Journal of Coastal Research 1100-1110 West Palm Beach, Fall 2000

AnODla10US Response of Beaches to Hurricane Waves in a Low-Energy Environment, Northeast , U. S. A. Timothy R. Keen] and Gregory W. Stone'] tNaval Research Laboratory tCoastal Studies Institute Oceanography Division Louisiana State University Stennis Space Center, Baton Rouge, LA 70803, MS 39529, U.S.A. U.S.A. ABSTRACT _

KEEN, T.R. and STONE, G.W., 2000. Anomalous response of beaches to hurricane waves in a low-energy environment, .tllllllll,. northeast Gulf of Mexico, U.S.A. Journal of Coastal Research, 16(4), 1100-1110. West Palm Beach (Florida), ISSN 0749-0208. ~.~

---- :...... -.....: '::J Submarine sandbars were deposited on the post-storm subaerial beach at Carrabelle Beach, Florida, by Hurricanes --A tz! Elena and Kate in 1985. These bars contained stratification similar to swash bars and berms, as well as an unusual .-- stratification consisting of interlayered beds and heavy-mineral laminae, which were slightly convex upward. Based .. on their internal morphology and location above the high-water line, these bars appear to be a relatively unknown type, the stranded bar. Field relationships and grain-size distributions have been examined in order to identify the principal sedimentation mode during deposition. These data support an origin by grain settling from suspension as storm wave energy decreased, but nearshore water levels remained elevated. The sediment pool comprising the bars was progressively sorted during the two hurricanes, which occurred within ten weeks of each other.

ADDITIONAL INDEX WORDS: Nearshore sand bars, hurricanes, granulometry, Florida.

INTRODUCTION coast, indicating the importance of the neritic zone as a source and sink during hurricanes. DOLAN and GODFREY The majority of published data pertaining to hurricane im­ (1973) examined the morphological impacts of Hurricane Gin­ pacts on mid-latitude coasts demonstrates that the over­ whelming response of beaches to such events is a net sedi­ ger, which made on the coast in 1971. ment loss, caused by the combined effects of the This and other work (DOLAN, 1972) showed that stabilized and wave-generated currents (see reviews in FINKL and dunes along Cape Hatteras experienced extensive dune ero­ PILKEY, 1991; STONE and FINKL, 1995). In this paper, we sion and recession during Hurricane Ginger, with significant present evidence indicating an anomalous response of a low­ quantities of sediment being transported offshore and along­ energy beach to two hurricanes, during which large sand bod­ shore. Natural barriers along the Core Banks responded with ies emerged in the nearshore. The study site is located along a flattening of the beach face, retreat of the berm, deposition the northeast Gulf of Mexico coast adjacent to Apalachicola on the backshore, and trapping of material by grasses and Bay, Florida (Figure 1). These findings are considered impor­ marshes. The natural barriers thus were able to survive high­ tant in that they shed new light on the morphosedimentary magnitude events and recover more rapidly than the stabi­ response of beaches to infrequent high-energy events and dis­ lized barriers. These findings were re-examined by LEATH­ pel the notion that such events are unequivocally erosional. ERMAN et al. (1977) and LEATHERMAN (1979), culminating in In addition, a detailed evaluation of the internal character­ a refined model of overwash processes during storms. istics of these sedimentary bodies is used to evaluate the tex­ Important contributions on the morphological impacts of tural evolution of the sediment entrained by the storm waves. hurricanes in the Gulf of Mexico include the following: Hur­ ricane Audrey, 1957 (MORGAN et al., 1958); Hurricane Cam­ Conceptual Framework ille, 1969 (WRIGHT et al., 1970); , 1975 (BUR­ Perhaps the earliest, most significant contribution to our DIN, 1975); Hurricane Frederic, 1979 (SCHRAMM et al., 1980; present understanding of the influence of hurricanes on bar­ NUMMEDAL et al., 1980; KAHN and ROBERTS 1982; STONE rier islands was the work of HAYES (1967). Hayes discussed and SALMON, 1988); Hurricanes Juan and Danny, 1985 (PEN­ the morphological response to Hurricanes Carla (1961) and LAND et al., 1989); Hurricane Gilbert, 1988 (PENLAND et al., Cindy (1963) along the Texas coast. This particular study 1989; DEBUSSCHERE et al., 1991); Hurricane Andrew, 1992 shed new light on the redistribution of sediments between (STONE et al., 1993; 1997; STONE and FINKL, 1995); Hurri­ the inner shelf, nearshore, and subaerial portions of the cane Opal, 1995 (STONE, 1998; STONE et al., 1996) and Hur­ ricane Georges, 1998 (STONE and WANG, 1999; STONE et al., 99072 received 30 June 1999; accepted in revision 27 January 2000. 1999). Many of these studies support the concept that the Beach Response to Hurricane Waves 1101

Figure 1. Gener al physiographic setting of Carr abelle Beach (Solid circle) and vicinity, Florida.

