ITNG DUNG MO HINH THUY LUC 2 CHIEU TRONG QUY HOACH QUAN LY VUNG NGAP LU - GIAM NHE THIEN TAI
TS, TO TRUNG NGHIA', ThS. N G U Y 6 N HUY PHUDNG-,
ThS. THAI GIA KHANH'
Tdm tdt: Bao bao trinh bay ung dung eiia md binh thuy luc 2 chieu trong cdng tac quy hoach quan ly vung ngap 10 cho tinh Quang Ngai. Md hinh 2 chieu dugc thiei lap da su dung bd phdn mem SOBEK cua Delft (Ha Lan). Md hinh bao trum mdt khu vuc rdng 700km" vdi hon 600.000 dan. Nhung trinh bay tap trung vao nhung giai phap mdi trong viec thiei lap cac md hinh thuy lire dien rdng cho vung ngap 10 vdi nhieu dac tinh thuy luc quan trgng.
L Gidi thieu chung
Md hinh thuy lire 2 chieu dugc ung dung cho hai vung ngap 10 ha luu hai sdng Tra Bdng va Tra Khue thude tinh Quang Ngai. Ket qua eiia md hinh tinh toan dugc su dung trong viec lap quy hoach quan ly vOng ngap 10 ha du.
Nhiem vu eiia md hinh thuy lire la cung cap eac ban dd ngap 10, cac ban dd canh bdo nguy CO ngap 10 eOng nhu dua ra cac canh bao ddi vdi eae tdc ddng ciia quy hoach su dung ddt, cOng nhu phat trien co sd ha tdng den tinh trang ngap 10.
Viec sit dung md hinh thuy lire 2 chieu vao cdng tac quy hoach qudn ly vung ngap 10 thuc su la mdt van de mdi me. Md hinh SOBEK la mdt md hinh tien tien eOng dugc su dung ldn ddu tien d Viet Nam. Sd lieu sir dung cho md hinh ddi hdi rdt nhieu thdng sd va phai cd do chinh xac cao.
/./. Gidi thieu vung nghien edu
Qudng Ngai la mdt tinh thude vung ven bien mien Trung. Vdi dan so khoang 1,2 trieu ngudi ehu yeu sdng tap trung d vung ddng bdng ven bien nhd va hep. LO dugc hinh thanh do lugng mua ldn (do anh hudng eiia gid mua hoae dp thdp nhiet idi) tren luu vuc. Do dia hinh kha dd'c, tham phii kem do dd tdc do truyen 10 rat nhanh, 10 cd sire tan phd rat ldn. Hang nam 10 lut da gay thiet hai nang ne ve ngudi va tdi san. Khoang 600.000 ngudi bi anh hudng do ngap 10, dac biet mdt sd xa chiu muc ngap hon 3m vdi nhung tran 10 tan suat 20% va 10%.
Trong vung nghien cuu cd cac he thdng sdng chinh gdm: sdng Tra Khue. sdng Ve va sdng Tra Bdng. Tdng dien tich luu vuc lan lugt la 3.250 km', 1260 km" va 700 km'. Cac sdng chay
1, 2. 3. Vien Quy hoach Tlniy loi.
theo hudng chinh la tir Tay sang Ddng cdt qua phdn ddng bdng ha luu ven bien vdi chieu rdng tir 10 de'n 16 km.
Su kei hgp dp luc giua ngheo ddi va thien tai hang nam la bao 10 thuc su la mdt trd ngai rat ldn de'n sir phat trien cua vung nay. Trong 5 nam tir nam 1996 den nam 2000, tong thiet hai vugt qua 120 trieu USD. Nhung ngudi ndng dan ngheo thudng la nhung ddi tugng chiu tac ddng nang ne nhat ciia thien tai.
1.2. Gidi han cua md hinh
Vung ngap 10 ciia sdng Tra Khue vd sdng Ve dugc ndi vdi nhau bdi mdt he thdng sdng rach phiic tap. Tdng dien tieh bi anh hudng do 10 khoang 350 kml
Vung ddng bdng ha du sdng Tra Bdng ndm each thi xa Quang Ngai 20 km ve phia Bdc, day la he thdng sdng dgc lap. dien tieh bi anh hudng bdi 10 hang nam la 75 kml
Hien tugng ngap 10 trong ea hai he thdng sdng deu bi tac ddng rat ldn tir hai he thdng dudng sdt va dudng bd. Them vao dd he thdng edu va cdng qua dudng ddnh cho thoat 10 cdn thie'u va chua du do ldn,-cac cdng trinh xay dung bam dgc theo cac con Id cOng lam can trd thoat 10, ldm cho muc nudc 10 dang cao.
Mdt yeu td khac cOng dnh hudng den qua trinh thoat 10 dd la he thdng kenh tudi noi, he thdng de bdo ve cho khu dd thi va viec nudi trdng thuy san vung cira sdng cung tham gia vao qua trinh ngap 10 trong cac luu vuc.
