indus delta csr 45591

7/21/2019 Indus Delta CSR 45591

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Department of Geography, University of Bucharest, N. Balcescu No.1, Bucharest, RomaniaDepartment of Geology and Petroleum Geology, University of Aerdeen, Aerdeen AB!" #U$, U%

National &nstitute of 'ceanography, ()*"+ Bloc 1, -lifton, %arachi +/00, Paistan

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-ontinental (helf Research !/ 2!00/3 1//451/4"666.elsevier.com7locate7csr

Recent morphodynamics of the &ndus delta shore and shelf

iviu Giosana,8, (tefan -onstantinescu, Peter D. -liftc, Ali R. )are9d,

:uhammed Danishd, Asif &namdaDepartment of Geology and Geophysics, ;oods


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at an even greater rate than efore. )his dierential ehavior of the delta shoreline suggests a signiLcant role for delta frontsediment transfer processes in the evolution of aandoned deltaic coast.r !00/ $lsevier td. All rights reserved.

%ey6ordsH River discharge? -oastal erosion? (uaueous delta? -linoform? Paistan? Araian (ea

1. &ntroduction

-onstruction of dams for Cood control, 6aterconsumption, and po6er generation has resulted insigniLcant reductions of 6ater and sediment dis*charged to coastal regions y rivers 2Morosmartyet al., 1==+?;alling and Fang, !00#3. 'ver "0 ofthe river 6ater discharge and close to #0 of thesediment discharge on a gloal scale are interceptedy large man*made impoundments 2Morosmarty

et al., 1==+?(yvitsi et al., !003. -hanges in Cuvialfresh6ater discharge can drastically impact coastalecosystems, 6hile reduction in river*supplied sedi*ment can lead to coastal retreat. Deltaic coasts,6here the sediment udget is dominated y riversupply, e@hiit lo6 relief that renders them espe*cially vulnerale to retreat. &n many cases, themorphological eects of recent, often dramatic,human*induced reductions in sediment discharge ofdelta*uilding rivers remain to e uantiLed. Aprominent e@ample is the &ndus River, 6hich is one

the largest rivers that is intensively impounded2:illiman et al., 1=4"3. Furthermore, the &ndusdelta has a high 6ave energy coast that issusceptile to erosion 2;ells and -oleman, 1=4"3and rapid sea encroachment due to sea level rise2


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Fig. 1. ocation map of the lo6er &ndus asin and &ndus delta sho6ing the general physiography, former river courses 2after


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average3 6ith variale uantities of sand andclay 2%a9mi, 1=4"?%han et al., 1==#3. :icasare typical of &ndus sediment and could add upto /0 of the sand fraction in shelf sediments 2Nairet al., 1=4!3.

Aandoned older courses of the &ndus River2Fig. 13 6ere identiLed y


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from south6esterly during the summer monsoonto northeasterly during the 6inter monsoon 2Ri9viet al., 1=443. Further southeast on the coast of&ndia,Nair et al. 21=4!3proposed that strong cross*shore tidal currents up to 1./ m7s oshore the Gulfof %utch 2or %achchh?Fig. 13 act as a dynamicarrier preventing dispersal of &ndus sediments pastthe mouth of the Gulf to southeast 2see also-hauhan et al., !0003.

!.". &ndus delta

During the


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During the recent historical period, a maKoravulsion of the &ndus from east to 6est of


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Fig. ". Digiti9ed athymetric surveys and shorelines used for generating the D): for the Paistani &ndus coast in the 1=th -entury. )hesurveys include the 14"450 Grieve survey 2British Admiralty, 1=13 and the 14=5=/ 'ldham survey 2British Admiralty, 14=+a, 3. )he

o@ indicates the region of overlap et6een the 'ldham survey and the 1=!5" Paistani survey 2


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)he term clinoform 2see e.g.,;alsh et al., !00"3 has een

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Fig. . Digiti9ed athymetric surveys and shorelines for the Paistani &ndus coastH A. the 14=5=/ 'ldham survey 2British Admiralty,14=+a, 3? B. the 1=!5" Paistani survey 2


