- ;~7' re~~~ .\ 212?S~ WESTERIPORT BAY ENViRONMENTAL STUDY \.'.:.'6»:':. i L':...... _..-e-- . . J 1113 - 1974 ... ·P'FO,j e ct Report . . :,. ~ - "" .....- ~-;":~
4.1. 4
MJRPHOLOGY AND SEDIMENT DISTRIBurION, WES'IERNPORI' BAY
M.A.H. MARSDEN AND C.W. MALLE'IT
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4.1. 4
MJRPHOr.cx;y AND SEDIMENT DISTRIEUTION,
~VES'IERNPORI' BAY
M.A.H. MARSDEN AND C.W. MALLETT
REPORT 'ID THE WESTERNPORT BAY ENVIRONMENTAL STUDY
Prepared by M.A.H. MARSDEN. AND C.W. MALLE'IT GEDr.a::;y DEPARIMENT, UNIVERSITY OF MELBOURNE
DECEMBER, 1974 [~MSM 0002606 4 .]
551. 30 4- 0'1~ lotS"2- MOte..
~ 222..'8S- NOTE
The investigation reported herein was carried out with the support of the Westernport Bay Environmental Study, Ministry for Conservation, Victoria, Australia. This report is one of the various project reports received by the Study from participants. The contents do not necessarily represent the official view of the Study. Copies are available from:
Environmental Studies Program Mini~try for Conservation 240 Victoria Parade East Melbourne 3002 Australia ------=,
TABLE OF CONTENTS
PREFACE page 1·
1. I NTRODUCT I ON 2
2. METHODS 4
2.1 :. INTERPRETATION OF }~ORPHOLOGY 2.2 SEDIMENT SAMPLING AND ANALYSIS 2.21 Sampling 2.22 Size Analysis and Data Computation
3. MORPHOLOGY OF WESTERN PORT BAY 6
3.1 OUTLINE OF THE HAJOR NORPHOLOGICAL SYSTEMS 3.2 DESCRIPTION OF l-!ORPHOLOGICAL UNITS 3.21 Tidal Channel Systems 3.22 Embayment Plains 3.23 Intertidal Flats and Banks 3.24 Inshore Marginal Sandy Zone 3.25 Offsbore Banks and Shoals 3.26 Mangrove Zone and Salt Marsh Zo.ne
4. SEDIMENT DISTRIBUTION IN WESTERN PORT BAY 22
4.1 DISCUSSION OF SEDlllENT ANALYSIS DATA 4.11 Distribution of Grain Sizes 4.12 Mud Distribution
4.13' Factors Controlling So~ting 4.14 Inter-relationships of Sediment Parameters
·5. CONCLUSION 30
6. ACKNOWLEDGEMENTS 32 7. REFERENCES 33 APPENDIX 1 APPENDIX 2 "
).
LIST OF FIGURES AND MAPS
Page Figure 1. Major Marine Physiographi~ Features of lvestern Port Bay. 8' Figure 2. Textural composition of Western Port Bay sediment samples .• 23 Figure 3. Binary scatter plot - Mean grain size against sorting. 27 Figure 4. Binary scatter plot - Hean grain size against skewness·, 28 Figure 5. Binary scatter plot - Sorting against skewness .29
Map 1 A to D. Morphology of Western Port Bay - Preliminary Edition, 1:25,000. Map 2. Sand-silt Mean Size distribution, 1:50,000. Map 3. Sorting distribution, 1:50,000. Map 4. Mud distribution, 1:50,000. Map 5. Sediment type distribution, 1:50,000. ... !i
1.
PREFACE
This project was started in 1971 by the Geology Department, University of Melbourne, under the supervision of M.A.H. Marsden, and with the permission of Professor J.F. Lovering. In December 1973, a grant f~om the l~esternport 3ay Environmental Study enabled the project to be en1aOrged and linked with zoobenthos study of the Fisheries and Wildlife Department. 2.
1. I NTRODUCT I ON
The complexi ty of the dynamics, s.ediment movement and morphology of the Western Port system is highlighted in this report. In this regard Western Port differs greatly from Port Phillip and from many embayments and estuaries elsewhere.
Lying in a mildly tectonic region, l-les '.ern Port is a drowned e:!Ibayme:nt, in which present-day sedimentation processes are still responding to a progressive series of changesiu sealevel, which, about 5000 years ~go, reac~ed a height of about 1 to 2m above the present·day level. The general rise, . followed by relative f"ll of sealevel has imposed some of the interacting morphological and sedimentation characteristics of Western Port Bay, either external but marginal such as the entrenched river and terrace systems, stranded beach ridges, spits and other associated sand bodies, and raised rock platforms, or internal characteristics, particularly controlling the evolution of the submarine topography and the provision of sources of relic sediment for re-working within the bay.
Among the unusual factors controlling the behaviour of Western' Port are:
the complexity of its morphology, principally controlled by distribution of bedrock rather than by sediment deposition, as is normally found in more typical estuaries and barrier- lagoon-tidal flat systems. As a result, the behaviour of Western Port Bay is dominated by its elongate, linear channel systems which open through a cliffed coastline to the high wave-energy zone of Bass Strait, complicated further by the smaller, and younger(?) Eastern Entrance,
the lack of fresh water and sediment input from the hinterland, except from the Bass River, and the consequent absence of any 'significant mechanism for seaward sediment transport. Marked changes in sedimentation patterns are now occurring locally,
however, as a result of the recent drainage ':If the Koo-wee-rup Swamp, and probably of forest cleariv2,
the major role of tidal currents in transporting sediment, in the absence of any "salt-wedge" sediment drive. Large areal differences in tidal range and velocities, complex differences in ebb and flood movement paths, and tidal velocity asymmetry, control mally of the sedimentation patterns,
the orientation of the Western Entrance and major arms of the bay in relation to the domina-r.t directie;ns of wind-
generated wave movements (essentially between 1800 and 3600 ), and
the availability of a range of different seqiment types and
sizes, both terrigenous sedi~ent and biogenic carbonate, and the occurrence of significant net landyard tranaport and
derosition fnto the bClY, with th,' concen~:ration of the m;oljor
tfdal flat arc3,,' 1n th .. ~ hC3d of the bay. ,
3. The resulting range of sedimentation and 'morphological complexity is evidenced, by the number of units d':lineat'ed and described herein, and also by their variability. The \ range of variability broadly embraces:-
gross variation between neighbouring units, illustrated by the contrasts between the lagoon-sand bank complex of The Nits Inlet and Cowes Bank, the clay-dominant Churchill Tidal Flats, awd the sandy sediment influx area of the Bass Delta.
rapid variation within individual units, illustrated by the, close juxtaposition in the Hastings Bigbt,Tidal Flat of overwash sands from the channel, of eroded shell beds, of grassed fine-grairied tidal flat sediments, and of Inshore Marginal Sandy Zone sediments backed by mangrove and salt marsh sediments.
gross variation in sediment type between units having similar morphology and dynamics, illustrated by the 'contrast between the mud-dominated Tooradin Tidal Flats and the morphologically similar sandy Post Office Tidal Flats.
Generalisations regarding the sedimentation behaviour of Western Port Bay' will need to be based on appreciation of the complex relationships existing in the system. 4.
:2. METP-ODS.
2 .. 1 INTERPRETATION OF HORPHOLOGY
This was based essentially on interpretation of colour aerial photographs, particularly for the northern half of the bay. The main source of photographs was the lYesternport Project 1106 flown in 1973-1974 at an approximate, but variable scale 0: 1:15,000. The basic ground experience used as the reference for extrapolation of the photo-interpretation was provided by detailcj mapping projects ir. the southern part of the bay, carried out by the School of Geology from 1970~1973 (Bass River delta area - Power (1971), Tickell (1971); Rhyll/Newhaven area - Brennan (1972), Gray (1972); Cowes/The Nits area - l.falter (1973), Walker (1973). Elsewhere, a limited number of spot ground checks 'has been carried out.
The 'photo-interpretations, which were uncontrolled, were compiled at 1:15,000, then reduced and fitted to the controlled 1:25,000 base map sheets of the
R.A.S.C. a~d Department of Crown Lands and Survey Oiap 1, A to D). Data from the ground surveys was also incorporated. Earlier interpreta tion ·work by Jenkin (1962), particul· arly on selected coastal Kreas was valuable, as were contributions by Hills (1942) and Keble (1950).
Because of the close relationship between morphology and sediment type, and particularly as these also reflect the complexity of the controlling factors in Western Port Bay, it was planned that selection of sediment sample 10'cations would be based on this morphological interpretation. However, unfortuna·te delays in the supply of photographs necessitated completion of the sampling progra~ before the interpretation of morphology was available. A further difficulty arose because much of the photography was conducted at relatively high tide, which significantly reduced the amount of observable detail over much of the area.
The criteria used to delineate morphological units included: .(a) surfa;,;E: textures of sediments such as drainage patterns and patterns of relief differ~nce; (b) shapes and contrasting elevations of sediment bodies; and (c) vf'.get_1tio:1 CU"/F.r, "::lo::!J uniformity of type and relative density. The deeper tidal channels were identified by absence of light return, which unfortunately also preve:.ted differentiation of units, witl~ the exceptio n of 'the shoal areas.
2.2 SEDIMENT Sfu~LING fu~ fu~ALYSIS
2.21 SAMPLING
Samples were collected either by taking the top 3 cm (approximately) of sediment from Smith-McIntyre grab samples collected by the Fisheries and ~ildlife Depart ment from H.V. Ca?itella (sampl"es from No.252 through No.44l, and from No.47L through
No.496), or using a small van Veen grab, yielding a sample approxi~ately 5 cm deep, collected by the Geology Depirtment, Unive~5ity of Xelbourne, from the R.V.William BucklanJ.
The bulk of the s~mples were collected fro~ late September 1973 to March 1974, but ~om~ selected samples fro~ the 1971-1973 Geology Departm~'lt studies were also incorpo~3teJ. 5.
The sites of samples collected by the Fisheries and tVildlife Department were selected by them as part of their zoobenthos survey, either by random selection or at intersections of the 1 km grid. They were occupied by use of radar navigation with an accuracy of 60 m or better. Sample. locations selected by the Geology -Department, University of Melbourne, as far.as possible were selected progressively'on the basis of the photo-interpretation, for reasons set out above. . TheY,were located in the field by visual identification of local features using aer.ial photographs and charts.
'Thus, there was no overall .consistent rationale for the choice of sample locations.
2.22 SIZE At'lALYSIS ~ID DATA COMPUTATION
Organic matter was oxidized by 100.vol~ H 0 and the sand (>62 micron) and 2 2 mud «62 micron) fractions were separated by wet sieving. No separation of the terrigeno~s
and the biogenic carbonate fractions was attempted, except for hand-picking of coal'~e shell material when present.
For each sample, the sand (weight between 50 gm and ,100 gm) was sieved at 1$ size intervals, and individual fractions in eXceSS of 10 gm weight were re-sieved using
$/4 intervals (see Appendix 1 for definition of ~ scale~. Pipette analysis of the mud fraction was undertaken to differentiate silt (4 microns to 62 microns) and clay «4 micr ons).
