74 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II
XAC DINH GIA TRI LU'U LU'QNG XA C6 DINH T 6 I THlfeU
C U A ' H 6 CHLFA H O A
BlNH
X U 6 N G H ALU'U DUY TRI Du'ac DONG CHAY, DAM BAO DUOC
SU
S 6 N GQUA SONG
ThS. Nguyin Nggc Bach KS. Bill Thi Ngan
Tom t^t:
Bai nay gidi thieu ket qua tinh toan lu-u lu'gng xa co djnh toi thilu cua hd chira Hda Binh xudng ha lu'u duy tn dirge ddng chay, dam bao du'ac sy sdng cua sdng.
D§ tai khoa hgc c i p Nha nirdc "Nghien CLPU xac dinh dong chay moi tru'dng cua he thong sdng Hong - sdng Thai Binh va de xuat cac giai phap duy tri ddng chay mdi tru'dng phu hgp vdi cac yeu cau phat then ben vii-ng tai nguyen nu'd'c" du'ac Vien Khoa hgc Thuy lgi Viet Nam chu tri, thyc hien tir thang 04/2008 d i n thang 09/2010.
Du'dl day trinh bay tdm tat ve each xac dinh ddng chay tdi thilu xudng ha lu'u hd Hda Binh dam bao sy sdng cua sdng va irng dung phuang phap Tennant danh gia hien trang ddng chay sinh thai giai doan sau khi ho Hoa Binh di vao hoat ddng (1990-2007), la ket qua nghien cifu, thudc ndi dung 5 cua de tai tren.
*
* *
I. Gio'i thieu phiro-ng phap Tennant
Phuong phap Tennant (hay phuang phap Montana) la mdt phuang phap tiip can tuang ddi re tien, nhanh va de ap dung. D I xay dyng phuang phap nay cin cd nhiing nghien cim va dau vao tir cac chuyen gia. Cac kit qua so vdi kit qua tir cac phuang phap can nhieu dir lieu la tuang ddi phii hgp. Phuang phap nay dya tren cac xu hudng tdng hgp tir cac khao sat thyc dia d My trong mdi quan he giOa diiu kien cua sdng, lugng ddng chay trong sdng va mdi trudng sdng cua ca. Cac phuang phap nay dugc sir dung de dua ra cac gia tri Ddng chay Mdi trudng (Environment Flow - EF) dl duy tri cac loai ca, cac sinh vat hoang da, giai tri va cac nguon tai nguyen lien quan. EF tinh cho hai miia khac nhau trong nam d My, Xuan Ha va Thu Ddng theo phdn tram cua trung binh ddng chay nhieu nam tai tuyin tinh toan tiiy theo yeu cau bao ve mdi trudng sdng du^ tri d mirc tdt, trung binh hay kem. d nudc ta, van dung tinh toan cho miia can vamiialu (Bd«g 7).
PHAN I - THUY LUC, SONG BIEN VA PHONG CHONG LUT BAO.. 75
Bdng 1. Phdn tram dong chay binh qudn ndm (AAF- Percentage of Average Annual Flow) duac yeu cdu de dgt cdc muc tieu khai thdc khdc nhau
Muc tieu bao ve moi trudng va he sinh thai ciia song Dong chay ldn nhit hay xoi manh
Pham vi tdt nhat cua AAF
Phin tram AAF dd nghi Mua can
200 60-100
Miia 10 200 60-100 Ph^n tram dong chay yeu ciu di duy tn mdt diiu kien song theo yeu ciu
Hoan hao Rat tot T6t
Trung binh hay dang bj suy giam Kem hay t6i thieu
Suy thoai rit nang
40 30 20 10 10 10-0
60 50 40 30 10 10-0 Vi du, neu tri sd ddng chay binh quan nam (AAF) trong sdng la 1707 m /nam, thi ddi vdi mirc do mdi trudng sdng la hoan hao thi ddng chay trong sdng trong miia can se c4n 40% tri sd ddng chay binh quan, hay 683 mVs. Phuong phap cd the ap dyng vdi nhiiu loai sdng va kich thudc sdng khac nhau. Khi mdi quan he ban dau giiia dieu kien sdng va ddng chay dugc thilt lap cho mdt khu vyc, yeu cau dir lieu ciia phuang phap d mirc do trung binh, yeu chu tai lieu thiiy van thang tinh toan hoac thyc do.
