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Resolution 023-1981 \- L- RESOLUTION NO, 23 -1981 vlliEREAS, the BOARD OF COUNTY COMMISSIONERS OF MONROE COUNTY, FLORIDA, has received an application from the FLORIDA DEPARTMENT OF TRANSPORTATION, DISTRICT 6, and WHEREAS, in compliance with State Statute, it is necessary as part of the permitting procedure to read the following Biological Assessment into the Record, as follows: The Applicant proposes the replacement of the existing bridge over Vaca Cut and the expansion (widening and deepening) of the existing channel to reduce water velocity in Vaca Cut. Reduced current velocity and increased piling spacing (spaced at approximately 75 feet as opposed to approximately 15 feet at present) should provide safer navigation under the bridge. Approximately 13, 028 cubic yards will be excavated below the mean high water line and approximately 15, 195 cubic yards will be excavated above mean high water (causeway area on Miami end of bridge). The excavation and dredge methods have not yet been determined. The existing bridge will remain in place (as well as the northern cause- way section) until the southbound bridge has been constructed. At this time the existing bridge will be removed and the remainder of the excavation accomplished. Contingent upon further permit and contract approval, the bridge remains will be used for artificial reef construction at an undetermined site off Atlantic coastal waters (personal communication with Bob Mannix of D.O.T., 8/21/80). The new bridge will have the same clearance and length as the existing bridge. Pilings (four rows) will be drilled inside of casings to a minimum of 10'. The channel will be dredged to -18' MHW (present depth at deepest point of channel) and will extend at this depth for a width of 235'. Side slopes of the channels will be 3:1. The forward slope of the proposed bridge and the side slopes of the bridge embankment will be 2:1 and composed of cyclo- pean stone and slurry. Excavated fill from the present causeway and channel will be utilized for the new bridge embankment, where possible. Excavated fill in excess of that needed for bridge construction, or not suitable for embankment purposes will be deposited on an upland site not yet determined (personal communication, Allan Sosnow, D.O.T., 8/21/80). All stormwater from the bridge surface will be collected and retained on site. No positive drainage will enter the waterway except on an emergency overflow basis. Turbidity devices will be utilized where possible during construction activities to maintain existing conditions. Vaca Cut is a natural break in the land separating Vaca Key and Fat Deer Key. It is approximately one-half mile long and reaches depths approaching 20 feet in some places. It has been altered, primarily by filling and narrowing so that currents are unnaturally swift. Bottom substrate in areas exposed to the current are extremely hard and rocky and exhibit benthic biota as would be expected for an area continually subjected to intense currents. Farther away from the existing bridge and extending in either direction, water currents slow and sea-grass beds are encountered in the shallower waters. Page 1 of 4 FLORIDA DEPARTMENT OF TRANSPORTATION, DISTRICT 6 RESOLUTION NO. 23 -1981 Except where channel dredging has occurred, the shallow waters of the Atlantic where Vaca Cut connects, exhibit extensive Turtle grass (Thalassia testudinum) flats. These flats gradually slope into Hawk Channel. From Hawk Channel seaward a coral ridge is encountered forming a shallow reef which then drops into the Florida Straits. The waters of Florida Bay recelvlng and feeding water into Vaca Cut exhibit 5-9 foot depths with soft corals and patches of seagrasses. Some shoaling is found at the mouth of the Cut, however, these shoals are fairly well vege- tated and stabilized. The southwest quadrant of the cut, as positioned from an axis point located in the center of the bridge, has been developed with housing and man-made canals. A marina is located adjacent to the mangrove (Rhizophora mangle) fringe that extends to Florida Bay and is interrupted in only one place by a narrow man-made channel that provides partial access for an undeveloped inland basin. The southeast shoreline also supports a well-established growth of red mangroves. The northeast shoreline has been riprapped for several hundred feet before connecting to a man-made canal and single family housing farther down. Because of the intense currents in Vaca Cut, turbidity is slightly higher than in the outside waters of Florida Bay and the Atlantic. The existing