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10

PRELIMINARY ASSESSMENT ON EFFECTS OF HOA BINH DAM ON

COASTAL FISHERY RESOURCES

Tran Due Thanh, Do Dinh Chien

H a iph o ng In sti tut e o f O cea n ography Ana l yz in g d t a o n cur r ent , sa linit y, b tt o m t o og raph y and se dim e nt s, an d s u s p en ded

sedime nt s s h ows th a t th e w at e r vo lum e a n d acco mp a ni e d m a t e r f ro m th e R e d Ri ve r a pp e ar

t o i nfl ue n ce o n th e w h l e T o nkin Gul , h owever , s t ro n g e ff ec t o n th e d e pth o f 30 m and

o v i o s e ff e ct o n th e d e pth o f 50m In th e T o nkin Gulf , th e b es t fi s hin g g r o und s are distribut e d in th e V i e tnam e se s e a part and in shallow w at er l ess than 50m d ee p The

s pa w nin g season i s f ro m April to S e pt e mb e r , and th e fi s hin g se a so n is fr o m Ju ne to

N ove mb e r Du e t o buildin g and o peratin g Hoa Binh Dam , the ch a ge and l oss of a g reat

vo l u m e o f fre s h wa t e r , se diment s and nutrients , which are dischar g ed fr o m th e R e d R ive r int o

th e sea h v e ma d e se ri o s impa c t o n r eso ur c es and the envi r onment in e stua ry and coas tal

sea Th e re d uc ti on o f coas tal fi s h r e so u rces is o ne o f th e h eav i es t i mpa c t s It i s a combine d

conse q ue n ce o f r e du c i ng nutri e nt s; chan ge in eco lo g i ca l fa c tor s ( c urr e nt, s al in it y , tllrbidit y

e t c ) l os s or d eg r a dation of habitats and br ee din g gr ounds, bl oc k o f b e a r in g m ig r a t io n o f som e fish s pe c i e s, and pollutant concentration in coastal envi r onment.

An initial c alculation shows that during the last years, fish st ock in V i e tn a m ese se a o f

th e T o nkin Gulf has b ee n reduc e d by 185,500 ton equal to 24.6% o f th e o ri g in a l s t oc k The

i mp ac t s o f buildi ng a nd o e ratin g Hoa Binli Dam ha ve c ontribut e d t o r e du ce 42,665 t OI1 of

f is h , of w hi c h 3,710 t o s h ave b ee n r e du ce d b y d ec r e a s in g nut rie nt s disc h arged d i rec tl y

fr o m ri ve r ; 24,115 t o s b y de c r e asing ph os ph o r o us nutri e nt m ove d f ro m sea b ed up war din

th e s itu a ti o o f fr e sh wat e r store in the dam during th e rain y sea so n ; a nd 14,8 0 t o s due

t o o th e r reas o ns This assessment needs to be referral to the bigger h y droel e ctri c dam o f

S n L a whish is under preparation upstream the Hoa Binh Dam

BVOC DAU DANH GIA TAc DONG CUA HO HoA BINH

DOl Val NGUON LOI cA BIEN VEN BO

Tran Due Thanh va D o Dinh Chien

Phdn vi e n Hdi duang 1z9Ctai Hdi Ph o g

1.MO DAU

Theo thong ke narn 1998, tai dat co 47.6 5 ho mrcc Ia a tren 150 ruroc, trong d6 nhieu ho chira da gay ra thiet hai Ian cho nghe ca bien yen ba (WCD, 2000) 6VietNam,

tir sau 1975, viec xay dung cac ho phat trien kha manh C a mroc da co khoang tren 650h6 472

COASTAL FISHERY RESOURCES

Tran Duc Thanh, Do Dinh Chien

H ai ph ong I nst i tute of O ceanography Ana l y z ing data on current, sa l ini t y, bottom topography and sediments, and suspended sediments shows tha t t he wate r volume and accompanied maters from t he R ed R iver appear

to inf l uence on the whole Tonkin Gu lf , h owever, s t rong ef f ec t on the dep t h of 30m and obvious effect on the depth of 50m I n the Tonkin Gu lf , th e bes t f ishing gro u nds are dist r ibuted in the V i etna m ese sea p ar t an d i n s h ll ow water l ess t han 50m deep The spawning season is f r om A p r il t o S e pt em b er, and th e f is hin g season is from J une to

