KHOA HOC
DANH GIA BIEN DQNG LONG DAN VA DONG CHAY TAI KHU VjTC S6NGVUGIA-QUANGHUE SAU KHI XAY DUNG C 6 N G TRINH CHINH TRI
ThS. Nguyen Ngpc Ding PGS.TS Nguyin Ngpc Qu^-nh
PGS.TS Tran Xuan Thai Phdng Thi nghi$m Trgng diim qudc gia vi Dgng life hgc sdng bien
Tom tat: Dua tren viec phdn tich diin biin long ddn khu vuc sdng Qudng Hui tic sau khi thuc hien du dn chinh tri sdng Qudng Hui cho din nay. bdi bdo da trinh bdy ket qud nghien cieu vi ldc ddng cua qud trinh diin biin ndy din viec ldm gia tdng ty le phdn luu luong tic spng Vu Gia sang sdng Thu Bin. Kit qud nghien cieu ndy da khing dinh nguyen nhdn chinh ddn den hien tuang thiiu hgt luong nudc trong miia kill a hg du sdng i^u Gia trong dd co thdnh phd Dd Ndng.
Summary: Basedon the analysis of changes in Quang Hue river bedsince the implementation of Quang Hue river training project so far, the paper has presented research findings an the impact of this river bed change process to increase the flow rate distribution to the Thu Bon river. Results of this study confirmed the main cause leading to water shortages in the dry season in the Vu Gia river downstream including Danang city.
MO DAU
Hien tuong cdt dong a ha du cac song Vu Gia - Thu B6n xay ra trong lu nam 1999 da tao nen song Quang Hue mai va lam suy thoai, b6i lap doan song Quang Hue cii la con song n6i tir song Vu Gia sang song Thu Bon (hinh 1).
Bien dpng nay da lam cho dong chay s6ng Vu Gia don vao song Thu Bon, gia tang ng^p lut viing h£i du s6ng Thu Bon trong miia lfl, ding thoi lam tang luu lugmg phan tit song Vu Gia qua song Quang Hue moi sang song Thu B6n trong miia kho, din den vimg ha du song Vu Gia trong do co Thanh phi Da Ning bi thiiu nuac nghiem trpng [1].
Truoc tinh hinh tten, nam 2002, "Chinh tri song Qudng Hui" da bat diu dupc thitc hien, din nam 2010, cac hang myc chlnh cua dij an da hoan thanh. Cac hang muc nay da phat huy hipu qua, dpt duoc muc tieu chinh dpt ra la: 6n dinh khu vvic s6ng Vu Gia - Quang Hui ching tai phat smh cua song mod. Cong tttoh da diiu hoa dupc dong chay cua s6ng Vu Gia va Thu Bin gSn nhu trang thai tu nhien truac klii cSt dong.
Tuy nhien, tir khi du an chinh tri s6ng Quang Hue duac trien ichai den nay da co rat nhieu van de phat sinh tren luu vuc song Vu Gia - Thu Bon khong con giong thoi diem lap du an.
Nhieu cong trinh thuy dien duge xay dung a thupng luu, viec van hanh ciia chiing da anh hudng toi can bing nuac noi chung, nhjt la vao miia kiet. d ha du song Vu Gia - Thu Bin su phat triSn kinh te xa hpi trong do co thanh pho Da Nang vdi quy m6 lon d§n den yen cau dimg nuac tang cao. [ 3,4 ]
Dac biet, khi song Quang Hui mod da dupc lap lai bing he thing cac dpp ngan thi biin dpng long dan song Quang Hui cii da diin ra rat manh liet, long song bi xoi sau, ma rpng, lam cho ty le phan luu tir song Vu Gia qua song Quang Hui cu vao song Thu Bin tang hon so vdi giai doan trudc nam 1999. Hi$n nay, vao miia kiet, d ha du song Vu Gia, dJc bipt la thanh phi Da Ning, luong nudc thiiu nhieu hon, thdi gian thiiu nudc dai han anh hudng rdt ldn tdi dan sinh kinh t i xa hpi viing hp du.
Ngir&iplian bifn: PGS. TS Ll yUn Nglij
86 TAP CHl KHOA HOC VA C O N G NGHE THCIY L<?I SO 16 - 2013
I KHOA HOC~
'„''•^'^.
