f ~',

'\~""'" Wilt" It •• "'.

Prepared for:

Technical Report No. 31for PE/CCSP/Kl.4

November 1983

TECHNICAL REPORT 31on

COASTAL EROSION IN KIRIBATI;VISIT TO SOUTH TARAWA

23 August - 8 September, 1983by

Russell Howorth

As a Contribution by:

Committee for Co-ordinationof Joint Prospecting forMineral Resources in SouthPacific Offshore Areas(CCOP/SOPAC) Work Programme.

Dr. R. Howorth,Department of Geology,Victoria Un i vers i.t.y ,Wellington, New Zealand.Advisor/Consultant toCCOP/SOPAC Project Office,Suva.

rI'.I I

I :I' •:f""'

.:\'

.h••".:;:~:.

:,.,I.•.:

",.

f ~

i."I.

;'<:~;

I'

i1•(/':t~'II:L<'."o'

~I"

l I:,I,,·, I:;,,, ".I""Li:~!.'

!':'I

'j:\~.

,1\1

I'i I~

!"

, ';1! I'

I,.,

CON TEN T S .-

...

INTRODUCTION and BACKGROUND 1

OBJECTIVES 2,...

PERSONNEL PARTICIPATING 2: ~.'..''.'

EQUIPMENT and FACILITIES " . 3

RESULTS:

(i) Beach profile resurveys 3

(ii) Date of changes 4

(iii) Cause of the coastline ~hanges 5

(iv) Other possible causes of coastline movements 7 '.."I:(v) Erosion forecasting index .. 7

;.. '(vi) New coastal protection work 8 ·..i

"\! r

(vii) Increasing the awareness of coastal erosionamongst the Kiribati people 8

CONCLUSIONS . 9i'tj'

(viii) Sediment studies 9

. i

I:,I"REFERENCES 11

"

i't"

,TABLES 12

FIGURES 16 !r,i·,-:lI'Appendix 1: Comments on present state of beach profile sites 23

Appendix 2: x-squared test of relationship between westerliesoccurring in Tarawa and the value of the SouthernOscillation Index (SOl) 24

Appendix 3: A pamphlet on coastal erosion prepared by Town andCountry Division, Ministry of Works and Development,New Zealand 25

·'

Technical Report No. 31for PE/CCSP/Kl.4

...."

November 1983.

COASTAL ~kuSION IN KIRIHAT1VISIT TO SOUTH TARAWA23 August - 8 September, 1983 ,.

:~

I ~

i.I.I

.,

:;.

lNTRODUCTION and BACKGROUND

Coastal erosion studies in Kiribati being carr1ed out as part of CCOP/SOPACproJect element CCSP/Kl.4 have so far been concentrated on Betio and Bairiki at thewestern end of South Tarawa. The reasons for this are; (i) with the exception ofBikenibeu by far the largest proportion of the population in South Tarawa live on Betioand Bairiki; and (ii) the coastline of the greater part of South Tarawa eastwards fromBairiki is protected by beachrock and elevated remnants of former reef platforms. As aresult, few areas of concern with regard to coastal erosion exist 1n South Tarawa to theeast of Bairiki. Work will, however, be required at Bonriki, and the adjacent southeastcorner of South Tarawa, if the airport runway is to be upgraded.

:,-

i'l

The coastal erosion project was implemented 18 months ago, in January 1982,and work has continued at 6 month intervals since that time (Howorth, Technical ReportNo. 22, ·January-Feuruary 1982; Howorth, Technical Report No. 25, June 1982; and Carter,Cruise Report No. 76, January 19B3). This present report is, therefore, the fourth inthe series on coasta~ erosion in South Tarawa. Except where otherwise stated, thisreport deals exclusively 'with Betio and Bairiki.

i'

, I~~, Itl"~~~''''''I''I!'",-,\U''I!~'''''.J'1'I" . Work completed to date includes: The documentation of historical evidence of

coastal changes Slnce 1943; a description of coastal protection zones in existence atpresent; ocean current observations in the Betio-Bairiki causeway area and to thesouthwest of Betio; initiation of beach profile surveys and monitoring at approximatelysix-month intervals; initiation of sediment transport studies.

"1'

• I

:i;11'

I.

.j

I:.1I

It was established by Howorth (Technical Report No. 22) that the beaches ofBetio and Balrik1 are erod1ng, accreting, and experiencing longshore transport of sandas both natural and man-induced processes. The man-induced changes have been describedpreviously, this report wlll concentrate on dlscussing natural changes and rates ofchange.

.:

It is now obvious that the project has been fortunate in the timing of itswork wlth respect to the weather pattern which has prevailed during the past 12 months.The phenomena 1,'1 Ninu in the eastern Pacific and the SoutheI'n Oe o i l l a t i o n in the central-southwest Paclfic have been active, and at their most intense yet recorded. It is nowpossible to quantify the effects of what is possibly the major cause of coastline changesin South Tarawa. This is discussed fully below.

OBJECTIVES

III '1'<>r e s urv c y the Lea"t. p ro t r Le s : anu mak", a c ompe r r son ••••r t h p r e v i ou s

surveys t.odetermlne any trends and rates of change. I.,.:

lil) EstaLllsh, partIcularly by talking lO local residents, as closely asposslble •••.hen any coastline changes took place.

I.

lili) Determlne the cause of the coastline changes; investIgate the •••.eatherpattern for the pasl year to determine the meteorological conditIonsat lhe tIme that changes occurred; and investigate the past meterorologlcalrecord to determlne a likely return period for similar conditions. (Somedala •••.as made avallable to Ralph Carler by myself for use in his report;sUbsequently, more extensive data has been found at the MeteorologIcalOffice in Wellington •••.hich extends back to mid-1946) .

!',

(v) Investigate the possibility of determining a forecasting index for riskof coastal erosion.

(iv) Comment on other possible causes of coastal movements.

:,-(vi) Discuss and re-evaluate coastal protection measures in the light of recent

events.

1lI • .., ••••• , •••• ,. _ •••• ~_ ••. , .~_ ••••••••••• .;. ••••••

(vii) Discuss the possibility of increasing the a•••.areness of the problem, andits implications amongst the Kiribati people.

(viii) Contlnue sediment transport studies.

The objectives fall very clearly into two parts, those involved with fieldwork on Tarawa, and those involved wlth meteorologlcal studies which have been carriedout in Wellington.

ti) Dr. Russell HOWORTH, Geologist, Principal Inve<tigator, Geology Department, VictoriaUnIversity, Wellington, New Zealand.

(ii) Mr. Ian GRAINGER, Liaison, Chief Engineer, Ministry of Works and Erie rqy , KiribatiGoverrunent.

(iii) Gilbertese field assist.ant, Works Department, Betio, Kiribati GoveJ,runent.

(IV) The following personnel provided help in many varled ways. Without that help, itwould have been Impossible to carry out the fieldwork in the short time available;

:~

- Mr. Marae lRATA: Senior Assistant Secretary, Minlstry of Natural ResourcesKiribatI Government and National Representative to CCOP/SOPAC.

- Mr. Tapetulu MERANG: Superintendent, Works Department, Bairiki.- Professor Klaus WYRTKI: Department of Oceanography, University of Hawaii,

Honolulu.- Meteorological Office, Department of Transport, Wellington, New Zealand.

,I:'/, II:1"

"~1

I"~

I!i~"i,1

,11. !J\,';

3

EQUIPMENT and FACILITIES

(i) Gilbertese field assistant.

(ii) Made available from Senior Civil Engineer's Office, Ministry of Works and Energy,Betio, was the necessary equipment for levelling.

(iii)'Motor cycle from Works Department Vehicle Pool made available for duration of visit.

RESULTS

(i) Beach prof~le resurveys.

The present state of the beach profile sites (Figure 1)vertical and horizontal datum point~ is described in Appendix 1.Betio 2 and Bairiki la, need new vertical datum points and Betiodatum point. Generally, all sites were becoming overgrown which,s~ghting from the vertical datum point onto the profile line very

and in particular theAt least two sites,

2 needs a new horizontalin some cases, makesdifficult.

The data for the August 1983 resurvey of the beach profiles is listed in Table1, heights are quoted with respect to mean sea level. At each station along a profilethe vertical height differences between this survey and the January 1983 survey are listedin Table 2. As discussed by Howorth (Technical Report No. 25) height differences of lessthan O.lm are not regarded as significant.

The criteria for recognising change along a profile during the past 18 monthsis that described by Howorth (Technical Report No. 25): no change, where less than O.lmdifference in elevation was determined between surveys for all stations along a profile;probabZe change, where between surveys 4 to 10m of profile length indicated O.lm or more

~,.~felevation d~fference; and d~finite change, where between surveys along more than 10mfI.,."\.t,~.~,I.J\r-ll,,JIf' ••tH"'I""I" U." •. I,I

of profile length more than O.lm of build-up or lowering Wil.i....:!i~,c;P:d..~?:.....•~_ •__ '~~ ••.• 1.•~~~~ ••toW,~.~~,.••,,~tM."':.•'" I~i.,.~.l'.~

Changes in the 26 beach profiles for the three 6-monthly (approximate) surveyintervals January-June 1982, June-January 1982-83 and January-August 1983, are shown onthe left-hand side of Table 3. It is clear that during the first period, January-June1982, the majority of the profiles were stable; by far the most active period wasbetween June 1982 and January 1983 when only one profile was stable; in the past sixmonths, January-August 1983, less activity has taken place with six of the profilesbeing stable.

