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Journal of Coastal Research 785-S00 Fort Lauderdale, Florida Summer 1993 I
The Effect of Tide Range on Beach Morphodynamics and Morphology: A Conceptual Beach Model Gerhard Masselink and Andrew D. Short
Coastal Studies Unit Department of Geography University of Sydney Sydney, New South Wales ~:OO6,Australia
ABSTRACT
MASSELINK, G. and SHORT, A.D., 1993. The effect of tide range on beach morphodynamics and morp.hology: A conceptual beach model Journal of COCI8talResearch, 9(3). 785-800. Fort Lauderdale (Flonda), ISSN 0749-0208.
Natural beaches may be grouped into several beach types on the basis of breaker height (H ) wave period ('!'), hia:h tide sediment fall vel~ity (~,) and tide r8lll!e (TR). These four variables are qu:n'tified by two dlmens~onl~ par~eters: the dimensionless fall velocity (0 - HJw,T) used byWRIGHTandSHORT(1984) to classify ml~ro-tld.al beaches, and ~e !elative tide range (RTR - TR/H..) introduced in this paper. The valu~ ~f the ~Imenslo.nless fall ve~oclt~ mdicates whether reflective, intenaediate or dissipative surf zone condl.tlons will prevail. The relative tide range reflects the relative impodance of swash, surf ZODeand shoalmg wave. processes. A co~ceptual model presented in which beach morphology (beach t.nJe) may be predicted using the . i~ dimensionless fall velocity and the relative tide range, whereby the mean spring tide range (MSR) is used to cal~ulate the re!Ative tide r8lll!e. The model consists of the existing miao-tidal beach types, which as RTR I~creases, shift from reflective to low tide terrace with and finally wi&hout rips; from intermediate to low tide bar and ~~s an~ finall! ultr~-diasipative; and from barred dissipative to non-barred dissipative and finally ultra-dissipative. USing this model, all wave-dominated bead1esin all tidal ranges can be . classifil'd.
ADDmONAL INDEX WORDS: Beaches and tide range, micro-tidal, maero-tidal, beach model. beach change.
INTRC.DUCTION planar, moderate. wave multi '-bar, and low wave On all natural bea.ches, processes and mor- to tidal flats. .This grouping, while illustrating the phology arepredomiI1laDtly influenced by waves range of morphologies associated with macro':tid- and tide. Whereas the importance of waves is self- al beaches, is still based largely on wave height evident and well documented (WRIGHTet al., 1984, and does not enable differentiation based on tide 1985), the influence (Jlftides, though recognised range> 3 m. (e.g. WRIGHTet al.j 1987), is more subtle and less This paper addresses this problem by combin- well understood. Tide ranges have been classified ing wave height and tide range into a singledi- by DAVIES(1964) as being mlcro- « 2 m), meso- mensionless parameter, and calibrating the ap- plicability of this parameter using field data and (2-4 m) or macro-tid:al (> 6 m). Consequently, ~ beaches can be classified accordingly. .However, the literature. as DAVISand HAYES(1984) indicated, beach mor- BACKGROUND phology is not simply dependent on the absolute wave height or tide range, but on the interaction Several beach models are available to predict beach state as a function of wave and sediment of the two. " . Existing micro-tidal beach models assume a mi- parameters (SONU, 1973; WRIGHT and SHORT, 1984; SUNAMURA,1989; LIPPMANN and HOLMAN, 1990). cro-tide range « 2 D1)in the presence of oceanic waves. Therefore, they can not automatically be The models are generally representative of micro- applied to macro-tidal beach environments. SHORT tidal beaches and do not take account of the tide. (1991) addressed this problem, suggesting the mi- Numerous studies (reviewed later) have also in- vestigated the effect of tides and increasing tide cro-tide threshold be I"aisedto 3 m, and proposing range 'on beach morphodynamics. However, the a grouping of macro-tidal beaches into higher wave overall contribution of tides to beach morphology remains unresolved. 92017 received 2A:iFebruary 199)!; accepted in revuion 6 December 1992. The model of WRIGHTand SHORT(1984) is use- 787 .,.~o,.;..III"u...U -'U...... Conceptual Heach Model 'au ful hr describing the morphodynainic variability es with highl) .able tide ranges, sediment sizes tide level and the. lIebreak point and. the shoal- !«iN rw LOwI1Df of micro-tidal surf zones and beaches. This model and morphologies. In order to examine the rela- in!! wave zone extends seaward from the ~ ~IOOuvn U'YfI. tive contribution of both Hb and TR, this paper point. For each zone, an empirical relationship , describes plan and profile configurations of six ~g between the equilibrium beach gradient and wave major beach states. In addition to providing a combines and extends the ideas in WRIGHT and ~~ 75 spatial classification. the model enables~he pre~ SHORT (1984) and SHORT (1991) by considering and sediment characteristics is assumed. The sim- ~~ diction of beach change and equilibrium beach the relative effects of waves and tides on beach ulation model combines these relationships with e!j so states (WRIGHTet ai., 1984,1985). The beach states morphology. Following a suggestion in DAVISand the relative occurrences of swash. surf zone and g't: HAYES(l984:Figure 8), the relative tide range RTR shoaling wave processes for different parts on the .~; 2S. are related to wave and sediment characteristics ~:; via the dimensionless fall velocity, 0 -= Hb/w,T is introduced as a new parameter. The relative beach profile and computes an "equilibrium" .c beach profile, Input parameters to the model are 0-0 (GOURLAY.1968; DEAN. 1973), where- Hb is the tide range is given by the ratio of tide range to ~ 0.25 0.50 0.75 1.00 1.25 1.50 TR/H,J. Large values of wave height, wave period, sediment size and tide breaker height (m), w. is the sediment fall velocity breaker height (RTR = non-dimclUional dcpch rclativc 10 hilh tide IeYeI range. For more details. see MASSELINK(in press). (m/see) and T is the wave period (see). RTR indicate tide-dominance and small values Figure 1. Relative occurrence o( awash and aurl wne proceasn Figure 1 illustrates the results of the simulation - According to WRIGHT and SHORT (1984), con- express wave-dominance. over a dimenaionle.. beach profile (or relative tidr ranCeI (TRI mode] using wave height 1 m, wave period ditions when 0 < 1 result in a reflective beach A conceptual model is presented according to = = 8 H.) 0(2. 