Dao Truong Sa nam don Ie, chu yeu cau tao tir cuoi ket, san k~t manh san ho... Nhieu dau hieu cho thay mire mnrc bi~n hien nay khu vue d~lO dang dang cao dan.. Trir khu goc Tay Nam, gan
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HQI NGHl KHOA HQC TOAN ouoc VE BIEN
L A N T H l1 III
( H a N Q i J 28 - 3 0 ZYXWVUTSRQPONMLKJIHGFEDCBA t l u i n g 11 n a m 1 9 9 1 )
T ~ P II
K H I T U Q 'N G T H U V V A N , D Q N G L l)'C ,
D !A L V - D !A C H A T , D !A V ~ T L V , K Y T H lY ~ T
C O N G T R IN H , K IN H T E - X A H Q I B IE N
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r -s « D u e T h { } l 1 h , N g 1 l y e n H L ( u c a D i n h V { 'i n H u y
Tran Due Thanh, Nguyen Huu Cu, Dinh Van Huy
t.e X u d n H o n g
PROCESS ALONG TI IE SEA COAST OF RI,::D-RIVER DELTA
282 230
c e D u y B a e h
L e D u y B a c n
244
t.e T r ( m g C a n , T r o " , H t i u T h a n , P h a m X u / I n t n o
L e T r a n g C a n , T r a n H u u T h a n , P h a m X u a n T h o
T r i n h T h e n u «
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DONG Ll)'C BOI Tl} XOI La so VA str THAY DOl HINH D~NG
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I T r u n g t a m n g h i e n c t i u b i e n H d i P h o n g
I MODAU
dfm 1989, chiing toi da tien hanh khao sat chi tiet dia chat - dia mao dao va quan
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Dao Truong Sa nam don Ie, chu yeu cau tao tir cuoi ket, san k~t manh san ho.
Dien tich dao 9,4 ha, cao 2,4- 3 m Dai bai bi~n vien quanh bo dao cau t~'? bang cuoi
cat rong 5 10 m den 50 80 m, day trung binh 3,5 m Chan bai throng cao 0,5
-0,8 m/O HD Them san ho quanh dao rong khoang 30 ha, cao trung binh 0,3 - 0,5
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tiep 4v a 10 toc d¢ gio yeu, trung binh durri 5 m/s ve rnua gio NE, song N&co din suat 90 %. Song cao cue dai toi 4,5 m, cao 2 - 2,5 m co tan suat 20 - 25 % ve rnua gio NSW, song huang Tay Nam co tan suat 68 %, song cao nhat 3 m, song cao 2 -2,5m co tan suat 6 - 8 % /2/ Thuj trieu co bien d¢ ClJC dai 2,1 m, ki€u nhat trieu khong deu Thai gian trieu len dai hon hltn ( 15 h, 30') thai gian trieu rut ( 9h,20') Trieu manh VaG cac thang song, gio manh ( thang 6,7 v a 12,1),yeu VaG cac thang chuyen tiep co song, gio yeu (thang 3,4 v a 9,10) ve rnua He dong chay huang thong trj W va SW toc d¢ 0,4 - 1 hai Iy/gia ve mua Dong huang chu dao Eva NE toc d¢ 0,3 - 0,8 hcii IY/gia Nhieu dau hieu cho thay mire mnrc bi~n hien nay khu vue d~lO dang dang cao dan
2 D~c di~m d()ng hrc va SIf bien d(1i hlnh thai trdc di~n tfr Dac di~m q(mg luc boi tu, xoi la bo, bai va kern theo la Sl! chay d{Sihinh thai trac dien bo va hinh dang dao duoc thE hien qua 4 xu the sau day:
2.1 -ZYXWVUTSRQPONMLKJIHGFEDCBA X u TSRQPONMLKJIHGFEDCBA I llf r b ie ll d d i t h e o g i a t h u y t r i e u :
Xu the nay biEu hie n r6 trong cac ngay trieu cuong, khi mat bai trtnrc kha dcm gian va nghieng deu Khi tr ieu dang cao aan,a chan bfli hinh thanh mot g a cuOi cao
5 - 30 ern v a di chuyen d a n ve phia dinh bai Khi trieu rut, go cuoi di chuyen xuong phia chan bai va bien mat