In order to evaluate the changes that have taken place during the monitoringperiod the maximum vertical sh~ft recorded between each survey for a particular profileis listed in Table 3. The values range from +1.16m in northwest Betio to -2.57m onnorth Bairiki immediately east of the harbour. Both these changes took place during theJune 1982 to January 1983 period. The vertical shifts have been converted to horizontalshift using the tangent of the beach slope angle; 10 degrees for the ocean-facing beachesand 6.3 degrees for the lagoon and west-facing beaches. These s10pe angles werecalculated from the January-June survey period 1982 when most of the beaches were stable(Howorth, Technical Report No. 25). The maximum horizontal shifts range from +11.6m innorthwest Betio and -25.7m in north Bairiki east of the harbour. In both these areas theshift was reversed during the following January-August 1983 survey period. The northwestBetio profile returned to the June 1982 positioning, and the north Bairiki site east ofthe harbour has accreted about half the loss.

~--._---

I:;~II

i'~".

"

I

, I

, I

"

4

, ,-

The net horizontal sh~ft for the 18 month survey period for each profile islisted in Table 3. Values range from +8.Sm in northeast Bairiki to -lS.Sm in northBairiki east of the harbour. Some 14 profiles during the 18 month period show netaccretlon whilst 12 show net erosion. 8 of the profiles have shown progressive changethroughout the 18 month survey period, the remainder have shown fluctuating change ofaccretion followed by erOSlon or vice versa.

'.<",",,.

I.:

" .It is likely that the June 1982-January 1983 data is not indicative of normal

seasonal fluctuations ln the coastline responding to .normal weather conditions. As isdlscussed below, the weather in the latter part of 1982 was quite unusual and it islmportant to establish the return period for such unusual weather and thus establishthe likely return period for movements of the magnitude recorded at that time. Further,it is important to continue the beach profiling until normal weather conditions areresumed. These can be expected to take up to another 12 months to be achieved. It willthen be possible to establish whether the beaches have reverted to their former positionsor have suffered a progressive shift during the unusual conditions.

:'.

It is interesting to note that during the latter half of 1982 whilst most ofthe beaches (17) showed accretion, the most dramatic effect was undoubt.edly the erosionof approximately 26m of the coastline along an estimated 100m of beach front immediatelyeast of Bairiki harbour. The sand lost from th~s area appears to have been added to thebeaches to the east, and subsequently that sand is beglnning to return to the area fromwhich it was initlally lost. Further, it is lnteresting to note that at sites (Betio 13and Bairiki 6, 9, 10) net accretlon over the past 18 months of S-lOm has taken place.Whether this accretion will cont~nue and stabil~se long enough to tempt people to buildin these areas rema~ns to be seen. Of the areas showing net erosion during the past 18months, Betlo 2, 7 and Balrikl 1 are of particular concern. In each of these three sitespermanent bUlldlngs w~11 be at.rlsk if thlS trend continues.

t,, I,'

, I

The monitor~ng data for the past 18 months confirms the suggestion made byHoworth (Technical Feport No. 22) that based on the historlcal data since 1943, thenatural processes act to generate a fluctuatlng coastl~ne for Bet~o and Bairiki. Net

~~(itjfj"'~~g~Hi<o~·d·lj~~~;"'~i··'~·h~~9~·"~'~·1~Ul~l~d"·i;o~"data"spanni"ng'd'itref'iri'lt ..•.r'h'~~t1I'n~'".!'Mt!I"JI"I~~,...H~,

(geological, historical, or regular monltoringl may not yield the same results. It isvery important that this be fully appreciated ln order to prevent erroneous conclusionsabout the dynamics of a coastllne by extrapolating from either data source to the othertwo time frameworks.

I'!.i;',I, ,,

(ii) Date of changes.

,I

,':1I

':1.'"

I,I'

I III I,

i :!

:~I.,~'f"

!I

"

:~;,

r'J

",

Two questions still remain. Is the maXlm~ expected natural fluctuation of thecoastline at anyone time, 12Sm restrlcted to a 200m length of beach? And, if so,is the return perlod? The latter is discussed below.

As reported by the Engineering Superintendent at Bairik~, beach movementscommenced during the last week 01 June and extended into the following month. By the24 July, immedlately east of Bairlk~ harbour the line of coconut trees behing the beach-head had been lost; and a vertical seawall of loose coral boulders had been erected forprotect~on, Some two weeks later, at the next hlgh tlde, this wall was lost andconstructlon of a gablon basket seawall was commenced. Construction of this seawall wascomplete by the end of October, by which time it was evident that the period of erosion

'IiJ

I·I

i II

5

was over and sand was returning to this beach. By the time of the January 1983 surveythe seawall was partially buried by sand, and at the time of the August 1983 survey theseawall was completely buried to a depth of half a metre. Thus, it would appear thatthe changes were initiated at or close to the periods of high spring tide during theperiod late June-mid August.

Betio and Bairiki tide gauge records for 1982 are shown in Figure 2. Unfortunately,the record for Betio is intermittent during June to November, and for Bairiki the record isonly from mid-July. The records show mean sealevel for 1982 to have been at a maximumduring August (.100mm above average) followed by a progressive lowering to more than 200mmbelow average by the end of the year.

It can, therefore, be concluded with reasonable certainty that the changes recordedin the beach profiles during the June 1982-January 1983 survey period occurred at, or closeto, times of high tide during July and AugustJ that is, July 21-23 and August 18-21 (datesfrom 1982 Tarawa tide tables supplied by MArine Division of Kiribati Governmentl. Further,towards the end of 1982 the beaches were protected by an unusually low sea level.

(iiil Cause of the coastline changes.

Weather puttern dkring the past 12 month ••

Normal weather conditions on Tarawa are well-documented and dominated by the steady4 to 5 knot easterly trade wind. From June to December 1982 the following daily windstatistics were reported; westerlies blew on 5 days in June, 21 in July, 20 in August, 27days in September, 28 in October, 26 in November, and 3 in December (Table 41. The 'Tarawawind rose diagram for June to December 1982 i. compared with the wind rose diagram forthe 25-year period 1941-1911 inclusive in Figure J.

Force 5 westerly winds were reported regularly at 09.00 hrs during June-December1982 with force 6-1 on August 29, 31 and September 1. Gale force winds were reported inthe synoptic data on July 5, August 28, September 1, 2, 25, 28, October 2 and November 13,18, 19, 20.

This period of prolonged, strong westerlies coincided with the development ofthe El Nino and Southern Oscillation phenomenon. At Tarawa during these periods the tradewinds cease to blow and are replaced by westerly conditions. Furthermore, the normal netbuild-up of surface water in the west of the Pacific flows eastwards in equatorial latitudesproducing changes in mean sea level of several centimetres.

El Nino occurs when the monthly mean departures of sea surface temperatures fromthe 25-year long-term monthly mean values for four consecutive months exceed one standarddeviation at three of five coastal stations in Peru (Scientific Committee on OceanicResearch, Working Group 551. During a typical El Nino exceptionally warm surface watersare first recorded in February and March and expand westwards over the following months.The 1982 El Nino was anomalous, the warm water in the western Pacific gradually spreadeastwards into the normally cold eastern Pacific (Philander, 1983).

Current meter, sea level, hydrographic and surface drifter data in equatorialPacific waters east of l40·W during 1982, show the development of the latest, anomalousEl Nino during the latter half of the year. By the end of July sea level at the GalapagosIs started to rise, and by October was 22cm above the long-term mean (Halpern et al., 1983).

tmm:::C:!j

. <u'"

:"

~...r'i.-I,:!'",1.=1

! I

"

:'jlI'f

I'I'.i

:}:.1

.'

Table 4 l~sts for each month during 1947 through December 1982 corresponding values, '~~"'fflt~,....,er 'Of days in that month wi th wester ly conditions and the value of t.neSQJ.l1;.h~A.,_"""'"~'r"".,...""''''''''''''''

Oticillation Index.

6

I;;~I,!"

In August 1982, shortly after I visited Kiritimati (Christmas) Is. 157°W, Mr.Eric Bailey wrote me on August 25:

"We have j~Bt had - indeed are Btill having a B~cceBBion of abnormallyhigh tideB and h~ge areas of the iBland are in~ndated ... AB there haBat the Bame time been very little wiNd and very q~iet BeaB we did nothave any add i t i ona L cro e i on at Lo nd on , HuJ we had high s e c s the ef f eo t:

wo~ld have been devastating".

The effect of the 19U2 El Nino at Tarawa (173°E) ~s shown by the progressivelowering of mean sea level towards the end of the year.

The Southern Oscillation is related to the Tahiti-Darwin pressure differenceand expressed as an index for any month by comparison with the standard deviation of thelong-term mean pressure difference (Troup, 1965).

"I,'"J

,0

:'.

The 3-month runn~ng mean of the index is shown in Figure 4, the monthly valuesfrom 1947-1983 are listed in Table 4.

The value for that index between June and December last year wa" as follows:'""~.'June -23; July -17; August -25; September -17; OctJber -19; November -29; and

December -24 (Table 4).'0'

The first five months of 1982 were characterised by only six days of westerliesand a value for the Southern Oscillation Index of 10, 0, I, -3, -7 from J~nuary-Mayrespect~vely.