elevated water levels and high wave energy during a hurri­ struck the northwest coastline of Florida (TANNER, 1986). cane cause considerable erosion of the nearshore-beach-dune followed a westward track and passed to the system. Recent work also reveals attrition along some bar­ south between August 31 and September 2. Hurricane Kate riers in the Gulf of Mexico during winter storms (STONE, made landfall west of Apalachicola Bay on November 21. 1998; STONE and WANG, 1999; STONE et al., 1999). During both events, a nearshore bar was deposited by waves Although little work has been conducted on th e precise spa­ at Carrabelle Beach, Florida. The objective of the present pa­ tiotemporal adjustment of barrier islands to hurricanes, it is per is to summarize the results of a study of the bars depos­ well established that the post-storm phase is one character­ ited by these two hurricanes, and interpret these data within ized by deposition (cf, HAYES, 1967; SEXTON and MOSLOW, the framework of sediment dynamics during hurricane con­ 1981; THIELER and YOUNG, 1991; SEXTON and HAYES, 1991; ditions. The sedimentary structures of th ese two bars are DINGLER and REISS, 1995). For example, the formation of evaluated, because it was these same features which led to depositional sequences such as overwash fans has been well the introduction of the term, stranded bar, by COLEMAN documented (LEATHERMAN et al., 1977; STONE et al., 1996). (1978). From thi s analysis, some inferences can be made In some instances this process has resulted in a barrier island about th e processes constructing them. The sediment con­ conserving mas s during catastrophic hurricanes (STONE, tained within these bars represents the storm sediment pools 1998; STONE et al., 1996; 1999). Review of the literature in­ and as such, it is used herein to evaluate the textural evo­ dicates the lack of a heuristic model, incorporating both sed­ lution of th e sediment entrained by the storm waves. imentary processes and transport pathways. Such a model would serv e to identify and elucidate the post-storm adjust­ BACKGROUND ment of the beach . Study Area Objectives Fieldwork for this investigation was conducted on the pub­ In 1985, six hurricanes made landfall along the Atlantic lic beach at Carrabelle Beach, Florida, situated approximate­ and Gulf of Mexico coasts of the United States, two of which ly 100 km southwest of Tallahassee, on the northern flank of

Journal of Coasta l Research, Vol. 16, No.4, 2000 1102 Keen and Stone

to September 1. The maximum hourly wind speed recorded at Apalachicola (Figure 2) was 20 m s· ' . Hurricane Kate passed directly to the west of Apalachicola Bay and a maxi­ mum wind of 23 m s·' was measured. The Gulf side of St . George Island was exte nsively eroded by Hurricane Elena, as I I I 2400 8/31/85 2400 9/1/85 2400 was its Apalach icola Bay shoreline and th e landward margin of St. George Sound west of East Pass. During Hurrican e 20 rn/sec Kate, however , significant erosion occurred at Carrabelle Kate .-11_ Beach and east of Dog Island becau se these areas were un­ 9/2 protected from th e sustained onshore winds that also pro­ duced large stor m surges. The effects of Hurri cane Kate on I I 2400 11/21/85 2400 St. George Island were difficult to judge becau se of the pre­ vious damage cause d by Elena, but some erosion and over­ was h were evident. Tidal records from Apalachicola Bay were unavailable be­ cause of the failure of th e tide gauge during both storms. The 3.------, astronomical tide varied from 0.21 m to 1.1 m above LLWL Hurricane Kate (lowest low water level) (NATIONAL OCEANIC AND ATMO­ Carrabelle, Florida SPHERIC ADM INISTRATION , 1985). A reconnaissance of th e study area revealed a distinct band of flotsam at the maxi­ mum incursion of the strand line, which was used to estimate the total water depth during th e storm. The resulting maxi­ mum water elevations of 1.5 m above mean water level (MWL) during Hurrican e Elena and 3 m during Hu rrican e Kate included the sto rm surge superimposed on the astro­ nomical tide. The storm surge during Hurrican e Kate has been hindcast using the ADCIRC-2DDI hydrodynami c model (BLAIN et al., 1994; BLAIN, 1997). The predicted storm surge o at Carrabelle is shown in Figure 2. The maximum surge of L--L_..l.--l._...l...----l_....l--l_....l-_':---:l 14 15 16 17 18 19 20 2.8 m is in good agreement with th e field estimate, given the November 1985 uncertain ty in the actual storm surge as discussed above.