channel proposed for dredging exhibits a Key Largo limestone substrate that is extremely irregular in contour. The biotic community in the primary channel flow is limited, for the most part, to depressed or otherwise protected incongruities in the rock formation. These areas provide excellent habitat for various species of grouper (Epinephelus sp, and Mycteroperca sp), jewfish (Epinephelus itajara), snapper (Latjanus sp), margates (Anisotremus sp), porgies (Calamus sp), moray eels (Gymnothorax sp), triggerfish (Bolistes carolinensic), yellowtail snapper (Ocyurus chrysurus), grunts (Haemulon sp), angelfish (Holacanthus sp and Pomacanthus sp), hogfish (Tachnolaimus maximum), nurse sharks (Ginglymostoma cirratum), spiny urchins (Echinometra subangularis), pencil urchins (Cidans tribuloides), spiny lobsters (Panulines argus), stone crabs (Menippe mercenaria), and sea anemones (Activaria). Among the organisms growing on the exposed rock surfaces are various species of sponges (Porifera) and stony corals (Madreporaria). The shallow water and backwater areas where currents are minimal support a variety of tropicals, included in which are sergeant majors (Abudefduf saxatilis), parrotfish (Acanthurus chirurgus), wrasses (Labridae) and damsel-fish (Pomacentridae). Pelagic species found here, which utilize the area for feeding purposes, include tarpon (Megalops atlanticus), jack crevalle (Caranx hippos), barracuda (Sphyraena barracuda), needlefish (Stronglura notata), mojarra (Gerreidae), pilchards and menhaden (Clupeidae) and various species of juvenile fish. In these shallow water and backwater areas, bottom sediments are composed of limestone rubble and inorganic muds. Padina sp and Caulerpa sp are the primary macrophytes here. In one of the backwater areas (Northeast quadrant) protected by the existing causeway, a healthy turtle grass flat has established itself. This area is not included in the dredge site, but may be indirectly affected by the project. Another one of these backwater areas (Southeast quadrant) abutting the existing causeway supports a thriving shoreline growth of red mangroves, black mangroves (Avicennia germinans), white mangroves (Laguncularia racemosa), sea purslane (Sesuvium portulacastrum), bat is (Bat is maritima) and sea daisy (Borrichia sp). Page 2 of 4 / FLORIDA DEPARTMENT OF TRANSPORTATION, DISTRICT 6 RESOLUTION NO. 23 -1981 Several species of periwinkles (Littorina sp) and a great white heron (Ardea occidentalis) were observed here. A portion of this community is included in the proposed dredge site. The portion of the causeway to be excavated (eastern or Miami end) is an unproductive conglomeration of old roads and bridge escarpments. This area supports several scattered patches of sea daisy, smartweed (Bidens pilosa), and alligator weeds (Alternanthera philoxeroides). The original Key Largo limestone rock substrate has been overlain here by crushed limestone and marl (partial remains of an old road surface). A single laughing gull (Larus atricil1a) was observed here. Dredging of the existing channel will temporarily eliminate approximately 1.47 acres of productive benthos. Repopulation of the channel bottom should be rapid if dredging techniques are used that will retain bottom irregularity. With decreased current velocity, it is probable that benthic species less toler- able of strong currents will become established (e.g. soft corals and a1gaes). With the excavation of the proposed .57 acres of presently disturbed upland causeway area, additional marine habitat will be formed. There will be an immediate destruction of those sedentary organisms unable to escape from the dredge site, however, most of the fish and a good many of the crustacea should be mobile enough to temporarily relocate. There will be approximately 30 linear feet of mangrove fringe directly eliminated on the southeast quadrant of the proposed dredge site. As proposed, this will be a permanent removal. The turtle grass flats in the northeast quadrant (approximately 1000 sq. ft.) presently thriving in the back water created by the existing causeway may, as a result of the causeway removal, suffer some erosion and an eventual decrease in overall size. In all, removal of the causeway will reduce the filtering effectiveness of the shoreline and shallow water communities. This may be somewhat offset by the reduction of a large organic/debris trap, on either side of the causeway, therefoIErequiring less filtration for the area. Because of the excellent water circulation of the entire area, nutrient assimilation should not be a rpoblem. The storm water retention ponds proposed should