2 2 - B o i I L I , x o i f a v a S ~ ( t h a y d 6 'i h t n l i t h t i i t r d c d i e n b o b d i t h e o k y c a ll m a l e
t r i e u :
ThO; gian quan trac bai narn trong giai doan sung gia J6n n hat cua mua Dong
va keo dai trong 4 ky rnnrc cuUng va 3 ky nurrc kern (xem bang 1) Trir khu goc Tay Nam, gan nhu toan bO cac doan bai quanh dat deu boi tu trong ky trieu kern va xoi
la trong thoi ky trieu cuUng (h inh 1) T6ng hop, bai bi xoi la a bir Tay, goc Tay Bac,
bo Bac va xoi Ja rn a n h a goc Dong Bac Nguoc lai, bai boi tu manh {yba Dong (rura phia Narn) va rat rnanh a goc Tay Narn
Sau 42 ngay quan trac, m~t bai sau bi xoi 1& liii 2 m & bo Tay, 3 m a bo Bac va 23,5 m & brr goc Dong Bac Bai sau boi tu mo rong 17,5 m a bo Dong Nam, 58 m a
goc T a y Nam a goc Dong Bac, toc dO xoi \('1trung birth 0,6 m/ngay, cue dai 3,4 rn/ngay a g6c Tay Narn toc dO boi trung blnh 1,3 rn/ngay, CI!C dai 4,2 rn/ngay Den ngay 6/1/19890 bo Tay chi con 1 - 3 m, g6c Dong Bac con 9,5 m mra bai se xoi 10 den vi tri x6i cua mua gio Dong bac tnnrc a bo Tay toc dO xoi cham nhirng bai hep nen vach xoi 10 gan doc dung dfl tien sat gan ria tang cuoi san ket mat dao a bo
Hac, xoi 10 dfl d~t den vi trf cua mira xoi truce
Trang 5Vao ky mnrc trieu cuong, -trac di~n ngang bai thuong don gian, hoi 16m ( do xoi 16edcbaZYXWVUTSRQPONMLKJIHGFEDCBAI1 U the ), vao cac ky trieu kern, trac dien ngang bai rat phirc tap, co hinh thai
mi (do bOi tu uu the) v o i 1 - 3 tharn chi 4 bac bai p h u tren suon cua b a i tnnrc V~t lieu mat b5i ky trieu cuong co d<)hat nho hon (cat, san, cuoi nho) mai tron, chon loc
totZYXWVUTSRQPONMLKJIHGFEDCBA h a n Vao kY,trieu kern, v~t li¢u tao bai rat tho (dam, cuoi, tang nho ),mai tron chon 10c kern voi nhieu manh san h6 vun moi dua tir suon am tieu len (50 - 55% manh dang canh, 15 - 20 % dang la, 25 - 30 % dang khdi )
a mat cat bai xoi la, su boi tu ky mroc kern chi tamthoi Cu6i cung thi v~t lieu lai bi xoi la dua xu6ng chan dao va tao thanh dong boi tich doc bo di chuyen ve goc Tay nam Do hien nrong hOi luu song gay boi tu 6 goc bo Tay narn.bai a day tao thanh cac gCluon cong, IlIQ'nsong ma Krernpf !l/ goi la "Con luoi lie m gia". Su luan doi huang gio thong tri NE h~'c NNE lam cho true huong boi tu goc Tay Nam dao lien tuc di dOng trong khoang goc phuong vi 200°- 220° Vao d'flU rnua gio Dong Bac, gio huang thong trj NNE nen true lech ve phuong 200° Vao cuoi gio mira Dong Bac.huong gio thong trj NNE va true nay di dong ve phuong vi 220°
2.3 -TSRQPONMLKJIHGFEDCBA B o i t u , x o i h I v d s i r t l i a y d 6 'i h i n l i d a n g d d o t h e o m u a g io :
Hinh dang va kich t hinrc dai rong dao luon thay d6i.phl,1 thuoc van mua gio Bo' huong don gio bi xoi la nen doc, hep Beyhuong khuat gio dune boi tu ne n rong thoai M6i mat cat bai deu rnn luot duoc boi va bi xoi mot Ian trong narn do dong boi tich ven dao doi huang hoan hru
Hinh dang va kich thurrc dao ( dai 680m, rong ~ 10m tinh tir chan bai) xac dinh ngay 14/12/1988 duoc tarn coi la gia tr] trung binh
