THE MAJOR CHANGES IN NORTHERN BISCAYNE BAY
Figures 16 through 21 are three paired sets of interpretive maps. Figures 16, 18 and 20 are the "before" maps based on aerial photography from 1925 to 1940. Figures 17, 19 and 21 are the "after" maps that are interpreted from the 1976 aerial photography. Figures 16 and 17 show the before and after distribution of developed terrestrial areas' Figures 18 and 19 show the distibution of dredged, spoil and filled areas within the
Bay. The filled areas are modified from maps in U.S. Department of
Agriculture 958!. FIgures 20 and 21 show the distribution of benthic vegetation. The past or present shoreline is shown on each, and if the maps are removed from the text, they can be superimposed one upon the other for shoreline comparisons.
For ease of discussion, northern Biscayne Bay is divided into seven
Areas Figure 12!. The west and east boundaries of the seven Areas are, in general, the Florida East Coast Railway on the crest of the mainland coastal ridge and the ocean surf zone, respectively. The approximate north and south boundaries are defined by the following:
Area I: North of Broad Causeway
Area II: Broad Causeway to 79th Street Causeway
Area III: 79th Street Causewayto Julia Tuttle Causeway I-195!
Area IV: Julia Tuttle Causeway to Venetian Causeway
Area V: Venetian Causeway to MacArthur Causeway I-395!
Area VI: MacArthur Causewayto Rickenbacker Causeway
Area VII: South of Rickenbacker Causeway
This division is totally arbitrary and based on convenient physical features causeways!. The sameseven Areas are used whenreferring to the 46
FIGURE 20 1925 BENTHIC VEGETATION
KILO ET~ LL
VISABLE BENTHIC V EGET AT I ON 1925 11928l VISABLE BENTHIC VEGETATION 1940
I,AND
OTHERBOTTOM DEPTHCONTOURS IN METERS
NOTE'IN GENERAL NO DATAFROM DREDGE HOLES "before" maps even though many of the causeways were not constructed at the time. The author recognizes a danger that some readers will assumes that these artificial boundaries are real and thereby assume that an Area is a separate body of water. The seven Areas are connected to one another at breaks in the causeways.
The following sections describe major changes in selected features as interpreted from the aerial photography. Data discussed is presented in
Tables 3 through 10 and was obtained by planimetering features shown in
Figures 16 through 21. Shoreline data presented here was obtained from a redraft of the 1887 U.S. Coast and Geodetic Survey coast Chart 4'165 and therefore yields data from an essentially pristeen Bay and not the Bay of
1925. All other data spans the 1925-1976 period.
Measurements were made of the total area studied and all land and water areas within the boundaries described. North and south boundaries are the map edge and the limits of each of the seven Areas as described previously. It should be noted that many features had to be subjectively generalized during map production, and, to avoid possible misinterpretation of mapped data, the following definitions and qualifications should be understood:
1! Land area is that portion of the bay region that has surface
elevations above mean low water level. This includes all
mangrove and coastal swamps.
2! Develo ed land areas are those portions of the land area that
have observable manmade features including but not restricted
to buildings, roads unimproved as well as improved!, canals
excluding mosquito ditches!, agriculture, forested timber as
53 in manymangrove areas in 1925! and all exposedportions of spoil islands. Non-agricultural vegetated areas that have undergone changesin plant species as a resuLt of humanintervention are
not mapped as developed land. 3! Man rove areas are those portions of the land area that have living mangrove trees growing on them in sufficient abundanceto
be mappedat a scale of 1:40,000. Inevitably, small patches have
been missed, but they should be more than made up for by the
inclusion of small holes in mangrove areas mapped as mangrove.
4! Other land areas are those portions of the land that have not
been developed and, if vegetated, are not mangrove.
5! Three types of shoreline have been identified. a! Man rove shorelines are those having mangrove trees growing at the water's edge without an intertidal or supratidal
beach visible in the air photographs. ALL mangrove
vegetated coastline in 1887 is included here.
b! Vertical bulkheaded shorelines are shorelines that have
essentially vertical intertidal zones composedof rock or any of several artificial construction materials. Vertical rock outcrops seawalls and bulkheads at the shoreline are
included.
c! Slo in shorelines are those having a sloping shore composedof unconsolidated sediment. All beaches are included here as are spoil islands and so called "rip-rap"
rubble! shorelines.
54 at mean low tide. All waterways, canals and rivers having narrow
openings to the bay are excluded. As an example, the present
Interama property in Area I has a large, dredged central basin
with many small "finger" canals leading from it. The central
basin is included in open water area, but not the canals which
are excluded from land areas as well.
7! Dred ed bottom areas are those portions of the water area that
were, at any previous time, increased in depth by dredging. No
distinction is made for those areas that have regraded to
original depths subsequent to the dredging. If they have been
filled or buried with recognizable spoil, they are included in
spoil bottom areas.
Dredging of submergedbottom lands in northern Biscayne Bay has
produced a patchwork of poorly connected holes. The geomorphic
pattern produced by this bottom modification is similar to the
topographic pattern found in terrestrial areas with unreclaimed
strip mines. Most have steep-sided "walls" and their bottoms
range in depth from about 2 m to well over l0 m. The average is
probably close to 3 m. Dredged holes vary in morphology but most
are found along artificial shorelines. The following types of
dredge holes are seen in the aerial photography:
bottom sediment for use as fill material or as an economic
resource. Borrow pits dug for fill are morphologically
55 diverse and many abut t against bulkheaded shorelines
Figure 22!. Isolated borrow pits are usually associated
with causeway construction. Borrow pits are especially
coamonalong the entire mainland shoreline Figure 22b! and
one can be found north of Rickenbacker Causeway
Figure 22d! and just north of Broad Causeway. b! Shoreline channels are interconnected borrow pits which
parallel a filled or spoil shoreline and are long enough to
be used as a waterway by boats or ships. Much of Miami Beach is bordered by a shoreline channel Melloy Channel!.