3, 5, 10 and 15 ca1culaud over half a tidal cycle (low 0.03 m/sec and vary- tide to high. tide). The importance oC awash and surC wne pro- state. The beach face will be steep and is generally which the beach state is a function of dimension- sec. sediment-fall velocity = cessea deereuea as relative tide range increases. Swuh and lurC cusp ed, and a pronounced step is usually present less fall velocity n and relative tide range RTR. ing the tide range from 2 to 15 m. It shows that the contribution of swash and surl zone processes wne proceaaes ahow a aecondary maximum oCoccurrence around at the base of the swash zone. Generally wave Beaches on the macro-tidal central Queensland low tide level, where the tide remaina relatively Il4tionary Cor height is small and beach sediments are relatively (Australia) coast and the literature are used to decreases as the relative tide range and the con- BOrne time. The relative occurrencea are calculated by . limu. coarse. Intermediate beaches have values of 0 illustrate the model. tribution of shoaling waves increases. Swash and lation model described by MASSELINK (in preaa). The input parameten to the model are wave height 1m,.ave period ranging from 1 to 6 and are characterized by bar surf zone processes always dominate the upper - - EFFEcr OF TIDES ON SURF intertidal and have a.see.ondary maximum around 8 .ee, lediment Call velocity -0.03 m/aec and tide ranee - 2,3, and rip morphology. Four different intermediate ZONE DYNAMICS 5, 10, 15 roo beach states are defin~d and with increasing 0, low tide level where the- tide level remains rela- these states are low tide terrace (LIT), transverse According to DAVIS(1985), tides playa passive tively stationary during the turn of the tide. The bar and rip (TBR), rhythmic bar and beach (RBB) or indirect role in sediment transport and changes lower part of the intertidal profile, however, may and longshore bar trough (LBT). When n > 6, in beach morphology. The primary role of the tide become completely dominated by shoaling waves to the more accentuated topography during neap the beach is in a dissipative state. On dissipative is to alternately expose and submerge a large por- for large relative tide ranges (RTR > 10). Other tides. beaches. the wave energy level is generally high. tion of the beach and the inner surf zone. The net results of the simulation model further suggest In addition, tides have three pronounced effects sediments are fine and the surf zone is wide. Sub- . result of this movement of sea level is to retard that as the contribution of shoaling waves in- on three dimensional water circulation in the dued bar morphology may be present but rips are the rate at which sediment transport and changes creases with increasing tide, beach gradient de- nearshore zone. First, in rip current systems...!iE! usually absent. in morphology take place. This may be illustrated creases (MAssELINK, in press). are strongest at low tide. when the water is suf- by the findings of DAVISet ai. (1972) who showed The dominating role of shoaling waves on ficiently shallow to concentrate the flow oC the The model of WRIGHT and SHORT (1984) was that bar migration rate decreases with increasing beaches with large relative tide ranges has been current within the rip channels (SHEPARDet 0/., developed on and for micro-tidal environments - (TR <2 m) and the tide range is not accounted tide range. verified in the field by WRIGHT et ai. (1982b) who 1941). Maximum rip current velocities occur dur- for, preventing application of the model to envi- However, the tide does more than just retard conducted field experiments on Cable Beach. ing the falling tide (McKENZIE. 1958); and ac- cording to COOK (1970), on most beaches, rips ronments with larger tide ranges. The first, and surf zone processes. During a tidal cycle. the po- Western Australia (mean spring tide range 9.5 m sition of the swash zone, surf zone and shoaling -and RTR = 12). They concluded that under modal become better developed when the tide is falling so far only. attempt to include the tide into some . Bort of conceptual beach model is by SHORT(1991) wave zone is shifted with the tide both vertically wave conditions in the low- to mid-tidal zones, or low. Second, offshore directed bottom flow (of- who proposed a tentative grouping of micro- to and horizontally. causing the intertidal beach pro- most ol the work was performed by unbroken ten misnamed as "undertow") is~enhanced at shoaling waves rather than surf zone processes.. macro-tidal beach and tidal flat systems. Accord- file to be influenced to varying degrees by each of the falling tide, as shown by RUSSELLet 0/. (1991). ing to SHORT (1991), beaches with macro-tidal these processes every 12 hours. This is illustrated and only in the high tide zone did surf zone pro- who monitored suspended sediment transport cesses dominate. during a storm (Hb , ranges (> 3 m) may form the transition between in the results of a simulation model developed by = 3 m) on a beach with a large wave-dominated micro-tidal beaches and tide- MASSELINK(in press) which investigates the im- The movement of the three morphodynamic tidal range (up to 9 m). They found a distinct dominated tidal fiats. He distinguishes three types portance of swash, surf zone and shoaling wave ZODes across the profile during each tidal cycle asymmetry in the cross-shore suspended sedi- of macro-tidal beaches on the basis of the wave processes over the beach profile as a fU!lction of has strong implications for cross-shore bar for- ment transport about high tide, with little net energy level. High waves (Hb >0.5 m), and par- relative tide range. mation and morphology. Laboratory studies have transport on the flooding tide, and strong net off- ticularly swell. produce moderate gradient (1-3°), This simulation model calculates over half a shown that the presence of a tidal range inhibits shore transport on the ebbing tide- Third, on concave, planar beaches. Moderate waves and sea tidal cycle (from low water to high water) the offshore bar formation (e.g. WATTSand DEARDUFF. beaches with large tide ranges, shore-parallel tidal 1954), while HEDEGAARDet ai. (1991) found that conditions result in lower gradient (0.5°), multi bar relative amount of time that different locations currents play an increasing role in longshore sed- (ridge and runnel) topography. As wave energy on the beach profile are in the swash, surl and the formation of bars is suppressed when RTR > iment transport on the lower intertidal and sub- drops even further, a third type is produced with shoaling wave zone. The swash zone is defined as 3. From field experiments on micro-tide beaches, tidal zone of beaches (WRIGHT et al..-1982b). a high tide beach fronted by a tidal flat. the zone between the quasi-stationary mean sea WRIGHT et ai. (1986, 1987) concluded that in- The following points may bCtsummariz~ about creasing tide range resulted in more subdued bar- This grouping, however, is primarily based on level (tide level) and the maximum runup height. the influence of the tide on beacnmorphodyna- The surf zone is defined as the area between the trough topography during spring tides, compared mics: (1) incr~_asing ti!i_e_J'8Ilg~ft!ta.rds the rate at . H" and as a result includes in single groups beach-
n ., ~n.n... .J,,"m..1 r.OIO~tJl' Vol. 9. No- 3. \993 ,..1'(' 1D L "...' "r RPI'''''rch- ''''''n~.' ""'- 1--
. 788 Masselink and Short Conceptuel Beach Model 789
T.Ye L Mean .spri",! tide range. infe~ modal wave conditions. sediment c""roderisti.. for tM m,h lide beoch. relotWe lide ro,.,e ond tM dimenslonleu faU velocity of the studied beaches.