The size analysis data was processed by the University of Melbourne computer, and for each sample, percentages of sand, silt, clay, and oud (silt plus clay) were calcul ated. Additionally, the sediment parameters of mean grain size, sorting, skewness and kurtosis (see Appendix 1 for definitions) were calculated on the data from the individual sand fractions and the silt fraction, re-calculated·to 100%. The clay fraction was omitted from the calculation (page 22).
The values for individual sample sites are tabulat2d in Appendix 2. The data for mean grain size, for sorting and for mud percentage was generalised by grouping, and plotted on maps at a scale of 1:50,000 (Maps 2 to 4). Binary scatter plots of values' for mean grain size, sorting and skewness are shown in Figs. 3 to 5.
No~e~clature of sediment types was based on relative proportions of sand, s l.1t &.r..d clay according to the scheme shown in ,Appendix 1 (Shepard, 1954). Sediment type
for each locality i~ t.:lbulal:ed in Appendix 2, and the locality data plotted on a gener~l sand-silt-clay triangular diagram (Fig. 2).
The sediment type data for each locality was used, in conjunction with thr: mapped d.istribution of morphological units, to compile on interpretative map of the dis::: ibution of sediment types within Western Port Bay, at a scale of 1:50,000 (Map 5). 6.
3. MORPHOLOGY OF WESTERN PORT SAY
The varied and complex morphology of Western Port Bay directly reflects the complexity of the processes operating within it. The morphological units recognized therefore delineat~ areas of the bay showing differences in water movement and sediment transport patterns, in sediment type and in other processes and characteristics, for example, differences in biological/ecological systems. As such, 'the morphological interpretation provides basic data applicable to a variety of research areas.
Eight major or significantly different morphological systems have been recognized in Western Port Bay, the main characteristics of each being summarised below. Within each system, a number of morphological units have been grouped, all of which share to a greater or lesser degree, the common characteristics of that system. A large number of such units has been recognised, but it should be stressed that because of the complexity of the processes of ,Western Port Bay, it would be possib~e to recognise more variations in detail within many of the units delineated.
Reference should be made to the "Major Marine Physiographic Features of
Western Port Bay" (Fig. 1), and to the four 1:25,000 map' ~heets of the I~orphology of Western Port Bay" (Map 1, A to D), both for the outline below of the eight morphological systems, and for the more detailed description of the morphological units which follows.
The names proposed herein for the morphological units are provisional, but in view of·the complexity of the bay, it is necessary to have some acceptable nomencla ture, which hopeful.ly will become s·tandardised in the future.
3.1 OUTLINE OF THE MAJOR MORPHOLOGICAL SYSTEMS
THE TIDAL CHlU~EL SYSTEMS comprise the minor dendritic channels incised into seagrass-covered flats flanking either side of th'e tidal watershed, and into other smaller tidal flat areas; the main trunk systems of the North Arm and East Arm, leading to the dominant Western Entrance; and the more limited channel system of the Eastern Entrance.
THi!: DffiAYMENT PLAINS are permanently submerged. They have relatively low but irreg~lar relief, and slope gently to their deepest margin, where they are terminated abruptly by a steep descent into a large tidal channel.· The, shallow inner margins are va~i3ble i~ character, commonly being formed by the outer fronts of even-shallower banks. :l.1d ltd".l flats. These are relatively extensive and may partially surr,ound the embayment p.laiu.
THE INTERTIDAL FLATS AND BAl'lKS are very extensive and ."how the gre.:ltest. v:!ciabi- lity in aspect, in configuration and in sediment type. They are characteristically grassed, a~e largely exposed at.low tide, and usually dissected by dendritic channels. !~ormally their seaward margins descend steeply, or almost vertically into channels, and in the landward rli:-ectton they shelve to the Insho!"e t".arginal Sandy Zone. Areas of overwash It ,}, sand accu!lll!lation occur on and within the flats, particularly along channel margins.
THE INSHORE HA ..l{GDIAI. Si\;'TDY ZONE is generally grilss-free, and consists of sand· 7. with varyi~g proportions of mud. It lies marginal to the shore. sloping very'gently out- wards to grassed ttdal flat areas', and characteristically shows interaction betwef:"n onshore- offshore and longshore movements. There are ho~~ever. three significant modifications to' this. pattern; namely a) where' longshore movements dominate. b) in inlets which show m:Jre" uniform; lower-energy movement, and c) where land~derived sediment infl~xes occur •
. .THE OFFSHORE BANKS A.t~1) SHOALS show similar g'ras's,free or poorly grassed charact- eristics to the Inshore Marginal Sandy Zone. Thr. offshore banks are however mostly sub- tidal and the generally grass~free, mobile sand, characteristically shows large~scale bedforms il:dicating periods of high...,energy transport.
THE MANGROVE ZONE lies just below the high-tide mark, is well defined and €xten- sive although relatively narrow. Sediments are relatively muddy, cut stabilized.
THE SALT MARSH ZONE lies landward of' the mangrove zone aud is only inundated periodically, at high~.ater spring tides and in storms. Sediments are generally clayey, with some peats, often impure. The zone is often cut by small· meandering tidal creeks.
BEACHES AhlD ROCK PLATFO&~S etc. occur discontinuously. j=--igure 1 Major Marine Physiographic Dendritic Features of Tidal Western Port Bay Channels
Scole in Kilometres 0 5 10 E3 E3 E3 I=--i E3 \\ ,t/; "'","Lang Long French Is. . ~\V)&)
. '~~"'___::=.'':7:=.-.=e:;;,-. .. ) ouun'f Inshore Marginal Sandy \. Zone. plus some offshor", Arm j sands. Oultine opproximates outer Phillip . Is. limit of mongrove zone or beach. ------~------9. 3.2 DESCRIPTION OF MORPHOLOGICAL UNITS 3,21 TIDAL CHANNEL SYSTEMS In the major channels, the water depth .restricted the detail ·which could be interpreted with confidence, but in places a ~ariety of linear channel bars, and other features fqrmed by bedload material, can be distinguished. The prominent linear "streaming" features Sf:en on some photographs, E'speci- ally those in the trunk channels, need careful interpretation. Some clf these extremely elongated, thin features may be bedload sand..,·:ibbons especially those in shallo", water. However, those in deeper water (where light penetration is poor) also indicate movement patterns, but are most probably individual unmixed streams of differing densities of suspen~ ded matter, originating from a number of individual sources. such as the larger tidal flat channels feeding into the· trunk channels. Concentrations of cloudy suspended load were observed for example on photographs of the East Arm off Observation Point, originating f~om the Churchill Tidal Flat channel near Rhyll. Although rapid mixing has been reported (Hinwood, 1969; 1972, para 2.2), some of these strea~s show a surprising degree of down channel persistence, for example extending across Uiddle Bank and als6 into the ';-1estern Entrance channel, and this has important irnplicatio~s for the question of sediment-water mixing generally, especially lateOral mixing in the bay • .--.2 (i) Minor Tidal channels and creeks. In the North Arm dendritic channel patterns become relatively more prominent eastward towards the main tidal divide. The meanders generally have 101. sinuos- ity, and anastomosing patterns are rare, with the exception of the headwaters of Bouchier Channel, and also in Watsons Inlet and Blind Bight. This is clearly a complex zone, and individual channels of the system have different sedimentation roles. In this report no systematic account has been taken of differences in ebb-tide and flood-tide velocities and paths. but morphology and sediment characteristics (particularly mean grain size and sorting) suggest certain gross features. For example, the occurrence of sediment of coarser mean grain size, but poorer sorting and higher mud percentage in the Bunyip River-Lyall Channel system, and in the Yallock Creek- Bouchier Channel system, shows that these carry much of the lando-derived sediment influx from the north, the former system being dominant. This role is confirmed by the presence of suspended sediment in these channels. Ebb-flow sediment transport (assisted by stream discharge) is further suggested by the linear channel bars at the junctions with the major trunk channel. Grassed overwash sand bodies on the western bank of Lyall Channel are inactive but have an uncertain origin. In the southern part of North Arm, net down-channel transport of sand in Horseshoe Channel, Inside Channel, and Chicory Lane·Channel occurs. However, evidence of this type for ebb- movement for Boulton Channel is. noteably lacking, indicating some degree of flood-tide dominance. Other intertidal areas with dendritic chanilel systems include the Corinclla, Churchill, Peck Point, Hastings Bight and Hanns Inlet Tidal Flats. The \~atsons Inlet Channel System, (anJ Blind Bight), however, shows ditfcrent characteristics, having a 10. weakly reticulate, more irr.egular channel pattern, and the channels themselv,es are broader and shallower than in other intertidal areas (page 17 ). At the mouths of the channels from Watsons Inlet and Rutherf()rd Inlet'; at their confluences with the main trunk channel, sand bodies akin to ebb-deltas are found. Sand, brought down-channel by ebb-currents, is subjected after deposition to net flood tide movement, the shape of the ::;and bodies being modified, and sand transport then occurrin:~ up.channel and onto the adjacent bank areas, showing movement generally northeastward. In the East Arm, the minor channels immediately south of the tictal divide contrast strongly in morphology with the dendritic system to the north, in that they are relatively long and straight. Differentiation of ebb- and flood-tide circulation patterns is clear in the channel system between Stockyard Point and Sandy Point. Large washover sand fields associated with the easternmost channel are a response to net flood transport, and in the western channel ebb-dominance is indicated by the presence of a sand ebb-ship.ld. The channels within the Freeman Point Banks trend generally southwest to .j northeast.' arrange~ en ec.helon between the individual banks and the Inshore Marginal Sandy . ~ Zone. Net flood transport occurs up these channels (page 14). 