Other examples include Vanderbilt Channel, the CapeFlorida Channel Figure 22e! and the Julia Tuttle Causewayborrow
pit. c! Navi ation channels navigable waterways! are elongate
trenches dredged to provide a traversable route through
areas of shallow bay bottom. They are usually very narrow
and most are straight. The Miami Ship Channel and Govern-
ment Cut comprise the deepest and widest navigation
channels in the Bay Figure 15d, f!. The Intracoastal
Waterway Figure 19! is the longest. The oldest, the
abandoned Florida Coast Line Canal and Transportation
CompanyChannel is still visible in Area III. The old FEC Railway Channelin Area VI now called Fisherman's Channel! is easily located in the aerial photographs Figure 35a!.
d! Utilit dred ed lines usually take the form of a long, Figure22. Holesproduced by dredging:A: 1940-1976pho tops ir of Pan Americanseaplane operating basin at DinnerKey arrow!. This large featureis nowpartially usedas a marina USCS, CJP-14-82; Fla. Dept, Transportation,PD 1638-22-21!. B: 1976view showsdredge holes altg ' l d t PA VII. P ll, I' ll 'I d, ' tt t ! Pl . D pt. I p t t', PD !939-22-23!. C: 1923 viewof activedredging in theTurning Basin ! andinfilling of old dockarea north of BayfrontPark !, Dodgelslard is at the top ! Fla. Dept.Transportation, PD1274-12-07!. D: 1976view of dredge hole created duringthe constructionof RickenbackerCauseway arrows! Fla. Dept. Transportation,pD 1638-21-26!. E: 1951view of CapeFlorida Channelshows extensive dredge scars on bottom arrow!, Southend of KeyBiscayne was bulkheaded and filled theprevious year. Filled area is nowBill BaggsState Park USGS,0-3621!. straight and very shallow trench dredged into the bottom. An electrical, gas, water and sewer pipeline is placed in the trench and of ten covered with sediment or buried by natural processes. Thesefeatures canbe seenas long, thin
black lines crossing the Bay in Figure 19. e! Dred ed marinas are basins dredged to provide anchoragefor boats or ships with draf ts in excess of natural bot tom
depths Figure s3! . Actually few bayshore marinas are dredgedfor boat usage, since most marinas are built in previouslydredged borrow pits whichreduces construction costs. One feature, possibly unique to Biscayne Bay is the
abandonedPan AmericanAirway Dinner Key seaplane landing strip. This large, shallow rectangular dredgehole is in part used as Dinner Key Marina. For a description of the landing strip as plannedsee the United States ArmyCorps of Engineers' report dated 1932 Figure 22a!. f! Shi turnin basins are dredgedholes that are connectedto navigable channels. They provide maneuveringroom for large ships and, therefore, are dredgedas deep as the largest channel to which they are attached. There are two ship turningbasins in northernBiscayne Bay Figure 25c!. 8! S oil bottom areas are those portions of the water area that have
unconsolidated dredgedmaterial covering the preexisting bottom whether original or dredged!. Their boundariesin Figures 18 and19 are generalizedbecause it is rarely possibleto determine Figure23. 1945-1951-1976sequence of the north endof KeyBiscayne The developmentof CrandonHarina can be seen USGS,C-1616: USGS, 3625; Fla. Dept. Transportation, PD 1638-20-22!. the boundarybetween spoil and other bottom areas with any precision.Since some benthic plants canrecolonize spoil, the boundary between the vegetation and bare spoil, although distinct in the photography,may not define the extent of the
spoil. 9! Disturbed bottomarea is the sumof all dredgedbottom areas and all spoil bottom areas. Becausethese have been defined as a part of the open water area, total disturbed area does not include the exposedportions of manmadespoil islands and fill
islands. 10! Benthic ve etation areas are those portions of the water area that have visible bottom vegetation. Since only visible vegetation is mapped,readers are cautioned not to interpret "other bottom" areas as devoid of benthic vegetation. This is not the case as somebare areas are bound by blue-green algal mats or very sparse macrofloras that are not visible in the photography. No distinction is madebetween different seagrass
or algal species. 11! "Grass" index is defined as the total benthic vegetation area, as observed in the aerial photographs, divided by the total amount of undisturbed bottom area and expressed as a percent. The "grass" index can be expressedby a formula as follows:
V = BV x 100 U where V = the "grass" index BV = the total area of mappedbenthic vegetation
60 U = thetotal undisturbed bottom area total open water area minus the total disturbedarea!
Thisindex is usedto assessthe extentto whichvarious vegetationtypes utilize theremaining natural bay bottom in eachArea. However, since no distinction hasbeen made between plantsgrowing onspoil disturbed bottom! andplants growing on undisturbedbottom, the "grass" index is nota purenumber. Theremay be less natural bottom colonized bybenthic plants than the indexwould indicate, although, since spoil areas are generallysmall, the difference is usuallyless than 5X.