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22o Saurashtra

23o-20

-60

V

24o -100

m 20 60 100 140 km

70o -20

-60

-100

IV

Kori Shoal m 20 60 100 140 km

69oSir Shoal

Great Kori

Bank

-20

-60

III

68oOchito

Lobe

-100

m 20 60 100 140 km

10 -20

-60

-100

II

67o

-20 I20 60 100 140 km

-60

-100

m 20 60 100 140 km

Fig. /. Digital terrain model for the &ndus shelf ased on 1=th century surveys 2British Admiralty, 14=+a, ?British Admiralty, 1=13.)ypical athymetric proLles across the &ndus delta and (aurashtra coast 2i.e., &north6estern shelf clinoform? &&&ndus -anyon? &&&

southeastern shelf clinoform? &M%utch clinoform? M(aurahstra shelf3 are also presented 2in lac is the proLle at the locationindicated y the arro6? in gray are the other proLles for comparison3. &nland geography is visuali9ed on a AND(A) image from !000.

and E405=0 m 6ater depth, respectively, and it ischaracteri9ed y relatively large and constantgradients et6een 0.#1 and 0."1. )he mid*shelf

clinoform is continuous along the delta coast, ut ismuch more advanced to6ard the shelf edge on theeast side of the &ndus canyon 2E/0 m closer tothe shelf edge at the level of the Q"0 m isoath3 vs.the 6est side of the canyon 2Fig. /3. A some6hatdistinct loe of the mid*shelf clinoform is apparentin front of the %utch mainland and the entrance tothe Gulf of %utch, ut it is less steep and e@tendsonly et6een E#0 and +0 m 6ater depth 2Fig. /3.Along the (aurashtra coast, on the other side of theGulf of %utchs entrance, the shelf displayed aconcave up proLle 6ith a steep nearshore 6ith nomid*shelf clinoform present 2Fig. /3.

".!. :orphological changes on the &ndus shelfet6een the 14=5 =/ and 1=!5 " surveys

At the time of the 1=th century survey, the active&ndus river mouths included the )urshian, the%hoar, the Gaghiar, and the %har. For descriptivepurposes, 6e deLne a central 2active river mouth3sector of the coast 2named A inFig. +3, anorth6estern sector 2sector B inFig. +3, and a

southeastern sector for the aandoned delta plain

coast on either side of the active mouths 2sector - inFig. +3. Bathymetric changes et6een the late 1=thcentury and 1=0s sho6 that the delta front

prograded along most of the delta coast 2Fig. +3.)he main depocenter of the delta front developed infront of the active river mouths 2sector A?Fig. +3?the seaed there shoaled / m on average, 6ith ama@imum accumulation of over # m in the head ofthe &ndus -anyon. Using a sediment ul densityvalue of 100 g7m#, 6e estimate that over 1=0million tons of sediment had accumulated per yearon the delta front in sector A et6een 14=5=/ and1=!5" 2Fig. +3.

'shore the aandoned delta plain coast, E!"million tons of sediment per year accumulated onthe delta front in the north6estern sector B that 6asalanced y the same amount of sediment eroded.

)his corresponds to rates of / cm7year averageaccumulation and erosion, respectively. Aout #0million tons of sediment accumulated in the south*eastern sector - to the (ir -ree alone 2Fig. +3,corresponding to an average accumulation rate of cm7year. &n contrast to the arealy continuous deltafront deposition east of the active mouths, sedimentaccumulation in the north6est sector appears tohave een more locali9ed, 6ith a large erosional

area et6een the )urshian and


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Fig. +. Bathymetric changes et6een the 14=5=+ and 1=!5" surveys of the &ndus shelf for the region of common coverage sho6n overthe simpliLed 14=5=+ athymetry. )he oshore limit of coverage is indicated y the old dashed lac line. Searly values for erosion and

accumulation of sediment and sedimentation rates are discussed in the te@t for several areas noted A through D. (horelines from 14=5=+2thic 6hite dashed line3 and 1=!5" 2thin 6hite continuous line3 are sho6n overlapped on a !000 satellite photo of the &ndus delta.

2Fig. +3. )his erosional area appears to e related tothe early !0th century aandonment of the 'chitodistriutary that discharged through the


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the clinoform is actively prograding at this location.&n total, /# million tons of sediment accumulatedet6een 14=5=/ and 1=!5" in sector D.

".#. (horeline changes

Bet6een 14=5=/ and 1=!5", the delta shorelineadvanced at an average rate of E" m7year. (everalerosion areas occurred on the coast north6est of the

)urshian mouth 2Fig. 4a and c3, ut the sectoret6een Paitiani and -hhan 6as strongly prograda*tional 2E+0 m7year3. )he shoreline advanced muchfaster near the active river mouths et6een the%hoar and the ;ari mouths at an average rate ofE10 m7year 2Fig. 4a and c3. All shoreline advancerates calculated using the 'ldham chart and themodern Paistani chart should e considered as

minimal estimates until a lo6 tide datum for theearlier map is conLrmed 2conversely the erosionrates proaly represent ma@imum values3.