FIELD METHODS Figure 2. Tracks and wind vectors meas ured at Apalachicola (solid squa re in Figure 1) during Hurricane Elena and Hurricane Kate (Upper). The stranded bars were deposited with their seaward mar­ Storm sur ge computed for Carrabelle, Florida, using ADCIRC-2DDI mod­ gins within th e mean swas h zone (Figu re 3). The bar crests el (Lower)(from BLAIN, 1997). were less tha n 1.5 m above MWL. Figure 3A shows the un­ disturbed backshore at Carra belle Beach two weeks aft er Hurricane Elena made landfall. The scarping at th e crest of St. George Sound (Figure 1). Barrier islands of late Holocene the bar (Figure 3B) and the lack of storm debris are apparent. age form the seaward margin of St. George Sound; Dog Island The photograph in Figure 3C was ta ken 18 days after Kate to th e east and St . George Island to the west. The landward made landfall. Thi s image reveals th e effects of the increase d margin of St . George Sound cons ists of extensive shoa ls, storm surge. The Kat e bar (Figure 3D) was deposited slightly tran sverse bars and pocket beaches. The greatest water further above MWL and was eroded very little by post-storm depth within the lagoon is less than 7 m and it is cha racter­ waves. More debri s was introduced into th e surf zone becau se ized by low wave energy, having mean annual breaker of greater flooding. This material was deposited within th e heights of 0.1 m or less (GORSLINE, 1966). Local physiogra­ bar itself. Both bars exceeded 2.5 km in length. The base of phy, offshore bath ymet ry, and the location and size of tidal each stra nded bar was marked by a seaward-sloping erosion­ passes, combine to cause the greatest wave effects on land­ al surface that was used as the datum for vertical position ward beaches when the prevailing winds are from the south and height. The Elena bar's maximum height was 0.6 m at or southeast (KOFOED and GORSLINE, 1963). The littoral the crest. The Kate bar measured 0.7 m. tran sport system is cha racterized by a complex set of drift To evaluate the sedimentary structures and sediment tex­ cells, which at present are experi encing no net excha nge of tures of th ese two stranded bars, sampling sta tions were es­ sediment (STAPOR, 1971; 1973; STONE and STAPOR, 1996). tablished as shown in Figure 4. Two weeks after hu rrican e Elena, trenches were excavated across the bar at stations 2 Hurricanes Elena and Kate and 4, with pits placed at stations 1, 3 and 5.Two weeks Hurrican e Elena followed an irregular path (Figure 2) and after Hurrican e Kate, trenches were placed at stations 0 and remain ed south-sout heast of th e study area from August 31 3, and pits were dug at sta tions 2 and 4. Photomosaics were

J ourn al of Coasta l Research , Vol. 16, No.4, 2000 Beach Response to Hurricane Waves 1103

A un disturbed vegetation

Figure 3. (A) Photograph of th e backshore at Car ra belle Beach after Hurricane Elen a, showing the lack of erosio n at th e pavilion. View is to th e southwest. (B) Photograph taken on September 14 of the Hurricane Elena bar deposit ed on September 1, 1985. View is to the northeast . Note th e erosional scarp, which was cause d by storm waves during frontal passage aft er the hurrican e. (C) Photograph looking to the eas t of the pavilion in A, showing extensive erosion of backshore area . Note the debris th at was deposit ed in th e swale behind the bar. (D) View (looking southwest) of the bar deposited by Hurrican e Kat e, 21 November 1985. compiled of the trenches at station 4 after Hurrican e Elena (TANNER et al., 1961). The weight-percent heavy minerals for and station 3 after Hurricane Kate (Figure 5). suites E3, KO , K2 and K4 was determined by heavy-liquid A suite of sediment samples was collected at each station. separation after the sediment was recomb ined into two size 6 Laminar samples were collected at the crest of the bar from classes, two-to-three phi (250X10- 6 - 125 XlO- m) and horizontal layers at intervals of 0.05 m within the more ho­ greater-than three phi « 125X10- 6 m ), Note that th e letters mogeneous sections, and 0.025 m where finer structures were "E" and "K" refer to Elena and Kate, respectively. found . Where the lighter-colored beds became less th an 0.025 m thi ck, samples were tak en from successive light beds or RESULTS laminae but heavy mineral laminae were not sampled. Be­ Internal Geometry caus e these samples were taken internally from the bar crest, no post-storm modification of the sediment texture could The Elena Bar have occurred. Each sample was separated into size fra ctions by sieving at 0.25 phi interva ls for 30 minutes on a Ro-Tap The bedding within the Elena bar (Figure 6) was variable mechanical shaker after rin sing and drying. both in the vertical dimension and alongshore. The lower part One of the fund amental characteristics of the stra nded of the bar contained a large quantity of fine-grained material bars from th e Florida study area is the horizontal interl ay­ at station 1, making the section appear darker (Figure 6A). ering of heavy mineral laminae with quartz sand beds (Co­ The concentration of heavy minerals increases at station 2 LEMAN , 1978). STAPOR (1973) reported heavy mineral con­ (Figure 6B), where the distinctive lamination is evident. A centration s of about 62 percent for such layers within Apa­ cross-section of the bar at station 3 (Figure 6C) is similar to lachicola Bay, with th e common occurrence of ilmenite, stau­ station 1. Profiles at stations 4 (Figure 6D) and 5 reveal rolite , kyanite, zircon and rutile. The concentration of the se rhythmic, heavy-mineral lamination within the middl e part minerals within thi s area is commonly less th an one percent of th e bar. The lower section is composed of quartz sand and