"

.,",

Based on the assumption that there should be equal distribution of westerlieswith respect to any value of the Southern Oscillation Index a x-squared test for thisassumpt~on indicates that the distribut~on of westerlies w~th respect to value of theindex is not due to chance, The index was divlded into ten classes and the number ofmonths with westerly conditions attributed to each of the ten classes. For 9 degrees offreedom at the O.l~ level X' ; 26, the value of A' for this data was 44.73 (Appendix 2).

,',

, ;'j", 'I

:.1

i,i" '1,"'During the 36-year period 878 days of westerlies were recorded which is equiva-

lent to 6-7% of the time or approx~mately two days per month. Out of the 432 months only213 recorded at least one day of westerlies; therefore, an average 213 recorded at leastone day of westerlies; therefore, on average westerlies blow for 4 days per month forthe months when they are recorded. "

":,

"IThe number of months wlth greater than or equal to 4 days of westerlies is plotted

against correspondlng monthly values for the Southern Oscillation Index in Figure 5. It isap~arent that the westerlles tend to have occurred dur~ng periods of negative value for theSouthern Osclilatlon Index. If the total number of days that westerlies blew are plottedagainst the lndex a shift to the more negative value of the index is also apparent (Figure5) .

.- - -----= ,

"

LtII!,"I.·..•.

For each value of the rrid ex t.he total nuuu.er of days which westerlies blew isexpressed as a percentage with resfJ"ct. to t.he maximum possible days that. westerliescould have blown. This clearly deloonstrat.es (Figure 5) t.hat west.erlies blow duringpe r Lcd s uf ne':!atLVtlva Lue o r Lhe UI<Jux anl! ru r t ne rmo re that they aetl more" cousuon withincreasingly negative values of th" Lndex.

It can thus be concluded that the change of westerlies blowing for more thana few days in anyone month Lnceeased maekedly with development of negative values forthe Southern OscLllaLLon Index. It is afJpaeent, however, that there are plenty of timeswhen the'Lndex has been negative and westerlies have not. occurred. For example, duringthe period May-December 1977 the index ranged between -10 and -19 and the number of ~aysof west.erlies was 31. This contr""t.s wJ.t.hthe same period in 1982 where the index rangedfrom -7 t.o -29 and the nWlwer of days of westerlies was 132.

SLnce 1947, signitLcant fJerJ.uds of westerly conditions were recorded in September-December 1957 and 1958, 1963, July-UecemLE:e 1965 and 1972, July-September 1976 and June-November 1982. Some 7 fJeriods over a 36 year perLod indicating a return period of approxi-mately 5 to 6 years. The lungest period wit.hout sLgnificant westerly conditions was the 6~year period from 1966 to mJ.d-1972.

!,"

r:i,',I,:!'

ConsLdering the tLllIing of the coastal movements over the past 18 months, it isclear they: occurred at the tLme of peak mean sea level for the year; coincided with aperiod of well-develofJed, st.rong westerlies which weee associated with the development ofa strongly negative value for the Southern Oscillation Index; coincided with the onset ofan anoma Lou s £1 NUIO, J f mean sea level had no t, t a Ll e n WJ.th the max i.mum development off:l NLno t.he coastal movement.s are IJ.kely to have been more severe.

I"

(iv) Other kJos"llJle <.:",u"esot <.:o",,,[llnemovement".

In December 1969, a heavy swell was oLserved in the South Pacific and causedsignificant damage in French Pulynesia, Cook Islands and Western Samoa (Matthews, 1971).The swell originated some 4UOO nautical miles away in the Nox'th Pa c r f rc and was associatedwith the pas sag", of a stoem cent.ee at. 45°N moving east.waeds feom 11>5°E to 1500W (Figure 6).Though t.he only e"poet. from Tarawa at. t.he tilllewas of inceeased small wave activity in thelagoon, t.he potentJ.al for such events causing coastal damage in Kiribat.i should berecognised.

i·

,;,, '; ,"

tv) Erosion forecasting index.: '"

It can now be reasonably confidently stated that periods of coastal movement arelikely to occue during peulonged kJeriods of westerlies which are a:lsociat.ed with negativevalues of t.he Southern Osclllation lnd"x. In oeder to develop a first attempt at a fore-casting Lndex it. is assum"d t.hat t.he kJrobability of erosion occurring is related equallyto t.he three pa raruet.er s . (i) So u t h ern Os c i Ll.at i cn Index; (ii) the numbe r of days on whichwesterly conditions have been recoeded; and (iiil mean sea level. In other words, if theSoutheen Oscillat.ion Index is negat.ive and the number of days on which westerlies have blownJ.S anc re a s i nq , then Lt LS almost ce r t a i n t ha t t ne re will be significant coastal movementat the tuue of the next sp r i nq t i de s . It should also be remembered t.hat vdeve Lopment; of ElNino conditLons Ln t.he f:ast P",clfic are lLkely to ~esult. in a fall of mean sea level atTaeawa.

,!

"I

q"

I.

!':JI'I

'.Il

It is evident t ha t. ti,e s i nq Le missing f ec t.or in the forecasting index is some

value to relate the nWIlb",r of di.tys of we!iterly conditions to wind strength and sea

conditions. In ord",r to acquire this information a wave cllmate stu~y should begin as

!.IOUl' a" \>u""lI.>1e. Lt. Ui lu ue hUl,,,t! lhal the lit!" 'Jauy"" •.•l UelLu •.•nel U•.•r r Lki will

co n t r nue to ope r a t e . In the me•.•n t i mc, •.•n e r o s r on f o re c a s c inq index s hou Ld be developed

and a check ma i n t a i ned on how r e LreLLe the r o r e c a s t Luq Index i!i. At the same time, this

will e nab l e confidence tu q row 111 the return pe r i od va l ue ca l c uLat ed above. The deriva-

tion of the f o r e c a s t r nq inde x s ho u l d be re f i ncd dS more da t a be come s av a i Lab Le .

(viI New cOdstal .1~rotecl10n w"ek.

Hepdirs dnd add i t ions to ex i s t.i nq co a s t.a I protection zones (tor po s i t ion of zones

see Howor t h 'l'edmic<.ll Heport 22) w",re carried out du r i nq the latter part of 1982 in the

f o Ll owr nq ared!i. 1l",t10 co a s t.a I pr o t e c t i on zone s 1,2 and J f ac r nq the northwest were

r epu r r ed "nd ro rrued i n t.o a COnt1nUOU!i pro t cc t i ou zone t r oiu the no r t h end of the wes~

harbour mole around to the WC!itern end of coastal protection zone 3. Uild scourlng took

p Lcce , pdrtlcularly r n pr o t.e c t r on zones 2 ant! J, dur rnq the Lat t e r part of 19t12. Coastal

p ro t.ec t i on zan" '> on U",ttO "lung the so ut hwes t coa s t Li ue was e x t.end ed some 4001 to the north.

Th", s c hoo I toilet u10ck ha s now d i s appe a r ed dnd a good de a I of the new WillI existing at the

begln/llng of 1Y1l2 i!i now ln d very bad state w1th extenslve areas of baskets falling forwards

and/or losing their f r Ll iuat e r r a L, Behing t he qab i ons , particularly towards the south,

extenslve scourlng hds taken pldce. In the early pilrt of 1982, coastal peotection zone 7

Wils "xtended westwiled" along th" frontdg", of •.• lurther peopeety. 011 Udlriki coastal

protection zone 8 innedliltely west at the harbour was "Xtended westwdrds in late 1982 and

to the east of the h"rbour a one m"tre h1gh gab ton wall was constructed approxlmately 80m

eastwards from th" haebour.

Th" cost of building the new sedwall In north Bairikl as <1result of the erOSlon

whlch took place during July-August of la!it y""r WaS A$6,9'>O for labour and materials. It

is uncertaln "xdctly wh•.•t vehlcle CO!its weee lncurred but vehlcl" hire would certainly

double but pr oua b Ly not treble the figure. It can, t he r e ro r e , reasonably be estimated that

the cost of construction of the 80m at seawall W"!i c Lose to A$l'>,OOO. One must bear in mind

that this !ieawilll is now e nt a r e l y bu r i ed as t.he be ac h has replenished itself through

natural processes. On the oth"r hand, tht: area to the east which tempordrily gained sand

during the Idtter p•.•rt of 1982 lS now eroding. The landowners in that drea hdve already

approached goverl~ent wlth d ee4uest for a !i",awdil along their beach frontage.

It s e erns clear that t hi s exarupLe r e co rcled during the 18 month survey period is

typical of whdt h"ppen:; to the beaches at Uetlo dnd l.ldiriki. The historicdl d•.•ta re!Jorted

in Technical Heport No. 22 cie<1rly shows the coastlines to be fluctuating and in some

areas sedwalls have been Luill prevlously and dee now completely buried, for example Betio

cOilstal protectlon ~one b. Sllllliarly, sam", cOd:;tal !Jeotection zones are now in an almost

total s t a t e of d i s r e pa i r , for e xampl e Betio prutecl ion zone 9 and UdiriJ...l protection zone 1.

