ICES 1989

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C.M.1989/C:43Hydrography Committee

VOLUMETRIC ANALYSIS OF RESIDUAL SEDIMENT MIGRATIONS ONCONTINENTAL SHELF SAND BANKS IN THE SOUTIIERN BIGHT

(NORTH SEAl

G. De Moor, J. Lanckneus, F. Van overmeire, P. Van DenBroeek, E. Martens

Lab. for Physieal Geography, State university Ghent,Krijgslaan 281, B-9000 Ghent Belgium

ABSTRACTSediment transport resul ts in erosion and deposition

and therefore in ehanges of form, loeation and volume ofsea-bottom struetures, espeeially sand banks. These ehangesean be studied over several time intervals. Residualsedimentdynamics eoncern net sediment migrations overlonger periods as resulting from suecesive short timedirection and intensity varying displacements. In anenvironment with high sediment migration variations,residual sedimentdynamies ean be approaehed bygeomorphological techniques.

The paper analyses the residual sedimentdynamies onthe Flemish Banks over the period 1983-1988 on ground of amonitoring of vOlumetrie changes of sand banks along fixedreferenee profiles. The monitoring departs from sequentialdetailed bathymetric profiling along the referenee tracks,high ~recision navigation and positioning and profilenormal~sation to make sueeessive data eomparable, usingappropriated software equipment. Sequential profiling at a1 mile distance alllows bank eovering over one tidal cyele.

It presents numerieal and eartographic data aboutevolution trends in the sedimentdynamies along the FlemishBanks over the period 1983-1988.

1 INTRODUCTIONAssessment of residual sediment dynamies on a shelf

sandbank can be based on two main approaches : the analysisof the residual sediment transport paths in relation to thebank stability and maintenanee, and the monitoring of thevolumetrie evolution of the bank in a number of test sitesin order to eva1uate thc real effeet of the sedimentmobility pattern and to express numerically and graphiea11ythe short term evolution trends.

In 1984 a sand mobility model has been published forthe Kwintebank, one of the Flemish Banks on the Belgiancontinenta1 Platform (Oe Moor, 1984). It shows the residualsediment transport paths in 1982. It was based on theeartography of types and geometrie eharaeteristies ofbedforms such as sand waves and megaripples, as deduced

from side-sean sonar registrations, and diagnostie for thedirection of the residual bed load transportation.

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That sand mobility model put forward that maintenanceof the Kwintebank results from a residual sand supply fromtwo opposite directions towards the bank's main axis. thewestern steeper side, In the Kwinte swale, dominated by thewestern steep side of the Kwinte bank, nett movement ofmegaripples is seaward due to a residual flood current. Inthe Negenvaam swale, along the eastern slightly dippingside of the bank, nett movements of megaripples islandward, due to a residual ebb current.

In these swales the bedforms are transversal to thebank axis, but on the bank flanks they are deviated partly

because of friction, so that they become almost parallel tothe bank axis and climb up the bank, providing a sedimentuppiling on the bank top. There the sediment is reworked bywave activity and by tidal currents, especially as peaktidal currents overtopping the bank are slightly oblique tothe axis.

In the period 1983-88 the chronologie and geographieconstancy of the model has been tested by sequential sidesean sonar registrations on the Kwintebank and by extendingthe registrations over adjacent banks (see Lankneus ,e.a.1989).

This artiele pays special attention to the short termvolumetrie evolution trends on the Kwintebank between 1983and 1988.