&n contrast to the largely progradational coast inunaltered river sediment discharge conditions thatcharacteri9ed the &ndus et6een 14=5=/ and1=!5", shoreline changes during the post*dam*ming period 21=+45!000?Fig. 4 and c3 sho6 thate@tensive sectors of the &ndus delta coast haveecome erosional after damming. )he shorelineretreat 6as greatest in front of the formerly activeriver mouths et6een %hoar and ;ari -rees,reaching rates of E0 m7year. 'n the north6esterncoast et6een the %hoar -ree mouth and%arachi the retreat rates 6ere signiLcantly lo6erat E10 m7year, 6ith the sector et6een Paitiani-ree and %arachi even prograding at an average

Fig. 4. (horeline change rates for the &ndus delta coast forH A. the pre*damming period et6een 14=5=+ and 1=!5"? B. the post*damming conditions 21=+45!0003? and -. a comparison et6een shoreline change rates of the t6o intervals. ocations of largest tidal cree

mouths are indicated.


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rate of E10 m7year. )he aandoned deltaic coasteast of the ;ari mouth to (ir -ree continued toprograde during the post*damming period 2Fig. 4and c3 at E+0 m per year 6as on average, a rategreater than the E" m per year advance rateet6een 14=5=/ and 1=!5" for the same sector.

Neither the 'ldham, nor the Paistani chartse@tend far enough inland to allo6 us to analy9elong*term changes in the morphology of the tidalchannel net6or. -omparing the 1=+4 and !000satellite images, 6e have not een ale to detect anysystematic 6idening or narro6ing of the tidalchannels.

. Discussion

.1. Delta front vs. prodelta clinoforms

)he morphological components of a river deltahave een traditionally considered to include theCat, mostly suaerial, delta platform continuing6ith the completely sumerged, relatively steepdelta slope that e@tends further oshore into thelo6*gradient prodelta 2Reading and -ollinson,1==/3. Process*ased terminology euates the deltaplatform 6ith the delta plain that is dominated yCuvial processes and the delta slope 6ith the deltafront, the 9one of continuous interaction et6een

marine and Cuvial processes. 'n the lo6*gradientprodelta, sedimentation from suspension has eenassumed to e dominant 2Reading and -ollinson,1==/3. )he dip proLle of a delta has a clinoformshape 6ith a 6edge*lie regressive stratigraphy2(cruton, 1=/0?Reading and -ollinson, 1==/3. &nthis classic frame6or, the suaueous delta haseen considered to consist of the delta front and theprodelta.

Recent studies on supply*dominated shelves nearaundant sources of Cuvial sediment 2(6ift and

)horne, 1==13 sho6 that strictly suaueous clino*forms 2also called sometimes suaueous deltas3can develop on high*energy deltaic shelves largely6ithin the prodelta region e@hiiting a sigmoidalregressive pattern 2Nittrouer et al., 1==/?%uehlet al., 1==+, !003. )o avoid confusion introducedy using parallel terminologies, 6e propose theterms delta front clinoform and prodelta clinoform todistinguish et6een the t6o types of regressive unitsthat characteri9e suaueous deltas. &n oth cases,the clinoform foresets have the highest accumula*tion rate, 6hereas the topset and ottomset,

6here intense physical processes occur and7or

sediment supply is lo6 are characteri9ed y lo6eraccumulation rates 2;alsh et al., !00"and refer*ences therein3.

Development of a prodelta clinoform can econcurrent 6ith the progradation of the delta frontclinoform, leading to compound clinoformmorphologies 2e.g.,Nittrouer et al., 1==/3, as inthe case of the Ganges5Brahmaputra 2Allison, 1==4?%uehl et al., !003. &n other cases, lie the Ama9on,the development of the delta front clinoform coulde drastically diminished or spatially oset along*shore 2Nittrouer et al., 1==/3. -onversely, deltasdeveloping on lo6*energy shelves 6ould not devel*op a prodelta clinoform 2e.g., the :ississippi;right and Nittrouer, 1==3. )he tridimensionalarchitecture of the clinoforms is also a function ofthe shelf energy regime 2Driscoll and %arner, 1===3.

For e@ample,-attaneo et al. 2!00#3sho6ed thateven if the Po River uilds a typical delta frontclinoform 2e.g.,-orreggiari et al., !003, it alsocontriutes sediment to a mid*shelf prodelta clino*form that is far oset alongshore from the rivermouths due to an advection*dominated regimealong the Adriatic coast.

