Hgi nglu Khoa hoc va Cong nghe bien loan quoc lan thii V
DAC DIEM TRAO D O I N I T O C DAM 6 LOAN TRONG TRl/OfNG HOP DONG M O C I T A DAM
Nguven Chi Cong. Le Dinh Mau Nguyen Van Tuan, Phan Thanh BSc Vien Hai Duong hoc. 01 - Cau Da, Nha Trang, Khanh Hoa
Email: vnio.(a),.ora.vn
Tom tat:
Cdc kit qua tinh todn dd mo phdng trudng dong chdy vd qua trinh trao doi nude ciia ddm 6 Loan qua hai cim trong thdi ky miia mua. Kit qua tinh todn cho thdy rdng khi cira phia nam chua duac md, trao ddl nirac giita ddm va biin chi thdng qua cica phia bdc. Lini luang tnmg binh khodng 190m /s. Toe do ddng chdy cue dgi tgi cira ndy co thi lin den I,7m/s. Trong truang hap cira phia nam dugc md, trao doi nude trong ddm vd ngodi ddm chii yiu th'ong qua cira phia nam. Gid tri hm lugng trung binh qua cua ndy khodng 135m /s.
Trong khi do, luu luang nuac trung binh tgi cira phia bdc con khodng 58m A, gidm gdn 4 ldn .90 vdi trudng hgp cifa phia nam bf dong.
FEATURES OF WATER DISCHARGE IN O LOAN POND Abstract:
Some caculated results had simulated the current field and sea water discharge processes passing two mouths in O Loan dam in rain season. The result shows that, the discharge between dam and sea is passed only by northern mouth when the southern mouth was not opened. Average discharge is about 190 m /s. The maximum current speed round in 1,7 m/s. In case the southern mouth is opened, the inside and outside dam discharge is mostly passed by the southern mouth. Average discharger passing this mouth is about 135 m^/s. Meanwhile, the average discharge at northern mouth decreases only to 58 m /s, 4 times decreasing when compering with southern mouth being closed in case.
I. MO DAU
Dam O Loan co dien tich khoang 300km^ duoc su dung cho muc dich nuoi trong va khai thac thuy hai san dong thai ciong la nai neo dau cua cac tau thuyen. Hang nam khu vuc nay dem lai gia tri kinh te cao cho virng. Trong nhiing nam gkn day, hien tugng 6 nhiem nuoc trong dam dang a muc bao dong va co xu huong ngay cang tang. Nguyen nhan cua
'J2§ii_han Khi tucmg. Thuy van vd Dong luc hoc Bien
hien tuong nay la do nuoi tr6ng thuy san, cac chat thai da vuot qua muc cho phep. Dong thoi viec xay djp cac ho nuoi torn dpc theo hai ben ba da lam ngan can cac qua trinh trao doi nuoc trong dim vai ben ngoai bien qua cua dam phia bac. Mgt hien tuang rat dac trung cua d4m O Loan la su dong ma cua phu phia nam cua dam vao thai ky mua mua, khi luong nuoc ngot d6 vao dfim vuot qua sue tai cua cua chinh nam a phia bac cua dam. Su hinh thanh cua dam phu phia nam co the duac ma mot each tu nhien boi qua trinh dong luc tac dong len hoac CO nhimg nam do hien tuong muc nuac dang len nhanh chong, nhimg nguoi dan dia phuang da tao ra mot lach nho de nuac co the thoat ra ngoai. Viec danh gia qua trinh trao doi nuoc trong dam va ngoai dam thong qua cac ciia dam cung nhu dac diem dong chay tai cac cua vao thoi ky mua mua trong hai tnrang hap dong va mo cira phu phia nam la rat quan trpng. Mpt trong nhung each co the danh gia dupe qua trinh nay la su dung mo hinh thuy dpng luc MIKE21 HD de mo phong truang dong chay cho khu vuc nay trong thai ky mua mua, tir do tinh toan de dua ra duoc mpt so cac dac trung trao doi nuoc qua cac mat cat cira.
Ket qua tinh toan c6 the lam co so cho viec danh gia tac dpng moi truang, quan ly va khai thac thuy hai san, nen hay khong nen mo cira phu phia nam.
II. TAI LIEU VA PHU'OfNG PHAP
S6 lieu su dung cho mo hinh la so lieu dupe lay tii cac ket qua khao sat ciia cac de tai nhu D6 tai dpc lap 2007, De tai cap Vien Khoa hpc va Cong ngh| VN bao gom
S6 lieu dia hinh, duang ba So lieu dong chay, mirc nuoc
Hinh 1: Dia hinh vd luai tinh khu vuc dam O loan.
