GEOMORPHOLOGY and SEDIMENTS ofthe | NEARSHORE CONTINENTAL SHELF MIAMI to PALM BEACH , FLORIDA by David B. Duane Edward P. Meisburger TECHNICAL MEMORANDUM NO. 29 a NOVEMBER 1969 a U. S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING RESEARCH CENTER in) G6 This document has been approved for public avlease and sale; | 450 its distribution is unlimited . M4 | : 7 IDATA LIBRARY| | i Woods Hole Oceanographic Institution ABSTRACT The Continental Shelf bordering southeastern Florida between Palm Beach and Miami was surveyed by the U. S. Army Coastal Engineering Research Center to locate and evaluate sand deposits potentially usable for shore protection and restoration projects. Survey data covered that portion of the Continental -Shelf between 15- and 100-foot depths, and consisted of seismic reflection profiles and sediment cores of the sea floor and shallow subbottom strata. ‘South of Boca Raton to Miami, much of the shelf is essentially rocky with a thin sediment veneer. Relatively thick deposits of sediment have accumulated locally in troughs on the shelf surface formed between low reef-like ridges lying parallel to shore. Shelf sediments south of Boca Raton consist almost entirely of sand-size calcareous skeletal fragments. North of Boca Raton to Palm Beach, most of the shelf is overlain by a thick blanket deposit of homogeneous fine-to-medium, gray sand about half of which consists of quartz particles and the remainder of calcareous skeletal fragments. A total volume of 201 million cubic yards of sand-size sediment occurs on the shelf south of Boca Raton. Although generally suitable for beach fill in terms of size, degradation of size by abrasion and fragmenta- tion of the delicate particles may occur in the shore environment. More than 380 million cubic yards of sand-size sediment lies on the shelf north of Boca Raton. However, because of its fine size, this sand is not con- sidered ideally suited for use on local beaches. In terms of potential as beach sand, sand size sediment from the shelf bordering southeastern Florida is of marginal quality. FOREWORD This report is the first of a series which will describe CERC's Sand Inventory Program. David B. Duane, Chief of the Geology Branch and Edward P. Meisburger, a CERC geologist, prepared the report under the general supervision of George M. Watts, Chief of the Engineering Development Division. The field work was done by Alpine Geophysical Associates under contract (DA-08-123- CIVENG-65-57) to the Jacksonville District, Corps of Engineers. Cores taken during the sand exploration are stored at the Smithsonian Oceanographic Sorting Center (SOSC). Microfilms of the seismic profiles, WHO! TU VAT i 301100010 the 1:80,000 navigational plots, and other ancillary data are stored at the National Oceanographic Data Center (NODC). Requests for information relative to those items should be directed to SOSC or. NODC. At the time of publication, Lieutenant Colonel Edward M. Willis was Director of CERC; Joseph M. Caldwell was Technical Director. NOTE: Comments on this publication are invited. Discussion will be published in the next issue of the CERC Bulletin. 7 This report is published under authority of Public Law 166, 79th Congress, approved July 31, 1945, as supplemented by Public Law 172, 88th Congress, approved November 7, 1963. CONTENTS SCetvonel s or lNTRODUGTION Sais aioe Se eo eet eh een t eM CHe Set Steen Wem Baek round © Skt thee Feo Re et a Mere ere een Maya: SN rent pe by Sea Mara Zeer SCOPE tee tee iren we iret thse oe cis Ome tes tara ieee ares La Uo coc Un nea ed a aca ai aT Section II. HYDROGRAPHY AND GEOLOGY OF STUDY AREA ........ lPeiivdrooraphiy hac ese. eee atin ct ee eater Rarely Recueil at ae Aaa TN Zoe GEOLOPMENS SEE UNG tents ts co vie ER UN Sao SS ik ae feat eanian yaaa Secelanm lll) DES CUSSION ais ek Goh ole La ES SNS RN aR San: cohen Io SSGlimenne [Dsistersorwo cao hovel Opeseshy 95 35055 5 oc Boe Ae 2. Sand Requirements .. . etc cok witucr sot etaa sh meet 3. Areas Suitable for Offshore conan! SED SIA os GOO RR ie ete Are SUM talbaslal eyes ee an ies Sais sew in re ae ERS eS As SRS ARE Shae eahan ene RneS Searle ai eSUMMARY “AND CONCLUSIONS. 2 8-20 aoe en PIGRE RAMU RIEM CIHR D | sae ote Wee Bes Bera. ene maa, ule ier eine ta Table Ie Il. JEL Appendix A Exploration Techniques Appendix B - Core Data and Sediment Description Appendix C - Granulometric Analyses Appendix D Geophysical Data ILLUSTRATIONS Stratigraphic Column for Southeastern Florida ....... ErhioRequirementse ine ther study Area sis es em ere ecen te Volumes of Sand Available in Various Morphologic Elements . . Page 14. WS): 20. Rapid Sediment Analyzer . Chart of the northern part of the Straits of Florida Plot of survey tracklines and core borings Plan of southeastern Florida shelf morphology . Average size distribution of shelf sediments ...... Schematic profile of southeastern Florida shore and shelf morphology . Shelf profiles off southeastern Florida showing subbottom reflectors : Photomicrographs of typical Section A sediments . Photomicrographs of typical skeletal fragments in Section “Aysediments! 1. 5 ae 5 eeu aaa Photomicrographs of typical sediments from Section B . Typical dual channel marine seismic reflection record . Bedrock surface topography in the Miami grid area . Cumulative curves, representative of offshore sediments in Section A . Cumulative curves, representative of offshore sediments in Section B Bottom morphology in the Miami grid area Isopachous map of sediment thickness over the bedrock Surface in the Miami grid area Median diameter of beach and nearshore and offshore samples in the study area . Limits of Study by OSE for Broward County Erosion Control Committee 5 Whe. olka tua) qatar sete Ls) dene Seah cues al geenngareeetene Areas most suitable for sand borrow ........ - Photographs of typical beach material in Section A Photographs of typical beach material in Section B vi Page Section I. INTRODUCTION 1. Background Ocean beaches and dunes constitute a vital buffer zone between the sea and coastal areas and provide at the same time much needed recrea- tional areas for the public. Neglect of the ocean beaches can result, and indeed often has resulted, in disastrous consequences either through long- term progressive erosion or through sudden overwhelming of coastal lands by storm waves and surges. Under authority of Federal Laws the U. S. Army Corps of Engineers is directly involved in the study of beach erosion and storm protection problems. Through its various division and district offices and research facilities, the Corps conducts basic studies in coastal phenomena and coastal engineering techniques, develops plans of improvement for spécific shoreline areas, designs protective structures, and in some instances, undertakes the project construction. Types of shore protection structures and methods, means of obtaining design criteria, and planning analysis are presented in Technical Report No. 4 (1966) of the Coastal Engineering Research Center (CERC). As indicated in Technical Report No. 4, the con- struction, improvement, and maintenance of beaches through the artificial placement (nourishment) of sand on the shore is one of several protection methods. This technique has gained prominence in coastal engineering largely as a result of the successful program initiated at Santa Barbara, California, in 1938 (Hall, 1952)*. Where the specified plan of improvement involves shore restoration and periodic nourishment, large volumes of sand fill may be involved. In recent years it has become increasingly difficult to obtain suitable sand from lagoonal or inland sources in sufficient quantities and at an economi- cal cost for beach fill purposes. This is due in part to increased land value, diminution and depletion of previously used nearby sources;and added cost of transporting sand from areas increasingly remote. Material com- posing the bottom and subbottom of estuaries, lagoons, and bays, in many instances is too fine-grained and not suitable for long-term protection, because the fines are immediately winnowed out and removed. While the loss of some fines is inevitable as the new beach sediment seeks equilibrium with its environment, it is possible to estimate the stability of the beach fill and therefore keep the loss to a minimum through selection of the most Suitable fill material (Krumbein and James, 1965). Regardless of