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Notice: ©1993 Coastal Education & Research Foundation, Inc. [CERF] http://www.cerfjcr.org/ . This manuscript may be cited as: Finkl, Jnr. C. W. (1993). Pre-emptive strategies for enhanced sand bypassing and beach replenishment activities in Southeast Florida: A geological perspective. Journal of Coastal Research, Special Issue 18, Beach/Inlet Processes and Management: A Florida Perspective, 58-89.

58

COASTAL PHOTOGRAPH FROM UNIVERSITY OF FLORIDA'S COASTAL ENGINEERING ARCHIVES

PHOTO 2. View of Government Cut. Photo dated February 17, 1936.

Journal of Coastal Research, Special Issue No. 18, 1993 Journal ofCoastal ReIC8l'Ch Fort Lauderdale, Florida Fall 1993

Pre-Emptive Strategies for Enhanced Sand Bypassing and Beach Replenishment Activities in Southeast Florida: A Geological Perspective

Charles W. Finkl, Jor.

Department of Geology Florida Atlantic University Boca Raton, FL 33431, USA ABSTRACT

FINKL, C.W., Jnr., 1993. Pre-emptive strategies for enhanced sand bypassing and beach replenishment activities in southeast Florida: A geological perspective. Journal of Coastal Research, Special Issue No. 18, 59-89. Fort Lauderdale (Florida), ISSN 0749-0208.

Although beaches on the southeast Florida coast are periodically replenished in an effort to reduce shoreline recession, such efforts have been only moderately successful. Erosion of sandy beaches on the downdrift (south) sides ofjettied inlets is a chronic problem that requires remediation. In order for erosion control measures to be effective, e.g. function harmoniously within the natural balance of coastal systems, coastal protection measures must consider the geological framework for this subtropical coast as it influences strategies for coastal management. Important to coastal engineering design are such factors as climate change (Greenhouse Effect), sediment discharge into the oceans, long­ and short-term causes of sea-level rise, sediment sources and sinks in terms of gross/net littoral budgets. The limited reserves of offshore borrow materials that are suitable for beach renourishment and the loss of nearshore sediments to deep offshore regions requires consideration ofalternative sand sources and enhanced sand bypassing options. Environmental impacts and socio-economic constraints of sand management schemes are related to the on-going "sand wars", and the consideration ofecologically-favored alternatives. There are several action items that need to be implemented if politically expedient solutions, such as long-range setbacks or abandonment of coastal sectors, are to be avoided. These action items are: (1) initiate full-scale comprehensive environmental monitoring of bypassingand replenishment projects, (2) set up continuous long-term ecological monitoring, (3) standardize methods and sampling techniques, (4) form Florida reference ecological stations, (5) include ecologically sensitive areas in data management plans, (6) monitor beach, borrow, and bypass installations on the basis of ecological performance, and (7) establish a central depository for environmental performance data. The advantage of beach replenishment combined with enhanced sand bypassing is a pre-emptive strategy over conventional techniques. The initiation of comprehensive, long-term environmental (ecological) monitoring is needed as a means to approach a balance between engineering solutions to erosion control and environmental concerns.

ADDITIONAL INDEX WORDS: Beach erosion, borrow material, coastal erosion, coastal management, dredging, environmental monitoring, sand management, shoreline stabilization, tidal inlet.. 60 Fink!

INTRODUCTION in accordance with local conditions. Even though most erosion control measures are Erosion of sandy beaches, a world-wide prob­ specifically designed to incorporate local pecu­ lem (BIRD, 1985), is related, in part, to long­ liarities of individual inlets, mitigation of the term (background) relative sea-level rise (RSL). downdrift beach-erosion problem has been less Beaches along the southeast Florida coast (Figure successful than anticipated. In addition to the 1) are no exception to this general trend. Because technical and engineering aspects ofsand bypass­ the value of Florida beaches as a revenue source ing and replenishment activities are other consid­ has increased in proportion to population growth erations of equal import that include, for exam­ (STEVENS, 1990), there is considerable interest ple: societal perceptions of what constitutes a in maintaining beaches as a tourist-based re­ problem, estimates ofits extent and severity, and source that will continue to support coastal what constitutes an "acceptable" solution; eco­ development (CULLITON et al., 1992). One nomic and political constraints that may limit measure ofrapidly increasing coastal populations some types ofengineering solution; and concerns is the number of residential and non-residential over the impacts of engineering works that may construction permits, as shown graphically in degrade the environmental integrity of these Figure 2. This intensive coastal development in fragile subtropical coastal zones. To this setting, subtropical Florida has increased the pressure on which already resembles a complex montage, coastal resources, particularly on sandy beaches should be added the geological framework with that have multiple uses for recreation, natural which all of these other activities play out and habitat, and storm protection. Thus, more than interact. 100 km of Florida's beaches have been rebuilt Knowledge of the geological framework is (artificially renourished, replenished) under the relevant to considerations ofcoastal modification Federal Shore Protection Program. because natural processes will tend, in the long In an effort to ascertain the causes of short­ run, to override human-induced perturbation of term beach erosion, researchers have recently environmental systems. Short-term consequences focused attention on shorelines that are adjacent ofinappropriate construction, such as longjetties to inlets because it has long been suspected that and deep entrance channels, can accelerate long­ navigational entrances have a substantial potential term (natural) erosional trends that ripple down to interfere with natural sediment transport the coast. processes in such a way that downdrift erosional impacts can be severe. In the example of South Purpose and Scope Lake Worth Inlet, the downdrift Boynton beach was eroded for 280 m landwards from the time It matters little what methodologies are consid­ of inlet cutting and stabilization in 1929 to 1955 ered "acceptable" if shoreline stabilization tech­ (BRUUN et al., 1966). Extreme rates of shore­ niques do not operate in harmony with natural line recession in isolated "hot spots" along the coastal processes. The purpose of this paper is southeast coast now approach 4 m yr-I , causing thus essentially twofold: (1) to briefly identify substantial loss of sandy beaches and oceanfront some relevant aspects of the geological evolution property, but in the early part of this century and framework of the southeast Florida coastal some downdrift shorelines retreated after inlet belt that may influence strategies for coastal cutting and stabilization at rates in the range of management, and (2) to indicate some new sand 20-25 m yr-I . DEAN (1990) estimates that on the management techniques that may be compatible Florida east coast, navigational entrances, espe­ with environmental conditions along this coast. cially those stabilized by jetties, are responsible for about 85 percent of the beach erosion prob­ EVOLUTION OF THE FLORIDA SOUTH­ lem. Mitigation of the beach erosion problem is EAST COAST thus clearly focused on stabilized inlets with attempts to resolve specific problems at each inlet The southeast Florida shore, which embraces

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 61

PALM BEACH him

GULF 260 _ OF MEXICO

DADE

Study Area ~~~

~ 0 ~5 60 Miles .:!i ~ I "I f , '. 1 ~ 0 25 50 Kilometers 25 I 820 81 0 800 Figure 1. Location ofthe study area in the southeast Florida coastal zone showing the location of Palm Beach, Broward, and Dade counties.

the seaward parts of Palm Beach, Broward and environmental conditions and processes, as Dade counties (Figure 1), is regarded for man­ described by DOLAN et al. (1980), that may not agement purposes by state regulatory agencies as be applicable here. Unfortunate and unforseen a barrier island coast. The "barrier islands," as results may follow attempts to implement man­ identified by the Florida Department of Environ­ agement practices based on the assumption that mental Protection, are comprised by that section this coastal zone will behave or react to certain of the coastal zone lying between the Intracoastal stimuli, such as secular and punctuated sea-level Waterway (ICWW) and ocean beaches. Such rise or storm surge events, in a known or per­ administrative divisions should not, however, be ceived manner as based on management of other confused with natural (topographic, geomorphic, types of barrier islands (see, for example, geologic) units. Although perhaps useful for PILKEY et al., 1984). The point here is that regulatory purposes, application of the term barrier island evolution follows specific pathways 'barrier island coast' implies a whole range of (e.g. SWIFT, 1975; FIELD and DUANE, 1976)

Journal of Coastal Research, Special Issue No. 18, 1993 62 Finkl

coasts because each environment IS subject to specific geodynamic frameworks. TOTAL COASTAL CONSTRUCTION AUTHORIZED BY PERMIT 11970-1989) Geological Framework of Coastal Environ­ ments .,

il;' ;. 300 Segments of the Florida east coast differ mark­ edly in shoreline and shelf configuration. Evolu­ tionary styles of this subtropical coast have been k influenced by the tectonic setting of the continen­ I~ tal margin (trailing edge plate-margin), regional 100 ~" & trends in bedrock geology (structure and litholo­ b gy), nearshore sediment supply, and fluctuations o in sea level. On the basis of regional geology, Palm Beach Broward Dade '" the Florida east coast may be approximately Non-Residential divided environmentally into two unequal seg­ 1000's of Units o OJ Residential ments, the northern two-thirds of the state be­ longing to the South Atlantic Province and the NON-RERSIDENTIAL CONSTRUCTION southern one-third to the South Florida-Caribbean Province (MAHER, 1971). AUTHORIZED BY PERMIT 11970-1989) Trailing edges of migrating continents are often characterized by barrier-island coastlines (INMAN and NORDSTROM, 1971) and those in eastern North America are among the most extensive in the world. The northern Atlantic coastline of Florida is commonly depicted as one comprised by chains of barrier islands (e.g. GIERLOFF-EMDEN, 1961) separated by large capes or headlands, e.g. Cape Canaveral, where­ as the southern coast is primarily mainland and keys (FINKL, 1985, 1992). Although the transi­ Palm Beach Broward Dade tion from northern Florida Atlantic barrier coasts Number of Buildings £J Recreation to the southern province may, in the first in­ o Hotels stance, seem obvious, there is no clearly defined boundary. The transition is in the northern part Figure 2. Number ofconstruction pennits issued of the study area near Palm Beach. The geo­ in southeast Florida coastal counties for the graphical demarcation of processes associated period 1970-1989: (A) residential (individual with barrier island systems from those associated units) and non-residential (buildings), (B) hotels with mainland coasts and keys require, however, and recreation-related (buildings). (Modified further and more detailed investigation. The from Culliton et al., 1992). elucidation of these coastal frameworks is impor­ tant because barrier islands, mainland coasts, and that respond to variables such as the rate and keys develop their own sets of morphodynamic amplitude of relative sea-level change, tide and processes that respond different to coastal engi­ wave regimes, sediment supply, slope and width neering works. of the continental shelf, local relief of bottom Increased understanding of the geologic frame­ topography, and rock outcrops, among others. It work in which the dramatic and accelerated thus seems reasonable to anticipate different coastal processes (erosion and sedimentation) is response patterns on barrier islands and mainland presently taking place and which directly impinge