2 TIIE KWINTEBANK AND ITS OYNAMIC ENVIRONMENTThe Kwintebank is a shelf sandbank in relative1y

shallow water, having a 1ength of 25 km, a width between 1and 3 km, and a relative elevation varying between 10 and

20 m (fig. 1). The mean water depth varies from 6 m in theeentral part to more than 10 m on the northern and southernedges. Having a SSW-NNE direetion, the bank runs oblique tothe coastline. There is a distinct kink in the lengthprofile at the transition between the northern and central

part. The bank shows a distinct and constant transversaldissymmetry with a steep western slope dominating theKwinte swale. This swale reaches greater depths than the

Negenvaam swale situated at the eastern side, and which

presents a shallow threshold at its landward end. The steepside proved not to be a residual progradation side (OeMoor, 1983). The sandbank shows transversal and

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longitudinal superfieial grain size variations : the bottomsediment being eoarser on the off shore part and on thewestern steep slope (Oe Moor, 1984, 1985a ; Lankneus ,e.a.,1989). Different types of bedforrns oeeur on the bankitself. Sandwaves, up to 8 m elevation and running more orless parallel to the bank axis oeeur on the bank top,espeeially on the northern and southern edges. Hence athreefold longitudinal partition of the bank is obvious.Megaripple fields oeeur on the bank top and bank flanks,with opposite progradation sides on both bank flanks.Megaripple fields on sandwave backs very often stretchunder a direction oblique to the sandwave crests,suggesting transport by a different tidal current componentand possibly grain size differentiation as weIl. In betweenthe sandwaves, temporarily bank longitudinal scouringehannels have been observed (Oe Moor, 1986), suggestingimportant but discontinuous longitudinal sand transfers.

The hydrodynamics around the Kwintebank arecharaeterised by semidiurnal tides of megatidal range andwith a distinet differenee between neap and spring tidalrange. Near to the coast, situated at about 25 km, meantidal range reaches 4,5 m. The tidal movement presents adistinct elliptic eurrent rose with SW-NE axis : generaldireetion of floodpeak eurrents being SW-NE, of ebb peakcurrents NE-SW. There is a distinet velocity and durationdissymmetry of ebb and flood peak currents. Surface peakcurrents velocity reaehes up to 2,0 kts. Maximal wavedireetion frequeneies are from SW and from N. Longest fetch

is from the North.The anti-cloekwise rotation of the tidal currents with

their gradually ehanging velocity between a slaek minimumand two different peak maxima is very important for thewhole pattern of direct sand transport and sediment

sorting.sinee 1978 the Kwintebank, especially its northern

part, has been sUbject to a sand dredging at an estimated

mean rate of about 400.000 mJ/year.

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3 METIIODOLOGY3.1 Field observations

In order to monitor the volumetric changes of theKwintebank during the period 1983-88, sequentialbathymetric profiles have been sailed at 10 kts with amean interval of 3 months along fixed reference 1ines, usedas test sltes, and situated at about 1 mlle from eachother.

These reference tracks correspond to loxodroms betweenflxed beg in- and end points sltuated upon red Decca llnes(SB network). They run approximately transversally to thebank. Eleven reference 1ines have continuously been used.

Navigation and posltioning have been based on Deccaand Toran up to 1987 and on Syledis since 1988. Toran butespecially Syledis provide an accurate, high frequency, andgeographically reliable positioning. Position, groundvelocity components, bottom course and ships heading havebeen registered simultaneously every 30 seconds by theship's IIP1000 computer using the OOAS acquisition programme(M.U.M.M.). After transfer to the HP600A laboratorycomputer these data have been used for detailed trackplottlng, allowing a control of the accuracy of the tracksand opening a way for elimination of the data alonginaccurately sailed tracks.3.2 Corrections of bathymetric registrations

Raw bathymetric registrations were taken by anHydrographic Oeso XX echo-sounder after adaptation forsound velocity and ships draught. These registrations havebeen digltlzed and corrected partly by means of tidalreduction, (using the Van Cauwenberghe method (1972) andtidal curves simultaneously registered in 3 Belgian coastalstations); partly by corrections for ship's velocityvariations; partly by scale uniformization, etc... Aftercorrection nett bathymetric profiles have been plot in

relation to a zero datum level (corresponding to the localMLLSS). Flgures 2,3 and 4 provide examples of correctedbathymetric profiles on the Kwintebank. They il1ustrate the

great variations in morphology and sand stock of the threebank parts.

