Tap chi Khoa hoc va Cdng nghe Bien; Tap 14, Sd 2; 2014: 122-131 ISSN: 1859-3097 http://www.vjs. ac.vn/index.php/j mst
]Vl6 PHONG BAN CHAT HOAN LUU VEN DAO BACH LONG VI BANG MO HINH TOAN HOC
Pham Hai An*, Trin Anh Tu
Vien Tai nguyen va Mdi trudng Bien-Vien Han lam Khoa hgc va Cdng nghe Viet Nam
*E-mail: [email protected] Ngay nhin bai: 2-1-2014
TOM TAT; Bach Long VT la mot trong nhung huyen ddo xa bd nhdt tren vinh Bdc Bg thuoc he thong nhom ddo tiin lieu ciia to quoc Viet Nam. Bdi vdy nhdm thdng lin chi tiet ve cdc yeu to thuy dgng luc nhu sdng, dong chdy, thuy trieu Id ddc biet cdn thiet doi voi viic tiip can ddo cung nhu viec thiet ke cdc cong trinh bdo ve biin ddo. Do Men trgng ngudn so lieu quan Irdc ve cdc yeu Id thuy dgng luc con chua day du hoac cd rdt it, nen viec ung dung cdc mo hinh todn Id mgt gidi phdp hOu hieu nhdm bo sung nhicng khiem khuyet tren. Qud trinh chi tiet hda khu vuc nghien cicu kit hgp vdi viec sir dung ky thudt ludi long trong bg mo hinh DelflSD se giiip chung ta co dugc buc tranh chung ve mo phong trudng thiiy dgng lire cUng nhu hodn luu viing ven quanh ddo Bach Long VT bdi su dnh huong ciia hai ihdnh phdn Irieu vd gio be mat. Kel qud mo phong ban ddu cho thdy, hodn luu khu vuc xa ba chiu su chi phoi chung cua hodn IUTA vmh Bdc Bg, dong chdy cd hai huong chu dao Id Dong -Dong Bdc vd Tdy-Tdy Nam. Trong khi do, tai khu vuc ven ddo co su xudt hien cdc xody thudn cung nhuxody nghich cue hg .
Tir khoa: Mo hinh, hodn luu, xody thuan, xody nghich
MO DAU
Nam trong he thong nhdm dio tien tieu ciia to quoc, Bach Long VT la mpt huyen dao thudc thanh pho Hai Phdng xa bd nhit tren vjnh Bac Bg, each Hai Phdng 133 km, each dao Hai Nam 130 km. Dil dien tieh phan noi ciia dao chi 2,5 km^ nhung dao Bach Long VT lai cd mdt vi tri chien luge rit quan trgng ve an ninh qudc phdng va kinh te xa hgi, da dugc Chfnh phu va thanh pho diu tu phat trien thanh khu djch vu hau cin nghe ca vimg vinh Bac Bd. Trai qua cic giai doan khac nhau, nhiau dieu tra va nghien cii'u ve die diam hoan luu ven dao eiia Dao Bach Long VT da dugc tien hanh [!], Moi nghian ciiu ung vdi cac muc dfeh rieng trong timg du an nen cac danh gia chua mang nhilu tinh tong hgp. De thiy rd ban quy md ciing nhu ban chat ciia hoan luu ven dao trong viec gdp phan cung cap ca sd khoa hgc cho viee xiy dung, quy hoach phat trien kinh t l xa hdi huyen
dao, tap tha tac gia da tien hanh tip hgp, phan tfch dya tren cac tai lieu dieu tra da cd va bo sung nhirng dii lieu mdi ve khi hau, khi tugng, hii van, tren co sd dd dua ra nhii'ng danh gia, md phdng cd tinh quy luit, cap nhat ddi vdi van da hoan luu ven dao Bach Long VT.
TAI LIEU VA PHUOfNG PHAP NGHIEN CUtl
Tai lieu
Dii lieu su dung chfnh trong cdng trinh nay bao gdm eac du lieu khao sat trong hai miia ve khi hau - khi tugng, hai van thudc de tai;
''Nghien cuu bdn chdt hodn lint ven ddo tai mgt so ddo tien tieu trin vinh Bdc Bg phuc vii bdo ve moi trudng. sinh thdi vd phdt trien bin vUng" ma sd VAST 006.03/12-13, kit hgp voi ngudn du lieu thu thip nhieu nam qua tai ciing khu •vyc, cu the nhu sau:
Mo phong ban chat hoan luu ven dao ...