T r o n g m u a g i6 D 6 1 lg s s ; Bai xoi 1&6 bo Tay, bo Bac va xoi k1 manh agoc Dong Bac; boi tu manh a bo Dong va rat manh & goc Tay Nam, vao cudi mua (thang 4/1988) dao dai 700 m, rong 300 m va goc Tay nam boi tu mo rong 80 m
T r a n g m u a g io T d y f la m B5i bi xoi 16a biyDong, bj xoi la rat manh a goc Tay Nam.boi tu abaTay,baBac va manh a goc Dong Bac.Vao cudi mua (thang 9/1988) dao dai 650m, rong 320 m( ngan lai 50 m.rong ra 20 m so voi mira gio Dong bac)
a cau tau Truong SaC gan gilia bo Dong cua dao) ve mira gio Dong Bac.goc Dong Bac cau bi boi lap con goc Tay Nam diu bi xoi la Tlnh trang xay ra nguoc lai van mila gio Tay Nam
Dao Truong Sa hinh tam giac Trang ba goc dao, goc Tay Nam lau dai co xu huong boi tu keo dai ra phia them san ho, con goc Dong Bac va Tay Bac co xu the
268
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Vmax = m/s 10 - 28 12 - 20 12 - 18 10 - 14 10 - 14 10 - 16 10
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-bi xoi la lui ve phia dao Trong ba canhedcbaZYXWVUTSRQPONMLKJIHGFEDCBAb o dao, b o Bac va brr T a y co qua trinh xoi 1& iru the con b o Dong co qua trinh boi tu uu the Dac bietZYXWVUTSRQPONMLKJIHGFEDCBAa b o T a y , tuy boi va xoi co toc d¢ nho nhung xoi la lai U U ' the hon han Tai day, ve cudi mira gio Dong Bac, vach xoi la tien sat vao tang da tram tich cau tao nen dao
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III KET LU~N
Trac dien bo, bai va hlnh dang dao Truong Sa lien t\1Cthay d6i luan phien do cac qua trinh boi tu, xoi 1&co lien quan tm che dO trieu, song va gio Hinh thai bai trurrc thay doi ro theo trieu len, xuong trong cac ngay trieu cuong.vao cac ky trieu cuong, xoi la ( cue dai 3,4 m/ngay) lIU the & cac doan bo va trac dien bai 16m, don gian.Vao cac ky trieu kern.boi tu (Cue da: 4,2 m/ngay) lIU the va trac dien bai IOi, phirc tap ve mua gio Dong Bac, dao dai ra ( 700 x 300m) do boi tu & bo Dong,rat manh & goc Tay Nam; xoi 1&& bo Tay.Bac va xoi 1&manh & goc Dong Bac, ve rnua gio T a y Nam, dao ngan lai (650 x 320 ) do xoi ]('1& bo Dong va x6i 1&manh & goc
Tay Nam; boi tu & bo Tay, Bac va boi tu manh & goc Dong Bac Ve lau dai, bo dao boi mo rong & be Dong, keo dai & goc Tay Nam; bi x6i 1&dfiy lui & g6c Dong Bac,
bo Bac va Tay.
TAl Lltu HUaNG DAN
1 - Krempf.A., 1927 La forme des recifs coralliens et le regime des vents alternants Memoire No 2 de L' I.O.N.,P.] - 29
2 -L u o n g Xuan Thieu, 1988 Dac diEm khi tu o rig hai van dao T ru o n g Sa "Khi tuong thuy van" II - 335 Narn 1988
SUMMARY
DEPOSITION - EROSION DYNAMICS AND CHANGE OF THE
MORPHOLOGY OF SPRATLY CORAL ISLAND
T r a n D u e T h a n h
H a i p h o n g C e n t r e J a r M a r i n e R e s e a r c h
Report presented by the authors survey results on the deposition - erosion dynamics of coast and beach concerning the changes of island morphology Four
changing tendencies of coastal profile and island morphology were definited and estimated
Trang 9- To the tidal hour
- To the tidal period
- To the wave - win season
- To the long time
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