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3.3 Volumetrie caleulationsFor each of the bathymetric profiles a bank base has

to be defined. It eorresponds to the horizontal planeerossing the highest of both the base eoncavities of thebank along the eorresponding reference line at the startdatum of the monitoring. The introduction of additionalreference levels, situated at different fixed depthsbeneath the zero datum level, allow to calculate the areaof the cross seetion above these levels as weIl as betweentwo successive such levels.

To introduce the volumetrie concept, unit volumes havebeen defined. They correspond to the volume of atransversal bank cross section having I m width.

Different types of such bank unit volumes can bedefined :- the total bank unit volume above the reference level justabove to the bank base- the full unit volume of a slice between two referencelevels, the two most important being the base slice and thetop slice. The base slice is comprised between the twolowest reference levels above the bank base; the top slicebetween both the highest reference levels crossing thebank.

Such unit-volumes have been calculated per referenceline and per registration datum.

The resulting comparable unit-volumes show importantvariations. These are due to different reasons : naturalsediment transport, navigation errors, tidal reductionerrors, etc•••• , and possibly sand dredging as weIl.Matching of suceessive profiles along a same referenceline by superposition is used to eliminate unreliable unit­volurnes. Superposition is based on coincidence of fixedreference points along each of the reference

transversals. Moreover the corresponding sailed tracks arecompared with the referenee lines. Figure 5 shows anexample of such matching by superposition of comparablenett bathymetric profiles.

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After such eliminations reliable unit-volumes forsuccessive days along a same reference transversal stillshow important variations as indicated by the volumetrietime series on fig. 6 and 7. They are due to residualsediment transportation related to an important short termsediment dynamism or to human impact. As on beaches, hereas well short term sediment mobility seems to be much moreimportant than residual sediment dynamics over longerperiods. This is due to the impact of rapid variations inthe directions an intensities of the hydrodynamie factors.

3.4 Regression analysis of volumetrie dataTo define the volumetrie evolution of the bank or bank

slices along fixed reference lines regression analysis hasbeen applied upon time series of unit volumetrie data perreference transversal. Examples of such time series aregiven in fig. 6 and 7.

That analysis provides a value for the mean annualchange of the absolute unit volume of the considered type(A in m3/m/y for the considered reference line). As thesedata are insufficiently suited for a good evaluation of thebank morfodynamies themselves, and do not allow to comparemorphological effects of volumetrie changes betweendifferent reference lines, due to the great variations intotal unit-volume, they are normalized in relation to areference unit volume Band expressed in a mean annualchange to the relative unit volume (R in %/y). The

reference volume B is the initial unit volume correspondingto the volume to be read on the linear trend line at thedate of the first of the considered time series.3.5 cartographie representation

The trends for A and R represent the residualevolution along different transversal referenee linesacross the bank. They have been introdueed in a

cartographie representation. That cartographicrepresentation opens a way to a numerical and geographicalevaluation of the presently existing trends in the residualsediment dynamism and morphodynamism.

Fig. 8 provides a generalised flow chart of thesuccessive main steps.

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4.RESULTSThe maps (fig.10 to 15) show the unit-volumetric

evolution trends for the different reference transversalsused as test sites for the Kwintebank over the period 1983­

88.4.1 Total bank evolution

Mean annual change of the absolute total bank unitvolume along the successive reference lines is shown in

fig. 9.

Sediment losses are most important on the south sideof the northern part (rG23) near to the kink in the lengthprofile of the bank. They are as weIl important on thesouthern bank part, along the reference line rG17. Mostimportant gains are situated just south of the northernpart, along reference line rG22 and in the southern part ofthe bank (around rG18 and rGI6).

As the available sand stock at these test sites isquite different, the impact of these gains and losses uponthe morphology of the bank and upon the sand reserve isquite different. That impact is given by the mean annual

change of the relative total bank unit volumes along thereference lines (fig 10.). Diminishing of the total bankonly occurs at its northern edge around the reference 1inerH02. Rather important enlargement only occurs on the

southern edge of the bank.