The Major Changesby Area
Area I Therehas been a slightincrease inshoreline length from 10.4 km 2 to 11.1km, since 1887. The entire shoreline ofArea I was mangrove linedin 1887 U.S. Coast and Geodetic Survey, 1887! whereas only0.4 km X! of mangroveshoreline is seen in the1976 photographs. Forty-one percent of Table 3 Area I North of Broad Cause~ay Total Area 12.6 km Percent of Northern Biscayne Bay 6X B-A! A 00! km 8.9 70 0.6 -6 Total Land 9.5 75 7.5 85 6.0 400 Developed 1.5 16 1.4 15 1.2 -46 Mangrove 2.6 27 B ! 00! 10.4 13 11,1 6 0.7 7 Total Shoreline 0.4 4 -10.0 -96 Mangrove 10.4 100 6.1 55 6.1 Vertical/Bulkhead 0 4.6 41 4.6 Sloping 0 B-A! A 00! 3.1 25 0 Total Water Area 3.1 25 2.0 65 1.7 567 Dredged 0.3 9 0.1 4 <0.1 >100 Spoil <0.1 1 2.1 69 1.8 600 Disturbed 0.3 10 0.3 Benthic Vegetation 0 0.3 10 28X "Grass Index A = 1925 B = 1976 C = 1887 62 the present shoreline in Area I is sloping and 55X .1 km! is bulkheaded. Dredgingof the Florida CoastLine Canaland TransportationCompany Canal and work on the as-yet unopened Bakers Haulover Cut had disturbed 0. 3 km2 of the bay bottomin Area I as of 1925. Sixty five percent .0 km2! 2 of the presentbottom has beendredged and about4X .1 km! covered with spoil for a total of 69X of the bottom. This is the second highest percent of disturbed bottom.by Area in the Bay. In spite of the extensive bottom modifications, there has been a net increase in benthic vegetation since 1925 Figure 24!. The "grass" index has increasedfrom zero to 28X, This is largely related to the openingof BakersHaulover Cut in 1925 and the resulting changesin water chemistry and circulation. In summary,Area I is the only Area to showa significant increase in openwater area, whichis largely the result of the Interamadredging. The only substantial mangrovecommunity north of HacArthurCauseway is foundat Interama Figure 17!, but most of the trees are not isolated from the present shoreline. A large percent of the original mangrovecoastline has been convereted to sand and spoil beaches sloping shoreline! while the majority 5X! of the shoreline is nowbulkheaded. Only Area V has a higher percentageof disturbed bottom, yet the aerial photographyshows a significant increase in the amountof benthic vegetation. The increase in Area I's grass index results from the colonization of the shallower undredgedBay bottoms after the opening of Bakers Haulover in 1925. Area II Area II comprises23. 3 km2 which is split relatively evenly between 63 Figure 24, 1940-1973-1976 sequence from Area I. Denthic vegetation increases significantly on both sides of the abandonedwa'terway !. The !.ong row of spoil islands seen in 1940 is not seen in later photos. Note the densevegetation growing on the submergedportions of the two email spoil ielanda ! in 1926 aeo Pisuta 33! VSGS, CJP- 1S-02;. Fla. Dept, Transportation, PD 1274-14-13; Fla. Dept. Transportation, PD 1628-21-35. Thin vertical black lines are artifacts!. 64 landand water areas Table 4!. Since1925 fill islandconstruction has increasedland area from 9.3 km 2 2 to slightlymore than 12 km in 1976. Openwater area has been reduced by 25X due to theconstruction of North BayVillage, Stillwater and Biscayne Points, and the enlargementof Normandyand Indian Creek Islands. Seventy-twopercent of theavailable land in 1925had been developed, butby 1976 the entire 12 km 2 is modifiedfor humanuse. The thin mainland mangroveswamps and those that oncedominated the easternshores of Area II, werereduced to 1.6km 2 by1925 and entirely eliminated by 1976. Islandconstruction andexpansion hasincreased the shoreline length of AreaII fromabout 15 km to 29.3km, a 93%increase. The present shorelinecomprises 5.4 km 8%! of slopingintertidal shorelineand 23.9km 82%! bulkheaded shoreline. Area II hasthe largest percentage of bulkheadedshoreline in northernBiscayne Bay. Thirty-eightpercent .9 km2 ! of the presentday bottom in AreaII hasbeen dredged, up from only 4X in 1925.Spoil covers about 5X. The greatestnatural depths north of MacArthurCauseway and exclusive of Indian Creekoccur in AreaII. A depthof 2.4m 8feet! is foundon the 1887 nauticalchart U.S.Coast and Geodetic Survey, 1887! a shortdistance northeastof Little River,just above79th Street Causeway. AreaII also showsa netincrease in benthicvegetation since 1925. In 1925only one percent of thebottom had visible plant cover while today this figureis upto 11X .2 km2 !. Therewas more benthic cover by 1928 thanthere is presently,because large portions of themore shallow eastern half of AreaIL werestill undisturbed.Dredging along Miami Beach after 1928eliminated grass and algal beds that hadcolonized these shallow 65 Table 4 Area II Broad Causeway to 79th Street Causeway 2 Total Area 23 ' 3 km Percent of Northern Biscayne Bay 11X 00! A B-A! C 2 2 2 km X km km Total Land 9.3 40 12.1 52 2.8 30 Developed 6.8 72 12.1 100 5.3 78 Mangrove 1.6 