Hinh 1: Phgm vi khu vuc nghien cihi - khu vuc sdng Qudng Hue noi lic song Vu Gia sang Thu Bon
I. DANH GIA H I | U QUA CHINH TRI SONG VU GIA - QUANG HUE DA THVC HIjN 1.1 Cac h^ng muc c5ng trinh chinh tri da hoan thanh den nam 2011 (hinh 2) 1.1.1 Tren song Quang Hue mdi [2j - Dap dap chdn d ngay cijca vao cd eao trinh dinh + 7,5 (ngang bai ben)
- Dap 2 dpp khda d doan song sau cira vao - Dap 1 dap khoa cira ra vdi cao ttinh dinh+6,5m;
- Ke bd dopn song tai khu vuc cua ra noi tiep vdi doan sdng Quang Hui cii, dai 750m, cao trinh dinh ke +6,5m;
1.1.2 Tren song Vu Gia d doan cira vao song Quang Hui mdi [2]
- Ke bao vp phia bd phai dopn cda vao song Quang Hui mdi dai 1300m bam theo tuyin d^p cira vao sdng Quang Hue mdi cd cao trinh
dinh ke +7,5m.
- Xay dung he thing cac md han bd phai tai khu vuc ciia vao song Quang Hue mdi vdi so lupng va hinh thirc ket cau nhu sau (xem hinh 2) + 3 md han dpng dao chiiu hoan luu tit V3 den V5
+ 1 md han hudng ddng V2 (thupng Iuu mo hanV3)
+ 3 md han chit T (hp luu md ban V5) 1.1.3 Tren sdng Quang Hui cu [2]
Til cira vao song Quang Hui cu (thon 7 - xS Dai Cudng) tdi hpp luu vdi Quang Hui mdi (thon Thanh Vdn - xa Dai Cudng) dupc npo vet ldng dan di giam siic ep dong ehay lfl ddi vdi cac cong trinh tren song Quang Hue mdi, cao trinh day nao vet +3m d doan cua vao va +l,7m d doan ciia ra, chieu rpng nao vet 15m.
TAP CHl KHOA HOC VA CONG NGHE THCIY LOI SO 16 - 2013 67
MAT B A N G B 6 TRi T I S N G T H ^ C O N G T R I N H
Hinh 2: Mat bdng hd tri tdng thi cdng trinh chinh trj sdng Quang Hue
1.2 Hieu qua cac cong trinh [5]
- Tren song Quang Hui mdi: viec xay dung dap chdn d cila vao va cac dap khda tren sdng Quing Hue mdi da lam luu lupng lu cua hai song Vu Gia va Thu Bin dupc dieu hda gdn nhu trpng thai tu nhien. Cac cong trinh dap chan ddng cira Quang Hue mdi va cac dap khoa in dinh phat huy tac dung gay bdi ldp ddn long song Quang Hue mdi sau mdi miia lu - He thing 7 md ban tten sdng Vu Gia da phat huy tac dung lam giam tac ddng bat Ipd do chii luu sdng Vu Gia hudng vao bd 16m khu vuc cua vao Quang Hue mdi, hd tta tdt cho viec chdng tai phat sinh cira song mdi.