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 63 on the current urban setting, is directly related to Worth Inlet (1920), Bakers Haulover Inlet coastal management practices. True barrier (1927), Port Everglades (1928), and Ft. Pierce islands, which are susceptible to a wide variety (1930). There are now nineteen permanent of geomorphic processes (e.g. island lowering (stabilized) inlets on the east coast, the last one and thinning, washover, and migration), react in (Sebastian Inlet) cut in 1948. The cutting of a manner that is distinct from processes associat­ inlets has thus transformed certain coastal seg­ ed with mainland rock-eored coastal segments ments into barrier islands, an artificial creation. (older perched beaches, dunes and keys) that Inlet cutting also contributes to the mis-identifi­ characterize much of coastal southeast Florida. cation of coastal types in another important way because cuts through long barrier spits disrupt Definition and Recognition of Coastal Barriers the nearshore sediment regime. With time, the beheaded spits migrate shoreward and eventually Summarizing the barrier system in terms of become welded to the mainland (Figure 3), as in interactive sedimentary environments, OERTEL the case of New River inlet (FINKL, 1985). (1985) lists six elements required to impose the Charts prepared by the u.S. Coast and Geodetic designation "barrier island" on littoral sand Survey (USCGS) in the late 1800's and early bodies: (1) mainland, (2) backbarrier lagoon, (3) 1900's (e.g. USCGS, 1884, 1887, 1928) clearly inlet and inlet deltas, (4) barrier island, (5) show these natural coastal barriers as long south­ barrier platform, and (6) shoreface. Application ward downdrift-trending spits. Barrier islands, ofthe principles ofmorphodynamic and sedimen­ the subaerial expression of an accumulation of tary evolution of each element, as it affects sediments between two inlets and between the adjacent environments, is crucial to the under­ shoreface and the backbarrier lagoon, are not standing of barrier island systems. evident on early (i.e. pre-19th Century) Preliminary investigations (e.g. FINKL, 1985, charts/maps (see discussion below). 1992) suggest that the southeastern Florida coast may be more complex than originally perceiVed Lithologic Control of Barrier Platfonns (e.g. WHITE, 1970) because brackish- or salt­ water backbarrier lagoons, for example, were The barrier platform, the substructure which absent or intermittently present from the coastal supports the barrier island, is critical to the system prior to inlet cutting or canalization that evolution ofa barrier island system (GILL, 1967; was largely introduced during the 1920s. In a KRAFT et al., 1973; BELKNAP and KRAFT, natural barrier island setting, these coastal ele­ 1985; LEATHERMAN, 1985). Platforms are ments exist as open-water lagoons or expandable provided in various forms from pre-Holocene tidal lagoons with salt marshes. The presence of topographic highs on submerged mainland surfac­ backbarrier lagoons is essential to the concept of es as, for example, in the barrier island chains barrier islands because every element of the off Virginia and Georgia. Unconsolidated sedi­ barrier island system influences or is influenced ments derived from glacial moraines and outwash by the backbarrier lagoon (OERTEL, 1985). plains provide the platforms off the southern The presence of natural inlets is necessary to coast of New England (McCORMICK and establish the barriers as islands rather than TOSCANO, 1981), as do fluvial sediments in the barrier spits. About a century ago, Florida had western Netherlands (VAN DER VALK, 1992). eleven natural inlets along the 585 km of ocean Lithified materials may constitutebedrock control shoreline between the Georgia border and Miami. in some of the west Florida barrier island sys­ Natural inlets along the 250 km of microtidal tems (e.g., EVANS et al., 1985). Bedrock shoreline between Ponce de Leon Inlet at control in southeast Florida, as described by Daytona Beach and Jupiter Inlet near Palm Beach PETUCH (1986), may be related to the subsur­ were intermittently breached, depending on face position of Pliocene reefs. Here, in the weather conditions. In the decade beginning in middle Pliocene (Buckinghamian time) coral reef 1920, several new inlets were opened: Lake complexes extended along the eastern edge of the

Journal of Coastal Research, Special Issue No. 18, 1993 64 Fink]

Figure 3A. Ba"ier spits in the vicinity ofFort Lauderdale, Florida, circa 1925. Note that the 1CWW has not yet been dredged through the fresh water marshes and that there is no inlet cutting through the bay mouth ba"ier into Lake Mabel for what was later to become the turning basin of Port Everglades. A large ba"ier spit, beheaded and destabilized by the New River Inlet, has moved shoreward across the New River Sound becoming welded to the Lake Mabel bay mouth bar. The spit is again stabilized by the cutting ofa small canal on the south side ofLake Mabel to provide inland access to New River Sound.

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 65

Figure 3B. Barrier spits in the vicinity ofFort Lauderdale, Florida, circa 1925. Note that the 1CWW has not yet been dredged through the fresh water marshes and that there is no inlet cutting through the bay mouth barrier into Lake Mabel for what was later to become the turning basin of Port Everglades. A continuation of the barrier spit southwards past the Dania Cutoff Canal. The spit terminated just south ofDania Beach Boulevard where the New River Sound opened to the Atlantic Ocean. (Photo modifiedfrom original 1925 print by Fairchild Aerial Surveys, Inc., Long Island City, New York).

Journal of Coastal Research, Special Issue No. 18, 1993 66 Finkl continental shelf from Palm Beach County above sea level (e.g. Blowing Rocks and lap through Broward and southward into Dade Rock in Palm Beach County) as well as underwa­ County. These zoned coral reefs, the eastern part ter where they are locally referred to as hard ofPetuch's so-called Everglades Psuedoatoll, are grounds. Sabellariid worm reefs also occur along purported to have provided the foundation of the the surf zone and comprise a unique and impor­ Atlantic Coastal Ridge and oolitic limestone of tant rocky habitat. the Miami Formation that formed during the Sangamon high sea-level stand. Outcrops of the Destabilization of Barrier Spits Anastasia Formation along the present shoreline (WHITE, 1970; LOVEJOY, 1992) further Inspection of aerial photos dating back to the suggests bedrock control ofcoastal barrier evolu­ early 1920's and older historical maps of the Fort tion. This formation (Anastasia), a late Pleisto­ Lauderdale area verify the presence of well­ cene coquinoid limestone, appears to be a developed coastal spits, bars, and deltas prior to nearshore (high-energy) deposit but there is still man-made developments. The New River, which some speculation concerning the exact environ­ drained eastwards from the Everglades through ment of deposition (LOVEJOY, 1992). It now Fort Lauderdale, fed into New River Sound. The constitutes the rock core of many of the newly sound averaged one or two meters depth and created "barrier islands" (e.g. Hutchinson Island, flowed south, landward ofthe barrier spit, before Singer Island, Hillsboro Beach, Fort Lauderdale emptying into the Atlantic Ocean near Dania, Beach, Dania Beach, Miami Beach). five or six kilometers distant from Fort Lauder­ The geological development of the present dale. southeast Florida coast was strongly influenced Coastal features such as spits and bars, which by pre-Holocene topographic highs upon which existed in a natural condition ofdynamic equilib­ coastal barriers were built. They provided a rium, were destabilized almost immediately after stable base where sediments could accumulate inlets were cut and fortified by rock jetties. and as sea level rose in the mid-Holocene, the Cutting and stabilization of some of the larger rock-cored sedimentary accumulations were inlets (e.g. Port Everglades) typically took a year bypassed with bays and estuaries forming on the or two because a large amount of rock (Anastasia landward sides of islands, spits, and bars. Along Formation) had to be blasted prior to dredging. the southeast Florida coast the Iithified remains After the inlet was opened, however, the of older shorelines associated with lower stands destabilized coastal spits migrated shoreward of Pleistocene sea level also served as traps for across the sounds and eventually became welded coastal sediments being driven shoreward by to the mainland (if Figure 3). Initial phases of Holocene sea-level rise. The submerged this process took about three to five years and paleoshorelines form reef systems containing within two decades the process was nearly com­ both rock outcrops and corals that are well plete with only small segments of the spits known to scuba divers and sports fisherman as remaining as barriers in front of landlocked the first (0.5-2 m), second (3-6 m), and third (8­ portions of the former sound. In the case of New 10 m) reefs. These submerged shorelines are River Sound, the entire sandy spit migrated 100 separated not only in bathymetry but also by m shoreward in about 5 years. Thus, about 6 x inter-reefal "soft bottoms" of relatively thin sand 106 m3 of sand comprising the spit1 were either sheets that range up to 10 or 15 m in thickness (DUANE and MEISBURGER, 1969). Much of lCalculations of sediment volumes are based on the present shoreline consists of one or two analysis of aerial photographs (circa 1925; see meters ofbeach sand that overlies lithified sands, Figure 3) and charts showing the location of the beachrock, and coquina belonging to the barrier spit. The spit was about 100 m wide by Anastasia Formation. Rock outcrops are common 4-9 km long and, judging from water depth to along the coast at about the mean tide level but bedrock and height of the dunes, approximately there are notable outcrops at one or two meters 4 m thick giving a sediment volume on the

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 67 welded to the mainland making new beaches, carbon dioxide and other greenhouse gases entrained in the littoral drift system, or lost to continues, by the 21st Century the Earth's mean deeper water beyond the third reef by cross-shore global temperature will rise between 4 and 150 transport. The height and width of the present C. This temperature rise would cause the water dune-beach system (the older perched strand) has in the oceans to expand and eventually some decreased since 1926 by about 30 % so that the melting in the massive polar ice sheets causing volume of sand withdrawn from the Port Ever­ sea level to rise a conservative 0.3 m glades to Dania coastal segment over the last 65 (]ASTROW et al., 1990). Such a rise in sea years resulted in a net loss of at least lOx 106 level is regarded as unlikely or problematical by m3 (including additions by littoral drift). some critics (e.g. IDSO, 1989) and possibly not a basis for taking immediate engineering action DYNAMICS AND TIMING OF LARGE­ (e.g. KAZMANN, 1992). An attempt to deduce SCALE PROCESSES, AS THEY AFFECT the present climate pattern in terms of cyclic COASTAL FRAl\fEWORKS changes from interpretation of paleoclimates suggests to some researchers that the present Most investigations of large-scale processes warm trend is simply an oscillation in the have focused on the role of sea level in produc­ interglacial period but may well continue if ing coastal erosion, mainly by evaluation oflong­ greenhouse gases keep building up in the atmo­ term rise due to glacial melting and thermal sphere. On the other hand, there may be a expansion of sea water. From a dynamical point possibility of a rapid degradation of the present of view, there are several other major mega­ warm conditions as the climate collapses into a processes that affect shoreline change. These another glacial cycle (IDSO, 1989). Not knowing include climatic change and periods of stormi­ the direction of future climate change is therefor ness, variations in sediment discharge into the generally a predicament and one might wonder oceans, atmospheric forcing of sea-surface if, at least in principle, it is even possible to height, climatic forcing of longshore drift, and predict abrupt climatic change from long-term geostrophic balance between ocean currents and trends. Ifa significant portion ofclimate variabil­ the offshore sea-surface slope, among others. In ity is probabilistic in nature, as suggested by addition to the long-term changes in sea level, MITCHELL (1976), the predictive value of there can be significant fluctuations at climate modeling for determining abrupt change periodicities of days or weeks that can cause may be limited (BERGER and LABEYRIE, short-term sea-level changes on the order of 10 1987; IDSO, 1989). to 30 cm (KOMAR and ENFIELD, 1987), Translation of global trends in sea level to depending on the configuration ofspecific coastal assessment of local rates of erosion presents locations. many problems. Rough estimates, based on closure depths (generally accepted as 10 m along Climate Change the U.S. Atlantic coast), suggest that some losses must be apportioned to sea-level rise (i.e. equi­ Global warming is a recent manifestation of librium response of shore profile to increased climatic change claimed to be brought about by water depth) on a decadal time scale. Evaluation the so-called "Greenhouse Effect. " According to of coastal land loss volumes due to erosion its proponents, if the man-made increase in associated with the combined effects oflongshore currents, offshore transport, and sea level rise of lorder of 4-6 x 106 m3• In contrast, the older 1-3 mm yr-1 in Broward County suggests annual perched barrier which today forms the mainland losses on the order of 4600 m3 km-1 (COASTAL beach at the John U. Lloyd State Beach Park, PLANNING & ENGINEERING, 1985). Based was then about 150-200 m wide by 5 m or so on land loss estimates for John U. Lloyd Beach thick by at least 9 km long giving a sediment in the interva11976-1985, over 90% of the beach volume around 6-10 x 106 m3• materials moved offshore to achieve the equilibri-