17 0 1.6 -100 B-C! 00! Total Shoreline 15.2 19 29.3 17 14.1 93 Mangrove 15.2 100 0 -15.2 -100 Vertical/Bulkhead 0 23.9 82 23.9 Sloping 0 5.4 18 5.4 'a-A A B-A! A Total Water Area 13.6 58 10.2 44 3.4 -25 Dredged 0.6 4 3.9 38 3.3 550 Spoil "Grass" Index 10.9X !8.9X B.OX A = 1925 B = 1976 C = 1887 66 bottomsfollowing opening of BakersHaulover Cut. The"grass" index increasesfrom 10.9%%d in 1925 to 18.9%%dtoday. In summary,Area II hasmore land now than in 1925;all of thepresent landis developed.The original mangrove shoreline has been replaced by onethat is largelybulkheaded andtwice as long.Over 40/. of thepresent Baybottom has been disturbed, in spite of whichthere has beena significantincrease in benthicvegetation. Slightly less than 20/ of the undisturbedbottoms in Area II arecovered with benthic plants in 1976,up from 1 ss than 1/o in 1925. Area II I AreaIII incorporates26.5 km2 of whichabout two-thirds is openwater area Table 5! . Landarea has been increased byll%%d 8.3 to 9.2km 2 ! since 1925and open water area has decreased correspondingly. Most of this hangeis attributedto theconstruction of the 79th Street Causeway, the attachedNorth Bay Village Islands,Julia Tuttle Causeway,and the enlargementof Normandy Isle, AllisonIsland in IndianCreek, and the Mt. Sinai Hospital grounds. In 1925,84/ of theland area in AreaIII waspartially developed or completelyaltered. Only 5K {0.4 km 2 ! of the1925 land area had living mangroveswith most of thesegrowing on the undisturbed southern Normandy Isle, Today,the entire land area of AreaIII is developed. Since1887 shoreline length has increased from 8.3 km of mangrove shorelineto 25.2 km.Eight kilometers of presnt shoreline is sloping; 17.2km 8%%d! is bulkheaded. The sloping shoreline here consists almost entirelyof unconsolidatedspoil that lines a portionof 79thStreet 67 Table 5 Area III 79th Street Causeway to Julia Tuttle Causeway 2 Total Area 26.5 km Percent of Northern Biscayne Bay 12X 00! B-A! 2 2 km km X km ll Total Land 8.3 31 9.2 35 0.9 2.2 31 Developed 7.0 84 9. 2 100 0.4 -100 Mangrove 0.4 5 0 C 00! Total Shoreline 8.3 10 25.2 15 16.9 204 8.3 Mangrove 8.3 100 0 100 Vertical/bulkhead 0 17. 2 68 17.2 Sloping 0 8.0 32 8.0 ~-A B-A! A 2.3 -13 Total Water Area 18.2 69 15. 9 60 Dredged 3.5 19 4.3 27 0.8 23 Spoil .1 0.3 0.1 1 .1 00 0.8 22 Disturbed 3.6 20 4.4 28 Benthic Vegetation 11.6 64 7.9 50 3.7 -32 "Grass" Index 79.6X 68.2X 11.4X A = 1924 B = 1976 C = 1887 68 Causeway,Julia Tut t leCauseway andthe numerous spoil islands along the Intracoasta1 Waterway. Bird Keyopposite Lit t leRiver, was an original mangroveisland that hassubsequently been enlarged with spoil. AreaIII nowhas 15.9 km2 of openwater area, downfrom its 18.2 km2 in 1925.Nineteen percent of thebottom was dredged by1925. This figure has increasedto 27X .3 km2!. Thetotal amountof disturbedbottom has increased since 1925 from 20 to 28X. Early mapsand aerial photographsshow a broadshoal that crossesArea III from the Little River on the westto Mt. Sinai Hospitalon Miami Beach. Thisshoal is similarin formto CutterBank and Card Bank dividing Card Sound in southernBiscayne Bay!. Most of thisshallow -2 m deep!bottom remainsintact, althoughit is isolatedby channelsdredged along the perimeter.The cross-bay shoal had sparse and patchy benthic plant cover in 1925which since has becomelush Figure25a!. Mostof the shoal retains a lush coverof algaeand seagrass today, but the northeastcorner is less dense as is the southeast corner in Area IV. Figure20, the"before" vegetation map, was compiled with a composite of 1925and 1928 aerial photographsbecause the 1925surveys pictures of the centerof AreaIII no longerexist. Thecombined photography shows that64X of thebottom 1.6 km2! wasvegetated but most of theplant cover was extremely sparse in 1925 Figure 25a!; the "grass" index was 79.6X. Today50X of thebottom is still vegetatedby generally lush growth and the "grass"index is 68.2X. AreaIII hasthe highest"grass" index value for northernBiscayne Bay, in spite of completecoastal developmentand moderate dredging adjacent to the floral beds. In summary,Area III has increasedslightly in landarea while all of 69 figure 26. C!iangesin benthicvegetation .1 1923 left horn!;in.!Iri?8 p!iiti pair n vri,rtrircrlrross-hay shoal. IIewvegetation is verysv* n ei' .icdcrer!1'!rsh in 19288!ght phrrnria ii»hirerLl rl v grratlcedoes not extendIrt ~ thr deeperster to t!ie uuih Il!am!-0*lecib eiv, 9.AA, i97-!6!92 II ! err-!9?8 photrpsir shove, I os!on~ fridal barksend seagrsrsss in dearcrit hy rtie 19?6huir rane!:!iemi-ped I l!rory; vcca,ri!!7.1 i!, hqiireI *'ncsoil. upper Photosare arC! !sets! . C 1'!29-1928Phu! c!i*sr !ic s:hr..'ncrccscin brntl!r v, oariiricn!n A: s !I! after the openingof gakersI!aulover I I92, t i thr n rrh. '.igiriil ipecaci atc!y;cbi!.,it!or,ia its!i,iri! veryevmi aft r three sears arrov! i!!em!