also be of value in this respect. A small amount of leaf litter and biomass essential for the marine food chain will be lost. This would seem to be more than offset by the increase in deep, oxygen-rich benthic habitat and its associated production of vegetative communities also important for the promotion of the food chain and its con- sequential imput into the commerical and recreational fisheries of the area. The problem of major concern, primarily from a short term aspect, is that of excessive turbidity resulting directly from dredge and, to a lesser extent, spoil placement operations. Because of strong currents, turbidity containment will be difficult. At best, excessive turbidity should be temporary and rapidly dispersed by currents during excavation procedures. The area expected to cause highest turbidity will be the causeway, which will disseminate finer- grained particles than the rocky, sediment-deficient channel bottom. The tur- bidity anticipated would have its most detrimental effects upon the grass flats at either mouth of Vaca Cut. The grasses and benthic biota here are regularly exposed to inorganic sedmientation that highly fluctuates with wind and weather conditions. In this respect, higher turbidity might stress the system, but should be naturally absorbed. Shoaling in the cut or in adjacent waters is not expected to occur as a result of bottom alteration. Because of the severe short term effects this project may have on water quality (excessive turbidity), it will be necessary for the applicant to more thoroughly address this aspect of the project. Page 3 of 4 FLORIDA DEPARTMENT OF TRANSPORTATION, DISTRICT 6 RESOLUTION NO. 23 -1981 Excessive turbidity should be controlled by every effort possible. To this end, it would be beneficial to excavate the interior of the causeway first, working toward the outside (waterward) and leaving intact a narrow (approximately 10-15 feet) strip. This land strip could then be excavated, with the side downward from the prevailing current removed first, working up current. Turbidity curtains might be of some value in the backwater areas, primarily to prevent inorganic sedimentation in these areas during dredge operations. To a lesser extent, turbidity curtains might be used along the shorelines of the backwater areas in order to minimize the extent of turbid conditions spreading to outside waters. Containment devices should be used during dredge operations to retain on- site spoil and later to contain bridge embankment spoil runoff. Dredging of Vaca Cut channel should be done with consideration given to bottom contour as well as bottom depths. The bottom should be broken up so as to produce ridges and holes for fishery habitat. The other alternative, not necessarily advocated here, that might decrease water currents within Vaca Cut without causing large scale turbidity problems, would be the opening of several causeways to the east in the area of Fat Deer Key and Crawl Key. These manmade causeways do not allow a natural exchange of water between Gulf and Atlantic waters. If these areas were opened up, possibly by the placement of box culverts, water pressure flowing out of Vaca Cut might be lessened. Specifics would need to be addressed in a hydrographic study. BE IT RESOLVED BY THE BOARD OF COUNTY COMMISSIONERS OF MONROE COUNTY, FLORIDA, that the above Biological Assessment has been read into the record and duly considered pursuant to Florida Statute 253.124 by the Board of 27th d County Commissioners of Monroe County, Florida, this ay of January , 1981 at a regularly scheduled meeting. (Seal) Attest: Page 4 of 4 APPROVED.u TO FORM BY :PJli Clerk iJo1- 0Jcd:Z: BOARD OF CQUNTY COMMISSIONERS Wilhe'lmina Harvey, District 1 Curt Blair, District 2 Mayor Protem Jerry Hernandez, Jr., District 3 MA YOR George E. Dolezal, District 4 Ken Sorensen, District 5 ~, .:=.~ '.~~' ~---.-I- .--r' ,7~', ~~-"''''</' ~,' ;';j ,~~ OFFICE OF: Planning & Zoning Dept. Public Service Center Key West, Fl 33040 (305) 294-4641 .:-.~. . . ". _ft'!.'l'. Monroe County Legal Department Key West, Florida 33040 T, the undersigned, do hereby attest that all data and information is complete in the package of the applicant as follows: 1. Certificate of Complete Enclosures V- 2. Permi t V 3. Application for Permit J/' 4. Site Plan V 5. Location Map v 6. County Biologist Report V- 7. DER Assessment V 8. Resolution v BY 7i?~ o. ~ Administrative Secretary DATE ~/ r JY/ ZONING BU-l to northwest of existing Vaca Cut Bridge; BU-2 and RU-3 to the southwest; RU-l to the northeast and RU-3 to the southeast. PERMIT MONROE ~ PLt\.1'NING, BUILDING & ZONING DEPARTMENT PER11IT COUNTY PE&~IT FOR EXCAVATION, THE DEPOSIT OF NO. ~ - --...