4.2 Eyolution at the bank baseEvolution at the bank base is shown by the mean annual

change of the absolute unit volume of the basal slice alongthe successive reference lines (fig. 11)

The bank base shows quite important losses at the

northern edge(around rH02) as weIl as around reference linerG17 on the southern part of the bank. Important gains onthe bank base are only observed nearto the southern edge

(rG16). Else in the northern part the bank base unit volume

remains stable while the bank base in the central part

shows some losses.

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The impact of this residual sediment budget upon thebank morphology is shown by the mean annual change of therelative unit volume of the full basal slice along thereference lines. The map (fig. 12) distinctly illustratesthe break down of the bank base at its northern edge andthe growth on the extreme southern part.

4.3 Evolution of the bank top.Evolution of the bank top slice, which not allways

corresponds to the very bank top itself, is shown by themean annual change of the absolute unit volume of the fullbank top slice along the reference lines (fig. 13). On the 4Itnorthern part of the kwintebank, especially aroundreference line rG23, the bank top shows a general sedimentloss, which is particulary important along reference linerH01- Sand dredging could be one of the factors for thisloss. On the central part the bank top shows little gains,in the southern part however quite important sedimentgains.

The impact of this budget is particulary important forthe bank top morphodynamism, and, as the available sandvolume in this top slice is generally low, for theavailable sand stock as weIl. This impact is shown on fig.14. The break down of the bank top is quite important overthe whole northern part. Mean annual losses there reach10%. Bank top growth on the contrary is important on thesouthern part. In the central part some break down andgrowth alternate from place to place.

5.CONCLUSIONThanks to the use of highly accurate Syledis •

navigation and positioning, to Oeso XX bathymetricregistration, to different correction procedures, tocomputer facilities and to the development of originalsoftware programmes, it has been possible to obtain an

acceptable numerical evaluation of residual sedimentdynamics along reference lines on a shelf sandbank by meansof abasie geomorphological technique adapted to off shoreconditions.

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The method of sequential unit-volumetrie measurementsalong reference lines has been preferred to theconstruetion of volume difference maps based onsequentional hydrographie charting because of the factthat, despite analogy of fundamental technologicalproblems, this method opens a possibility to cover a

complete bank with a relatively high resolution within onetidal cyele.

Total sand mobility and morphological ehanges arequite varying along the shelf bank. On the Kwintebank mostimportant residual losses occur at its northern edge andthe short term evolution seems to trend in that way •Morphological break down of the Kwintebank top is mostsignificant at its northern part. Impact of sand dredgingis questionable. Growth of the bank is most considerable onits southern edge, suggesting a possible longitudinalshifting.

This volumetrie approach distinctly shows that asediment dynamic model of the bank cannot be based merelyon the analysis of residual sediment transport paths.Moreover it suggests that complicated processes, probablybound to the hydrodynamism, are conditionning the sedimentdynamism. It suggests that beside transversal sanduppiling, longitudinal residual displacement could beimportant as weIl, as already inferred from morphologicalarguments.

The evolution trends detected here from a 6 yearsobservation period, are not likely to continue over a longtime. This is shown by the fact that, using quadratieregression analysis instead of a linear one, some of thereference transversals already show maximal and minimaltrend eurves, indicating areversal in the residualsediment dynamism during the period 1983-88 (fig.15) •

Comparative analysis of half bank volumetrie evolutiontrends eould be of great help for a better understanding ofthe evolution of the bank's position, the transversaldissymmetry, the kink phenomenon and the relateddissymmetry inversion (De Moor 1986) that affects manyshelf banks.

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6 ACKNOWLEDGEMENTSThe authors thank the Belgian Ministry tor Sience

po1icy tor its grant, the belgian Management unit

Mathematical Model North Sea tor its continuous support andthe commanding officers and the entire crew of the Belgicator their help during the campaigns

7 REFERENCES

De Moor, G., 1984. Morfodynamiek en Sedimentdynamiek rondde Kwintebank. Volume I (tekst: 219 p.): Volume 11(tabellen: 71 p.): Volume 111 (Figuren, Kaarten,doorsneden: 65 p.): Volume IV (Figuren; 39 p.):Volume V (Figuren: 36 p.). Gent, Geologisch Instituut,R.U.G.. - Brussel, Ministerie van Economische zaken,Departement Mijgwezen, 1984.