-na Ir I!'il iri; 9 m i i 87-er' I 0: 19? i 928p!ivl upi!I' showl the 6"rmi! o nsi, Iieiihic vcgca" i ~ npreviously bale st'allnw bottom s.nith or !n!isn i!rie..:. lsn!. nolothai. I!i urertati .ii !s iird in !erewhich indicatesthat morethar. ~ I.er lsnrcnecres i%roc!vec. !colin Crcvk:s!.o. '.:Idoe'. '.;;:;:ginsl mangroveform but the t~eesare det'nllaterl arrr r rhc 1 ri '.: .ricaie,' i*.".ri s'. '.";: mi-:a?c I lhrri;"3,', 'IA. 697-467! F. '!921-1928- 1932sequen. e of the Sa!ty's!ve hanks!ust cult f,cy Iiscayir..7 r 1,;6, lant v r ri-rr in 1920and 1928 shows sevcrcerosional setbark !I Iq I rrors t..r c'h*c s vl t is 19?9!iui i!ro..c r I,lml-pa;"rI.il ri ry; 00AA,687 129, 80AA, 806-108,-110, -112! 70 the landis nowdeveloped. Shoreline length has nearly tripled, and bulkheadshave largely replacedthe original mangroveshorelines. Dredgingdisturbed about one third of thebottom, principally along the Bay margins.A shallowcross-bay shoal remains upon which grows most of Area III's abundantbenthic vegetation. The "grass" index of 68.2Xis the highest in the study area. Area IV In 1925,Area IV's 13.1 km of totalarea was 35X land and 62X open water Table 6!. By1976 land area had increased to43X .6 km2 ! andopen water declined to 55X. Ninety-twopercent of theland area was developed prior to 1925,so thereis verylittle changeby 1976 when 100X is developed.Area IV has lost 0.4km 2 of mangrovesince 1925, however the total amountlost since 1887must be greater as much of thebayshore of Miami Beach was mangrove swamp. In 1887Area IV had6.7 km of mangroveshoreline U.S. Coast and GeodeticSurvey, 1887!. An 8.7 km increase for a total of 15.4km! in total shorelinelength by 1976was the result of the constructionof islandson the Venetian Causeway andJulia Tuttle Causeway' Sixty-five percentof thepresent shoreline is bulkheadedand35X is sloping. Thereduction in water area is theresult of dredgeand fill projects. By1925, 21X of theBay bottom around Miami Beach and along the Venetian Causewayhadbeen dredged. Thirty-one percent of thepresent bottom is disturbed. Therehas been a sharpdecrease in bottomvegetation in AreaIV since 71 Table 6 Area IV Julia Tuttle Causewayto Venetian Causeway 2 Total Area 13.1 km Percent of Northern Biscayne Bay 6X B-A 00! A 2 2 2 X km X km km 5.6 43 1.1 24 Total Land 4.5 35 4.2 92 5.6 100 1.4 33 Developed 0.4 -100 Mangrove 0.4 8 0 ~-C B C! C 00! 8. 7 130 Total Shoreline 6.7 8 15.4 9 6. 7 -100 Mangrove 6. 7 100 0 10.0 Vertical/Bulkhead 0 10.0 65 5.4. Sloping 0 5.4 35 00! B B-A! 0.9 -ll Total Water Area 8. 1 62- 7.2 55 0.5 29 Dredged 1.7 21 2.2 30 0.1 1 O.l Spoil 0 2.2 31 0.5 29 Disturbed 1.7 21 -83 Benthic Vegetation 2.9 36 0.5 7 2.4 35. 7X "Grass" Index 45.1X 9.4X A = 1925 B = 1976 C = 1887 72 1925. Nowonly 7X . 5 km2 ! o f the bottomis coveredwhere as 36Xwas vegetatedin the earlier photographs. The "grass" index has gonefrom 45.1Xto only 9.4X. Mostof the presentbenthic cover is locatedin the northeastcorner of AreaIV on the easternend of the cross-bayshoal discussedpreviously. This cover has been diminishing and thinning since at least 1973, In summary,Area IV's entire coastalland area has been developed and filling hasproduced a slight decreasein openwater area. Theorignal mangroveshoreline has been replaced by onethat is morethan twice as long andessentially bulkheaded.Thirty-one percent of the presentbottom is disturbed.Area IV hasvery little benthiccover, and it, therefore,has the lowest"grass" index in the studyarea. Thereare large quantitiesof bottomhere that havenot beendredged or coveredwith spoil andthat support little or no macro vegetation. Area V Area V is the location of the earliest major modifications in northern BiscayneBay both on Miami Beach and downtown Miami. It is the focalpoint of mostof theurban modification prior to 1925and is directlyadjacent to the MiamiHarbor complex of artificial channelsand islands in AreaVI, The present4.6 km2 of land is entirely developedas was99X of 1925's 4 3~ km3 Table7! . None of the mangrovesgrowing along the bayshorein 1887remained in 1925,though they were still extensiveprior to the late 1910's when Miami Beach construction started. A total of 3.1 km of shoreline in 1887has been increased to the present 19.6 kmof which 78Xis bulkheaded. This impressive532X increase 73 Table 7 Area V Venetian Causeway to MacArthur Causeway 2 Total Area 8.3 km Percent of Northern Biscayne Bay 4X ~A 100! B-A! 2 2 2 km km km Total Land 0.3 Developed 4.3 52 4.6 55 Mangrove 4.3 99 4.6 100 0.3 00! C Total Shoreline 3 ' 1 4 19.6 11 16.5 532 3.1 100 Mangrove 3.1 100 0 Vertical/Bulkhead 0 15.4 78 15.4 Sloping 0 4.3 22 4.3 B-A A B B-A! 0.4 -10 Total Mater Area 4.1 49 3.7 Dredged 3.1 76 3.5 93 0.4 13 Spoil <0.1 1 0.1 0.2 <0.1 <100 0.4 13 Disturbed 3.1 77 3.5 94 Benthic Vegetation 0.7 17 0.1 2 - 0.6 -86 "Grass" Index 75.4X 25.0X 50.4X A = 1925 B = 1976 C = 1887 74 dramatizesthe fill