11 (ii) 7runk Channels North Arm Trunk Channel. ,The general position and morphology is controlled by bedrock outcrops on the mainland and French ',Island. Subtidal outcrops of ,bedrock have not been differentiated. One striking exception to bedrock control is the development of the relatively inactive, minor Middle Spit Channel, which, at present shows ebb-dominance. but may have had an earlier period of flood-dominance (page 15) . , Channel bathymetry and tidal conditions must control 'the observed variation in sediment distribution. In the area of the Tortoise Head constriction, the sediment is very coarse sand and gravel, showing very poor sorting (and negative skew suggesting lag sediment) ,but northward it changes to coarse sand off Crib Point, then to fine sand as far up as Crawfish Rock where the sediment reverts to coarse sa~d again. This c!istrib,uti()n is clearly related to channel bathymetry, shallowing northward to the vicinity of Eagle Rock, where rapid deepening occurs. East Arm Trunk Channel. Conditions of transport and supply differ from the North ArM, and the bedload samples indicate that medium sand, showing moderatQ sorting, is distributed relatively uniformly throughout the channel. Coarse biogenic carbonate material is an important constituent, including large proportions of brachiopod and molluscan debri~. The marginal overwash dej)osits, for example on the Peck Point Tidal Flats, also contain similar d~uris. Western Entrance Channel. This is confined between tIll', larr,e ly ro,=ky n'nthern margin of Philli? Island, and the seaward margins of Middle dank [lnci che Hcstcrn ~ntrance Embayment Plain. Virtually none of the confines which fix ~h", p0siti0(1 of the entrance are formed by sediment deposition. Evld~nce for variation in ebb and flood patterns can be seen over the -" adjacent IHddle Bank and Heste:-n Entr<:!nce Errbayment Plain, which probably indicates 11. ~ated variation in conditions in the Western Entrance itself. No facilities were available for sampling b'ut this is obviously a high...,.energy channel, with coarse sediment. Core sampling on higher areas of the Westerp. Entrance during the Western Poit Seabed investigat-. ion, although not designed to give bedload sediment samples, indicates the presence of pebbly sandy gravels in part (Barton, 1974). 3.22 EMBf.YMENT PLAINS Three submerged embayment plain areas (Western Entrance, East A~, Queensferry) have been delineated, the term being used to denote relatively flat areas with only minor, but often irregular, relief (rarely greater than 2 m). These areas have an almost basin~like morphology, in that they are partially ringed on their inner margins by depositional complexes of tidal flats, banks, etc. The latter are commonly being built outwards from the shoreline with a relatively steep front, into the deeper water of the embayment plain, for example, the prograding Bass Delta. The embayment plain areas slope gently outwards, until· they are abrJF~ly terminated by a sudden steep descent to a major trunk tidal channel. The relatively nat but gentle slope is probably largely an inherited feature from an earlier Quaternary depositional surface, and the positions of the trunk tidal channels may have been determined by subsequent erosion during a phase of low sea-level, thus largely determining the nature and position' of the outer margins of the embayment plains. The cause of the irregular relief is not known but is probably due both to erosion and to construction by present~day sediment deposition modified by current and storm activity. Shallow rims along the outeT margins tend to ~nclose the embayment plains and a~centuate the basin~like morphology, for example along the outer margin of the East. Arm Embayment Plain. This is largely the result of depOSition of sandy sediments derived from the adjoining channel, .forming s\;b merged l~vee-like, overwash features. (i) The Western Entrance Embayment Plain slopes gently southward. Its depth increases from about 4 or 5 m at its northern margin, to about 18 m at the Western Entrance, sloping fairly uniformly with gradients of up to 1:1000 (approximately). The embayment plain is flanked on its west and north margins by coastal zones of the Mornington Peninsula. In the shallow zone offshore from Somers, irregular but patterned patches of s~agrass occur, but the f~ctors controlling its distribution are not knoTHr-. Rock outcrops play sonle part. The eastern flank of the plain is formed by the shallow Middle Bank. (ii) The ~ast Arm 2mbayment Plain is close to horizontal in its central portion where it lies at a depth of about 4 m. Its shallower boundaries are foemed ~y the Churchill Tidal Flats, and by Inshore Marginal Sandy Zone sediments near San Re~o, in the Bass Delta area, and also between Reef Island and Corinella. In the latter however, rock platform areas are found more extensively. The outer edge is bounded by the main trunk channel of the East Arm, 12. embayment plain, are composed of medium sand, apparently brought from the main East Arm channel by dominant flood-tide transport'. The only other operative mechanism for sand transport on to the embayment plain is provided by the sand influx from the Bass RiVer supplying the Bass Delta, and from the relatively minor tidal flood-delta inside the ,Eastern Entrance (page'13). Sand from these sources does not extend to the centre of the embayment plain, as shown by the deposit ion of silt and clayey sediments in the central and eastern portion of the plain (Map 5). The sand-sized material present is all biogenic carbonate. Further, the mud percentag~s, although variable, increase toward the centre of the embayment plain, where sor~ing is poor to very poor. (iii) The Queensferry Embayment Plain is both small and complex and differs in significant ways,from the other two embayment plain areas. In particul.r~ it is shal- lower and grades into intertidal areas (page 16). On the western boundary of the embayment plain the main trunk channel bifurcates and linear channel-derived sand bodies are accumulating on the banks of both branches. Complex circulation patterns are suggested by tbe bank morphology, and incon- sistent bedform orientations. The sampling evidence suggests predominance of fine sedi- ment, including admixcures of sand and silt. 3.23 INTERTIDAL FLATS k\~ BANKS The Intertidal Flats and Banks are largely exposed at low tide but some parts such as the sloping seaward margins are only rarely exposed. Generally the sedi ments are muddy but variable, with some noteable sandy exceptions. Areas of sand also are found on the mareins and within oth~rwise muddy flats due to overwash from channels. Shelly material may be an important constituent, either as discrete shell beds within the tidal flats or as concentrations of lag material, the latter partly reworked and partly from present-day o'cganisms ('e. g. Churchill, Peck Point, Hanns Inlet, Tooradin Tidal Flats). (i) Churchill Tidal Flats Named after Churchill Island, these extend from Newhaven [0 Rhyll, and ~re largely sheltered especially from the southerly and westerly wind-generated waves. It is therefore a low-energy eu:.rirorunent, and this is reflected by total dominance of clay-siz~ material within the flats, except near the channels ,and along the Inshore Marginal Sandy Zone. The available evidence relating to composition clearly indicates that transport of fine sediment occurs frem offshore areas on to the flats, probably by flood tides dominantly moving up the tidal channels, followed by settling and scour lag deposition after spreading across the fl~ts. The high percentage of quartz in the ,clay~size fraction is particularly indicative of offshore source. The balance between accumulation and erosion of the clays of th~ flats varies locally. In some internal areas, and along the front margin of the flats, erosion occurs particularly by the flow of ebb-tide water directly over the edge of the flats, or through minor tidal creeks. There are tl.'O areas w~ere external processes are modifying the. 3cnerill tidal flat cha-::-acteristics. The restricted distributi.on of sand along the Inshore .. ~ I \ 13. ~Clrginal Sandy Zone is yery marked and is the :result mainly of longshore mOVeI:lent, with possibly a component of up-channel bedload tr~r.sport. The addition of sand to this tidal flat system from the Cowes Bank area, west of Rhyll, is indicated by the Inshore ~!arginal Sandy Zone south-east of Rhyll and the cuspate beach area at Rhyli itself (pagel6). The outer margin of the tidal flat and the outer Dank just offshore a:so show ~odification. Two different sub-zones can be recognised - firstly the northwester~ segment from Rl.yll to Churchill Island, where the sediment is a silty clay, and secondly the southeastern segment from Churchill Island to Newhaven where coarser sandy clays occur. This difference probably reflects interaction between tidal movements from the main Western Entrance and from the Eastern Entrance, ~vith some northwesterly incursion of sand from the latter. The northwesterly deflection of some of the tiual flat channel entrances in the southeastern segment also suggests some net northwesterly sediment movement by flood tiqes, The sediment offshore from this segment also shows relatively high sand content (Sample No.486 - 31% sand). This also probably has its origin in northwesterly transport since there is no sand source further offshore, as shown for example by Sample No. 487'which is a silt (with only 6%. sand) (Map 5), '(ii) Peck Point Tidal Flats The morphology of these flats is dominated by a major non-meandering inner channel (Peck Pt. Channel), opening at both ends·into the East Arm Trunk channel, and dividing the area into an inner and outer flat. This contrasts with the meandering patterns of the Churchill and Corinella tidal flats. Tidal circulation patterns are important in the development of the outer f13t, but in part it may owe its position to a core of older sediments or bedrock . . Clayey silts and probably sandy clays are accumulating on the more sheltered inner flats on the shoreward side of Pe.ck Pt. Channel, whereas the outer flat shows signifi- cant variations. rhe internal part of the outer flat is relatively fine-grained, being of ,;, sandy clay, and is largely grassed. The marginal zones are typically coarser, particularly on the outermost margin facing the East Arm channel where sands and clayey sands grade out- wards to sands in the offshore shelving margin south of Tortoise Head. The margin of the outet flat along Peck Pt. Channel has a greater content of fine sediment, b~ing of clayey or silty sands. Shell layers and shell lag de?osits on the flats reflect both supply from nearby sources and re-working of older shell beds. The dist.ibution of sand, together with bedform orientations indicate net northwesterly transport of s3nd on to the outer flat and across its western shelving margi~, by dominant ebb-t ide movement , l!lodified in part by northvlBrd onshore sediment movement by wave action. (iii) Corinella Tidal Flats These are morphologically• similar to the Churchill Tidal Flats in havil!!: meander.ing channels, which probably are clayey sands. The development of isJ,,'!:v.is in r.L€ main channels suggests differentiation of ebb ~nd flood movement. At the sotlth'."e.