J ourn al of Coastal Research, Vol. 16, No. 4, 2000 1104 Keen and Stone

the horizontal bedding extended throughout the bar height. This station most resembled the Elena bar. Individual larni­ /~ nae were traced several meters parallel to shore at this end of the study area. -.>.~~ , carrabe lle Beach 1)t.-<9r '-_, . ~.-.-.-. ---. ' ...... --~--_- 5 - 4 - 3 -2- 1 ------0 -,_ Sediment Texture 3 Suite data are used instead of individual samples in ana­ lyzing the sediment texture. This method reduces the amount o of variability displayed in plots of the sediment grain size 1 ...--A distribution (granulometric) moments. The results of the kilometers grain size analysis for each suite are given in Table 1. The mean and standard deviation represent the average size, and Figure 4. Detailed map of the study area . The numbers indicate the scatter of sizes about the average. The skewness indicates sta tions used for collecting samples and placing trenches and pits after both hurricanes. The darker stippled area is a shoal partially exposed at asymmetry about the average. The kurtosis is an index for low water. the peakedness of the size distribution curve. The typical sediment weight distribution plot consists of three components, the modal swarm, and the coarse and fine tails (TANNER, 1983). These components can be analyzed sep­ has thicker layering. The upper part of the bar consists of arately using bivariate plotting techniques. The four granu­ homogeneous quartz sand with no apparent bedding. Eroded lometric moments treat the modal swarm's granulometric debris from the backshore was found within the upper section character, as demonstrated for fluvial sediments by FOLK of the bar at station 5 (Figure 6E). and WARD (1957), in which study they proved useful because The Elena bar was evenly bedded perpendicular to the wa­ of the large range of sediment sizes available within a river ter line (Figure 5A). Individual beds and laminae could be bar. In attempting to differentiate sediments with less inher­ traced more than 1 m. Seaward-dipping cross-bedding was ent variability, it is necessary to analyze the three compo­ found at the seaward margin of the bar, however, beneath nents separately. the horizontal lamination. Because the internal layering of Within the Florida study area, only mature beach sands the bar was dominantly horizontal and individual laminae are available. Thus, any distinctive granulometric signatures and beds did not intersect or truncate one another, it has for these two storms must be sought within the more sensi­ been described as concentrically bedded (KEEN, 1986; 1987). tive tails of the grain size distribution. Kurtosis contains in­ Thus, the Elena bar is considered to contain the character­ formation about the relative size of the modal swarm and the istic bedding of the stranded bar as defined by COLEMAN two tails, whereas skewness indicates relative sorting be­ (1978). tween the tails. FRIEDMAN (1961) found that cross-plots of these two moments were useful in distinguishing sediment of The Kate Bar different maturity. Figure 8 is such a plot for th e sediment In contrast to the predominantly concentric bedding and suites from Table 1. The suites from the Kate bar have very lamination within the Elena bar, bedding within the Kate bar low values of skewness (a value of 0 indicates a perfectly sym­ contains both horizontal and cross bedding, as well as erosion metrical size distribution) and kurtosis (a Gaussian distri­ surfaces. The bar's internal structure consists of overlapping bution has a value of 3), indicating that they are close to concentric bedding sets at the eastern end of the study area being normally distributed. They also have less variability (Figure 7A). This stratification is similar to hummocky cross­ than the Elena suites. beds (DUKE et al., 1991). The lowest part of the bar is slightly Very mature sediments will be normally distributed. The darker because of the presence of fine-grained sediment. degree of maturity can be further evaluated by considering Dark laminae are sparse, however. This bedding extends to the weight-percent sediment finer-than or equal-to 4 'P the top of the bar. This same bedding pattern was found at (62.5X 10- 6 m). Immature sediments will contain a greater station 2 (Figure 7B). The most interesting internal struc­ percentage of silt and clay. As seen in the Tail-of-Fines dia­ tures within the Kate bar were found at station 3 (Figure gram for these suites (Figure 9), the Kate suites reveal both 5B). The lowermost part of the bar contained landward-dip­ a smaller percentage of fine sediment, and less variability. ping cross-bedding, with angles ranging from 8° to 12°. The Consequently, they would be considered as more mature. The top of this section is not truncated. Instead, the overlying placement of the Elena suites outside the mature beach field bedding is horizontal and concentric. The transition from suggests that they contained excessive silt and clay and were cross-bedding to horizontal lamination is apparent in Figure not uniformly reworked by the storm waves; thus, the higher 7C. Dark laminae, which were found above the cross-bedding, means of standard deviations. extended for several meters across the bar. These heavy-min­ Systematic trends were found in the vertical distribution erallaminae were offset and disrupted by storm debris within of the sample means and standard deviations within the the topmost part of the bar. Heavy minerals were more dif­ Elena bar. Plotting of the mean and standard deviations of fuse within the top as well, which was more homogeneous. individual samples against their relative height revealed a No cross-bedding was found at station 4 (Figure 7D), where discontinuity within the Elena suites, with finer grain sizes