Trong cac phuang phap danh gia nhanh, phuang phap Tennant la phii hgp nhat vdi khu vyc, trong trudng hgp nay, viing phia Tay nudc My - la ncri phucmg phap da dugc xay dyng, cac dac trung thiiy van va sinh thai cua sdng duge nghien cuu va tim hilu ky. Phuang phap nay da dugc xay dyng nham muc tieu bao ve mdi trudng sdng cho loai ca hoi cd gia tri thuang mai d day. Do vay, mirc do img dyng cd the ban che ddi vdi cac khu vyc khac tren the gidi.
Q mdt so khu vyc, nai ma thdi gian la mdt rang huge chinh, phuang phap Tennant dac biet phii hgp. Dya tren cac cudc khao sat thyc dia ve phan img mdi trudng cua quin thi sinh vat dang nghien cuu trong khu vyc dd, se dua ra mdt phuang phap xac dinh EF kha tdt. Phuang phap cd thi sir dung d mgi noi, tuy nhien cac chi sd chinh xac can dugc tinh toan lai cho tirng khu vyc, tren co sd nhiing do dac thyc nghiem phii hgp vdi noi ma chiing dugc ap dung.
LTu dilm ciia phuang phap la khi chu trinh chung dugc xay dyng, viec img dyng yeu chu tuong ddi it cac ngudn tai lieu. Tuy nhien, chua cd bang chiing nao chiing td cac chi so thuy van dan gian cd thi chuyen ddi giira cac viing va vi the chiing chi trd thanh "nhanh" khi dugc hieu chinh lai cho khu vye mdi. Cac chi sd nay chi dya tren cac sd lieu thuy van, nen chiing rat de hieu chinh lai cho mdt khu vyc mdi, nhung khdng cd gia tri sinh thai va vi thi khdng chac chan dat dugc ket qua tdt. Nhiing chi sd
76 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP H ma dya tren tai lieu ve sinh thai rd rang cd gia tri ban trong viec danh gia ve mat sinh thai cho ddng sdng, nhung viec thu thap cac tai lieu nay cd the tdn nhieu thdi gian va chi phi. Ket qua ciia phuang phap Tennant se la mdt bang tuang tu nhu bang 2, tuy nhien sd phan tram xac dinh trong bang la ung vdi sy phat trien cua ca hdi, cdn van dung vao danh gia EF ndi chung thi chua cd each xac dinh.
II. Lfng dung Tennant, xac djnh lu'u lu'gng xa tdi thi§u cua h6 chira Hoa Binh duy tri dong chay, dam bao sir sdng cua dong song
* Xdc dinh dong chay toi thieu xuong hg Iwu ho Hoa Binh dam bdo sir song cua song Cdng trinh hd chira Hda Binh la cdng trinh ldn, phuc vu da muc tieu. Tuy nhien, trong dieu kien nude kiet nhat trong nam, cdng trinh can cd che do xa tdi thieu xudng ha luu de duy tri ddng chay, dam bao dugc sy sdng cua sdng. Ap dung phuang phap Teimant de xac dJHh lugng xa tdi thieu cho ho, chia thdi ky ddng chay trong nam ciia luu vyc lam 2 thdi ky: miia lii tir thang IV den thang X, miia kiet tir thang XI din thang III nam sau, tinh toan cho thdi ky tir nam 1972 din nam 1989 (trudc khi xay dyng hd chiia). Sir dyng phan mem IHA phien ban 7.0 ciia Ca quan bao ve thien nhien (The Nature Conservancy - TNC) xay dyng va phat triin dl tinh toan sd lieu ddng chay tai tram Hda Binh.
* Phan mim IHA (the Indicators of Hydrologic Alteration) phien bdn 7.0
De tai da sir dyng phan mim IHA dl danh gia 67 loai thdng ke ddng chay bao gdm 33 Chi sd bien ddi thiiy van va 34 Hgp phSn ddng chay mdi trudng.
* Chwc nang Phan mem IHA
Chuc nang chinh ciia phan mem la thdng ke. Tir so lieu ddng chay ngay nhap vao, phan mem se ty ddng tinh toan, thdng ke dl dua ra cac dac trung ddng chay ngay, ddng chay nam va cac chi sd khac.