Tren song Quang Hue cu: viee nao vet da khdi phue lai long din va dua lai mpt phan lim lupng lfl tir song Vu Gia sang song Thu Bdn qua song Quang Hue cfl
II. TINH HINH SONG QUANG HUE CU SAU Km THl/C HlfN DU AN CHINH TRI SONG QUANG mit (GIAI DO.«iN 2002 - 2010) Tir nam 2000 tdi nam 2007 do luu lupng nudc don do vao sdng Quang Hue mdi nen sdng Quang Hui cu bi boi lap dan, ddng chay miia
kiet hdu nhu khdng cdn. Ldng sdng bdi cao tdi cao trinh +3m + 4m. Ndu di nguyen tinh ttpng bii ldp tren sdng Quang Hui cu nhu vay, lu khdng thoat qua sdng Quang Hui cfl dupc ma s5 chuyin hdu hit sang sdng Quang Hue mdi gay mdt an toan cho cdng frinh dang xay dimg. Vi vpy da thuc hipn nao vet tao ludng mdi tten song Quang Hue cu di ho trp chuyen mdt phdn ddng chay lu tit Vu Gia sang Thu Bdn. Cao trinh nao vet xudng den +2m tten chiiu dai khoang gan 2 km. Tpi thdi diem do, vipc nao vet la can thiet
Tuy nhien, khdng lau sau khi thuc hien du an chinh tri sdng Vu Gia va Quang Hue mdi,, tren khu vuc sdng Vu Gia - Quang Hue cu da xay ra cac bien dpng ldn ve ehe dp thuy dpng l\rc gdy xdi Id mat dn dinh long dan sdng Quang Hue cu va thay ddi ty le phSn ciiia luu luong tir Vu Gia qua sdng Quang, dac biet la vi miia kiet theo hudng bat lai ddi vdi nhu cdu sii dung nudc d ha du sdng Vu Gia
2.1 Dien bien dia hinh, long dan trSn sdng Quang Hue cfl [5]
2.1.1 Dien bien tten mat bSng doan sdng Vu Gia tai ciia vao sdng Quang Hui cu
88 TAP CHl KHOA HOC VA C O N G NGHE THOY LOI SO 16 - 2013
KHOA HOC CONG NGHE - d dogn cira vdo sdng Qudng Hue cU: khu
vyc nay cd nhifiu bien ddng so vdi khi chua xay dyng cdng trinh chinh tri. Tgi day, giai doan trudc nam 2008 ciia vao bfin bd hihx sdng Quang Hufi bi bdi lap nghiem trpng, mdt bai boi hinh thanh md rdng keo dai an ngii gin hfit ciia vao. Cao trinh bai dgt tdi +5,5m, chieu rpng tdi 150m. Hi?n nay bai nay khdng cdn nua, cao trinh ha thSp xudng +2m . Cira vao sdng Quang Hue md rdng va xudi thuan cho
ddng chay vao sdng Quang Hue . Gdc phan luu ciia vao sdng Quang Hufi cu giai doan trudc 2008 la a = 90^ dfin nay cdn a = 30° - 40° (xem hinh 3,4)
- Trong khi do d khu vuc hg luu cira sdng Qudng Hui cU hinh thanh mot bSi bdi ldn, trudc nam 2008 khdng cd bai bdi nay. Bai bdi cd cao trinh +5m-^ +6m, lin ra giiia sdng va keo dai can trd hogt ddng cua tram bom Ai NghTa (xem hinh 4)
Hinh 3: Cua vdo song Qudng Hui cd -2007 Hinh 4: Cua vdo sdng Qudng Hue cd - 2012 l.l.l Difin bifin ldng dan sdng Quang Hufi cu
Tu sd Ii?u thu duoc qua he thdng quan trdc mat cat ngang sdng Quang Hufi cii da so sanh difin bifin ldng dSn sdng Quang Hufi vao cac thdi difim 2006-2007 (trudc khi ngo vet sdng Quang Hue cii), nam 2008 (ngo vet sdng Quang Hufi cu) va hien tgi (nam 2012)
Trfin hau het cac mat cat ngang, xdi Id xay ra ca theo chifiu sau va chifiu ngang. Xdi sau dien ra manh me trfin doan sdng dai 3100 m, tinh tir cira vao sdng Quang Hufi cii tdi vj tri sdng Quang Hufi cat vao. CJ dogn sdng nay nay toan bo long dan sdng dfiu bi xdi sau va md rgng (hinh 5). Trfin mgt cat doc thfi hifin ro ha thap ldng sdng Quang Hufi (xem hinh 6)
tru'dc nam 2007 nao vet nam 2008 nam 2012
Hinh 6: Diin bien long ddn theo chiiu doc song Quang Hue cu
TAP CHl KHOA HOC VA C O N G NGHE T H G Y LOI SO 16 - 2013 89
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ldng sdng tgi MC cdch cua vdo 1600 m ldng sdng tgi MC cdch cua vdo 2400 n Hinh 5: Dien bien tgi mdt sd mat cdt ngang sdng Qudng Hui cU Xdi ngang da Iam chieu rdng long sdng Quang