N ov ember D ue to bui l ding and ope r a ti ng H oa Binl i Dam , t h e change and loss of a grea t

v olume of fresh wa t e r , sediments a n nutr ie nt s, w hi c h are di sc h r ged from t he R ed R iver into the sea have made serious impac t on r eso u rces and th e env i ro nm ent in es tu ary and coasta l

sea The reduction of coas t a l f ish resources is one of the h eavies t impac t s It is a combined consequence of reducing nutrien t s ; change in eco l ogica l f actors (c u rrent, sa l ini t y, t urbidit y etc.); l oss or degrada t ion of habi t ats and br eeding grounds, b l ock of bearing migration of some fish species, and po ll u t ant concen tr ation in coas t al environment.

An initia l ca l cu l a t ion shows th a t during t h e l as t years, f is h s t ock in Vie t namese sea of the Tonkin Gu l f has been re d uced b y 1 5,500 t o eq ual t o 24.6% of th e o r iginal stock The impac t s of bui l ding and operating H oa B i nb D am h ave con tribut ed t o reduce 42,665 ton of fish, of which 3,71 t ons have been reduced b y decreasing nu t rients discharged directly from r i ver; 24,115 t ons by decreasing p hos ph orous nutrien t m oved from seabed li pward in the si tu a t ion o f fresh wa t er s t ore in th e d m du r i ng th e r ainy seaso n ; a n 14,840 t ons d u e

to o t he r reasons T h i s assess m e nt nee d s t o b e re f e r al to th e bi gg er h y dr oe l ec t r i c dam of Son La w h is h is und e r pr e p rati o n up s tr e am th e H o a Binli Dam

BlfOC DAU DANH GIA TAc DONG CUA HO HoA BiNH

DOl Val NGUON LQI cA BIEN VEN BO

Tran Drrc Thanh va Do Dinh Chien

Ph dn vie n H d i du ang h oc t ai H di P hong

1 MO DAU

Theo thong ke nam 1998, trai dat co 47.655 he mroc Ian a tren 150 mroc, tro g d nhieu he chira dii gay ra thiet hai Ian cho nghe ca bien yen be (WCD, 2000) aViet Nam, tir sau 1975, viec xay dung c~c he phat trien kha manh Ca mroc dii co khoan tren 650he

co Ion va vira, tren 3.500 ho COnho (ADB, 1993; WB et al, 1996) Cac ho co sire chira Ion tap trung tren hru vue song Hong va Dong Nai, trong do 3 ho Hoa Blnh, Thac Ba va Tri An diroc xep van nhom 18 ho Ion nhat chau A co dung tich chira tren 1 ty rrr' mroc

Cong trinh ho Hoa Binh khoi cong ngay 6/11/1979 va t6 may so 1 bat dftu van hanh tir ngay 30/12/1988 Hd Hoa Blnh co dung tich chira 9,45 ti rrr', thuoc loai Ion tren the gioi va dirng hang thir ur achau a (tlnh den 1995) Tac dong tieu cue cua ho Hoa Blnh tren hru vue dil diroc danh gia qua mot so cong trinh nghien CUu(Nguyen Thuong Hung va nnk, 1995; Vii van Tuan, 1999) Tuy nhien, viec danh gia anh huang cua cluing tai moi tnrong cira song va yen bo con rat han che (Trdn Dl(C Thank va Do Dinn Chien , 2002) SI! thay d6i phan bo va mat di mot hrong Ion mroc ngot, tram tich va dinh duong tu song Hong dira ra bien do xay dung ho Hoa Blnh dil gay ra nhirng hau qua nghiem trong nhieu mat ve moi tnrong, tai nguyen vung cira song va bien yen bo nhir thay d6i che d¢ dong chay, xoi la bo bien, xam nhap man, mat noi cu tni, bai giong va baide cua sinh vat, suy giarn dinh dirong

va giam sire san xuat cua vung bien yen bo, dan den thiet hai ve da dang sinh hoc va nguon lei thuy san danh bat, nuoi trong

