C hanging o f shoreline during the Late Q u a tem ary in relationship with geodynam ics and th eir affect to the

VNU Journal of Science, Earth Sciences 25 (2009) 40-47

C hanging o f shoreline during the Late Q u a tem ary in relationship with geodynam ics and th eir affect to the

Coastal environm ent o f th e R ed River

C h u V a n N goi*, D o M in h D uc, L u o n g T h i T h u H o ai

College o f Science, VNU

Rcccivcd 5 January 2009; received in reviscd form 16 Jaiiuary 2009

A b stract. In maiiy ycars, changing o f shoreline has causcd a lot o f diíTĩcultics for Uic suslainablc dcvclopmcnt o f socio-cconomics in thc Coastal zone o f tlie Red River dclta. Hcrc, in aílcr the Flandrian ưansgrcssion, accrction proccss o f cxpanding dclta has conlinuously dcvelopcd. The croded sections o f shoreline appcarcd át Ihe bcginning o f the Twenticth ccntury (1905). The most intcnsive scgment is in Hai Hau disưict. The Erosion related mainly to th e lack o f sedim cnt causcd by exogcnous and human activitỉcs. AlTcct o f endogenous proccss to crosion is vcry weak. The Erosion iii Hai Hau has continuously dcvcloped bccausc scdimcnt at tlie Red River mouth is m ainly being ưansportcd to the s w to llie dcpứi o f 5-25m, 62 pcrccnt o f which is transported cross-shorc. Iii ordcr to usc laiid cíTcctivcly in the Coastal zone, at iiitcnsivc crodcd shorclincs gcotechnical mcasurcs liavc to bc applicd such as strong sea dykc and groins. In casc o f arcas typhoon landing at the spriiig tidc, pcopỉc in the vulncrablc areas at thc coast have to movc to safe areas.

Kcywords: Holocenc; Red Rivcr Delta; Shorclinc; Coastal Zone; Hai Hau coast.

1. C h a n g in g o f s h o r e lin e in L a te P leisto cen e T he tra c e o f an cien t s e a activ ities left on la n d (an cien t sea level, sea b en ch es, geological fo rm atio n s) an d sed im en t o n b o tto m surface a llo w reco n stru c tin g an cien t sho relin es. The V in h P hu c íb rm atio n fo rm ed in Late P leisto cen e w as d evelo ped an d d istrib u ted on a la rg e scale o n la n d an d sea floor. O n land, they a re ex p o se d in B ac N in h , B ac G iang , V inh Yen, H a T ay and

N in h B inh p ro v in c e s. O n th e se a íloor, they are exp osed a t the d e p th o f 2 5 -3 0 m [1]. T h e identify c h ara cteristics o f the ío rm atio n is the w eathered clay w ith m o tley co lo u r. The V inh P h uc form ation fo rm e d in relatio n sh ip vvith the V in h P hu c tra n sg re ssio n an d the shoreline had reached in m e n tio n e d p ro v in ce s, som ew here reach ed to D ong T rie u in the N o rth o f b asin that created a n e ro d e d s u ría c e at the h eig h t 10-15m (F ig .l).

* Corrcsponding autíior. Tcl.: 84-4-35630466.

E-mail: ngoicv@vnu.cdu.vn

4 0

c. V. Ngoi et al. / V N U ịủurnnl o f Science, Earth Sciences 25 (2009) 40-47 41

\hATn

LEIA-Í40

L E l-2 0 á

L T 12A -M 4 % Don* Eui'1

LES114M S c r » T t y

U21-H m

Kaởi Men L n o i í ĩ - 5 J

LĐ 14M

Hít u ữiu

,LD M J

L U U C

B t ú B n l MnA L E Z 0 J J 6

LEGEND

S h oreline ỉn P erio u s

^X20-Ỉ04

N a n DbJi

1 1111 I I 111 Late Holocene

L D 2-202

t t -t Early Midclle Holocene Late Pleistocene

» L ư Mouữ, LD02-H • / \

Plĩocene Mitldle Miucene EarlyMiocene Late Olioocene

N um ber c4 b o r t h d t

(LK81-36)

Fig. I Schcma o f shorelines in Red River Delta in Cenozoic.

