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^ T i N H T O A N T R U O N G D O N G L U C VA VAN C H U Y E N BUIV C A T
^ P H U C VU T H I E T KE K E B A O VE B O B I E N XA T A N T H U A N , H A M T H U A N N A M , B I N H T H U A N
Vu Thanh Ca, Lc Due Dung, Vu Thi Thuy
Vien Nghien cim quan ly biin va hai dao, Tdng cue Bien va I lai dao Viet Nam Email: cavuthanh®!!mail.com
Tom tat:
Trong nhirng nam gdn ddy hien tuang xdi Id xdy ra a khu vice xd Tan Thugn- Hcim Tlnidn Nam- Binh Thuan rit die ddi gdy nhieu thiet hat kinh le- xa hot va kim anh hudng ldn din ddi sing ngudi ddn. Dimg trudc linh hinh xdi la ngay edng cd xu hudng Idng cd vi quy md ldn cuang do, huyen Ham Thudn Nam quyit dinh xdy dung he thing cong Irinh bien de bdo ve bd xd Tdn Thudn. Vice dua ra phuang dn Ihiil ki hap ly phu thugc vdo ril nhieu yeu Id irong do cdc yiu li irudng dgng luc vd xu hudng van chuyin biin cdl Id cdc yeu Id quan
trong nhil. Bdi bdo ndy trinh bay cdc kit qua linh lodn truang diing iicc va xu • Ihi van chuyin biin cdl bdng md hinh si Iri lam ca sa cho cdc nhd Ihiil ke dua 1 ra duac phuang dn lii mi vira dam bdo an todn vira till kiem ve kinh phi
COMPUTATION OF HYDRODYNAMIC AND SEDIMENTARY PARAMETERS FOR DESIGN THE SHORE LINE PROTECTION JETTY IN TAN THUAN COMMUNE,
HAM THUAN NAM, BINH THUAN PROVINCE Abstract:
In recent years, serious coastal erosion occurred in Tan Thuan beach. Ham Thuan Nam, Binh Thuan, cgusing large socio-economic damages and influence normal life of local inhabitant. Facing Ihe situation of increasing coastal erosion, Ihe Ham Thuan Nam district authority decided to build sea wgll to protect the coastline. The optimum design of the revetment requires information on many processes, among them the most important ones are coastal dynamic and sediment transport processes. This report presents results of Ihe calculation on these processes by numerical models and provides technological bases for proposing such optimum design of Ihe revetment.
I. TONG QUAN VE KHU VlTC NGHIEN ClTU
Tan Thuan la xa mien nui, bai ngang ven bien thugc dien khd khan cua huyen Han Thuan Nam vdi tdng dien tich tu nhien la 6577,5ha, nim phia Tay Nam ciia huy?n Hat Thuan Nam each trung tam huyen 13 km ve phia Nam, xa cd vj tri:
F Tic'u ban Nang linrng. Kv ihudi cdng irinh. Van idi vd Cdng nghe Bien
- Phia Bdc giap xa Tan Lap, thj trin Thuan Nam va xa Ham Minh;
- Phia Nam giap bien Dong;
- Phia Dong giap xa Thuan Quy va Tan Thanh;
- Phia Tay va Tay Nam giap thi xa Lagi va huyen Ham Tan.
Viing bai bien iren dia phan xa Tan Thuan rgng khoang 750ha, ihdi gian gan day linh hinh xoi lo bd bicn khu vue nay kha nghiem trgng vdi cudng dd ngay cang tang. Nhirng thang cuoi nam 2008 dac biet la cac thang dau nam 2009 su xam thuc dien ra kha manh me. nhieu noi bd bien bi xam thue vdi chieu rgng khoang 50m uy hiep true lilp din khu dan cu, dong mudi, khu nudi torn. Diing trudc linh hinh xoi Id ngay cang xay ra dO dgi va CO xu hudng tang ca ve quy mo lan cudng dp, huyen Ham Thuan Nam quyet djnh xay dung eong trinh bao ve bd bien xa Tan Thuan. Viec tim ra duge nguyen nhan xoi lir do lira chon dugc loai eong trinh phii hgp la van de dang dugc quan tam.
II. MO HINH SO TRI TINH TOAN TRlTONG D Q N G LlTC VA VAN CHUYEN BUN CAT
1. Cg sd ly thuyet mo hinh tinh toan trui song)
ing dong chay (gom dor He phuong trinh vi phan cho cho dong chay duge viet nhu
Phuong trinh lien tuc:
He phuang trinh chuyen dgng:
S(i.t 1 9((iV dl dx[d ^
^ f a \ 5 ^^v
dq, ^ d (q,q.
dl ^ dxy d
dyy" dy ) ) dy{ d
gn'u^lu'
"" d'"
Ad_U ) Sy[d
gn^v-^u^
"" d"' dq, 3?,
dx dy
••Y'^'i-
+"' -cu
yi'
*"' -CV.