Journal of Coastal Research, Special Issue No. 18, 1993 68 Fink! um profile at a closure depth of7 m (COASTAL Some fluvial sediments and reworked channel PLANNING & ENGINEERING, 1985). The materials associated with inlets are, however, offshore transport of beach material was a re­ deposited as flood- and ebb-tidal deltas. Ebb­ sponse to the cumulative effects of increasing sea shoal storage along the Florida east coast, for level and interruption of longshore drift by the example, is estimated to be about 420 x 106 m3 strong tidal jet in the Port Everglades navigation­ (MARINO and MEHTA, 1988). al entrance. RIGGS et ale (1992) describe how Quaternary fluvial sand and gravel sediments were brought Sediment Discharge into the Oceans across the coastal plain to the Carolina coast during periods of lowered sea level and subse­ Evaluation ofworld budgets of riverine materi­ quently transported onshore and alongshore by als discloses that river loads are not only essen­ transgressive phases. Although the provenance of tial to information databases of land erosion rates silica sand comprising northeast Florida beaches (e.g. MEYBECK, 1988) but also to estimates of was probably from weathered crystalline rocks in the delivery of river sediments to the oceans Georgia and the Carolinas, there is an increasing (MILLIMAN and MEADE, 1983). In spite of contribution of carbonate materials in southern the fact that anthropogenic actions have stimulat­ coastal segments. The greater carbonate content ed landsurface erosion so that present rates of of southern beach sands is largely due to inputs erosion are much higher than rates prior to from recycled shell fragments from widespread farming and deforestation (which has paleotopographic surfaces now exposed offshore only been on a major scale in the United States in the Anastasia Formation as well as contribu­ during the last 100-200 years, but in Europe and tions from contemporary biogenic sources such the Middle East began 2000-6000 years ago) as contemporary Halimeda platelets. In spite of (MILLIMAN and SYVITSKI, 1992), construc­ biogenic and offshore carbonate sources, silica tion of dams and improved land stabilization sand still comprises a significant proportion of techniques have greatly reduced sediment input beach materials (about 50% by composition) as (NRC, 1987; HOLLIGAN, 1992). Before the far south as Broward County. Quaternary fluvial proliferation ofdam construction in the latter half sand and gravel sediments were brought across of this century, rivers probably discharged about the coastal plain to the Carolina coast during 20 x 109 t of sediment annually to the ocean periods of lowered sea level, as described by (MILLIMAN and MEADE, 1983). Trapping RIGGS et ale (1992), and subsequently transport­ sediment from the Amazon River alone will, ed onshore and alongshore by transgressive according to McLENNAN (1993) account for a phases. further 6 % drop in global sediment discharge. In the example of the Ebro River which discharges Sea-Level Change into the western Mediterranean, the present annual sediment discharge of 1.5 x 105 t into the World sea levels have fluctuated dramatically sea is less than 1% of the discharge before throughout geologic history. Low sea-level stands construction of the dams (GUILLEN and in the Tertiary may have been as much as 300 m PALANQUES, 1992). This kind of extreme below high levels in the early Cenozoic (VAIL et reduction in sediment supply allows marine al., 1977; WORSLEY et al., 1984). More erosional process to dominate many coastal recently and by way of contrast, about 120,000 segments as they become sediment starved. In years ago eustatic sea levels were 2 m or more addition to the decrease in sediment supply from higher but in the last glacial maximum (about upland source areas to the north of Florida, the 15,000 years ago) sea levels may have been interruption of natural littoral drift systems by about 135 m below today's levels (ANDREWS, engineering works such as stabilized inlets along 1987). Short-term eustatic fluctuations seem to the Florida east coast further contributes to exhibit less amplitude than those associated with coastal erosion by diverting sediments offshore. greater spans ofgeologic time and tend to exhibit

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 69 high-frequency cyclicity dominated by Quaterna­ Estimates of present sea-level rise, based on ry depositional patterns (RIGGS et al., 1992). study of tide gauges located in some of the more The slope of the continental shelf between stable coastal regions in mid-oceanic locations Miami and Palm Beach is comparatively steep, (e.g. PIRAZZOLI, 1986) or in the Caribbean with the shelf break being only about 8 km region (UNEP, 1988), indicate an increase of 1.0 offshore (along the 200 m depth contour) to 2.0 nun yr-1 (WARRICK and OERLEMANS, (TEALE, 1948). The mean axis of the Florida 1990). Some scenarios for sea-level rise under Current (Gulf Stream) is about 27 km offshore global warming, though still somewhat uncertain, where it flows northward at a maximum velocity predict increasing rates that may be three to six of about 2.8 m sec-1 ; a low-velocity counter times those over the last century (HOUGHTON current usually flows southward between the Gulf et al., 1990). Stream and the shore, but may be accelerated or In addition to pulsatory changes in sea level reversed by longshore winds (MAUL et al., due to the associated effects of global warming, 1990). there are short-term changes that can be related to other causes such as dynamic fluctuations in Long-Tenn Changes oceanic circulation patterns. Thenatural variabili­ ty of flow regimes, ofwestern boundary currents The causes of long-term fluctuations in sea for example, is an additional mechanism which level are related to many factors including post­ can force sea-level change in some areas over glacial isostatic rebound, hydroisostasy, changes time spans ofdecades to centuries. Global warm­ in the Earth's rotational axis, tectonic move­ ing should lead to global weakening of ments, and deep mantle convection (GURNIS, geostrophic circulation as the equator-pole ther­ 1992; MORNER, 1992). Decreased mid-ocean mal gradient decreases. Such short-term fluctua­ ridge volumes coupled with lithosphere destruc­ tions in sea level have a more direct bearing on tion in oceanic trenches, as associated with a contemporary conditions along the southeast decrease in global spreading rates, resulted in a Florida coast and, perhaps more importantly, corresponding lowering of eustatic sea level they exhibit a potentially causal relationship with during the past 80 million years beach morphodynamics. Annual or inter-annual (ENGEBRETSON et al., 1992). Field evidence changes in sea level along the Florida coast are for first-order changes in eustatic sea level is of related to changes in the mass transport of the the same order as predicted models using simple Gulf Stream which ranges from about 15 x 106 assumptions about the overall distribution of m3 sec-I to 38 x 106 m3 sec-I, but averages about lithosphere entering trenches coupled with global 26 x 106 m3 sec-1 (STOMMEL, 1965). Maxi­ spreading rates. Operating on the same time scale mum cross-stream slopes between Cat Key of orogeny and climate change (i.e. 10 to 100 (Bahamas) and Miami, which are asymmetrically Ma), these geodynamic concepts reflect the displaced (down) toward the Florida coast and capacity of the world's ocean basins to hold amount to about 1 m, occur in July when the water ("tectono-eustasy"), but do not involve flow is the strongest. An increase in GulfStream glaciation ("glacio-eustasy"). transport causes a lowering in sea level along the southeast US coast and, conversely, when the Short-Tenn Changes transport decreases there is a corresponding rise in sea level (KOMAR and ENFIELD, 1987).The Even though there is a general consensus that decrease in current velocity means that the Gulf a global increase in sea level is presently occur­ Stream surface is less tilted by the Coriolis force ring, the data are based on inference from study and water levels will ride higher up on the US of tide gauge records (e.g. PIRAZZOLI, 1986; shore. It is interesting to note that with the DOUGLAS, 1991), the distribution of which breakdown of the Bermuda-Azores atmospheric around the world is very skewed and poor for high-pressure cell, the northern fringes of the determining a global average (WUNSCH, 1992). trades disappear and there is an accompanying