.!. )he delta front clinoform of the &ndus

)he &ndus shelf e@hiits a clear compoundclinoform morphology 2Fig. /3. &n the nearshore,on the delta front clinoform, sediment accumulation6as highest close to the active river mouths at anaverage rate of 10 cm7year 2Fig. +area A3, 6hichis comparale to accumulation rates estimated forother river*mouth pro@imal depocenters of theRhone 2(aatier, !0013, the Red River 2van :arenand


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-anniali9ation of the suaerial delta through thedevelopment of a tidal channel net6or could haveprovided some sediment for accumulation on thedelta front clinoform as suggested y the develop*ment of e shoals at the mouth of the largest tidalcrees 2Fig. /3. (ediment dispersal on tide*domi*nated deltaic coasts has a strong on5oshorecomponent, leading to e@tensive development ofelongate tidal shoals 2', 1=/#?;illis, !003.Although e shoals are present at the mouth ofthe largest &ndus tidal crees, they are limited ine@tent. &n contrast, similar shoals along the coast ofthe Ganges5Brahmaputra delta e@tend 40 m o*shore, imparting a digitate aspect to that delta front2Allison, 1==43.

At the shoreline, the e@tensive retreat after late1=0s contrasts 6ith the almost general advance

typical for the delta shore during the 14=7=/51=!7" period, 6hen the discharge 6as less aected yCuvial engineering 2Fig. 43.


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et6een "0 and 100 m 6ater depth. )he depth ofthis clinoform 6ould increase further, if thedispersal system for the &ndus sediments is taento e@tend along the aandoned coast, as more 6aveenergy is availale to move less sediment. )he


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our analysis does not cover the entire shelf, it isliely that in natural conditions the &ndus Riverdischarged more sediment to the coast than

support came from a ;ohn-reaser from the lirary of the University of-alifornia at Bereley and the personnel from theBritish irary for their indefatigale search forcharts. )horough revie6s provided y Antonio-attaneo and -arl Friedrichs 6ere insightful andhelped shape the Lnal form of the paper. Fundingfor this study 6as provided y the National (cienceFoundation through a6ard '-$*0#!"4#+ to -lift

and Giosan. Part of (. -onstantinescus Lnancial

tative modeling of clinoform development. :arine Geology1" 215"3, #4#5#=4.

Fahlusch,


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ournal 1#" 2#3, #/+5#4!.

ournal of (oil (cience !0213, !#5#+.

ournal of :arine

(ciences ! 213, ##5#=.%han, ).:.A., Ra99a, D.A., -haudhry, T.*U.*O., Tuadir,

D.A., %air, A., (arer, :.A., !00!. (ea level variations and

geomorphological changes in the coastal elt of Paistan.:arine Geodesy ! 215!3, 1=51+".

%uehl, (.A., evy, B.:., :oore, ;.(., Allison, :.A., 1==+.

(uaueous delta of the Ganges5Brahmaputra river system.:arine Geology 1"" 215#3, 415=/.

%uehl, (.A., Allison, :.A., Goodred, (.., %udrass, .P. 2$ds.3, River Deltas-oncepts, :odels, and

$@amples, ($P:5(ociety for (edimentary Geology, vol. 4#.

(pecial Pulication, pp. "115"#!.amric, .P.:., Morosmarty, -.>., %ettner, A.>., Green, P.,!00. &mpact of humans on the Cu@ of terrestrial sediment to

the gloal coastal ocean. (cience #04, #+/5#40.
http://www.megadelta.ecnu.edu.cn/main/upload/Asifpaper1.pdfhttp://www.megadelta.ecnu.edu.cn/main/upload/Asifpaper1.pdfhttp://www.megadelta.ecnu.edu.cn/main/upload/Asifpaper1.pdfhttp://www.megadelta.ecnu.edu.cn/main/upload/Asifpaper1.pdf


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)ro6ridge, >..)., -oleman, >.:., 1=4". Deltaic morphology and

sedimentology, 6ith special reference to the &ndus Riverdelta. &nH .D. 2$ds.3, :arine Geologyand 'ceanography of Araian (ea and -oastal Paistan. Man

Nostrand Reinhold, Ne6 Sor, pp. 45100.;ilhelmy, ., !00. Deposits of tide*inCuenced river deltas. &nH

Giosan, ., Bhattacharya, >.P. 2$ds.3, River Deltas-on*

cepts, :odels, and $@amples, ($P:(ociety for (edimen*tary Geology, (pecial Pulication 4#, pp. 4+51#!.

;P;PDA 2;est Paistan ;ater and Po6er Development

Authority3, 1=//. o6er &ndus ReportH

indus delta csr 45591

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