Dya vao cac tiiy chgn, phan loai ddng chay trong sdng thien nhien ra thanh cac Hgp phan ddng chay mdi trudng.
Phan mem IHA cd kha nang:
- Thdng ke, so sanh chi sd ddng chay cua hai chuoi sd lieu (trudc va sau khi xay dyng cdng trinh) de dua ra danh gia vl tae ddng ciia cdng trinh ddi vdi ddng chay trong sdng thien nhien.
- Thdng ke, phan tich xu thi biln doi cua ddng chay tir mdt chuoi sd lieu (phuc vy cho bai toan dy bao).
- Thdng ke cac chi sd Hgp phin ddng chay mdi trudng, danh gia tac ddng biln ddi thiiy van tdi he sinh thai.
^et qua tinh toan theo IHA thu dugc nhu trong hinh 1.
P H A N I - THLIY LUC, SONG BIEN vA PHONG CHONG LtJT BAO... 77
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3 6 1 . 3 5 » 1945 3 2 3 5 3 6 6 5 2 7 5 3 1580 1105 6 6 2 . 5 5 3 3 124 3 3 0 . 5
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0 . 4 5 8 1 0 . 8 2 5 5 0 . 7 1 9 3 0 . 2 7 2 0 . 3 5 6 1 0 . 1 8 1 1 0 . 2 8 4 3 0 . 5 0 6 3 0 . 3 8 9 1 0 . 3 4 9 9 0 . 2 6 1 7 0 . 3 1 5 1
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1990-2007 ( 1 8 y e » s )
M V I A T I O M FACTOR Me<4«re C D .
0 . 5 7 8 1 0.6714 0 . 5 6 7 3 0 . 3 5 i 4 0.4892 0 . 6 7 6 9 0.3564 0.2972 0 4 1 8 1 0 2 9 6 3 0 . 4 0 6 1 0 . 5 6 9 8
0 5 5 3 0 1 9 2 3 0 4402 0 4052 0 3 1 2 1 0 . 1 4 3 5 0 1697 0.2262
1.38 1.245 0 . 0 6 9 4 1 0 7 0 0 2 0 . 0 5 5 9 3 0.3724 0 . 0 6 3 2 9 0 . 1 2 % 0 . 0 6 3 5 8 0 1 3 4 3 0 7 8 1 8 1.212
0 6 1 6 6 0 7 3 1 7 0 . 7 5 2 8 0 . 9 4 6 7 0 . 6 0 0 3 0 . 1 8 6 3 0 . 2 4 1 1 0 . 2 9 3 1
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0 . 2 6 2 1 0 . 1 8 3 0 . 2 1 1 1 0 . 2 9 1 7 0 . 3 7 3 8 0 . 1 0 6 2 0 . 2 5 1 1 0 . 1 1 2 9 0.15O6 0 . 1 5 3 3 0 . 5 3 4 9 0 . 8 0 6 5
0 . 8 0 5 2 0.95O1 0 . 8 1 0 9 0 . 6 1 2 5 0 . 0 0 9 6 4 7 0 . 5 9 1 6 0.1787 0 . 2 5 9 6
0 . 0 0 0 . 0 0 D.7077 0 . 0 0 0 . 3 5 5 1 0 . 0 0 6 0 0 6 0.1O11 0 . 1 7 4 2 0 . 5 9 4 6 O.OT 0 . 0 0 0 . 0 0
0 0 0 O X 0 0 0 0 0 0 0 . 0 0 0 . 0 0 8 0 0 8 O.OOIOTI 0 0 0
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0 1341 0 1071 0 1051 0.1121
0 971 0.2052 0 . 1 8 1 2 0-4004
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—
• 1 Hinh 1. Kit qua tinh todn ddng chay trung binh nhieu ndm (sir dung IHA)
Bdng 2. Ty le phdn trdm (%) dong chay sinh thdi theo kien nghi ciia Tennant Muc tieu bao ve moi trudng
va he sinh thai cua song Dong chay ldn nhat hay xoi manh Pham vi t6t nhit cua AAF
Dong chay 6e nghj theo Tennant (m'/s) Miia can
3180 952-1590
Mua lu 3180 952-1590 Dong chay yeu ciu di duy tn mot diiu kien song theo yeu ciu
Hoan hao Rat t6t T6t
Trung binh hay dang bj suy giam Kem hay toi thieu
Suy thoai rit nang
635 476 318 159 159 159-0
952 794 635 476 159 159-0 Dong chay trung binh nhieu nam tai tram Hoa Binh tinh bang phan mem IHA cho kSt qua 1588 mVs. Dong chay trung binh cho miia can va miia Ifl theo ty le ciia Tennant de xuat, ap dung cho luu lugng xa 6 ha luu cong trinh ho Hoa Binh (Bang 2).