Journal of Coastal Research, Vol. 16, No.4, 2000 Beach Response to Hurricane Waves 1105 and smaller standard deviations found within the sand from Storm waves generated by the southerly wind would have the upper part of the bar. The variance between and within entered St. George Sound between 1700 and 2400 GMT on these two populations of sediment was analyzed using the November 21. The steady increase in wind caused the storm ANOVA test (HUNTSBERGER and BILLINGSLEY, 1975). The surge to build slowly after 1200 GMT November 20 (Figure results support this separation for both the mean and stan­ 2) and reach a maximum 36 hours later. Consequently, storm dard deviation at confidence levels greater than 99 percent. waves would have been significantly diminished at Carra­ A weak alongshore pattern of westward fining (Table 1) was belle while the storm surge remained high. This scenario discerned for suite means of means (R2 = 0.6907) and means would continue until 0600 GMT November 22, by which time of standard deviations (R2 = 0.6177) for the Elena bar. The the model-predicted water levels had returned to normal. samples from the Kate bar contained no evidence for the ex­ Although there was flotsam within both bars, the quantity istence of separate populations for any of the granulometric was much greater within the Kate bar. This debris intersects moments, and no alongshore pattern was apparent. the concentric stratification without obliterating the heavy The average content of heavy minerals for the Elena suite mineral laminae (Figure 7). Since it would have been floating was 2.92 percent for the coarse fraction and 14.3 percent for near the water surface, the observed stratigraphic relation­ the fine fraction. The Kate suites averaged 4.04 and 39.1 per­ ship between the debris and laminae would occur only if the cent, respectively. Furthermore, the concentration was dis­ debris were deposited simultaneously with the laminae. In tributed uniformly within the Elena bar, whereas reversed many instances, these laminae do not become diffuse as they trends were found within the Kate bar; the percentage de­ approach the debris either, implying that flow was not dis­ creased with height at station 0, and increased at stations 2 rupted by the debris, such as would occur if it were in place and 4. prior to laminae deposition. The debris seen in Figures 5B, 6E, and 7C does not extend below the horizontally bedded DISCUSSION section of the stranded bars. Consequently, the concentric stratification within the Kate bar was produced when the wa­ The stranded bars discussed in this paper appear to have ter depth was very shallow and flotsam was being deposited, been produced in the same way as that deposited by Hurri­ rather than during the maximum storm surge. Furthermore, cane Eloise, as described by COLEMAN (1978). Because of the this deposition occurred while the storm surge was waning, difficulty of directly observing hydrodynamic processes in the since the observed quantity of debris would not have been nearshore zone during hurricanes, however, any discussion available until after the maximum surge. Deposition of the of the mechanisms responsible for deposition of these strand­ more complex bar at station 0, and the lower part of the Kate ed bars must be somewhat speculative. Nevertheless, using bar elsewhere (such as at station 3), is more problematic. the field observations, model results, sediment texture data, The cross-beds within the Kate bar at station 3 dipped land­ and general principles of coastal storm flows and sedimen­ ward at no more than 120 (Figure 5B). Such low-angle cross­ tation ie.g., HAYES, 1967; DUKE, 1985; SWIFT et al., 1986; beds result from either a large suspended sediment load, or NUMMEDAL and SNEDDEN, 1987), we can shed some light on very deep water relative to the height of the lee slope of the sediment dynamics during hurricanes at Carrabelle Beach. bar (BLATTet al., 1978). The bedload-dominated shallow-water transport occurring during swash bar (or berm) construction Deposition of the Stranded Bars at Carrabelle Beach produces dip angles near the angle of repose , as seen in accre­ Accretion of sediment on the beach during hurricanes is tionary berms (HAYES, 1972). It is reasonable to assume that unusual. The recurrence of stranded bars at Carrabelle the suspended load was large during the hurricane. The max­ Beach suggests that the local bathymetry and coastal geom­ imum water depth over the Kate bar could not have been etry promote a unique combination of water elevation and greater than 2 m at the height of the storm. The foresets were storm wave histories in this part of St. George Sound. The tangential at the bottom and the top, indicating that deposition internal stratification of the stranded bars is also dependent was continuous during bar construction. The uninterrupted de­ on the timing of the storm surge and waves . This section will position at this site is in sharp contrast to the multiple erosion thus discuss the specific timing of waves and elevations at and deposition events recorded at station O. Carrabelle Beach, as they pertain to sedimentation at the Examining the stratification within the Kate bar with re­ study site. Because of the lack of direct observations during spect to the environmental conditions discussed above sug­ the storms, however, this discussion is limited. gests that the cross-beds were deposited while storm waves A cross-section of the Kate barjust west of the river (Figure were still entering the sound, before 2400 GMT November 7A) reveals stratification similar to swash bars (ALLEN, 21. The wave energy steadily decreased after this and the 1982). Neither bar contained this bedding to the west. Within water level began to drop. The transition to concentric bed­ the central part of the study area, both bars consisted of thin ding occurred before the storm surge had fallen by more than beds and laminae of quartz and heavy minerals. This concen­ 1 or 2 m. The shift in depositional mode, from bedload to tric stratification was more common at the western end of suspended load, was accompanied by a translation of the surf the study area, which is farthest from the mouth of the Car­ zone to seaward and a decrease in wave energy. The resulting rabelle River. rapid change in flow and wave conditions permitted deposi­ The storm wind during Kate (Figure 2) was similar to that tion of horizontal laminae and flotsam. during the last part of Elena's passage; th e main difference The wind (Figure 2) was blowing from the north (offshore) was the slow build-up of onshore winds on November 21. for most of Hurricane Elena, and it shifted rapidly to south-