~ FILL, OR STRUCTURAL ACTIVITIES IN THE WATERS OR \fETLANDS OF MONROE COUNTY 11) Property owners name & mailing address 2) Date FOR DEPARTHENT USE ONLY 1 1 I Florida Dept. of Transportation Resolution No. Miami Regional Service Center 3) Phone number 401 N.W. 2nd Ave., Suite 590 Date: Miami, Fl 33128 (305 ) 377-5360 4) Contractor or agent's name, mailing address & phone number i Not available until awarding of contract. Will provide as soon as known. I I 5) Legal description of property: I .. 1 Section 5 Key Vaca Cut Key Subdivision I Township 66 S Lot Block I I Range 32 E Street, road or mile marker Bridge Volume of material: dredged/excavated filled/deposited 13028 c.y. 15195 c.y. . c.y. c.y. watenvard landward waterward waterward of M.H.H. of l1.H.W. of M.H.W. of M.H.W. j Cost of Permit Estirrated cost of Construction ZONING - BU-l to northwest of existing Vaca Cut Bridge; BU-2 and RU-3 to the southwest; RU-l to the northeast and RU-3 to the southeast. PURPOSE - Dredging to provide navigational safety. Approved by Chairman BOARD OF COUNTY COHMISSIONERS OF MONROE COUNTY, FLORIDA Biologist Comments - Restrictions or Special Conditions if any: "Approval" Copy in File Date Building Official PLANNING. BUILDING & ZONING DE ENT PER~IIT APPLICATION FOR EXCAVATI ON, THE DEPOSIT OF FILL, OR STRUC11TIfA[~CTIVITIES IN THE l-JATERSOR WETLANDS OF MONROE COUNTY 1) Property owners name & mailing address 2) Date For Department Florida Department of Transportation November 7, 1980 Miami Regional Service Center 3) Phone number 401 N. W. 2nd Avenue - Suite 590 Miami, Florida 33128 MONROE C'lJuNTY @ Use Onlvi (305) 377-5360 4) Contractor or agent's name, mailing address & phone number Not available until awarding of contract. Will provide as soon as known. --5) Legal description of property: Section, 5 Key, Vaca Cut Key Subdivision, Lot, Block , Township, 66 S Range, 32 E (i f acreage) 6) Describe the proposed activity, methods of construction & amount of material, (in cubic yards), to be excavated or discharged. Street, road or mile marker, Bridqe To replace one bridge and construst a new bridge, both approximately 415 feet. The proposed project will involve the elimination of channel construction by dredging 13028 c.y. and excavating 15195 c.y. This action will reduce the velocity of water at the cut, thus providing safer navigation under bridges. dredqed/excavated filled/deposited volume of material: (l.47ac) 13028c.y. 15195c.y. c.y. c.y. waterward landward waterward landward of M.H.W. of M.H.W. of M.H.W. of M.H.W. -" 7) Name, address & zip code of adjoining property owners whose property affronts I'/ater way. (1) John W. Armsby (3) Emma M. Thompson,et al Trustee 2575 Peachtree, N.E. Apt. 12-C 1241 Van Phister Street Atlanta, Geor ia 30305 Ke West, Florida 32040 - (2) Bruno Manno, et ux Nick J. Aldacosta, et ux 308 South Street Vaca Cut Bridge Ridgeway. Pa. 15853 Marathon Shores, Florida 33052 This completed application form will be accompanied by the following, or it will NOT be processed. a) Two (2) sets of drawings, on 8~ X 11 paper, shOldng location, plot plan, top vie\\' and cross section of proposal, drawn to scale. b) Application processing fee as follows: $25.00 for dredge, fi 11, docks OR any structures affronting natural water bodies. $10.00 for vertical seawalls onlTIan-made bodies of water. $25.00 for any combination of the above acti vi ties per site. Application is hereby made for a permit to authorize the activities described herein. I certify that I am familiar with the information contained in this application, and to the best of my knowledge & belief such information is true, complete & accurate. I further certify that I possess the authority to undertake the proposed activities. All provisions of laws and ordinances governing this type of work will be complied with, whether specified herein or not. The granting of a permit does not presume to give authority to violate or cancel the provisions of any county, state or federal 1 al'l regulating construction or performance of construction of this type of facility. lfor Department Use Onlyl x~p.~ ESE Signature of applicant/ aqent JlhJ./nJ Date P~rson accepting application f;ep / ~-qV' Fee & r: e i p t ,# Approved by /\ssistant Director Cost of permit Estimated cost of construction -~- --- .~. -- -... ~ -- :':~;~:I;n -"~ '.. : ,~~.' ,,$ .. -::'~7~, $ 6 . , PROPOSED I '( A I 1 ~ '0 . 8 -s N II . 7 7 .. I&J ..J 7 c( U Cf) 7 b t' V"c" K,', flO( " ~'~"""l>' ".)1 J ' , <) , . I :1 I.:' I . I ~ I' J I .