• KHOA HQC CONG NGHE •
TAC DONG KE DANG T BAO VE GIAM XOI L& B6 B I ^ N U MINH
TS. HO TUAN DtTC, PGS.TS. NGUYEN T H 6 N G , PHAN QUANG Hl/NG Khoa Ky thugt Xay Dfrng-HCMUT-VNUHCM TRAN THANH THAO - Trir&ng Dgi hgc Xay dtptg miin Tdy NGUYEN BCTC VU - Hgc vien Cao hgc CTT, HCMUT- VNUHCM
Tom t i t : Tinh todn md phong tdc dgng chdng xdi Id bd bien U Minh bdng gidi phdp cdng trinh dgng ke chic T du(rc thuc hien trin ca sd ket hgp ly thuyit giica cdc bdi todn thuy dgng luc ddng chdy, bdi todn sdng vd bdi todn van chuyin bun cdt. Kit qud tinh todn vdi cdc ke chQ T cd kich thudc diin hinh (chiiu cao 400m, cdnh rdng 600m, chiiu ddy 1.5m vd khodng cdch hai ke liin Hip trung binh 50m theo hudng ven bd) cho thdy cdng trinh phdt huy tdc dung lam gidm hi$n tugng xdi Id ven bd biin ciing nhu hien tugng bdi trong pham vi ke chic T. Nguyin nhdn chinh gidi thich cho kit qud bdo ve bd cua logi cdng trinh ndy la khd ndng gidm ddng chdy dgc bo vd gidm ndng lu^mg sdng khi di vdo ven bd. Nhd vdo cdc kit cdu thdn ke chic Tgiie vai trd nhu cdc ddp trdn si hgn che ddng chdy ven bd vd ngdn sdng tgi vi tri cdnh T khi sdng di vdo bd tgi vimg nghien cicu. Ddng chdy ven bd cd xu hudng bi ddy xa bd vd chdy dgc theo vi tri cdc cdnh ke chii T.
T u khoa: Telemae2D, Tomawae, Sisyphe, Bd bien U Minh, Ke ehd T
Abstract: Simulation of coastal erosion prevention in U Minh beach by T-head shape groyne solution was carried out on the basis of combining theory between hydrodynamic flow problem, wave problem and transportation problem. Results with typical T-shaped groyne (height of 400m, width of 600m, thickness of 1.5m, distance of two successive groynes of 50m along the shoreline) shows that this type is effective in reducing shoreline erosion as well as accretion in the T-groyne.
The main reason for this capacity of protection is the ability to reduce longshore currents and reduce wave power going to the shore. Thanks to the T-shaped structures, which act as spillways, will limit coastal currents and prevent waves at the T-wing when the wave enters the shore at the study site. Coastal flows tend to be pushed away from shore and flow along the position of the T- groynes.
Keywords: Telemac2D, Tomawae, Sisyphe, UMinh beach, T-head shape groyne
1. DAT VAN DE khu vyc. Xuit phat td danh gia nay, mpt trong Sy xdi Id bd bien vung ven biin U Minh ede gidi phdp d l xuit la tim each chu dpng tieu thudc DBSCL da dupe ghi nhan trong nhiiu tan d l 1dm "gidm" ndng lugng sdng khi tiln vdo nam trd lgi va tdc dp xdi Id gia tang nhanh trong bd va gidm hi$n tupng ddng chdy dpc ven bd vdi ndm gdn day. Mdt trong nhirng nguyen nhan mang theo bim edt bang cdch xay dyng cdc ke dugc ddnh gid Id do tdc ddng eua sdng va ddng dgng ehu T dgc theo bd bi6n. Dudi tac dyng cua chdy ven bd ed xu hudng ngay cdng b i t lgi eho kit ciu ndy se chii ddng giam tac dpng sdng di
60 TAP CHf T A I NGUYEN U\JCiC 5(5 4-2018
vao ba tir ngoai khcri va giam dong chay dgc ven bo bi6n. Day la 2 ySu 16 duge danh gia eo khi nang gay ra hien tugng x6i Id ven ba bien.
Phuong phap nghien cuu se su dvmg ket hgp 3 m6 hinh toan s6 gom Telemae2D giai bai toan thuy dgng lire, mo hinh Tomawae gi^ bii todn song va mo hinh Sisyphe giai bai toan bien hinh long din, van chuyen bim cat.
a63(3Ste^!»i*T-". ...