~:( ex~remity of the flats, flood transport is dominant and brings over-bank sand frum t~l~ '';; ; 14. main East. Arm channel on to the flat. This forms an irregular sheet, with reticulate drainage patterns similar to the Inshore Marginal Sandy Zoue. (iv) Freeman Point Banks This is a system of elongate, somewhat i.rregular overwash bodies of medium sand, formed in response to flood-tide transport from southvest to northeast. This system shows pronounced tedforms, predominantly flood-oriented but some suggesting modification by ebb-tide transport. Flood movement occurs up the blin·d channels behind the bank sys tem, and water then ovel·-s?ills across the banks back into the main channel. The banks are basically stabilized by g::-ass but rapid sand movement-alternately covers and unC0vers the grassed areas. These banks may be regarded as _extending north of Stockyard Point --and include the flood-tide overwash sands on the southern extremity of the Tooradin Tidal Flats -(page ICJ) . The Freeman Point Banks contrast_ strongly with the intertidal -flats, in being areas of high-energy sand transport, but are included with them because of their position in the intertidal zone, and their grass cover. (v) Tooradin Tidal Flats The whole of the large int~rtidal area dt the head of Western Port Bay has a ~orphological continuity and is included in the Tooradin Tidal Flats. However, two sub- areas, are recognised. The main sub-area extends from Rutherford Inlet eastwards along the north side of the main channel to the main tidal divide of the bay, its southern boundary being defined approximately by a line along Boulton Channel, s~inging towards Palmer Point. The second, smaller sub-area lies south of the tidal divide, extending to~ards the Stockyard Point - Sandy Point constriction, and is distinguished by having straight rather than meand ering tidal channels. The western part of the main sub-area is noteable for the presence of sand, as seen in the development of offshore sandy banks and shoals (part of the Barrilliar Island Banks). The sand content diminishes rapidly eastward, and an essentially sand-f-ree segment has been approximately delineated in the eastern part (Map 5). The channel margins are also sandy, due to some flood overwash transport. Evidence for this may be seen in small irregular washov~r sheets, for example, on the divide between the Boulton and Bouchier channels, on which flood-oriented bedforms -are also -found. Although mostly grassed, a few parts are bare, and appear to be stable, perhaps having developed sufficient mud cohesion. There is no evidence of rapid ~ater~1 migration of the lesser channels, probably partly for the same reason. (vi) Post OFfice Tidal Flats These occupy the principal area south o-f the main North Arm channel and Boulton Channel, extending eastward from Scrub Point as far as Palmer Point. The striking, somewhat eiop.gated depression of the "Post Office" lies centrally. Its- origin is not certain. These flats contrast sharply with the Tooradin Tidal Flats, in being gen0rRlly 15. sandy throughout and in having'a greater development of associated offshore sandy banks and shoals. The margins of the channels are relatively diffuse and difficult to define on the photographs, which may reflect grass~d. relatively gently-sloping channel walls, contrasti~~ with the steeper (vertical or near-vertical) channel ..... alls of the Tooradin Tidal Flats. This may be due to lower stability of the sandier sediments of the Post Office Tidal Flat·s. (vti) Tyabb Tidal Flats and Banks This is the marginal but narrow system running from Long Island to Quail Island, eniarging and, extending into the entl'ance of Watsolls Inlet. The Long Island - Watons Inlet segment forms' a grassed, shelving margin on the west side of the main channel. In marked contrast, in the segment to the south of Quail Island, overwash sands accumulating on the steeper, higher banks are derived at least in part by the efflu~nt sediment from the inlets being transported on to the margins of the flats by flood currents (page 10) • A similar transport pattern occurs in the vicinity of the entrance to Rutherford Inlet. Sediment of sand-silt-clay composition is found only rarely in the bay as a whole, but occurs both off Scrub Point an.d south of Quail Island (Sample Nos.450,453). It is possible that this unusual sediment type reflects b'Jth unusual sedimentation and source characteristics of the major bend in the North Arm. (viii) Hastings Bight Tidal Flats This is a small, complex inlet, closest in morphology and' degree of protection to the Churchill Tidal Flats. Fo!' this reason it contrasts with the ~i.d(ne 3pit Tidal Flats on the opposite side of the North Arm channel, and probably has finer grained sediment. (ix) Hanns Inlet Tidal Flats Towards H.M.A.S. Cerberus ,the inner part of this flat is unusually sandy, the dominant source of which is ·the Sandy Point area, probably as a result of aeolian transport. Modifications by ~,an complicate the inte1Cpretation. In contrast to the ~nner sandy area, an outer nuddy area (sample No.443 - 100% mud)· extends northwards fro~ the ir.let possible to the Stony Point-·Crib Point flat of similar muddy character, and also .southwards. ne~rly to Sandy Point. Shell material is an important component here also, especially as shr.:.l beds, exposed along the w,argin of the North Arm trunk channel, and underlying the flat (x) Middle Spit Tidal Flats The lens-shaped tidal flat areas are dissected by systems of relatively linear channels, the main one being the Hiddle Spit Channel. The term "spit" is inappropr- iate in a morphological sense. The dominant sediment of the flats is clayey silt, with sand derived from prominent overwash s&ndwave systems, particularly on the westernmost margin but'also some flanking the Xiddle Spit Channel. At the northecn end of this channel some grassed ",- Hi. sandwave systems may be older and non-active as their oblique orientation suggests a flood transport pattern, whereas at present, the bank and shoal morphology suggests ebb-dominance. In the zone north from Tankerton the channel edges are relatively poorly defined, as a result of the presence along their margins of grassed areas lying'at greater" depths than normal. 3.24 INSHORE MARGINAL SANDY ZONE This system and the O,ffshore Banks and Shoals (para 3.25) are, in general, sandy and relatively grass-free. This differS in being a marginal, but not enLirely continuous, sandy zone with varying proportions of mud, normally narrow except where it is modified by abnormal processes. Characteristically the sediment transport involved is a bimodal combination of longshore and onshore-offshore (largely tidal) movement processes which typically icpart a well defined reticulate drainage pattern, clearly visible on the aerial photographs as a textured pattern on the sediment surface. The gentle outward slope of the zone normally leads to grassed tidal flat areas. Three marked modifications to this relatively simple zone occur, namely (i) where longshore drift becomes dominant, (ii) where its c~ntinuity is broken by inlets in which water movemen~ patterns are much less ma~kedly bimodal, and (iii) where land-derived influxes provide ,the dominant sediment source and transport mechanism. Exceptional variat- ions from the normal or modified features of this zone occur in the complex Queensferry Embayment Plain area. Here the Inshore Marginal Sandy Zone extends offshore from a p~int near the northern extremity of the plain area (}~p IB, grid reference 710543), southwesterly to join an area of overwash sand bodies derived from th~ adjacent channels. Modifications of the Inspore'Marginal Sandy Zone are found in the areas discussed below. (1) Dominant Longshore Drift Cowe..o Ba.n.k. This is a wide, linear sand bank stretching from Cowes to Observation Point, near Rbyll. In its more offshore parts, the mean grain size is medium sand, showing only ruoderat.e sorting, but better sorting is shown by the beach sands. The vE!ry prominent offshore saI".dwave field shows a comple:c interaction between tidal and wave transport, with indications of flood-dominance contributing to ea5t- ward longshore dr.i;:t. St~ong supporting evidence of prolonged net eastward transport to construct The Nits Inlet will h~ discussed below. The bank terminates near Observation Point in recurved spits and variations in distribution of sediment near Observati~n Point have occurr.ed with the last thirty years. Tran~port of sand still further eastward is indicated by its accumulation in the cuspate . ~ beach area at Rhyll, which has been considerably enlarged during this centu~y (local resid~nt personal conmlUnication), and also by the longshore mOV2me:nt of sand into t.ii~ Insh(,re ~:ar ;in: j Sandy Zone of t~le Churchill Tid;'!l Flats beyond RhylL ',; , .~ 17. La.l'!g La.ng Bea.c.h Immediately offshore from the beach, a set of distinctive linear features occurs oriented southwesterly, oblique to the shoreline. The associated sediment is a moderately sorted medium sand with a small (14%) mud content. These owe their morphology in part to longshore sand movement, but controlled by the distribution of structural features of bedrock outcrops. (11) Presence of major inlets" The four major inlets discussed fall naturally into two genetic groups - firstly, The. N-U:.