FAU Institutional Repository http://purl.fcla.edu/fau/fauir This paper was submitted by the faculty of FAU’s Department of Geosciences. 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,