Bai viet nay trinh bay ker qua phan tich, danh gia hau qua cua cong trinh ho thuy dien Hoa Blnh doi voi nguon loi nghe ca bien yen be tay Vinh BAc B¢ (VBB) Viec suy giam nguon lei nghe ca bien yen bo do rat nhieu nguyen nhan va viec danh gia hrong suy giam

do ho Hoa Blnh dua thee phtrong phap chu dao la ph an tfch va tinh di~m trong so tac dong moi tnrong, ket hop sir dung kinh nghiern danh gia cua Chen T.A.C (2000) cho tnrong hop

ho Tam Hiep tren song Truong Giang Do han che ve tai lieu, nhirng ket qua trinh bay a

day moi chi la biroc dau, co tlnh ban dinh hrong, nhirng co y nghia dinh hirong cho nhfrng nghien cull tiep'theo, nhat la danh gia tac dong cua he thong bac thang thuy dien song Da (Nguyen Van Trang va nnk, 2000)

2.1 Liru vue song va dong vat chat tit he thong song Hong

Cac song d6 van bo' tay VBB co th~ ph an chi a thanh 4 luu vue chinh: hru virc cac song vung Dong bac; hru vue he thong song Hong va Thai Blnh, hru vue cac h~ thong song Mil -song Ca va luu vue he thong -song Gianh - Tri-Htrong Theo hlnh thai dia hlnh, dai batay VBB diroc chia thanh 4 vung yen bo: Mong Cai- Do San; Do San - Lach Truong (ven be chau th6 song Hong hien dai); Lach Tnrong-Mili Ron va Mfii Ron- Hai Van (Tran Dire Thanh va nnk, 1985) Khi d6 ra bien, cac nhanh song cua cung mot he thong hru vue co th~ d6 van cac vung bo khac nhau, tao nen su khong dong nhat giira hru vue va vung yen be chiu anh huang Truce day, nhfrng tinh toan co ban cho VBB thuong chi tinh gioi han den khoang Mili Lay, het dia phan Quang Blnh Do vay, nghien ciru nay chap nhan gioi han vira neu d~ tien so sanh so lieu Theo do, hru lirong mroc song Hong-Thai Blnh chiern khoang 78% tong hru luong mroc d6 van be tay VBB (125km3/nam so voi 160 krrr'znarn) va dien tfch hru vue chiern 73,6% tong dien tich cac hru vue bo tay thu mroc van vinh (155.000km2

so voi 210.624 krn")

Hang nam mroc cac song d6 ra VBB tir be tay thuoc dia phan Viet Nam chiem 94,5%

va tir yen bO ' Trung Quoc chi 5,5% (Doi dieu tra Lien hiep Viet-Trung, 1965) Theo Nguyen Viet Ph6 (1984), trung blnh hang nam cac song phia Viet Nam d6 vao vinh 179 krrr' mroc

va 125 88 trieu tan bun cat lo lirng Neu uac tinh ca bun cat di day chiem ty l~ 10% so vdi

bun cat lo lirng thl tong bun cat tir song d6 ra khoang 138,6 trieu tan H~ thong SOng Hong

va Thai Blnh hang nam d6 ra bien mot khoi hrong mroc khoang 125 ty rrr', mang 116 trieu tan cac chat ran, 70 trieu chat tan ran hoa tan va mot hrong dang ke chat gay a nhiem do heat dong dan sinh-kinh te d9C theo cac trien song

Dinh dirong cung cap cho vung yen be chau th6 song Hong (Cl'SlI) tir nhieu nguon khac nhau Nguon tir song hang nam khoang 40.296 tan t6ng nito khoang hoa tan, 1.200 tan photpho khoang hoa tan, 17.600 tan silic khoang hoa tan Nguon dinh duong khoang nito 0 hai dang N03' va N02 - tir mroc mira cung cap true tiep cho vung cira song khoang 1.066 tan/nam RUng ngap man yen bo hang nam cung cap tir 6.237 tan nito va 205.435 tan