Pu r t he r mor e , the need t o r t liem ap!Jedls to no langei" exist. Ove r the pa s t five years the

Kiribati Gove r runent has spe n t A$LOO,OOOon coa s t a I protection work in Sou t h Tarawa. It is

now eVldent th<1t d good de •.•l at th •.•t money may hdve been saved if the type and magnitude

of coastill change!i h"d been more fully understOOd.

(v t i) th~ (JWu.ll.:llt.!:j~ ut CU'-.i~l..Jl t.;rU~!UIIliter l.:d~ IlllJ the Kielbdtl I_caple.

It I" llOWcv i de n t t nu t. every t rve or :;IX y e a r s the r i s k of co a s t a I movements in

SOm" pdrt o r UellU d"d/o.· UulClkl 15 h1gh. WltI. Lhe e x t r cme popu Lat i on density in these

,i,1'i

"

:.:.

j ~

.,

I

",",

"i''J

:1I'

ilI

• •••

I

art:as, the reslllellls dC'U LJeilly t:xposud lllcrt.:dsillyly to the risk of property damage or Los s

as a re s uLt 01 coa e t a I e ro s r on . 'I'h" i n ro ru.a r i on coming out of t h i s project: qua n t a f y r nq

the processes at work, their maynlt:ude and return period should be passed on tu the people

in these areas, t oqe t he r Wllh a I i s t, of r e couuuerrded ac t ion s which the people might adopt

in order to reduce t ne r i s x . 'rillS i n f orma t r on can best be developed in the fo rru of apamphlet simllar to thal lliustialed In AppendlX 3. This pamphlet :;hould be produced ln

Gilbertese by the dppruprlal" guverCUl\ent nu n r a t ry and ac t i ve Ly p r omot ed amorrq s t the people

of Betlo dnd Bdlrlki.

It is LJecoming lncced:;lngly eVldent thdl the people living on Uetlo an<.l Ualriki

are qo i nq to have to Le a r n to IlV" wilh tl..., p r ob l eru of oo a s t.uI erO:;lon but they s nou Ld be

made well-dware at the r r s ks r nvo I ,<1 LlI" mea:;uc'es they might t ake t o reduce that risk.

It is un Li ke Ly that Gove rruue n t w i L. L" to a r f o rd to continue to erect se awa Ll a along

small, mayLJe up to 100m s t re t.c hc s o , :h, each t in.e a pl"ce of be ach i" mod i t i ed by

erosion for what is likely to be d s ho rt, pe ri od ,

To a l e s s c r e xt.en t, , " s i.uu Lar prob1ell\ lS Lr ke Ly lO p r e va r I on other atolls in

Kiribati.

(v i i 1) Sed line n t s Llj{j Ic es ,

A yruup ut fuur :;<1l11pl""had be cn collected a t; each of four s i t.e s r Bikenibeu,

J::ita, Ambo and tse t i o (I-'lyure 7). Each gruup cUUlprl:;e:; :;amples from the outer reef flat

and beach face uf uoth the layoull and oce"n slde:; uf the atull. III addltion, :;amples have

been collected t roin two bureliolu" ca l, dept.ll:; up tu J, L:' iuet.r e s to t.lle west of Bai r i k r ,

The:;e boreholes Were d rr Ll ed during s r t e i nve s t r qa t i ou work for the p r opo s ed causeway.

~'or s ed rruen t t r uu spo r t s t.ud i e s 111 a t o Ll cnv r r oruuen t s , the Limi t ed value of grain-

size statl:;tic:; due to the lnfluunce of graln shape 15 well-establl:;hed. Similarly,

because of the un i que cha r ec t e r of the s ed i men t, the use of traces can prove un r e Li ab Le .

,'~!I1'" .• , • i.f' any specles c an be used a:; t r ec c r s , Secondly,, ~ , " II ..••••• ·' •• 1 ••• " •••••••• ,."' •••• I.~II.~••...••••"•••••••~".,t'U .•..•~I'~

to :;ee, if dny pollution-sensitive species

exist. If species are pr e se n t whi c n c an be us ed as t r a ce r s , lt may be possible to prove

or disprove whether sdnd is beillg trdn:;porled across the proposed Betio-Bairiki causeway

site. If p r ove n , it may be pos:;lble to estimate the a.mounts being transported together

with the conditloll:; ullder which tcan:;portatlon occurs.

The s ampLes are a~ pr e se n t being exaiui ne d by rm c ropa Leon t o Loq i s t s dt Victoria

Unlversity. The fdund lS yt:nurally good and the tdxonomy has )u:;t about been completed.

further samples are r equ i r eu f r oiu the wes t e r n , s utnuerqe d reef area and also it is desirable

to collect some Lr ve "f.'ec.l..,S, Sume additional samples collected by Ral ph Carter and Robert

Burne should be lnl:luded III tlils :;ludy. Ll is hoped that :;uitable saillpies can be identified

in Suva d ur r nq the f o r t hc ouu.nq s unuuer alld fUl'wdcded to Wellinglon.

CONCLUSIONS

(i) Ikdl:h p ro r i I.c c'u"ulv"'ys.ll .lIJploXIlII.ll.ely b 1Il0llUI .i n t e r va Ls during the pa s t

ItJ lIIUlltl,s con r r r iu lll.lt ua t ur a I prul:es"",s uc t, t o yell"1'at.., d f l uc t ua t r nq coastline for Betio

and BalClkl. M"XIIllWIlho ri zon t.u I s h i r t s u ur iuq the past III iuont hs range from Il.S metres of---~----~.-bUild-up lO l~,5'llU<l~'''':; uf e r o s i on . Louq sho r e t r an spo r t. of s end both to the east and

towards th.., we:;t was lndlCdted trom the :,urveys on th.., b"aches of north Bairiki.

I,,

ig~~~~,, ;I 'I,..

,~

" ,

; •..

, '

!;"

I"

. Ii ,i:,

, I"II. ,.:'1

:1I'

:~.:]::i

.',";!:,~ )1

:1r:I.

il11"

I'!1~ J

,.-(,~

II

\.

-- .- --_ .... ---=0.".-...- .,-.

IU

litif,~.,,1"'.I 'I,!.

" .I ~~•••

(iil Maximum changes were recorded d ur i nq the June 19lJ2-January 1983 surveyperiod and occurred close to or at t une s of h i qh tide during July and August.

,~..,,'"

'""-,

(ili) 'I'owardlithe end ut l';lULth" LtJach"li wurt, p ro t cc t.ed oy lUI unusually lowsea level.

(iv) The coastal movem"nts during July-August 1982 occurred at the time of peaklUean sea level for the year dnd coincided with a period of well-developed, strong westerlieswhich were associated with the development of a strongly negative value for the SouthernOscillation Index; which cOlncided with the ons~t of an anomalous El Nino .

'~

. (v) If mean lied level hu d not fallen IHth the maximum development of El Nino thecoastal movements are likely to h ave been much more severe.

:,

(vi) Westerly Cbl~ltions prevail durlng perlods of negative value for theSouthern Oscillation Index and, rur t ne rmo re , ale more couunon with i nc re e s i nq negative valuesof the index. It lS ap~alento however, that there are plenty of tlmes when the index hasbeen negative and westerly conditions have not occurred.

(vii) For weather data since 1947 a return ~eriod of 5 to 6 years is indicatedfor such events.

(vlii) Other possible causes of COastline movements are heavy swells associatedwlth litorm centruw 1n the north Paclf1C. '"

I, ,

( i x ] Muney likely tu L" s~"nt on ru t.ure coastal protection work may be saved nowthe t y pe s and maljnlt,ul1"sof coastal changes a re more fully understood.

(x) Peo~le liviny on !:Jetioand !:Jairikl are ljoing to have to learn to ll.ve withthe problem of coastal ero!>ion but they should be made well-aware of the rl.sks involvedand the measures they rniljhttake to reduce thdt rl.sk.

.,_._ ~... , ~.,.":'::'::'•.•~~:•.:,.;'~ ::.:...:.::~::;; .•;:.;,;: 1'1

(i) Carry out a liurvey of the !:Jonriki area in southeast Tarawa l.n preparation for anydesign work assoc1ated with the proposal to upgrade the airport runway.

(ii) Continue the beach prof1l1ng surveys to increase confl.dence that the naturalfluctuat10n 1n the coastl1ne of Betl.o and Bairiki is t25 metres along 100 metrestretches of beach at anyone tl.me.

I'

(iii) Implement a wave climate study to assist in the development of an erosion forecastingindex. A p re Lirruna ry attempt at deve Lop i nq such a forecasting index should be madeby hl.ndcdst1ng.

"

(iv) The Kiribati Go ve rruuent should implement me asure s to prevent any development thatmight obstruct lorlljshore transportation of sand, ~uch as the construction of channelsor barriers near to the beach 01 all/across Lhe reef flat. In addition, buildingshould be pl'evented on ar..,asWh1Ch are at present accreting, and a careful watchlihould be kept on the bUll111nys cluse to beach ~rofiles Betio 2, 7 and Bairiki 1which will be at rl.sk It the present trend of erOSlon at these sites continues.

;'I,o:1

,IiJi'

il(v) Sediment transport stUdleS are at present dt an early stage, these should be

continued.

---------

REFERENCES

IJI':'~!I •I"'I".·

11 ",:

.-,," ,,~',.i...

CARTER, R. (1983). Coastal erosion in Kiribati. Cruise ReportNo. 76, CCOrjsOPAC, UN Mineral Prospecting, Suva, Fiji. , .