A fter th is tran sg ressio n , it w a s a regression witlì large scale caused by th c last g lacier in Ọ u atem ary tliat th e sh o relin e m o v ed olTshorc to th e deptlì o f 100- I2 0I11 belovv th e present sea level. A s a resu lt o f th e re g re ssio n , th e Late P leistocene Ib rm ation s vvcrc exposed, w eathered an d intcn sivcly e ro d e d (F ig.2).

T h u s, in the L ate P leistocene ex isted 2 sho reline p osition s: a sh o relin e related to the sea tran sg ressio n an d a sh o relin e in 1 0 0 -I2 0 m depth related to th e se a regression.

42 C.V. N ỵo i ct nl. / V N U Ịournal o f Science, Earth Sciences 25 (2009) 40-47

1 3 Q 'Ẹ >

K ...

' Ế m

Fig. 2 Shorelỉnc in th c Latc Plcistoccnc [6].

2. C h a n g in g o f s h o r e lin e in th c lỉo lo c e n e A fter the se a re g re ssio n , th e sh o relin e c h an g ed w ith in th e s p a c e o f 2 m e n tio n c d ab o v e shorelin es. D uring th e re g re ssio n tim e, the V inh P h uc ío rm a tio n w as in te n siv e ly vveathered in th e hot an d dry clim ate. T h en , a t 17000 y ears Bp the F lan d rian tra n s g re s s io n started . T h e sh o relin e g en tly m o v e d upvvard to th e la n d fro m th e dcp th o f 100 -12 0 m T h e g ra p h o f tran sg ressio n p ro cess w a s sin u o u s (F ig.3 ). T h e sea level o f F lan d rian tra n s g re s s io n re a c h e d to m a x im u m a t 6 0 0 0 y e a rs B p , re a c h e d to H a N oi, B ac N in h an d D o n g T rieu , la ste d a b o u t 1500 y ears, created a se a lev el tra c e o f 4 -6 m h ig h on th e lim eston e sc a rp s a n d th e tc rra c e s o f 4 - 5 m h ig h [5].

S ho reline p o sitio n s b et\v een th e P leisto cen e tran sg ressio n an d th e F la n d ria n tra n sg re ssio n sh o w s th at the F lan d rian tra n s g rc s s io n scale w as sm aller.

A fte r the F lan d rian tran sg ressio n , the sea level c o n tin u o u s ly ílu c tu a te d up an d dow n c o n ip a re d w ith th e p re se n t level. T his process lastcd a b o u t 2 0 0 0 y ears an d \vas reco rd ed by the se a level tra c e a t lìigh o f 3 -3 ,5 m in C at Ba, N in h B in h , H a long b a y (Fig. 4 ,5 ) and the terraces at h ig h o f 2 -2 ,5 m in V inh Bao and T ien L ang [5]. F rom 2 0 0 0 years Bp to the presen t, th e s e a lcvel has b een relativ ely stable (Fig. 3 ).

Y e a r e a g o ( t h o u s a n d s )

Fig.3. Sca levcl changc in Plcistoccne-Hoỉoccne [7].

T h e sea level a fte r the F landrian tra n sg re ssio n slo w ly m o v e d offshore. In N inh B in h p ro v in c e th e s h o re lin e n early overlapp ed w ith th e s h o re lin e o f F lan d rian transgression.

T h is is s u ita b le \vith th e lo cally tectonic su b sid e n c e tren d o f the a re a Ũ1 the H oloccne.

T h is tre n d has c o n tin u c d up to now.

T h iis, v e rtic a l m o v e m e n t a ffected to the m o rp h o lo g y an d p o sitio n o f shoreline. In ad đ itio n , th e ro le o f v ertical m ovem ent also a ffe c te d to se d im e n t p ro c e ss in H olocene. T he g eo lo g ical ío rm a tio n fo m ie d in H olocene had reA ected th e ch an g in g o f sea level and c h a ra c tc ristic s o f v ertical m ovem ents.

c.v.