. MSR H. T D.. Q Lacation (m) (m) (see) (mm) ...... N RTR 0 - .' ~q Ce-.I Queenslaud Field Silel '\ a '" eo.- TreeB. 4.9 0.4 5 0.87 12 0.6 <10:'" 4 q ~bert.s B. 4.6 0.6 5 ...~"'...";' -!~ 0.69 8 1.3 ". ... c..- 88y 3.6 0.3 6 0.29 12 1.3 i Anastrong B. . ...F',. U 0.3 6 0.34 16 ""'" 5 "'", H8rbour B. 1.3 "I.. ". 4.6 0.6 6 0.52 8 1.6 "' ' Eo.aPark B. 3.6 0.36 . 6 0.24 10 1.9 .. ". ..p '"p NiBe MileB.south ~.~ "" '.'.. I" . ~ ~.!= ~ u.oo 6 2.2 - s.nioa B. .: /" ~ 4.9' 0.6 6 0.30 10 2.4 """'" \" Niae MUeB.central 3.9 0.76 "0 -- --. .. 6 0.26 6 3.7 6 . -. B. 4.6 0.4 6 0.18 12 4.1 Famborough B. south : -, -'.. 3.6 0.4 6 0.16 9 4.1 . I"8mborough B. central Coral 3.6 0.6 6 0.21 6 4.1 " .4$ 5 "'.y 0.3 6 0.13 16 4.7 Sea Mile B. north -- 3.9 0.76 6 0.21 6 6.1 Fanborough B~lIorth 3.6 0.6 6 0.14 7 6.9 W-.rT et aL (1982b)
c.we B. 9.6 0.8 10 0.26 12 2.4 J- and IiARnISTY(1984) PtmcIine Sands 7.6 0.8 7 0.17 9 6.8 KJM;(1972) BI8ckpooI B. 7.6 0.61 6? 0.22 16 3 Draridce Boy . . U 0.61 61 0.84 9 0.6 MSR spring tide range (m): H.-inferred IIIOdaIbreaker beicht (m); - - T -.modal wave period (see)' meaD hich tide .D.. - ~uediment size (1IUD):RTi\.-:-relati4eticierange (MSR/IIJ: 0 -dimensionless fall velocity
Ficure 2. The maao-tidal. centnl QueeD8landcoastline aDd the eo-tidal lines of the muimum spring. tide range (eo-tidallines Bumd's coastal observation prograni(COPE) and es .with 0 <2 and RTR <15 (Lambert's Beach, after BPA, 1979). Depth contours are in meten. filum offshore wave rider stations at Yeppoon Harbour Beach, Emu Park Beach, Grass Tree (SPA, 1979) and Mackay (BPA, 1986). Tidal Beach, Cooee Bay) all possessed three character~ chracteristics are published for the Standard istica. Firat, a steep reflective high tide beach, which sediment transport and' morphological Queensland coast were selected for field investi- .-u Hay Point and Mackay, and the secondary usually cuaped and composed of coarser sand. changes take place, (2) an increase in tide range gations (Figure 2). The aims were to 8II!M!88the. (MR1s Port Clinton and Rosslyn Bay (Figure 2) in Second, the high tide beach terminates at a dis- results in an increase in the importance of shoal- relative contribution of grain size, wave height Australian Tide Tables (1992). The high tide beach tinct break in slope and sediment, and finally, ing wave processes which in turn prodQce lower and tide range to beach morphology. To achieve &ecliment size; modal wave height and period are seaward of the slope break is a lower gradient, used beach gradients, (3) large relative tide rlmges in- this, a number of sites were selected having dif- to compute the dimensionless fall velocity finer sediment, more dissipative,low tide terrace. 9, and the mean spring tide range together with hibit offshore bar formation and even on micro- ferent sediment, wave and tide characteristics. Usually the beach groundwater outcrop (effiuent tile modal wave height is used for obtaining the tidal beaches can suppress accentuated bar-trough Following a visual survey of around thirty line) is located at the slope break, resulting at low morphology (RBB and LBT states), (4) rip cir- beaches located around Mackay and Yeppoon rela1ive tide range (Table 1). Cross-sections of all tide in a dry upper beach and a wet low tide listed beaches are illustrated in Figure 3. They culation and seabed return flow is enhanced at (Figure 2),11 were selected for more detailed field terrace. haw been positioned on the basis of their dimen- low tide and diminishes at high tide, and (5) on investigation, with 15 transects surveyed acroai Where 0 > 2 and RTR < 15, the beaches either macro-tidal beaches shore parallel, usually re- these beaches. For the purpose of this study, the aioDleas fall velocity (0) and relative tide range have a low gradient mid-intertidal zone and barf (B.TR) value. versing, tidal currents become increasing domi- following data were collected at each site: beach rip morphology around low tide level (Nine Mile . The beaches with a mean spring tide range <4 nant seaward of the lower intertidal zone. morphology and cross-sectional profile, beach Beach north,. central and lOuth, F~borough sediments, modal wave height and period and tide. m are. from the Yeppoon region, the other beaches Beach central) or are fiat and featureless through- characteristics. are found around Mackay. In addition to the cen- out (Famborough Beach north and lOuth, Sarina CENTRAL QUEENSLAND MACRO-TIDAL All beaches were surveyed at low tide using a tral Queenaland beaches, several beaches from Beach, Bucasia Beach). These two types of beach- BEACHES. theodolite and leveL Sediment samples were col- other macro-tidal coastlines, extracted from the esean not be discriminated on the basis ofO. They literature, are also listed in Table 1. In order to investigate the morphological char- lected from the high tide swash zone and analyaed do, however, have distinctly different relative tide acteristics of beaches with large (relative) tide using a settling tube. Wave characteristics were Based on Table 1 and Figure 3, four types of ranges (Table 1, Figure 3). The barred beaches ranges, several beaches on the macro-tidal central extracted from the Queensland Beach Protection beaches can be identified. The Queenalandbeach- all have relative tide ranges <7, while the fiat and \.,,,,, ih'/, .Hul!t:J '-I)lU". J" '1!:11
.: I D IMENSI ONLESS.FALt'Y-ELPCITY.."i(2.;::Hb/ws T I I "~~;P~M"PNSJ6N~LESSFAtLVEtObhIy~i~~Qi=-tHb/W~T .. 0 12345 6 REFLECTIVE INTERMEDIATE DISSIPATIVE 0 2 . 4 riJ.,~/ntlUJd 5 ~&'elnINUl .0 reflective barred barred dissipative ': - - '6.u",p~ip .D -4 .J::i ""' ' 0L 200 NinemileB. central NinemileB. nonh Mtp".,.,tIi ::r:: G/~":,,,/.. ::r:: -l - . ~ ...... --.. . (~ . ~ .~. ., ; .--, "- .--, U) ~ U) . - KII 100 B. B. f'.-du~ lciufu) . - - .w..a...J-.bipl;t...... Nin~~i~c Farn~~~;:'fh . ::;E r l'.[~~. ::;E 6,uplH.dif- . '.' -"-, " P' 1(1) II 0 '100 L TT LTT ~Farnborough B. nonh 11 - ..rip ~ . ~. E-< 8 - - ~B. Harbour B. JUu... riJp/ru_JLamben's ~ .~ ~ ~. ~ -- - --. P' ~~_. ~ f~ahuJC$S"'... fow~~~ce-+ rip-:- Drungcayd B LTT Faroborough B. south Pcndine Sands d " --. ~ d :io!:~;:~ Z - ~. ~Emu Park B. ~Sarina B. Z ~ -nf~~e ~ rid~/ntlUU' ~ ~ P' 0 lOG )GO ~ ..., - t::I fI41tUlJ ~/~nnd ..., ..., ...,..., ..., .; ..., ..., ..., )000004 ------;------..., L~T_. IUIlurdus or- '------12 ' - - - -' - - - - - E-< _ LTT low tide terrace ultra-dissipative ~ ~ 8 Gr.ISS Tree B. Cooee Bay LS .~ ~ OIblcB. BucasiaB. > :> . -1':">:' . ~ ~ '~,-, - ~.tttlJull4nku ...4 ...4 ~.. ~ ~. : ~ .~~1"~~*~;T"~ ~V) 0 IOO,:IDO JOCI G 5GD IiCIO ~-'''''rippl''' Blackpool B. ..., I~ ..., ..., ., ; ------1- _.- ..., ..., ..., ~ ..., Armstrong B. ------'------~ 16 ------~ transition to tide-dominated tidal flats Figure 3. Plot of macro-tidal central Queensland beach profiles and several other macro-tidal beaches listed in Table 1. The beaches Fig.,. 4. Conceptual beach model. Beach slate is a function of dimensionless fall velocity (0 have been positioned in the graph on the basis of their dimensionless fall velocity (0 = Hbw,T) and relative tide range (RTR = TR/ HJw,T) and relative tide rang~ Hb), Mean spring tide range (MSR) is used to calculate RTR and the high tide sediment fall velocity is used to calculate O. Positioning (RTR -TRIHb). HT and LT refer to mean high tide and mean low tide level, respectively. = of the beaches is based on the center of the beach profiles, but in order to avoid overlapping of beach profiles, the position of some beaches may be slightly off center. The origin of the profiles is the mean high water spring level and the dashed lines indicate the mean low water spring leveL Beach morphology is indicated on each profile including low tide terrace (LIT) and three dimensional bar/rip topography. Note that examples of micro-tidal beaches where RTR <3 are not shown, nor are tidal flats where RTR having some salt tolerant vegetation around the The different beach types illustrated in Figure :> 15- high tide level. 