HALPERN, D., llAYES, S.P., LEETllAA, A., HANSEN, D.V. and PHILANDER,S.G.ll. (1~83). Oceanographic Observations of the 1982 warmingof the Tropical Eastern Pacific. Science 221: pp. 1173-1175.

;,, ,

HOWORTH, R. (1982). Coastal erosion in Kiribati, South Tarawa.Teclmicdl Report No. 22, pp. 13, CCOPjSOPAC, UN MineralProspecting, Suva, Fiji.

• 1;:~HOWORTH, R. (lY8~). Co~stal erosion in Kiribati, South Tarawa.

TechniccJ.lReport No. 25, pp. 8, CCOPjSOPAC, UN MineralProspecting, Suva, Fiji. · -'I

i ~

!• I, ,MATTHEWS, L.S. (1971). Heavy swell observed in the South Pacific

in Decembe r 1969, 'rech~~al Note 196, pr. 11, New ZealandM~teorologjcal service, Wellington, New Zealand.

"

Nature 305:(1983) .

p. 16.Anomalous El Nino of 1982-83.

-I. '

TROUP, A.J. (1965). The Southern Oscillation. Quarterly JournalRoyal Meteorological Society 91: pp. 490-506.

"

:'iI

_~~!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!~ilI!'!!I!~!!I!!~,,------"'IM''''.~_~~''I'..•"'•.••.•.•...•••••••..,NW,' •••••••• --- •.. ~.~ •..••

No corrunun t s .

Appendix 1: Comments on present state of beach profile sites.(Refer to Appendix 2 in Howorth, Technical Report No. 22).

Betic 1

3

4

5

6

7

8

9

2 Iron stake bent over and buried by house occupants. UseSE corner of house as horizontal datum and concrete doorstep on east side of house as vertical datum in future.Metal stake was 11.Om from corner of house.Line of sight obscured by recent temporary buildings.Vertical datum becoming overgrown.Bunker.becoming overgrown.No comments.UT2 survey peg still exists (Carter, Cruise Report 76refers to it as lost).No comments.Becoming very overgrown, line of sight badly obscured.An extension has been built onto concrete verandah.

13

10, 11 and 12Metal stakes in fence missing. ~, ~

; .I..

14 and 15

No comments.

No comments.

Bairiki 1, 2 and 34 and 5

No comments.Lots of low vegetation growth close to highwater mark.

6 Con8rete surrounding manhole cover buried by compactedroad metal.

'. -.••• ~ •• i'\'~"'I •.•••'··"Gao})i0n··wal:l:, buil t ,1at.e ..J.982 now ..bu.r.i~Q-•., , •..••.

No comments.8 and 9...'tC~Ji'-V"ifrt"~C'~tt:I;~~Nlt~~:-.::~"'''~,~::''''''

~-~10 New vertical datum required because of fences around new

Australian High Commissioner's residence to east.Recommend new vertical datum concrete verandah by doorof house to west of profile. This is 0.06m lower thanoriginal vertical datum at British High Commission.No comments. \ .,.. ~11

..\.

;:.. .

t :..i.,..... .:.

..,

i<i< i<

i<i<i<

i<i<i<i<

00

,.;

I..

I' ~~(

1i. 'i

, '.

''1

L-o:x:

N NN

• I000000

M co 0'>N <:t<:t

000I I I

V'IQ)

o•...Q)co

· I000000

U)LONC""'1\.Or---.. q\.O(J"\lI'lO-otN....-4C)O <:t"ONM

• I000000 0000

I I I I

• I000000 0000I I I

OO"l.....-4U)"d"Q') M(Y).....-4'-"""...-4...-4N....-4OO .-("' •......•0

• I000000 0000

I

f"")'-D.q-\DO.....-t •.........•OO"lN....--4..-4NN....-4....-4Oo::::tNN

, I000000 0000,NCOCONU1r- \.O,........LC>N•.....••........•Noc:::t"C>N -"U1"d""d"

• I000000 0000

o ........•r-\.OMO ...-4ll1M....-4•.......•NNU).-4l.f) Mr-\DU)

• I000000 0000

Mo::::tr-....""""'Or-- 0000 •........•\.0.---4MNr-....-4\.O c::tmCX)oo000000 0000

\.OON •........•q-N lDm\'o-1......-llf)MONO' lD •........•O....-4

• I000""'-'00

• Io 000000000000I I I I I I I I I I I I

.---4 lJ) OMNOOO'...-tOOO\.Ooc:::t" 0 Nlflot:::tU1 •.......•M..-4Q<t;j-M00

M • I • I

00

m \.0 .---4 ex)lO r-MNoomCQo::::t0...-10 •........•0....-4

oI

oI

0000000000I I I I I I I I

...;V'IQ)L-•...Q)E

E::::l+J

'""0

~'"+JCoN

"d" N,........Moc::tr--OQO •.......•,........o r-4\Df"'1¢Noc:::T •....•O"d"M

.....•<:t

oI

• I

oI

0000000000I I I I' I I

00

m<d-O'LOOO •......•CV)C'l'"')NMr-co •......•....-..q-\.O....-4•.........•oomO ........•...--4N...-4...-40NNN,..-.4

I

• I

• I

• I

• I

,..,..:

"

N.....• .---40LO"d"-.:::t"COO"lr-OUlOo" •......•M"d"MO •......•qM

0000000000I I I I I 1 I

• I .• IoI

oI

NM

0'>o

<:tlDN 0.". 000 lD •....•00.---40 •......•N\.OM....-1M"d"M

oI

oI

0 •....•00000000I I I I I I

oM

NlDm\..OM\oNNWt'---O'O'm.....-4r-NMr-40MNMOOOOM0U1<:t"M000000 •....•00000000I I I I I I I I I I

r-oo::;tr-....-4.-tr-ooq-lOo\Omq-....-4l.f)•......•M •.....•OMl.f)ll)...--40 •....•MOCO<:t"M00

N 000000 •....•00 •....•00000I I I I I I I I

coN

ON....-4N\DMM\DCOr-MCOO'O-.::TNNNONr-OON •......•MMOC>¢M000000 •......•00....-400•.....•00

I I I I I I I I

OCOmO"lM\OM •....•'"d"U"'lCO\Dr-¢ONQ.....-l..--lNrnC7'¢Mr---. •.....•O\DNM

OOOOOQ....-4OO •......•oo .......•ooI I I I I I I'

NN

ornOMNI..D"d"mmoo::::tMr-r---..coroNO .......•.q-NNoQ-lOoQ-O"IOOo,\O...-OOOOO...-NOO...-OO~oo

I I I I I I

"'=:t.....-4.....-4Mr-q-I"QMOMONMO'IOa .....-4MO~O~MOOr-O~NOOON

OOOOO •....•NOONOONOOI I

~NLOlOOOlOO\O.....-4r-Nq- MIOro "'-lO"'-O'\"'-OOMOO'\O'\N~ N.....-4•....• • I

OOOOO"'-N~0.....-400I

...-4NooNr-I"Q~OO'\ooO"lr- \01..0~ OOOMMMmr-4oQ-.....-4COMlO MM•....• • I

ooO'lO'>oolD"OM"lD"O MlDN MMooOroOr-ooooor-o r-co•....• • I

O"'-ONON...-4N.....-4"'-0.....-4

o.....•I"Qr-----O'\0-4lOlClCOq-lOr-MO"l('\Jr-0-4LOONM...-40lOo\o\OOON.-4O"lNON.-4N0-4N0-4.......-40-40-4r-4.....-4NOr-4

DN...-4N"'- N •....•

M ~co M t--;o ...--40 CON• 1 • 1

N NN•....•NNNNEaL-.•.. 00.....• If) 0'>

NO• I • IN ...-.......-4NNN N NN "'-('\JQ)

uc'"+JV'I.~Cl

Ln\'olJ")O"r- M N CO...- LnM0-400000'\ "'=:t 0-4 MO •.........N• I • I • I • Io

.•..oL-

0..

..c:u'"Q)co

•......•NMVlOt..O •.........COo,\O •.......•NM'd'"LO~ •.....• ...- ......• .-. •.....•

If)O<:t''lDMlf)ooNlD<:tO .......•LO.....-4r-r-OOO"lOO'l.......-4('\.j...-4N...-4"'-0Nr-4N..-4

LOMll"lMO'\MOoQ-O'\ r-4M •....•oo •.....•Or-NOoo 0

If)MCOlf)MO'llf)MCO \.0..-100 •.....•NOOMOOO 0"1

NNNNN.....-40N..-t

¢\OCOVll"l'-Dr-4LnO N"'-O"o...-.......-4O"v)oo 0•....•N N...-4NNN...--40NN N

000'1co c-i

,...."r-...-tnr-OOLnO'"'l00\...-4...-...-4 or-...-4 0"N.......-4NNNNON0-4

• I•....•N N ON"'-

.....•M

00'>00 •....•mQ , 1"---"

'--N·000 •....•-- , lO Lf) IM~NO •. .,1 fill

• Li1....--...---..---..o Nlf)CX)I ••Lf) 0 (J'\~~ .

00<:t00 •....•'d'" a I I "---".~~.".·00000 •....•..--.. I 'd'" q- I<:t~N CXJ

• <:t~~~o <:t"0I "Li1C)O~~ .