So lieu do siu va dudng bd khu vuc quanh dao dugc sd hoa tu cac ban dd dja hinh UTM ty le 1:25.000 do Cue Do dac Ban dd xuit ban vdi He tpa do Qudc gia VN-2000; vimg ven dao va lin can dugc tham khio va bd sung tii co sd du lieu dja hinh ETOPO-5 cua Trung tam tu lieu Dja vit li Qudc gia My (National Geophysical Data Center) va GEBCO-1 cua Trung tim tu lieu Hai duang hgc vuong qudc Anh (British Oceanographie Data Centre - BODC).
Sd lieu khi tugng thu thap hi COADS (Comprehensive Ocean Atmosphere Data Set), ngudn tai tram quan trac Bach Long VT, Hdn Diu dugc quan trie lian tuc 6h/dp thudc mang ludi Khi tugng Thiiy van Qudc gia va Dai Khf tugng khu vyc Ddng Bac.
Chudi sd lieu quan trac thuy hai van ve luu lugng, ddng chay, sdng, dao dgng muc nude, cae hang sd dieu hoi thuy trieu trong khoang thdi gian dai tir mdt sd da tai, du an ciia Trung tim Khi tugng Thuy van bien, Phin vien Co hgc bien, Vien Tai nguyan va Mdi trudng bien [2, 3, 4], ciing vdi sd lieu nhiet mudi tu WOA2009 (World Ocean Atlas 2009), sd lieu tfnh toan tir md hinh NAO TIDE du bio thuy trieu ciia Dai Thian vin Qudc gia Nhat Ban NAO (National Astronomical Observatory).
Phuong phap nghien cii'u
Viec nghien cuu sir dyng modul thuy ddng luc Delft3D-FL0W va modul sdng Deflt3D- WAVE trong bg phin mem chuyan dung DelftSD (phien ban 3.28) ap dung ky thuat ludi long. Viec danh gii sai sd tinh toin su dung sai sd binh phuong trung binh RMSE (Root Mean Square Error) lam chi tieu d l danh gia do chinh xic cua md hinh thiiy ddng lye thdng qua kilm ehiing muc nude. Chi tiet cua cac phuong phap nay di dugc trinh bay trong [3, 5].
Thiet lap va Idem chirng mo hinh Thiet lap mien tinh
Mian ngoai: ip dung chay cho khu vuc vinh Bac Bd, diy la vjnh nam trong viing tham lue dja phfa Tay Gidi han giua l7"00'-2l"30' vTdd Bic va 105°40'-110^00' kinh do Ddng, cd 3 mat Ddng, Bac, Tiy bao bdi lue dja (chilu dai vinh 496 km, noi rdng nhat trong vinh 314 km), vjnh thdng vdi bian ngoai qua eo bien hep Quynh Chau d phia Ddng (hinh I). Die biet phia Nam vinh Bic Bd thdng va trao ddi nude chii yeu vdi khu vuc Bien Ddng, day vjnh tuang ddi bang phing, nhat la tCr 20" Bic trd len. Do sau ciia vinh khdng ldn, trung binh khoang 50 m. Mien tinh dugc chia thanh 365x391 d ludi trong he toa dg cau cong tryc giao, sii dung dieu kien ban dau dugc Iiy tir file VBB.ini.
IT'OC 1 7 W
Hinh 1. Dp sau (a) va \um tinh (b) mien ngoai
Pham Hai An, Tran Anh Tii
Miln trong (khu vuc ven dao Bach Long VT): Dp sau va miln ludi tinh dugc the hien tren hinh 2; su dung mien ludi vdi 242^242 o ludi. Dien tich miln tich: khoang 48 km theo chilu Ddng Bic-Tay Nam va 53 km theo chieu Tay Bic-Ddng Nam, vdi dien tich mat nude khoang 1.624 km^. Phan lop va ludi: hai lop (mat -I- day), sii dung ludi cong tryc giao, kfch thudc d ludi: bien ddi tir 25,4 m den 318,5 m;
Thdi gian md phdng: tinh toan trudng hgp hudng gid Tay Nam (10/2012) va trudng hgp hudng gid Dong Bac (4/2013) vdi budc thdi gian tinh toan la 0,5 phut.