suitabil- ity of material in shallow back bay areas, the potential ecological damage consequent to dredging in shallow back bay areas made exploitation of these sources highly undesirable. The problem of locating suitable and economical sand supply led the Corps to a search for new unexploited sand supplies. The search focused offshore with the intent to explore and inventory deposits suitable for future fill requirements, and subsequently to develop and refine techniques for transferring offshore sand to the beach. The exploration program is conducted through the Corps of Engineers' Coastal Engineering Research Center. Referred to as the Sand Inventory Program, it started in 1964 with *Refers to LITERATURE CITED. the purpose of finding the extent and characteristics of sand deposits on the nearshore Continental Shelf, in water depths of 15-100 feet. An initial phase in developing techniques for transferring offshore sand to the beach is described by Mauriello (1967). The exploration phase of the program uses seismic reflection profil- ing supplemented by cores of the marine bottom. Additional supporting data for the studies are obtained from USC&GS hydrographic boat sheets and published scientific literature. Survey tracklines were laid out by the CERC Geology Branch staff in either of two line patterns: grid and reconnaissance lines.. A grid pattern (line spacing at approximately one statute mile intervals) was used to cover areas where a more detailed development of bottom and sub- bottom conditions were desired. Reconnaissance lines are one or several continuous zigzag lines followed to explore areas between grids and to provide a means of correlating sonic reflection horizons between grids. Reconnaissance lines provide sufficient information to reveal the general morphologic and geologic aspect of the area covered and to identify the most promising places for additional data collection. Core sites were selected on the basis of a continuing review of the seismic profiles as they became available throughout the course of survey operations. This procedure allowed selection on the best information _ available while permitting the contractor to complete coring operations in one area before moving his base to the next area. Fundamentals of planning and field techniques, i.e., sonic profiling, coring, and posi- tioning, utilized in the conduct of CERC sand inventory programs are detailed in Appendix A. Sediment cores taken during the field operation for the Florida Sand Inventory Program were examined megascopically aboard the vessel by the contractor, capped and shipped to CERC for further analysis. Samples for laboratory processing were removed from the cores by drilling through the plastic liner at selected sampling intervals and withdrawing a 60- to 80-gram sample. All cores were sampled at top and bottom; additional samples were withdrawn at other intervals as needed to reflect vertical changes in grain size and lithology within the core. Samples were air- or oven-dried, broken into component parts if necessary, and split to 8- to 10-gram portions. The portion selected for Size analysis was rinsed in distilled water until a silver nitrate test for cK*pride was negative. Size analyses of the majority of samples were conducted on a Rapid Sediment Analyzer (RSA). The RSA at CERC, similar to those described by Zeigler (1960) and Schlee (1966), is used to determine the grain size distributional characteristics of. sediment, especially grains in the size-range from 62 to 2,000 microns, as they settle through a l-meter column of water. Coupled to a digital voltmeter and a card punch, pressure data from the RSA is recorded directly on punched cards and on a strip-chart (Figure 1). By means of a computer <4 = & ~ * Figure 1. Rapid Sediment Analyzer. Settling tube and pressure tube are shown at left of photo; connecting tubes supply and drain water. At right is console housing digital voltmeter with timing and sampling circuitry; atop console is analog strip chart record. for visual recording of pressure-time decay curve. In center is card punch for direct punching of data as sediment falls through metering column. program which relates actual pressure and time decay to equivalent fall diameter, statistical parameters descriptive of the sediment size- distribution curve are calculated. An analogous computer program for Sieve data computes the same granulometric parameters which are: median and mean diameter (central tendency); standard deviation (dispersion); skewness (asymmetry); and kurtosis (peakedness). These parameters are shown symbolically below: MEAN STANDARD DEVIATION late nh Og =v n nD. Xp =D %@ fi 2 (%,-X) fi lel 1=1 ip n SKEWNESS KURTOSIS nN 3 n 4 op =D (%-X)° fj pee OS) CGF: i=l i=l] o> of f; = frequency by weight of grains present in interval. n = number of sample classes. ise x X; = diameter of midpoint of sample interval, in phi units. Xy = mean particle diameter expressed in phi units. Oy = Standard deviation expressed in phi units. a, = skewness. a5 = kurtosis. No allowance is yet made for the effect of sample mass on the fall diameter. Median diameter is also computed. While it is recognized that that measure of central tendency is not as sensitive as the mean, median is used extensively in this paper to facilitate comparison with earlier studies and available published data where median is also cited. Never- theless, all samples analyzed by and for CERC in this Florida program and listed in Appendix B show mean as well as median values. Certain samples were also processed in the laboratory for determina- tion of the acid-soluble content. Visual examination of the samples shows that for south Florida shelf sediments the acid-soluble content is almost entirely calcium carbonate skeletal material. Weight percentage of acid- soluble constituents was determined by adding a dilute solution of hydro- chloric acid to a carefully dried and weighed sediment sample of 10 to 20 grams. Acid was added until all physical evidence of reaction had ceased. Acid was then decanted, the residue thoroughly washed in distilled water, dried, and weighed. The soluble content was calculated as the percent, by weight, of the total sample lost to acid solution. Visual classification of sediments in the laboratory was based on examination of samples under a binocular microscope and point counts of constituent particles of representative samples. Additional comments pertaining to sediment description are presented in Appendix C. Determination of sand volumes was made by planimetering areas of accumulation depicted on the isopachous map (Figure 16). The data were consequently applied to the prismoidal formula: ee ‘ Ve=l/6 0H (Sa 4S_ 20S) pega ST where ° f z j Aa e apt ee V = Volume Cee Ou is ee ilar oe H = Height See 7 S, and S, cross sectional areas of upper and lower bases 0 2 : Pp ? respectively. es : S}] = cross sectional area of the midsection. N Scope Field work off the Florida east coast from Fernandina Beach south to Miami was accomplished in 1965 by Alpine Geophysical Associates, Inc. of Norwood, New Jersey, under contract to the Jacksonville District, Corps of Engineers. Funding and technical supervision of the contract, includ- ing layout of survey lines and selection of coring sites was provided by the Coastal Engineering Research Center with administrative support from the Jacksonville District office. The area under study and reported in this document lies on that part of the Atlantic Continental Shelf which borders the southeastern coast of Florida between 25°40' N (Miami) and 26°48' N (Palm Beach) (Figure 2). Continuous seismic profiles and cores were obtained over the multiple reef area in the south and through a transition zone to the northern limit of the study area. The shelf region under study, comprising 141 square miles in area, was covered by 176 statute miles of geophysical survey in water depths ranging from 15 feet to 350 feet. The seismic profiles were supple- mented by 31 three-inch I.D. cores ranging in length from 1.5 to 11 feet. Tracklines and core locations are shown on Figure 3. Reports dealing with other sections of the Florida east coast based upon the 1965 data collection program will be published in due course. LITTLE ATLANTIC Palm Beach STuDY AREA "NORTHWEST Boca Raton Palm Beach Cou PROVIDENCE lye Broward ‘County CHANNEL Fort Lauderdale fi 7, Broward Count Dade County (= = & = “p) = [eng uJ x + [ag (e) = OF FLORIDA Chart of the northern part of the Straits of Florida. Figure 2. P| mactanoate fe en ee 366 Line 8 eee eae peo [c=19] Pabequnee: Sh. in horizontal scale which was enlarged to facilitate display. we | zs] 27570] | aS a ee () [samen [270 160 | Plot of survey tracklines and core borings. HF | it : H LAKE WORTH jess E fo} e s EXPLANATION ec-9 Core Boring —-* Survey Line and Navigation Fix BCH 29 © Beach Sample N-S Scale in Yards o 5000 10000 E-W Scale in Yards 2000 1000 CY) 2000 4000 Note change Section II. HYDROGRAPHY AND GEOLOGY OF STUDY AREA 1. Hydrography The northern Straits of Florida is a passage through which the Gulf Stream passes northward into the Atlantic Ocean. Flanking the Straits to the east is the Great Bahama Bank surmounted by the cays and islands of the Bahama Group; westward lies the mainland of Southeastern Florida (Figure 2). The thalweg of the passage is broad and lies in the central part of the northern straits. The rise of the east side of the "valley" toward the Bahama Banks is relatively steep with slopes averaging 9 percent; overall the western slope of the Florida Strait is more gentle than the eastern with slopes averaging 4 to 8 percent. In the area of study the western slope is interrupted by a broad terrace at depths from about 720 to 1,200 feet (Siegel, 1959; Hurley, 1962). Shoreward of this terrace the slope again steepens and rises to the shelf which extends from approximately 70-foot depths to shore. The seaward edge of this near- snore shelf is marked by a drowned reef-like feature with an irregular crest which generally lies at 40- to 55-foot depths. South of approximately 26°20' N the surface of this shelf rises from the outermost reef to shore in a series of step-like linear flats separated by rocky irregular slopes and ridges. North of 26°20' N, the step-like character of the topography gives way to a more or less con- stant sediment slope extending from shore to near the outer reef line (Figure 4). Sediments on the shelf can be divided roughly into two distinct es. Southward of 26°20' N the dominant sediments are white to gray careous skeletal sands and gravel (Figure 5). The acid-soluble con- t of this sediment is generally over 80 percent. North of 26°20' N to limits of this study area the dominant sediment type is a homogeneous ine to medium-grained gray sand composed of about 60 percent clear sub- angular and subrounded quartz grains and 40 percent brown, gray, or black calcareous skeletal fragments (Figure 5). oe rd by ch et OQ ct wo ~ * oO - 2. Geologic Setting a. Stratigraphy and Geologic History Strata cropping out or present in the shallow subsurface of southeastern Florida are summarized in the stratigraphic column of Table I. Along most of the east coast of Florida, rocks of the Pleistocene Anastasia Formation form the main coastal bedrock outcrop (Cooke, 1945). Locally, the Anastasia Formation is exposed in low cuts and benches - along the shore. A submerged rocky platform bordering the shore in many places is probably formed on the Anastasia Formation. LAKE WORTH EXPLANATION CJ _~—Ss Shoreline Shoreface = Reef Lines eee) Flats Zaza ~=©Sediment Slope N-S Scole in Yards 5000 t?) 5000 10000 E-W Scale in Yords 2000 1000 Co) 2000 4000 Figure 4. Plan of southeastern Florida shelf morphology. Millimeters 400 300250 200 1.50 1.00 80 60 50 40 30 25 20 : _ 10 08 062 on mW : =20) f=15 tO =O Ow! 105. 0) its meOOnma smu son s50 amalG Phi Units- GRANULE COARSE SAND | MEDIUM SAND | FINE SAND _|VERY FINE SAND Figure 5. Average size distribution of shelf sediments. Note the difference in grain size and the concomittant difference in carbonate (shell) content. "(8S6I ‘Te® 10 ‘SZapaoryos fpsGt ‘Te 19 ‘atopaozryss f4pET ‘9ayoo0D uo paseg) BptsioTy ‘Setjunoy youog wredq pure premortg ‘apeq jo Aydearst1e14s sUdD0TW asod pue ouscotp , [Trew aWOS pue 9UOJSOUITT 076-068 076-068 wy edwey sqTzeuw Apues pue Aakety) 068-001 aUs.OTW Wy uLOYyIMEH speq IT9Yys pue [Leu “pues AT LEW O0r-OL¢ 02Z-02T SUsIOTW 9387] Wy TWeTWe T quosqe [LeW “Trew TTSeYys pue pues ATTeIYS OSS-0EZ2 At qeqoid aUdd04STETd aay eyesoo[e) Spoq [TeYUS pue.osuojSaUTT] ‘pues 0€Z-0 OZT-02 9U9903STITd uj etsezseuy SN}IL}Op Foot pue Joe [e107 quesqy 0S-02 9uad03STITd SJ] oszey Aay QUOSOUTT uBvozAIq pue ITITIOO quesqy 0Z-0 9U9904STOITd Uy TWeTW 197 .eIeY) Ajqunoy) “O) piemorg ady dTsOTOaD UOT EULO yovog wed pue oprq x1SW MOTeq ooF ut syydop ozeutxorddy EPlLOTY] uULeIsSveyj Nos LOF uunzoy stydes311eV175 I aTaVl Although the classic aspect of the Anastasia Formation is that of a coquina, wells penetrating presumed Anastasia strata have encountered a complex series of interbedded limestones, calcareous sandstones, quartz sands and shell beds. Schroeder (et al, 1954) reports the formation has a thickness of 250 feet near the shore in Palm Beach County. To the south, in Dade and Broward Counties, strata identified as the Anastasia Formation reach a thickness of 120 feet under the coastal ridge. Overlying the Anastasia along the coast are quartzose sands of late Pleistocene Pamlico age-and Holocene (modern) beach and dune sediments. Near the Palm Beach-Broward County line the upper part of the Anastasia Formation undergoes a facies change and is recognized as the Miami Oolite which is the dominant stratigraphic unit cropping out on the southeastern tip of Florida. In this same region, Schroeder (et al, 1958) noted sev- eral wells which indicated that the lower part of the Anastasia Formation merged into or contained presumed elements of the Key Largo Limestone, a Pleistocene reef complex of considerable prominence in the northern Florida Keys (Hoffmeister and Multer, 1968). Hoffmeister (et al, 1967) found the Miami Oolite to be clearly divis- .lble into an upper oolitic facies overlying a lower facies characterized by extensive masses of colonial bryzoa. This bryzoan unit averages about 10 feet thick in the coastal area and contains a large number of bryzoan colonies up to 1 foot in diameter mixed with oolites, pellets and skeletal sand. The upper or oolitic facies reaches a thickness of approximately 30 feet under the coastal ridge. Hoffmeister proposed a redefinition of these units as the Miami Formation in recognition of the distinct importance of the lower unit. Schroeder (et al, 1954) determined a thickness of possibly 100 feet of Caloosahatchee sediments locally underlying the Anastasia in Palm Beach County. The Caloosahatchee is mainly shelly sand, sandy shell marl, with minor amounts of limestone and sandstone. Underlying the Caloosahatchee marl where present (and elsewhere the Anastasia Formation) along an uncomformable contact is the Tamiami Forma- tion which was redefined by Parker (1951) to include all upper Miocene material in southern Florida. The thickness of this formation ranges from about 70 to 100 feet in the study area, and is composed of beds and lenses of sandstone, limestone, sand, and silty shell marls (Cooke, 1945; Schroeder, et al, 1954; Schroeder, et al, 1958). Where these formations crop out or become exposed as the result of engineering works, they contribute sediment to the Holocene dunes, beach and offshore zone. However, the extent to which these formations now contribute sediment as a result of submarine outcrops is not definitely known. Locally, the presence of shell material in the littoral zone has been related to nearby exposures of coquina along the shore or nearshore bottom (Fineran, 1938); (Martens, 1931). Rusnak (et al, 1966) concluded that old shell material derived from coquina exposures may represent 20 to 60 percent of the carbonate material in east Florida beach sands. The remaining shell material is derived from modern biota and was found to be highest near inlets, where the environment favors large organic populations. Using deepwater seismic profiles off northeastern Florida, Emery and Zarudski (1967) made correlations of onshore borings and wells with offshore deep borings at the series level. The deep borings were obtained under the Joint Oceanographic Institutions Deep Earth Sampling (JOIDES) program. However, at the formational level little is known concerning the stratigraphy of the Continental Shelf off either northeastern or southeastern Florida. However, it is probable that beds of Anastasia age underlie the Holocene surface sediments on the shelf throughout much of the study area. South of the Palm