4 are: reflective beaches, grading with increasing RTR into low tide terrace beaches with rips and CONCEPTUAL BEACH MODEL low tide terrace beaches without rips, interme- featureless beaches have RTR >7. This suggests than the artifact of a high wave cyclone event. Figure 4 presents a conceptual model based on diate barred beaches grading as RTR increase into {} that when > 2 a RTR threshold exists around Unforturmtely, the majority of these beaches are the micro-tidal beach literature (RTR <3) and beaches with bar/rip-morphology at low tide level, 7, which controls the presence « 7) or absence not readily accessible and, heI!ce, exact morpho- the macro-tidal beach literature and field data dissipative beaches with subdued bars produced (> 7) of low tide bar and rip morphology. dynamical data is not availab!e. illustrated it..F!gt.!!'~3 ~d Tz.b!8 1 fv~ RTR > 3. by low RTR, grading with increasing RTR into Macro-tidal beaches with rhythmic topography Finally, the Queensland beaches with large rel- The usefulness of the dimensionless fall velocity {} featureless non-barred dissipative beaches, and at low tide level are not uncommon on the central ative tide ranges (RTR > 15) are fronted by very in classifying micro-tidal beach morphology is finally both low tide bar/rip and non-barred dis- Queensland coast. Analysis of three series of aerial fine inter- and sub-tidal sediment (0.1 mm) and well documented and in Figure 4 is indicated by sipative beaches grading into ultra.dissipative photographs from the area north of Yeppoon a rippled verylowgradient « 0.5°) intertidal zone. those beaches where RTR <3. Figure 3 shows that beaches when RTR > 7. When RTR > 15, the showed numerous beaches, including Nine Mile The upper intertidal zone, however, may be either as both n and RTR increase, a logical sequence beaches begin the transition to tidal flats along Beach, with various low tide bar configurations steep and relatively coarse grained (Armstrong of change in beach morphodynamics occurs and the lines of SHORT'S(1991) Group 3. Even larger and rhythmic wave lengths ranging from 150 to Beach) or may consist of very fine sediments and that micro- and macro-tidal beaches may be mor- relative tide ranges (RTR ::>15) will result in true 300 m. The photos were taken just before the have a very low gradient (Ball Bay). These beach- phologically gr{)uped into different beach types ,tidal flats. tropical cyclone season, suggesting that the bars es form the transition to tidal flat environments on the basis of these two dimensionless parame- In the following section, each beach type is dis- reflect modal trade wind wave conditions, rather (SHORT'S (1991) Group 3) as indicated by Ball Bay ters. cussed and illustrated with examples from the
Joumal of Coastal Reaearch, Vol. 9, No.3, 1993 Journal of Coastal Research, Vol. 9, No.3, 1993 \ Conceptual Beach Model 793 Masselink and Short 792
Low Tide Terrace without Rips central Queensland sites and from the coa~talli~- erature. Unfortunately, many sites descn~ed In As the relative tide range exceeds 7, the very the literature provide only limited informatlo~ on wide and dissipative low tide terrace becomes in- characteristics such as wave height and period, creasingly dominated by unbroken shoaling waves tide range, grain size and beach gradient (~ro- (see Figure 1) which produce a uniform, feature- , ",- . -. ,. . : :: ' . "-',.., files). Therefore, many well known macro-tidal less low tide terrace (e.g. Harbour Beach, Figure - - -- beach sites cannot be used owing to the lack of 5b) without the formation of rip channels. Ac- sufficient environmental documentation in the cording to CARTER(1988), this type of low tide :'.~,':',..,.,.~~~,.~""~'~'~:--~'.,,,'.'_':".~:,.- "~..'~':~'El"""'~.'.~'.' ,,'-,:~".'.. literature. terrace beach is commonplace on high latitude coasts where the high tide beach consists of gravel ,\., ':~ ',,"" -,' fronted by a fine grained low tide terrace. KOMAR ::---'-: :"'::"':'::' IMPACT OF SPATIAL VARIATION IN (lG,oJ shows an exampie oi this type oi beach 0 AND RTR from the coast of Wales (Figure 11-6, p. 297) and Reflective Group (D < 2) KING (1972) presents data on Druridge Bay (Northumberland, England), a low tide terrace Reflective Beaches \ beach with ridges and runnels (Figure 3). In ad- Fully reflective beaches only exist in environ- dition, they have been reported along the ?ulf of ments when 0 < 2 and RTR < 3. The beach face California (INMANand FlLLOux, 1960) and m NW is steep and commonly cusped, and a pronounced Western Australia (HESP, personal communica- coarse step is usually found at the base of the tion). swash zone fronted bya lower gradient, finer grained subtidal zone (WRIGHT and SHORT, 1984). Intermediate Group (D = 2-5) The height of the step increases with wave height Interrqediate values of the dimensionless fall and grain size (HUGHES and COWELL, .1987; Figure 5. Examples of the di1rerent beach types for relative tide ranges larger than 3: (a) Low tide terrace with rips. Embleton velocity (0 2-5) and a relative tide range of <7 Bay, Northumberland (U.K.) is a beach eJ:pooed to the North Sea with a mean 8pring tide range of around 4.5 m and coane high SUNAMURA, 1989). Waves are generally surgmg or = will result in beaches with distinct bar-morphol- tide beach sand. The photo 8hows the beach with a dry, reflective and c:usped upper part of the profile, a wet and dissipative low plunging on the beach and most of the wave en- ogy and cellular rip circulation.. Two types of tide terrace, and rip currents In the 8ubtidal zone~ (b) Low tide terrace without rips. Harbour Beach (Mackay, central Queensland) ergy is at incident and subhannonic (twice the beaches may be distinguished. is a low tide terrace beach with a relative tide range of around 8 and a II value of 1.5. The upper part of the beach is steep and dry, wave period) frequencies (HUNTLEY and BOWEN, and evidence of cusp\ng is visible at the lower end of the beach. A flat and wet low tide terrace characteriaea the lower part - (c) Low tide barf 1975; WRIGHT and SHORT, 1984). of the Intertidal profile. Under modal conditions this beach is reflective at high tide and dissipative at low tide. Barred Beaches rip. Nine Mile Beach (Yeppoon, central Queensland) is characterised by a relative tide range of 5-6 and II is around 3.5. Transverse For the lowest relative tide ranges (RTR <3) har-rip morphology is present on this beach 88 Indicated by the dye pattern. The upper part of the profile is cbaracterised by the of a low but extenaive 8wash bar. During a spring tidal cycle, morphodynamic signatures on this type of beach are compleL Low Tide Terrace with Rips several types of bars may occur (e.g. LIPPMANN Atp"""""spring low tide, the 8urf is dissipative, from low-to-mid tide the transverse bar.rip 8ystem operates, from mid-to-high tide the and HOLMAN, 1990). The bar-topography may 8urf zone is once again dissipative, and reflective conditions may occur at 8pring high tide. (d) Non-barred