J ournal of Coastal Research, Vol. 16, No.4, 2000

1106 Keen and Stone

A) STATION 1 B) STATION 2

C) STATION 3 D) STATION 4

FINE-GRAINED SEDIMENf E) STATION 5

SEA OATS DEBRIS AND HOMOGENEOUS SAND

!II:iooo---:"'" EROSION SURFACE

Figure 6. Photographs of pits dug in th e Elena stranded bar at (A) station 1,(B) station 2, (Cl station 3, (Dl station 4, and (E) sta tion 5. See Figure 4 for locations.

Journ al of Coastal Research, Vol. 16, No. 4, 2000 Beach Respon se to Hurricane Waves 1107

A) STATION 0 B) STATION 2 ~----,.--"n

OVERLAPPING DEPOSITION UNITS

C) STATION 3 D) STATION 4

SURFACE DEBRIS ONLY

DIFFlSE HEAVY­ MINERAL IAMINAE

LAND Figure 7. Photographs of pits dug in the Kat e stranded bar at (A) sta tion 0, (B) sta tion 2,(C) sta tion 3, and (D) sta tion 4. See Figure 4 for locations.

erly after 1800 GMT September 1. This onshore wind gen­ tained storm waves within the sound would have been a sig­ erated storm waves that entered St . George Sound through nificant factor as well. Oth erwise, th e deposition of the Elena East Pass. The peak storm surge would have occurred shortly bar was probably very similar to concentric deposition within thereafter. Storm waves with in th e sound would have de­ the Kate bar as described above. creased after 0400 GMT September 2 as th e wind died down. There is no evidence of swash bar constru ction during Hur­ Evolution of the Sediment Pool ricane Elena. Thu s, it app ears that the storm surge of Kate must have exceeded 1.5 m, which was the maximum during The sediment within th e Kat e bar was close to a Gaussian Elena, to deposit th e cross-beds of the Kate bar. The sus- distribution, which commonly results from sediment settling

Journal of Coastal Research, Vol. 16, No.4, 2000 1108 Keen and Stone

Table 1. Statistical moments for the grain size distribution data for sam- ple suites collected at stations indicated in Figure 2. For suite names, E represents Elena suites and K represents Kate suites. Mean and standard -1 deviation are given in phi units (Phi = -logJ)(mm.t). e e Elena No. Standard o Kate Suite Samples Mean Deviation Skewness Kurtosis 0 C/) 2.126 .373 -.129 3.471 C/) El 8 Q.) e E2 20 2.174 .327 .0128 4.560 c: 3= a E3 10 2.167 .339 .0967 3.746 CD ~ 00 E4 19 2.259 .300 .0499 5.583 C/) E5 10 2.243 .317 .0229 4.004 0 KO 9 2.224 .311 .0518 3.292 K2 7 2.188 .301 .0273 3.910 K3 9 2.181 .337 .008 3.779 +1 K4 19 2.264 .325 .049 3.954