Beach-Broward County line the Miami Oolite may crop out on the bottom close inshore. Because of its slight dip and because the base liés only about 20 feet below sea level at the coast, the Miami Formation is not likely to exist in water depths greater than 20 feet. The Key Largo Limestone and the Miami Formation are ascribed to the Sangamon interglacial. Coral reefs flourishing during Sangamon time created a shelter behind which the bryzoan facies of the Miami Formation began to form. During the later stages of this period the oolitic facies of the Miami Formation developed as a broad bar along the present-day coastal areas (Hoffmeister, et al, 1967). This depositional phase ended with the relative lowering of sea level and the consequent erosion and partial induration of the Miami and Anastasia Formations. The final de- positional event of the Pleistocene in southern Florida occurred with the rise of the Pamlico Sea which inundated the coastal area leaving a sheet of quartzose sand covering the eroded surface of both Miami and Anastasia Formations. Subsequent to ''Pamlico' time the relative sea level has been near or below its present stand. Holocene deposits along the coast consist chiefly of littoral and dune sediments, lagoon fill and shelf facies sands, much of which is probably derived from erosion of Pleistocene deposits and from modern organic production. b. Nearshore Shelf Morphology and Surface Sediment A generalized plan of the principal morphological elements ~ on the nearshore shelf off southeastern Florida is shown in Figure 4. This plan is based on USC&GS boat sheets at 1:20,000 scale and bathy- metric profiles obtained in the course of the Florida Sand Inventory Program. A schematic topographic profile across these morphologic ele- ments is illustrated in Figure 6. For the purposes of this report the Study area has been subdivided into two sections based on natural differ- ences; and referred to as Section A (25°49' N to 26°20' N) and Section B (a 20" ENG ton 26n48)" ON) adols rs] Pay ‘kSoToydzow FTays pue e10Ys epTLOTY usaysvayynos Fo oTtjJord It}ewWdsYyog “9 oANsTYy yO} 40 $924 puodas Wale] 39 NDAD} psy ND9\Djq puoras p99 184i ee He 434044 MO7 ubay ( 0} 4 40 nDayD}g 4S414) sau) 00!- 08- 09- Ob- 0e- qe 0 (2904 yo0ag) a104Sa104 aonjas0ys | yI09gG—ioz Ov Jaa4 U! UO!}OAI|q 14 Section A (Figure 7a) is characterized by a step-like bathymetric profile consisting of a series of linear plateaus (flats) each lower than its immediate shoreward neighbor. Separating the flats are irregular rocky ridges and slopes. In Section B (Figure 7b) the step-like character of the profile is replaced by a relatively thick mass of fine gray sand forming a gentle seaward slope over the central part of this portion of the shelf surface. ; Immediately seaward of the low water line and terminating at -10 to -18 feet MLW is the shoreface slope evident in both Section A and B. This Marrow zone seaward from the low tide shoreline is continuously influenced by the effects of waves, currents, and littoral sediment supply. At the seaward boundary of the shoreface slope the profile flattens and gives way to what is here referred to as the inner flat, a broad platform extending between depths of around -10 to -30 feet MLW. The surface of this flat is characterized by linear swales and ridges of low relief. The inner flat is essentially an exposed, partially lithified, deposit of algal.plates, mollusk fragments, foraminifers, corals and unidentified calcareous material. A considerable portion of the unidentified fragments may be debris from Sabellariid reefs (Kirtley and Tanner, 1968). South of Port Everglades (26°06' N) the main part of the inner flat lies at around -16 to -25 feet MLW with some depths to 30 feet. Northward, this feature becomes narrower, shoaler and less conspicuous. Za Succeeding the inner flat in Section A is a second plateau at a characteristic depth of -35 to -45 feet MLW. This plateau is separated from the inner flat by a rocky, irregular slope with 10 to 15 feet relief which is locally interrupted by a linear flat at around -30 feet MLW. The second plateau is level, and the surface for the most part is un- consolidated sediment. Its width ranges from 250 to 700 yards, but it is generally of the order of 350 yards and is terminated by a rocky reef- like ridge having irregular crest elevations of about 40 feet. South of 25°48! N, this reef line lies along the outer edge of the shelf and is succeeded by the major slope leading to the Miami Terrace. North of 25°48' N the second reef is fronted by a third plateau with depths of -60 to -70 feet MLW. Like the second plateau this feature is a relatively level sediment-floored depression 250 to 400 yards wide. The surface of this plateau hasa pronounced landward dip, particularly in the southern part of the region. Seaward of the third flat is a prominent reef-like ridge with 10- to 15-foot relief which is periodically inter- rupted by narrow passages and by very broad interruptions at around 26°00' N and just north of 26°30' N. The reef crests typically at approximately -50 feet MLW, but is quite irregular. Throughout Section A the shoreline is not quite parallel to the reef, consequently the shore trends progress- ively toward the reef from south to north, and the reef lies 3,500 yards seaward of Miami Beach but only about 1,500 yards seaward of Boca Raton. North of Boca Raton (26°20' N) the reef parallels the shoreline at a distance of about 1,500 yards. eel vel — — ee SS ae Ty Fort Lcuderdeie Palm Beach North ee ha oa is See Si === Mean Low water = =crt Lcudercaie-Palm Becch South a © - = - Meor Low mater : a = Re mi Lye mine iNew eyes Pek eur ea a im is Wosmi - Fors Louderdale 5 2 Meor Low W2'er < — - — — _- - = a — —_ = SSS SS — SS IE SS = ——— iC Wesmi Cric . Figure 7. Shelf profiles off southeastern Florida showing subbottom reflectors: a) Section A (25°40' to 26°47" N) and b) Section B (26°20' to 26°47' N). Upper profile of (b) is line 18; other profiles are composite of two or three juxtaposed lines. Both the inner flat and the third reef line are more or less contin- uous throughout the study area. North of about 26°20' N, i.e., Section B, the inner slope, the second plateau, and the second reef (and at least part of the third plateau) are overridden by a body of fine quartzose sand (Figure 7b). Topographically the shelf surface in Section B between the inner flat and the outer part of the third plateau exhibits in profile a long uniform sediment slope dipping continuously seaward (Figure 7b). While the shelf profile in Section B exhibits undulations, the relief is not great and the prominent stepped profile characteristics of Section A are no longer evident. Information concerning the character of bottom surface sediments in the study area is based upon analyses of cores supplemented by USC§GS boat sheets and other sources. Most of the cores for this study were taken from a rather narrow depth zone, -35 to -48 feet MLW. Information obtained from the boat sheets and the other sources indicates similar characteristics in the surface sediments landward and seaward of this extensively sampled zone. Sediment exposed on the surface in Section A is white or gray, medium to coarse grained, carbonate skeletal sand with an average acid soluble content of more than 80 percent (Figures 8 and 9). Sediment comprising the marine bottom in Section B is characteristically gray, fine, and well sorted calcareous quartzose sand (Figure 10). Size parameters and visual descriptions of surface samples, obtained for this report, are contained in Appendixes B and C. c. Nearshore Subbottom Morphology and Sediment Characteristics (1) Character of Seismic Reflectors. Information concerning sediment thickness on the southeast Florida shelf was gathered from chart notations, core samples and continuous seismic profiles. Cross-sectional profiles along all east-west survey tracklines shown in Figure 2 are contained in Appendix D. These profiles are line drawings showing the position and alignment of the bottom-water interface and subbottom acous- tic interfaces within sediment and rock masses. Figure 11, a photograph of the dual channel seismic reflection record is typical of the east-west profiles south of 20°20' N (Section A). Seismic reflection techniques do not provide direct evidence of the character of bottom and subbottom materials. Direct evidence must normally be gathered by drilling or coring into subbottom strata, or by tracing a stratum to an exposure which can be sampled more directly. The correlation of sediment or rock characteristics between data points is made easier by seismic data since it is possible in some cases to continuously define the strata identified in the core. Nevertheless, even where good acoustic definition is available, considerable error is found where lateral changes of sediment or rock character occur within the same bounding acoustic interfaces. Core 5 -1 foot Core 6 Top APPROXIMATE SCALE 0 ! 