Bl: Biin long 1; B2: Bien long 2; B3: Biin song;
MCI: Mat cdt cdu go, MC2: Mat cdt cua phu, MC3: Mat cdt cua chinh;
DS,D4: diem trich xudt muc nude
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Sir dung mo hinh MIKE21 HD tinh toan trudng dong chay hong hai hrudmg hgp ddng va mo cua dim phia nam (cira phu) dai dien cho miia mua. Luu lugng nuoc song la 200m'/s. Tir kSt qua huang phan bo ddng chay, titih toan hao ddi nuoc qua cac mat c5t MCI (mat c5t tai Ciu Gd), MC2 (mat cat tai ctia phu), MC3 (mat cSt tai cira phia bSc).
hioi nghi Khoa hoc vd Cong nghi hien toan quoc lan thir V
III. KET QUA VA THAO LUAN
Cac tinh toan duoc thuc hien cho hai trucmg hap: dong chay va qua trinh trao doi nuoc qua cac cua dam trong hai truang hop dong va mo cira dam phu (cua dam phia nam) vao miia mua. Cac ket qua tinh toan cho thay rang, truang phan bo dong chay va trao doi nuac trong hai truang hop tuong doi khac biet. Mpt so ket qua chinh xin dupe trinh bay duoi day.
L Dao dpng myc nir^c tai hai cusi dam
Dao dpng mirc nuac dupe trich xuat tir mo hinh tinh toan. Diem D3 la diem phia trong ciia cua phu, dai dien cho qua trinh trao doi nuoc qua cua phu. Dao dpng muc nuac tai diem D4 dai dien cho qua trinh trao doi nuac qua cua phia bac. Ket qua tinh toan cho thay rang tai vj tri D3, trong truang hpp eua phu chua duac ma, muc nuac trung binh trong mpt chu ky trieu co xu huang tang dan. Mpt trong nhiing nguyen nhan khien gia tn trung binh nay tang dan la do luong nuoc ngpt cung cap tir ciia song khong kjp thoat het ra ngoai qua cira phia bac. Su tich liiy nuoc song trong miia HI thuang lam cho muc nuac trong dam dang cao. Day ciing la hien tuong thuang thay a khu vuc nay trong mua mua, khi cua phu phia nam chua dupe ma.
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c tai cac diem D3 va D4 Irong hai truong hop dong/mo cua dam
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Hinh 2: Dao dgng mtic nude tgi cdc vi tri gan cira dam phu (Di) vd cira idm chinh (D4) trong hai truang hap dong/ma cira dam
Trong trudng hpp ciia dam phia nam duoc mdr hoan toan, qua trinh trao ddi nude co sir gdp phan ciia cijta phu phia narn, cd thS th4y ring dao dong muc nude tai digm D3 hrong tu vdi dao dpng muc nude tai diem phia ngoai cira cho thiy ring qua hinh trao ddi nude chii ydu la do qua dinh thuy trieu.
Tai diem D4 hong ca bai hudng hop dong va md cua dim phu, dao dpng muc nude hrong tif vai dao dong muc nude phia ngoai dim, Tuy nhien, van thiy co su khac nhau ve bien do hieu ttong tai didm nay. Muc nuac hung binh ttong trudng hcrp cura phu bi ddng co gia tri cao ban m\rc nude ttung binh ttong trudng iiqp cira phy duac md.
Tiiu ban Khi tugng. Thiiy vdn vd Dgng luc hgc Bien
2. Phan b6 dong chay tai cac cua d^m
Tnrang hap cira phu bi dong, phan bo dong chay ben trong dam tuong doi nho, gia tri trung binh vao khoang 0,2 m/s. Trong khi do, tai ciia phia bac ciia dam gia tri cue dai len din 1,6 m/s. Trong tnrang hop cua phu dupe ma, trao doi nuoc thong qua cira phu lai dong vai tro chinh. Tai cira phu, toe dp dong chay cue dai len den 2 m/s, trung binh khoang 0,8 m/s. Trong khi do, tai cua phia bac toe dp cue dai chi con 0,9 m/s. Tai mat cat Cau Go, khi cira phu duac ma, qua trinh trao doi nuoc Ion hon nen toe dp dong chay o day lan hon so vai tnrong hop khong co cira phu.