VNU

Sea level trace

Fig. 4. Sea level trace in Hoa Lu (N inh Binh province).

Fig. 5. Sea level trace in Hoa Lu (N inh Binh province).

T h e vertical m o v em en t w as illu strated by g eo lo g ical p ro cesses suclì as: G la c ie r o c c u re d in a large scale at th e end o f P le isto cen e. T h e Red R iver basin and C ontinental s h e lf h av e e x p erien ced a m a jo r p erio d o f vveathering and ero d in g thai created an e ro d e d s u rfa c e . A fter that at b eg in n in g o f H o lo c e n e th e ero d ed su rface vvas b ro k en by fa u ltin u a n d created hlocks. V ertical m o v e m en t o f th e b lo c k s vvith fealure: su b sid en ce m o v em en t in c re ased from cdge to th e center. T h is is shovvn c le a rlv in th e ch an g in g o f th ick n ess o f H o lo c e n e se d im e n t in the drilled-vvell d ata [ 1 ].

3. C h a n g i n g o f s h o r e li n c f r o m 20 00 y e a r s B p to th e p r e s e n t

F ro m 2 0 0 0 y e a rs B p to th e p resen t, th e sea level has been re la tiv e ly sta b le . T h e fluctu atio n o f sea lev el w a s n o i s im iiíìc a n t c o n ip ared vvith tlic p re se n t lev el. A t p re se n t, s e a level is risin g vvith a s p e e d o f l-2 m m /y e a r. B ased on th e stud y o f se d im e n t p ro c e s s an d h u m a n a ctiv ities. the c h a n g in g o f s h o rc lin e a fte r th e H a n d ria n tra n sg re ssio n up to n o w c an b e d iv id ed in 2 p h ases (F ig .6 ):

- T h e d e p o s itin g p h ase: the sh o re lin e c o n tin u o u s ly m o v e d o ffs h o re (fro m 2 .0 0 0 y e a rs

B p t o 1905).

- T h e e ro d in ti a n d d e p o s itin g p h ase (froni 1905 up to n o w ).

ỉn th e first p h a se , th e Red R iver d e lta w as e x p a n d e d an d th e s h o re lin e m ovcd o ffsh o re vvith a s p e e d o f lO O m /year. In Coastal zone, g e n e ra tio n s o f s e a d y k e s in tu rn vvere io rm ed in 1471, 1838, 1899 ( in N in h B in h , N am D inh, T h a i B in h ). T h e s c a d y k e s sy stem b asically re íle c te d th e p o s itio n s o f sh o re lin e . U ntil 1905 th e s h o re lin e in H ai H au vvas th e lầrth est o n e o ffsh o re and vvas ta k e n a s th e sh o re lin e m a rk e r to stu d y th e c h a n g in g o f s h o re lin e later.

A t th a t tim e , a c c o rd in g to th e c h ara cteristic fo rm , H ai 1 la u s h o re lin e vvas co n v e x (fig .6 ).

Noith

/

Fig. 6. Shoreline positions during period o f 1905- 1995 [2].

Sea lèvel trace

44

c.v.

T h e se c o n d p h a se o f ch an g in g shoreline (fro m 1905 up to now ) is c h a ra c te rừ e d by follo w ing íeatu res:

- S ection fro m D ay m o u th to L ac h G ian g m outh: th e sh o re lin e has b e e n acc u m u la ted and co n tin u o u sly e x ten d ed offshore.

- S ectio n fro m L ach G ian g m o u th to H a Lan m outh: th e sh o re lin e has b een eroded and co n tin u o u sly m o v e d into th e m ainland.

- S ectio n fro m Ba L at m o u th to T h a i Binh m outh: th e sh o relin e is relativ ely stable.

T here is lot o f stu d y d ealin g w ith accreting- ero ding p ro cess o f sh oreline. H ow ever, the an sw er fo r e ro d in g process in H ai H au shoreline so fa r h a s n 't b ccn satisfac to ry [4].