ChIc(Nguyen Duc Cl! va nnk, 1998)

2.2 Hinh thai dia hlnh yen be chau thb song Hong

VBB rong khoang 150.000km\ sau trung blnh 50m va cue dai 107m tai,mot triing sau gan cira vinh D9C doi bo vinh, co mat cac vilng vinh, chau th6, cira song hlnh pheu va cac darn pha Tong dien tich hru vue cac song d6 vao vinh khoang 300.000 krrr', trong do e6

155.000km2 hru vue cua song Hong 0 phia bo tay Cac dao trong vinh tap trung 0 vung ven

bo tay bac voi so hrong tren 2000 dao Ian nho Phfa ngoai vinh, ria them luc dia narn 0 dQ sau 120m Dia hlnh day vinh kha thoai voi goc gee nho hon SO, hiern khi tai 10-30°.

Dai yen bo CfSH gom cac chau th6 n6i, chau th6 chim va tnroc chau th6 Dei chau th6 n6i (dong bang chau tho) co dien tfch khoang 17 nghln km", Trong do, phan chau th6 hien dai duoc hlnh thanh trong khoang 3.000 nam qua, co dien tich 6.000 krn", dlnh nam phan Hung Yen, day trai dai khoang 150 km tir ban dao Do San den Lach Truong Dien tich chau th6 n6i trong de khong can chiu anh huang thuy trieu, rong 4500 krn" Phan chau th6 n6i ngoai de, hay la vung trieu,"r¢ng tren 500 krn' Dei chau th6 ngarn (delta front) la phan day nong, kha bang phang nam tnroc cira song chau th6, gioi han ngoai 0 d¢ sau 6-12 m ruroc, dien tfch khoang tren 1000 krn", rong 5-15 km va keo dai tir Do San den Lach Truong Phia ngoai chau th6 ngam la dci truce chau th6 (prodelta), 0 khoang do sau 20-30

m Tai day d¢ doc tang, bun cat song dua ra lang dong rat It, vai tro cua song cling nhir cua song 0 day giam h~n, v~t lieu tir luc dia dua ra chu yeu la cac san pharn rat min nhir bun set nau hong, tich tu nho dong hai hru yen vinh Bac B¢ (Tri ' in DL(C Thanli va nnk, 1986).

2.3 Dong chay yen bo'

Dong chay tong hop yen bo crSH rat phirc tap va gem cac thanh phan dong trieu, dong song, dong gio Moi dong thanh phan phat huy iru the 0 mot khoang nhat dinh cat ngang

bo Dong chay trieu thuan nghich trong ngay va co iru the trong vung mroc sat bo, trung binh d¢ sau 6 m tro vao, co noi den 12 m Dong chay song phat huy 0 doi song va bo, e6

huang phu thuoc vao huang gio, dia hlnh bo va bien d6i theo mua Dong chay gio co toe dQ khong Ion, thtrong 5-15 cm/s, irng voi toe do gio ph6 bien 4-5 m/s 0 yen bo, huang dong

phu thuoc vao hirong gio, thirong phat huy chi atang mat tren khong gian rong, dong gop

nam va tay nam vao mua dong Hoan hru VBB co hirong chay d9C yen bo xuong phia tay

nam quanh narn

2.4 Ngu truong vimg bi~n yen be tay vinh Bac B<)

Ph d , 1977), 33 van tan (Nguyen Xudn L9C,1985), 17,5 van tan (Le Van Dang va D ao Van

T~(, 1994) va chi 11,6 van tan tPham Thuac, 2000).