Hufi khoang 15 m (khi ngo vet nam 2008) da md rong lfin dfin 25m -r 45 m (quan tyac nam 2012)
Tinh tir sau nam 2008 dfin 2012 ldng sdng Quang Hue cu da bj xdi khoang 560.000 m^
2.2 Bien dong che do thuy van ddng chay tr8n khu vuc song Quang Hul cu
Hien nay sdng Quang Hufi cii da trd lgi diing nhiem vu la sdng phan luu giiia sdng Vu Gia va sdng Thu Bdn nhu trudc day. Qua tai lieu khao sat thiiy van thang 3, thang 7 nam 2012 cho thay, che dg ddng chay tgi doan sdng Vu Gia doan tir cua sdng Quang Hufi mdi dfin ciia vao sdng Quang Hufi cu va dge biet la trfin doan sdng Quang Hufi cu da cd nhiing thay ddi theo hudng bit lgi, de dga gay sat Id bd sdng ciing nhu lam mit dn dinh he thdng cac
2.2.1 Ty le phan liru vac sdng Quang Hufi cu trudc 1999 (trudc cat ddng tao sdng Quang Hufi mdi)
Giai doan trudc nam 1999 khi chua cd hi?n tugfng cat ddng vao mua kiet ti le phan liru vao sdng Quang Hue dao dong trong khoang 8%
tdi 20% luu luong sdng Vu Gia. Mot so ket qua cua cac dot do cd khac nhau song ti 1?
phan luu vao sdng Quang Hufi vao miia ki?t dfiu rat nhd.
Tir sau 1999 tdi 2007 do bi bdi lip nen luu lugfng vao sdng Quang Hufi cii trong mua kiet hau nhu khdng cd (Q « 0 m^/s), keo theo ty lfi phan luu a = 0 (khi myc nuac cua vao Quang Hufi cii < 4m).
Dudi day la cac s6 lieu vd ty le phan luu vao sdng Quang Hufi cu trong mua kiet theo sd lieu Tdng Cue khi tugng thuy van trudc day cdng trinh bao v? bd hien cd. Dac biet la thay va sd Ndng nghigp va' PTNT Da Nang (xem ddi ty le phan luu vao sdng Quang Hufi cu. bang 1)
90 TAP CHl KHOA HOC VA C O N G NGHg T H O Y L<?I S O 16 - 2013
KHOA HOC
Bang 1: Ty le phan lmi vio sdng Qudng Hui giai dogn trudc 1999 fl,3,4J Ngudn sd li?u
Tdng cyc khi tugng thiiy van Sd NN&PTNT
Da Nang
Myc nudc tgi ciia vao Quang Hufi cu (m)
2,61 ^ 3,05 2,25 -^ 3,75
Ty lg phan luu vao Quang Hufi cu a(%)
7 ^20 7 ^25
Ghi chii (Do giai doan 1977-
1980,1990) (sii dung lap quy hogchthuy lgi 2010) 2.2.2 T>^ 1? phan luu vao sdng Quang Hufi cii
hifin nay [5]
Tir sau nam 2008, ldng sdng md rdng ca chifiu sau va chifiu rgng cimg vdi tde dp ddng chay tang dan trfin sdng Quang Hufi cii da lam cho ti le phan luu vao sdng Quang Hufi tang lfin, rd ret nhit la trong miia kiet. Kfit qua quan trie
Bdng 2: Ty lephan luu trung binh vdo song Qudng Hui ngdy 26/3/2012 thuy van ddng chay trfin sdng Quang Hufi cii vao cac thdi difim thang 3 va thang 7 nam 2012 da cho thay luu lugng vao song Quang Hufi trong mua kiet da tang len, vdi ti le phan luu a lfin dfin 35% - 40% trong cac trudng hgp myc nudc ciia vao sdng Quang Hufi < 4m (xem bang 2, 3)
Luu lugng ttrung binh song Vu Gia (m3/s) thugng luu Quang
Hue cii 99,6
hg luu Quang Hufi cii
57,0
Ddng chay trung binh vao sdng Quang Hufi cii Muc nudc
cua vao (m)
= 2,8
Luu lugng (m3/s)
38,8
Ty lfi phan luu vao sdng Quang Hufi cil
a = ^*"*''- (%)
QvuGia
39 Bdng 3: Ty lephan luu trung binh vdo sdng Qudng Hui tu 22/7 din 8/8/2012 _ Gia tri
thiiy van dac trung max
TB
Sdng Vu Gia (thugng luu Quang
Hufi cii) H(m)
351 328
Q(mVs) 135,37 112,13
Sdng Vu Gia _ (hg luu Quang Hufi cii)
H(m) 292 270
Q(ni'/s) 81,87 72,60
Sdng Quang Hue cu H(m)
333 308
Q (m'/s) 54,86 39,51
Ty le phan luu; a
(%)
41,2 34,9
^
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. . - s * " ^ 1 _ — - - ' •
1 - * , - « ~siss • ' . • ™ — - j
Hinh 7: Quan he giiia ty lephan luu vdi mirc nudc tgi nut Qudng Hue cu.