Kiem chirng mo hinh
Sau lin hieu chinh cudi, viec danh gia do ehinh xae tu cac ket qua diu ra ciia md hinh da duoc tien hanh.
100 200 300 400
Hmh 3. So sanh dao ddng muc nude giiia quan trac (obs) va tinh toan tai tram Hdn Diu, (a) - hudng gid Tay Nam, (b) - hudng gid Ddng
(model) Bic Kat qua kiem ehii'ng ddi vdi mien ngoai (vjnh
Bac Bg): so sanh muc nude tfnh toin tir md hinh vdi muc nude quan trac tai tram Hdn Dau:
Trudng hop hudng gid Tiy Nam, sai sd binh phu'ong trung binh (RMSE), sai sd trung binh tuyet doi (MAE) cd gia trj lan lugt la 0,14139 va 0,13769, Cac gii trj nay thi hien ket qua tinh toan tir md hinh thiiy dpng lue la chap nhan duge, Ngoai ra, sai sd trung binh (ME) cho gia tri am (hinh 3b), diau nay tha hien xu the: trung binh cac gia tri myc nude tinh toan tir md hinh thap hon cac gia tri quan trie tai tram Hdn Diu.
Tru'dng hgp hudng gid Ddng Bac, he so tuong quan (Rvalue) giua muc nude tfnh toan va md hinh bing 0,97148. Gia tri RMSE = 0,15897 va MAE =0,15172 xap xi bing nhau, diau nay cho thay ket qua tfnh toan tir md hinh thiiy luc la tuong doi tdt (hinh 4). Mat khac gia tri ME duang (trai vdi xu tha trudng hgp hudng gid Tay Nam), the hien trung binh myc nude tfnh toan tir mo hinh cao hon cic gia tri quan trac.
Ket qua kiem chung ddi vdi mien trong (khu vuc ven dao Bach Long VT) qua so sanh muc nude tfnh toan tu md hinh vdi myc nude quan trie.
Md phdng ban chat hoan luu ven dao . Cac sai so binh phuong trung binh tuang
ling theo miia gid Tay Nam va mua gid Ddng Bic lin lugt la RMSEioaon = 0,169;
RMSEo«oi3 = 0.163. Hai gia tri nay dha thi
hien su phu hgp nhat djnh ca ve pha trilu va do ldn, cho thay sy phu hgp tuong ddi giiia kit qua tinh toan vdi sd lieu quan trie.
Hinh 4. So sanh muc nude tinh toan vdi chudi sd lieu quan trie (trai 10/2012, phai 4/2013)
Ktr QUA TINH TOAN
Ket quS mo phong hoan luu ven dao Bach Long VI
Hodn luu huanggio miia Dong Bdc Khu vyc vjnh Bic Bg cd miia ddng lanh do tic dgng cita che do gid miia, Trong cae dot gid miia Ddn^ Bic, toe dg gid trung binh 4-6 m/s, miinh nhit 20-24 m/s. Thudng thi trong chi do gid miia Ddng Bac, tren khu vuc vinh Bic Bd rat hay bat gap su xuat hien cac xoay thuin ngugc chieu kim ddng hd vdi ddng cd hudng Tay Nam, van tdc trung binh khoing 65 cm/s.
Qua cac tinh toin md phdng tru'dc diy, ddng hudng Tay Nam nay dugc the hien manh bdi ddng ven bd sat luc dia,
Dong chdy tdng mat: khac vdi kat qua mo phdng trong miia gid Tay Nam vdi hai xoay nghjch eye bd quanh dio, md phdng hoan luu trong miia gid Ddng Bac chi xuat hien mdt xoay thuan tdn tai trong mdt pham ban kinh 1,5 km each dao khoang 0,5 km ve phfa Bae Tay Bic (hinh 5a). Pham vi xoay thuin cue bd nhd do mpt phin anh hudng bdi xoiy thuan bj giam trong thing 4 khi miia gid Ddng Bic bj suy giim dan trong giai doan chuyen miia. Tai tam ciia xoay thuan nay, ddng ed gia tri khoing 30-40 cm/s; ngoai ria phia Bac cua xoiy thuan van tdc ddng ldn hon, bien thien trong khoang 50-75 cm/s. Sau dd theo quan tinh tiap tuc di chuyin nhip vai ddng ban phia Tay Nam dao dl theo hudng Tiy Bic. Cac ddng nay sau khi each xa anh hudng ciia dio, chuyen hudng mgt
phan di vao bd rdi tao ra ddng ven cd hudng Tay Nam; mgt phan do inh hudng tryc tiap ciia gio Ddng Bic ba mat nen chay thang theo hudng Tiy Nam, ddng khi dd cd van tde bien doi vao khoang 35-45 cm/s.