De Moor, G., 1985 • Shelfbank Morphology oft the Be19ianCoast. Recent methodological and scientlticdeve1opments. In : Recent trends in Physical Geography ­Liber Amicorum L. Peeters. V.U.B., Brusse1, 1985, Studyseries n' 20, 47-90, 24 t1g.

De Moor, G., 1985b • Present day morphodynamics on theKwintebank and their meaning for the evolution of theFlemish Bank. In : Van Grieken, R., & Wollast, R,(Editors), Progress in Belgian oceanographic Research,Belgian Academy of Sciences, Brussel, 1985, 102-113, 5tig.

Oe Moor, G., 1986. Geomortologisch onderzoek op hetBelgisch continentaal plat. BEVAS-SOBEG, 1986(2), 55,133-174, 11 tig.

Oe Moor, G., 1987a • Numerical data about present daysediment dynamics on the Flemish Banks (Southern Bight,North seal. In : Paepe, R., (editor), Applied QuaternaryGeology - I.F.A.C., GEOBOUND, Brussels, 1987, 8 tig. (inpress).

Oe Moor, G., 1987b • Akoestische teledetectie enelectronische radio-navigatie als hulpmiddelen bijmorfo1og1sch zeebodem-onderzoek. In : Resultaten vannieuwe technologien in de Geografie. V.L.A., Gent, 1987,107-125.

Oe Moor, G, 1988. Present day evolution trends ofsandbanks 1n the Southern Bight (North Sea).- BEVAS­SOBEG, 1988, 57(1), 49-54, 3 f1g.

Oe Moor, G., 1989. Maintenance on the Flemish Banks.In : Henriet, J.-P. and Oe Moor, G. (editors), Tertiaryand Quaternary Geology ot Southern Bight.Rijksuniversiteit, Renard Center Marine Geology, Gent,36 p., 17 fig. (in press).

Oe Moor, G., & Lankneus, J., 1988. Acoustic teledetectionof Sea-bottom Structures in the Southern Bight.- Bull.Soc. beIge Geol., Paleont., Hydrol., 1988,.97, .199-210,12 fig.

Lankneus, J., De Moor, G., De Schaepmeester, G., Libeer,L., 1989. Acoustic teledetection of shelf bedforms andtheir meaning for the sediment dynamies. In: Stud1edagNoordzee, Journee d'etudes Mer du Nord, Gent,14/2/1989(in press: this volume)

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f the Kwintebank •Fig. 1. Location 0

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/ ....

\rJl\\\\

\\\

Dunkcrqui

o 5 lOk",a..--

~Limit$of the Belglan~Continenlal Platform

WArea 01 the Fltmish Banks

11

....N

Fig. 2. Nett bathymetric profile across the northern partof the Kwintebank

~3Q0 SE.•~EGENVAAM

25001500 eIl,tane. (mI 2

KIJ'NTEBANK

500

NIJ

2ojt-----+7'-----------~~~::;~~:::

!'[ K\rI1NTEGEUL.;IOt----------fJ....--;r--------------------

5W(ml~+_- ....-._.;,~-.....--+-....;----..,--~-+-~--.t-- .....--+-~--~I -~--t_-""!--_+.-S,. I •

SO 2320 2318 2316 2314 2312

BIIITB BUlt .eterenee linel rGZZ.OO

Registration: 20/02/89 with: Atlas Oeso XX

Scale: distance: 1/10.000

•Oepth: 1/250

•Fig. 3. Nett bathymetric profile across the central part ofthe Kwintbank

590 lQOO 1590distancelml2000 2500 3000 3500

N.... g~31.Q I gG,31.5 SEE I

KI.fINTEBANK I NEGENVAA~KWINTEGEUL.c

Ii ~10

I ~ '" I

/ ~.