& Inlet, which is a constructional feature, resulting largely from previous eastward longshore sand transport, similar to the present-day processes of the'associated Cowes Bank, and secondly the WaUOn6 Inlet - BLi..nd Iiight - Ruthe/l.60Jc.d Inlet group, whose morphology (and sediments) is probably inherited to a significant degree as a result of the drowning of origin'al features of the Pleistocene Cranbourne Sand. The latter now occurs in. a disrupted belt of northwest-trending irregular ridges, both on the immediate mainland and on the northern part of French Island • . Regardless of origin, the inlets are areas where longshore movements are .only weakly developed, if at all, and relatively uniform, low-energy conditions prevail. This results in the general absence of the bimodal movement patterns and hence of the reticul· ate drainage pattern, characteristic of ·the normal zone. The N-Uo Inlet The Nits Inlet has a relatively broad but very shallow entrance through the eastern extremity of the Cowes Bank, ~nd is occupied largely by a salt marsh-mangrove complex. The Inshore Marginal Sandy Zone proper is confined to the eastern portion, nea~ the entrance. The sediments are sands and clayey sands with a variable clay content, and up to 30% mud. Sorting is moderate. Both the morph<;>logy and sediments give consistent supporting evidenc.e of long-term eastward longshore sand movement, resulting in progressive construction of the inlet and associated old spit and beach ridge systems. The inlet is backed extensively by an old cliffed coastline of bedrock, but where this is absent, old beach ridges are found, one set of which separates The Nits Inlet from the present Rhyll Swamp. In these features, this inlet differs from those discussed below. This complex ~~ inlets in the northwestern corner of Western Port shows both an unu~ual type of morphology and an unusually high concentration of sand. An understanding of their origin is -required to decipher to what extent their morphology and sediment distri·· bution are inherited, as opposed ~o being the result of present-day transport processes. The morphology does not bear any close resemblance to a drowned fluviatile drainage system, in particular Watsons Inlet and Blind Bight both being broad, flat areas, strikingl~ 5iol1ar to the isolated arCR of saltmarsh at the head of Cannons Creek. These. areas are thoughc to represent ol'igin31 icregular, but ·somewhat modified topographic 18. depressions lying betweer. northwest-trending dune ridges of the Pleistocene Cranbourne Sand. This is supported by the overall position of the complex of inlets w~thin the belt of Cranbourne Sand extending from the northern part of French Island (Post Office Tidal Flats) northwes terly to the m.ainland, to include Quail Island and also the area behind. Watsons . Inlet, Blind Bight and Rutherford Inlet. The possibility of formation of. the inlets hy marine erosion is discounted, on the basis of the similar morphology of the isolated salt marsh area at the head of Cannons Creek, and the evidence for general progradation rather than. erosion along this part of the coastline. The morphology of Rutherford Inlet (and of China Bay to the east) contrasts with the other two, however, in showing a long, narrow and straight northerly trend. . At Warneet, the trend of Rutherford Inlet changes abruptly to northeasterly, where the still .tidal Cannons Creek cuts through a .prominent higher ridge of Cranbourne Sand, to give way upstreao to the broad isolated area of low-lying saltmarsh. The 'reason for this behaviour iR not clear, but control by the dist~ibution of the Cranbourne Sand is partly responsible. The extent and dominance of sand in these inlets, and also in the Post Office Tidal Flats etc., also indicate the probable importance of the locally-derived Cranbourne Sand component. For example, in Watsons Inlet, the very low availability of mud is indicated by the unusual occurrence of saltmarsh sand deposits in an area where mud . might be expected, Also the're is no obvious evidence of any marine hydrodynamic processes concentrating sand to such a degree in this region~ In W~OI~ Inlet and ~nd B~ght and the grassed depression near Rolfe's Marina, the channels are unusual, sometimes interconnected in arcuate to intersecting patt erns within very broad a~d flat areas in the Inshore }~rginal Sandy Zone. Compared with those of other morphological units (especially the tidal flats), the channels have an unusual degree of variation in width and depth, and have very poorly defined edges. These features probably all reflect t~e dominance of poorly-grassed sand in a low-energy enyiron~ent. In Watsons Inlet, small tidal creeks ~erge from the mangrove zone into broader channels depos iting sand as small bars. Contrasting with the broad areas in the other inlets, in Ruth~6o,td Inlet the Inshore Marginal Sandy Zone is restricted to the narrow northerly-trending section of the inlet (and China Bay). Further upstream it is rapidly restricted in distribution in the narrow, tidal Cannons Creek, giving way to' broad saltmarsh upstream. (iii) I~flux Areas TIlere is relatively little natural direct drainage into Western Port Bay, the Bass River being t~e only Gfgnificant input. It is not knolvo whether the: sediment discharge characteristics of the Bass River have changed since clearing of the originally heav~ly-forested drainage basin but at least some dynamic and sedimentation response is likAly to have occurred in the Bafs Delta area. Other natural input streams drain relative ly very small areas with no great relief, and their' sedimentation effects are local. The relatively recent artificial straightening and opening of the Lang Lang· Rive~, the Buny~p River and its associated drain system and of other smaller drains is noticeably modifyicg the Ins~ore Marginal Sandy Zone. Draining of the Koo-Wee-Rup Sw~m~ 19. has allowed greatly increased l~ads of sedimer.t of much coarser grain size to be carried by rapid high-energy transport beyond the previous deposition sites in the undrained swamp and associated environments. In some cases, this sediment transport is associated with active headward erosion. For example on the Lan~ Lang River the knick point, 4.5· m high, has retreated approximately 12 km since 1909, by erosion of the.Heath Hill Si~t. Headward movement of. up to 100 m per day has been recorded (B.R. Thompson, pers. comm.). The delta-like form of the sejiments around the mouth of the Bass River results from·a combination of river discharge and the processes of the Inshore Marginal Sandy Zone. Its position and aspect allow both north to northwesterly and southwesterly winds to create relatively high energy conditions, and this is another significant fact·:>r in deve1·, oping the marked contrast between the sediments of Bass Delta, and those of the more prptected Churchill Tidal Flats. The Bass Delta forms the inner margin to the East Arm Embayment Plain, and is a relatively thin sand sheet prograding outwards over an eroded surface cut in more consol- idated, older Quaternary river terrace sediments. This older surface must continue outwards, probably beneath the present-day ~bayment plain sediments. More rapid sediment deposition in the vicinity of the Bass River mouth is indicated by levees flanking the relatively stabilized distributary channel, and by the general morphology. Size characteristics and composition of the sediment of the youne~st river terrace and of the delta sands are comparable, also indicating that the Bass River is the significant source. Sediment accumulation can, mostly simply, De regarded as being in two zones - an Inner Sandy Zone' of well-sorted sand, bounded by an Outer Muddy Zone of poorly sorted clayey very fine sand. There is no sharp boundary between these, the upper surfaces of buth being continuous and sloping seaward at approxicately the same gradient. The front of th2 outer zone then slopes more steeply to the embayment plain, where only finer sediments are found. This ftning-outward trend further indicates the dominance here of the Bass River as the sediment source. Lang Lang P"{'vvr. Influx from the Lang Lang River is forming a small sand sheet w~th dlschrl-ree from 6ne major, and other minor distributaries, also spreading as a thin veneer, but whos~ frontal slope is not as marked as that of the Bass Delta. Some slight southerly net trans- port is indicated by the general asymmetry to the south, and by the absence of any obvious Inshore Sandy Zone to north. Lower-energy conditions are further indicated by the occur- renee of poorly sorted medium sand with a mud content of 20%. R.:Ipid secl.imentation of a fan-like sand sheet is indicated, with distributary patternE which cont=ast strongly with die Bass Delta (and Lang Lang River). The prerlom:in-- ance of major and minor braided 'channels radiating fr0~ the d~ain mouths creates a m~~k~J anastomosing ?atter~, which is continued [urthe~ seaward than the outer limit of the Insl10r~ ------0------_ 20. Sandy Zone on either side. 'This distributary pattern is less stabilized than that of the Bass River ~nd'reflects in part, periodic large volume, high velocity discharge of the dratns, with the significance of tidal and wave processes being consequently reduced. The sediment characteristics also differ from the Bass ,Delta and include pebbly coarse sands, contrasting also with the Tooradin Tidal Flat sediments, over Which progradation, is occurring. 3.25 OFFSHORE BANKS AND SHOALS These also are relatively grass-free and mostly sub-tidal, with the excep tion of the Bartilliar Island Banks and the Pa~mer Point Bank, both of which are in the inter tidal zone, but slightly higher than the surrounding grassed tidal fiat areas. (i) Intra-channel Shoals These are relatively smal'l sand bodies lJhich have various origin3 and may be underpinned by bedrock in some cases. They include Joe's Island" Eagle Rock and Crawfish Rock in the north; shoals off Corinella; shoals on the west side of Middle Spit, and shoals in the }liddle Spit Channel. ·In the latter they indicate ebb-transport. (ii) Middle Bank This extencs southwesterly from Sandy Point, with its western margin defined approximately by the 6 m bathymetric conto.ur. Little detail is available on this high- energy area where medium and coarse sands fo~ a variety of sand waves and other bedforms, the features of which near Sandy Point indicate 'dominant west-to-east flood transport, with modification "by lesser ebb-tide transport. This pattern is probably part of an overall net flood-dominance across Hiddle Bank with movement patterns approximately paralleling the arcuate Flinders-Sandy Point shoreline. (iii) San Remo Bank Again there is little data available. l~e Eastern Entrance appears to be a young geological feature, probably developed ,at a late stage of Holocene sealevel rise. Strong tidal scou~ (and wave attack in the outer entrance) has eroded the main channel.into the bedrock (basalt), and also apparently has cut through the easternmost extremity of the Churchill Tidal Flat, w!1ere net sand transport has subsequ:.!ntly built a small floo,;-delta inside The Narrows. Transport also appears to· occur ia a northwest direction aloug the front' of the Churchill Tidal Flats. On the San Remo Bank itself, the bedforms indicate dominant ebb movement along the western side of the, entrance, with flood transport across the eastern part of the bank. The origin and transport directions'of ~he sand are unk~own the Cape Woolat11cd s3!ld dune complex may be one source. (iv) Barrilliar "Island Banks This term is used for the banks in sever::.l areas in the vici:-.ity of Barrilliar Island. They :i.nclude Barrilliar Island itself iind hanks east of Chicory L3nc Channel; banks offs~ore from Adams Point; and ba~ks ~lanking each side of the enlrance oE 21. Cen tIe Annie Channel. Their frequent occurr~nce in the interpolated connection between outcrop areas of the Cranbourne Sand, scpports a relic'.: origin. ~hese banks form smooth, flat intertidal areas of sand', and are surrounded by a peripheral area of textured sand, morphologically equivalent to the Inshore Marginal Sandy Zone. Unusual curvilinear, north- 'south trending sand ridges which occur in association, are composed of moderately sorted.mud free medium sand, with slight positive skew (Map IB, grid reference 544617). (v) Palmer Point Banks The Palmer Point Banks lie witi'in the Sandy Post Office Tidal Flats as irreg- u1arly-shaped, flat sand banks. The sediments are moderately sorted fine sands with a significant mud content (17% - Sample No.428). Their occurrence is again suggestive of relatively short-distance transport of relic sediment in'a low energy environment, in which admixing of introduced mud may occur. 