Bang 2." Cdc ddc dong chdy qua Dac trung dong chay
Cue dai (m/s) Trung binh (m/s)
cdc mdt cdt cda ddn Cira phu md'
MCI 0,46 0,22
MC2 2,06 0,84
MC3 0,92 0,36
Cira phu dong MCI
0,31 0,20
MC3 1,68 0,90 3. Trao doi nir^c tai cac cua dam
Trong truang hop eira phu bj dong, trao doi nuoc trong va ngoai dam thong qua cira phia bac. Ket qua tinh toan cho thay rang trao doi nuac qua cira nay dat gia tri trung binh khoang 190m^/s. Trong khi, trao doi nuac tai Cau Go co gia tri nho hon, vao khoang 161mVs. Trong truong hop cira phu duoc md hoan toan, trao d6i nuac tai tai ciia phia bac giam khoang gkn 4 lin so voi trucmg hap khong eo cira phu. Phan lan, trao d6i nuoc trong dkm va ngoai dkm duoc thuc hien thong qua cira phu voi gia tri luu luong tnmg binh khoang 146mVs.
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Hinh 3: Phdn bd ddng chdy tgi cdc cita dam trong thdi kji trieu len vd trieu xudng tgi cdc cira ddm (hinh a, b, c, d: dong chdy vao thai diem trieu xuong vd len tai
cua phia bdc vdphia nam tucmg img)
Hgi nghi Khoa hoc vd Cong nghe bien lodn quoc ldn thu V
Ranp 2.' Cdc ddc tnmg trao doi nuac qua cdc mdt cd Die trung trao doi nu*c
qua cac cwa dam LLTB qua mat cit (m'/s) LLTB chay ra (ra'/s) LLTB chay vao (mVs)
Cira phu ma MCI
165,0 178,5 -92,8
MC2 134,2 146.1 -84,7
MC3 57,5 62,5 -35,9
Cira phu dong MCI 161,1 169,1 -50,8
MC3 190,0 199,8 -73,9 D8 cd thd danh gia duoc vai trd cua hao ddi nuac qua cira phu. TCr cac tinh toan luu lupng tai mat cit MC3 cho thiy ring, trong ttucmg hgp cd cua phu, luang nude trao ddi qua cita phia bic da giam di dang kS (binh 4). Tuy nhien, t?i mat cat MCI, luu luang nude trao ddi qua mat cit nay ldn hem so vdi ttudng hop khdng tdn tai cira phu.
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Hinh 4: Trao ddi nuac tgi mat cat cua phia bdc (MC3) trong hai truang hap dong vd md cua phu (cua phia nam)
Qua Vkx qua tinh toan, co the thay dupe vai tro cua viec dong va mo cua phu lien quan toi qua trinh trao d6i nuac trong va ngoai dam, dac biet vao thai ky mua mua. Su ton tai ciia cua phu phia nam trong thoi ky nay lam tang kha nang thoat nuac tir cira song do vao dam. Cac ket qua tinh toan nay la buac dau de danh gia cac qua trinh khac nhu: qua trinh iam sach dam,-quy hoach va nuoi trong thiiy san. Tuy nhien de c6 the danh gia dupe tot han qua trinh trao doi nuac qua cac cua dam can phai eo nhiing chuoi so lieu khao sat thuc do ve truang dong chay, nhiet muoi, trong klioang thai gian dii dai phuc vu cho tinh toan va kiem chung mo hinh.
Tieu ban KhJ licgng. Thiiy vdn vd Dgng lire hgc Bien
TAI LIEU THAM KHAO
I • De tai Dpc lap. Bdnh gid tdc dgng ciia cdc truang song trong gio miia den ddi ven biin Nam Trung Bg tir Phu Yen din Binh Thudn vd de xudt cdc gidi phdp gidm nhe thiet hgi phuc vu phdt triin ben vimg. TS. Biii Hong Long chu nhiem. Nam 2007 2. Biii Hong Long, Tran Van Chung. Tinh todn ddng chdy 3 chiiu cho vitng cira song.
Tap chi Khoa hoc va Cong nghe bien, 4(3) tr. 43-53.
3. Greenberg, D., Shore, J.A., Dowd M. A finite element circulation model for embayments with drying Intertidel areas and its application to the Qouddy region of the Bay ofFundy. Ocean modelling. Elsevier, 10(2005), 211-231 pp.