dij dl
- / ? ,
,V^
= 0
S5„
* dx
l-i-K
dy
l+K
rsau:
dS„
+ — ^ - dy
= 0 + dS„
dx
= 0 dx\
dxy
ig chay gio va
dq,\
' dx J
" dx J
"" Trong do q.,, qy tuong ling la luu lugng ddng chay tren 1 don vi chieu rdng, tinh tit day len din mat va tuang img vudng gdc vdi cac true x, y; tj - dao ddng muc nude so vdi muc chuin; I - thoi gian; d - dd sau; g - gia tdc trgng trudng; n - do nham thuy luc; U„ , V„ -
lie)I light Khoa hoc vd Cdng nghe Bien todn cjud^J^lL. "' i^
cac Ihanh phin van loc gid theo Iruc x va y. va C, - he sd ma sat gid: S^,. S„, S>,. va S„ jj cac ihanh phan img suat biic xa ciia sdng-
rhco so lieu ihirc nghicni. he sd ma sal gid cd Ihay ddi trong khoang Idii Iif ^^^. '•i^^n 5x10'' \'.i la ham phu ihuoc vao tdc do gid. Garral (1977), idng hgp rai nhicu kcl quj imliicn cull \i3 he sd nia sal gid Iren ciic dai duang va cho rang ddi vdi van tdc gid nam, trong khoang 4<U<2I ni/s Ihi Cm cd the dugc xap xi bang ham mu nhu sau'
C,„=0.5lxlO'V,"' 2. Ly thu>ct md hinh tinh loan van chuyen biin cat 2.1 Phirong trinh vein chuyen bun cat
Ddng viin chuyen bim cat dual tac dgng ciia ddng chay dugc md ta bang phuong trinh san
a c diiC duC d ( dC) d( dC\ „
— + + = — K, — + — \ K , — + S dl dx dy dx \ i^x) dy\ dy J
Trong dd C la ndng do tich phan Iheo phuong thang dung tir mat den day ciia phii sa;
K, la he sd phan tan (bao gdm ca he sd khuyech tan rdi va he so phan tan) cua phli sa In IUIIB;_.S; la ngudn biin do xdi mdn day dua len hoac ijng dgng xudng day va dugc bilu Ihj qua tdc do lang dgng ciia pliii sa C, va tdc dp khuay len lit day ciia phii sa da ijng dong ('„.
2.2 Van chiiySn bun cat tho (la lung)
Van chuyen bun cat thd lo limg dugc tinh bSng each gia thiit ring cd the ap dung mo hinh van chuyln cat thd Ihco cdng thire cua Schultz (2003). Theo dd, ddng van chuyln cat tho dugc xac djnh theo phuong phap ham mu.
C„=i,K*'
_ Trong dd: k, va k^ la cac he sd hieu chinh va V la van tdc ddng chay trung binh theo do sau tai vi Iri nghien ciru.
2.3 Van chuyin bim cat di day:
Van chuyln biin cat di day dugc tinh theo Van Rijn (1984).
2.4 Biin doi dia hinh day:
_ Su biin ddi cua day kenh dugc tinh toan bang each giai phuang trinh vi phan dao ham rieng ve su can bang bun cat, cd tinh den bim cat lo liing va bun cat di day.
P ' Tiiu ban Nang lu-rnig. Ky thual cong Irinh, Van Idi va Cong nghe Bien
\
III. KET QUA TINH TOANf 1. Kit qua tinh loan truofng dong chay
K-..-
_L_j|"'"
200 4 0 0
1 Hinh 1: Trudng dong chdy trong gio miia Hinh 2: Trucmg ddng chdy trong gid miia Dong Bdc
2 Ket qua tinh to^n van chuyen bun cat
Tdy Nam
Hinh 3: Van chuyen biin cat trong thdi ky gid Hinh 4: Van chuyen biin cat day trong bao miia Dong Bdc
Kk qua tinh toan boi xdi tai mdt sd mat cat dai dien trong thdi ky gid mua Ddng B4C va trong bao:
lich nghi Khoa Imc vd Cdng nghe Bien lociiull«£„
Diin hiin mgl cdl ngang Irong thai ky gid
miia Ddng Bdc Diin biin mdt cdl ngang Irong
Hinh 5 Diin hiin bdi xdi Igi mdt sd mat cdl dgi dien trong Ihdi ky gio miia Ddng Bac vd Irong bdo
Trong Ihdi ky gid miia Ddng Bac trudng ddng chay khu vuc cd hudng Ddng Bac -lay Nam, miia nay trudng sdng tuong ddi ldn va chu yeu la sdng ngan cd nang lugng va do ddc Idn. Day chinh la loai sdng gay van chuyen bim cat ra xa bg va gay xdi Id manh ttong miia gid Ddng Bac. Theo linh loan chieu sau xdi Idn nhat len den 1,94m.