Journal of Coastal Research, Special Issue No. 18, 1993 70 Finkl decrease in transport ofwater through the Florida COASTAL & OCEANOGRAPIDC ENGINEER­ Straits. ING LABORATORY, 1969; MOORE, 1979; In the vicinity of Miami these annual differenc­ COASTAL PLANNING & ENGINEERING, es in sea level may amount to something on the 1985; CUBIT, 1986; COASTAL TECHNOLO­ order of 9 cm and, according to STOMMEL GY, 1988; OLSEN ASSOCIATES, 1990; HAR­ (1965), may be partly related to the wide zone of RIS, 1991; MEHTA et al... 1991). Nevertheless, anticyclonic vorticity where the channel is only there is still incomplete understanding ofregional about half as deep and wide as at Key West and sedimentary dynamics -- at least in terms of the conservation of potential vorticity of the gross littoral flow patterns, temporal sequestering isopycnic surfaces toward Miami to counteract in storage basins, and loss to the littoral system the axial pressure gradient in the upper accelerat­ due to offshore transport. Natural littoral cells of ing layers of the Gulf Stream. The effects of the type originally described by INMAN and maximum sea levels occurring in September and CHAMBERLAIN (1960) along the central Cali­ October, partly caused by summer heating of the fornia coast are bounded by submarine canyons. water and decreasing transport rates In a comparable way the jettied inlets along the (ZLOTNICKI, 1991), may continue into the late southeast Florida coast generally constitute end fall or early winter months when the coast is members for drift cells. Sediments comprising affected by strong frontal systems that produce the so-called longshore "river of sand" reside in northeasters and cause much beach erosion. beach deposits, in flood- and ebb-tidal deltas, and Severe episodes of beach erosion sometimes in offshore inter-reefal depressions. result from effects related to the passage of strong frontal storm systems, as described for Flood-Tidal Deltas, Ebb-Tidal Deltas, and much of the mid-Atlantic coast (e.g. DOLAN; Interior Sand Traps INMAN, and HAYDEN, 1988), combined with phases of slightly higher sea levels associated The ebb-tidal delta, a dominant feature of most with the delayed effect of summer heating of coastal inlets (MOSSA et al., 1992), occurs Gulf Stream waters (steric lag) and decreased when sediment is deposited offshore ofthe mouth transport rates. FAIRBRIDGE (1989, 1992), or navigational entrance. Sediment removed from describing these types of re-enforcing (positive) the littoral drift system is typically accumulated feedback mechanisms as "crescendo events," has in a crescent- or kidney-shaped feature which emphasized that it is not the small pulsatory may serve as a platform where sediments can be changes that are so important in themselves but transported from the updrift beach to the their coincidence in a spatial and temporal frame­ downdrift side of the inlet (OERTEL, 1988). work which produces a combined effect greater Large shoals constitute a potential source of than anyone of the components. Specific rates of sediment for beach replenishment. Factors affect­ perigee-syzygy tidal maxima, when reinforced by ing the use of this material in beach frootal storms, have been documented by WOOD renourishment projects include ratio of stored (1986) and account for almost every destructive sediment to amount needed, accessibility, grain event since colonial times. Wood's list of these size, tidal range, and wave climate for dredging. danger signals for the last decade is reprinted in Adverse impacts related to shoal removal may be FAIRBRIDGE and JELGERSMA (1990). related to navigability of the inlet or increase in wave energy reaching the shore. SEDIMENT SOURCES, SINKS General characteristics of the Florida continen­ AND BUDGETS tal shelf environment, relevant to sedimentary transport, include a narrowing in shelf width Sediment budgets have been worked out for from north to south, at least to the Lake Worth many of the Florida east coast inlets (see for Inlet after which the width narrows to a nearly example: FLORIDA ENGINEERING & INDUS­ constant width of about 2900 m. The spring tide TRIAL EXPERIMENT STATION, 1965; range in the northern inlets is somewhat higher

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 71 than in those from Sebastian Inlet to the south, the jetty. Loss ofsand from the downdrift beach, and there is a general but non-uniform decrease due to jetty construction, is also related to off­ in ebb-shoal storage and littoral drift rate from shore transport of sand into deeper water north to south (MARINO, 1986). (COASTAL and OCEANOGRAPHIC ENGI­ From laboratory studies on the development of NEERING LABORATORY, 1969). ebb-tidal shoals (e.g. MAYOR-MORA, 1977; OZSOY, 1986), it was concluded that sediments Case Studies of Sediment Transport in the supplied by littoral processes are entrained into Vicinity of the South Lake Worth Inlet the tidal residual circulation and finally deposited in the shoals and that the pattern of deposition South Lake Worth Inlet lies about 25 Ian south depends on bottom friction, slope, inlet current of the Lake Worth Inlet and about 23 Ian north intensity, and the size of the sediment. Another of the Boca Raton Inlet in Palm Beach County important relationship is that as the tidal prism (Figure 1). Erosion south (downdrift) of the inlet increases so does the inlet area (JARRETT, was observed soon after its opening in 1927. 1976; WALTON and ADAMS, 1976). Sand was quickly impounded along the north In addition to laboratory studies (controlled jetty and drifted into the inlet creating a large environments where the variables are limited), flood-tidal delta. Several systems designed to empirical observations suggest that inlets may reduce the adverse impacts of the inlet on sedi­ behave more dynamically in natural settings ment transport were implemented as early as where their natural evolution as well as their 1932 (EDGE, 1986), including hard engineering engineered stabilization may dramatically affect structures such as sea walls, groins, and revet­ adjacent shorelines. WALTON (1974), for ments that were accompanied by a sand bypass example, illustrates one impact of inlet cutting system in an attempt to establish a littoral equi­ where the St. Lucie Inlet (opened in 1892 and librium across the inlet. Most attempts, however, later jettied in 1926-1928) caused a 1000 m failed to have significant impact on beach erosion retreat of the southern downdrift shoreline, the south of the inlet. Recommendations for im­ majority ofwhich took place prior to 1948 for an proved sand management in the 1960's (e.g. astonishing annual rate of shoreline recession of BRUUN et al., 1966) included curved extensions 20-25 m yr-I . No ebb-tidal delta existed prior to to the north jetty, increased capacity of the fixed the inlet being opened. MARINO (1986) reports sand bypass plant, and construction of a mobile that the southern lobe of the ebb shoal that bypass system. In spite of attempts to increase developed in direct response to inlet cutting now sand bypassing, the net deficit in downdrift lies directly over the location ofthe pre-construc­ supply of sediment caused continued erosion for tion shoreline. Although there was significant several km along the beach south of the inlet so shoreline retreat, some of the sand eroded from that today there is an 88 m landward offset of the downdrift beaches was washed through the inlet mean high water lines between the north and and deposited in the lagoon behind the northern south beaches immediately adjacent to the inlet. part ofJupiter Island. MARINO (1986) estimates Net littoral drift occurs from north to south that sand sequestered in this way contributed near the inlet. A portion of the southward drift­ about 500,000 m2 to the island's areal extent. ing sand is directed seaward to the ebb-tidal delta MEHTA et ale (1991) interestingly report, by the inlet's hydraulic influences on the littoral from field studies of Jupiter Inlet, that sand is system. A northward elongation of the ebb shoal often transported around the south jetty and into extends about 985 m north of the inlet, apparent­ the inlet by eddy currents during ebb-tidal flows 1y in response to a drift reversal during the and, when waves are from the northeast. These summer months. The northward shoal extension patterns of sediment transfer around the jetties may also be influenced by changes in the littoral thus seem to control the influx of sand into cell as a result of sand impounding against the interior traps and flood-tidal shoals thereby north jetty. Sediments in the littoral system that contributing to downdrift beach erosion south of continue to drift south are either (1) impounded

Journal of Coastal Research, Special Issue No. 18, 1993 72 Finkl against the north jetty fillet, (2) mechanically ment is moved past the inlet in the littoral drift transferred south of the inlet by the sand bypass­ system each year. From his studies of fross ing plant, (3) carried landward or seaward of the transport, Bruun suggest that 53 x loJ mare inlet by flood and ebb tidal currents, or (4) mechanically bypassed annually, 38 x 103 m3 are naturally bypassed to the south of the inlet. directed seaward beyond the -2 m isobath, and Sand accretion north of the inlet has extended 69 x loJ m3 shoals in Lake Worth. Completing the shoreline approximately 65 m seaward from the most recent evaluation of the inlet's sediment its pre-inlet location. Some of the sediments budget, BODGE (1990) reports that differences carried into the inlet are deposited in a flood-tidal between his and Bruun's budgets can be attribut­ delta that contributes to the areal expansion of ed to the 1967 jetty modifications. Bodge esti­ Beer Can Island to the north of the inlet interior. mates the average rate ofebb-shoal accumulation Material which enters the inlet but does not shoal to be about 30 x loJ m3 from 1927 to 1955 and or settle in the sand trap, which is periodically lOx loJ m3 thereafter for rates of about 1 x 10' dredged, is swept seaward by ebb-tidal currents. m3 current annual accretion. His estimates of Sand deposited alongshore of the ebb shoal decreasing annual flood-shoal accretions range accumulates 700-1000 m south of the inlet. from 42 x loJ m3 from 1927 to 1945, 30 x loJ Strong currents in the inlet (2.6 m sec-1 during m3 from 1946 to 1966, and 3.8 x 10 m3 per year spring tides) may jet a significant portion of the from 1966 to 1990. drift seaward of the terminal lobe (approximately These sediment budgets indicate that beaches to -4.6 m MSL) during ebb tides. Sand transported the north of the inlet are accreting at an average beyond the so-called "closure depth" is effective­ rate of about 11 % of the net drift rate, i.e. 16.8 ly removed from the near shore transport system x 103 m3 yr-1 or approximately 1.3 m yr-1 The (DEAN and O'BRIEN, 1987). computed drift rates south of the inlet ranged from 109 x 103 m3 yr-1 to 147 x 103 m3 yr-1 and Characteristics of the Ebb-Tidal Delta averaged 84 % of the drift rate north of the inlet. This suggests that the inlet acts as a littoral The ebb shoal began to develop seaward of the barrier to approximately 16 % of the net drift inlet shortly after its construction in 1927. toward the south (BODGE, 1990). According to BODGE (1990) reports that the shoal contains Bodge's budget, the inlet removed about 17 % of 6 3 between 1.2 and 2.3 x 10 m of sediment, the net drift from 1955 through 1975 and approx­ 3 1 accreting at a rate of about 9740 m yr- • The imately 42 % of the net drift from 1929 to 1955. shoal, which occurs as a wide plateau between -1 In sum, erosional rates of the downdrift beach to -3 m isobaths, moves landward in the summer range from 0.3 m to 1.3 m yr-1 with a net loss to months in response to increased onshore trans­ the littoral system south of the inlet possibly as port under the influence of the southeast trade large as 3.4 x 106 m3 since construction of the winds and swell. The shoal migrates seaward inlet. during the winter months when long northeast swells increase erosion and turbulence in the Impacts of the South Lake Worth Inlet on nearshore zone. This seasonal movement results the Adjacent Beach and Nearshore Zone in a 30 to 65 m annual shift in the center of the shoal (BODGE, 1990). Sediments comprising the Changes in the natural sediment transport shoal are poorly to well graded sand with varying system are reflected in nearshore morphologic proportions (generally less than 10 %) of shell. features, distribution of coastal vegetation, and These sediments are considered to be a potential wave and current patterns. Aerial photographs source of sand for beach renourishment. and on-site visual observations suggest that the shoreline exists in a stable to accretional condi­ Sediment Budget at South Lake Worth Inlet tion for a distance of 1 or 2 km north of the inlet. This area (Manalapan Beach) has accreted BRUUN (1964) estimated that a gross transport about 30 x 103 m3 of sand since the 1967 jetty volume of approximately 160 x 103 m3 of sedi-