~ ...., Ii f,{orothon Shores r H II 01 II II II " II I' II I! 0) . '. , . , " ',,,' :1 . , i2 ~.. 'w . .1 III i , -I . -4 " . . , . '" ' .' VICINITY MAP FROM U.S. GEOLOGICAL SURVEY MAP STATE PROJECT NO. 90040-3S06 FEDERAL PROJECT NO. BRF-48~-I(~S) B.I. NQ 6/66' 6 CHANNEL EXCAVATION FOR VACA CU,. 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I 0 , ci 1/ I/'l 0 ....; (IJ ..J W II E LaJ 0 - - '. .. 0 CD I II -;~ .- 0 oc .... LL1~ 90~~ - O~006 -, m I _ m2 II I: Z OI.lJ - ..J 1-<1: UU w(f) en .c. u - o 30tlNOn . , e .. TO~S . FORM. 3397 LITHO IN U. S. A. DEPARTMENTAL CORRESPONDENCE DATE December 31, 1980 To Florida Department of Transportation; Dredging and excavation of Vaca Cut Channel Henry Weinkam liJ2 DEP'T Director, Planning, Bldg. & Zoning Environmental Biologist, Planning, Bldg. & Zoning SUBJECT FROM Robert Dennis DEP'T LPr:f.Y, Tq~P 66~, vGE 33e, ~ECT 5, Vaca Kev Cut, ~arathon, vaca Key. Zonin~ is RU-l to northwest of existino VAca Cut Brid~e; BU-2 and ~D-3 to t~e southwest; nU-l to the north east and RU-3 to the southeast. PURPOSE: This project is to be reviewed by the County Commission in accordance with Monroe County Ordinance 13-1980; dredge and excavation. DISCUSSION: In the process of replacing the bridge over Vaca Key Cut, the Department of Transportation proposes to deepen and widen the existing channel to reduce water flow by approximately 50%. This is in response to a public hearing in November, 1975, where greater navigational safety was requested,by the public (Hydrology report submitted to Pavlo Engineering Company, 1978). _",.\' The channel basin will be 235 ft. wide and -18 ftJ M.H.W. with 3:1 sloping sides. Approximately 13,028 cubic yards of material will be dredged waterward of H.H.W. and another 15,195 cubic yards landward of M.R.W~Most of the excavated material will be used for the embankment of the new bridge with the rest to be placed on an, as yet, undetermined upland s~te. Stormwater runoff will be collected in temporary holding ponds and turbidity screens will be used during the dredging and excavation. The attached Department of Environmental Regulation report provides a detailed species list of flora and fauna. EVALUATION: Mr. Bernard Schattner, Monroe County Engineer, has reviewed the Department of Transportation's hydrologic report and feels that the project will reduce the water velocity as proposed. TOPS" FORM 3397 LITHO IN U. S. A. DEPARTMENTALCOR~ESPONDENCE DATE December 31, 1980 To Florida Department of Transportation; DredRing and excavation of Vaca Cut Channel. Page two DEP'T Su BJECT FROM DEP'T Biological effects include the removal of "approximately 30 linear feet of a mangrove fringe" from the southeast quadrant of the site (DER report p. 4) and a temporary loss of benthic flora and fauna. Impacts are also expected from turbidity and silting resulting from the dredging activity. On the other hand, reducing the water flow should' allow Tor revegetation and faunal recolonization of the affected area. Excavation of the upland is expected to have a minimal affect since this area is disturbed and not very productive. RECOt1!1ENDATION: Approval. The Department of Transportation should be encouraged to provide greater assurances that their dredging and excavation methods will be conducted to minimize turbidity and silting effects, which, because of the magnitude of the project, could have a major impact on the immediate and more distant areas. These impacts would include death of benthic fauna, seagrasses ~," and corals which could take many years to re-establish themselves. NOTE: 1. DER report attached. 2. DER and Army Corps permits are required. RD/jf ....... ~-'" DEPARTMENT OF ENVIRONMENTAL REGULATION PEID1IT APPLICATION APPRr~ISAL File No.:44-23956 County: Monroe Date: 8/26/80 Applicant Name: Add=ess: 401 N.W. 2nd Avenue, #560, Miami, Florida 33128 Florida' Department of Transportation. District 6 Agent (if applicable): 401 N.W. 2nd Avenue, #456, Miami, Florida 33128 Dr. John C. Goodknight, Acting District Engr. l~ddress : Location of project: Section(s) 5 Township 66~ Range J ') J:;' ~'-' Local Reference: Section(s) Township Marathon Shores/U.S. #1 Range i,;Ja tar 1 Body: Vaca Cut Wat(r Classification of Project Area: III Adjacent Waters: III ~quatic Preserve: No Outstanding Florida Waters: No On site inspection by: John A. Meyer Date of Inspection: Original Application: Yes~ No ~evised Application: Yes No Da te : Date of 2nd Insp. Biological and Water Quality Assessment ,.. Oescriptio.l of proposed project and construction techniques. 