Xoay thuin dang nay thudng xuit hien trudc thdi diem nude rdng khoang 2 gid ddng hd va dugc phat trien trong pha trieu len (hinh 5b), Khi xoiy thuan phat trien, nd each xa dao ban, bin kinh inh hudng khoang 2 km.
Trong giai doan nay, khu vuc tim xoay thuan, ddng ed gii tri khoang 25-40 cm/s; phia Bac ria xoay thuan van tdc ddng ldn bian thien tir 60 cnVs dan 75 cm/s di chuyen nhap vdi dong ban phia Tay Nam dio hudng ve phi'a Tiy Bic vdi tdc do khdng suy giam, trung binh dat 70 em/s.
Ciing nhu trong thdi diem bat diu xuit hien xoay thuin, liic nay sau khi tach xa dio ddng chuyen hudng mgt phan di vao bd; mdt phan tilp tue chay thang theo hudng Tay Nam, van toe trung binh 40 cm/s. Thdi gian tdn tai xoay thuan ngan, khoang 2-3 gid (rieng trudng hap xody thudn trong pha triiu ten ngdy 17/4 keo ddi han, no xudt hiin truac thai diem nuac rong 1 gia, sau do ton tgi khodng 6 gid nhiiu gdp 2-3 ldn so vdi xody thudn cua cdc ngdy khdc trong thdng dugc mo phong)^ thudng thi khdng cdn xoay thuin trudc thdi diem giira pha trieu lan.
Dong tdng ddy: So vdi tang mat, su hinh thanh xoiy thuin trong pha trieu len tai tang day khdng dugc ro net (hinh 6). Xoay thuin
Pham Hai An, Tran Anh Tii
nay nim each dao khoang 0,4 km vl phia Bic 0,8 km, ddng trong xoay thuan cd van tdc dat Tay Bic, c6 ciing vj trf vdi xoiy thuin tang 25-30 cm/s. Phia ria xoay phan phia Bac van mat, tuy nhien bin kinh anh hudng giam di cdn toe ddng ldn hon ban, dat 60-70 cm/s.
500 m/s , — 0.500m/3 , . J. .
Hinh 5. Trudng ddng chay tdng mdt trong miia gid Ddng Bac vao pha trieu len (a): 09h ngay 8/4/2013; (b): lOh ngay 8/4/2013
Hinh 6. Trudng ddng chay tdng ddy trong miia gid Dong Bac vao pha trieu len (a): 09h ngay 8/4/2013; (b): 1 Ih ngay 8/4/2013
Tai ting day xoay khdng dugc thi hien rd, gia tri trung binh 30-40 em/s. Trong khi do, xong nhung dac tfnh ve dong each xa ben phia phan phia ddng dao thdng trj bdi ddng hudng Tay Nam dao ciing mang nhu^ng net tuang Tiy vdi gia trj ddng 40-50 cm/s, ddng hudng ddng nhu tang mat, ddng nay di theo hudng Tay Nam vdi gia trj 45-50 cm/s. Sy tdn t?i ciia Tay Bac sau do mgt phin tiep tuc di vao bd, xoay thuan tang mat liu va ldn hon so vdi tang mdt phin chuyen hudng thanh Tiy Nam vdi day, neu tai tang mat xoay thuan tdn tai tir 2-3
gid thi tai ting day xoay thuan chi tdn tai hon 1 gid ddng hd (hinh 6a), sau do khdng cdn xoay nua (hinh 6b). Khi khdng cdn xoiy thuan nua, ben phia Ddng cua dao bj chi phdi bdi ddng hudng Tay, mdt phin ddng hudng Tiy Bic. Ca hai thanh phan ddng nay khi qua dio deu mang hudng Tay Bic do it bj anh hudng bdi gid Ddng Bac be mat.
Md phong ban chat hoan luu ven dao ...
Hodn luu huanggio miia Tdy Nam Ddng chdy idng mat: sy tdn tai ciia dao Bach Long VT trong vinh Bac Bd tya nhu mdt vat can khien cho hoan luu ven dio cd nhung net dae thu rieng, dd li sy xuit hien ciia cic xoay nghich cue bd cung chieu kim ddng hd, each dao khoing 0,5km ve phia Tay Bic dao.