O n th e b a s e o f an aly zin g d ata o f the acc retin g -ero d in g p ro cess an d ch ang in g o f sh o relin e in H ai H au, this p ro cess is explained as follow s:

- U ntil 1905, th c sh o relin e in H ai H au was convex. T his sh o w s th at the accretin g process w as do m in ated. C o m p a red w ith H ai H au section, th e D ay, La ch G ian g an d Ba L at ones exp an d ed o ffsh o re w ith a slow er speed. It shovved th a t th e sed im en t d istrib u tio n b e ío re 1905 vvas d iffere n t fro m present. T he accretin g p ro cess o c c u rre d rap id ly , c a u se d b y con ditio n in w h ich th e re w e re n o t riv er dykes fo r a long period.

- F ro m 1905 up to no\v sh o relin e in H ai H au gradually h a s b ack e d into the m a in la n d and in the o th er h a n d th e sh o relin e in D ay m outh, L ach G ian g m o u th and B a L at m o u th h av e rap id ly ex p a n d e d o íĩs h o re w ith a sp eed o f

lOOnVyear.

T h e ero d in g p ro cess in H ai H au is closely related to the c h a n g e in sed im en t su pp ly and shoreline f o im

T h e s h o re lin e in H ai H au ruiis throu gh 7 com m unes: H ai L oc, H ai D ong, H ai Ly, H ai C hinh, H ai T rieu, H ai H oa, an d H ai Thinh. The

ero ding p ro cess an n u a lly causes m u c h loss in in írastru ctu re a n d changes o f geo log ical en v ừ o n m e n t th a t affects b ad ly th e socio - eco n o m ic d e v e lo p m e n t in this area. T he eroding pro cess has sta rte d sin ce th e b e g in n in g o f 20 century. T his re la te d clo sely to th e d eg rad atio n o f H a L an m o u th w h ich used to b e th e m ajor estuary o f the R ed R iv e r a t th at tim e. T he clear evid en ce o f th e d e g ra d a tio n o f th is estu ary was the sh o relin e in G ia o L o n g a n d G iao P hong com m unes co n tin u o u sly ex p an d ed o ffsh ore vvith sp eed up to 200nV year fro m 1905 to 1930 b u t afte r th at in th is sh o relin e acc retio n ch ang ed into erosion

T he d eg rad a tio n o f H a Lan estu ary an d the dev elo p m en t o f B a L at m o u th c a u se d the defícien cy o f se d im e n t in H ai H au. L eng th o f eroded sectio n co n tin u o u sly in creased, to the

1980s and then sh o rte n e d g rad u ally b e c a u se the sh o relin e w as p ro te c te d b y the sea d y k e s y s te m H ow ever, th e e ro d in g in ten sity clearly in creased in th e p e r io d o f 1985-1995, it w as 1.5 tim es m o re th a n th a t in th e p e rio d o f 1965- 1985. E specially in H ai C h in h -H ai H oa, the ero ding ra te re a c h e d 15-20nV year. T h e erod in g p ro cess u su ally ta k e s p la c e s tro n g ly in m o n soo n and the erosion is m o v in g tovvards H ai T hinh com m une w ith a v e ra g e sp eed o f 4 0 0 m /y ear.

T he H ai H a u co m m u n e is lo c a te d b etw een tw o large estu aries: B a L at m o u th in the N o rth an d L ach G ian g m o u th in th e S outh. A nnually, the sed im en t a m o u n ts tran sp o rte d th ro u g h the estuaries are 29.1 m illio n tons an d 5.82 m illio n tons (fo r th e p e r io d o f 1956-1998), respectively.

H ow ever, a c c o rd in g to G ao an d C ollins m cthods [3] to d cfin e the net o f sed im cn t transport, th e se d im e n t ta k e n fro m the estuaries does n o t su p p ly fo r the H ai H au coast [2].