Hinh L Gidi han md hinh sdng Tra Khiic va sdng Tra Bdng
Cung vdi sir phat trien cua ca nudc, trong nhung nam gan day Quang Ngai cOng ed nhung bude phat trie'n manh ve kinh te, viec phat trien tap trung nhieu d vung ddng bdng ha du, chinh vi vay da ed nhieu khu cdng nghiep da va dang dugc hinh thanh, kem theo nd la he thdng co sd ha tang: dudng sa, khu dd thi mdi, he thdng de bao ve... dugc hinh thanh. Viec lua chgn mo hinh thuy ddng luc hgc 2 chieu la mdt su lira chgn thich hgp nhat de md phdng dugc qua trinh lu tu nhien cOng nhu md phdng dugc eae phuong an phat trien trong luu vuc.
1.3. Thiei lap mo hinh 1.3.1. Md hinh thuy life
Su lua chgn md hinh thuy luc dugc danh gia bdng nhieu tieu ehi nhu: Gia ca, do on dinh,
tdc do tinh toan, khd nang md rdng..., sau khi can nhdc bd sdn pham md hinh SOBEK da dugc lira chgn. SOBEK la mdt phdn mem md hinh boa cd the tinh toan kei hgp so dd tinh 2 chieu kei hgp vdi 1 chieu va qua trinh mua tren luu vuc. Toan bd cac thao tac vdi md hinh dugc thdng qua giao dien GIS rdt than thien vdi ngudi su dung.
Sd lieu chinh cho md hinh bao gdm: sd lieu thuy van (muc nudc va luu lugng tai eac bien), sd lieu dia hinh (md hinh cao do sd DEM). Sd lieu ve do nhdm.
Kei qua ciia md binh se la muc nudc, luu lugng va van tdc ddng chay tai tirng diem theo thdi gian.
1.3.2. Thiei lap md hinh
Tai lieu dia hinh dung de thiei lap md hinh cao do sd DEM dugc lay tir nhieu ngudn. Mdt ngudn chinh la tir binh dd khu tudi cua dap Thach Nham. Tdng sd diem dia hinh thu thap dugc khoang 30.000 diem. Mat do eae diem ldn lugt la 40 va 51 diem tren 1 km' d luu vuc Tra Khue vaTra Bdng.
Mdt trd ngai trong qua trinh xu ly dia hinh dd la tai lieu dugc do dac trong nhieu he toa do (he toa do HN72, VN2000, he toa do gia dinh...) va cao do khdc nhau (he HN72, he cao do Thach Nham, gia dinh...). Cac sd lieu da dugc xir ly va chuyen ve he cao do va toa do qud'c gia (VN2000).
Sd lieu ve do nham dugc thiei lap dua tren ban dd hien trang va phuong hudng sir dung dat cua tinh Quang Ngai. Cac loai ddt khac nhau nhu: ddt trdng lua, ddt rirng, khu dan cu, khu cdng nghiep... dugc gan eae gia trj do nham n khac nhau va dugc chuyen thanh sd lieu dOng cho md hinh thdng qua Vertical Mapper^"^^ va Maplnfo.
Sd lieu thuy van dung cho md hinh dugc tinh toan true tiep tir mua thdng qua md hinh mua ddng chay va tir cac so lieu thuc do ciia cac tram thuy van cd tren luu vuc.
Cac sd lieu dia hinh gdm toa do va cao do cua cac diem dia hinh dugc xir ly bdng phdn mem Surfer®, Vertical Mapper^"^ va Maplnfo®. Ngoai ra khoang hon mdt chuc phdn mem do nhdm chuyen gia thuy luc phat trien dung de' xir ly tai lieu dia hinh.
1.3.3. Hieu chinh ind hinh
Md hinh thuy lire Ifl cho hai luu vuc sdng Trd Bdng va Trd Khue dugc kiem dinh bdng tran 10 thang 11 nam 1999. Cac tai lieu ve muc nudc 10 dugc thu thap tir 32 edt bao 10 dugc xay dung tren luu vuc va 583 diem dugc khao sat ngay sau khi tran 10 xdy ra.
Tai lieu ve ddng ehdy sir dung trong md hinh dugc tinh toan true tiep tir tai lieu mua, dugc kie'm dinh vdi tdi lieu thuc do trong eac tram do thude hai luu vuc Tra Bdng va Tra Khue.
Luu lugng dinh 10 cua tran 10 1999 ldn lugt la 10.700 mVs, 2.600 mVs va 1.900 mVs tai sdng Tra Khue, sdng Ve va sdng Tra Bdng.
1.4. Cdc phuong dn tinh todn
Rat nhieu phuong an tinh toan dugc dua vao trong md hinh. Cac tran 10 cd tan sudt 1%, 5%, 10% va 20% dugc dua vao tinh cho cac phuong an. Cac phuong an phat trie'n khac nhau cOng duac md phdng: Cac khu cdng nghiep, san lap vOng ngap 10 de xay dung khu dd thi mdi,
xay dung eac tuyen dudng, de, ke, cang neo tru tau thuyen...
