Bin dng ca dm pha tam giang cu hai

~ TH6NG TIN • , • sa KHOA HQC, CONG NGHe vA MOl TRUONG THerA THIEN HUE Trong sO'nay: • Hoa cau vuon trau • Bien dQng cua dam pha Tam Giang-Cau Hai va h~u qua moi truong, sinh thai Co che tai I~p cva H6a Duan tran 10 dau thang 11.1999 Oi san va canh quan Hue: cu li~u tai nguyen cho quy hoach phat tri~n th] Hue Cau ki~n go di tlch kien true Hue Giao due trieu Nguyen, cai gia cua Nho hoc • Ghi chu ve mai quan h~ giO'ati~u thuyet va sv thir Trung Quac NhO'ngsai lam ve danh nhan van h6a £)~ng Huy Trv SL!phat tri~n cua Dao giao tnroc Huynh Dlnh kinh xuat hi~n • Truyen Ba tien Thien Y A Na • Va nhieu bai khao cuu khac So 2(28).2000 du# TAP CHi THONG TIN KHOA HQC vA CONG NGH~ THUA THIEN HUE S62(28) 2000 MUCLUC ,., KHOA HOC & DOl SONG - vO QUANG YEN Hoa cau, viron trau - LE vAN MIEN Buoc dau nghien CUu cau true quan dan cac loai thuy san tir bien vao pha qua cira Thuan An - NGUYEN KHOA LAN, TR~NH DONG THU MQt so dac diern da dang sinh hoc cua cay an qua & phc Hue - Ph6ng sir anh: Chuan bi truce mua lu nam 2000 _ = 12 19 DlEN DAN KHOA HQC - NGUYEN THANH, NGUYEN VAN SAU, TRAN HaU TUYEN Danh gia so' bo hoat dong dia dong hrc chu yeu cua bien doi voi sir an dinh bo' bien khu vue Thuan An-Tu Hien - TRAN DUC THANH, NGUY~N CHU HOI, NGUYEN HaU CU Bien dong cira dam pha Tam Giang-Cau Hai va hau qua moi truong, sinh thai - NGUYEN THANH, TRAN HaU TUYEN, NGUYEN MAl SAU Danh gia so' bo co che tai lap cira Hoa Duan tran hi dau -, thang 11.1999-tr~n hi the ky & Thira Thien Hue -: 25 31 47 BAD TON & PHAT TRIEN NGUYEN LUA-N Di san va canh quan Hue: Cir lieu tai nguyen cho quy hoach phat trien thi Hue - HoANG DAO KiNH Mot vai dong g6p cho viec bao ton di san van h6a vat th§ co Hue giai doan hien - DoAN CONG DIEN Vai net co ban v§ cau kien g8 di tich kien true Hue _ 53 58 61 vAN HOA - L!CH sO' -~ ,., , - LE NGUYEN LUU Giao due trieu Nguyen, cai gia cua Nho hoc - DUONG NGQC DUNG Ghi chii v§ moi quan h~ gitta ti§u thuyet va sir thu Trung Qudc - PHANVAN HoANG Buoc dau tim hidu bao "L' Ere Nouvelle" va "Nhut 'I'an bao" (1926-1929) 67 77 83 OAT NlmC-NHAN V~T _ - NGUYEN vAN DANG Hai van Son sir sach trieu Nguyen - TRAN DtNH SON Nhirng sai lam v§ danh nhan van h6a Dang Huy Trir (1825-1874) - THI:JtN MQC LAN N8i truan chuyen cua mot nha van: Tu BU'u Dinh den T~ Dinh 87 97 104 TlJ LI~U - ROLF HOMANN (Le Anh Minh dich) S~ ph at trien cua Dao giao108 truce "Huynh Dinh kinh" xuat hien - LYVI:JtT DUNG Truyen Ba tien Thien Y ANa 115 31 rong phil Hai to u to g , , / ? BIEN DONG CUA DAMA' PHA TAM GIANG-CAU" HAl 'A VA H~U QUA MOl TRUONG, SINH THAI " A A" " ? Tr~n