Trong nhom ca noi, ca trfch, ca nuc so, ca com la nhirng loai quan trong nhat Cac loai

sari, 1996)

2.5 Pharn vi anh huong cua dong v~t chat song Hong

DQ man mroc tang mat VBB amire cao ph6 bien 32-33%0 va chiu anh huang cua rnroc song cung vat chat di kern, chu yeu tir song Hong den gan toan bo khong gian vinh arrurc

dQ khac nhau Theo chi thi v~ hlnh thai dia hlnh, tram tich day va 10' lirng, dQ man, khci mroc song Hong anh huang rnanh, thirong xuyen den dQ sau khoang 30 m (ranh gioi ngoai cua doi truce chau thd) va anh huang r5 den khoang dQ sau 50 m Khoang do sau 50 m la mot bien tl! nhien quan trong doi voi nghe ca bien ma anh huang cua khoi nuoc song la mot trong nhirng yeu to quan trong Khoang 70% -80% san pharn ca bien Viet Nam hien dang duoc khai thac aphia trong dQ sau nay Ra phia ngoai dQ sau nay, anh huang cua mroc, v~t chat tan va tram tich 10' hrng yeu di, chu yeu vao mua mira Hi

D9C bo v~ phia dong bac, tram tich 10' lirng tir Mthong song Hong - Thai Blnh anh huang manh den dong nam Cat Ba va Vinh Ha Long, can mroc va vat chat tan anh huang den vinh Bai Tir Long va c6 the can xa hon D9C be v~ phia tay nam, dong cat ur song Hong anh huang r5 den Sam Son, dong bun anh huang r5 ret toi tan MUi Dau Rong (vi d¢

19°15'N) tTr d DLfC Thanb va nnk, 1985) Anh huang cua dong vat chat tan, trong d6 eo

cac chat gay 0 nhiem c6 the den tan miii Hai Van (Luu Van Dieu v a nnk , 2001).

Nhu vay, dong v~t chat tir song Hong c6 anh huang tren dien rong cua vung bien ven

be tay VBB, noi ph an bo cac bai tom, ca va mire quan trong va la cac ngir tnrong danh biit chu yeu VI the, day ciing la khong gian tac dong cua ho Hoa Binh den nguon loi ca bi~n

yen bo

3 TAc DONG CUA HO HoA BINH DEN MOl TRlfONG VUNG CUA SONG vA

BIENVENBO

3.1 Dac di~m ho hoa binh va che' dQ dieu tiet

Song Da c6 chieu dai 980km, trong d6 440km aTrung Quoc, 540km aViet Nam, dien tich hru virc 51.700km2 (52,4% tren lanh th6 Viet Nam), chiem 37% dien tich hru vue song Hong (141.892 krn') Luu lirong trung blnh nhieu nam cua song Da tai Hoa Binh la

1.770m3/s Tong hrong chay tinh den Hoa Blnh la 55,83 ty rrr', bang 51 % tong hrong chay song Hong

Cong trlnh ho thuy dien Hoa Blnh nam tren song Da, tai thi xa Hoa Binh, khoi cong ngay 6/11/1979 va T6 may so 1 bat dau van hanh ngay 30/12/1988 Ho c6 chirc nang chinh

Ia san xuat dien nang, sau d6 Ia ngan ngira, phong chong Hi lut Cac nhu cau khac sir dung

ho chi la san pham phu Ho c6 chieu dai 230 km, dien tfch 208 km2 va dien tich hru vue cap mroc 51.700km2 Hd chira c6 cao trlnh 123 m, mire mroc dang blnh thirong 115 m, dung tich tinh toi mire mroc dang blnh thuong 9.450 trieu rrr', chiem 8,29% tong thuy hrong h~ thong song Hong; dung tich htiu Ich 5.650 trieu rrr': dung tich chong Hi den rmrc ruroc gia cuong 5.870 trieu rrr' Ho c6 cong xuat lap d~t 1.920 MW, san xuat 7,8 ti Kwh dien, cung cap 40% nang hrong dien cua Viet Nam va c6 the giam mire IU Ha NQi nam 1971 tir 14,8m xucng 13,3m

Che d¢ dieu tiet mroc cua h6 dam bao uu tien khong diroc d~ rmrc nuoc h6 vuot rmrc mroc lii cuong birc quy dinh voi rnoi tran lfi c6 t~n xuat 0,01 % irng voi hru hrong dinh lii song Da tai Hoa Blnh la 37.800 m3/s va iru tien tham gia dt lil cho ha du bao g6m lii thirong xuyen va Iii thiet ke, V& nhiem vu chong lii tir ngay 15/6 den 15/9, ba thai ky van

hanh diroc quy dinh Ia: lil som tir 15/6 den 15/7; lfichinh vu tir 16/7 den 25/8 va lilmuon tir 26/8 den 15/9 Duy tri mire mroc +91m ±2 m trong thai ky lii som, 90 m ±2 m trong thai ky

lil chinh vu Dung tich ky lii muon tuy theo tlnh hlnh thai tiet cuoi thang 8, du bao dau

thang 9 va dam bao hieu Ich ph at dien trong cac thang sau lii (Ban chi dao phong chong lut bao Trung UO'Ilg,1997)