F igu re 7 show s th a t th e sed im en t am o u n t o f the R ed R iver has n o t acc u m u la ted n e a r sho re but tran sp o rte d o ffsh o re to the depth o f 2 5 m A rea o f the scd im en t tran sp o rte d offsho re to 5-25 m

C.V. Ngoi et a i / VNU Ịoum al o f Science, Earth Sciences 25 (2009) 40-47 45

depth are G iao L ong and H ai Loc. A lo n g the H ai L oc-H ai T h in h Coastal zo ne, sed im en t is m ainly tran sp o rte d alo n g sh o re tovvards the southw est. A long the ero d ed G iao P ho ng -G iao Long C o a sta l zone, the sed im en t is transported along shore to w ard the n ortheast. T his is caused by w aves d irec ted fro m the n o rth ea st w hich sto pp ed b y san d b ars in the estu aries causing less im pact to the shore. S ed im en t taken from Lach G iang m outh is m ain ly tra n sp o rte d to the southvvest.

Q u antitatively, b a la n c e o f sed im en t su pp ly in H ai H au sh o relin e w as calcu lated b y sedim ent v o lu m e tran sp o rte d alo n g co ast and offshore. T h e sed im en t volum e tran sp o rted along coast w as calcu la ted b y C E R C tb n n u la based on m o n ito rin g w av e d ata fro m 1976 to 1994. T h e cro ss-sh o re sed im en t tran sp o rt was d eĩin ed b y K ạịim a fo rrau la (198 2) w ith experim ental co efficien t calib rated acco rd in g to real con dition in H ai H au. T he calcu latio n

results p o in te d o u t th at sed im en t vo lu m e tran sp o rted alcmg the co ast to the southvvest by no rth east an d n o rth w aves in the n o rth east m o n so on w in d w as 6 5 4 ,0 7 8 m 3/y c ar. In the sum m er, th e so u th east an d South w ind dom inated, the sed im en t w as tran sp o rte d to thc n o rth ea st (6 2 ,8 8 4 m 3/year). B ut in g en eral the m ain trend o f sed im en t alo n g the c o a st was tcnvards th e so u th w est. T he sed im en t v o lu m e o f cross-sh ore tran sp o rt into the deep w ater w as l,2 8 6 ,3 2 2 m 3/y e ar. Som e p e o p le co n sid er that the ero sio n o f th e H ai H au sh o relin e vvas related to active te c to n ic su b sid en ce. In fact the tectonic m o v em en t tren d in Q u a te m a ry and H olocene has m a in tain ed a n d co n tin u ed upto th e present. T h o u g h the sh o relin e h ad co n tinu ou sly m o v e d offsh o re fro m the F landrian tran sg ressio n u p to 100 y ears BP (accretion d o m in atcd ) an d then ch an g ed in erosion. T h at's w hy accretio n a n d ero sio n w ere n o t related to tccto n ic activities

Fig. 7. Schema o f sediment ữansportation in Hai Hau C o astal zone [2].

4 6

c.v.

S u m m arizing the in teractio n o f cndogenous factors, h yd rosphere and the Coastal zo n e shovvs th a t the erosion in H ai H au sh oreline w as cau sed by the declinc o f H a L a n m outh. Then, th e croding p ro cess \vas continuously d ev elop ed b ecau se the area w as not supplied enough sedim ent fro m the estuaries. In addition, the sed im en t tran sp o rte d offsh ore b y sea w aves o f 1.940.400m V year (38% along sh ore and 6 2 % offshore). At present, the sho re fro m H ai Loc to H ai D ong is ch ang ed into accretio n, in o th er sectio n s th e ero sio n speed m ay con tinuously increase. T he stro n g dyke a lo n g H ai D ong-H ai H oa has increased the sea w av e energy destroy in g the sh o re lin c a t the southvvest that created an ero d in g sho reline m o v in g to H ai Thinh.