3.26 !-1ANGROVE ZONE AND SALT H..\RSH ZONE No great attention has been paid in this report to the characteristics and sedimentation processes of these zones. Their ~ediate importance stems from their exte~- sive development and easily recognizable characteristics on aerial photographs. As such, they have been used as a reference for definition of "coastline" in the accompanying maps. Also, during the course of this interpretation it became clear t~at in a number of previous map compilations the "coastline" has been based on inconsistent criteria, both on individual maps and from one map to another. Also the important role of these zones in sedimentation has not been consid ered. It should however be stressed that the sediment !:ype accumulating in these zones can be quite variable, being dependent on local factors of supply··and energy. The dominant sediment can vary, for exaIilple from 'sand in the salt marsh of Hatsons Inlet, to clay in· zones behind the Churchill Tidal Flats, with sediment starvation producing saltmarsh peats in sume areas. The net balance bet';Neen sedimentation and erosion in different parts of these zones is particularly delicate, especially in relation to recent variations in sea level; to erosional and constructional effects of storms; and to variation in vegetation density, affecting sediillent stability. This has been more than adqua tely ·.lemons tra ted by the changes evident following removal of vegetation from variolls area,,; for example near Harneet and in the Hastings Bigh:. 22. 4. SEDIMENT DISTRIBUTION IN WESTERN PORT BAY Preliminary examination only, of the sediment size analysis data and of statist ical parameters was undertaken to assess their applicability, firs tly,' to the recognition of sediment provinces, their characteristics and variations, both of the recognised morphological units and of regional provinces (e.g. major areas of sand or mud dominance).; and secondly to interpret operative sediment sources and processes by correlating regional characteristics with bathymetry, energy, etc .. In the light of the great complexity of the sedimentation pattern& described herein, the whole question of sediment distribution and movement in the bay will require a more systematic and .intensive attack than has been conducted to the. present. Extrapola'tions on ,the data available, as discussed below must be regarded as tentative, and in particular, care should be taken in assessing the variation in values seen between individual sample locations. 4.1 DISCUSSION OF SEDlltENT A..~ ..6,.LYSIS DATA 4.11 DISTRIBtrlION OF GRAIN SIZES The calculations of mean grain size were based on the sand and sill: frae tion~: only (recalculated to ,100%) and the values obtained (in 4> units) were grouped according to classes of the Wen~worth Scale. The names used to express this mean grain size (and their abbreviations on }!ap 2) should not be confused with the names used for sediment type based on sand-silt-clay ratios (Fig. 2; Map 5). The clay fraction data was omitted from the mean size calculations because of uncertainty regarding the mechanisms of- clay transport, and of its incorporation into the sediments sampled. The mean grain sizes therefore are =re meaningful for the bedlcad population (traction, saltation), for example in interpreting zones of.higher-energy transport, such as channels, and in demonstrating the absence of coarser material in lower-energy zones. Mean grain sizes were not obtained for the low-energy zones, such as most of the tidal flat areas. Within the overall distribution of mean grain sizes (Table 1) the samplei'.: having mean grain sizes of fine and very fine sand, and of silt are largely accounted for by the Tooradin (and ocher) Tidal Flats, and in particular, the region containing the East Arm Embaymen t Plain. The mean size data for the major tidal channels (North Arm and East ~ Arm) has been excracted separately (Table 1), showing the prevalence of mean sizes of I coarse and medium sand in these . For the East Arm, all' samples had a mean size in the . medium sand range, both from ~he lower reaches and the headwaters, suggesting that mean size of medium s.:.nd can be expected throuehout the length of the channel. No correlation of mean grain size with depth or with other detaileci co~trol~ has been Qade. However, in the bay as a whole, even In the high-energy channel systems, it is striking t~lat medium sand is the nlost frequently occurring mean size, made still u;o::c apparent if q~alitntive allcw3nc~ is made for the relatively higher biogenic caFbo~ate contenl of the coarser 5 sortlne valu(!s. in(iic.:ltes th.:lt sizes closely clu::;tered arolln~ nH?c.!ium sand do [onll an 1,-,:',01't ant comrn~cnt of the p0pulation (rather th.:tn re[l~ctinE H ~iJc ~?r~~rl bctwc~n extreme SiZ0S 23. CLAY :.1 0 0 0 00 0 0 I 0 0 0 0 0 0 0 \ \ 0 o· 0 '. °0 0 "\ ,0. ° \ SA r~ 0 S I LT " ; " Fig. 2: Textural composition of Western Port Bay sedi:nent samples. 24. the samples analysed, of approximately 40%. The sample data also indicates that fine sand is the second-most 'irJportant component, furthe; supported by the 'prominence of fine mean sizes (Table 1) . Trunk. All Samples Channels Only 1 1 SAND Very coarse 2 1 Coarse 22 15 Hedium 62 35 Fine 36 6 Very fine 19 SILT 7 149 58 Table '1: Distribution of mean grain sizes (based on sand plus silt fractions). A further feature of the grain size distribution of ~yestern Port Bay is that silt sizes are relatively deficient, only one saffiple having a mean grain size' in the sil~ range (Sample No.487 - East Arm Embayment Plain). Supporting evidence is found in the sand-silt-clay ratios (Fig. 7), showing emphasis on sand and clay. 'Only 16 samples have more than 30% silt and only 3 have more than 50%. It is clear that medium sand (and fine sand), mixed with varying proportior.s of clay, is a 'co=on sediment type. in a'variety of env:lronments of different energy. This may indicate one of the important provenance characteristics for the Western Port system. The province associated with the East Arm Emba)~ent Plain is marked by the essential absence of coarser sediment (sand). No mean grain size values for the Churchill Tidal Flats are quoted but they are known to be clay-size (Brennan, 1972;. Gray 1972), 3n~ the Bass Delta represents an influx of fine sand. The only coa'rser sediment known (medium sand mean size) is being added from the main East Arm c1-.'.annel by flood-tide overwash across the -outer margin of the embayment plain; eastward from \,Ihich the mean size decreases, inward towards the centre. No samples have been obtained from the flood delta inside The Narrows, but probably this also is contributing coarser sediment at the margin. 4.12 MUD DISTRIBUTION The Hud Percentage data has been grouped as "Lt!ss thap 5% mud"; as "5 ~v 50% mud"; and as "Hore than 50% mud" (Hap 4), ;, Hud percentage distribution data ~s unlikely to indicate mud ~ources, rather it is wIre indic The baffling, sediment trapping, and binding role of seagrass is important in mud accumulation. The grassed areas vary in their substrate type and in their ability to retain sediment. The presence of gras's is not a simple indicator of the presence of trapped mud, the other possibilities including sandy substrates (either fixed or mobile), and muddy substrates developed under suitably low-energy hydrodynamic conditions subsequently being colonised. by grass. The area south of Stony Pt. (Sample No.443, 100% mud - Hanns Inlet) is an example of mud accumulation ~hich would not have occurred without the presence of grass. As anothe'~ example, the Peck Pt. Tidal Flat grassed areas show both trapping (mud) and non-trapping conditions (sand) within close proximity to each other. As a result of these processes, Western Port Bay shows an overall ouelurd trend of decreasing mud percentage, particularly well demonstrated by the Tooradin Tidal Flats. However, the nearby Post Office Tidal Flats show unexpectedly low mud content (e.g. Sample No.430 - 12% mud), which has been interpreted as an inherited feature (page 26 ). The "Less than 5%" class lies further offshore, and in general represents channels and other high-energy sandy areas, either 'of relatively strong winnowing or lack mud admixing. The limit of 5% mud l.as chosen, rather than 0%, to allo..... for mud accumulation which can occur in small quantities. in high-energy areas, even ill channels, by processes additional to settling and scour lag deposition. These include high-energy transport of· sand-size biogenically pelleted mud, and of sand and pebble-sized eroded mud clasts, and mixing by bioturbation 'of previously-deposited sandy and clay-rich sediment types. An exception to this general offshore trend is found in the permanently submerged East Arm E:nbayment Plain, where the more cen\.xal area is mud-rich as a result of declining transport energy towards the deeper, more offshore parts. 