3.2 Nhftng tac dong cua ho Hoa Blnh anh huang den nguon IQica bi~n yen bO'

Lam mat hoac anh hirong den noi cu tni, bai de, bai giong va chan dirong di cir di de cua mot so loai thuy sinh '

H6 Hoa Blnh da chan dirong di cu tir bien len thirong ngu6n di de cua mot so loai ca

kinh t€, trong d6 n6i bat nhat Ia ca moi va ca chay Nhieu h6 tren the giai c6 thiet ke cau virot cho ca di de, nhimg h6 Hoa Blnh khong c6 loai cau virot nay H6 con lam mat bai de cua cac loai ca kinh te nhir ca moi, ca chay do vung thi xa Hoa Blnh bi chlm trong long h6,

mat bai de cua ca moi va ca nganh do long song tu h6 den Trung Ha bi x6i sau 7-8m

Khoang 500 trieu ca bot (khoang 40-50% ca bot song H6ng) bi giam do xay dap (B¢ Thiry san, 1996) Dai ven bo rayVBB, trong d6 c6 vung tnroc cira song H6ng la cac bai giong bai

de cua cac loai thuy san Hau het cac Ioai tom ca va thuy san khac di CUvao vung ven bo di

de trong khoang thang 4-9 Day la thai gian dieu kien sinh thai cac bai de bi xao dong

nhieu do dieu tiet ho

Gidm khoi luang Ian bun cat dua ra c£ta song ven bii'n

Cac so lieu cong bo khac nhau (Ngo Trong Thuan , 1997; Nguy e Ki e n Dan g, 1999 ;

H o a Mann Hun g , 2001), nhirng deu cho thay hrong bun cat bi giii lai day h6 la rat Ian Theo tai lieu cua Trung tam Tai nguyen mroc va Moi tnrong (1999), so sanh thai ky

1990-1993 va 1961-1970, 91,8% hrong phu sa song Da, hay 48,6% t6ng luong bun cat song H6ng lang diroi day ho Khi trite dien long song can bang sau thai ky dai, t6ng hrong b6i tich song H6ng se giarn thirc te trung blnh khoang 48,6%, nrc la g~n mot nira do b6i lang diroi h6 Hoa Blnh, khoang 55 trieu tan moi nam Do vay, 6 vung ven bo x6i 16 tang len va b6i W giam di, dan den giam mire gia tang W nhien cua dien tich noi sinh cir cua cac loai thuy san ven be chau th6

Trong giai doan 1930-1965 tee d¢ tien ra bien trung blnh la 28,7 m/nam, Trong giai

doan 1965-1990, toe d¢ tien ra bien trung blnh 29,1 m/nam iTrdn Due Thanh v a nnk,

1996) Tinh toan bang phuong phap th~ tich vai hrong bun cat thay d6i tnroc va sau xay h6 Hoa Blnh cho thay toe d¢ b6i W ven bo CTSH giarn tir 27,4 rn/narn xuong 14,7 rn/nam, mat

di 12.7 m/narn, tuong dirong 190 ha/nam, C6 th~ nhan dinh rang, hau qua x6i 16 be chau th6 va giam toe do b6i se rat 100 va th~ hien ngay cang r5 trong thai gian toi Su thieu hut bun cat tir luc dia ra bien do bi hru giii lai 6 day h6 Hoa Blnh la mot trong nhirng nguyen nhan quan trong g6p phan tang cuong x6i 16 bo bien BAc B¢ voi cuong d¢ Ian (Trdn Due