Trong dieu kien bao dudi tac dung ciia sdng ldn va ddng chay lam cho van truydn biin cat trong bao chu yeu la ngang bd (xdi cap tinh), lire la bun cat 6 chan cdng trinh dugc van chuyen ra ngoai gay bdi lang phia ngoai. Xdi Id d chan cdng trinh do van chuyen bun cat ngang bd cd kha nang lam cdng trinh hu hdng neu do sau xdi ldn hon do sau chan
khay.Theo tinh toan ehieu sau xdi ldn nhat len din 2,2m. | Nhu vay trong qua trinh thiet ke can phai chu trgng kit cdu va chilu sau bao ve chan
cdng Irinh sao cho chieu sau bao ve chan cdng trinh it nhat phai ldn hon chilu sau ho xoi Idn nhat lite la Idn hon 2,2 m theo nhu tinh loan d tren.
IV. KET LUAN
Viec tinh loan va md phdng duge trudng ddng luc, van chuyln biin cat ciing nhu diei bien dudng bd cua khu vuc Irong qua trinh lua chgn phuang an thill kl la rdt quan ttong no giup nha Ihiel ke cung nhu nha quan ly cd dugc co sd khoa hgc de tinh loan cac thonj sd thiet ke cdng trinh. Tit cac phuang an tinh toan trudng ddng chay, truong sdng va xu tli
Ticu han Ndng hiring. Ky ihudt cdng trinh, Vdn lai vd Cdng nghe Bien
van chuyen biin cat se cd dugc cac thong so song tai chan cong trinh. chieu sau xoi lai chan cong trinh tir do co duge phuang an thiet kl hgp ly vua dam bao cong trinh dirge an loan vira tiet kiem ve kinh phi xay dung.
Dua vao ket qua mo phdng thi nguyen nhan chinh gay xoi d khu vuc xa Tan Thuan la do su mat can bdng Irong qua trinh van chuyen bim cat. vao miia gio Dong B5c song tac dung vao khu vuc chii yeu la song ngan va co do cao ldn do do khi Ian truyen vao bd song lam xao trdn biin cat day ldn mang bim eat lir bd ra phia ngoai, lugng biin cat nay dudi tac dung ciia dong chay Dong Bac - Tay Nam mang biin cat tir khu vuc xu6ng phia dudi gay thi6u hut biin cat. Nhu vay trong miia gio Dong Bae khu vuc cd xu the xoi dpc biet xoi manh khi co gio miia Dong Bac Idn.
De khac phuc dugc cac van de xoi Id dang dicn ra hicn nay chiing toi kiln nghi mot sd giai phap sau:
- Co the xay dung he Ihong dc bien va ke lat mai de bao ve khu vuc phia trong. tuy nhien phuang an nay chi giai quylt dugc xoi trudc mat vi he thong dc biin va kc ehi ngan chan dugc xoi Id khong lan sau vao dat lien nhung lai lam gia tang xoi tai chan de d5n din mat on dinh chan dc. Vi the can chu y neu xay dung he thdng dc bien thi can phai Ihudng xuyen duy tu bao dudng dae biet la trong thdi ky gid miia va trudc khi co bao.
Van chuyen biin cat gan bd chii yeu la do song gay ra vi the can phai giam chieu cao song dc khi song vao chan cong trinh cang nho cang tot. Dc lam dugc van de nay ta eo the xay dung mgt he thong cac dc pha song phia ngoai khoi, xay dung phia ngoai vimg song vo la tot nhat.
- Co llie xay dung he thdng eac dap mo ban dgc khu vuc bao ve, he thong mo han eo tac dung hudng ddng dac biet trong dieu kien gio miia cac ke md han se hudng dong chay ra phia ngoai va gay boi lang biin cat phia trudc ciia ke mo han. Tuy vay, vi dap md han gay xoi phia ha luu dap, can tinh toan thiet ke can than de giam thieu hieu ung nay.
TAI LIEU THAM KHAO
1. Garrat, J.R. (1977) Review of drag coefficients over oceans and continents. Monthly Weather Review, 105, 915-929.
2. Mase H., Takayama T., Kunitomi S. and Mishima T.{1998) Multi-directional spectral wave transformation model including diffraction effect. J. Hydraul. Eng., JSCE, 1-11.
3. Schultz, CL. 2003. Calibration of the TAM/WASP sediment transport model - Final Report. Interstate Commission on the Potomac River Basin, Rockville, Maryland, October 2001, Revised April 2003, ICPRB Report No. 03-01.
4. Van Rijn, L. C. (1984) Sediment transport, part I: bed load transport.' J. Hydraul. Eng., 110-101,1431-1456.
5. Wei Y., K.F. Cheung, G.D. Kurtis, and C.S. McCreery (2003) Inverse algorithm for tsunami forecast. Journal of Waterway, Port, Coastal, and Ocean Engineering, Vol. 129, No. 2, 60-69.
6. Cdng thuc thuy luc (2000). Hdi ky su cong chinh Nhat (Tieng Nhat).