dissipative. Rhossili Bay, As relative tide range increases to be~wee~ 3 consist of alternating transverse bars and rips, South Wales (U.K.) is expoeed to Atlantic 8well, consists of line sediments and is 8Ubject to a mean 8pring tide range of 9.5 m. The (e) and 7, and 0 remains <2, the steep, reflective high whereby the bars are attached to the shoreline beeeh is wide, planar and feature1ess. DissipatiVe surf zone conditiona prevail throushout the tidal cycle. mtra-dlssipative. Cable Be8dt (Broome, Weatem AustraIia) is an ultra-dissipative beach with a relative tide ranee of 12 and II is aroun4 2.5. Although the tide beach remains, while a relatively flat terrace and rip currents flow between the bars (e.g. SONU, forms around low tide level with rips. Usually the Intennediate value of II Indicates that rhythmic topography may develop, the relative tide range is too large, resulting in a flat and 1972; WRIGHT and SHORT, 1984; SHAW, 1985; JAG- featureless lower Inter- and suhtidal profile. A subdued ridge and runnel is often present around neap high tide level, while reflective h' h tide beach consists of significantly coarser GER et al., 1991). Alternatively, the bar may have coaditiona can produce cusps at 8pring high tide. (0 mtra-dissipative. Farnborough Beach south (Yeppoon, central Queensland) is se~iments than the low tide terrace. The textural a sinuous crescentic form (e.g. GREENWOOD and an uIUa-dissipative beach with a relative tide range of 6 and II is around 4. The Inter- and suhtidal profile is featureless and dissipative discontinuity is associated with a distinct break DAVIDSON-ARNOTT, 1979; GoLDSMITH et al., 1982; 8urf zone conditiona prevail throughout the tidal cycle. of slope and often the low tide beach gr?und v:a~r MGAARD, 1988a) or be linear (SALLENGER et al., outcrop (effluent line) is located at thiS position 1985; WRIGHT et al., 1986). WRIGHT et al. (1986, saturating the low tide terrace (Figure 5a). Beach 1987) found that even on micro-tidal beaches in- per iQtertidal zone, but are fronted by a low gra- Recent work on Nine Mile Beach suggests that cUsps may be present around high tide level and creasing spring tide range suppresses the forma- dient mid-intertidal zone, possibly with swash the bar and rip morphology is mainly driven by the low tide terrace can be dissected by small tion of the LBT and RBB with their deeper shore- bars, and then bar and rip morphology around processes occurring during neap (low) tides (un- (mini) rip channels. . . linear troughs in favour of shallower rip-driven low tide level (e.g. Nine Mile Beach, Figure 5c). published data). The higher energy central At high tide, surf zone processes are similar to TBR. Thus, an increase in (relative) tide ranges These beaches have more complex morphodyna- Queensland beaches (Nine Mile Beach and Farn- those on reflective beaches and waves are gener- will result in more subdued bar-morphology, but mie signatures and may experience reflective (high borough Beach central) and the meso-tidal beach- ally breaking or surging up the beach fac.e, ~he~e- with enhanced rip circulation at low tide. as during low tide the surf zone will be dlsslpat~ve tide), iQtermediate and dissipative (low tide) surf es (TR 4 m; Hb 1-2 m) of the Oregon (AGUI- zone conditions through the tidal cycle. The bar "" '" with several lines of spilling breakers. For relative Low Tide BarJRip LAR-TuNON and KOMAR, 1978; Fox and DAVIS, processes and rip morphology only exists on the low tide 1978) and the New England coasts (ZEIGLER and tide range values of up to 7, surf ~one = 3- lay a significant role on the low tide terrace re- As the relative tide range increases (RTR beach and is active only on either side of low tide. TuTTLE, 1961) belong to this group. 7), the beaches maintain the relatively steep up- ~ulting in the formation of rip channels.
, 1 ~. ~------" " --~-" .. 794 Mas:selink and Short Cunceplual Beuch Model 795
Consequently, a beach type diagram can be con- .Dissipative Group (0 > 5) IMPACT OF TEMPORAL VARIATION IN structed in order to locate beaches with certain 0 AND RTR wave period Rip currents and associated rhythmic topog- environmental conditions and suggest how beach =8 see; sediment fan velocity =0.04 mJs raphy are generally absent on dissipative beaches state may change under the influence of changing 10 The transformation of beach morphology illus- .' (WRIGHTet al., 1982a) and the surf zone is char- uttra-dissipa~.,... wave (and tide) conditions. Figure 6 illustrates non-barred dissipalNe trated in Figures 3 and 4 has several implications e transition; / ~: acterized by the presence of numerous spilling such a diagram for a set wave period (T ';'8 totidal / ~ for both understanding and predicting beach = 8 sec) 00 ..,.,... lines of breakers. Sediments are often fine to very and sediment fall velocity (w. c:: flat f ~ ...... change as tide range increases. Firstly, temporal = 0.04 m/sec), but ~ ..,., fine and the beach gradient is low. with variable Hb and TR. ~ 6 ~ tide and spatial change in beach morphology is a func- :g bwMp._J...... -. As discussed above, beach morphology is rela- /~E-l/ tion of T and w, as well documented through bIJ Hb' . ~ Barred Dissipative Beaches {} (SHORT, 1987). tively insensitive to temporal change in tide range .5 4 / ' - .-.. the dimensionless fall velocity is.. ""/1 (?eap to spring cycle) and, in addition, increasing en ,...' ~~.~~ For !J > 5 IU)d RTR <3, the dissipative beach However, it is also a function of TR, and in com- LTT i tIde range retards beach response. Consequently, QJ~ 2 profile will be characterised by subdued longshore bination with Hb' of RTR. In examining temporal ": temporal beach change is primarily wave driven, E : bar-trough morphology. Waves are of the spilling change of beach, T and particularly w, may be ~:~:<:';?: e , ~ ~~ a' '::': : and the amount and rate of temporal change will 0 ' 1"""'."""'" type and the water motion in the inner surf zone considered as temporally constant parameters in ' ' ' ' deaease with increasing tide range, and also with 0 0.5 1.0 1.5 2.0 2.5 will be dominated by infragravity waves. Onshore comparison to Hb and TR (neap to spring) which decreasing wave height (WRIGHT et al., 1985). The breaker height (m) mass transport is by spilling waves and bores while usually experience greater change over time. response to rising waves is also larger than that Figure 6. Location of modal beach types hased on threshold a strong offshore directed bottom flow dominates Wave height is the major variable involved in of falling wave (WRIGHTet ai., 1985). The relative values of breaker height and mean spring tide range for a beach the return current pattern (WRIGHT et al., 1982a; temporal beach change, as summarised by SHORT with wave period T ~ 8 sec and the fall velocityw. ~ 0.04m/sec variability of temporal beach change as a function GREENWOOD and OSBORNE, 1990). (1987). On micro-tidal beaches, waves drive beach (D.. - 0.3 mm). The boundaries between beach types, as indi- change at rates dependent on the prevailing and of wave height and tide range is indicated by the cated hy the dotted lines. will shift in response to changes in T equilibrium !J. Also, the response to rising waves arrows in Figure 6. and w.. The arrows in the diagram indicate the direction and Non-Barred Dissipative Beaches relative, not absolute, rate of response to temporal changes in is faster than the response to falling waves As suggested by Figure 6,beaches with