0uantify area of project which extends into waters of the state ,including the submerged lands of those waters and' the transi- tional zone of the submer~ed land} as defined in Section 17-4.02 and Section 17-~.28, Florida Administr~tive Code. B. Biophysical features of general area. Include comments concerning extent of de'!e10p:ment of adjoining pr"operties as well as relevant historical facts about the area. C. Biophysical fe,itures of specific project site and spoil site if applicable. Include identification of bottom types and any relevant historical facts about the area of the project. D. Potential impact of project on biological 'resources and water quality. Address long-term impact as well as immediate impact for all aspects 0= the project. ~. Suggestions, where appropriate, for modifications that may reduce or minimize the potential impact of project. rER~ 16-10(Rev.6/79) ..,.. *~;:;:-,~-..~~/.,~ :",~.~~:~.r" /0. '.a;y ,-' FLORIDA DEPARnIENT OF TRANSPORTATION -ij44-23956 tionroe County - Vaca Key, Marathon Page Two A. Applicant proposes the replacement of the existing bridge over Vaca Cut and the expansion (widening and deepening) of the existing channel to reduce water velocity in Vaca Cut. Reduced current velocity and increased piling spacing (spaced at approx- - imately 75 feet as opposed to approximately 15 feet at present) should prpvide safer navigation under the bridge. Approximately 13, 028 cubic yards will be excavated below the mean high water line and approximately 15, 195 cubic yards will be excavated above mean high water (causeway area on Hiami end of bridge). The excavation and dredge methods have not ye~ been determined. ~ t The existing bridge will remain in place (as well as the-northern causeway section) until the southbound bridge has been constructed. At this time the existing bridge will be removed and the remainder of the excavation accomplished. Contingent upon further permit and contract approval, the bridge remains will be used for artificial reef construction at an undetermined site off Atlantic coastal waters (p<.,rs~-:mal cOITuTIunicati.. ~.~ 1-1, Rob ~1annix of D.O. T., 8/21/80). The new bridge will have the same clearan~e and length as the existing bridge. Pilings (four rows) will be drilled inside of casings to a minimum of 10'. The channel will be dredgEd to -18' ~mH (present depth at deepest point of channel) and will extend at this depth for a width of 235'. Side slopes of the channels will be 3:1. The forward slope of the proposed bridge and the side slopes of the bridge embankment will be 2:1 and composed of cyclopean stone and slurry. Excavated fill from the pre.:;ent cause~ay-and channel will be utilizec for the new bridge embankmeDt, where possible. Excavated fill in excess of that needed for bridge construction , or not suitable for enbankment purposes, will be deposited on an upland site not yet determined (personal corrmunication, AllanSosnow, D.O.T., 8/21/80). All stonnwater from the bridge surface will be collected and re- tained on site. No positivl:: drainage will enter the watenvay except on an emergency overilow basis. Turbidity devices will be utilized ~here possible during construc- tion activities to maintain existing coqditions. E. Vaca Cut is a natural break in the land separating Vaca Key and Fat Deer Key. It is approximately one-half mile long and reaches depths approaching 20 feet in some places. It has been altered, primarily by filling and natTmving so tr.l.::1t currents are unnaturally swift. ' o 'T':' ";"~7"'!!!w.~,.- '.;%~"'" 'J ...... FLORIDA DEPARTMENT OF TRANSPORTATION ,ii ~L~- 23956 . ronroe County - Vaca Key, Mara thon Pdge Three Bottom substrate in areas exposed to the current are extremely hard and rocky and exhibit benthic biota as vlOuld be expected for an area continually subjected to intense currents. Farther away from the existing bridge and extending in either direction, water currents slow and seagrass beds are encountered in the shallo~:er ~~ waters. Ex;::ept ~vhere channel dredging has occurred,. the shallow waters of the Atlantic where Vaca Cut connects, exhibit extensive Turtle grass (Thalassia testlldirum) flats. These flats gradually slope into Hawk Channel. l'rom Hawk Channel seaward a coral ridge is encountered forming a shallow reef \'Jhich then drops into ~ '1e Florida Straits. The waters of Florida Bay receiving and feeding W1.t ;:: into 'he' dut exhibit 5 - 9 foot depths with soft corals and patches or seagrasses. Some shoaling is found at the mouth of the Cut, however, these shoals are fairly well vegetated and stabilized. The southtoJest quadrant of the cut, as positioned from an axis point located in the ce..ter of the bridge, has been developed with housing and man-made canals. A,marina is