\.OMOON<:to 11-

'~~lDa l.O l.O .......-4"'''---''''d" <:t I

~lD(Y)q fIl •• "0N ....--...---..---..~

•..a r- It)

o --..(Y) a a aI r-; . I

-0 C>CJN-q • I I-V<:t0 ~~ 00<:t- oQ-c:::T...-4

<:t<:t<:t I..".

'"+J

'""0

o ...--..--..---..r-M ~ lD 00lJ) lJ)

·(""")"'-00ON '01 'CON I

"---"0 11--N"---""---"-ONQ"NNNNc:::T

v¢¢ 1

r-; 0'>OM

\D ,....".....-4 .......-4 -r-: 'r-~~0000·,....·,-'r- .,.....,.....,.... ~ \-

+J +J +J 4J -r-: .,....WWWWI\lI\lco co co co co CO'"c

a+J

"0"0«

i<i< i<

i< i< -l<i< i< i< -l<

i< i< i< .•• -l<i< i< i< i< i< .••

M.....•

NI

oM

.....•LO

coI

0::>I

ovo

Cl.....•I

"0

O'lC

"0Caa.V'IQ)L-L-

,.."g'l-

---- - - -----

.•..aL-a.

..c:u'"Q).0

..c:u'"Q)

S-o••...E::::l

+J

'""0

~'"+JCoN

L-a..c:

EaL-.•..V'IQ)uc'"+JV'I

VlW

-'u..o0::0..

:x:Ll«waJ

'''''.11.., .• ,'."-'1""""+J

'"coIo

I-wco::-w:>0::=>Vl

E::::l+J

'""0

'"U+JL-Q)>a+J

+JUQ)a.V'IQ)L-

..c:+J

<.!lz-'-'w:>w-'w0::

w-'co«I-

c

'"+J

'"Cl

..

. '

•••••••••• I.IIi-.-lii-jij-_-· ••· __ ~>liJ='''\'!".'''!'.•.'!!!''~$---'''!'', '!llSX"""""'-

i .

I'.'I,

t'

t',I:j,I,

I.

, :

E~.•...ro-0

~'".•...CoN

'"QJL.•...QJE

NM

o

Lo

::I:

EoL.•...QJUCto.•...'"'~o

• I

NNC)\.DO),-i(Y')qUlr-iOI"--1MNr--tOOOOOo <::>00<::l00000o

o

COI..UNCOQr-t\OCONNa c.')q•......•NODDDD

o C)OO <::l00000

• I

<r vJ M (Y1C\)N Ll")N (Y) q-N<:::::lLr'J..-1t-1C)OC)OO0<::>00 <::l00000o

• I

\oCOOM"J Ll"l\ONMMOLl"lO<::>0000·00000<::> 0000o

• I

r--4r-,Nr-oc:t l.D<:t"MNv<::>\OOO 0 •....00. '00<::>000 0000o

oM

aJN\OM¢I..I'JI..OOOM..--tl.()r-iLl")NMOOOv<::>\oOOOONO<::>

°OOOOoC::oooooooC::

coN

("t) ¢ M C\)N <:) N r-t co l.{) 1..'\,J r-c, t..D M •.......•C)<:t"OC)C)MOCO •......•OC-:)ONOO<::>00<::>000000<::>0000

Nr-",\,Q f..'\)Nr-q-¢ "'tl f'....OO•......•"d"NOMOOC)Mr-tO"lNC)C')ONOC>0000<::>0000C::<::>0000

U) co r-t \0 'JI <r N O"l r-t C) 0) 00 r-t C\:JU)a N r-40 C)N MOM C\) t-1 0 a t-i 0

0000<::>00 •....0<::><::>00<::>0

NN

CX)\oONlJ)q-C'\ll..DMO)C\)C\:}C'\lt.eJNON •....•CJC)r-i C\JNM t""'1 f'-1 CJ CJ "-10

000 CJQD (:..)•.......•0 ~ ~ (:::.c:; C:)o

oN

q- crv r-: N (0 ~l r-, N "--> 'Jl r-, I",)0) "tlo r-t 0 0 C) '"'1 r-t M (.x} t...'J (J "-> r-; CJ

OOOC)O~C)r-40CJ~~(jC":l~

co•....\D co N If) 1'0.) rv.:. ~.) m m ~1 (Y) "'J' C'<',)<r-a N r-t 0 c::::.1'"-1 1"-1 m M ,"",",j 0 CJ CJa

• I0000<::><::><::>00'00<:><::>0

qMN(Y)'J1(0....-1ml.{)~MCO NO)o .......•r-t •......•CJC)C)\,,()MC)OO r-tC)· ,0000<::><::>000<::>00 00

~' 1..0 rn '--t r-, 00 vr \.0 N r-t 00 N •........•c-, r-1 ••....••f""'1 c.....-,a ........•..-1 0 N r-4 N r-t

. . -0' I'000<::><;:)0000 00 00, '1'

N•....so co co (V) 1'0;) 00 aNN co l1) r-, q-<:::).-tr-40<:::::>ONr-4(y)NN Nr-4

. '0' I<::>000<"'>0000 00 00

o•....(Li 0) M 'I' r-, <r- 00 f--l r-, \0 \0 r-; mC)C)r-4Q r-tN"d"t:'.:>MNOr-tO

.0 IaC)oCJ oooC)oooc>c>'f,)r-mr-t\.DCJOr--tOO<::>0000co • I • I

00 00 00

00 00

1"-1r---iN r-,CJ a r-t f-t

• I • I<:>00 <::> • I00 00

N • I · ,• I o 0000

o • I00

-' L:u-oQJco

r--iNMqU)\Dr-eco,\O •......•NMc::1"U)r-1 r-1 r-t r-1 .---1 r--1

00

v C\J 1-1"""" ('t~ r-t C() \.D m0<::><::>0<::>.....000• I0<::><::>0<:>0 000

¢O}r-1CO'¢CJ'l f"J\Dm0<::>0000 NOO

• I0<::>0000 <::>00

co r-; {.\J 0 r-1 rn I"Q (Q 0) U1o a <'\J ,.......<:) 0 r-1 (;\J a 0· ,00<::>000 0<::><::>0

NMt-,CONr--1Q;)Or-,C)r-OOC>OOO~M"J~O. .00 <::>000<::>0<::><::l0

M(Y)Nr-NO"l C\lCO tv;) NCOOOOOOO(oNN~r-4000000 <::>0C::<::>o

Nr- qr--.,r-£'....(J)IJJNCX)00 O<::>O"-M<::>~N

'000 0<::>0<::>0<::><::>0•....

er- l.() tv;) I.•;) r-; L.{) r-t q- 0 C'.. 00

OOC':>CJc)OO)~ C\JN. . 0OOC><::>OO<::>O <::>0

roN C'\l<::t"NL.{) IJJqi,,{)Q;:)r-1

OOC::>OOOCJl.OOI"-iM00<::>000 NOO<::>O

r-; ~ Lf) t--; ex) 0) r-; r--, so r-;o (~ 000 r-,L.OO r-,N

·00<::> OOONOO<::>O

COcx.o"',,","JCO"-\Or--<ovC) CJ <:::) <...."") ao tv)\.DD Nr-t

O~c:)~'J0l-10c)CJC>

I..D <..) r-, •......•C"'-... •.••...• 'J' l1") I.'\J l...() q-o C) 0 t:") r--1 ~"-J I..D (J CJ ao c:.;'0O'0ONO <00<::>0

<r I.\} 0) N (Y) r- 1 CD 0 tv) '\;J. (,\)o t'i NOD CJr-, l..D r-, N "'1

OC::'0OOC>NOCJ'0<::>

q-r-,q-LOr-ooaCOLf)C'...C\JOr-;O 0 0 a ~'I..O 0 CJ t<')

a CJ0 a 0 a r-l 0 0 C) C)

'.l~ OJ 00 N '.1.J (y) (,L) N N ~l-iOOl~r-1tuO"""" <:::>

C::<::>OO'CJo~ooOC::

0) N l.D 1..0 lJ) 00 '-'J (Y) r-, (,J NC\)C;'J r-40 0 0 ~ 0 0 N CJ

<::><::>0000<:>00<::><::>

v,) (.) 00 -er- <r ,"'; ~lJ \D (Y) <;\J \.0N(V)DOOC)NC)r---iCJOC::C>OOO<oO<:::>OO<::>O

C't';)l.Qr-Lf)NJ-iOON rnr-,<:::>OOO~O...-t 0

o c:: <::0000 'CJoo '0

o 0 r-o:lq- (J~ <:..J U) cor--t •......•r-,D <:::>r-;OO

• I • IOOC:>O <.:>'000

N C.) <r t-l CJNr-;C) r-1t-,

• I .• 00 I0<::>0 <::><::>

OOrv;lN CJl.J)N r-,D NN

oc::>o'c;c;cooo

• I

"~ 1

I

'"co

E~.•...'"-0

ro.•...coN

•...ox:EoL.•... .•...

oL0.

x:u'"QJ..0

QJs:+'enco

<lJ>

'"~~Ul::

Ev•....+o.•... '"

'" VIC QJ0 •....~ .•...