^^msm ssaiw*^::
Hinh 1: Mat cdnh rimg phdng hd d Cd Mau da bi sgt Id sdu vdo hdng chvc met. Ngudn: Anh:
NgQC Huyin, bdo Tiin Phong 2. CO S6 LY THUYIT
Telemac2D la mpt trong nhflng phan mem thuy luc dupe Tap doan Dien luc Phap (EDF) chu tri cimg vdi sy tham gia eiia nhieu td chuc nghien cdu trSn thi gidi dung de md phdng dong chay 2 ehilu theo phuong nam ngang (trung binh theo phuong thang diing) dugc md td bdi h^ phuong trinh Saint Venant nhu sau:
- -I- div{hU) = q (1)
—+U--FV— = - g ^ + F , +-dii(hv^ra^)] (2) 3v 9v 9v ^u^-Hv^=-g^+F,-H^di^[hv,gra4v)] (3) „ ^ .
dt da dy dy h
Trong do: h(m) - ehilu sau, u & v(m/s) - thdnh phin van tde theo phuong ngang x & y
eua van tdc U, q(m/s) - luu lugng don vj cua ngudn, Zs(m) - eao dp mdt thodng, Fx,y(m/s^) - cdc ngogi lyc (khdng kl trpng lye, vi du lye Coriolis,...) tae dung tren mdt don vi khdi lugng chieu theo phuong ngang x &
y, Vj (ra^/s)- he so khuleh tan.
Md hinh Telemae2D duge Idp trinh cd the lua chgn phuong phdp phdn tu hdu ban hogc the tich hdu han. Bdi todn sd dugc Idp trinh ed the xii ly dugc eae dgng dieu kien bien nhu: Bi6n myc nude Z, bien lim lugng Q, bien luu lupng vd myc nude (Q&Z), bien vgn tde (u,v), bi6n vgn tde va mye nude (u,v& Z) hode dgng bien sdng din. Cdc dang bien khdc niu ed se dupe ngudi sd dyng lap trinh rieng nhd vao phin mem dupe to chiie dudi dang md ngudn md.
Dudi tae dung eua gid len be mat dai duong se gay nen hien tupng sdng. Hi?n tugng vat ly dugc md td bdi phuong trinh bieu diln sy biin ddi cua mat dd phd sdng theo hudng bdi phuong trinh sau va duge gidi bdi md hinh todn sd tinh sdng Tomawae phat triin bdi Tap doan dien lye Phdp:
3: ix
+^+'-^+^=<?feV.y.0(4)
)y ' Sx ' iyVdi N(X.y,k,t) = N(x,y,k^,ky,t) chi phd eua mat dp tae dyng cda sdng
X = (ar,y) vecta ehi vi tri trong h | tog dp Cartesien
Ic - {k^,ky) = (ksin$,kcos9)vecta chi sd sdng, 0 chi hudng sdng
dg dg dg dx dg dy ff =
dt dt dx'dt dy'dt Hien tugng biin hmh long dan cua mien nghien cdu hen quan din hai lunh thuc van chuyen bun cdt la di chuy^ ddy vd di ehuySn lo limg.
Bun eat di ehuyin lo Idng 2 chiiu theo phuong nim ngang duge md ta bdi phuong trinh sau:
TAPCHfTAl NGUYEN Nl/OC$64-2018 61
• KHOA HQC CONG NGHE •
dhC d(hUC) d(hVC) _ dt dx dy
dC dx\ dx
z. 5C1 ^
dy) (5)
(6) Vdi C = C(x,y,t) chi ndng dp bim eat lo limg
trung binh theo phuong thang diing Trong do: h = Zs - Zf ~ Zs - Zref Id chieu sau nude, gid thiet chieu ddy cua lap bim edt ddy rdt mdng; (U,V) la van tde trung binh theo phuong X, y; E: suat xoi Id; D: sudt bdi ty, (E - D) la lugng trd eua tram tieh lo limg; Ceq la ndng d0 bun cat d trang thai can bang sat day; Cref Id ndng dp bim cdt sat day.
3. MO PHONG CHE DQ THUY DQNG UJC HQC 2D VtNG VEN BIEN U MINH
3.1. Mien tmh va dia hinh mien n^ien ciru , A2 1 Y(m)
Hinh 2: Ludi miin tinh 2D (87,000phdn tic tam gidcphi cdu true) Mien tinh toan Id mot phin vung biin ven bd
phia Tay cua DBSCL duge gidi hgn phia Nam, Tay va Bac giap biin Tay, phia Ddng giap DBSCL Chieu rOng trung binh miin tinh la 40 km kl tu bd va dai khoang 126 km kl td miii Cd Mau vS hudng Bde. Miin tinh duge md ta bdi 87 nghin phdn tu tam giac phi cau tnic vdi ludi Idn nhit ngoai khoi 2000 m va nhd nhit 8 m (hoac 3 m trong trudng hgp md phdng ed kit eau tudng ehan sdng dugc xay dyng) eho vung ven bd.
