. A large amount of new sand was scheduledto be o.o Toll booth at the entrance to the Rickenbacker Causeway pumpedup on the beachesof' centraland southernKey Biscayne toll $o.75!. in r 984.And, as noted earlier, Miami Beachrecently has beenthe Drive out on the Rickenbacker Causeway which be- site of the largest and most costly beach replenishmentproject in comes Crandon Boulevard on Key Biscayne! to Cape American shoreline history. Florida State Park at the south end of Key Biscayne. The guide begins at the entrance to Rickenbacker Causeway Rickenbacker Causewaywas built during and just after reached by Interstate 95, exit t to Key Biscayne!.The tour leads World War II. The fill areas, including much of the road- you out the causewayacross Virginia Key to Key Biscayneto visit way on Virginia Key, have restricted water circulation in naturaland developed beaches on thissouthernmost barrier island. BiscayneBay. This causewayand five others to the north This portion of the trip could best be enjoyed by bicycle, whether havedivided northern BiscayneBay into a numberof sepa- Appendix D. Field guide 231 qo % y+eC miles 0 2 4 ~8 @0 kilometers Flg. D-1. Map of the Miami area and coasts! barrier islands showing locations of stops for this field trip, 232 Living with the East Florida shore ratebays, Each of thesecauseways serves as an evacuation this casefill associatedwith causewayconstruction. These route for island residents. However, all of them become beautifultrees are a greathazard to the inhabitantsof Key impassibleduring the early stages of a hurricane'sapproach. Biscayne.They are shallow-rootedand as a consequence are readilyblown overduring hurricanes.They will block On the left, PlanetOcean, created by the International 2.5 passageon and off the island. OceanographicFoundation, is an outstandingand enjoy- ableplace to visitto learnabout our oceansand also our 5.6 Enter the central one-third of Key Biscayne,which is resi- shorelines.It is well worth your time. dential and commercial. Enter Bill BaggsCape Florida State Park, whichoccupies i.g TheSeaquarium on the right has an exhilarating display of 7.0 marine life. the southern one-third of Key Biscayne. It is open from 8 A,M. to sundown; the entrance fee is $.5o per person. Onthe right is theUniversity of Miami'sRosenstiel School Write to the superintendentfor a waiverof feesfor educa- of Marine and AtmosphericScience. It has tours far the tionalgroups Key Biscayne,FL 33L49!. publicon Mondaysat i p.m, Therealso is a nicecafeteria on the water.! 7.$ Turn left into the parkinglot and park assoon as possible. On the left are the laboratoriesof the National Oceanic Walk out to the beach. andAtmospheric Administration and the Tropical Marine Stopt. Naturalahorellne with seaoat stabilization,beach Fisheries Center, ridges,and controlledaccess walkways. In t95o thebulk of CapeFlorida wasfilled by a devel- 3.0 Takethe bridge across Bear Cut, which separates Virginia Keyand Key Biscayne. Bear Cut is a naturaltidal inlet that operto its presentelevation by dredging material from the is notedon mapsfrom the earliest exploration of Florida bayside fig. D-2!. Onlythe section of beachridges at this waters. The tidal currents through Bear Cut have shifted stopand at an areanear the lighthouseremain in their muchof Virginia Key'ssouthward-drifting beach sand sea- originalnatural state fig, D 3!. Hence,the dominance of ward,forming a broad,shallow, underwater sand platform Australianpines throughout the park. Prior to filling, this seawardof northern Key Biscayne, southernthird of Key Biscaynewas a seriesof southward- arching, sandy beach ridges that in somecases were sepa- Comeon to Key Biscayne,The Australianpines Casurina! 35 ratedby mangrovesor small ponds fig. D 2!. Eachridge that dominatethis northerntip of Key Biscayneare exotic of sandwas once at the tip of the island,clearly showing treesthat rapidlygrow on disturbedor filled land in Ap pen di x D. Fi eid guide 233 that Cape Florida grew southward, Seaward of the beach is a very broad, shallow, littoral On the walk out to the beach, you will cross several sand platform on which the seagrassTha assiaflourishes. beachridges. These are quite young, having only seaoats Though important to the stabilizationof the offshoresands, and shrub vegetation. This is one of the few sections of the blades wash ashore in great abundance after winter beach in Dade County that has been building out during the storms, detracting from the aesthetic quality of the beach last 5o years. By coring into theseridges we have learned to many beachgoers.The various parks havevarious ways that each one was formed during a major storm, and that of handling this problem. Wisely, park managersof Cape seaoats subsequentlygrew on the ridges and causedsome Florida either do not disturb this seagrasswrack or they further growth as they trappedfiner sand blown or washed rake it to the edgeof the beachridges as a protection to the onto the ridges during lesser storms. ridge and as shore mulch. This, at the same time, deters Here as elsewhere sea oats and other coastal vegetation foot traffic in from the beach.Only litter is removed from are important to assure stabilization and preservation of the beach. To simply gather the seagrassfrom the beach the beach ridges and dunes. The beach ridges in the park and carry it away also would removeprecious beachsand. were severely damaged in areas where foot traffic destroyed The beaches of southeast Florida differ from those far- the vegetation. In r 982 Cape Florida park began a program ther north from Palm Beach north! in that the Bahamas of restricting accessto the beachesby putting up fencesto to the east protect the shoresfrom large wavescoming in define walkways. Notice the diA'erence in the beach ridge from the open Atlantic, In addition, certain stretches are elevations at and away from the walkways. protected by seaward reef ridges near the edge of the con- 'I'he shrubsof the round-leafedseagrape, the low, crawl- tinental shelf. Thesebreak up larger wavesgenerated in the ing vines of the beach peanut and the beach star, and Straits of Florida. Seaward of Key Biscayne,for example. the other grassesalso are important to stabilization of the is a shelf edge ridge rising from the deeper seafloor to a ridges. depth of 9 to r2 feet. In addition,north and south Key To encourage recovery of the previously damaged beach Biscayne have broad, shallow, littoral sand platforms ex- ridges, the park planted 20,000 sea Oat plants in i982 and tending about i mile seaward of the shore. These further l 983.As you will seeat the next stop, the park also is begin- dampenincoming waveenergy. As a result of the relatively ning to construct board walkways across beach ridges, a small waves, the beaches of Key Biscayne are composed of program they plan to expand. somewhat finer-grained sand than is present on the more 234 Living with the East Florida shore Fig.D-2. Aerial photographsfrom 1945,1951, and 1972of CapeFlorida, was severely modified in 1950 when dredged to provide fill for nearly the southern Key Biscayne.Cape FloridaChannel, just left of Key Biscayne, entire cape area. This fill covered the curving beach ridges that recorded Appendix D. Field guide 235 exposedbeaches farther north. From the beachhere you can look north to the developed part of Key Biscayne,Crandon Park, Fisher Island, and Miami Beach the buildings in the distance!, To the south you can seeCape Florida Lighthouse fig. D-3!, and if you look due south you may be able to see Soldier Key,the northernmost of the Florida Keys. Soldier Key is composedof coral limestone a reef formed some t 2o,ooo years ago during a previous interglacial stage when sealevel was about 2z feet higher than it is at present. Beach sand that is transported south past Key Biscayne is mostly carried southeastward across an elongated, shal- lowly submergedsand ridge that extendssouth about as far as the level of Soldier Key, Directly south of Key Biscayne is a carbonate mud bank cut by numerous tidal channels. Tidal ebb flow through these channels is responsiblefor shifting the southward-drifting beach sand seaward.