large As RTR increases >3, the dissipative beaches, relative tide range may be considered relatively wave height. Beach response decreases with increasing tide range (WRIGHT et al., 1985). As tide range increases, and decreasing wave height, and response to riaing waves is while maintaining similar dimensions, become waves remain the prime contributor to temporal stable beach systems. This is supported by results faster than to falling waves (WRIGHT et al., 1985). flatter and more featureless with no bars. Ex- beach change; however, as its energy is increas- of JAGO and IiARDISTY(1984) who monitored rel- amples are Farnborough Beach North, Rhossili ingly spread over a wider intertidal zone, the rates atively minor temporal changes in morphology on Bay, Wales (Figure 5d) and Llangenith Beach, of sediment transport per unit beach diminish Pendine Sands (MSR = 7.5) over a three year 1. In order to generate a considerable neap to Wales (RUSSELLet al., 1991). and beach change slows. monitoring period. Another indication of the mor- spring variation, two tidal constituents are con- phological stsbility of beaches with large RTR Tide range itself has a degree of temporal vari- sidered, the principal lunar (M2) and the prin- 7) mtra-Dissipative Beaches (0 > 2 and RTR > ability through the semi-diurnal inequality and values is the often sharp break in grain size be- cipal solar (S2), whereby S2 is given half the am- {} twleen the high tide and intertidal beach of the Beaches with > 2 and RTR > 7 are considered the spring to neap tidal cycle. Minor impacts of plitude of M2. Spring tide range is then given by to be ultra-dissipative beaches. The term "ultra- the spring to neap tidal cycle on micro-tidal high 1
Journal of Coutal Research, Vol. 9, No.3, 1993 Jouma1 of Coastal Research, Vol. 9, No.3, 1993 Conceptual Beach Model 797 Ma.selink and Short 796 cess .is not necessarily an absolute measure of the short period waves, large tide ranges and fine sed- relative importance of this process. Swash and iments. This encompasses a very wide range of ..,.. 100 ...'...... 100 ...... ,., surf 'ZOne processes are more energetic than shoal- environments and, therefore, not surprisingly, ing wave processes and may be more important ridge and runnels have been observed on low tide ~0 ..'.. 0 RTR = 7 even when they operate for a shorter time period. terrace beaches (e.g. Druridge Bay, KING, 1972; c::IS,) KI'R = 3 t: Results of WRIGHT et at. (1982b), however, sug- Dundrum Beach, ORFORD,1985), on beaches with :1 Uf,J gestthat the relative time of occurrence of swash, bar/rip-morphology at low tide level (e.g. Nine 0 surf and shoaling waves may serve as a surrogate Mile Beach, this study; Oregon beaches, Fox and g in assessing its importJJnce. WRIGHT et al. (1982b) DAVIS,1978) and on ultra-dissipative beaches (e.g. have calculated the time-averaged surf zone en- Blackpool Beach, KINGand WILLIAMS,1949; West = .~ ergy dissipation rate relative to the total dissi- Lancashire, PARKER,1975; WRIGHT, 1984), some >IS,) pation rate and its distribution over the intert.iQ~ :::f"'hid. ai'e iocateci in Figure 3. Therefore, rather U -10 prome of Cable Beach over a hiill' lunar tidal cycle. than identifying ridge and runnel beaches as a -5 150 0 0 50 100 distance (m) They only considered energy dissipation rate by separate group, we acknowledge ridge and runnel ,. bed friction, or equivalently the rate of doing work, topography as being an additional morphological 100 which is probably fundamental to molding the feature which may be present on beaches with a ,-... ., """"" ~II.) beach morphology (WRIGHT et al., 1..982b). For H relative tide range larger than 3. KI'R = 15 11 sec (RTR Another additional morphological feature which \ ~II.) = 1-5 m, MSR =9.5 m and T = "" t: 6), theyfound that at mean sea level 45-50% of needs to be addressed is that of multiple bar sys- 0= 0 springhigh the total work being done by waves is by surf zone tems. SHORTand AAGAARD(in press) have shown 0 ,- - - - waves- According to the siqlUlation model for a that on wave-dominated micro-tidal beaches (RTR nea hi RTR of 7, around 50% of the time over a half <3), bar number increases with decreasing beach ~ nea low lunar tidal cycle do swash and surf zone processes gradient and wave period. In Figure 4, multi-bar c:: operate at mean sea level, in agreement with in J()\Y beaches should occur as multi-bar versions of the .~ WRIGHT et at. (1982b). barred, the barred dissipative and the low tide 0> -0 bar/rip type. In fact, analysis of aerial photo- 1200 -200 DISCUSSION graphs has revealed that Nine Mile Beach (Fig- (m) distance A conceptual beach model is presented which ures 4 and 5c) occasionally develops a double bar surf zone "... shoaling waves relates the overall beach morphology (beach state) system. - - - - -. - - swash I I . to hydrodynamic and sedimentological parame- Since wave energy level is only considered in a . .." d h0 ali ng wave processes for relative tide ranges RTR of 3, 7 and 15 calculated tel&.. The model is a continuation of the work of relative way, it is tempting to scale the model Figure 7. Relative occurrence of swaah, surf wne . s) . . by MAssEUNK (in press). The input ~ lng agSl!11uI tion model described WRIGHT and SHORT (1984) and SHORT (1991). over a complete half lunar tidal cycle (neap to aprmg range 3, 7 and down and apply it to very low wave energy beach ~ 0.03 m/sec and tide, I m, wave pert od aec, ~iment fall velocity = = paxamete ra to th em odel are wave height. = = k t Several elements from these studies are incor- environments such as estuarine and bay beaches. tal seal.. for each bea, cb are different, but the vertical exaggeration is ept constan . 15 m. Note that the verti"",'-' an d bortZOn po;ra.ted in the model presented here. In general, Generally these environments have large rela- beaches with RTR <3 are found in micro-tidal tively tide ranges (RTR >7) and variable dimen- environments and may be classified according to sionless fall velocities. Using the model in Figure swash processes play an importJJnt role and will in amplitude and cross-shore spacing in. seaw~d WRIGHT and SHORT (1984). Beaches with RTR 4, these beaches may be described as low tide tend to plane off any surf zone process-induced between 7 and 15 largely overlap with Group 1 of terrace or ultra-dissipative beaches (depending direction. These maxima are associated With spr~ng irregularity. Hence, no bars will form at th~se high tide, neap high tide, neap low tide and sprmg SHORT (1991), which he sUIIimarized as macro- mainly on the sediment size) which agrees with locations although swash bars may be found in- low tide level, respectively. At mean sea level, less tidal beaches with a planar, concave upward beach what is observed in the field (NORDSTROM,1992). stead (Nine Mile Beach, Figure 5c). It may be profile. The transition to tidal flats (Group 3 of However, the absolute wave energy level is also than 50 % of the time do swash and surf processes suggested, on the basis of the simulation model, operate. On Nine Mile Beach,which is charac- SHORT, 1991) is indicated in the present model of importance due to the existence of wave energy that in order to develop bar morphology, surf zone terised by a RTR of 5--6, bar morphology was by the beaches with RTR larger than 15. Beaches thresholds. For example, the wave height may drop processes should dominate at least 25% of the qbserved just below neap low tide level. Bar mor- with RTR between 3 