4.13 FACTORS CONTROLLEC SORTING As wit~ mean grain size, the basis for sorting calculations was the sand and silt content, recalcula~ed to 100%. The values are therefore controlled by dynamics i'J. a related way to those controlling mean grain size, the effects of admixing of fines by bio"genic and other more lccal prqcesses being minimised. The calculated sorting values ~~re grouped intc descriptiv~ classes for plotting ('0.5 - ~ell-sorted; 0.5 to 1.0 - clOoeratcly-scrted; 1.0 to 2.0 - poorly-sorted; > 2.0 - very poor.J.y-sorted) (Hap 3). '{he data ave:i.lable is insufficient to determlne major trends but it is possible to demonstrate some of the factors wltich control variation in sorting in a complex area such as Western Port Bay. Poorer sorting may result from an increased spread of th~ distribution, by increased content of fine sediment as found from the Bas;,' Delta outwards, or by the prescr.ce of si3nific:.lnt coarse bio?,enic ft"action 3S in .the East Ann ("!lanne1. Elsewhere, fot" cxmnple in the North Arm, i rregul Improvement in sorting values by do.... n-channel winnowing is snown by the tidal Bouchier Channel. Sorting within the Bouchier and Lyall Channels is also affected b:r the addition of a wide range of. sizes of sediment from the hinterland. However, the moderate to good sortinr, of the grassed, sandy Post Office Tidal Flats is an inherited characteristic resulting from only slight modification of Cranbourne Sand (page 18 ). Not only.are these flats sandier but; they also show significantly better sorti:::lg than the adj,",cent Tooradin Tidal Flats. There is no great difference between these two areas of the bay, either in hydrodynamic characteristics or in sediment-trapping ability, the only difference being the local source of sand for the Post Office Tidal Flats. ".14 INTER-RELATIONSEIPS OF SEDIHENT PARAHETERS Binary scatter plots of mean grain size against sorting· against ske·;Y,1ess were constructed (Figs. 3 to 5), and three classes were differentiated on each «5% mud; 5 - 30% mud; > 30% mud). It should be noted that a different class limit (30% instead of 50%) has been used in these plots, but this has no significant effect (13 samples are involved in t'ne rangE' bet,..een 30% and 50%). The. envelopes shown by dashed lines simply delineate fields of occurrence of samples of "< 5% mud" from the other two groups. The "< 5% mud" group is essentially the channel population, sho,..ing a range of mean sizes from.very fine sand to a maximum of coarse sand (1 mm 0$), ,..ith the sorting becoming progressively poorer with increasing mean size (Fig. 2). The same population shows a striking negative (coarse) skewness, up to -0.6, with only a few samples showing even small positive .velues (Fig. 4). The most frequently occurring mean size is medium sand (page 22 ), but the occurrence of poorer sorting as size increases, together with the coarse skewed character, suggests that the channel sediments in addition to the "basic" medium (to fine) sand population, con::ain coarser material, concentrated as a terrigeno.us or biogenic lag. Samples No.366 and No.388 consistently plot in anomalous positions outside the en vcl- opes but consistently toe~ther. They are the coarsest sediments, poorly sorted and non- ske,..ed, from the high-energy environment off Tortoise Head. Samples from banks and tidal flats etc. are included in both the "5-30%" and" > 30%" mud groups, between which no obvious differentiation can be made. The two groups together hmvever, sho,.. contrasts ,..ith the channel sediments. The Dlaxilm:'Il Ulean grain size is finer (medium sand) which, together ,lith the lack of coarse-skew, reflects lack of high energy. On the contrary, negative (fine) skew is dominant, suggesting admixing Qf fines. Also the relationship between meRn size and sort- ing, v7hile confused, differs noticeably from that of the channel sediments. Many of the samples are well-s·orted, hut the more poorly-sorted sediments appear to be more commonly .those .lith finer mean grain size," rather than coarser as with the channel sediments. There is however, a large scatter, and for a given sorting value, some samples show finer. and coarser mean size. This probably reflects simply variations In local energy and supply aud bioturuatiL'n reixing in different E::wironmcnts, and hence the varying dC'i',ree of incorpor8- ~ tion of fine se·:.iment with the "u3sic" medium (to fine) sand populatinn. ~ ~ ]~* ~~ J¥ '" Figure 3 41- I!!!I 151 A Ila A 5j1l::l m m 3 - ' A - '" A c:: ::J S. " ~ A 2 - "- - 2: « " \ UJ G ~ 0 \ q)~@ A B!I \ U - 0 - ::c 0 Ell '0---_ J liI \ a.. ~ (') r--,----- 9 '{5%mud IA'~ -30 % mud -1 - Q 1m }30%mud 366 ------~ ,2 J 3 SO:1TING Figure 4 I Il!l 41- 1m r &lI - I ll! I rlil I \ ~_ - -.!!lID' I _. 0 .... iiSI \ .~ .,- \\iI. "- ....-' . \ A@ .~ !9 ,; .. 0 lAG> rli" /0 \ .Q rI .~ 3 I:lI • \' 'lA r:3 - / I:!lI A \ 0\ en ( \ . Q e :~l!. \. 0 \ @ at I \ A :. ::J \ . A.e(!J A \ 4- I @ A G , I / G \ ~ G (l) 2 \ ~G I G 00 ~@l G - / \ e III () Q \ I \ q;G G 2: / I EiI (;)0 \$1 0A Q) A J~8 e (S %mud 0 If I, A 5-30%mud J ~t~ I D } 30% mud co'" L I I I --.l . -0-7 -O'C -D,) -0-4 -0,3 -0,2 -0·\ 0 0·1 0·2 0-3 0'4 a·s 0·6 0-7 SKE·W NESS , /" Figure 5 2·5 JSB (j) I I 2 '0 , J66 , I) I I I I I -.-'-'-'-.-.~ C!J , 5 -.- ~ ., 2" ,, '-. ®o» ,. . \ G ,. ® \ €'i, ,. ,.." €I ,- \ (i) e 0 ,. 0 'Om ,. \ G' ,. \ I'Dl \ ,. ,. ,. ® '" \ '. 0j. "- e 0 "- "- " "- " e(5%mud ..... A 5-30%mud Bl )30%nJud -0,5 ,-0·3 -OA -0'2 -D" 0 a·' 0'2 0·3 0·4 0·5 0'6 0·7 SI(EWNESS ."",-. 30. 5. CONC!...USION The major aim of the sedimentological studies of Western Port Bay is to establish patterns of water mass movement, and of sediment movement and deposition. As will be seen from the report, a considerable amount of move~ent data has already been interpreted from: the position, morphology and behaviour of sediment bodies, such as washover sands, longshore movement in the Inshore Marginal Sandy Zone, and ·.. arious t):pes of ebb-tide and flood-tide constructed features. Although it has not yet been possible to apply this approach in the deeper waters of Hestern Port, valu!lble data can be obtained from both channels 'and immediately-offshore areas in Bass Strait. For example the arcuate Flinders Reef (Bank), at the mouth of the Western Entrance, is likely to be related to inward sediment build-up. the orientation and behaviour of bedforms en sandy sub strates, suc~ as mega-ripples and sand waves, for example on Middle Bank and the Freeman Point Banks. the distribution· and movement of suspended sediment in the water mass, of especial importance being the elongate "ribbons" referred to on page 9. grain size distribution dat~, ~articularly of bedload material. Variations in grain size, and in other param- eters, have very sig~ificant hydrodynamic implications b~t can cnly be interpreted when the other variables can be understood. Of particular ililportance is the indication that medium (fine) sand and clay are dominant populations in the bay, as is a knowledge of the distribution of submerged areas of relic sediment such as the Cranbourne Sand. sediment composition data. The various sediment sources for. the Western Port system range in composition, and this has already proved useful. ill determining movement paths, fer example tn demonstrating .the depositional areas for Bass River sediments, and of landward sediment tr.ansport onto tidal flats. Of importance is the occur- rence of Pleistocene aeolianite in the bedload of the North Arm channel which indicates some 5.nward movement frOl.l the Hes eern En trance. ' " 31. l No system~tic overall presentation of this ~ovement data is yet possible, as a considerable amount of further work has, to De done , " especially to determine net transport patterns. This will need to be based on both: measurements of short-term hydrodynamic and sedimen~ movements, of both bedload and suspended load, and studies of structure and composition of already-deposited s~diment bodies, aimed at providing long-term data relat iLg to the prevailing movement patterns. Further sedimentological work in Western Port is therefore recommended in the following areas:- 1. Hydrodynamic, and bedload transport 'measurements in channels (to be undertaken under an existing program - Sternberg and ~1arsden) . 2; Morphology and bedform studies, should be continued through out Western Port Bay with:- a) Further aerial photograph interpretation, at more favourable scales and also repeated photography of selected areas.' b) Ground mapping and progr~s of monitoring erosion and sediment accretion. c) Detailed,close-spaced fathometer profiling across the channels and intertidal areas. This will provide the basic detailed morph ology of channels and will monitor changes due to eros'ion, bedform movement etc .. 3. Hydrod)~amic, and suspended sediment studies~ to determine distribution, concentration, states of agglomeration, cl\inposition, and transport of adsorbed, included and coated impurities. 4. Distribution, structure and composition of already deposited sediment bodies by aCDustic su~-bottom profiling and coring, espeCially of the Embayment PlaiT'_s, Offshore Banks and Shoals, and the Intertidal Flats and Banks. 32. 6. ACKNOWLEDGEMENTS The assistance of the Westernport Bay Environmental ~tudy, of Professor M.A. Shapiro, and of members of the Core Group of the Study is gratefully acknowledged, as is the cooperation of the officers of the Fisheries and Wildlife Department, in parti~ular those associ~ced with the zoobenthos study. The use of facilit- ies at H.M.A.S. Cerberus is acknowledged with thanks. The following members of the Geology Department gave valuable assistance: Mr. D. Toleman, Mr. G.M. Walker, Mr. R. Krummel, Mr. N. Croll (field and laboratory program), and Mr. D. Campbell (draughting). The assistance of Mrs. E.A. Marsden in typing the report is gratefully acknowledged. 33. 7, REFERENCES BARTON, C.M. (1974). InteM.m Repo/t..t on P.W.V. WutVUt Po/t..t Seabed Il1vu.ttgalion. PltOjec;t notu and log ohe.w. Division of Applied Geomeehanies, C.S.L,R.O., 18 pp .. I BRENNAN, R.D. (1972). Qu.ateJr.l1a/ty o.tu.cU..u 06 two (lJU.teJr.11 Po/t..t env-UtOl1me.nto. Unpub. B.Se.Hons, report, School of Geology, University ~f Melbourne. FOLK, R.L. (1968). P~ol09Y 06 Se.cU..me.ntafl.y Roe~~ Hemphill's, Austin, Texas. Y GRAY, LB. (1972). Qu.ateJr.nMY J..ecU..me.n:t6 -i.n -the. WuteJtrl Poltt Bay Su.nk1a.rtd. Unpub. B.Se.Hons. report, School of Geology, University of He1bournc. HILLS, E.S. (1942). The. Phyo-i.og:l.aphy 06 the Koo-we.e-lWp SL\Ump. Proe. Roy. Soc. Viet. 54 (1), 79-92. HINI.... OOD, J.B. (1969). WuteJr.npo/t..t Bay - tidal. data 1969. GFDLPaper 32, Geophysical Fluid Dynamics Laboratory, Honash University" HINlmOD, J .B.' (1972). Hycvwdyvl.O.m-i.c.--!> 06 the. Bay in The Cha.f.lenge 06 WuteJr.rt POIt-t. JENKIN, J.J. (1962). The geology and hycvwgeology of, the WuteJr.rt Poltt Mea.. Geo!. SUTV. Vic t. Underground Water Inves tiga tion, Report No .•5, 81 pp." 'KEBLE, R.A. (1950). The. MOIt.lu.Hg,ton Pen-tnJ..tLta.. Geo!. Surv. Vict. Hem., 17, 70 pp .. POHER, C.J. (1971) The. ge.o.f.ogy and oed-i.me.n.tof.ogy 06 the BaM IUveJr. wateJr.Ohe.d. Unpub. B.Sc. Hons. report, School of Geology, University of He1bourne. SHEPARD, F .P. (1954). Nomence.a;twr.e. bMed 011 oand:'o-i..e.t-c.!.a.1j J"...a.;ttoo. Jour. Sed. Pet., 24, 151-158. TICKELL, S.J. (1971). The Geology 06 :the. BaM R-i.veJr. Mea. Unpub. B.Sc. Hons. report, School of Geology, University of He1bourne. WALKER,' G.HcK.H. (1973). The. Cowu-RhyU A/tea, Phil.Li.p Io.tcil1d. A otu.dy 06 Re.ee.n.t oe..W.iVLt-.!> -i.n a baJtJt-i.e/t-.ta.goon 'comp.f.ex., Unpub. B. Se. Hons. report, School of Geology, University of Melbourne . • r WALTER, A.C. (1973). The oe.d-i.me.nu and eOMwl ge.omoJtpl:o.f.ogy 06 a tidal. -i.rz-tet, PWlip Ibland, WuteJtn Po/t..t Bay. Unpub. B.Se. Hons. report, School of Geology, University of He1bourne. G R A I N S I Z E seA L E y- ~ '1>0>. 