located adjacent to the Vaca Cut bridge. The northT.vest shoreline exhibits a mature red mangrove (Rhizophora mangle) fringe that: extends to Florida Bay and is interrupted in only one place by a narrow man-made channel that provides partial access for an undeveloped inland basin. The southeast shoreline also supports a well-established growth ofudnln..;roves. The northeast shoreline has been riprapped for several hundred feet before connecting to a man-made canal anc single family housing farther down. Because of the intense cunents in Vaca Cut, turbidity is slightly higher than in the outside waters of Florida Bay and the Atlantic. C. The existing channel proposed for dredging exhibits a Key Largo limestone substrate that is ext cemoly Lrr,.<;ular in contour. The biotic community in the primary channel flo\\:' is limited, for the most part, to depressed or otherwise protected incongruities in the rock formation. These areas provide excellent. habitat for various species of grouper (Epin~helus sp, and Myc)~roperca sp), jewfish (Epinephelus itajara), snapper (~<ltjanus sp margates (Anisotrcmu~ sp), porgies Tg~}amus sp), moray eels (Gymnothonn~ sp) triggerfish (Bolistes carolinensic), yellowtail snapper (Ocyurus chrvsuru~ grunts(Hclernulon -.sp), angelfish (Holacanthus sp and Pornacanthus sp), hogfi'Sh (Tachnolaimus maximum), nurse sharks (Ginglymostorna cirl:~tum), sp~ny urchins (Echinometra subanyularis), pencil urchins (Cidans trj.buloides), spiny lobsters (Panu ines argus), stone et:abs 1Henippe mercemaria), and sea anemones (Activaria). Among the organisms growing on the exposed rock surfaces are various species of sponges (Porifera) and stony corals O~dreporaria). i - "".,.>;>'~~~"1'~~~ . ,', ?}'k;.1::?f~ / . , ,~,.. ,~~.ttl '.1f5 ...... FLORIDA DEPARTMENT OF TRANSPORT/\TION :jil+l.- 23956 Honyoe County - Vaca Key, Marathon Page Four The shallow water and bacboJat:er areas where currents are minimal support a variety of troph'..,ls, included in which are se1'.:'geant , majors (Abudefduf saxatilis), parrotfish (~~~..r'.lS sp) Priacanthus sp, and s~ar_isorna sp), doctorfish (Acanthurus --c11irurgus). wrasses (Labridae and damselfish (Pomacentridae), Pelagic species found here, which utilize the area for feeding purposes, include tarpon (Me~alops atlanticus), jack crevalle (Caranx hippos), barracuda ( 1hyraena barracuda), needIefish (Stronglura notata), mojarra Gerreidae), pilchards and menhaden (Clupeidae) and various species of juvenile fish. In these shallow water and backwater areas, bottom sedime~ts are cJmposed of limestOlw rubb Ie and inorganic muds. Padina sp and Caulerpa sp are the primary Inacrophytes here. In one of the back- water areas (northeast quadrant) protected by the existing causeway, a healthy turtle beass flat has established itself. This area is not includec. in r:he dredge sitl ~,.... 'TITY be indirectly affected by the proj eet. I.mother one cf these baCK\v,'lter areas (southeast quad- rant) abutting the existing causeway supports a thriving shoreline growth of red mangroves, black mangroves (Avicennia .erminans), l,vhite mangroves (~ag~ularia, raceE!2..~~), s~a purslane eSUV1.um portu lacas trt?TI) , a tl.S .(B'a'tis mari tima) and sea daisy (Barr ichia s1') . Several species of pe:dwinkles (Ll ttorina sp) and a great white heron (Ardeq ()cciden~alis) were ()'bservedhere. A portion of this community:rs-incIudea in-rhe proposed nredge site. The portion of the causeway to be excavated (eastern or Miami end) is an unproductive conglomeration of old roads and bridge escarp- ments. This area supports several scattered patches of sea dai~y, smartweed (Bidens pilosa), and alligator weeds (Alternanthera nhiloxeroides)-:--The-orrginal Key Largo limestone rock substraLe has been overlain here by crushed limestone and marl (partial remains of an old road surface). A single laughing gull (Larus atricilla) was observed here. D. Dredging of the existing channel will temporarily e~iminate approx- imately 1.47 acres of productive benthos. Repopulation of the channel bottom should be rapid if dredging techniques are used that will retain botcom irregularity, With decreased current velocity, it is probable that benthic species less tolerable of strong currents will become established (e.g. soft corals and algaes). With the excavation of the proposed .5] acres of presentl~ distur- bed upland cause~'vay area, edditj onal .marine habitat will be formed. There will be an immediate destnlction of those sedentarv organisms unable to escape from the dredge site, however, most of" the fish and a good Qany of the crustacc~ should be mobile enough to temporarily relocate. There will be approximately 10 linear feet: of mangrove fr Inge directly eliminated on the s()utheast quadrant of the proposed dredge . "'.' '.'