island constructionactivity focusedin this area. The 1887shoreline was entirely mangroveas wasBelle Isle Bull,sIsland in Lummus, 1940! . Becausemost of the developmentin Area V predates1925, there is little changeseen here since then. Intensepre-1925 dredge and fill activity disturbed77X of the bay bottom. By 1976,94X of the bottomis directly altered by dredgingand the dumpingof spoil. Only17X of the b:ttombetween the Bay's first twocauseways Venetian andMacArthur! had benthic vegetation in 1925. Todayabout a 2X cover is growingon what is left of theoriginal bottom and on spoil. Eventhough AreaV's bottomswere well modifiedin 1925,the "grass" indexwas 75.4X while today it is only 25X. In summary,Area V is themost modified area in northernBiscayne Bay. Its shoresare entirely developed,and the shoreline, over five times longerthan in 1887,is four-fifths bulkheaded.Ninety-four percent of the present bottom is disturbed, most of which occurredprior to 1925. There remainsvery little visible benthicvegetation growing on the unaltered6X. The "grass" index has droppedsharply since 1925. Area VI DowntownMiami is locatedat thewest side of AreaVI I s2 23.8km , just north of the MiamiRiver. Only27X of the total areawas land in 1925,but the constructionof two causeways,Fisher Island, the MarineStadium on Virginia Keyand the Port of Miamion DodgeIsland haveadded 67X more land Table8!. DodgeIsland is presentlybeing expanded,and a future enlargementof the Port of Miami is plannedto include LummusIsland. 75 Table 8 Area VI MacArthur Causeway to Rickenbacker Causeway Total Area 23.8 km Percent of Northern Biscayne Bay 11X B-AA oo! A 2 2 2 km km X km X Total Land 6.4 27 10.7 45 4.3 67 Developed 3.9 60 10.2 96 6.3 162 Mangrove 1.9 30 0.5 4 1.4 -74 B-C B ! 100 Total Shoreline 9.8 12 31. 5 18 21.7 221 Mangrove 7.8 80 1.1 3 6.7 -86 Vertical/Bulkhead 0.6 6 14.8 47 14.2 2367 Sloping 1.5 15 15.6 50 14.1 940 A 00! A B-A! -25 Total Water Area 17.4 73 13.0 55 4 ~ 4 Dredged 1 ~3 8 3.3 25 2.0 154 Spoil 0.3 2 1.1 9 0.8 266 Disturbed 1.7 10 4.4 34 2.7 158 Benthic Vegetation 10.2 59 3.5 27 6.7 -66 "Grass" Index 64. 7X 37.0X 27.7X A = 1925 B = 1976 C = 1887 76 In 1925, 60X o f the land area was developedwhile 30Xremained mangrove.By 1976these totals changedto 96Xdeveloped and 4X mangrove. Thenas now most of themangroves were located on Virginia Key; a fewwere growingon the southspit of MiamiBeach now Fisher Island; Figure 15d!. Theshoreline length has increasedfrom 9.8 kmto 31.5 kmsince 1887. Theold shoreline was 80X mangrove, 15Xsloping beaches, and the rest rocky vertical/bulkheaded!.The latter is an extensionof the MiamiOolite ridge that onceoutcropped at the shorelinejust north of CoconutGrove seephotographs in Parks, 1977!. Area VI's presentshoreline comprises 14.8km of bulkheads 7X!, 15.6km of slopingshoreline 0X! and1.1 km of mangrove X!. Thisis the onlyArea that hasmore sloping shoreline than it has bulkheaded shoreline. Waterarea in AreaVI has decreasedthrough time due to island and causewayconstruction. Dredging of deep water ship channels to connect fromthe oceanto theMiami River had disturbed 10X of the 1925bottom. The MiamiShip Channel, two turning basins, their connectingchannels, the IntracoastalWaterway, theMarine Stadium and various subsurface utility pipelines have raised the total of disturbed bottom to 34X. Benthicvegetation drops sharply from 59X of the 1925bottom to on1y 27Xin 1976. AreaVI's "grass indexhas dropped correspondingly from 64.7Xin 1925to 37Xin 1976. Thischange is largely attributableto the loss of seagrassbeds that oncecovered the shallowbottom just westof Norris Cut. AreaVI hasbecome the focus of man'sactivity sincethe early 1920's, whereasArea V wasthe focusprior to 1925. Fully half of all the land createdby man since 1925 lies in AreaVI, mostof it associatedwith port 77 construction. With the exceptionof a small tract of mangroveson Virginia Key, all the coastalland hadbeen developed. Shorelinelength has increasedby morethan 200X, and about hal f of the presentshoreline is bulkheadedand half is slopingsand and spoil beaches. Overone-third of the presentbottom is disturbedand more than half of the seagrassand algal bedsvisible in the 1925aerial photographshave been lost. The "grass" index is reduced accordingly. Area VII Fourteenpercent of the total area of Area VII was, and is, land; wateroccupies the other 86X about94 km2 !. AreaVII containsthe largest bodyof water in the studyarea Table 9! . In 1925 the land of Area VII was 44X developedand 35X mangrove. The remainderconsisted of areas of uplandvegetation most of whichwas located on KeyBiscayne. Today, 86X of the land is developedwhile mangroveshave beenreduced to the 2.1 km2 onKey Biscayne 4X of the presentland area!. Total shoreline length has doubledsince 1887 and is now41.5 kmThe extremecomplexity of canals,small spoil islands,filled