2 3 4 5 Millimeters Figure 8. Photomicrographs of “typical Section A sediemnts. Core 17 -3 feet Bryzoan colonies APPROXIMATE SCALE ; 0 10 : 20 Millimeters Figure 9. Photomicrographs of typical skeletal fragments in Section A sediments. Alcyonarian coral sclerites 19 Core 21 -6 feet ~~ Core 22 -5 feet APPROXIMATE SCALE | _y _}__4 ___} __| fo) ! 2 3 4 5 Millimeters Figure 10. Photomicrographs of typical sediments from = Section B. Core 30 -4 feet 20 i f *plodeq UOTIOOTJOI ITWsTes oUuTAIeM ToUUBYD Tenp TedTdA] ‘TT oansty % AEE POE SS 234 NOUVYLaNad 4330 H1idag 4334 Ni ve dezaNs yOLpaq Sy} IOAO SSeUySTY JUoWTpss Jo dew snoyosedosy ‘9T san3BTy €-Je $29} QO] 0} G Ajjo4sauag |= -|- == Sayojod ul 48a) G uDY} ssa} A}}D19Ua5 p-Je 30 Ridges are generally barren or contain only isolated, thin sediment hes. Other areas of Figure 16 indicating sediment accumulation esent the position of swales on plateaus where sediment accumulation zt 2 or 3 feet occurs. Topographic highs which terminate the plateaus re generally barren of sediment, or contain only thin and areally small accumulations. a a i ate i @) DEO eis ees (ay) ESS cat ‘ A large volume of sediment apparently does exist in the shoreface terrace because some borings have penetrated sediment sections 15 to 18 feet thick. Shallow waters and wave action precluded obtaining cores or seismic profiles; consequently no direct correlations of data from this area can be made with data obtained in the Miami grid. e. Coastal Morphology and Sediment Characteristics Between Government Cut at Miami and Lake Worth Inlet near Palm Beach the southeast Florida coastline extends in an almost straight line, bearing about 6° east from a north-south direction. It is a “barrier coast'' in the coastal classification of Shepard (1963). The immediate coastal area lies along sandy barrier islands and spits backed by bays, lagoons, marshes and improved sections of the Intracoastal Waterway. The highly developed coastal zone is broken by seven inlets, and protected by numerous groins and almost 20 miles (29 percent) of seawalls and bulkheads. Most of these shoreline improvements are concen- trated in the southern half of the area. Physical characteristics of the beach vary because it is influenced and localized by the numerous engi- neering structures and inlets. Figure 17 is a graphic plot of the median diameter of beach samples compiled from various sources. The wide range oz median size between relatively closely spaced stations and the lack of acreement between data from different sources do not favor generalization. The acid-soluble content of beach samples from the study area ranges trom 45 to 85 percent. Visual examination shows that the acid-soluble content is almost entirely of biologic origin with mollusk fragments the most significant constituent. These fragments are generally tabular, sturdy, and well rounded; many have a high polish. Occasional exposures of coquina rock appear along the beach. Numerous Dorings and probings in the waterways behind the beach encountered rock identified as limestone or coquina at less than -15 feet MLW; most prob- ably the Anastasia Formation or its facies equivalent. Offshore the rocky surface of the inner flat generally commences at less than -15 feet water depth suggesting that the rock is continuous under the beach zone. 3| “Opnit wy Ifteyi 0} Ssutpzos.e poqjoTd ore suotjed0[ e109 {sazod Fo sdoj 9yi worz o2e sotdwes ( etoyssJO ‘verte Apnys oyi UT soTdues etoysszo pue eLoysavou pue yoveq Fo ToOJOWeTp ULTpOW ‘ZT ean3ty BPN}14}D7 YJJON B[dwWiDg Jo UOIyISOY Nn > yn wo n o = a nN Nn w w a os nN on ow iF oO o a . a o oO So a ° re) a 5 3 5 °, o, @, 97 oo © o 99 © ° O° ° ° °° 290 ° ° ° ° be dee AB lg oh A ee ue | rhe my a wi Ob Ser © Ss wa a 5G / rr) & S So 2s = r) & ® Sa nes i oS in ake enna: 2 x ene eae Gee es ae O0¢ Nt Ne 2 BN a SSE Reece mn We \ va eee NEN ee Cae [oe AN ING pl Nr ge 7 ee UG K — foe eee 00b ‘ V y LY 7 AS UX a ~ ie \ i VA ‘ “.\ Je .. bE E [Pa es \ D \, eee 5B So ea a eo hares J ‘ / \ TA \ | \ Se oa | 009° . a . / Nes: \ ! Ww AS Y \ | AY \ | x \ ! Z IN 008 \ I VW Vy \\! 4 0001 $9109 slays LI-9 q Sajdwos asoysjjQ --—-—-— ‘ MAW 1224 9- —~----- \ ae asoysasoj ———___ ae \ VL BESS es s == J 902" asoysyoog) —.—.—.— ii NOILVNY 1dXJ 0Ov! ww ul azig uolpaw 32 Section III. DISCUSSION 1. Sediment Distribution and Origin Distribution of unconsolidated sediment on the shelf in Section A is largely controlled by configuration of the bedrock surface. Depres- sions such as the linear troughs between reef lines, shallow swales and bowls on the inner flat, and areas in the lee of topographic highs are favored sites of deposition. The effect of waves and currents on shelf sedimentation processes in this area are not known in detail. Available data indicate there is little if any sediment transported into the shelf area from the north (Section B) where shelf sediments are finer and much higher in quartz than those of Section A. Introduction of sediment from the slope is also highly unlikely since it would require migration upslope and across the outer reef line. No significant quantities of the material presently comprising the beach were found in the cores obtained offshore. Further, the general median sand size seaward from the beach shows a decrease to depths of -12 to -18 feet MLW (U. S. Army Engineer District, Jacksonville, 1956, 1960, 1961, 1963, 1965). Beyond this depth, the inner flat (essentially rocky) separates the nearshore zone from the shelf proper. Thus, there is a zone of relatively fine sand and rock separating two zones of coarser and compositionally dissimilar materials on the beach and shelf. Significant interchange of material between the beach zone and the shelf either ina landward or seaward direction within the study area is judged improbable. Shelf sediments of Section A are judged to be produced more or less in sttu from organisms presently comprising the biota of the shelf bottom, particularly that biota along the reef and slope lines. Sedimentary ma- terial thus produced could subsequently be swept into the adjacent troughs by wave or current action. Sediment produced under shallow water condi- tions extant during lower relative stands of sea level associated with late Wisconsin glaciation may account for some quantity of the trough sediments. However, as no age dating of these sediments has yet been undertaken, it is not possible to determine relative quantities of sediment contributed during Wisconsin or Holocene time. fo op Sediments comprising the beach and shoreface zone in Section A are believed to be a combined product of littoral drift from the north and south, local shell production, shoreward transfer of material eroded from the inner flat, and erosion of the shore. Impoundment of sediment at inlet jetties and other coastal engineering works is evidence of net drift from the north. Much sand has been lost from the littoral zone during recent years; a conservative estimate is that a net loss of 10 to 15 million cubic yards has occurred in the past 30 years (Watts, 1962). This material is probably transported to the deeper water of the shelf or slope. If littoral sedi- ment moving southward is lost to the littoral stream through movement into GQ Ow deeper water offshore, the character of the sediment indicates that off- shore movement does not occur in Section A. Loss of beach material in the Miami area could:then only be due to nearshore longshore movement, or solution of shell material. Rusnak (1966) concluded that loss by abrasion is insignificant. Because of the pH and composition of the sea water, loss by solution should be insignificant also. It is judged, therefore, that the observed loss of beach material (less that lost to inlets) is due to movement parallel to shore out of the area, rather than movement directly offshore. The