So sanh cac kfit qua do dge tryc tifip he sd phan luu vao sdng Quang Hufi cho thay, hifin nay (nam 2012 ) ti Ifi phan luu da tang hcfn trudc day. Dd la mgt trong nhiing ly do dan dfin thifiu nudc nghiem trgng d ha du sdng Vu Gia trong dd cd thanh phd Da Ning.
III. KET LUAN
Md rdng va xdi sau ldng dan sdng Quang Hufi cu tit yeu keo theo gia tang luu lugrig va tang ti le phan luu vao sdng Quang^ Hufi cu. Bifin ddng ldng dan sdng Quang Hufi cii la nguyfin nhan ma ciing la kfit qua cua gia tang luu lugng Q va ti lfi phan luu a vao sdng Quang Hufi cu.
Bifin dgng vfi ddng chay va ldng dan sdng
TAP CHl KHOA HOC VA CCJNG NGHf T H O Y LO'I SO 16 - 2013 91
KHOA HOC CONG NGHE Quang Hufi cii sau khi xay dimg cdng trinh tren sdng Vu Gia va Quang Hufi mdi la dang lo nggi. Bifin ddng ve luu lucmg va ti le phan luu tang hon so vdi giai dogn trudc nam 1999 da gay thfim bit lgi cho hg du Vu Gia, lam thifiu nudc trim trgng thfim vao mua kiet.
Vi vay, cSn thifit phai cd su khdng chfi hgp ly luu lugng miia kiet sdng Quang Hufi dfi bao dam
du nudc yeu cau ciia ha du sdng Vu Gia cung nhu khdng mau thuan vdi yeu cau dung nudc cua hg du Thu Bdn. Van de nay da duge dgt ra ngay tir khi lap du an chinh tri sdng Quang Hufi (2002) nhung chua duoc nghien ciiu cy the trong qua trinh thiet kfi xay dung cdng trinh. Ket qua nghien ciiu mod nhat ve van de nay se duoc gidi thifiu trong cac bai bao tiep theo
TAI LIEU THAM KHAO
[1]. Trung tam Ddng lyc sdng - Vien Khoa hoc Thuy lgi (2002), I)^ dn khd thi "dn dinh ddng chdy khu vi^c song Vu Gia, Qudng Hui phuc vii ddn sinh kinh ti Qudng Nam - Dck ndng "
[2]. Trudng Dgi hgc Thuy lgi (2008). Du dn khdcphiic chinh tri sdng Qudng Hui sau lu 2007.
[3]. Vien Quy hogch thuy lgi - Bg NN va PTNT (2010). Bdo cdo cap nhgt, bd sung Quy hogch tdng hop luu virc Vu Gia - Thu Bdn.
[4]. VifinKhoahgcThuy lgi Viet Nam (2012). Du dn quy hogch thuy lai khu vuc Nam Trung bg trong diiu kien biin doi khi hdu vd nudc bien ddng
[5]. Phdng TNTD QG ve ddng luc hgc sdng bien (2012): Bdo cdo dg: dn: Ddnh gid biin ddng ddng chdy sdng Vu Gia - Thu Bdn vd di xudt gidi phdp cdng trinh phii hgp cho khu vuc Qudng Hue trong tinh hinh mdi phdt sinh trin luu vuc
92 TAP CHl KHOA HOC VA C O N G NGH? THCIY L(?I S O 16 - 2013