78 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II
Nhu vay, theo phuang phap cua Termant va de xuat ty le phan tram dong chay ciia song, ap dung cho 2 thai ky dong chay mua lu va miia can ha luu ho Hoa Binh tren song Da thi dong chay duy tri t6i thilu de he sinh thai ton tai va phat trien binh thuang nen a miic T6t: luu luang dat khoang 30% dong chay trung binh nhieu nam vao cac thang miia can va 50% dong chay trung binh nhieu nam vao cac thang mua lii (tuang ling vai luu lugng 318 m''/s va 635 m^/s).
III. Lfng dung phifcyng phap Tennant danh gia hien trang dong chay sinh thai giai doan sau khi h6 Hoa Binh di vao hoat dong (1990-2007)
Tir chuoi so lieu dong chay nam tai tram Hoa Binh tir nam 1990-2007, ve dugc bieu do dong chay trung binh cac thang trong trong chuoi nam {Hinh 2).
Q(m3/s) 6000 5000 4000 3000 2000 1000
Dong chay trung binh thang tai tram Hoa Binh (1990-2007)
IV V VI VII VIII IX X XI XII I Thang
Hinh 2. Dong chay trung binh thdng tgi trgm Hoa Binh (1990-2007)
Qua bilu d6 tren, chgn cac thang XII, II va thang III la cac thang c6 luu lugng binh quan thang thap nhat miia can va thang IV, V la cac thang co luu lugng binh quan thang thap nhat miia lii trong chuoi nam tir 1990-2007 dl danh gia theo ehi tieu miic duy tri dong chay toi thieu de cho he sinh thai Iuon duy tri a trang thai phat triin t6t (vira tim dugc bang phuang phap Tennant a phan tren).
Nhu vay, danh gia theo phuang phap cua Tennant, trong chuoi nam 1990-2007 tai tram Hoa Binh dong chay binh quan cac thang kiet nhit diu nJm tren nguang duy tri toi thieu, dong chay cung cap dii de he sinh thai song phat triin t6t.
PHAN I - THUY LUC, SONG BIEN vA PHONG CHONG LUT B A O . . 79
Cdc thdng miia cgn:
a(m3/
1400
1200
600
200
3j D6ng chay trung binh thang tram Hoa Binh (1990-2007)
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1 - " - T h d n g XII - ^ Thdng II Thdng III Mi>c tdi t h i i u |
N a m
Hinh 3. Dong chay trung binh cdc thdng cd Iwu Iwffng thap nhat miia cgn trgm Hoa Binh (1990-2007)
Cdc thdng miia IU:
Qim3isi Dong ehdy trung binh thdng tram H6a Binh (1990-2007)
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 - . - T h i n g IV - ^ - T h i n g V Thing X - Mu'C toi thieu
Hinh 4. Dong chay trung binh cdc thdng co Iwu Iwffng thap nhat miia lu trgm Hoa Binh (1990-2007)
80 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II
Dong chay cac thang eo luu lugng binh quan nho nhat miia lii tai tram Hoa Binh tren song Da trong chuoi nam 1990-2007 co mgt vai lan xuat hien luu lugng thap han miic toi thieu 635 m^/s (tinh cho miia lu theo phuang phap Tennant), (Bang 3.2).
Bdng 3.2
Thang IV V X
S6 I3n xuit hien luu lugng thip hon muc toi thieu
4 3 1
Thip nhat (m'/s) 496 474 558
Tom lai, theo phuang phap danh gia cua Tennant, dong chay tren song Da - ha luu ho Hoa Binh dugc duy tri kha tot doi vai he sinh thai song. Co mgt so nam dong chay nam thap han miic dong chay toi thieu cung cap cho moi truang vao cac thang miia mua, tuy nhien khong thuang xuyen va miic do khong lan, vi vay anh huang khong dang ke tai siic khoe eiia con song.