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 73 improvements (CAMPBELL, 1985). Shore Retreat of shorelines due solely to rise in mean profiles with a dissipative to intermediate sea level may be estimated by reference to any longshore bar-trough domain, similar to the types one of several paradigms that quantify shoreline described by CARTER (1988), north of the inlet change. Basically, rates of shoreline change (i.e. are characterized by well-vegetated backshore shoreward translation) are related to incremental dunes, wide terraced berms, a low-angle fore­ rise of sea level and, in one way or another, are shore, and multiple inner sand bars in the surf extensions or refinements of beach response zone. Profiles down to the 6 or 7 m isobath are, models such as the Bruun Rule (see discussion in however, steeper than those documented in 1929 KOMAR, 1991). This concept of a simple equi­ (USACE, 1961). In contrast, profiles south of librium profile model is commonly used as a the inlet are characterized by higher angled, basis for projecting storm-induced profile change erosional dune scarps, narrower to non-existent and erosion due to elevated water levels berms and steep foreshores. The nearshore is (KRIEBEL et al., 1991). Although the model more typically intermediate to reflective. Evalua­ may at first seem to have almost universal appli­ tion of bathymetric surveys from 1883 to 1990 cation, it is limited by several initial assumptions suggest that the inner and outer longshore bars that confine its applicability to some rather have migrated shoreward becoming welded onto specialized coastal environments where (1) wave the mainland as part of a hydrodynamic re­ climate variations are not responsible for varia­ adjustment of nearshore deposits similar to that tion in the shape of the equilibrium profile, (2) described by FINKL (1992) for barrier spits in the shoreface is a two-dimensional system which the vicinity of inlets at New River (now closed) terminates seaward at the closure depth and and Port Everglades. Rock reefs (comprised of landward on the upper beach, (3) offshore bars worm rock or the Anastasia Formation) thinly are not important in determining profile adjust­ overlain by cover sands are frequently exposed ment to wave orbital interaction, and (4) there is by erosional processes in many locations both no cross-shore transport of sand across the depth above and below mean sea level (MSL). Expo­ of closure (PILKEY et al., 1993). sure of these shore parallel rock outcrops shows Although background rates ofshoreline regres­ how they affect the location and migration of sion due to rising RSL in this region are relative­ alongshore channels (STROCK, 1982). ly insignificant on an annual basis (see previous discussion and FAIRBRIDGE, 1989), the process CAUSES OF BEACH EROSION IN would become more significant on a decadal time SOUTHEAST FLORIDA scale especially if sea-level rise accelerates in response to the 'Greenhouse Effect' (RIND, The relative sea-level rise in this region, esti­ 1987). The amount of coastal land loss would mated to be in the range of about 1-4 mm yr-1 correspondingly increase and such losses would (WANLESS, 1989), causes maximum back­ become issues ofincreasing concern along devel­ ground shoreline regression rates of about - 0.3 oped coasts. to -0.4 m yr-1 (DOLAN et al., 1983) for the Florida Atlantic coast. The construction of deep The Relation Between Coastal Engineering navigation entrances, such as those serving Port Works and Beach Erosion Everglades and the Port of Miami, which are dredged to about -15 m, inhibits natural sand When designed and deployed in an appropriate bypassing. Long jetties, particularly those on the manner in an environment suitable for their updrift (north) sides channels, promote offshore placement, many coastal structures (e.g. groins; sand transport further exacerbating inadequate floating, offshore, or submerged breakwaters) downdrift sand supply. can effectively mitigate erosion induced by waves and currents (COE, 1986). One innovative Impacts of Relative Sea-Level Rise example is the Prefabricated Erosion Prevention Reef (PEP Reef), a submerged breakwater that

Journal of Coastal Research, Special Issue No. 18, 1993 74 Finkl was installed off Palm Beach in 1988. The PEP ALTERNATIVE SAND SOURCES FOR Reef reduced offshore sediment losses that were BEACH REPLENISHMENT associated with normal summer storms and was also effective during the high energy conditions Artificial beach replenishment provides an resulting from Hurricane Andrew, a major storm albeit temporary respite from shoreline erosion that made landfall in Miami (AMERICAN which is accelerated by stabilized inlets above the COASTAL ENGINEERING, 1992). Jetties, on general background levels associated with the other hand, are primarily designed to direct eustatic and local causes. Nevertheless, it seems and confine water flow into a channel and to to be the only practical means of controlling prevent or reduce shoaling of the channel by the beach erosion. Consideration ofinlet closure is a littoral current (COE, 1984). Although they requirement of inlet management plans, but the stabilize inlets on open coasts, they invariably concept is not really a viable option for large interrupt littoral drift patterns causing much of inlets because it would raise havoc with the local the critical erosion of sandy beaches on the economy and probably initiate long-ranging and Florida east coast (DEAN, 1990). Erosion imme­ undesirable political consequences. Some form of diately downdrift of the lee jetty typically takes enhanced bypassing, possibly combined with the form of a log-spiral curve, as described by beach replenishment, thus seems to be the only SILVESTER and HSU, 1993), and extends for a practical solution to critical beach erosion in distance of at least 700-1,000 m downbeach. some areas. Recent studies (this volume) suggest that the At first glance, sand in the south Florida envi­ effects of erosion caused by navigational en­ ronment would hardly seem to be a scarce com­ trances may, in extreme circumstances, extend modity. Although there are large sand deposits 10-15 km downdrift. sands inland, along the coast, and offshore, The inlets along the southeast Florida coast materials suitable for beach replenishment are not were cut to facilitate commerce and trade (e.g. overly abundant and they must meet rather Palm Beach, Fort Lauderdale, Miami ), for flood stringent specifications. Ideal deposits are largely control (e.g. Hillsboro), or to enhance water composed of fine to medium sand-sized grains quality (e.g. South Lake Worth Inlet). Cruise (0.074 - 2.0 nun median diameter) that are loose, ships, which now regularly use the ports of Palm with few rock fragments and little or no organic Beach, Fort Lauderdale (Port Everglades), and matter; fine-grained components (silts and clays) Miami, are an important aspect of the Florida should account for no more than 7.5% by weight tourist industry as are sport fishermen and boat­ (COE, 1984). Additionally, south Florida beach ers who use all of the inlets serving these impor­ sands often exceed 50% by weight carbonate tant commercial centers. Because the inlets are a content. The wide variety of potential local crucial link in the existing coastal infrastructure, sources includes inland quarry sands, previous it is economically essential to effectively mitigate spoil materials, dredged material from the their adverse effects on coastal beaches which ICWW or port expansion projects, flood- and themselves are multiple-use features related to ebb-shoals at inlets, and inter-reefal sands off­ recreation, storm protection, and natural habitats. shore. Even though shoreline changes in the vicinity Inland sand sources initially seemed like an of inlets show periodic advance and retreat, the attractive alternative because of their low silt and overall long-term trend is one of pervasive organic matter contents. Closer inspection, downdrift erosion (COASTAL TECHNOLOGY, however, shows that grain sizes tend to be 1988). Because most inlets along the southeast smaller than native beach sands and this could be Florida coast mimic this general trend, it be­ a serious disadvantage because the finer particles hooves coastal specialists to advance the ques­ will be winnowed out by wave action and when tion, "What can be done to alleviate the entrained in the water column they could be downdrift erosion that is caused by jettied in­ transported and deposited on living coral reefs. lets?" Additional disadvantages are related to the over-

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 75 land transport of large quantities of fill that normally afford are lost. Instead of damping would typically be required for beach replenish­ wave energy as it approaches the shore, the ment, viz. about 1 x 106 m3• The Florida Depart­ reduced shoals allow increased wave energy to ment of Transportation estimates a 50% reduc­ reach the shore, and this accelerates shoreline tion in road life would result from the haulage of retreat. Also associated with the hazards of 38,500 truck loads during a S3 week period, and dredging in a high energy zone over ebb shoals when this additional cost is charged back to are the possibilities of increased turbidity in the beach replenishment projects, the plan becomes water column, siltation of coral reefs, and burial uneconomic. ofhard grounds. Once large quantities of shoaled Other sources also look less attractive upon sediments are removed, there is no guarantee of close inspection, for a variety of different rea­ full replacement along this sediment-starved sons. Most previous spoil materials have already coast. Thus, there are several reasons why ebb­ been developed, are generally inaccessible, or are shoal mining needs to be regarded with caution. unusable as beach fill. Aside from deposits Having failed to locate potential inland and associated with flood-tidal deltas and some nearshore sand sources to sustain beach replen­ channel deposits residing in or near the ICWW ishment activities, one may hopefully return to (e.g. Jupiter Inlet-Hobe Sound), the waterway the offshore borrow sites that in the recent past contains few coarse-grained deposits ofsufficient have provided large quantities of suitable beach­ volume to warrant development as beach fill. It fill materials. Although originally it was perhaps is perhaps worth noting that the ICWW is largely tacitly assumed that there were immense offshore cut through bedrock to a maintained channel sand sources that could provide suitable fill on an depth of about 4 m. The rock-cut channel is ad infinitum basis, it is now becoming painfully stable (does not meander) and mainly accumu­ clear that offshore sand sources are indeed finite. lates fine-grained sediments that are often pollut­ Furthermore, it is clear that fairly large initial fill ed due to the scavagening effects ofclay minerals volumes are required prior to regular mainte­ and other chelates (complex organo-metallic nance (Figure 4). Recently it has been realized macromolecules). A similar situation occurs in that the offshore sand bo~ies occupy relatively the Port Everglades turning basin where the shallow depressions between reef tracts basin's floor had to be blasted prior to dredging (paleoshorelines) and that old borrow areas may to its present depth of 10-13 m. Little sediment not necessarily refill with sediments that are accumulates in the deep entrance channel, al­ suitable for beach replenishment, (that is to say, though some polluted fines accumulate in parts of they may refill with finer-grained sediments, may the turning basin, and there are no plans for port not reach predredging capacities for decades, or expansion in the immediate future. Sediment even may become anoxic). All this means that sources from here are clearly limited. the potential of offshore borrows is definitely With the lack of suitable sand sources inland, limited. The usefulness of inter-reefal sediments attention turns to the littoral zone offshore where as beach fills may be limited by intercalated there are suitable beach-fill materials sequestered organic matter and content of rock, silt, and in ebb-tidal deltas and inter-reefal tracts. With clay. Estimated sedimentary reserves have been nearly 420 x 106 m3 of ebb-shoal storage along categorized on the basis of more or less than 5 % the Florida east coast (MARINO and MEHTA, rock content (Figure 5), maximum percent silt 1988), mining these materials might seem to be and clay, and sands with less than 7.S % silt an attractive proposition. There are, unfortunate­ content (Figure 6). Just how limited these off­ ly, several disadvantages associated with the shore sand sources may be remains a moot point mining of large sediment volumes from ebb­ for now but present estimates of remaining fill shoals. Previous experience has shown, for quantities offshore indicate that there may be example, that mining of these shoals may signifi­ insufficient offshore quantities to support two cantly modify the bottom bathymetry in such a more replenishment operations at John U. Lloyd way that the protective effects that the shoals State Beach Park and Hollywood. The main point

Journal of Coastal Research, Special Issue No. 18, 1993 76 Finld

SEDIMENT VOLUMES ABOVE BEDROCK

• Shoreface a 3rd Inter-reefal Rat

rn 2nd Inter-reefal Flat

o 1st Inter-reefal Flat

Figure 4A. Offshore sediment volumes,jill requirements, and quality ofborrow reserves. Estimated reserves compared subregionallyfor the Miami area, Miami-Broward area (northern Dade County), Broward County, and Palm Beach County (PB Cty).