gray sand body covering most of the shelf in Section B is prob- ably detrital in origin, but the source of this material is not clear. The black or dark gray coloration of most of the shell-material in the sand provides the sand with a distinctive gray color. Such coloration of the shell material has generally been taken to indicate previous burial in a marsh or swamp environment; however, recent studies show that blackened skeletal fragments may form in a subbottom marine environment (Maiklem, 1967). Thus, the present color does not necessarily indicate a relict deposit or material eroded from a lagoon bottom or back beach source. In fact, on the Georgia nearshore Continental Shelf, recent sediment is colored gray and contains 25 percent or less of carbonate (Gorsline, 1963), Pilkey and Frankenberg, 1964), not too unlike the sediment in Section B. It is unlikely the gray sand comes from offshore for reasons ex- plained above, and a source area in the high carbonate environment to the ~ south is improbable in view of the high quartz content and the shape and compositional difference of much of the skeletal material here. Also, sediment northward in the Fort Pierce area is dissimilar to sediment in _ Section B, which would preclude a northward source. One other difficulty with the explanation for a northern source is that within the zone where cores were taken there is a general decrease in average grain size north- ward; the trend, therefore, would be contrary to the premise of a de- crease in grain size downdrift from a source. A possible explanation may be that the southward moving inshore sediments are washed seaward to deeper watér in Section B and then drift back northward because of nor- therly offshore currents. Research presently underway by John Milliman (personal communication) indicates a narrow zone of sediment with rela- tively high quartz content (25-50 percent) extending offshore between Fort Pierce and Jupiter Inlet to approximately the 100-fathom line thence ex- tending north for 150 miles and south for 90 miles. Current measurements near Miami show a northward drift over the shelf of about 0.5 feet per second (House Document 169, 75th Congress, 1937). General velocity of this drift is not competent to move particles greater than silt size (0.062 mm; 46) although periodic higher velocity northward currents capable of moving material in the size ranges characteristic of the gray sands of Section B might occur. 2. Sand Requirements At the date of writing of the report, Beach Erosion Control and Hurricane Protection Studies conducted by the Corps on the Florida east 34 coast, extending from Duval County at the north to Dade County at the south, were examined and proposed project requirements summarized by Duane (1968). The projects showed an initial fill requirement of some 26 million cubic yards of material with annual replenishment of slightly less than 2 million cubic yards. Over a 50-year maintenance period, 110 million cubic yards would be required. Corps of Engineers studies prepared for specific beach erosion control projects in Palm Beach, Broward, and Dade Counties estimate requirements of nearly 21.5 million cubic yards of sand for initial fill and maintenance requirements of nearly 900,000 cubic yards annually. Thus, for a 50-year economic life, an additional need of approximately 45 million yards of sand can be forecast. Requirements for specific coastal sections within the limits of this study area are summarized in Table II- Using erosion and shoaling data from Beach Erosion Control reports, Watts (1962) estimated that an annual net of 842,000 cubic yards of sedi- ment had eroded shoreward of -18 feet MLW between Lake Worth Inlet and Government Cut (Miami) for at least 30 years prior to that report. The annual loss into inlets during this period was estimated at 200,000 cubic yards, leaving a net residual loss to the shore area of 642,000 cubic yards. Impoundment and shoaling data for Lake Worth Inlet indicates that around 230,000 cubic yards of material moves south annually into the inlet area (Watts, 1962). Even if the entire amount lost at Lake Worth Inlet ™ were bypassed and allowed to reach the littoral zone to the south, a net annual deficit of 412,000 cubic yards of sand would occur in the littoral sand budget south to Government Cut. These figures indicate that such remedial measures as groins and inlet bypassing would not entirely prevent continued erosion of the beaches of southeast Florida and that periodic replenishment of at least some of the loss would appear to be the most effective measure of maintaining suitable beaches in the area. 3. Areas Suitable for Offshore Borrow The density of data collected by CERC for this study is adequate for sand volume calculations in the Miami grid area only. A study of the sand resources on the shelf off Broward County (25°58' N to 26°20' N; Figure 18) was completed in 1967 by Ocean Science and Engineering Company (OSE) for the Broward County Erosion Control Committee who have made the results available to the Coastal Engineering Research Center. The Broward County Study is based on marine seismic reflection profiles run from about 100 yards offshore to 1 nautical mile offshore at 600-foot intervals along the entire county frontage; these were supplemented by two long cross lines parallel to shore. Sediment characteristics of the bottom and to -12 feet below the bottom were determined by use of several sampling techniques: a 12-foot long airlift sampling device, a water-jet probe, and diver inspection. From the two sources (CERC and OSE studies), it is possible to make reasonably reliable sand volume estimates for most of the region south of 26°20' N (Section A). Only tentative estimates for Section B can be made because of the reconnaissance nature of the CERC Sand Inventory 35 Fill Requirements in the Study Area Palm Beach County Jupiter Inlet to Lake Worth Inlet Lake Worth Inlet to fi Boca Raton Inlet Boca Raton Inlet to Broward County Line Broward County Palm Beach County Line to Hillsboro Inlet Hillsboro Inlet to Port Everglades Dania to Hollywood-Hallandale Dade County Broward County Line to Haulover Beach Haulover Beach Park Bakers Haulover to Government Cut Key Biscayne and Virginia Key DABLE SET 36 Initial 1,560,000 3,760,000 240,000 800,000 1,538,000 1,339,000 1,670,000 310,000 1,670,000 1,065,000 Annual 65,000 115,000 10,000 50,000 100,000 160,000 135,000 20,000 135,000 48,000 HILLSBORO INLET LAKE WORTH HALLANDAL a Be \ 7 26° Pence 6 7322 80°04" D ne al EXPLANATION ame) 7 ieee ees Core Boring ee 3 Jes oe a | 77 Survey Line and Ae ue feo. jas Navigation Fix BCH 29 : $2251 ro. lop ee ee 2275 170 ec Sas LL fO) Beach Sample oe ee x : OSE Study Area N-S Scale in Yards FS 4 a5 3 Ce 3_1s9—3285 i, aa. 2 235 | io! C-T i260 3000 Q 5000 1ooce E-W Scale im Yards 2000 1900 ce) 2000 ; 4000 Figure 18. Limits of study by OSE for Broward County Erosion Control Committee. 37 program there, and because of the paucity of published information con- cerning the shelf in that area. Because of the line spacing involved in the CERC exploration program > at Miami, more closely spaced work might be required to more precisely define the most suitable bottow areas prior to exploitation. Such a program would be analogous to "development drilling" in the petroleum industry, and to "blocking-out the ore'' in the mining industry; conse- quently, it is not a requirement unique to the offshore Sand Inventory Program. Quantities of sand available are summarized in Table III. SECTION A The OSE Broward County report estimates a total sand volume of 66_ million cubic yards within 1.2 miles offshore of Broward County. Of this material, 36 million cubic yards is concentrated in the 60-foot plateau, within 1 mile of the beach. The remaining 30 million cubic yards lies scattered in patches and thin blanket deposits in the 40-foot plateau and on the inner flat. Over half of this material is concentrated in the northern two-fifths of the segment where isolated sand pockets within the 40-foot plateau begin to coalesce into larger bodies. From the south Broward County line to the Miami grid, a total of 66 million cubic yards of sand are estimated to occur. In the CERC Miami grid area, 14 statute miles south of the OSE Study, there is a sand volume of 69 million cubic yards exclusive of the thin and discontinuous patches generally occurring