bayfront andthe constructionof RickenbackerCauseway have addedthe extra 14.3 km. From 1887 to 1976 shoreline changesare: for mangrove 43 to 23X, for sloping 54 to 30Xand for vertical/bulkhead 2 to 47X. Bottomdredging in AreaVII hasintressed from Ig to 6g, andspoil has increasedto 1Xof the presentbottom. Thepresent 7X disturbedbottom in Area VII is located principally along the Bay margins. Area VII seemsto have a large drop in benthic vegetation 4X cover to 39X!and the "grass"index has gone from 65.1X to 41.5X. Thisdrop is 78 Table 9 AreaVII -- Southof RickenbackerCauseway 2 Total Area 110.4 km Percent of NorthernBiscayne Bay 51X A 00! B-A! A 2 2 km X km Total Land 15.8 14 15.6 14 0.2 -1 Developed 7.0 44 13.5 86 6.5 93 Mangrove 5.5 35 2.1 14 3.4 -62 B ! B- C 00! Total Shoreline 27.2 34 41. 5 24 14.3 53 Nangrove 11.8 43 9.6 23 2.2 -19 Vertical/Bulkhead 0.6 2 19.3 47 18.7 3117 Sloping 14.8 54 12. 6 30 2 '~ 2 -15 A A 00 Total Water Area 94.6 86 94.8 86 0.2 0.2 Dredged 0 8 1 5 7 6 4 9 613 Spoil 0.1 0.1 0.9 1 0.8 800 Disturbed 0.9 1 6.6 7 5.7 633 Benthic Vegetation 60.9 64 36.8 39 -24. 1 -40 "Grass" Index 65.1X 41.5X 23.6X A = 1925 B = 1976 C = 1887 79 largely the result of pooraerial photographiccoverage of the central deep axis of Area VII ' The "before" vegetation map Figure 20! uses 1940 photographyhere, and data is lacking for 1973 and 1976 becauseof turbidity. Mapspresented in Roesslerand Beardsley 974! andThorhaug 976! suggestthat someof this loss couldbe real compareFigure 11 and Figure 21!. In summary,Area VII is the southernmoststudied and it can be considered to be a transition d.onebetween north and south Biscayne Bay. Four-fifths of the coastal Land has been developed, and its shoreline lengthhas doubled. Over half the mangrovespresent in 1925have been lost with the only substantial communitiesnow found on Key Biscayne. Most of Area VII is open water area of which only 7X is disturbed. 2 This seemslike a smalL number, but of the total 25 km of dredged bottom in northern BiscayneBay Table 10! 23X occurs south of Rickenbacker Causewayin Area VII. About two-fifths of the bottom of Area VII has vegetativecover and the "grass"index has decreasedthrough time. As noted previously, the present benthic covermight be moreabundant because photographic coverageo f the centra1 deeper port ions o f this Area is Limited. Summaryof Major Changes Table 10 susmarisesthe major changesin the categories examinedfor the entire study area. Total values are providedboth for the sevenAreas discussedabove, and for the northernmostsix I-VI!. The latter is providedbecause many previous workers consider northern Biscayne Bay to be the Bay north of Rickenbacker Causeway. CI CI 0 Cl 0 ch IO N CI m Ch hCCh 'Cl Cl ~l ~ ao M ch 4 I N I N adN 0 co N 4»O hd'0 ~ e CO0»O Ch ICICO w COw C! ah I I I O»»OW 0»cc aC<1 N N dc w + Ch0 y 4 I O '0 C u 0 M W 0»Owr at 0 uC al CI 0 NP»O 0 w 0 0 ~ »0 0 dl N w N 0CI 0 ICIN N MChN O»a~+ P N I co N Nl ChN I»l O N»O I e ac ch co N N»»l I ICI N BIO Pl Fj N I»l I I I I o<»o 0 0»O ~ Qc NCh »0 ch+NNO N O IO w 0 CI chI/l N Ill 'N O N Ih N h chN Pl 0 0 e N 0 ch H»O chmCI ml CO cc N e al ac O 4 '0Id C0 co dl »» N '0 al Id udt u ac M al at '0 C al cf W '0 at Cl 4 dl Cl al dc 0 0 ! Id bd uat a 0 C cd cd 0 0 0 0 C al a» v 4 M IO~ »0ch C dc ad u Ch '0 '»»ul u Ia N P CO »a 4 Ig ! C M C 0 Ct 0 ca C Ia ChCh CO Id cd cj al ct al at al al 4 cd u u V uAX u g M CIM 0 0 0 dl 0 0 0 M d II II Ca R C» »dCl CJ Figure 26 shows graphically the major changes by Area as discussed above. The first three graphs in Figure 26 show changes in terrestrial environments, the second three show changes in shoreline, and the remaining four pertain to bay bottom features. Note that the shoreline graphs plot data from 1887 maps; the rest use data obtained from the historical aerial photography. The solid lines represent the older data, while the most recent data is plotted as a dotted line. Average values taken from the total northern Biscayne Bay values on Table 10 are plotted to the right of the data from the seven Areas. Both total northern Biscayne Bay averages and those from the Bay north of Rickenbacker Causewayare plotted with a small arrow that shows the historical trend, either up or down. As Figure 26 shows, land area has increased throughout the Bay except in Area I and VII. Developed land areas have increased except in Area V where most of the development predates 1925. As one might expect, the majority of new development occurred well north and south of the central older urbanized Areas. Mangrove land showed a. corresponding decrease throughout time as land development continued. The total shoreline length has doubled since 1887 and most of the original mangroveshoreline has been lost. The amountof wave reflecting bulkheaded shoreline has increased dramatically in all seven Areas. Spoil island construction has produced large amounts of new sloping shoreline in the northern six Areas. Forty percent of the Bay north of Rickenbacker Causewayhas been disturbed by dredging and spoil emplacement. The average amount of disturbed bottom for all seven Areas is only 20X, however. Both the amount of dredged bottom and the amount of disturbed bottom have increased since 82 100 100 lANQ AREA DEVELOPED % of AREA! lANQ g of land Area ! I UII = S Iv U VI Ull P 1825 average 1825 average - - -1878 --- 1876 100 100 MANGROVE MAN6RQVE I% of land SHOREl INE Area ! %! 