FILL REQUIREMENTS IN SE FLORIDA 4_. 3.~ - 3_ - 2.s_

~ i- I.s_ ~

I- i- ~}~ o.s_ .. ,:. ~ I'·' "" 0_ ...... I I

-• Annual Maintenance Fill Requirement o Initial Placement Figure 4B. Offshore sediment volumes, jill requirements, and quality ofborrow reserves. Estimated jill requirements, initial and average annual maintenance, for selected coastal segments where JI= Jupiter Inlet, LWI = Lake Worth Inlet, BRI = Boca Raton Inlet, BCL = Broward County Line, PBCL = Palm Beach County Line, HI = Hillsboro Inlet, PE = Port Everglades, D = Dania, HH = Hollywood-Hallandale, HB = Haulover Beach, BH = Bakers Haulover, GC = Government Cut, KB = Key Biscayne, and VK = Virginia Key.

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 77

REMAINING FILL QUANTITIES FILL VOLUMES BY % ROCK

3.5

3 3

2.5

10". m' 2 2 10".m' 1.5 1.5

0.5 0.5

o o DlIIHB PBIlBTS Fll JULP HWIHl OflIHB P81LBTS Fll JULP HWIHL • Total Fill • < 5% Rock 0> 5% Rock Figure 4C. Offshore sediment volumes, jill requirements, and quality of borrow reserves. Figure 5. Estimated sedimentary reserves in Remaining offshore borrow capacities regardless offshore borrow areas represented by millions of ofquality or suitabilityfor beach renourishment. cubic meters with greater or less than 5 percent DB/HB = Deerfield Beach/Hillsboro Beach, rock (limestone) content. DB/HB = Deerfield PBILBTS = Palm BeachlLauderdale-by-the-Sea, BeachlHillsboro Beach, PBILBTS = Palm FIL = Fort Lauderdale, JULP = John U. Lloyd BeachlLauderdale-by-the-Sea, FIL Fort State Beach Park, HW/HL Holly­ Lauderdale, JULP = John U. Lloyd State beach wood/Hallandale. (Modified from Duane and Park, HW/HL = Hollywood/Hallandale. (Modi­ Meisburger, 1969). jied from Coastal Planning & Engineering, 1985). here is that it is not the total amount of offshore sand that is available for replenishment but rather near Miami (BODGE and OLSEN, 1992). Place­ amounts that are "acceptable" for extraction and ment costs, estimated to be about $13 m-3, are at use (Figure 7). Current estimates of acceptable least twice the cost ofnatural offshore fill materi­ beach fill materials stored offshore in inter-reefal als that could be placed several times a year by tracts along Broward County range from 3.8 x small hopper dredgers with pump-out capabilities 106 m3 at Deerfield Beach/Hillsboro Beach to a (BRUUN, 1992). Aside from the high costs mere 0.32 x 106 m3 for John U. Lloyd Beach associated with its placement, there are many (COASTAL PLANNING & ENGINEERING, environmental considerations that require assess­ 1985). ment. Among these are possible adverse impacts Aragonite (crystalline CaC03), widely available on sea turtle nesting habitats along southeast on the Bahama banks with reserves estimated to Florida beaches. Such considerations are impor­ be on the order of 70-90 x 109 t (EARNEY, tant because sea turtles are an endangered species 1980), has also been suggested as an alternate that depend on Florida beaches for suitable sand source. Importation of aragonite into the materials in which to dig nests. Parameters United States was, until recently, illegal, but now apparently related to successful clutch hatching in it has recently become potentially available beach sands include: incubation temperatures, because it is now permitted by the U.S. Depart­ levels of relative humidity and oxygen within ment Agriculture. A field test of its suitability on pore spaces between sand grains, grain-size the Florida east coast is presently being conduct­ distributions of the beach sands, compaction, ed in the small littoral drift cell of Fisher Island steepness of the beachface, width and elevation

Journal of Coastal Research, Special Issue No. 18, 1993 78 Finkl

Percent Fines in Offshore Borrows

100

80

% 60

40

20

o DBlHB PBlLBTS FLL JULP HWIHL •% Max Silt + Clay % Sand with < 7.5% Silt

Figure 6. Percent fine-grained materials in offshore borrows, based on percent sand with less than 7.5 percent silt content and percentage of maximum silt plus clay content at renourishment sites. DB/HB = Deerfield Beach/Hillsboro Beach, PBILBTS = Palm BeachlLauderdale-by-the-Sea, FU = Fort Lauderdale, JULP = John U. Lloyd State Beach Park, HW/HL = Hollywood/Hallandale. (Modified from Coastal Planning & Engineering, 1985). of the benn, among others (MRSOVSKY, 1987; edges. It is well known, in some coastal areas, MORTIMER, 1990). Aragonite beaches may be that glass particles winnowed out of coastal less desirable for turtle nesting sites because their rubbish dumps have accumulated in large enough cooler temperatures tend to produce a high male quantities to produce a glass beach. Examples of to female sex ratio among hatchlings (YNTEMA such 'natural' processes include beaches along and MRSOVSKY, 1982) and because the coarser the west shore of Lake Michigan (north of more loosely packed aragonite beaches (com­ Chicago) in the late 1940's and early 1950's and pared to beaches composed of native sand) tend presently at Glass Beach near Fort Bragg, Cali­ to cause nest cave-ins from which many hatch­ fornia. Advantages of recycled glass include a lings are unable to escape (MANN, 1977). In composition similar to natural silica sand beaches spite of the potential environmental drawbacks (Broward County beaches are about a fifty-fifty associated with the importation of exotic beach mix of silica and carbonate grains), grain size fill materials such as Bahamian aragonite, the can be controlled prior to placement, and it depletion of offshore borrows may leave many probably will cost about the same or less than coastal communities with few options for stabi­ other natural materials. Disadvantages mainly lizing accelerating rates of shoreline retreat. focus on the potential quantities that might be­ A new alternative in the search for beach come available. Although tonnages in private renourishment materials is the possible use of recycling programs are carefully guarded by reclaimed glass, i. e. mixed crushed glass cullet proprietary concerns, it is rougWy estimated that that can be further processed to predetermined Palm Beach, Broward, and Dade counties each size fractions and tumbled to remove sharp produce about 9-11 x 103 t of glass annually for

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 79

not a drop to drink" and recant instead "Sand, ESTIMATED ACCEPTABLE FILL sand everywhere but nary a grain to spare!" Because the best source of beach sand is the natural littoral drift system, management strate­ r2= gies should focus on rationalization of enhanced bypassing techniques with limited use ofoffshore '-- 2.5 borrows. r-- 10" m3 2 ENHANCED SAND BYPASSING 1.5 - OPTIONS FOR THE SOUTHEAST -- FLORIDA COAST r-- 0.5 ==~ Strategies for sand management are becoming o ~ I increasingly more important as a coastal man­ D81H8 P8Il8TS Fll JULP HWIHL agement tool. Rising sea levels, increased shore o Total Fill erosion, decreasing supplies of accessible and • Usable Fill suitable fill materials (both on- and offshore), Figure 7. Comparison of total offshore borrow and increasing concerns over environmental capacities and fill reserves that are acceptable impacts associated with coastal protection mea­ for beach replenishment. Units along the vertical sures are some of the reasons for renewed inter­ axis are millions of cubic meters. DB/HB = est in these coastal problems. Attempts by coastal Deerfield Beach/Hillsboro Beach, PB/LBTS = engineers to alleviate shoreline erosion hazards in Palm BeachlLauderdale-by-the-Sea, FU = Fort the southeastern Florida urban coastal corridor Lauderdale, JULP = John U. Lloyd State beach originally focused on "hard stabilization" mea­ Park, HW/HL = Hollywood/Hallandale. (Modi­ sures (e.g. groin fields, jetties) but more recent fied from Coastal Planning & Engineering, efforts have been spearheaded by "soft stabiliza­ 1985). tion" techniques that feature artificial beach replenishment. Although "successful" in some recycling (Loisa Kerwin, personal communica­ cases (e.g. Miami Beach) and useful as a tempo­ tion). Using a conversion factor of 1.2 (l m3 = rary protective measure against critically eroded 1.2 t) means that small volumes are produced segments along the southeast coast, the method is compared to those required for a typical beach not without criticism (e.g., LEONARD et aI., replenishment project (0.5 to 1.2 x 106 m3) in 1990; PILKEY, 1990). Many innovative tech­ Broward County. By using slightly coarser grain niques have been suggested for erosion control sizes, compared to borrow materials, so that along sandy beaches and some (e.g. jet pumping, smaller volumes will be required to maintain fluidization of bed sediments) show some beach stability, it might be possible to use recy­ promise as effective strategies for increasing sand cled glass in selected critically-eroding pockets or bypassing around stabilized inlets. When en­ to just mix the recycled glass with natural fills. hanced bypassing is combined with periodic Even though there probably will never be enough beach replenishment, shoreline erosion may be recycled glass to meet the needs of large-scale significantly mitigated. beach replenishment, this material may merit Engineering schemes must, however, be imple­ consideration as an alternative beach-fill material mented within the natural geological framework in Florida, beyond the attention that it is already of the region and, at the same time, be compati­ receiving by the City of Encinitas in California ble with societal needs and perceptions of what (WOODWARD-CLYDE, 1991). constitutes an "acceptable" solution to the beach With all of these caveats associated with alter­ erosion problem. Although the socio-economic nate sand sources, one might be prompted to constraints are not yet fully articulated, engineer­ modify the adage "Water, water everywhere but ing and scientific endeavors are advancing toward