on the inner flat. Of this amount, about 48 million yards are contained within the confines of the 40-foot flat 3 to 4 miles from the beach (Figure 19). A smaller concen- tration of about 5 million cubic yards lies on the offshore part of the inner flat (Figure 19). Because of the nature of known accumulations, similar but smaller areas of recoverable sand can be forecast with reason- able assurance to occur elsewhere on the flat. Approximately 16 million cubic yards of unconsolidated sediment occur in the shoreface zone of Dade County. However, calculation of sediment volumes in the shoreface is based on sparse data; no seismic lines were run in this area due to the shallow water. Borings by the Corps of En- gineers (Jacksonville District, 1961; 1968) indicated up to 18 feet of sediment in the shoreface off Key Biscayne and less than 5 feet off Virginia Key. SECTION B On the basis of the limited data available, morphology of the shelf and subbottom, and geology of the region, the volume of material available within the shelf area of Section B (north of 26°20" N) is estimated at 380 million cubic yards. The bulk of the sand is believed to have characteristics similar to the fine gray sand recovered in the 10 cores 38 a ee | qUSTOTFFNSuUyT 000‘000‘08¢ eB yep ON 2eTd PatyL ado[s juUsUTpas Ajunoy yovog wpted aTqe[teae oq (s961 atodey gso) , Auwy 27/1 nOay, ei4ep ON Ajzuno) 000‘000‘9¢ 000‘000‘Sz 000‘000‘S Premorg OTGeTTeAe oq Aew ¢/T ynoge 000‘000‘¢z 000 ‘000‘8z 000‘000‘ST eiep ON WNUWTUTU queseid 30N 000‘000‘8r 000‘000‘S 000‘000‘9T 1e8TA paxztuL 1eTq puodsss 2TH yWs1ITY ade FaLOYS Iu ITsoTOydrow (spzeA otqno ut) adeFiInsg YIOLpeg 9y} O9AOGY SdUNTOA .pues pezeUWTIs| III dATaVL aut] Aqunoy) piemotg yanos 0} TWETW Pr4p TWeTW uot .99Sqns u0T}99S 39 PEEL a a : | | mR SI [wane LUPE N SONANN ic [os) ‘) bh nN SS ee : a N Vee erg U NE BNI RL EXPLANATION oiteala eet alab/ zc pa eee AEE 77 Survey Line and Navigation Fix NSS BCH 29 (0) Beach Sample WS Gray Medium Quartzose Sand Dark Gray Coarse Calcareous Sand : VY, Gray Med-Coarse Calcareous Sand =| White Med-Coorse Calcareous Sand E-W Scale in Yards 5000 P) 5000 10000 2000 5000 C) 2000 4000 Figure 19. Areas most suitable for sand borrow. 40 collected. Near the reef lines and at depths not reached by the cores under the gray sand blanket, the sand may be similar to the calcareous sand of Section A. 4. Suitability Corps of Engineers studies for Palm Beach, Broward, and Dade Counties indicate a possible requirement of some 6 million cubic yards of sand over a 50-year period; more than enough sand to meet these needs exists in the study area. Indeed, enough sand-size material exists off- shore in just the Miami grid to meet initial requirements (21.5 million) and some years of annual nourishment. Sand comprising the beaches of Dade and Broward Counties has a high carbonate content, but the aspect of the carbonate fraction existing offshore in the Miami grid is different (see Figures 20 and 21). Shell debris on the beaches is somewhat larger and much less delicate than the shell occurring in the potential offshore borrow zones. This is due to the difference in the type of organism contributing to the shell. Off- shore the shell debris is from-algae and foraminifers indigenous to the quieter offshore zones, while onshore it comes from mollusks indigenous to the high energy littoral zone (Figure 19). Although median diameters of beach and offshore sediment are not too dissimilar (Figure 17), the compositional differences indicate there is some question if the offshore sand-size material would maintain its integrity once placed on the beach; that is, it might disintegrate under surf action. Therefore, while ample material exists off Miami, the degree of its suitability can be determined only through further study. Sediment comprising the shoreface terraces and the bottom offshore in Section B are compositionally more suitable for beach fill but the Size characteristics (small median diameter) make the sediment not wholly satisfactory for long-term projects. Section IV. SUMMARY AND CONCLUSIONS The southeastern coast of Florida between Cape Florida and Lake Park is bordered by a narrow, shallow submarine shelf which is characterized by two distinct morphological and sedimentary aspects, one donianG in the north and the other dominant in the south. As part of a larger study, a subbottom exploration program covering this 141 square mile shelf area was carried out by the U. S. Army Corps of Engineers in 1965. In this program 176 miles of continuous seismic reflection profiles and 31 sediment cores were collected. The low coast bordering the southeastern Florida shelf is covered by relatively thin sediment deposits consisting of late Pleistocene sands and Holocene beach and dune sediments. Underlying these sediments are 4\ Beach 9 42 Beach 47 APPROXIMATE SCALE |__} +--+] 0 I 2 3 4 5 Millimeters Figure 20. Photographs of typical beach material in Section A. (25°40'N to 26°20' N) Beach 34 43 Beach 38 APPROXIMATE SCALE (0) ! 2 3 4 5 Millimeters igure 21. Photographs of typical beach material in Section B. (26°20' N to 26°47! N) nts of the Pleistocene Miami and Anastasia Formation; both highly calcareous and rich in biogenous material. Bordering the shelf to seaward beyond the shelf break at around -70 feet MLW is the western slope of the northern Straits of Florida. South of Boca Raton (26°20' N) the shelf is step-like in profile, consisting of two or three linear flats separated by low reef-like ridges. The two outer flats are formed by the underlying bedrock surface and the outer ridges which create trough-like linear depressions partially filled with sediment. The inner flat is predominantly rocky with thin and dis- continuous patches of sediment throughout. Characteristically, sediments comprising the southern part of the shelf in the study area-are composed or fragments of the biota, poorly sorted, and ranging in size from-silt to very coarse sand. In the outer trough-like flats there are accumulations of about 5 to 15 feet of sediment. The deposits on the broad inner flat rarely exceed 5 feet in thickness and are generally much thinner than this. The total volume of sediment in the two outer (second and third) flats is estimated to be 160 million cubic yards. About 100 million cubic yards is located in the second flat at around -35 to -50 feet and is therefore more readily accessible to existing dredging equipment. Sand accumulation on the inner flat may aggregate approximately 20 million cubic yards, but the location of most of this material and the nature of the deposit are not favorable from the standpoint of recovery. South of Government Cut at Mieni, the shoreface terrace contains an estimated 16 million cubic yards of sediment but the removal of any substantial amount of this material may have an unfavorable effect on the shoreline. In terms of accessibility and lateral continuity of the deposits, the most readily available supply of sand lies in the linear second flat at desth of -35 to -50 feet MLW, and from 1 to 3 miles offshore. The size characteristics of the material when compared to existing beach sediments on the adjacent coast are such that much of it would be usable for local each restoration and nourishment. There is a difference, however, in the character of the constituent particles in that the offshore material con- ains a substantial amount of delicate material which may become mechani- lily degraded in the turbulent littoral zone. Further study and tests of the material are therefore needed to fully appraise its suitability. North of Boca Raton (26°20' N) to the northern limit of the study area the shelf topography and sediments change dramatically. Most of the shelf here is covered by a blanket of homogenous ‘fine to medium gray quartzose sand which produces a gently dipping relatively smooth shelf surface topography. Near the shore this sand blanket may reach a thickness oz around 40 feet, thence it thins progressively seaward to a feather edge in the vicinity of the shelf break, a distance of approximately 1,500 yards from shore. The total volume of sand available in the northern shelf segment is estimated to be 380 million cubic yards. In general, this sand is considerably finer than most sand presently ound on southeastern Florida beaches and, therefore, of doubtful value or local beach nourishment projects. ——— ——————— - Feat Miami - Fort Lauderdale “1 8 Miami Grid 400 Figure A-4. Reduced seismic reflection profile data. A-I| AVP EP ME SN Dig Xena IB CORE DATA AND SEDIMENT DESCRIPTION Appendix B contains graphic size distribution plots and visual description of sediments contained in cores from the Study area. Size distribution curves for selected samples are identified by notations on each curve showing depth of sample below the water- sediment interface. Visual descriptions are based on both megascopic and microscopic examination. The descriptive statement generally contains (in order) the following elements: 1. Color descriptor 2. Color code per Munsell Soil Color Charts (1954 ed.)