1'0" y". Yi.. \4. ~ tTI.M Yi. Yo \4 ~ 8 16 32 64 128 256 512 1024 2048 4096 PJrtide diam. (mm) sCQle ?;; tTl t.. Colloid, '" ~,gl r I Pebbles ICo bbfes I Boulders----+- Z'" I I I I I I t:J H -10 l' scale :x: I I mn_:. r _ •• _._. I I f--.-r,,.,-r,rIT·1 Ilil!1 111111/ /illli 111111 I1I11I II11II r-IIIIIIII 1I1I11I 1"'''1-'-'''"111 1 ...... 8 1111 6 4 1 10- 1(1-' 10- IO-~ 10- 10- 10-2 10-' 10 102 10) em I ~ucm unit (A) I miRitnicron (m;.) I micnr. (Il) (I mm) .(1 ".~ltr) UNITS OF LENGTH" (em) Inereasing __ Grain size scale, showing the relationship between the Wentworth Scale and ~ Scale, and also size ranges of-gravel,sand,silt,clay and mud groups. ,..... r" '-" ~.~~~~.$?~~~.ftr.j ".~ AI~ (ii) NO'vlENCLAl1JRE OF SEDI~1ENTS Nomenclature of sedinent types based on relative percentage.s of. sand, silt and clay, after Shepard (1954). CLAY 100 % 25r-----~r-----~ si Ity clay <:::). . clayey "V sand - silt - clay sand sand sandy silt SMIO 100 % SILT 100% SHEPARO'S (19!i4)' CLASSIFICATION (iii) SEDIMENT PARAMETERS The size analysis data for sand fractions and silt was plotted by computer as graphs of cumulative percentage by weight against '~rain size. Percentile values were then obtained for the calculation of the foll~wing statistical parameters (Folk, 1968). (i) Graphic ~rean, a measure of the average grain size (san~ plus silt). X ~16 + ~50 + ~84 3 (ii) Inclusive Graphic Standard Deviation (Sorting) A measure of the tendency of the grain population to cluster around the average (mean) grain size. ~84 - ~16 ~95 - ~5 4 + , 6.6 (iii) Inclusive Graphic Skewness, a measure of whether there is a relative excess or deficiency of fine material compared to the coarse. Positive skew - tail to right, excess 'fines. Negative skew tail to left, excess coarse. Sk = l ~16 + 4>84 -2 4>50 + ¢5 + cp95 - 2 ~50 2(¢84 - CP16) 2 (ti>95 CPS) (iv) Graphic Kurtosis (peakedness), 2 measure of the ratio between the sorting ~n the tails of the distribution to the sorting in the central part of the dist~ibution. 4>95 - 5 2.44(4)75 - ¢25) ------~~~~------~~~ APPENDIX 2. (i) Grid Percentage Shepard Percentage Graphic Sorting Reg. No. Ske'o'11ess Kurtosis Reference Sa."ld Silt Clay Name Hue! Mean Sl SKI Kg X * 515419 ~39 . .; 35.5 25.1 szc 60.6 2.61 1.23 -.07 .83 II 4 516421 70.3 12.~ 19.4 cS 31.9 1.97 .92 +.24 1.0 * 7 506422 84.4 4.4 11.2 S 15.6 1.44 .43 -.06 .91 * 10 497421 68.2 9.2 22.6 cS 31.8 1.71 .3 -.26 1.1 * 12 502421 90.3 1.8 7.9 5 9.7 1.4 .42 -.07 1.06 * 27 498416 29.9 .. 31. 7 38.4 szc 70.1 1. 65 .54 - .1 1.4 * 36 513426 100 5 1.51 .24 -.02 .71 252 443546 100 S 3.01 .47 -1.06 2.04 254 469556 100 5 1.9'J .23 .09 2.05 255 451551 100 S .n 1.24 -1.33 .98 256 . 466553 10:) ·5 1.55 .46 -.09 1.16 .257 448526 100 s 1.62 1.03 -2.63 1.15 260 477515 100 5 2·.35 .48 -.34 1.07 261 466545 100 S 2.01 .33 -.43 2.54 265 455536 100 5 .55 1.2 .23 1.44 272 467536 100 S 1.84 .34 -.56 3.18 273 445539 100 S 1.91 .98 -.22 .79 275 452562 100 S .87 1.54 -4.59 .81 277 459560 100 S 1.88 .42 -.69 1.24 290 459525 100 S 1.27 1.02 -.76 .83 294 471527 100 S 2.05 .79 -2.75 1. 95 297 449539 100 S 1.63 .96 -1.09 1.1)1 299 4475111 100 S .57 1.14 -.29 1. 05 302 457527 100 S 1.60 .79 .26 1.07 304 449539 100 S 1.33 1.26 -2.02 1.19 .~ . 1.26 .25 -.39- 1. 39 305 466522 100 S * parameters calculated 011 sand fraction only. (11) Percentage Shepard Percentage Craphic :Sorting Ske-.mess Kurtosis Reg. No. Reference Sand Silt Clay Name Mild Mean x 306 449532 100 S 1.87 .96 -.27 1.03 307 461530 100 5 1.14 .43 -.09 1.15 311 471536 .100 5 2.67 .22 .06 .90 314 444557 100 s 3.03 .78 -3.91 2.79 342 484542 100 5 1.21 .73 -.24 .93 343 483536 100 5 1.05 .45 .38 1.17 344 479532 100 s .90 1. 01 -2.65 1. 39 346 533452 100 S 1.16 .62 -.28 1.29 350 466612 s 1.77 1.01" -3.14 .86 352 566454 100 S 1.48 .91 -2.47 1. 61 353 572451 100 S 1.82 .64 -.89 354 561419 83.9 1.8 14..3 S 16.1 .98 2.1 -10.01 .82 357 569390 24.8 26 49.2 szc 75.2 3.3 2.29 -12.7 1. 38 361 450590 87.5 7.4 5.1 s 12.5 2.74 1. 37 -6.34 1. 37 362- 450600 90.9 4.4 4.7 s 9.1 3.37 .54 -.95 363 460460 100 S 1.07 .55 -1.24. 1.6 364 460470 100 s .25 1.44 -6.42 1.1 366 460490 100 S -1.05 2'.02 -.02 .71 367 460500 100 !' S 1.53 -1.48 -3.98 1.0 370 460580 100 S 1.5 .67 -.32 1. 28 373 460610 100 S 1.17 .97 -.29 .89 376 470480 100 S .92 1.39 -1;.03 1. 17 377 470490 100 S .57 ·1.14 -5.77 1. 96 380 470:;90 100 S 1.57 .52 -1.12 1. 53 386 480460 100 . S· 2.54 .47 -.06 1.3 387 480470 100 S 2.2 .42 -1.01 1.46 . 388 480480 100 S -.62 2.39 -.66 .69 390 480500 100 S 1.4 .6 -.16 1. 17 391 480610 100 S 2.03 .28 .16 1. 17 39~ 480630 95.4 .9 3.7 S 4.6 1.55 1.23 -3.54 .8'4 394 490620 100 S 2.15 .43 -1. 03 1. 59 396 490640 89.4 2.1 8'.5 S 10.6 2.35 .56 -.57 1. 12 397 500630 100 S .73 .82 -1.33 1. 05 (iii) Percentage Shepard Percentage Graphic Sorting Reg. No. Skewness Kurtosis Reference Sand Silt Clay Name Mud Mean Kg x 399 510630 100 s .77 1.14 -1.53 1. 21 400 510640 100 s 2.63 .65 -1.17 1.14 402 '530622 95 -2 -3 s 5 2.91 .43 .08 .98 403 530630 100 s 1.03 .85 -1.53 .94 ! 405 550625 I 100 s 1.94 I. • 33 .03 1.64 . ; 406 560625 100 s .07 1.34 -2.31 .81 408 580625 100 s .16 1.4 -.37 .77 410 455536 100 s .35 1. 39 -2.47 1.04 421 566662 3.7 15.7 80.6 C 96.3 422 571666 100 s 423 549663 86.5 3.3 10.2 S 13.5 2.69 .82 -.64 .99 424 574647 27 15.4 57:6 sC 73 2.93 2.24 -8.78 1.71 425 626658 36.2 63.8 zC 100 426 606632 94.3 1.3 s 4.4 5.7 L52 .64 -.i 1. 46 427 639608 21. 14.7 64.3 sC 79 2.5 2.0 9.35 .92 428 639603 , 4.2 12.6 s 16.8 2.95 .56 .2 1.39 429 . 577614 99.05 .95 s .95 1.24 .75, -.84 1.12 430 578587 87.5 ·1.7 10.8 s 12.5 1.97 .7 -.38 1. 04 431 550458 81.8 1.3 16.9 s 18.2 1.67 ,.79 -.46 loG7 432 549460 63.6 36.4 cZ 100 433 505428 100 s 1.1 .58 -.45 .97 434 484479 100 s 2.7 .29 -.16 1. 02 435 619399 63.2 16 20.8 cS 36.8 1. 76 3.84 1. i1 437 715509 31. 3 24 44.7 szc 68.7 .98 2.14 1. 04 438 479657 97.7 1.3 1.0 S 2.3 2.42 .64 .52 .75 439 63.8 19.5 16.7 zS 36.2 2.2.2 2.51 7.61 1. 09 440 440584 . 80.2 13.4 6.4 s 19.8 3.53 .52 1.01 1. 91 441 423576 69.117.9 13.0 zS 30.9 2.9 1.09 .48 I. 12 4 :115·)(- 84.7' 10.2 5.1 S 15.3 3.15 .58 1. 66 2.13 443 449503 6.1 93.9 C 100 444 493544 99.6 .4 S ,.4 1.9 .87 .31 .59 445 490549 84.5 12.3 3.2 S 15.5 2.55 1. 24 -.91 .96 " ; (iv) f>ercentage Shepard Percentage Graphic Sorting Ske\roess Kurtosis Reg. No. Reference Sand Silt Clay Name Mud Mean • S . 1 x. 446 494553 99.1 .45 .. 45 S .. 3 .77 .21 1.1 447 479564 60 40 cZ 100 448 493602 S .• 72 .56 .47 1.4 449 494605 84 6.4 9'9 S 16 2.7 .56 . 1.23 1. 61 450E 506624 100 S 1.48 .41 -1.38 1. 28 8.58 .79 450 506624 40.7 32.1 27.2 szc 59.3 4.2 1. 75 451 487650 76.6 22.3 1.1 S 23.4. 3.28 1.49 9.23 1. 99 452 513644 100 S 2.0 .43 .68 1.0 453 514644 21. 7 28.3 50 szc 78.3 1.08 1.28 -5.31 .25 454 523619 100 S 1. 33 .65 .43 .95 455 642627 98.6 1.4 S 1.4 1;18 .84 -.83 .87 456 642629 12.3 87.7 C 100 457 635630 100 S 1.17 .68 .45 .88 458 643682 87.9 ,8.2 3.9 S 12.1 .78 1.48 4.9'7 1.41 460 594663 45.7 54.3 cZ 100 461 621658 97.9 .76 1.4 S 2.1 .05 1. 39 -2.54 .78 462 6~2653 100 S .25 1.02 -.69 .85 463 645650 46.4 27.5 26.1 szc 3.90 1.57 5.03 1. 05 464 647651 30.7 69.3 zC 100 465 651599 54.!. 17.2 28.4 cS 45.6 3.0 2.05 13.89 1. 99 466 668588 4.9 95.1 C 100 4107 681615 35.7 64.3 zC 100 468 699608 80.1 8.1 11.8 S 19.9 1.27 1. 78 5.26 1. 29 469 699562 86 7.0 7.0 S 14 1. 57 .88 .54 1. 15 470 699554 10C S 1.72 .29 -.31 .99 471 690550 . 97.3 0.17 0.9 S 2.7 1.43 .61 -.94 1.22 472 715543 .21.6 78.4 C 100 473 480450 97.3 0.6 2. 1 S 2.7 1.5 .86 -1.39 I. 09 474 490450 97.5 0.7 S 2.5 1.53. 1.04 -2.16 I. 03 476 510450 92 .2 3.1 4.7 S 7.8 1. 23 1.46 .2 1.01 477 520450 99.3 0.7 S 0.7 1.43 1.14 -4.29 1.S::' 479 540450 99.4 0.6 S 0.6 1. 27 1. 26 -5.07 1. 11 480 55,)450 97.4 0.5 2. I S 2.6 1.3 1. 25 -5.38 1. 21 481 560450 96 1.0 3.0 S 4.0 1. 23 1.16 -2.57 1. O! 484 590450 ~5.6 0.6 3.7 s 4.4 1. 95 .63 -1. 15 I. 64 (v) Percentage Shepard Percentage Graphic Sorting Skewness Kurtosis ,Reg. No. Reference Sand Silt Clay Name Mud Hean Kg' 486 570390 31.6 38.5 29.5 szc 68.4 4.02 2.54 . -2.60 .71 487 580400 5.9 80.2 13.9 z 94.1 ()5.75 1.32 o .86 489 600400 60.3 29.4 10.3 zS 39.7 3.63 1.07 -.48 1.13 490 580420 65.0 5.0 30.0 cS 35.0 2.42 .44 -.14 1.46 492 600430 49.9 16.7 33.4 cS 50.1 1.1 3.05 5.25 .64 494 595444 48.5 4.3 47.2 . cS 51.5 2.33 1.68 -12. 17 3.15 495 600450 83.5 5.2 11.3 S 16.5 2.76 .57 1.02 496 583460 98.4 0.2 1.4 S 1.6 1.2 1.~4 -5.34 498 413461 100 S 1.42 .60 -.33 1. 01 499 438467 100 . S 1. 79 .70 -1.12 .8 500 435471 100 S .42 1.01 . -1. 78 1.27 501 626368 97.4 .1 2.5 S 2.6 3.12 .4 -.38 1.11 504 622368 94.5 .5 5.0 S 5.5 3.29 .33 -.07 1.0 506 622364 97.4 .3 2.3 S 2.6 3.1 .5 -.69 1.13 507 615408 13.5 ·47.4 39.1 cZ 86.5 4.57 .77 -.76 .99 510 608405 25.3 58.0 16.7 sZ 74.7 4.64 .79 -.1 .68 512 625399 58.7 13.6 27.7 cS 41.3 3.3 .94 2.14 1. 45 513 628394 92.5 2.0 5.5 S 7.5 2.74 .47 -.4 1.3 514 627390 99.1 .9 .S .• 9 1. 98 .56 -.32 ·1.17 517 627386 97.8 0.5 1.7 S 2.2 2.27 .76 -.34 .9 519 619389 44.2 '21.0 34.8 szc .55.8 3.55 1. 39 -.27 1.15 520 618386 48.4 18.9 32.7 cS 51.6 3.16 1.02 1.16 1.03 521 621376 55'0 16.0 29.0 cS .45 2.86 .84 1. 62 3.28 522 62537.6 97.5 0.5 2.0 S 2.5 2.67 .43 -.33 1.11 523 625381 91. 6 2.8 5.6 S 8.4 2.86 .66 -.44 1.1 524 552382 35 65 525 563364 72.5 4 23.5 cS 27.5 3.03 .61 .1 ,97 526 571360 30 4 66 sC 70 2.86 .8 .65 1.15 527 576367 32.7 3.6 63.5 sC 67.3 3.13 .73 .66 1.16 528 567371 0.6 17.7 81.7 C 99.4 529 558379 10.4 6.1 83.4 C 89.5 3.56 1. 33 2.25 .76 530 548390 1.7 20 78.3 C 911.3 .76 -1.16 1. 01 531 536402 15.7 16.5 68.8 sC 90.8 532 565380 36.1 5.8. 58.1 63.9 '.i (vi) Percentage Shepard .Percentage Graphic Sorting ·Skewness Rep,. No. .Kurtosis Reference Sand Silt Clay ·Name Mud ~ean SI 533 533408 5.0 46.9 48.1 zC 95.0 534 539392 !i1. 3 6.6 32.1 cS 32.7 535 544383 1.3 18.7 80.0 c 98.7 536 :<.0 6.6 91.4 c 98 537 531369 5.8 10.7 83.5 C 94.2 538 535376 47.2 1.3 51.5 sC 52.S 539 542375 5.4 14.6 80 C 94.6 540 526376 25.5 74.5 zC 100 541 523383 38.5 4.9 56.6 sC 61.5 542 528410 17.0 4.7 78.3 C 83 543 531400 34.7 65.3 zC 100 544 532391 9.2 7.3 83.5 C 90.8 545 561381 1.1 21.5 .77.4 C ·98.9 546 552392 8.3 45.2 46.5 zC 91.7 547 548398 19.3 8.5 72.2 sC 80.7 548 541405 9.0 22.4 68.6 zC 91.0 549 51.8402 20.5 3.9 75.6 C '79.5 550 521393 37.4 9.2 53.4 sC 62.6 551 526403 1.8 5.0 93.2 C 98.2 552 527392 1.6 5.2 93.2 C 98.4 553 537388 7.5 19.9 72.6 zC 92 .4 554 530383 5.0 3.5 91.5 C 95 555 509390 46.1 7.5' 46.4 sC 53.9 556 '512387 57.6 0.9 41.5 cS 42.4 557 519371 65.9 1.3 32.8 cS 34.1 558 533368 2.3 15.6 82.1 C 97.7 ( 562 621355 93.9 .6 5.5 S 6.1 3.53 .24 .02 1.15 567 618362 92 .5 .9 6.6 S 7.5 3.38 .56 -1.75 2.48 568 517481 81.9 1.7 16.4 S 18.1 2.5 .52 .3 .76 569 511472 37.7 11.2 51.1 sC 62.3 3.87 1. 23 o .73 570 521464 72 .6 19.!3 7.6 zS 27.1, 4.12 .91 -.2 .7 571 . 510~73 84.2 2.6 13.2 S 15.8 2.78 .52 1. 33 2.15 .. I 572 498459 99.3 .2 .5 . s /1.7 2.77 .2 -.J3 .89 573 90.7 2.3 7.0 S 9.3 3.22 .46 .65 1. 53 574 61. 6 8.2 30.2 cS 38.4 3.58 1. 29 -1.28 1.2