Hinh 7. Trudng ddng chay trong rniia gid Tay Nam vao thdiky nwo-c/d?? (7/10/2012) (a): ting mat; (b): ting diy
Hinh 8. Trudng ddng chay trong mua gid Tay Nam vao thdi ky nude xuong (7/10/2012) (a): tang mat; (b): ting day
Pham Hai An, Tran Anh Tii
Sy tdn tai ciia xoay nghich cue bd nay thudng bat dau xuat hien trudc pha nude ldn khoang 2 den 3 gid, khi dan thdi diam nude ldn (hinh 7a) van tdc ddng ven dao giiia xoay nghich va bd phfa Tay Bic dio mang gii tri nhd hon so vdi khu vuc xung quanh^ thudng la 8-10 cm/s, phfa Nam dio bi chi phdi bdi ddng hudng Nam lan; do anh hudng can cua dao:
hoan luu re nhinh lam hai, mdt phan re trai tham gia tao nen xoay nghich cue bd, mgt phin bian tinh sang hudng Nam Tay Nam tiep tuc di chuyen len tren nhap vdi ddng tiep tuyln phia
ngoai ciia xoay nghjch hudng ve phfa Bac vjnh Bic Bp vdi gia tri dong thay doi trong khoang 45-60 cm/s. Sau do tiep tuc keo dai khoang 3 - 4 gid trudc thdi diem giiia cua thdi ky nude xudng. Tai thdi diem nude xudng (hinh 8a), khdng cdn sy tdn tai ciia xoay nghjch ben phia Tay Bac dao, bao quanh dio la ddng cd gia tri 40-50 cm/s vdi hudng chii dao Tay Bac - Ddng Nam, rieng viing nude ven dao ve hai phia Tay Nam va Ddng Bac dao ddng cd gia tri ldn hon, dat 50-70 cm/s.
Hinh 9. Trudng ddng chay trong miia gid Tay Nam vao thdi ky nude rong (7/10/2012) (a): tang mat; (b): ting day
Hmh 10. Trudng ddng chay trong miia gid Tay Nam vao thdi ky nuac len (7/10/2012) (a): ting mat; (b): ting diy
Mo phong ban chat hoan luu ven dao . Den thdi diem nude rdng bit diu hinh
thanh mgt xoay nghich khac ben phia Ddng Nam dao vdi pham vi inh hudng (ban kinh xoay khoang 4-6 km) (hinh 9a) ldn hon xoiy nghich ben phan Tay Bac dio trong thdi ky nude ldn (bin kinh xoay khoang 2-3 km).
Trong thdi diem nude rdng, ddng ed van tdc ldn gan hit vimg xoay nghich, trung binh khoing 60 em/s. Tuy nhian, ehfnh vl viing xoay ldn phia Ddng Nam dao nen ddng phia Tiy Bic dao mang gia tri thap 7-13 cm/s. Thoat khdi vimg xoiy nay, hoan luu theo hudng Ddng Nam vdi gia tri bien thian trong khoang 40- 50 cm/s. Cling nhu eac xoiy nghjch cue bd khac, xoay nghich ban phia Ddng Nam dao tdn tai khoang 6 - 7 gid, nd bi suy giam manh trude thdi diem giua ciia thdi ky nude lan (hinh 10a) ddi vdi hiu het cic ngiy trong thing gid miia Tiy Nam, Tai thai diem nude len, ddng cd hudng ngugc vdi pha nude xudngj thoat ra xa dao la ddng chii dao hudng Tiy Bac vdi gia tri 50 em/s, Nhu vay phan ldn trong ngay deu xuit hien hai xoiy nghjch cue bg, tdn tai 6 - 7 gid, pham vi xoay nghich ben phia Ddng Nam dio ldn hon pham vi xoiy nghjch ben phfa Tay Bae dao. Ddi vdi xoiy nghich ben Tiy Bic dao, van tdc ddng tai tim khoing 15-26 cm/s thip hon bian ngoai ciia xoiy, noi van tdc ddng bien thien tir 35-42 cm/s. Ddi vdi xoay nghjch ben phan Dong Nam dao, vin tde ddng tai tim cung nhu tai bien ngoai cua xoay tuong ddi dong dau, van toe bien thien trong khoang 45- 70 cm/s.