Kei qud tinh toan dugc the hien bdng cde ban dd: ban dd do ngap sau, ban dd canh bao vung nguy hiem (van tdc ddng chay x do sau), ban dd van tdc ddng chay...
Hinh 2. Ban dd ngap lu sdng Tra Khiic va sdng Ve
Hinh 3. Ban dd ngap lu sdng Tra Bong
2. Ket luan va kien nghi
Md hinh thuy lire hai chieu thuc sir la mdt cdng cu huu ich trong cdng tdc quy hoach phdng chd'ng 10, giam nhe thien tai. Pham vi irng dung cua md hinh rai ldn: tdi dinh cu, quy hoach ha tdng, quy hoach phdng chd'ng 10...
De dp dung md hinh 2 chieu trong dieu kien nude ta ddi hdi phai xir ly so lieu ddu vao rai phuc tap, dac biet la tai lieu dia hinh (yeu td quan trgng nhat trong md hinh) bdi sir thieu ddng bd va thieu ca do dac. Vi vay cac tien ich dugc lap trinh de xir ly tdi lieu dia hinh da ddng gop rdt nhieu vao thdnh cdng cua md binh. Cac tien ich ndy cdn cd the' dugc u'ng dung cho cac luu vuc khac.
Thiei lap md hinh 2 chieu ton kem ban nhieu so vdi md hinh 1 chieu, tuy nhien nd lai cho nhung kei qua ma md hinh 1 chieu khdng the cd dugc, giup ich rat nhieu cho cdng tac quy hoach ndi chung va quy hoach 10 ndi rieng, giam thdi gian vd chi phi cho cde hoat ddng danh gia tac ddng cua quy hoach. Mgi boat ddng lam thay ddi hinh thai ciia luu vuc deu cd the m6 phdng tren md hinh 2 chieu da dugc lap, va kei qua kiem tra tren md hinh dugc dua ra rat nhanh, hd trg viec ra quyet dinh cua nhd qudn ly...
Tu kei qua cua md hinh eac ban dd: ban dd ngap lu, ban dd do sau ngap, ban dd phan bd van tdc. hudng thoat 10 va ban dd mu'c do nguy hiem... dugc dua ra phuc vu dugc cho nhieu linh vuc va nhieu nganh khac nhau.
Trong qua trinh sir dung md hinh, hang loat cde phdn mem hd trg da dugc ap dung. Cdng nghe GIS dugc su dung mdt each tdi da. Day la cde cdng cu khdng the thieu khi xay dung mo hinh thuy lire hai chieu. Cdng nghe GIS phdt trien da giup nang cao chat lugng cua cac dd an quy hoach.
Kien nghi
De sir dung tai lieu dia hinh ddng bd va cho nhieu muc dich. cac du an cd do dac binh dd cdn sir dung he toa do qud'c gia (VN2000) thay vi cd du an vdn dung he toa do gid dinh hoae he toaddcQ(HN72).
Ngoai viec tinh toan nghien cun ddng ehdy trong mdt khu vuc nhd (mdt doan sdng de danh gid xdi Id) vdi d ludi tinh todn nhd (Im hay nhd hon), SOBEK cdn dugc sir dung lap md hinh 2 chieu vdi ty le ldn (mdt luu vuc). Dac biet rat thich hgp khi ap dung tinh toan bai toan thuy lire ngap 10 cho cac vung thude mien Trung va ddng bdng sdng Cim Long, noi ma he thdng de hau nhu khdng cd, nude 10 ehdy tran tren mdt dien rdng.
Viec kiem dinh md hinh 2 chieu rat phiic tap (rat nhieu so vdi 1 chieu) vi vay can sir dung mdt phan mem cho phep tu ddng hoa kiem dinh md hinh trong giai doan tinh toan ban ddu. Hien nay da cd mdt sd phdn mem nhu vay. Trong thdi gian tdi khi ap dung SOBEK cdn phai nghien cuu va irng dung viec kiem dinh ndi tren.
TAI LIEU THAM KHAO
[1] I.E. Wood, S.E. Murphy, N.H. Phuong: Disaster Mitigation in Central Vietnam:
Application of Two-dimensional Hydraulic Models, 8"' National Conference on Hydraulics in Water Engineering, Brisbance, Australia (2004):
[2] Doberty, J. (2002): PEST Model-Independent Parameter Estimation, Watermark Numerical Computing, 279p.
[3] Maplnfo Professional Version 7.0 User's Guide, Maplnfo Corporation, 2002, Troy, New York, 759p. Surfer Version 8 User's Guide, Golden Software Inc. 2002. Golden, Colorado, 640p. Vertical Mapper User Guide, Northwood Technologies Inc. and Marconi Mobile Ltd, 2001, Canada, 243p.
Summary
The paper describes the application of two-dimensional hydraulic models as part of a floodplain management planning process for Quang Ngai Province. Two hydraulic models were developed using SOBEK from DelftlHydraulies. These covered a total area of over 700km- containing a population of over 600.000 people. Discussion focuses on the innovative solutions applied to the challenges of developing large-scale models on a floodplain containing many features of hydraulic significance.