Hinh 3: Md phdng ke T dien hinh vung ven bd biin U Minh 3.2: Dieu ki^n bien
Bien Idng tinh toan gdm eac bi6n luu lugng di vdo mien tinh td cdc sdng rach tir dit liin ra bien vd bien hd ngodi khoi bien tay.
Myc nude Z tren bien hd tai vi tri bien long tren bien lay theo trieu thien vdn cdng thdi ky dugc liy vdi 11 sdng chinh (M2, S2, N2, K2, K l , 0 1 , Pl,Ql,M4,MS4vaMN4)tireasddii lieu TPXO cd do phan giai 1/30**. Dd thj sau trinh bay myc nude tai vi tri diln hinh tren cac bien long (hinh 4) tren bien miin tinh.
62 TAP CHfTAl NGUYEN NUOC 5(3 4-2018
nay tuong ddi nhd duge giai thich do hai nguyen nhan chinh Id sd lieu triiu thien vdn thu thap tu du lieu todn eau NOAA trong vimg biin Tay la khd phuc tgp, ed dp chinh xdc kem vd sd lieu dia hinh vimg nghien edu ehua duge cgp nhdt.
Hinh 4: Biin trieu tgi eac vi tri diin hinh AI vd A2 cua thdng 8-9/2016 Md phdng van ehuyin bun eat trong khu vye dugc xem Id bim cat rdi khdng dinh. Dit lieu vl phdn bl biin cat day dupe gid thiit Id ddng diu trong toan bp vung nghien cim. Tu cae dd lieu do dac bun edt day sdng, thdnh phin cd hat dupe chia 1dm 4 ed hgt dgi biiu 0.08mm, 0.25mm, 1.0mm, 2.0nim; vdi ti le ban diu lin lugt Id 40%, 30%, 20%, 10%.
Luu lugng tgi sdng nhanh Ong Ddc dugc tham khao so bp nhu sau:
1 °« ?
0 6 • r M .
0" jltl
0.2 Vm 0 H -0.2 0 -0.4
48
till 'w\\
V* II 9.6'
! 1 W U
!445
Observation
™ Calculation
• A ft A
iwAAiii'iiWW^
B 2 ? 4 0 ' 288 336 T(h)
Hinh 6: Muc nude quan trdc vd mo hinh tgi Ong Ddc tie 17/10/2016 din 3I/I0/20I6
— Calculation
96 144 192 240 288 336
Hinh 5: Lim luang thdng 8/2016 tai cua sdng Ong Doc 3.3. Hieu chinh mo hinh
Mo hinh dugc ilieu cliinh voi s6 lieu quan trac mifc nude t^ s6ng Ong D6c va do song ttong vung trong thoi gian tit 15/10/2016 dfa 31/10/2016 tai vj tri toa do (464620,1029689.9).
Ket qua hif u chinh muc nuoc tai song Ong D6c trinh bay tren d6 thi sau:
Chi s6 NASH danh gia tinh phii hpp gia tri quan ttjc va gia tri tinh toan khoang 0.56. Gia tri
Hinh 7: Sdng HMO tgi vi tri (464620,1029689.9) trong thdi gian 17/10/2016 dm 31/10/2016 Ket qua do thi cho thay gia tri trung binh cua song HMO giGa quan trdc va tinh toan la tuong doi phu hgp, tuy nhien cac gia tri Ion nhit va nho nhat la kha khac nhau.
360 0 ,-, 30CI,O ^ ^ , 2 « 0 Jy^
180 D 120 0 1
eoo 1 0,0 • 0
M
48
Calculatton
/•', „4r[I,\
«ikY*Tnyyi
' 1
96 144 192 Ob..m
'Nviiiii \
I'N,
•
240 288
h '
'V.