Dong chdy ldng day: do sau trung binh vjnh Bic Bg khdng ldn, dp siu •vimg ven dao Bach Long VT khoing 30-40 m va phfa Tiy Bac, 40- 50 _m ve phfa Dong Nam len tai tang day eung xuat hien eac xoay nghich cue bd cung pham vi va tam xoay nhieu net gidng vdi cae xoay nghjch tang mat. Cach dao khoang 0,6 km ve phia Tay Bac tdn tai mdt xoiy nghjch xuat hien trudc pha nude ldn khoang 2 gid. Tai thdi diem nude ldn (hinh 7b) ddng sat ven giira xoay nghich va bd phia Tay Bac dao mang gia tri 20- 40 cm/s nhd hon so vdi khu •vyc xung quanh.
Phia Nam dao bi chi phdi bdi^ dong hudng Nam, chia lam hai nhanh: mdt phan re trai tham gia vao vong ngoai ciia xoay nghich, mgtphin lech sang hudng N a m T i y Nam di chuyan lan tren nhap vdi ddng tiep tuyen ngoai eiia xoay
nghjch di ve phia Bac vinh vai van tde dong trung binh 50 cm/s. Sy tdn tai ciia xoiy nghjch nay suy giim sau 2 - 4 gid trudc thdi diam giiia ciia thdi ky nude xudng. Tai thdi diem giua cua triau nude xudng (hinh 8b), xoiy nghich ben phfa Tay Bic dao khdng cdn, thay vao la ddng bao quanh dio ed van tdc 50 em/s, hudng chii dao Tiy Bae-Ddng Nam. Dae biet •viing nude ven dio ve phia Tay Nam va Dong Bac dao, van tdc ddng ldn hon, dat 60-70 cm/s. Nhu vay neu chi xet xoay nghich trong thdi diam nude ldn, cd tha nhan thiy van tde ddng xoiy nghich d ting day ldn han mgt chiit so vdi tang mat.
Suy giam xoay nghjch phfa Tiy Bae dao dien ra trong thdi ky nude xudng. Den thdi diem nude rdng: bit diu hinh thanh mdt xoay nghjch khac ban phfa Ddng Nam dao vdi ban kfnh anh hudng 5-6 km (hinh 9b), Pham vi anh hudng eiia xoay nghich niy ed phin ldn han pham vi xoiy nghich ben phan Tay Bac dio (thdi ky nude ldn ban kfnh xoiy 2,5-3,5 km).
Tai thdi diem nude rdng, ddng cd van toe ldn gan het •viing xoay nghich, trung binh la 60 em/s. Khdng cd su khac biet ddi vdi viing xoay ldn ban Ddng Nam dio giira hai ting mat va diy, ddng phia Tiy Bac dao cung mang gia tri thip, khoang 6-10 cm/s. Tai ting day, mot phin dong phia ngoii ciia xoay nghich tham gia vao hoan luu hudng Tay Tay Nam, sau dd chuyen hudng thanh Ddng Nam di ra phia cira vinh, Ra xa khu vyc xoay, each tam dio khoang 18-20 km ddng tap trung theo hudng Dong Nam vdi van tde bien thien trong khoang 30-42 em/s. Su tdn tai xoay nghich tang day phfa Ddng Nam dao trong khoang 5-6 gid, sau do nd suy giam manh trudc thdi diem giira ciia thdi ky nude len (hinh 10b), Trong thdi diem nude len, khu •vyc phia Tay Bac viing nghien cuu ddng hudng Tiy Bae vdi van tde 40- 50 cm/s ngugc hudng vdi pha nude xudng. Hai ben dao ve phfa Ddng Bae va Tiy nam, dong cd gia trj ldn bien thien tir 55-78 em/s, pham vi anh hudng ciia loai ddng nay each dao ve hai phia mdt khoang tir 16 km den 19 km. Thoit khdi khu vyc nay, dong chu dao hudng Tiy Bac vdi van tdc trung binh la 50 cm/s,
Tai ting diy, trong ngay eiing xuat hien hai xoay nghjch tdn tai khoang 5 - 7 gid, pham vi xoay nghjch ben phan Ddng Nam dao thudng ldn hon pham vi ben phin Tay Bae dao.