Th a nn va nnk, 2000). Vung trieu Cl'Sll la noi co tiem nang Ian phat trien dam lay su vet va

he sinh thai rirng ngap man co nang suat sinh hoc thuoc loai cao nhat &vung ven bo Do tee

d¢ boi tu giam di va xuat hien xoi 1&manh & mot so doan bo dan den thiet hai ve da dang

sinh hoc va cac san pharn cua he sinh thai Theo tfnh toan, moi narn toe d¢ boi tu giam 150

ha, tirong irng voi giam kha nang hlnh thanh 3.000 ha rirng ngap man sau 20 narn

Th ay d i ph d b o nu a c , bun cat la LUng 0 cua song v e n biln

do tich du dung tfch hiru Ich de dat mire mroc dang blnh thirong vci dung tich 9,45 t rrr'

VI the day la thai diem gay thay d6i dot ngot dieu kien sinh thai ven bo Khi ho di vao

hoat dong deu dan, mire d¢ tac dong xao tron It di trong dieu kien thich ling maio Trong qua trlnh van hanh thuy dien va cat Iii, ve nguyen tac ho khong gay tieu hao mroc, chi

tru mroc mua Iii va xa mroc mua kho Nhirng hrong tru mroc mua mua lil cho dung tich

htru ich 5,65 ti rrr', chiern khoang 4,95% tong hru lirong mroc he thong song Hong -Thai Blnh, d1'l lam giarn 6,6% tong hrong mroc mua lil va tang 18.8% t6ng luu lircng mroc mua can Mac du hrong mroc qua ho duoc hoan nguyen qua nam, nhung lucng

mroc xa Ian hen ve mua kho tao co hoi cho sir dung mroc nroi vung ha du tang len Vi

vay, tong hru hrong rnroc song Hong ra bien van bi giam, nhung khoi hrong chua ducc

danh gia cu the

Khi ho Hoa Blnh xa mroc ve mira kho,hrong chay he thong song Thai Blnh va Van Uc tang len so voi tnroc ( Tr ung t a m Tai n u ye n nu ac va M o i tr ua n g, 1999) Tong hro g mroc

p an phci cho he thong song Thai Blnh tang len r6 ret Thai ky 1956-1989 song Ho g

chuyen mroc cho song Thai Blnh qua song Duong trung blnh la 24,5% hrong mroc qua San

Tay van mira Iii va 19,95% van mua can Ty l~ nay la 27% van mua lfi va 24,6% VaGmua

can sau xay h Hoa Blnh Neu tfnh trung blnh nhieu nam thl ty l~chuyen mroc nay la 24%

tnroc xay h Hoa Blnh va 27% sau xay ho Hoa Blnh ( Luong Phuo ng H du va nn k , 2 002).

Tren song Carn, hru hrong mroc VaG dau nhirng nam 60 khoang 9-10 krrr'znam (khao sat cua

cac chuyen gia Lien Xo cii) va VaG dau nhtrng nam 90 hru hrong mroc la 12 - 13 krrr'mam (tai lieu duan UNDP VIE-88/014, 1992)

Sau xay ho, tong hrong bun eat tai tram San Tay giam tir 114 trieu tan xuong con 69,2

trieu tan Trong khi do, luong bun eat qua tram Thirong Cat (tren song Duong) giam khong dan ke, tir 26,3 trieu tan xuong 25,9 trieu tan, chi giarn khoang 1,5% Sau xay h , t6ng hrong bun cat song Hong tai San Tay 69,2 trieu tan narn, h~ thong song Thai Blnh khoang 1,8 trieu tan va tong hai he thong la 72 trieu tan Ty l~ phan bo bun cat khu vue cua h~

thong song Thai Blnh, dac biet la & cira Nam Trieu tang len va ty l~ bun eat khu vue phia

nam Cira Ba Lat giam di sau xay ho Tnroc xay ho Hoa Blnh, hrong bun cat dira ra ven bien

tu Do San den Kim San 113 trieu tan narn, ra vung cira Cam-Nam Trieu khoang 3 trieu

tan/narn Tuong quan nay la 67 trieu tan va 5 trieu tan sau xay ho

Th ay d i d o g c h dy va phdn bo ' d¢ mdn v ung clta s o ng

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