T(h) 336
Hinh 8: Hudng sdng (dd, so vdi hudng Nam) tgi vi tri A(464620,1029689.9) trong thdi gian
17/10/2016 din 31/10/2016
TAP C H l T A l N G U Y 6 N N L r ( 3 C 5(34-2018 63
• KHOA HQC CONG NGHE • Ket qud do thi cho thdy hudng sdng tgi vi tri
A (cdch bd khoang 14 km) cd hudng gan nhu di thang gdc vdo bd (270°). Ket qud nay phu hgp vdi vi tri do sdng khdng xa bd va chieu gid chinh di ve hudng Ddng trong khoang td 17/10/2016 din 26/10/2016 d-ong thdi gian nay.
Trong khi dd sd lieu quan trie eho thay hudng sdng di theo xu the ve hudng Bac vdi gid trung binh so vdi bd la 50 . Ket qua hudng sdng sau 240 gid md phdng ed gid tri dao ddng nhiiu cd the duge gidi thich do nguyen nhan sir thay ddi hudng gid trong thdi doan xem xet.
Dd thj sau ddy trinh bdy ket qud so sdnh ve bun cat la lung tgi vi tri A xem xet. Gia tri ndng dp bun cat lo Idng trung binh quan trie la 4.05 mg/l va gia tri md phdng la 4.19 mg/l. Sai sd tuong ddi la 3.45%.
Sdng khi lan truyin vdo bd sS gap kit cdu ke chu: T. Tde dyng giam eudng dp sdng eua logi ke chii T dugc trinh bay tren cdc dd thi dien hinh sau.
Hinh 10. Chieu cao sdng HMO trung binh thdng 1-2 nam 2016 giira 2 ke Tke tiep dien hinh
s.sog 5.00 i^.
^•^° i i n 4.00 fyl 3.50 v' 3.00 • 2.50
1 1 V M
Observation Calculation
K /'w^ 'V^l'^K^IlA 'TL "nil
IJL' WAI MAI 1 ^/TWiV^li7W r,^^.
« M C
one HMO T8 (m)
KhdnK cd ke
£&^1
96 144 192 240 288 336 -T(h) Hinh 9: Ndng do bun cdt la limg tdng cdng SSC (mg/l) quan trdc vd kit qud mo hinh tit
25/2/2017 din 12/3/2017 4. KET QUA
Nham nghien cihi ch6 do thu^ luc cung nhu xu the boi lang trong khu viie, mo phong dugc thvrc hi^n cho 2 mua dai bifa: miia gio mua Tay Nam va miia gio miia Dong B5c. MSi mCia dai bifa mo ph6ng dugc thuc hiSn trong 2 thang:
- Miia gio Tay - Nam dai bifa; thang 8 va 9 nam 2016
- Miia gio Bong - BSc djii bifa: thang 1 va 2 nam 2016
Ket qui mo phong s6ng
Hinh 11: Chieu cao sdng HMO trung binh thdng 1-2/2016 tgi mat cdt 2-2
Hinh 12: Chieu cao song HMO trung binh thdng 8-9 ndm 2016 tgi mat cdt 2-2 64 .TAPCHfTAlNGUYeNNl/(3CS64-2018
• C o k e T
~~~-l£U£siya2is^T
Hinh 13: Chiiu cao sdng HMO trung binh thdng 1-2/2016 tgi mat cdt 3-3
K h d n g c d kfe Cotsg.T
- Gida khoang each hai ke T (phan hd Lg), sdng van ed the lan truyen vao bd. Tuy nhien eudng dp sdng tuong ddi gidm so vdi trudng hpp khdng cd ke (xet theo mgt cdt 2-2).
- Sdng khi di qua khe khoang each gida hai ke T cd hien tupng khuleh tan theo phuong ngang (xet theo mgt cat 3-3).
Ket qua md phong biin cat
Kit qua sau day so sanh hi?n tugng bdi xdi vung gidi hgn giiia 2 ke T liSn tiep cho cae trudng hpp khdng ed ke va cd ke ehii T.
oaeo
0 3CT)
0 1B0
c a .
COBO
0 D 4 a HMO TB (m)
! .-.•',
.•' i '"••,
/ 1 \
- / 1 ''•
I r y € g i a a 2 k e T
Hinh 14: Chiiu cao sdng HMO trung binh thdng 8-9/2016 tgi mat cdt 3-3
Ktt qua tir cae d6 thi neu tren cho phep nit ra ^ ^ ^ ^^ ^^ ^^^ ^^^ ^^^ ,^;^^ ^ ^ ^^^^ ^^ ^ ^ mot so n h ^ xet sau: dungke chuT cuathdng8-9/2016
- Sdng khi lan truyen den ke ehu T gan nhu dupe ngan chgn hoan todn trSn phgm vi ehi§u rpng Ls eanh ke.