and 7 are generally high to below some critical level below which the response phology may develop at this location because surf time over a lunar tidal cycle. moderate energy macro-tidal (TR >3 m) beaches time becomes infinite; i.e., no change occurs. Also, For a RTR of 15, swash and surf zone occur- zone processes concentrate at this location fo~ a which were not included in any of the previous a minimum wave energy level is required for the rence display similar maxima as was observed for sufficient amount of time, illustrated by the third models. excitation of infragravity edge waves (GUZAand a RTR of 7 (Figure 7). However, only between maximum in surf zone occurrence in Figure 7. T~e Beaches with ridge and runnel systems (Group DAVIS,1974), which are strongly implicated in the neap high tide and spring high tide do swash and fourth maximum around spring low tide level IS 2 of SHORT, 1991) have not been identified as a formation of rhythmic topography (BOWEN and surf dominate over shoaling waves. At mean sea separate beach type in the proposed model. Ac- INMAN, 1971; HOLMANand BOWEN, 1982; AA- too small' and surf zone processes do not have level, less than 20% of the time over a half lunar enough time at this location too fo.rm bar~. At ~he cording to SHORT(1991) and others (e.g. ORFORD GAARD,1988b).lfthe wave energy level is too low, tidal cycle do swash and surf zone processes op- two upper maxima, associated with sprmg high and WRlGHT, 1978), ridge and runnel topography infragravity edge waves may not form and bar erate. and neap high tide level, surf zone processes.can is formed under the influence of moderate energy, morphology may not develop, even when the val- The relative time of occurrence of a certain pro- potentially form bars. However, at these locations
~- -~-~---- Journal of Coastal Research. Vol. 9, No.3, 1993 ---~ -~------
---~- ;, i~jS Masseliflk and Short Cont:eptuaJ Beach Model 799
Q BP A, 1979. Capricorn Coast Beaches: A Detailed Study HUNTLEY,D.A. and BOWEN,A.J., 1975. Comparison of ue.sof f) and TR/Hb predict the formation of bars. termediate (2-5), beaches with various bar con- of Coastline Behaviour. Queensland: Beach Protec- the hydrodynamics of steep and shallow beaches. In: Therefore, care should be exercised when apply- figurations are produced in micro-tidal environ- tion Authority, 250p. . HAILS, J. and CARR,A. (eds.), Nearshore Sediment ing the model to very low wave energy environ- ments (RTR <3) (WRIGHT and SHORT, 1984), BP A, 1986. Wave Data Recording Programme: Mackay Dynamics and Sedimentation. London: Wiley and ments (Hb <0.25 m). while increasing tide range moves the rhythmic Region. Queensland: Beach Protection Authority, 47p. Sons, pp. 69-109. Also as the converging threshold lines in Figure surf topography down to the low tide level, pro- CARTER,R.W.G., 1988. Coastal Environments. London: INMAN,D.L. and FILLOUX,J., 1960. Beach cycles related Academic Press, 617p. to tide and local wind regime. Journal of Geology, 68, 6 indicate, at low values of tide range and wave ducing low tide bar and rip morphology. On higher (Q CLARKE, D.J.; ELIOT, I.G., and FREW,J.R., 1984. Vari- 225-231. height, small differences in one or the other can wave dissipative beaches >5), the beach con- ation in subaerial beach sediment volume on a small JAGGER,K.A.; PSUTY,N.P., and ALLEN,J.R., 1991. Cal- theoretically result in markedly different mor- tains multiple subdued bars on micro-tidal beach- sandy beach over a monthly lunar tidal cycle. Marine eta morphodynamics, Perdido Key, Florida, U.S.A. phological response. The morphological sensitiv- es. As tide range increases (RTR is 3-7), the bars Geology, 58, 319-344. Zeitschrift fur Geomorphologie, Supplement Band COOK, D.O., 1970. The occurrence and geological work ity to small changes in environmental parameters disappear and a wide non-barred dissipative beach 81, pp. 99-113. of rip currents off southern California. Marine Ge- JAGO, C.F. and HARDISTY,J., 1984. Sedimentology and has also been shown by DAVISand HAYES(1984) results. When RTR is 7-15 on both intermediate ology, 9,173-186. morphodynamics of a macrotidal beach, Pendine for the micro-tidal low wave energy Florida coast- and dissipative beaches (Q >2), wide, flat and DAVIES, J.L., 1964. A morphogenic approach to world Sands, SW Wales. Marine Geology, 60, 123-154. line. More detailed observations of these systems featureless ultra-dissipative beaches result. As the shorelines. Zeitschrift fur Geomorphology, 8, Mor- KING, C.A.M., 1972. Beaches and Coasts. London: Ed. relative tide range increases even more (RTR > 15), tensen Sonderheft, pp. 127-142. ward Arnold, 570p. are required to clearly delineate both the wave DAVIS, R.A., 1985. Beach and nearshore zone. In: DAVIS, energy thresholds required to produce certain KING, C.A.M. and WILLIAMS,W.W., 1949. The forma- it is suggested that the resulting beaches form the R.A. (ed.), Coastal Sedimentary Environments. New tion and movement of sand bars by wave action. Jour- morphodynamic systems, such as standing and transition to tidal flats, which are fully tide-dom- York: Springer-Verlag, 379-444. nal of Geography, 113, 70-85. progressive edge waves and their morphological inated. DAVIS, R.A.; Fox, W.T.; HAYES,M.O., and BOOTHROYD, KOMAR, P.D., 1976. Beach Processes and Sedimenta- imprint, in addition to the relative contribution It is stressed that the model presented in this J.C_, 1972. Comparison of ridge and runnel systems tion. New Jersey: Prentice Hall, 429p. in tidal and non-tidal environments. Journal of Sed- of waves and tides in these systems. paper is conceptual. Especially for the beaches LIPPMANN,T.C. and HOLMAN,R.A., 1990. The spatial imentary Petrology, 42, 413-421. and temporal variability of sand bar morphology. The absolute tide range is also of importance. with large relative tide ranges (low tide terrace DAVIS, R.A. and HAYES, M.O., 1984. What is a wave- Journal of Geophysical Research, 95, 11575-11590. Recent work of TURNER (in press) suggests that beaches and ultra-dissipative beaches), our dominated coast? Marine Geology, 60, 313-329. MASSELINK,G., in press. Simulating the effects of tides the formation of a low tide terrace is related to knowledge is quite restricted. More information DEAN, R.G., 1973. Heuristic models of sand transport on beach morphodynamics. Journal of Coastal Re- the drainage capacity of the beach in relation to is required on these systems to improve .our un- in the surf zone. Proceedings of Conference on En- search. gineering Dynamics in the Surf Zone, pp. 208-214. McKENZIE, P., 1958. Rip-current systems. Journal of the tide. Since this is a complex function of the derstanding of their morphodynamics so that not Fox, W.T. and DAVIS,R.A., 1978. Seasonal variation in Geology, 66, 103-113. sediment characteristics (permeability and po- only a better understanding of the controlling heach erosion and sedimentation on the Oregon coast. McLACHLAN,A.; JARAMILLO,E.; DONN,T.E., and WES- rosity), beach gradient, the duration of the tidal processes is attained, but also more rigourous Geological Society of America Bulletins, 89, 1541- SELS, F., in press. Sandy beach macrofauna commu- cycle and the absolute tide range (TURNER, in thresholds can be delineated to separate the dif- 1549. nities and their control by the physical environment: GOLDSMITH,V.; BOWMAN,D.; KILEY, K.; BURDICK,B.; press), the RTR value of 3 separating the reflec- ferent beach types. The conceptual model pre- a