20

I/",

SW I(m)I I , . ·50~

I ·I , I6'1'

I ·608 610 612 616 618

RIIITB BAIIlt Ret.renee line, rOl'.OO

Registration: 21/02/89 with: Atlas Oeso XX

Scale: distance: 1/10.000 oepth: 1/250

Fig. 4. Nett bathymetric profile across the southern partof the Kwintebank

SE

NEGENVAAM

3500 '000

K'JINTEBANK

1500gG,33.o:I

10005 0

N....].: K....INTEGEUl~'Cl

101+-------------------=';;<7',c:;;..--------~~--------

.ererSDOS liDS' rG1I.OO

Registration: 21/02/89 with: Atlas 08so XX

Seale: diatanee: 1/10.000

•Depth: 1/250

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Fig. 5. Visual cornparison of succesive nett bathyrnetricprofiles by superposition.

500 1000 1500 distoncelml2000 2500 3000

~NW 9FltS,S SE

I&. I

ö- I.."0

K'w'INTEGEUL K'w'INTEBANK NEGENVAAM

.,~...................201--------:ff.:,~'---------..::l~.lc_-,..------

~""':".-';""""OO.-r. '".~ w ,........., , .....----..--..------....--

DIBTS BAIIJt .ererenee 1ine: rB01.00

Reqistration: 30/11/87 with: Atlas Deso XX

Registration: 22/02/88 with: Atlas Deso xx

"..,.,.v'vJ I............. ) ...

VI

Fig. 6. Unit-volumetric time series with regression lines.Kwintebank total unit-volume along reference line rHOl. .....

'"

Corre1ation: -0.70341 -0.71027 -0.71842

117

'lope

1

49.48 ,

-0.03646

+

+

2

50.45 ,

3

51. 61 ,

Polynomial first degree :

Polynemial second degree: - - - ­

po1ynomial third degree : ••••••••••

- +

1: - +tot

E:J •Ö>

0 •

1:345 6

1983 19847

1985\~ 17

1987 198823

.ereranoe 1ine. rH01.00

Bank velume abeve: -12.5 m

•

1. 30/11/822. 07/05/833. 16/05/834. 10/06/835. 11/07/836. 07/09/83

7. 21/08/848. 28/05/859. 11/09/85

10. 11/09/8511. 11/09/8512. 13/09/85

13. 28/11/8514. 11/02/8615. 11/11/8616. 12/11/8617. 24/02/8718. 23/11/87

19. 30/11/8720. 22/02/8821. 21/03/8822. 01/06/8823. 08/11/88

- -------------------------------------------..,

Fi~. Unit-volumetric time series with regreSSion~es.Kwintebank total unit-volume along reference line rHOO.

1 2 3

Correlation: -0.55037 -0.57293 -0.62681 Po1ynomia1 first degree :

112 30.29 , 32.83 , 39.29 , Polynomial second degree: ----S10pe -0.04411 Polynomia1 third degree : .... "" """"

275 +

+

+

++

++

+~-_ ~ .- - ~........ ......... - - .." -- --.~.- . ...... -:- -- ....

+ • - -- -••.•••• +.

"""""""." "" ... """" .-:-:. =""-"" ...-47

+ ++

1983 1984

7

1985

8

datt

9111012 13 14

1986 1987

171

1988021

billte Bank .ererenoe line. rHOO.OO 1. 30/11/82 7. 21/08/84 13. 28/11/85 19. 22/02/87Z. 16/05/83 8. 28/05/85 14. 11/02/86 20. 21/03/88

Bank volum. above: -12.5 BI 3. 10/06/83 9. 11/09/85 15. 11/11/86 21. 01/06/884. 13/06/83 10. 11/09/85 16. 12/11/865. 11/07/83 11. 11/09/85 17. 23/11/876. 07/09/83 12. 13/09/85 18. 30/11/87

...~

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BATREG • ~aw bathymetric registrationDIGPRO • Digitalisation programme for BATREGDIGFlLE • Datafile of digltized BATREG~ORPRO • Complex correction programme for BATREGBATFILE • datafile for corredted dlgfileVOLDMPRO • programme for calculation of unit-voluaeeHUV • measured unit volume.VOLPLOT • programme for regres.ion analysi.HUVTIMSER • time .eries for measured unit-volumes