Pham Hai An, Tran Anh Tii
Toan bd hoan luu trong miia ^id Tay Nam, van tdc ddng ludn cd gia tri bidn thien trong khoing 50-70 cm/s. Phan ldn dien tich viing nude quanh dao van tdc ddng trung binh dat 60 cm/s. Dudi anh hudng ciia gid mua Tay Nam, xuit hien nhiing xoay nghich nhd xung quanh dao.
KET LUAN
Che do hoin luu khu vyc dao Bach Long VT mang tfnh tdng hgp chfnh ciia hai thanh phan trieu vi gid be mat. Dudi anh hudng ciia xoay thuin thdi ky gid miia Ddng Bae va xoay nghich thdi ky gid miia Tiy Nam tren phan ldn vinh Bic Bg, cdng them dae diam dja hinh dao Bach Long VT len khu vyc ven dio da xuit hien xoay thuan va cae xoiy nghjch cue bd. Ra xa dao khoang 18-20 km, hoan luu nay chju sy chi phdi chung cua hoan luu vjnh Bae Bd, khi dd dong chay co hai hudng chil dao la Dong-Dong Bac va Tiy-Tiy Nam.
Dao Bach Long VT cd dien tich nhd, day bian khu vuc xung quanh dao viia cd cat, san hd va da ngam; ngoai ra sd lieu dja hinh chua duge chi tiat nan viec mo phdng chinh xae hoan luu la rat khd khan, nhung hoan toan cd tha khie phuc dugc d nhii'ng nghien cuu tiep theo.
Loi cam ffn: Nhdm tic gii xin trin trgng cim on Ban chii nhiem da tai "'Nghien ciru bdn chdt hodn luu ven ddo tgi mot sd ddo tiin tieu trin vinh Bdc Bg phuc vu bdo vi moi trudng, sinh
thdi vd phdt trien bin vi?ng" ma sd VATS 06.03/12-13 (2012-2013) da tao dilu kien cho viec hoan thanh cdng trinh nay.
TAI LIEU THAM KHAO
1. Viin Tdi nguyen vd Moi trudng biin. Bao cao dieu tra tdng hgp vinh Bic Bg, 1965.
Phan II. Vit ly thuy van. Luu trii tai Vien Tai nguyan va Mdi trudng bien.
2. Hd Thanh Huang, 2013. Bien ddng cau tnic hoan luu vjnh Bac Bp. Tap chi Khoa hoc DHQGHN, Khoa hgc Ty nhian va Cdng nghe 29, Sd IS (2013), 80-88.
3. Trdn Anh Tu, VU Duy VTnh, Nguyen Huu Cir, 2008. Md phdng qua trinh tran dau khu vuc dio Bach Long VT bang md hinh delft- 3d. Tuyan tip Tai nguyen va mdi trudng bien. Tap XIII. Nxb. Khoa hpc vi Ky thuat HaNdi, Tr. 342-351,
4. Tran Anh Tu, Le Due Cuong, Pham Hai An, 2013. New results on temperature-salinity vertical structure in water of Hai Phong coastal area. Proceedings of VAST - IRD Symposium on Marine Science, Haiphong- Vietnam, November 28"' - 29'\ 283-288, 5. WL\Delft Hydraulics. 2010. Delft3D-
FLOW User Manual Version 3.05, Delft3D Waq User Manual Version 3.01, Delft3D - Part User Manual Version 1.0 WLIDel'ft Hydraulics, Delft, Netherlands.
Mo phong ban chat hoan luv ven dao ,
SIMULATING CIRCULATION NATURE AROUlsfD BACH LONG VI ISLAND BY A MATHEMMATICALIVIODEL
Pham Hai An, Tran Anh Tu Institute of Marine Environment and Resources-VAST
ABSTRACT: Bach Long Vi is the furthest offshore island in the Tonkin gulf. As one of the frontier islands, the information about the hydrodynamic factors such as wave, current, tide is especially needed for scientific researches as well as designing protection engineering. Due to the limitation of hydrodynamic observation data in this area, the use of mathematical models to simulate hydrodynamic regime is a good way lo understand about circulation around the island. By using the nesting techniques in DelflSD model, the circulation around Bach Long Vi island was simulated, from that the picture of circulation in this area is clear because of the influence of tidal and wind surface The initial simulation results show that the circulation of offshore area has been controlled by the circulation of the Gulf of Tonkin, the flow has tivo main directions, including east- northeast and west-southwest. Meanwhile, the coastal island has the appearance of the local cyclone and anticyclone as well.
Keywords: model, circulation, cyclone, anticyclone.