Kurtosis through the water column (TANNER, 1983). This depositional Figure 8. Bivariate plot of skewness-versus-kurtosis for sample suites mode is in agreement with the stratigraphic relationships be­ from both bars. Solid circles are Elena suites and open circles represent tween the flotsam and laminae. This greater maturity also Kate suites. suggests greater reworking of the Kate sediment than the Elena sediment. The Elena sediment had a larger silt and clay component ready been concentrated within the Elena stranded bar be­ than did the Kate sand pool, which implies that the finer fore Hurricane Kate. particles were not completely removed from the area before deposition. The Elena sediment contained a statistically sig­ CONCLUSIONS nificant vertical division within the bar. This temporal trend towards finer and better-sorted sediment implies that the Evaluation of the sedimentary structures and textures of wave energy level was decreasing and the suspended sedi­ the 1985 stranded bars from Carrabelle Beach, Florida, sug­ ment load was not homogeneous, i.e., the sand pool was be­ gests that these bars were partly constructed by sediment coming texturally more mature during deposition of this bar. settling from suspension in very shallow water. An exami­ If the Elena bar was deposited as quickly as the Kate bar nation of the winds and storm surge during Hurricane Kate appears to have been (less than 6 hours), this implies a very (November 1985) indicates that this mode of deposition was possible after the storm waves diminished, but while coastal efficient winnowing process. Sediment texture is not typically uniform across the near­ shore zone. The coarsest and poorest-sorted sediment is found at the plunge point. The swash zone contains finer and bet­ 10r------, ter-sorted sediment (BRENNINKMEYER, 1978; STAPOR and MAY, 1982; STONE, 1991; STONE et al., 1992). During high­ energy events this cross-shore variability should be smeared out, as was found for the open gulfbeaches northeast of Car­ c:: rabelle Beach by RIZK and DEMIRPOLAT (1986). They recog­ o nized homogenization events in swash and plunge-point sam­ ~ 'S; ples collected following Hurricanes Elena and Kate, with tex­ OJ tural recovery beginning almost immediately after each (:) 0.1 "C L- storm. This result is supported by the lack of any cross-shore ~ "C textural trends within the Eloise stranded bar (COLEMAN, c: ~ 1978). The weak alongshore pattern in the mean and stan­ en 0.01 e Elena dard deviation for the Elena bar may have been caused by o Kate shore-parallel flow during most of that storm. MAy (1973) proposed that relict heavy minerals may be stored and concentrated within the sediments of the lagoon because of limited exchange with the open ocean. In addition, 0.01 0.1 1 10 erosion of the heavy-mineral-rich berms on the beach during Mean (%) storms supplements the lagoon source (STAPOR, 1973). Both Figure 9. Tail-of-Fines Diagram. The mean of the weight-percent fines of these sediment pools were entrained during the hurricanes for each suite is plotted against the standard deviation of its weight­ at Carrabelle Beach but, because greater backshore erosion percent fines. Solid circles are Elena suites and open circles are Kate occurred during Hurricane Kate, the second process would suites. The divisions on the plot represent observed limits from modern environments. have predominated. Furthermore, these minerals had al-

Journal of Coastal Research, Vol. 16, No.4, 2000 Beach Response to Hurricane Waves 1109