geographical comparison. Journal of Coastal Re- MART, Y., and SOFERS,S., 1982. Morphology and dy- search. tive beaches from the low tide terrace beaches is sented in this paper may provide a framework in namics of crescentic bar systems. Proceedings 18th NORDSTROM,K.F., 1992. Estuarine Beaches: An Intro- rather arbitrary. which this future work is carried out. Conference on Coastal" Engineering, pp. 941-953. duction to the P~ysical and Human Factors Affect- GOURLAY,M.R., 1968. Beach and Dune Erosion Tests. ing Use and Management of Beaches in Estuaries, CONCLUSIONS ACKNOWLEDGEMENTS Delft Hydraulics Laboratory, Report No. M935/M936. Lagoons, Days and Fjords. Barking: Elsevier, 225p. GREENWOOD,B.G. and DAVIDSON-ARNOTT,R.G.D., 1979. Natural beaches may be grouped into several Many thanks to Ian Turner for assisting with ORFORD,J.D., 1985. Murlough Spit, Dundrum Bay. In: Sedimentation and equilibrium in wave-formed bars: WHALLEY,B.; SMITH,B.J.; ORFORD,J.D., and CARTER, beach types on the basis of breaker height (Hb), the surveying of the central Queensland beaches a nview and case study. Canadian Journal of Earth R.W. (eds.),Field Guide to Northern Ireland. Belfast: wave period (T), high tide sediment fall velocity and the exchange of ideas. Funds for this study Sciences, 16(2), 312-332. Queen's University, pp. 68-76. (w,) and tide range (TR). These four variables are were generously provided by the Department of GREENWOOD,B. and OSBORNE,P.D., 1990. Vertical and ORFORD,J.D. and WmGHT, P., 1978. What's in a name?- quantified by two dimensionless parameters: the Geography, University of Sydney (GM) lind the horizontal structure in cross-shore flows: An example Descriptive or genetic implications of "ridge and run- of undertow and wave set-up on a barred beach. dimensionless fall velocity (Q Hb/w,T) and the Australian Research CQuncii (ADS). nel" topography. Marine Geology, 28, Ml-M8. = Coastal Engineering, 14, 543-580. PARKER,W.R., 1975. Sediment mobility and erosion on relative tide range (RTR = TR/Hb)' The mean Guu, R.T. and DAVIS,R.E., 1974. Excitation of edge a multibarred foreshore (southwest Lancashire, UK). spring tide range (MSR) is used to calculate the. LITERATURE CITED waves by waves incident on the beach. Journal of In: HAILS,J. and CARR,A. (eds.), Nearshore Sediment relative tide range. The value of the dimensionless Geophysical Research, 79, 1285-1291. Dynamics and Sedimentation. London: Wiley and AAGAARD,T., 1988a. Nearshore bar morphology on the !!A"~"':..~:,~!" ~9B2. Iiltcitictiil iii:~iU:l"iiwy fii.cUC~U1"eson Sons, pp. 15i-i79. f~!l ".'~l~~ity i::dic2.~z Wh2t~~:, :,~f!c~t~;~a, ~~tz:'- low-energy coast of northern Zealand, Denmark. Geo- macrotidal beaches. Journal of Sedimentary Petrol- RUSSELL, P.; DAVIDSON,M.; HUNTLEY,D.; CRAMP, A.; mediate or dissipative surf zone conditions will grafiska Annaler, 70, 59~7. ogy, 52, 785-795. HARDISTY,J., and LLOYD,G., 1991. The British Beach AAGAARD,T., 1988b. A study of nearshore bar dynamics prevail. The relative tide range indicates the rel- HEDEGAARD,I.B.; DEIGAARD,R., and FREDSOE,J., 1991. and Nearshore Dynamics (B-BAND) programme. in a low-energy environment; Northern Zealand, Den- ative importance of swash, surf zone and shoaling Onshore/Offshore sediment transport and morpho- Proceedings Coastal Sediments '91, pp. 371-384. mark. Journal of Coastal Research, 4, 115-128. logical modelling of coastal profiles. Proceedings of SALLENGER,A.H.; HOLMAN,R.A., and BIRKEMEIER,W.A., wave processes. AGUILAR-TuNON,N.A. and KOMAR,P.D., 1978. The an- Coastal Sediments '91, pp. Small values of f) and low relative tide ranges nual cycle of profile changes of two Oregon beaches. 643--054. 1985. Storm-induced response of a nearshore-bar sys- . HOLMAN,R.A. and BOWEN,A.J., 1982. Bars, bumps, and tem. Marine Geology, 64,237-257. produce the classic reflective beach type. Increas- The Ore Bin, 40, 25-40. holes: Models for the generation of complex beach SHAW, J., 1985. Morphodynamics of an Atlantic coast ing relative tide range results in the formation a BLACKLEY,M.W.L. and HEATHERSHAW,A.D., 1982. Wave topography. Journal of Geophysical Research, 87,457- embayment: Runkerry Strand, County Antrim. Irish low tide terrace at the base of the beach face and and tidal-current sorting on a wide surf-zone beach. Marine Geology, 49, 345-356. 468. Geography, 18, 51-58. low tide rips, grading with increasing tide range BOWEN, A.J. and INMAN, D.L., 1971. Edge wave and HUGHES, M.G. and COWELL,P .J., 1987. Adjustment of SHEPARD,F.P.; EMERY, M.O., and LAFOND,E.C., 1941. into a steep (reflective) beach face fronted by a crescentic bars: Journal of Geophysical Research, 76, reflective beaches to waves. Journal of Coastal Re- Rip currents: A process of geological importance. wide dissipative low tide terrace. In areas of in- 8662~71. search, 3, 153-167. Journal of Geology, 49, 337-369.
Journal of Coastal Research, Vol. 9, No.3, 1993 Journal of Coastal Research, Vol. 9, No.3, 1993 800 Masselink and Short
SHORT, A.D., 1987. A note on the controls of beach type M.O., 1984. Beach and surf zone equilibria and re- . ~ and change, with S.E. Australian examples. Journal sponse times. Proceedings of the 19th Conference on of Coastal Research, 3, 387-395. Coastal Engineering, pp. 2150-2164. SHORT, A.D., 1991. Macro-meso tidal beach morpho- WRIGHT, L.D.; NIELSEN, P.; SHI, N.C., and LIST, J.H., dynamics-An overview. Journal of Coastal Re- 1986. Morphodynamics of a bar-trough surf zone. Ma- search, 7, 417-436. rine Geology, 70, 251-285. SHORT, A.D. and AAGAARD,T., in press. Single and mul- WRIGHT, L.D.; NIELSEN, P.; SHORT, A.D., and GREEN ti-bar beach change models. Journal of Coastal Re- M.O., 1982b. Morphodynamics of a macrotidal beach: search. Marine Geology, 50, 97-128. SoNU, C.J., 1972. Field observation of nearshore circu- WRIGHT, L.D. and SHORT,A.D., 1984. Morphodynamic lation and meandering currents. Journal of Geo- variability of surf zones and beaches: A synthesis. physical Research, 77, 3232-3247. Marine Geology, 56, 93-118. SONU, C.J. 1973. Three-dimensional beach changes. WRIGHT, L.D.; SHORT, A.D.; BOON, J.D., III KIMBALL, JourTUII of Geology, 81, 42-64. S.. and LIST. J.H.. 1987. The morohO(lvn..m;~ AffA~'O SUNAMURA,T. 1989. Sandy beach geomorphology elu- of incident wave groupiness and tide ;~g;~n-;-e-';:: cidated by laboratory modelling. In: LAKHAN,V.C. ergetic beach. Marine Geology, 74,1-20. and TRENHAILE,A.S. (eds.), Applications in Coastal WRIGHT, L.D.; SHORT, A.D., and GREEN, M.O., 1985. Modeling. Amsterdam: Elsevier, pp. 159-213. Short-term changes in the morphodynamic states of TURNER,1., in press. Water table outcropping on macro- beaches and surf zones: An empirical model. Marine tidal beaches: A simulation model. Marine Geology. Geology, 62, 339-364. WATTS, G.M. and DEARDUFF,R.F., 1954. Laboratory WRIGHT,P.,1984. Facies development on a barred (ridge study of the effect of tidal action on wave-formed and runnel) coastline: The case of south-west Lan- beach profiles. U.S. Army Corps of Engineers, Beach cashire (Merseyside), U.K. In: Clark, M.W. (ed.), Erosion Board,"Technical Memorandum, 52, 21p. Coastal Research: U.K. Perspectives. Norwich: WRIGHT,L.D.; GuZA,R.T., and SHORT,A.D., 1982a. Dy- GeoBooks, pp. 105-118. namics of a high-energy dissipative surf zone. Marine ZEIGLER,J.M. and TUTTLE, S.D., 1961. Beach changes Geology, 45, 41-62. based on daily measurements of four Cape Cod beach- WRIGHT, L.D.; MAY, S.K.; SHORT, A.D., and GREEN, es. Journal of Geology, 69, 583-599.