0 I II HI!VVVIVII I 1825 average 1887 average 1876 --- 1876 100 UKRT IC AI. SNPING BvlKHEADE SHQREllNE SHQRElIHE IX! IQ! 0 I II III IV V VI Vli g I 1887 average 1807 average 187$ -- 1876 10 100 DREDGED OISTURBEO BOTTOM BOTTOM 5, af Water 'L of Water Area ! Area ! II III Iv V Itl VII g I II III Iv It UI UII I, I 1825 average 1825 ~ vorage --- 'I$76 --- 1$7C 100 BENTHIC VEGETATION I%of Water Area ! I IV V VIVII g 5 V It VI VII g 1925 overo9e 1025 aecf e9e --- 187C 1876 FIGURE 26. SUMMARY OF MAJOR CHANGES 83 1925. I The amount of benthic vegetation seen in the aerial photographs has increased in Areas I and II, but there are substantial decreases in the five Areas farther south. The Bay averages for benthic cover have decreased through time as has the "grass" index. The latter fact means that overall there is less benthic vegetation found on the undisturbed bottoms today than there was in 1925. Turbidity Turbid water areas can be seen in all aerial photograph sets used in this study. The actual components that produce these turbid patterns can be organic or inorganic particulates of sufficiently small size to stay suspended in the water under the prevailing wave-current energy conditions. Turbidity has been seen in historical aerial photography, during over flights of the bay, and during field excursions to the bay. Based on this limited number of experiences, the following turbidity observations are presented: 1! During the period covered by vertical aerial photographs 925- 1976!, there is an apparent overall increase in turbidity. More Bay bottom is obscured in the more recent photographs. The water area around 79th Street Causeway,clear in 1925, is obscured in all later photos, as is the case for most of Areas IV, V and part of VI. Water in the center of Area VII parallel to the Bay's axis is clear in 1940 but obscured in 1973 and 1976. Increases in wave reflecting shorelines, dredged bottom areas, spoil, runo f f, marinas and the number of boats are important influences on turbidity levels. Turbidity levels can be expected to increase until there 84 is a significant reduction in one or more of these influences. 2! Presentlythere are twowater areas where turbidity appearsmost persistent: the area north and south of 79th Street Causewayand the area around DodgeIsland, especially in the vicinity of the Turning Basin. The bottom in these two regions has been obscuredby turbidity in all the aerial photography since 1925. The abundant,persistent turbidity around 79th Street Causewayis influenced by one or more of the following factors: a! Thearea is the nodal point for tides in the bay andtherefore poorly flushed Michel, 1976!. b! Pith the exception of the abundantspoil shorelines, the adjacent Areas II and III are entirely bulkheaded. Mind wave and boat wave energy, reflected off bulkheads, is accentuated. c! A relatively large percentof the bottomin AreaII is naturally deep or dredged. Below 2 m deep these bottoms are essentially bare and dominated by soft muddy sediment. d! Boat traffic is concentratedover bare dredgedbottom areas. Boat waves can cause resuspension of bottom sediments Appendix B!. e! The extensive vegetated shallow bottom in nearbyArea IlI is a potential source of large quantities of suspendedsediments. Persistent turbidity in the Miami River-Harbor area is also influenced by adjacent bulkheaded shorelines, adjacent deeper bare and disturbed bottoms, boat traffic, and nutrient influx. The Miami River discharges large quantities of nutrients into this area. These nutrients are a source for maintaining high phytoplankton levels D'Amato, 1973!. 85 The Miami River also releases large volumes of turbid waters into the Bay. Much of which is organic material from high phytoplankton levels within the Miami River D'Amato, 1973!. The abundance of locally concentrated large to very large boat and ship traffic in the river and harbor provides continual agitation for the deep bare mud bottoms. This agitation can resuspendparticulates and river-borne nutrients Figure 21!. 86 Figure27. Turbidityproduced by vesselsusing Dodge Island: A: 1978 obliqueview of turbid plumeproduced by tugboatpropeller wash photo byauthor!. B: 1978 oblique view of turbidplume produced bysidp thrustersof cruiseship that Left dockabout five minutesprior to photography photo by author!. 87