Bang 1: Can bing bdn cat vung bd cua thang 8-9/2016 Truong hop
Khong CO ke Ke chir T
Bang 2 Truong hgp
Khong CO ke Ke ehu: T
Vao (m') 454.4 1693.8 : Can bang biin
Vao (m') 780.4 2348.4
Ra(m') 12373 2003.9 eat viing bo* ciia
Ra(m') 27850.9 4370.3
(Vao-Ra), m' -11918.6
-310.1
Ghi chi (+) b6i (-) xoi thang 1-2/2016
(Vao-Ra), m' -27070.5
-2021.9
Ghichii (+) b6i (-) xoi TAP CHllAlNGUVeN NUOC S6 4-2018 65
• KHOA HQC CONG NGH? « Kit qud tir eae dd thi n^u tren eho ph6p nit ra
mdt sd nhan xet sau:
- Cd hien tupng xdi nhe tai vi tri trude ehan tudng. Hien tupng nay ed thi gidi thich bdi hien tupng bun cdt bi xdo ddng mgnh khi sdng va dap vao mat tudng va td dd gay nen hiSn tupng bim cat lo lung trong vung nay gia tdng tgo thudn Ipi eho hifn tugng xdi Id.
- Vung bd trong pham vi bdo ve eua ke chft T gin nhu khdng cd hien tupng xdi Id, ngogi tru vung hd giua hai ke cd xdi nhe. Ket qud nay cd thi giai thich song vdn cdn lan truyen td ngodi vdo bd tgi cae vi tri khoang hd nay.
- Phia sau cdnh ehii T sdng gin nhu duge ti6u tdn ndng lugng todn va ddng chay trung binh ven bd bi gidi hgn trong pham vi giua 2 ke chu T kl tilp, do do hien tugng xdi Id gidm ro rang.
5. KET LUAN
Td cdc kit qua neu tren cd the rut ra mdt sd kit luan chinh vl tae dung cua ke ehu T len hi^n tupng xdi Id ven bd bien U Minh nhu sau:
Ke ehd T vimg ven bd U Minh cd tdc dung 'bdy' bun cdt trong phgm vi gidi han bd 2 ke T lien tiep. Ket qua trinh bdy tren bang 1 vd 2 cho thiy diiu ndy.
Ke ehd T cd tde dung gidm sdng viing phia trong ke vd td do tao diSu kien thuan lgi cho hien tugng bdi lang. Khodng cdch tdi uu gida 2 ke T lien tiep cdn phdi nghien cuu them, day la bai toan xem xet hai tae dung mang tinh ngugc nhau len tae dung bdi lang ciia bun cdt trong pham vi sau ehd T. That vgy, vdi khodng each 2 ke T lien tiep edng Idn se tgo dieu kien thugn lgi eho bun cdt lo lung cd ndng dp cao di vdo phia sau ke vd cd xu the ling dpng, trong khi do tdc dung gidm sdng eua canh ke chii T lgi giam di 1dm gidm tinh ling dpng cua bun cdt la Idng vd ede tac diong se ngugc lai khi gidm khoang each 2 ke T lien tiep.
LM cam on:
- Nghien edu duge tai trg bdi Dai hpe Quoc gia Thanh phd Hd Chi Minh (DHQG-HCM) trong khudn khi D I tdi ma so C2018-20-23.
- Cdc md phdng da dupe thuc hi?n tren he thdng may tinh hi?u nang eao (HPCC), trudng Dgi hpc Bach Khoa Tp. HCM.
TAI LIEU THAM KHAO 1. PHAM Van Huin (2002). Ddng lycc hoc Biin-Phdn 3: Thuy triiu. Dgi Hpc Qude Gia Ha Npi.
2. HERVOUETJean Michel (2007).
Hydrodynamics of Free Surface Flows modelling with the finite element method.
WILEY.
3. LANG Pierre et al.
(20lO).Telemac2d manuel_utilisateur v6p0.
EDF.
4. MEISSNER Loren P. (1995). Fortran 90.
PWS Publishing Company.
5. NOAA. National Geophysical Center.
http://www.ngdc.noaa.gov/mgg/global/globaI.html.
6. OTIS Regional Tidal Solutions.
http://volkov.oce.orst.edu/tides/region.htinl.
Ngudi phdn bi^n: TS. Liru Xuan Lgc Phdn bi4n xong: \$l9l2(in
66 TAP CHf T A I NGUYEN N U O C S O 4-2018