The H oa Binh h y d ro electric d am has red u ced 56% o f sed im en t in the lo w erp art o f rivers. In the íu tu re vvhen T u y en Q uang, Son La an d other hyd roelectric d am s w ill b e pu t into con struction an d op eratin g, the a m o u n t o f scdim cnt sup plying for Coastal areas w ill be con tinuously decreased. W ith in ílu e n c e o f H oa B inh hydroelectric dam , the acc u m u la tin g sp eed in Ba L at m o u th has red u ce d fro m 84 m /year (1965-1985) to ÓOnVyear (19 8 5 -1 9 9 5 ). So, the v o lu m e o f sed im en t tran sp o rte d to n ear area o f riv e r m ouths also redu ced . T h is is th e m a in íactors affecting to the erosion process in H ai Hau.

E rosion has m ade im pact to the Coastal environm ent, altered th e en v ừ o n m en t and a íĩe c te d to hum an lives.

First, erosion cau sed loss in land-an essen tial reso u rce to h u m an b ein g s. T he erosion process from 1905 up to novv h a s lost a very large area. O nly fro m 1965 to 2001 in H ai H au district 2.1 km 2o f land \vas lost, cultivated lan d chan ged into tidal flat (Fig. 8,9). By loss in land, the n um ber o f resid ents liv in g n c a r shore ío rc e d to m ov e in to land, m ade pop u latio n

density in creased so th at increasing th e life d iíĩĩcu lty .

Fig 8. Church and villagc was desưoycd by crosion.

Fig 9. Tidal ílat was forraed by crosion

E ro sio n h a s d e stro y e d sea dyke sy stem an d red u ced the ab ility to p rev en t storm s and flo o d tidcs. In addition, e ro sio n has m ade sh o relin e back ed to m ain lan d th a t caused salinization, reduced q u ality o f g ro u n d v a te r. Erosion has d estro y ed landscape, se a beaches and affected to to u rism acrivities (F ig. 8,9 )

E ro d in g changed th e geo.ogical environm ent on sho re, d estro y ed cco system o f niang rov e forest, d estro y ed h a b ita ts o f many species.

c V. N goi et ai. / VNU lournal o f Science, Larth Sciences 25 (2009) 40-47

47

4. C o n c lu sio n s R efere n ces

A fter the F lan d rian transgression, accu m u late-ex p an d in g d elta h ad con tinuously d evelo ped to 1905.

The crosion p ro cess alo n g Coastal zo n e o f the Red R ivcr delta fro m 1905 up to now has been caused by th e in tcractio n o f river-sca m otivatio ns, ch an g in g in form o f sh o relỉn e and hum an activities.

For erosion p ro cess, the endogcnous dynam ics ex p ressed vveakly

E rod ed sh o relin c caiiscd great losses o f property an d cn vironm cnt.

A c k n o \v le d g e m e n ts

T he article vvas co m p lcte d on carry in g out project Q G T D 0 7-06, V N U H a Noi.

[1] c .v . Ngoi et al, Geodynamic Characteristics of Red Rivcr delta in Holocene, Journaì o f Geology Serics A, 2000. (Vielnamcse)

[2] D.M. Duc, p.v . Ty, N.H. Phuong, T.D.Thinh, Tlie ỉlai Hau Coastal crosion analysis based on

sta n d |X )in t o f r a tio n a l e x p lo ita tio n a n d u s e o f

gcoiogical environment. Journal o f Engineering Geology and the Environment, 2004.

(Vietnamese)

[3] S.Gao, M. Collins, Net Sediment Transporl Pattcms Inferred from Grain-size Trends, Based upon Dcfmition o f “Transporl Vectors”, Sedimentary Geolog}' 80 (1992) 47-60.

[4] N.T. Thon, Neo-tectonic and active tectonic movcmcnts o f Coastal zone from Mong Cai to Cua ỉ ioi niouth, Journal o f Geology series A, No. 223 (1994). (Vielnamese)

[5] LT. Viet, About the Coastal line change and climaíe o f Hanoi basin in Cenozic, Proceeding o f International Syniposium: Miligalion and Ađaptation o f climate change- Induccd National Disasters, Hue City, Vietnam, 2007.

[6] Westpac Paleo-geographic map o f the last glacial maximum 1:20.000.000, Shanghai, 1995.

[7] William c . Putnam, Geology. Oxford University Press Ix)ndon, Toronto, 1971.