.•..• QJ-r-« E

I ~ '" ·~I· t<U'II'VJ lltllll,.II"O"',lll •.•••••M.lIl'.Il' ••I.I1l.. ..~\tOCa..~

EoN

I

'"co

en '"c .•..•~c3l::o0.VI<lJLLoU

C '"QJ .•..•

<lJ '"~-o.•...QJ>,

..oQJ

>'" L.•... ~

.•... '".~

..eM"'CO

O'lr-r- ••..•

'"u .•..•'~ VI.•... ~....enQJ ~>c:(

.....QJ~o-'

N

W-'coc:(I-

w en(.!) c:Z """-or-

e:t:<lJ~:J:>'"LJ or- ::::s

l/l~•..•...l/lUO<lJ~~~w en u,0..0>- ~I- a..

c:N 0~ or- c:O::I-~Oo u, QJ or-:I: ..- S- Vl

IUOI-l/)U~I- "'<lJw:z + I

(.!)

=>e:t:

M~ 1 CO.~ z:., .~ e:t:

I.~ '"":>

p..- I-u, z:~ e:t:

M:J: '"":>COl/) I....• ~ W I

-J >< z: N, . e:t: '" => COl- E .....,:z~0N W~ z:., er: =>0 .....,

N:J: I COz:~' e:t:'., '"":>

-'

"_., r

I 0, '"

",'", . .,I

f•

/. ~

I'~:.,

o, o, o, o,

1-----+--------------------,.,

\-----+------,-------------i------------.,'

r-M\.DmMvvl..DNr-tOVMO"N

~9c:?~~~r-;-~~~~"7r:;:i?~

r-; N r-M\Dl.OQr---<+\.O\Dr-qN(V)NtrlNu-JNNN~

I l..-t I + I I I I I

I

I I

o, o, a.. o, o,

.,

..,I-u,

~'IIJ,,,, ••~~~.~ 11al9"~~~IIl1I_M\lI~., -J ><e:t:'"~5I-er:w:>

w:z=>'"":>N.,tCOe:t:'"":>

N •...•I I

....•.--4\,D\.OO'\..-l(J"'l\D '1..01..0

'N\DN .......•OONNM .........•MM+ l..-t+ 11++++

+

OJ M ot::t a \.D 0 U") ••...•Ln M \,J)

OMO..-t •.......•L{)l.f)~cor-o1+11++..-11+++

I

CO en co NCO\D .....••....•

o lON-<t'M..-tl++ I+

l/l<lJ.L:U

'"<lJ.D

~l/l<lJ~'0c:'"c:ooen

'"

'0c:

'"l/l<lJ.L:U

'"<lJ.D

c:

'"<lJUos,o.•..

<lJ'O~<lJ s,'O<lJ<lJ ~~ 0<lJ~~O~

~O

.•..o<lJa.o~l/l

N..-l..-t..-t..-tU)lf)U""ll.OMM,+ I I++N++++

I

....•I

lO

NI

.; ,1 ;,

..,

W-J~~'~•...... ~oer: w. a.. (.!)

:z:J: e:t:U :J:e:t:uwCD

z:e:t: M'"":> COI I

WNz: CO=>'"":>

wz:=>'"":>N

1 COz:e:t:.....,

....•I

•...•MN1 I I

O-<t'N

NNN+ I I

.L:U

'"<lJ~~ .D

N N 0\ \D U').()l'}•.•••.M·O\ No r-.. ~ •. .•.._.,~."'~~.~.,v·N· •...••...•.•·N·<\O,U) U'l ~ M-t'!"'), •.••..•..•.• ,.",.•,"' ••'~' •• ,••_~ •.•

~ c:

I I

M lO•...• N

o 0I I

OOOOOQJOWOOO

~------1---+-----------------~-----------j..-t N M 'd" lJ) I..D r-, co m 0 ~..•....• ~~

W-J•...•LLoo;o,

00I I

VM\DLOQ..-t\oI..Or-v<d-MNLI)NLONNN.-I

99~9~~9999

00 co rn •.....• r-; \0 \D m •.....•·m \D --..l"Q l..O",,11N II"") N'rn •.·~.r••.• '4'10 ••••• OO'C'lt-<""J·M ~ ~ M ~

O-<t'NNNN

aN

aI

000I I I

000+ I I

'" '" '"OWWDDWWWW<:«JJ<lJQJWQJ

rowe:t:e:t:e:t:Oe:t:we:t:e:t:QJQJe:t:e:t:e:t:e:t:

QJODOOWO QJW QJO tOW CV I I

•....•N M «r Lf) \D r-, co m 0 ..-t N M <:j- In.--4 •........•.--4 •......•..-l .~

o.....I-wCD

e:t:CD

'" a.~::> l/l~a.~::>~ ~.~ .•...~ ::>

~~.D .L:~'~ l/l~ ::> <lJO.D~a. '"<lJ<lJ ••.• Uer:~0.~~ ~N ••.. a. s,COO QJ~ .•.. ><lJ a. 0c: E::> ••.. II> 0

'"":>0<lJ s;s; .•..E~

~8lM "0QJ~ I ~

~-<t' <lJ '"0 ~ ~~ 0 ::>0 E U:J: QJ ~

en~ '"QJ c: 0 U<lJ '"l/l.L: a ~~U •...• .•..QJ QJ .L:en~ l/lc: .D <lJ

'" '" en.L: .D c: '"Uo'" ~s, .L: c:oo..u 0:z N

11 11 s,<lJW 0

~\0 ",e:t: I

l-~''I-~

r--- ----------.-------------- ------- -----

>C>Z

q~WN~~~N~OO¢~OO~~ON~~V~~M~~M~N~O~NOON~VU I NI......-4,..-t II ...-41 II ~ '-'...-4, N...-4111 NW I I I I I ICl I U') C) I C\) I f"-.4r-, tv') 0) I "J C\) c-r I t---{ lr,) -. lr,)I lV:J ~ -. r-, C\) "'~ f'o?~ ~

- -------------- ---- -------------------------- -------------

1

_-

"-1-,

~~mN~M~N~...-4~WOVM~ONO...-4W~~O~~¢N~m~~~~~I~1...-4111 "-'1...-4,..-....-4....-4 NIIIIC'J 1M I""'" ..-t'11 N

I I I I

I If"J r-, -. f-l I I ~ ~ r-, tv)

"1 N

l'I) r-... I I IV) I "'1 I C'J lI)N

M~VWOO~...-4MWN¢MN~O¢MN¢NMMrn~Nmro~N~~NN~rn•....... I ...-4....-4 I 1.......-l....-4 I I I ...-4•....•..-..--. I I I r-~ ,......f ~ ...-4.----t I I I I •.....•

U I I , ,

C>1-4 IV) I I C,) I tv) I I O:J 0';) C'... l't') T--1 I ~l I <"(\ I I C\) f'o,l I I 0) I

N "JI t-l I r~'O I I Q;)

cor--- ------------------ ----------------------------

...-4ro...-4Wm~¢NMM ......•NO~WW~~~N~M..._4MWMMWNMO...-4M~M~

...-4 I I 1...-4 •.........•, •.........•I I 1...--. ......• I 1.....-4....-t•...•...•r--4...-4....--iN................. I"""'"

I I I I I I , I

- -

CLUJVl

<!>=:Jc:(

-'=:J...,

.•. ' , ,Z=:J...,

-- -->-c:(::E

cr:CLc:(

cr:c:(::E

COUJu;

Zc:(...,

. -,

r- :

I C'J I I f-i ";Jl I 'to I I f"-i C" I I •....•I

N ""

I v:> I I V) V';) I

~~W •.....•M~OOOOMmON~q •.....•~Mv ......•qmo~¢¢mN~OMM ......•¢ •.....•V~I 1...-4 I , •.......•....-I ...-4 I I I................ 1...-4 I •........•N...--4...-4 I I N

I I I I I I

I '::11 I I l"--i I I •....•I~I f'o';) I rv::. I I •....• I I CO IN

m ......•MOOMNNOO~~M~N~O~~M~~~~~~~~N~M~~NN~~I N~ I '~~ liN I I I ..--. r--fN •......•..-t •...•.••I •......•

1 I I , 1

INNIC\:)I 1"':lt..r.lf'...NC\Jf¥;)C\JlI)~NC\)NC\J~C\J It..r.l IN 1Q:)t-e IN N

1---+-------------- ------------N~~W~~,W~~OM~~~M~OOOMO~N~ONMNN~ •......•m~m~~M,I,....-.4N 11.....-1.....-11 I I I I ~ r--f ..-4tr-4,....-.4..--........4,•......• I •......•N