Journal of Coastal Research, Special Issue No. 18, 1993 80 Finkl technical solutions. A range of possible engineer­ operations in Australia, Denmark and The Neth­ ing methods are continually being presented as erlands. Increased sand gathering capabilities in possibilities and, although it may be desirable to the immediate vicinity of navigational inlets and have a national policy on erosion control, it deployment to eroded downdrift coastal segments probably will be up to local authorities to decide may be the most cost effective and environmen­ which strategies are most appropriate for their tally-eorrect course to chart. particular coastal jurisdictions. Notwithstanding innovative techniques that Coastal engineers have long appreciated the fact involve the installation of beach dewatering that jetties and tidal jets often direct sand normal­ systems (to stabilize the berm) or bubble curtains ly entrained in the littoral drift system in an (to inhibit seaward sediment transport) or artifi­ offshore direction. Some of these sediments are cial seaweeds (to dampen wave energy), manage­ deposited in ebb-tidal deltas, some naturally ment strategies along the southeast Florida coast bypass the navigational entrance by the action of will in the future probably need to focus on new currents, but often large volumes can be lost technologies associated with the modification of offshore. In the latter case when sand is trans­ existing jetties or bypassing plants as well as ported offshore it is essentially lost from the testing the feasibility of fluidizing channel bed or littoral drift system causing a net deficit shoal materials which can be entrained by downdrift of the navigation entrance which longshore currents to bypass navigational en­ results in beach erosion. trances. Alternatives for sand placement at the Attempts to increase the efficiency of sand John U. Lloyd State Beach Park include, accord­ bypassing involve a variety of inlet modification ing to the inlet study prepared by COASTAL schemes. Curved jetties (e.g. Baker's Haulover) TECHNOLOGY (1988), beach renourishment have proven useful in this regard as have weir coupled with a fixed bypassing plant, a jet pump jetties (e.g. Boca Raton Inlet, Hillsboro Inlet). system, a weir jetty and sand trap, channel The concept of a weir jetty of the type developed maintenance, or a jet pump system in combina­ at Hillsboro, for example, was based on observa­ tion with dune restoration. The implementation of tion of natural sand overflow across a rock ledge combined multiple technologies is undoubtedly a on the updrift side of the inlet. As now construct­ future trend because it is probable that beach ed, the jetty bypasses sand into the channel replenishment alone will not provide adequate where it is dredged and pumped via a submerged shore protection for the entire design life of the pipeline to the eroding downdrift beach in Pom­ project. Although the durability of replenishment pano. Although local circumstances vary, many projects has recently become a contentious issue, mechanical bypassing systems can be improved mainly due to claims that replenished beaches do by relocating the bypass equipment, extending not last nearly as long as their design life indi­ the boom length, mobilizing the bypass intakes cates (LEONARD, CLAYTON AND PILKEY, on rails or cranes, deploying mobile jet pumps, 1990), it is likely that critical beach erosion can or by installing seabed fluidizers (BRUUN and be mitigated by smaller but more frequent nour­ ADAMS, 1988; BRUUN, 1990). It is estimated ishments that incorporate advanced technologies. that such efforts may significantly increase the efficiency ofbypassing to levels of 80 % or more, ENVIRONMENTAL IMPACTS OF SAND which is certainly better than some current MANAGEMENT efficiencies that range from only about 30% to 50%• Still other techniques feature spudded, Some sort of environmental impact is associ­ jack-up platforms with jet pumps that can be ated with each and every sand management plan. moved about following the sand supply and split­ This is so because all sand management schemes hull dredgers with over-the-bow pumping capa­ involve, in one way or the other, the transfer of bilities. The use of small coastal dredgers for sand from one location to another, albeit by a profile nourishment has been championed by variety of means. Even 'no action' can have a BRUUN (1992) who reports successful economic negative impact on downdrift beach ecosystems

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 81 because the lack of remedial action along coastal The environmental impact of beach replenish­ segments where secular erosion is taking place ment on coral reef communities has been a long­ ultimately results in the loss of the entire beach term concern, especially because the patch reefs ecosystem, including turtle nesting sites and even are already stressed by pollution, are impacted by dune vegetation. Action plans that incorporate heavy recreation use, and because cold shelf enhanced bypassing and beach replenishment will water in the winter limits their northern extent. maintain beach habitats and foredunes, but turtle In addition to these secular and often cumulative nests will have to be relocated to uneroded impacts, the added stress associated with periodic natural beaches or safer sites already replenished. offshore dredging activities could be the coup de Parts of the engineering community believes grace for these fragile coral reef communities. that there is little, if any, ecological damage DODGE et ale (1991), investigating the reefs associated with beach replenishment (STAUBLE offshore from John U. Lloyd State Beach Park, and NELSON, 1985). Such opinions, which report no obvious renourishment-associated seem natural enough, may be due in part to the damage or pattern ofecological degradation. This vantage points offered by the consulting firms is indeed good news and an encouraging sign that that conduct contract research and monitoring. present sand management practices, as outlined Perhaps more to the point, however, are the facts in part by STAUBLE and HOEL (1986), are that (1) there is but meager ecological kno~ledge adequate to protect the offshore coral reefs. of the impacts of sand management activities on Turning from offshore impacts to potential organisms and communities, and (2) negative onshore environmental degradation, one finds a results of many engineering projects are consid­ more complicated set ofcircumstances where the ered case-specific. Such interpretations of envi­ water column, seagrass beds, hard grounds ronmental impacts are likely related to the lack (submarine outcrops ofthe Anastasia Formation), of pre-project monitoring data. Sabellariid worm reefs, and beach are often Environmental impacts associated with beach adversely impacted by turbidity, siltation, or replenishment, and occurring between the off­ heavy burial by sediments (MAUCK and shore borrow site and target beach, may involve FLETEMEYER, 1987; NELSON and MARTIN, the following major habitats: borrow and sandy 1985). There are many problems associated with beach benthic communities, coral reefs and hard the fair and unbiased assessment of damage to grounds, sea grass beds, worm reefs, and pelagic these environments because there is little biologi­ environments. Recent studies show, for example, cal and ecological information available. Exam­ that physical changes at borrow sites influence ples could, for instance, focus on evaluation of recolonization, successional sequences, and the environmental tolerances of subtropical subsequent structure of climax communities Sabellariid worms (Phragmatapoma lapidosa), (GROBER, 1992). Many misconceptions are the wide range of sessile organisms that are associated with interpretation ofborrow recovery affected by siltation or drifting sand, fish, sea times. Short-term studies commonly attribute turtles, and avifauna. rapid recovery (12-18 months) to species density and diversity. Biologists now emphasize that it is DISCUSSION more relevant to evaluate ecological progress toward pre-dredging community structure than to Erosion control along the southeast Florida just count the numbers of different species that coast features innovative measures that have have moved into the disturbed borrow site. mechanically assisted the bypassing of sand Longer-term studies that investigate the types and around navigation entrances. The fixed sand functional groups of organisms, e.g. studies of bypassing plant at the South Lake Worth Inlet is, community structure and taxonomic levels as for example, one of the oldest continuously investigated by SALE and GUY (1992), will running plants in the world. The weir jetty at hopefully provide a better assessment ofdredging Hillsboro Inlet was the prototype for similar impacts and recovery time. structures that permit the natural bypassing of

Journal of Coastal Research, Special Issue No. 18, 1993 82 Fink! sand alongshore past the jetty into the channel or disappear, in spite of protection by periodic trap where it can be dredged and pumped to the beach renourishment or seawall projects, may eroding downdrift beach. Such efforts are among , have prompted some researchers to sound retreat many attempts to achieve adequate coastal protec­ from the coast (e.g. PILKEY et al., 1984; tion. The deepening of navigation channels and PILKEY, 1990). An acceleration of future rates increased lengths and heights of jetties has, of global sea-level rise (RIND, 1987), would nevertheless, caused severe erosion on the make many coasts such as southeast Florida more downdrift (southern) sides ofinlets. Sea-level rise vulnerable to crescendo (storm and tide) events, and·offshore transport ofsand beyond the littoral decreasing supply of offshore borrow materials drift system may also have exacerbated the beach for beach replenishment, and limited alternative erosion problem. At any rate, it has now reached sand sources. the point where it has become a disaster of The backdrop to the erosion problem and its regional proportions. control is the geological framework in which all Recent attempts to mitigate the chronic impacts remediation efforts must be encompassed. Of of shoreline retreat along Florida's developed primary concern is consideration of sea-level rise coasts have focused on the replenishment of as related to the greenhouse warming. Although eroded beaches downdrift from inlets. With the there is a vast literature on predicting future exception of the Miami Beach renourishment trends in sea level, most estimates suggest an project, most beaches have not been as durable average rate of eustatic increase, based on the as the 10-year design life (in most cases) re­ existing sea-level data set, of about 1 to 2 nun quired. The erosion along some coastal segments yr-1 (BARNETI, 1990). Analyzing post-1870 has become so bad that many beaches now European tide gauge records, WOODWORTH require periodic replenishment in order to ensure (1990) found little evidence for a significant the integrity ofcoastal infrastructure. The replen­ acceleration in regional mean sea level, exclusive ishment process itself has recently come under of minor positive accelerations between 4 and 9 scrutiny, not only because of its potential envi­ x 10-3 nun yr-1 in four of the longest records ronmental impacts but because the supply of (Brest, Amsterdam, Sheerness and Stockholm). suitable offshore borrow material is dwindling. These estimates of sea-level rise are far less than With limited offshore supply of beach fill materi­ those previously reported for global warming als, it is imperative that sand moving alongshore scenarios (e.g. HOFFMAN et al., 1985). There be bypassed around inlets as efficiently as possi­ are, however, still many uncertainties regarding ble. The future of many beaches may well ride the causes of variations in relative sea-level on the successful deployment of new and innova­ change, including probabilities of direction and tive techniques for keeping the sand moving rate ofchange (SHLYAKHTER and KAMMEN, alongshore. Techniques that incorporate jet 1992; MILLER and VERNAL, 1992) which pumps on movable bypassing plants or bed make it difficult to rationalize coastal manage­ fluidizers may increase the efficiency of sand ment schemes that will provide adequate future bypassing but an important factor in their appli­ protection from erosion during increasing RSL or cation depends on whether the developing tech­ shoaling during falling RSL. With the possibility nology becomes economically feasible. In the that impacts of a "greenhouse" sea-level rise are near future, these new methods ofsand bypassing probably several decades away (PIRAZZOLI et may be used in conjunction with more frequent al., 1987), there may be sufficient time to test replenishment by small hopper dredges with various hypotheses that can unambiguously over-the-bow pumpout capabilities. explain and predict changes in RSL. From consideration of engineering capabilities Turning from considerations ofglobal sea-level and technical expertise follows the sobering change to observations of local conditions, it is thought that such Herculean abilities may not be perhaps important to note that southeast Florida enough to effectively stall shoreline recession. beaches consist ofonly about 2 m of sand overly­ The fact that some beaches erode and eventually ing limestone. The true coastal barriers, mainly