* = 3. Dominant size or size range. 4. Major compositional element or elements with the dominant constituent listed last. 5. A phrase identifying readily recognized constituent elements with an estimated percentage occurrence in terms of total particles. Described subdivisions of the core are indicated by limiting lines drawn across the graphic scale to the left of the descriptions. The hachured line shows the depth to the bottom of the hole. *Munsell Color Company, Inc., Munsell Soil Color eee 1954 Edition, Baltimore, Maryland. 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ONYS 3SYvOd AY3A JINNVYS 00% ‘ON 3409 ae OGEe OOF OGL OV O'2- AYOLNAANI GNVS VOIYOTS untpouw ‘Avis ySTMOT Tad 0} sapr.ty *SLOFTUTUBIOZ ‘vOZ0AIG atraydstuoy 4g ‘squowdeAZF snoarRd =jro youyq Anis 6OVTYM 45g Spins (ON) Amag Sno, ipr yoypua NOlLdIY9SI0 Loarodd O'F) Oe! Oe! 08 OL 09 os O'b o€ 0? Ol 199 $904 wojjog mo 32 JN YDS SBS ID) Oe AG GRANULOMETRIC ANALYSES SEDIMENT DESCRIPTION Core Interval Median Mean Standard ING (feet) ) mm. d mm. Deviation Skewness' Kurtosis 1 0 De iie) WAS 2.56 .169 “Bi S25 2.50 1 Meal 4.66 On GAS WsO40u 15 Dare 3 WG2e) 526 1.36 .389 IAOM S10 2.63 3.5 1.74 300 157) 25.56 92 -.16 2.75 2 07 1O7PN 47S MeN) [aul 74 250 2.36 2 182) 2565 04 {Ace 74 81 3.04 3 0 1680) O05 1552599 .60 .19 2.36 1.5 .93 .526 96 .514 81 28S 2.78 0 2.03 .245 DU ST 63 64 2.96 0 S762 6536 1.60 .330 .68 .04 2512 1 Desay 4398 Ag 3 S6n 505 -.09 2.63 : 3 1.55 .343 Te AS yee Sizal 95 -.06 2.14 6 1594) 512 1.69 .310 91 -.05 3.58 7 1459), S58 1:27, |-.413 1.01 25 2.15 6 0 DoW 6 BBD 2N09 1 254 59 10 2.42 3 IS) e502 WG s8U8 82 eo 2.49 7 0 LW 4207, 179290 .68 2 2.60 1 1.00 .500 1.20 .435 81 87 So 2 nO S79 1.44 369 1.06 -.44 3.35 3 17S) 280 AAs 00 £95 42 2.94 4 eye aie 1.49 .355 87 525 2.16 5 168 5B 1.62 .326 92 =. 2i 2.28 6 Weise .458 Pr ANS 92 59 2.43 7 .60 .658 8634 S50. 0a Or Aan 4.07 8 N54 A768 .60 .660 70 1.49 5.00 8 0 1240) 579 1.48 .358 . 87 59 Zed 2 [SO . 707 $68) 018622 5 78 1.58 - 6.75 4 N82 567 One eA .88 1.31 4.63 9 0 OSes Tet) Aa .70 nis 3.24 1 .59 .664 572 306 .78 1.33 5.49 SEDIMENT DESCRIPTION Core Interval Median Mean Standard nOEmn (feet) 0) mm. Oo) mm. Deviation Skewness Kurtosis 2 .65 .636 SY 5589 LOS: cB 2.88 10 0 Zi. (AS 1.34 .394 -99 -.05 2.01 1 1615 ASO 20 sy 90 -.19 2.60 iit 0 -89 .539 1.14 .455 -79 -89 2.91 0. 56 GO) -68 .624 oS -95 3.49 Le 7/ 3.03 .122 228205 1.08 -.73 1.82 12 0 2.04 .244 1.96 .257 - 60 -.01 2.47 1 1.53 .347 1.48 .358 393 -13 Bo SE 3 508 5528 1.14 .455 1.04 -60 2.41 7 JO 655 S35 5057 - 86 : 1.29 4.43 13 0 1.90 .268 1.82 .284 -73 -.10 2.36 2 2508 -s256 1298 2253 -63 -.16 2.39 3 1.45 .366 1.36 .390 1.08 -.19 2.45 6 1.32 .401 1.46 .362 1.04 - 46 2.00 8.5 1.09 .469 1655 ~ SE -93 -74 2.58 14 0) 2.03 .245 1.89 .269 -71 -.33 2.34 2 oSll SZ HA02, 7491 -88 -55 2.41 5 584 (557 1.01 .496 - 84 74 3.04 15 ) BoM 5 BS 2E06) W524 - 56 -.33 2.66 Ht 188 5272 179 Zig ole -.12 2.45 6 LoS 6297 1.70 .308 -76 aS 2.17 16 0 oi oid .87 .546 .89 . 67 3.26 1 585 37/87 559) OT -81 -50 3.03 2 .29 .819 sk HAT 72 1.52 6.54 6 58d o LIZ -51 .700 -69 - 80 4.20 17 0 -50 .707 05) 1059 -57 74 3.03 1 -58 .667 -73 .601 -65 1.23 5.03 2 -42 .750 -66 .631 -81 1.35 5.22 S .50 .708 -72 .608 . 67 1.9 5.68 5 595 555 .84 .560 -78 1.36 5.80 Core No. Wi 18 19 20 21 22 25 24 25 Interval (feet) 6 Sy OS 0s) IS) (SS) SS On) SY Oe Sa eS te) rh jo) Pe Oo oO Ob FY OO WW WN © Sy Ss SSS aS a eS) Ss) SS sy o Median mm. 572. OOS 387/ o54@ .03 .491 .63 .646 ESO 60/7) “41-2752 .26 .419 -63 .645 798) 1595 -18 .221 ew 2 5.0 -74 .300 Oa el OI .21 .216 -68 .312 .58 .336 -52 .401 -44 2369 659 S82 -69 §.310 ~ 84-2279 -94 261 OS) 525 .84 .280 -80 .287 530. Bay Ay) 5 SxS) .58 .334 558. oOlO7/ .854 -23 Po a Oe DO OO = NO TO ¢ .90 . 03 23 Mean SEDIMENT DESCRIPTION mm . 5 OS -491 ~425 -534 . 630 -618 -428 -537 548 » 233 . 236 - 508 202 aa 5OOH 321 . 380 .359 321 .310 . 282 .273 357 . 289 . 290 . 290 ~312 334 .593 .812 Standard Deviation .90 83 74 83 91 1.00 69 Skewness . 56 -35 -79 1.26 1.55 1.05 -.05 87 - 20 -.24 -17 -.25 — 12 -.11 -.25 Kurtosis 3.47 3.59 2.78 4.14 5.28 3.87 2.13 3.32 2.69 2.04 3.34 2.55 2.61 2.11 2.27 1.92 2.38 3.10 2.70 2.58 2.37 2.28 1.86 2.13 2.40 2.38 4.01 2.43 2.66 3.59 SEDIMENT DESCRIPTION Core Interval Median Mean Standard NOs: (feet) ) mm. () mm. Deviation Skewness Kurtosis 25 2 AO 59 63 .648 U7 ih 2.55 3 V7 5 S85 90 .536 67 65 3.03 9 See aou! No 2S. oAay 62 70 3.29 26 0 2oSS) slo DoH 5205 -48 -.30 2.70 1 BB 5 ANS Be Wb 5 BAY 51 =F 40 2.70 27A 0 BOS “oll ES 2.61 .163 37 -.04 3.63 1 2.63 .162 2.61 163 -30 -.21 2.94 4 250) oAlIS 2.46 .182 9 -.34 2.39 7.8 2.60 .165 Bo D2 174 44 -.66 3.02 29 0 Ze ASS 6m m2eS8\ LOD AGE. 17 3.07 3 22 QZ ZolS 5226 59 -.38 2.34 30 0 2566 5159 2.60 .165 -40 -.50 3.16 9 BOQ og IOS 2658 ol@7 -35 -02 2.89 31 2 BoM ABB 2.05 .242 -65 - 06 2.72 7 1.97 255 1.91 .265 58 ecole) 2.26 10 WeQ) 5252 13965 o257 -61 -O1 3.08 hy cat ; es i ‘ AY tite Vi JN 12 JP 1 Nf 1B) IEG JD) GEOPHYSICAL DATA Appendix contains cross-section line profiles of the study based on seismic reflection profiles. Hachured lines represent the bedrock reflection. Solid lines show the bottom and strong subbottom reflectors. Dashed lines show weak reflectors. Ambiguous or very weak reflection surfaces are _ shown by a dash-dot line. Ol 000! X 1334 NI JONVISIG 602), 9109 Py @ !woly ‘ajijoug GON xl V IWOIW ‘al!jorg . 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DESCRIPTIVE NOTES (Type of report end inclusive dates) - AUTHOR(S) (Firat name, middle initial, laat name) David B. Duane Edward P. Meisburger 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS i 9a. ORIGINATOR'S REPORT NUMBERIS) ba. CONTRACT OR GRANT NO. TECHNICAL MEMORANDUM NO. 29 . PROJECT NO. 96. OTHER REPORT NOS) (Any other numbers that may be asai gned thia report) - DISTRIBUTION STATEMENT This document has been approved for public release and sale; its distribution is unlimited. - SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY 13. ABSTRACT The Continental Shelf bordering southeastern Florida between Palm Beach and Miami was surveyed by CERC to locate and evaluate sand deposits potentially useable for shore protection projects. Survey data covered 141 square miles of that part of the Continental Shelf between 15- and 100-foot depths, and consisted of seismic reflection profiles and sediment cores from the sea floor. d South of Boca Raton to Miami, much of the shelf is rocky with a thin sediment / veneer. Relatively thick deposits of sediment have accumulated locally in troughs formed between low reef-like ridges lying parallel to shore. Shelf sediments south of Boca Raton consist almost entirely of sand-size calcareous skeletal fragments. North of Boca Raton to Palm Beach, most of the shelf is overlain by a thick blanket deposit of homogeneous fine-to-medium, gray sand about half of which consists of quartz particles and the remainder of calcareous skeletal fragments. About 200 million cubic yards of sand-size sediment occurs on the shelf south of Boca Raton. Although generally suitable for beach fill in terms of size, degradation of size by abrasion and fragmentation of the delicate particles may occur in the shore environment. More than 380 million cubic yards of sand-size sediment lies on the shelf north of Boca Raton. However, because of its fine size, this sand is not considered ideally suited for beach fill. In terms of potential as beach sand, sand-size sediments from-the shelf bordering southeastern Florida is of marginal quality. DD Sh.1473 sacha UNCLASSIFIED i secuiG Ciasmiicaticns cer UNCLAS Securit y 7 Classi ification KEY WORDS Artificial beach nourishment Beach sediments Continental Shelf Miami to Palm Beach, Florida Seismic profiles Sea bottom cores p oumKe | INGE UNCLASSIFIED Security Classification