I I • 1 I

l.r;) ~ I I N I

~~~oo~~mMMOO~~wMNmvNO~M~WMO~~M~NNOOVM~~r--f I IN •......•..-1•.........•1 .-l 11..-11..-4..-4 •......••......• .._ I I, I I I

I Nf'0 1 1"":) I I C\J I l""-4 C\J

~N..-400VMMM~OMN~~._lO~Wmm~mN~~OOqNw..-tM •......•.._NmMI ' •......•1.._' ' •......•1 •......• ..--l...-flll...-fI~-.11...-4 •......•1.,.-1•......••......••......•11

1 I 1 I I 1

~ , I,.....• I I r-r I N I t--l I 1 C\) "I 1

------------ --- .----------------•......•OOM~~M •......•m .......•~mvWN~qwro •......•OO~WM •.........•OONN...-fNqomm~ •......••......•, •......•11r-t11 II NI ..- IIIN IN..-..-r--f •.....•llr-t

I I I' I

1 Nil N I C'l I 11'"-1 N I r-.... 1 I C\1 , I Cl) I

------------------ --- ---- --------------------~Wo..-mN...-f~~ •.....•~oroMWqNN..-4~MmomW~~~¢MmNwOMOI IN ..--.•.....•1.._4.._' •......••......•' I 1..-1 •....••.......•..- •.....•r-4 •......• M •

, I 1 I 1 I I I

~qmq~N •......•~OO ......•¢OOOO..-4MroooqmMm¢WNNM¢MOONmqmMNOlll.-t.-l l..-t •......•• I , •......• I I •......••.....••......••.......• INIr-tl' I •......•

I I

I (.\1 I r-, I N C\J 1--4 I C'I,)1"-.1 IN

I f'...V) NC\JI

1--+-------------- ----- ------------- ----------------1~oomO •......•NM¢~w~oomO.-lNM¢~w~romO •.........•NM¢mw~OO~O •......•N~¢qmmmmmmmm~~~WillWWWWWWW~~~~~~~~~~OOOOOO()'\....•

INco

'----'----------- ------ ---------- ---_._----- -----------------'

VIU

VICo•...-oCoU

>,~s,Q)•...VIQ)

3.•..o>,ucQ)

::>crQ)s,.•..

.•..oQ)

>VI::>~u~cu

.0

N '"ro~C1\ '"....• ~,r-, xq-Q)C1\ -o•...•c~"oc.~ 0~-~Q) ••.•

0.'"~~~o-~••..u

VIVlOQ)::>c~~"'Q)> .s:•...>,::>

~Os: Vl•...c"~~

__------=' ~.--..--.--'0

'< .

~r,.:.'t:o .. 0

r

;,0

FIGURE 1: Location of beach profiles around Betio and Bairiki.

------------------'---_.--=::=~:!!!!!!!!!!!!!!!!!!!. ~_!!!!!!!!_._---

oo•....••....•

ooo....•ONo C7'lC7'l CO

uwCl

.'-:.::.. -=..-

,.-- ----.•.~--.-~------>-0z

I:I

/. ~u

t 0

I

Q...

WVI

-:.~--",-------------- - --------

,,===~~~A >

_----.r---------------e--:.•._--

cowu..

..,

ooCO

oor--.

>,.0

"<11.,...r--:0.0.::::::lVl>,

r-

"c-or- or-::.<: .,...

10~-10

Vl:::I:s,::::::l4-o 0.0s, >,IO+-'£.,...

Vl.,... ~.:¥<11

>

u.Jr...!J

LeJ ::;)........~..•.-.•.. ~ .. ~.::;)<:(C.!:l w

a~ .....•Cl I-.....~ 0:::~a::: 0~ co0 a:::co ~0::: I<:::I: ~0

a::~w ~co ::n

">'c£100.

10o ~

.,... C7'l

4 __ .• M.' ••..••••• ~ .••• 01_ ••• "......;~;_i;:;,j,iNu;..;;COlO

<11~ U004-

4-VlO

"~+-'o cU<1I<11 E~+-'s;<1110en 0.

~~en-

r-.,...E

Vl<11::::::l

10>

<11'''''" -"".,... +-'~~ >,N3coC7'l•••.• ::.<:

N

z:c:!"J 38mt8 01139

0 0 .q- 0 0 00 0 .q- 0 0 0q- M N N ....• 0r-4 .....• .....• ~ ~ .....•

1"

, '~

IW I

Is, I;a~"

WIZ nJ I~ Ii nJ I-0

I,II.

I<lJ nJ IU > !

.,..... ::J I~ V'l I~ Ia IVI Ir-- <lJI, nJ·,..... Iu s,

!.,..... aen~ II: V'l 0·,.....

Iz: r-- s,i a s,

s, <lJ ,N oI-

II co <lJ0') ~ ci .....•

~.~ II s; VI IL QJ -0 VI, ..0 C'r-E nJ

~<lJ r--U nJ a<lJ <lJU0 NI .I:::.

<lJ ~ en, IC <lJ'r-::J z: ::r:::3 'Jz: E u0·,.....

~~co ~.,.....U3 N nJ

(/') co 0...0')•....• Cs;s, <lJ<lJ ~ ,..0 VIE <lJ 1<lJ3U I<lJ s,

~lCl aI ~..

<lJw C c-,::J s,,',~ 'J nJ

s, ~~I "~II~,J a ::J

~ V'l

nJ r--. -~ nJnJ U0·,.....

ena

• r--nJ a~ s;ro as; <lJnJ~I- <lJ

Ls;Or--~ nJ

::JVI C

(/') E Cz: nJ<t:s;O'lEnJ 0

-r-: s;-0 ~

<lJ •.•..•VI r-,00')~ •....•

I'- 'Or--.c<::t-.....• .,.....0')

r--. 3 •....•...,0')':;'. -, .....•

rI

'- r-, (V)<::t-O') w~ 0:::.....'~ :::)

t!J-<t: LJ...

".~:1.(:..-t -

- 4.030

4.0

.2.0

- 2.0

j aL a

f'~ ~::.. " '\

o

I I I I I I

-

,Alt ~~

~ -... ,I~\

~J

JI "q~''l~~

I!I~ ~ ,~

~~~I \l~ - ---- - -- - -

I

~!}{

... , -I I I I I I

, -

~' . "~ ... ,-. . ,..

40 50 50YEAR

70 9080 , ,

-!~. il I(.,~ . ft-- .,

.'

~. fI ,

~

•..I . \\....

~

~~s:;>~.j• 'I

!

.._~.."""'*._----,..•.•............-~ ...•.••~~

FIGURE 4: Three month running mean of Southern Oscillation (suppliedMeteorological Office, Ministry of Transport, Wellington),

f I,- ~Ir·

·1by ·~

:,-.'1

~ :i:;1, .

...o' ,~

'j

toOJ

;,.;.,,- ;~- '1L -.. '1.' -•.~..L,;-- .. -.....s .f

" .v-•I·.....

iO .~• 200 20

c / I

/ ,/II I

• I

I ,:

B 15 A

// I

I

/ iI

/ "I ,/

\A\

150

\

\

\

\

100 10

,,

•

SOUTHERN OSCILLATION INDEX

550

For each 0.5 interval of the Southern Oscillation Index:A = Number of months with 4 or more days of westerliesB = Tota 1 number of days of westerlies

C (_B ,) 100~, = ~_tal number of days of westerlies) 100= 30A ax. possible number of days westerlies could have b' own)

FIGURE 5: Relationship between Southern Oscillation Index and frequencyof westerly winds at Tarawa.

; ,

~-.

i--"',· :; .'

:

tt·.' I~ , .

..·~~·~-i. - -r ~ '..r- - -

,',' ..

::--

,-

t -_

\Ir-~.-,i-.r<~- -

f'"c:0.-' ••

"

_i• I.•..!

·.,.: ',

, ,

- \

,.'~-

r -~.• -.. Ir-,:

,j

•SON--------....--------.------..----""""T"----+----.,-.-.e-. \ \ e' - .--30 Nov 1'02 Dec

-._'-' ~ j"., 01 Dec ./\ \, ~I ._ .•• -.-.-. "-'-e.. e"'"\ ~ .' .,•.......

.•..40N

30N

20N

10N

EO

30-

/

X\

'\\

//

/'

/01- - -Honolulu•

--02--

Butaritarl --03--e

- - --_ Tarawa

.\ Beru_ Arorae

./

• Christmas Is/'

./

105-__ F....Jflafutl

- Nlulak.lta••• M'M';fH'Mf++4i~IIItIt~~.,.. fI••• 114"'I'Iew.,.'oftlt ••••"'~""' ••-...,W"'. Nf ••••• '1,11': ••,I lit ""'-r'~I'"

04- '-

.Apla

205

e Nanume:. __--

• Yz sawa - I - rara-Nandi

05- --

---__ -- -Niue-Nukualofa

170t. 180 17CW 160W 150W

FIGURE 6: Track of December 1969 storm and the computedisochrons of swell onset for 00 GMT each day.Great circle swell tracks out of generating areatowards Honolulu, Rarotonga and Yasawa-I-Rarashown (from Matthews, 1971).

140W

;. ,'". -

'" '.L- . IL . ,

~r..--.- '

i"""-,,.-~.,

~~~"'-

I H'

,,",/~

~ '\/~ \,

/""UARIKI I'/ i \r 'II ry "

J r: ): 1Vr"'w •• i

r \ -,

, r'-, \

I

l1TOO' 17 0)

[ffi~~[lli[L~© @[f ~~[ffi~[lli&\uD1f[iiJa~J[j(}flJ £1f@[,[L

l'\

\<

o Appro! ".r' Edgt(3 Appro. l.goon Edge

E3 C'VHw.ylISlhT., ••• ,

_.- ••...

•••• ~.4 •• '..... thr ",,".,•.•••• , •••

FIGURE 7: Location of samples collected by the authorfor sediment studies.

.__ ._.__ .,. -- _.---_._-.-----

L,

··'~'., ,--I

I

,,"' !,-.~.:

'---

l·" ,·,L ••

...<

kL -~"-t;.-~~,.....~\-:' I• .'~,••.,,,~l -ii'~,'.'