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 83

long spits, were destabilized by inlets in the early in sand management schemes, those researchers part of this century. They became welded to the capable of providing adequate environmental mainland almost immediately after inlet cutting base-line data need to start collecting information and stabilization by jetties so that today the shore in a systematic manner such that it will properly more closely approximates a key rather than a represent all affected habitats in the southeast true barrier island which overlies a considerable Florida coastal zone. Again, the problem here is thickness of unconsolidated sediments. The not one so much based on the lack of interest by important point here, as far as erosion control is the bioscience community but lack of funding. concerned, is that engineering solutions and man­ Until state, federal, or local agencies (or com­ agement options are somewhat different when binations that share responsibility) require and dealing with a key. The usual sequence of island support adequate pre- and post-project monitor­ thinning and then rollover, which is a ing, it is unlikely that sufficient information will geomorphological response of a true barrier become available under present 'business as island to sea-level rise, is impossible here but usual' scenarios. The track record is at least overstepping may be possible if sea-level rise is clear on that account for the present amount of rapid enough. Because these beaches are essen­ usable base-line data is dismal, to say the least. tially perched on the Anastasia Formation in Enhanced sand bypassing, as described for many places, the thin sand cover (including example in a recent engineering manual (COE, beaches and dunes) may be washed away, but 1991), is an essential supplement to periodic erosion can not easily proceed in this hard indu­ beach replenishment and it is a credit to the rated limestone that extends from about 3 m engineering community that emphasis is being above to below present MSL. The limestone will placed on new and innovative techniques to thus naturally inhibit shoreline recession at points accomplish this goal. If it is not achieved, it where it outcrops above sea level and where probably will not be due to the lack of technical exposed as submerged hardground in the or engineering know-how but to bickering among nearshore zone. political antagonists, parties with local self­ Finally, there are concerns that engineering serving vested interests, or environmentalists solutions to the beach erosion problem will in with extremely conservative views that favor "no some way degrade the coastal environment. human interference" with natural systems. The Some concerns may be based on previous blun­ simple fact is that the Florida east coast has ders that are no longer tolerated, but the fact suffered massive interference by the inlets and remains that no effort to protect the coast from ICWW, and no one is prepared to go back to the erosion will result in a shore that is radically status quo another 100 years ago. different from todays. It thus seems that some Unless progress is made to solve the on-going sort of protective effort is required. That there is "sand wars," it is possible that enhanced sand some sort of ecological impact of sand bypassing bypassing and continued beach replenishment and beach replenishment is a foregone conclusion may not become a reality along the southeast (HOLDERMAN, 1992). Questions should not Florida coast. In order to avoid the future possi­ focus on whether environmental impacts result bility that beach replenishment may not be con­ from sand management in the coastal zone but sidered the attractive alternative that it is today rather should be directed toward comprehending (HOLDERMAN, 1992) and that long-range which impacts are minor, moderate, or severe planning via setbacks may become the most and which ones are short-term or have long economical, politically expedient, and ecological­ lasting undesirable effects. SUlVey of the litera­ ly-favored alternative, several action items need ture suggests that it is not yet possible to answer to be implemented immediately. These tasks these questions in a way that will provide mean­ include: ingful guidance to coastal managers and the (1) Initiation of full-scale comprehensive envi­ engineering community. Before such consider­ ronmental monitoring of bypassing and replen­ ations can be addressed, much less incorporated, ishment projects. In order to be effective, such

Journal of Coastal Research, Special Issue No. 18, 1993 84 Finkl monitoring must be truly broad-based in scope) othelWise normal longshore sand flow into inlets not subject to adverse political pressures or or offshore. Attempts to enhance sand bypassing conducted under the aegis of parties with vested around navigational entrances via fixed pumping interests. stations, weir jetties and inlet dredges have (2) The establishment of continuous long-term historical precedence in southeast Florida. New ecological monitoring. and innovative techniques, such as jet pumps or (3) Standardization of methodologies and sam­ seabed fluidizers, may supplement these tried and pling techniques. true methods by making use of sand in the (4) The imposition of Florida reference (con­ littoral drift system that does not naturally end up trol) ecological stations, possibly along existing on beaches immediately downdrift from inlets. DEP survey lines. Whatever erosion-eontrol technique is applied, (5) The delineation of ecologically sensitive it is abundantly clear that the sand management areas and incorporation of those data into man­ strategy must reflect sensitivity to environmental agement plans made generally available through concerns. Public awareness of not only the GIS-based systems. fragile nature of marine environments but also (6) Requirements that beach, borrow and by­ their important role in the whole· ecological pass installations are additionally monitored on system is becoming increasingly acute, as evi­ the basis of ecological performance. denced by recent laws that protect mangroves, (7) The establishment of a central depository sea turtles and manatees. The stage upon which for environmental (ecological) performance data. all of this is played out is the coastal geological framework which itself is susceptible to change, CONCLUSION mainly by the combined effects ofjettied naviga­ tional entrances, offshore sediment transport, and Beach replenishment is) at the present time, the rising relative sea level. Although the historical most politically favored erosion control measure coastal barriers, spits and bars, were destroyed for the southeast Florida coast. The success of by inlet cutting near the tum of the century, the this strategy for sand management is related to present developed shoreline must be protected as the fact that, as a "soft stabilization" technique, long as possible so that coastal infrastructures it meshes well with natural dynamic coastal remain viable. New strategies for enhanced sand processes and has fewer undesired environmental bypassing and beach replenishment will thus pre­ impacts compared to hard structures such as empt techniques that are now inefficient, out­ seawalls, groins, andjetties. Beach replenishment moded, or environmentally unacceptable. In­ is not, however, a final panacea for Florida's creased levels of long-term environmental moni­ coastal erosion problems because it (1) is only a toring are seen as part of renewed efforts to temporary measure that forestalls the inevitable provide increased coastal protection at reasonable loss of shoreline that must accompany sea-level costs. rise, (2) depends on the availability of alternative sand sources that are suitable for beach fill, and LITERATURE CITED (3) is susceptible to increasing costs associated with the mobilization of large outdated ocean AMERICAN COASTAL ENGINEERING, 1992. dredges. In some areas such as along the Final Test Plan; Experimental PEP Reef Project, Mid-Town Section, Town of Palm Beach, Palm Broward coast, offshore sand borrows retain Beach County, Florida. (Report prepared for the limited reserves of suitable materials for beach Department of Natural Resources, West Palm replenishment and alternative sources must soon Beach, Florida), variable pagination (vp). ANDREWS, J.T., 1987. Glaciation and sea level: A be located. case study. In: Devoy, R.J.N, (ed.), Sea Surface The prominent role ofjettied inlets in the beach Studies: A Global Review. London: Croom Helm, erosion problem requires increased understanding pp. 95-126. of how stabilized navigational entrances affect BARNETI, T.P., 1990. Recent changes in sea level: A summary. In: Geophysics Study Committee, nearshore processes that in tum re-direct the Studies in Geophysics. Washington, DC: National

Journal of Coastal Research, Special Issue No. 18, 1993 Sand Management Strategies 85

Academy Press, pp. 37-51. COASTAL TECHNOLOGY, 1988. Port Everglades BIRD, E.C.F., 1985. Coastline Changes: A Global Sand BypassingStudy. Vera Beach, Florida: Coastal Review. Chichester: Wiley, 218p. Technology Corporation, Inc., 64p. (Submitted to BERGER, W.H. and LABEYRIE, L.D., 1987. Broward County Erosion Prevention District). Abrupt climatic change- an introduction. In: Berger, COE (Corps of Engineers), 1984. Shore Protection W.H. and Labeyrie, L.D. (eds.), Abrupt Climatic Manual. Two Volumes. Washington, DC: U.S. Change: Evidence and Implications. Dordrecht: Government Printing Office, variously paginated. Kluwer, pp. 3-22. COE (Corps of Engineers), 1986. Design ofbreakwa­ BELKNAP, D.F. and KRAFf, J.C., 1985. Influence ters and jetties. Engineering Manual No. 1110-2­ of antecedent geology on stratigraphic preservation 2904 (8 August 1986), Vicksburg, Mississippi: potential and evolution of Delaware's barrier sys­ CERC, variously paginated. tems. Marine Geology, 63, 235-262. COE (Corps of Engineers), 1991. Sand bypassing BODGE, K.R., 1990. South Lake Worth Sand Man­ system selection. Engineering Manual No. 1110-2­ agement Plan. Jacksonville, Florida: Olsen Associ­ 1616 (31 January 1991). Vicksburg, Mississippi: ates, Inc., 23p. (Submitted to Palm Beach County CERC, variously paginated. Board of County Commissioners). CUBIT, 1986. Preliminary Evaluation of Proposed BODGE, K.R. and OLSEN, E.J., 1992. Aragonite Alternatives for Sand Bypassing at South Lake beach fill at Fisher Island, Florida. Shore and Worth Inlet. West Palm Beach, Florida: Cubit Beach, 60(1), 3-8. Engineering Limited, 9p. (Prepared for Town of BRUUN, P., 1964. Coastal engineering study ofSouth Ocean Ridge). Lake Worth Inlet. UFL/COEL-64/005, Gainesville, CULLITON, T.1.; McDONOUGH, J.1.; REMER, Florida: University of Florida, College of Engineer­ D.G., and LOTT, D.M., 1992. Building Along ing,89p. America's Coasts. Rockville, Maryland: NOAA, BRUUN, P., 1978. Stability of Tulal Inlets - Theory Strategic Environmental Assessments Division, 49p. and Engineering. Amsterdam: Elsevier, SlOp. DEPARTMENT of COASTAL & OCEANOGRAPH­ BRUUN, P.; BAlTJES, J.A.; CHIU, T.Y., and IC ENGINEERING, 1969. Coastal Engineering PURPURA, J.A., 1966. Coastal engineering model Study of Jupiter Inlet, Palm Beach County, Florida. studies of three Florida coastal inlets. Engineering Gainesville, Florida: University of Florida, 5Ip. Progress at the University ofFlorida (Florida Engi­ (Prepared for Jupiter Inlet Commission). neering and Industrial Experiment Station), Bulletin DEAN, R.G. and O'BRIEN, M.P., 1987. Florida's No. 122, 20(6), 52-68. east coast inlets - shoreline effects and recommended BRUUN, P., 1990. Improvement of bypassing and action. UFLICOEL-87/017, Gainesville, Florida: backpassing at tidal inlets. Journal of Waterway, Coastal and OceanographicEngineeringDepartment, Port, Coastal, and Ocean Engineering (ASCE), University of Florida, 65p. 116(4), 494-500. DEAN, R.G., 1990. Channel entrances: Impacts on BRUUN, P., 1992. Bypassing and backpassing at coastal erosion. Proceedings o/the 53rd Meeting of harbors, navigation channels and tidal entrances: Use the Coastal Engineering Research Board (5-7 June of shallow water draft hopper dredgers with pump­ 1990, Fort Lauderdale/Dania, Florida). Vicksburg, out capabilities. Journal ofCoastal Research, 8(4), Mississippi: CERC Final Report, pp. 51-53. 972-977. DODGE, R.; HESS, S., and MESSING, C., 1991. BRUUN, P. and ADAMS, J., 1988. Stability of tidal Final Report: Biological Monitoring of the John U. inlets: Use of hydraulic pressure for channel and Lloyd State Beach Renourishment: 1989. Port Ever­ bypassing stability. Journal of Coastal Research, glades, Florida: Nova University Oceanographic 4(3), 687-701. Center. 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