.~"..'.:".' ......."... .... ;:'JI-'~~' '<", l;'-.: . .. " , "', .,;,",.. "~, . .(,~.,. '46 -' FLORIDA DEPARTMENT OF TRANSPORTATION 4/ l~4 - 23 9 56 Monroe County - Vaca ~ey, Marathon Page Five site. As proposed, this will be a permanent removal. The turtle grass flats in the northeast quadrant (approximately 1000 sq. ft.) presently thriving in the backoJater created by the existing cflus'eway may, as a result of the causeway removal, suffer some erosion and an eventual decrease in overall size. In all, removal of the cause't;.:~ ~ill reduce the filtering effectiveness of the shoreline and shallow wflter communities. This may be somewhat offset by the reduction of a large organic/debris trap,on either side of the causeway, therefore requiring less filtration for the area. Be- cause of the excellent water circulation of the entire area, nutrien assimilation should not be a problem. T~e sturm water retention ponds proposed should also be of vall!e in this respect. J A small amount of leaf litter and biOIl1ass essential for the marine food chain will be lost. This would seem to be more than offset by the increase in deep, oxyg2n-rich benthic habitat and its associa- ted production of vegetative cOIlhl1unities also important for C~UC! promotion of the food chain and its consequential imput into the cammerc ial and reCl: en tiv~~_ _ '.sheries of the arf<'l. The problem of major concern, primadly from 2. short term aSp8ct, is th:lt of excess i ve turbid i ty re::';1..11 t ing c1 i::ec tly from dredge and, to a lesser extent, spoil placement operations. Because of strong currents, turbidi ty containment will be difficul t. At bes t, ex- cessive turbidity should be temporary and rapidly dispersed bj currents du.ini, Px(~(,vation prc-"rlllrP~. The area expected to cause highest turbidity will be l~e causeWdY, which will dissemin&te finer-grained particles than the rocky, sediment-defficient, chann~l bottom. TI1e turbidity anticipated would have its most detrimental effects upon the grass flats at either mouth of Vaca Cut. The grasses and benthic biota here are regularly exposed to inorganic sedimentation tlmt highly fluctuates with wind and weather condi- tions. In this respect, higher turbidity might stress the system, but should be naturally absorbed. Sh,'lali.ng in the cut or in cdjacent 'V\'aters is not expected to occur as a result of bottom alteration. ~'i:,r.::~~'~)~~' ~\;.~,. '" ::\j~jF'~ i.JI - FLORIDA DEPARTIIENT OF TRANSPORTATION 4f44-23956 Monroe County - Vaca.Key, Marathon Page Six E. Because of the severe short tenn effects this project may have . on water quality (excessive turbidity), it will be necessary 'for the applicant to more thoroughly address this aspect of the project.~Excessive turbidity should be controlled by every effort possible. To this end, it would be beneficial to excavate the interior of the causew~y first, working toward the outside (waterward) and leaving intact a narrow (approximately 10-15 feet) strip. This land strip could then be excavated, with the side downward from the prevailing current removed first, working up current. Tprbidity curtains might be of some va~ue in the backwater 2reas, primarily to prevent inorganic sedimentation in these areas during dredge operations. To a lesser extent, turbidity curtains mi~ht be used along the shorelines of the backwater areas in order to minimize the exte: ':: of turhid conditions spreading to outside waters. Containment devices should be used during dredge operations to re- tain on-site spoil, apd later to contain bridge embankment spoil runoff. Dredging of Vaca Cut channel should be done with consideration givE:n to bottom contour as well as bottom depths. The bottom should be broken up so as to produce ridges and holrs for fishery habitat. The other alternative, not necessarily advocated here, that might decrease water currents within Vaca Cut 1vithout causing large scale turbidity problenls, would be the opening of several causeways to the east in the area of Fat Deer Key and Crawl Key. These man- 'la'::~::a1i~t~\'ays d,.) not allow a natural exchange of water between Gulf and Atlantic waters. If these areas were opened up, possibly by the placement of box culverts, water pressure flowing out of Vaca Cut might be lessened. Specifics would need to be addressed in a hydrographic study. ( ---..... ( G {' r . \ \ I.. ,~ .,_._--\ t;: . "..v...._ . . _~. \: \ l_.\_.-.....~',/.. JOHN/f.. HEYER, ENV. SPEC. .\11 ( , . Date: Se ber Read: JAM/dvo