water levels remain ed elevated. The sediment dynamics th at significance of grain size parameters. Journal of Sedimentary Pe­ produce such a localized settling phenomenon are poorly un ­ trology, 27, 3-26. FRIEDMAN, G. M., 1961. Distinction betw een dune, beach , and river derstood. sa nds from their textural characteris tics. Journal ofSedimentary The data presented here also show th at th e generally ac­ Petrology, 31, 514-529. cepted notion of an erosional beach response to hurrican es is GORSLINE, D.S., 1966. Dynamic characteristics of west Flor ida Gulf not univ ersal. Storm sequences th at are deposited as sheets coast beaches. Marine Geology, 4, 187-206. from suspension are common on the inner shelf. Storm sed­ HAYES, M. D., 1967. Hurrican es as geologic agents: Case studies of Hurricanes Carla, 1961, and Cindy, 1963. Report ofInvestigations imentation also consists of localized bars constructed by bed­ No. 61, Bureau of Economic Geology, Texas University. load transport processes within the surf zone or the swash HAYES, M.D., 1972. Forms of sediment accumulation in the bea ch during the relaxation stage of the storm. Observation of zone. In MEYERS, RE. (ed.), Waves on Beaches and Resulting Sed­ storm-related bar formation, however, ha s been limited to ac­ iment Transport. New York: Academic Press, pp. 297-356. cretionary berm s. Bars formed during severe storms ha ve not HUNTSBERGER, D.V. and BILLINGSLEY, P., 1975. Elements ofStatis­ tical Inference (5th Edition). Boston: Allyn and Bacon , Inc., pp. 243­ been observed directly. 273. KAHN, J .H. and ROBERTS, H.H., 1982. Variations in storm response ACKNOWLEDGEMENT along a micro-tidal transgressive barrier island arc. Sedimentary Geology, 33, 129-146. The first author was fund ed by the Office of Naval Re­ KEEN, T.R, 1986. The sedimentology of a stra nded bar and impli­ search, program element 62435N . Cartographic assistance cations for its origin. In : TANNER, W.F. (ed.), Suite Statistics and was provided by Mary Lee Eggard and Clifford Dupl echin of Sediment History, Proceedings ofthe Seventh Sy mposium on Coast­ al Sedimentology. Tallahassee: Florida St ate University, pp. 167­ Louisiana State University. 179. KEEN, T.R, 1987. The compara tive sedimentology of two stra nded UTERATURE CITED bars and implications for their origin. M.S. Thesis, Florid a State University, Tallah assee. ALLEN, J .R.L., 1982. Principles of Physical Sedi mentology. Boston: KOFOED, J.W. and GORSLINE, D.S., 1963. Sedimentary environ­ George, Allen , and Unw in , 272 p. ments in Apalach icola Bay, Florid a: Journal of Sedimentary Pe­ BLAIN,C.A , 1997. Modeling methodologies for the prediction of hur­ trology, 33, 205-223. rica ne storm surge. In: SAXENA, N. (ed.), Recent Advances in Ma­ LEATHERMAN, S.P., 1979. Barrier dune systems: A reassessment. rine Science and Technology, 96. Honolulu, Hawaii: Pacon Inter­ Sedimentary Geology, 24, 1-16. na tional, pp. 177- 189. LEATHERMAN , S.P.; WILLIAMS, AT., and FISHER, J .S., 1977. Over­ BLAI N, C.A; WESTERINK, J .J ., and LUETTICH, RA, JR., 1994. The wash sedimentation associated with a large scale Northeaster . influenc e of domain size on th e response characteristics of a hur­ Marine Geology, 24, 109-121. ricane storm surge model. Journal of Geophysical Research, 99, MAY, J.P., 1973. Selective tran sport of heavy minerals by shoaling 18467-1 8479. waves. Sedimentology, 20, 203-211. BLATT, H.; MIDDLETON, G., and MURRAY, R , 1978. Origin of Sedi­ MORGAN, J.P.; NICHOLS, L.G., and WRIGHT, M., 1958. Morphological mentary Rocks. New York: Pr entice-Hall, 634p . effects of Hurricane Audrey on the Louisian a Coast. Coastal Stud­ BRENNINKMEYER, B.M., 1978. Littoral sedimentation. In: FAIR­ ies Institute Report 58-3, Louisian a State Universi ty, Baton BRIDGE , RW. and BOURGEOIS, J. (eds.), The Encyclopedia of Sed­ Rouge. imentology. Stroudsberg, Pennsylvani a: Dowden , Hutchinson and NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, 1985. Ross, pp. 448-457. Tide tables 1985, High and low water predictions, East Coast of BURDIN, W., 1975. Surge effects from Hurricane Eloise. Shore and North and South America, including Greenland. Beach, April , 2- 11. NUMMEDAL, D. and SNEDDEN, J .W., 1987. Sediment exchange be­ COLEMAN, C., 1978. The stranded bar: A study of bar formation dur­ tween the shoreface and continental shelf-evidence from the ing sto rm surges at Carrabelle Beach, Florida. M. S. Thesis, Flor­ modem Texas coast and the rock record . Proceedings of the Spe­ ida State Univers ity, Tallah assee. cialty Conference on Coastal Sediments '87 (American Society of DEBusSCHERE K ; PENLAND, S.; WESTPHAL, KA; MCBRIDE, RA, Civil En gin eer s), pp. 2110--2125. and REIMER, P. D., 1991. Morphodynam ics of the Isles Demieres NUMMEDAL, D.; PENLAND, S.; GERDES, R; SCHRAMM, W.; KAHN, J. , barrier shoreline, Louisian a. Proceedings of the Specialty Confer­ ence on Coastal Sediments '91 (America n Society of Civil Engi­ and ROBERTS, H., 1980. Geologic respon se to hurrican e impact on neers), pp. 1137-1151. low-profile Gulf coast barrier s. Trans actions, Gulf Coast Associa­ DINGLER, J . R and REISS, T.E., 1995. Beach Ero sion on Trinity Is­ tion of Geologic Societies, 30, 183-195. land, Louisian a Cause d by Hurrican e Andrew. In: STONE, G.W. PENLAND, S.P.; SUTER, J .R; SALLENGER, A.H.; WILLIAMS, S.J .; and FINKL, C.W. 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Hummocky cross-stra tification, tropical hurri­ sity, Tall ahassee , p.129-142. can es, and intense winter storms . Sedimentology, 32, 167-194. SCHRAMM , W.E.; PENLAND, S.; GERDES, RG., and NUMMEDAL, D., DUKE, W.L.; ARNOTT, RW.C., and CHEEL, R. J. , 1991. Shelf sand­ 1980. Effects of Hurrican e Frederic on Dauphine Island, . stones and hummocky cross -stra tification: New insights on a Sh ore and Beach, 48 (4), 20--25 . stormy debate. Geology, 19, 625-628. SEXTON, W.J . and MOSLOW, T.F., 1981. Effects of Hurrican e David, FINKL, C.W. and PILKEY, O. H.(eds. ), 1991. Impa cts of Hurrican e 1979, on the beache s of Seabrook Island, South Carolina . North­ Hugo: September 10--22, 1989. Journal Coastal Research, Special eastern Geology, 3 (3/4), 297-305. Issue 8, 356 p. SEXTON, W.J . and HAYES, M.D., 1991. The Geologic Impact of Hur­ FOLK, RL. and WARD, W.C., 1957. Brazos River bar: A study in the ricane Hu go and Post -Storm Shoreline Recovery along the Unde-

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