H • mean daily change of absolut. trendunit volume

B • initial trend-unlt-volumeA • mean annual change of absolut. trend-

unlt-volumeR ••ean annual change relative trend-

unlt-volumePOSDAT • positloning at 0,01- every 30 sec.ODAS • MUMM programme for data-acquisition end

storagePOSLIST • li.ting of position-fixe.COVELIST • li.ting of ground cour._ and qround v_locity

co_pan.nt.COF-FILE • HP 1000 Dataflle of position-, course,-

velocity- and .steorologieal dataCOFDAT ODAS to HP600 transformation programmeFIXFILE HP600 datafil_ of COTTlLEXAART • Track plotting programm_TRACKPLOT • map with referene_ lines and sailed treck••

Fig. 8. Generalised flow ehart.

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-57

+119

-22

-207

+2

KWINTEBANK02

1100

G23•

Fiq. 9. Kwintebank; period 1983-88; A (m3 .m-1 .y-1);

absolute mean annual change of the total bank unit-volume

20

•

-0.2

KWINTEBANK

Hoo

+0.0 •-1.8

G21 +1.3

-0.7

GIS

GIB

GIß

GI7

oE ;; d

Fig. 10. Kwintebank; period 1983-88R; R (%.y-1); relativemean annual change cf the total bank unit-volume

~----------- - - - - - -

.21

•

1100

G21

GI8

GI7

GI6

GIS

oi

KWINTEBANK

+3

+4.5

-19

HT

2 m

Fig. 11. Kwintebank; period 1983-88; A (m3 .m-1 .y-l);absolute mean annual change of the unit-volume of the bankbase slice

22

•

-0.8

-0.4

+0.2

+0.2

-0.4

KWINTEBANK

GIS

GI6

GI7

oi

Fig. 12. Kwintebank; period 1983-88; R (%.y-1); relativemean annual change of the unit-volume cf the bank baseslice

G21

G20

GI9

GI8

·G17• GI6

GIS

0

i

•1100

G23

KWINTEBANK

-16

-14

+27

-21

+16

HT5m

_ ....._"-.J.5 m

B

Fig. 13. Kwintehank: period 1983-88: A (rn3 .rn-1 .y-l):ahsolute rnean annual change of the unit-volurne of the banktop slice

24

GI7

GIB

GIG

oi ~

KWINTEBANK

-8.7

-4.4

+6.2

H

•

•Fig. 14. Kwintebank; period 1983-88; R (%.y-1), relativemean annual change of the unit-volume of the bank top slice

Fi9.15.regressionevolution.line rH01

Unit-volumetric time series with qu.tiCline showing an inversion of the sedimentdynamic

Kwintebank total unit-volume along reference

--.... ..

• •.•• ::-•••••••-::-••-::.,,4:..-.,.;.••••••••--..

Polynomial first degree : ------­

Polynomial second degree: -- - -­

Polynomial third degree : •••••••••••

....

......

3

34.98 ,

0.59164

..••• •••• •• -,;:- :.:•••.:,1. _ ...... r'r'•••••••• 11 '

........:;. -- ... -- .+

..

.. •••••• + +••• ..- ;:s

~.......--:.. .-.'....

1 2

Corre1aUon: 0.44115 0.56528

a 2 19.46 , 31.95 ,

• 1op. 0.06935

1315

..

1 23 4 5 6 717 ,lJ 21'8 11

1983 1984 1985date 1988

biDte BaDk aeterenoe linel rB01.00 1. 30/11/82 7. 28/05/85 13. 11/02/86 19. 22/02/882. 07/05/83 8. 11/09/85 14. 11/11/86 20. 21/03/88

Bank volume above: -20.0 m 3. 16/05/83 9. 11/09/85 15. 12/11/86 21. 01/06/884. 11/07/83 10. 11/09/85 16. 24/02/87 22. 08/11/88 '"VI5. 07/09/83 11. 13/09/85 17. 23/11/876. 21/08/84 12. 28/11/85 18. 30/11/87