Due Th~nh, Nguy~n Chu H8i, Nguyen Hihl CU" I M& dAu ~n tren hi to 01.1, n an CUll -D!a H~ dam pha Tam Giang-Cau Hai (TG-CH) co tam quan dac biet doi voi su phat trien kinh te dan sinh khu vue 'I'hira Thien Hue nho cac gia tri tai nguyen, ma n6i bat la sinh hoc va cac chirc nang v~ sinh thai, moi trirong cua no Cac gia tri va chirc nang giin lien v6'i trang thai phat tri~n cua hai lach cira chinh Thuan An va Ttr Hien ton tai nhieu nam thong n6i dam pha voi 'bien Tuy nhien, cira lach thirong khong 6n dinh v~ Vi tri va trang thai dong mo', gay nhung hau qua tieu cue v~ sinh thai, moi trirong va kern thee nhung thiet hai IOn v~ kinh te, dan sinh Co th~ coi viec lap cira, chuyen cira dam pha la cac dang tai bien nang n~ 6'ven bo mien Trung ma khu virc Thira Thien Hue la di~n hinh Bai viet danh gia hau qua moi trirong va sinh thai cua viec lap cira, chuyen mo' cira cua he darn pha Tam Giang Tu lieu diroc sli' dung chu yeu hi· cac d~ tai cap nha mroc KT.03.11 "Nghien ciru sli' dung hop ly cac he sinh thai tieu bieu ven bien Viet Nam", KT.DL.95.09 "Nghien ciru khai thac, sli' dung hop ly tiem nang pha Tam Giang" va "Danh gia tiem nang va d~ xuat hra chon khu bao ve dat ngap mroc h~ diim pha Tam Giang-Cau Hai" Phan vien Hai dtrong h9C tai Hai Phong phoi hop voi S6' Khoa h9C, Cong nghe va Moi trirong Thira Thien Hue thirc hien cac nam 1991-1999 II Qua trinh hinh thanh, phat tri~n dfun pha va s,! dOi cua cac cira narn 'hfnh Dieu kiijn hinh th.anli Cac dam pha diroc hinh 6'khu bo' cat co nang hrong song manh Qua trinh hinh va phat trien cac darn pha da diroc nhieu nha khoa h9C n6i tieng the gioi nghien ciru nhir: Zenkovich (1962), Phleger (1967, 1981), Emery (1967), Nichols (1981) _ 1.1 Vai tro ciia kien true oa chuyen d9ng kien tao hien dai Pha Tam Giang nam 6' ria dong bang Hue, phat trien tren nen kien tao hien dai nang yeu va chuyen tiep voi cac d6i sut tren them luc dia So voi cac khoi nang manh tay Hue va Bach Ma, no tr6' vung sut tirong doi 'I'ren nen nang yeu xuat hien cac bon trung cue bo (Cau Hai, cira song Hirong) co • Phan vien Hai dironq hoc tai Hai PhOng Sa Khoa Tap chi Thong tin Khoa hoc va Cong ngh$ hoc, Cong ngh$ va Moi trlrong Tlura Thien Hue 31 e rong' t anphu ~a Hai rti'ngtO yeu to ,A ? ~., ~ BIEN DONG DAM PHA TAM GIANG-CAU HAl CUA ?,,' 'A , VA H~U QUA MOl TRUONG, SINH THAI Tr~n Due Th~nh, Nguyen Chu H6i, Nguyen Hfru co' I M& dftu c chin a tren (ygu to 5, Vol 1, 96 B7 u~n an ien CUll a Iy-D!a H~ dam pha Tam Giang-Cau Hai (TG-CH) co tam quan dac biet doi voi S,! phat trien kinh te dan sinh khu virc Thira Thien Hue nho cac gia tri tai nguyen, ma n6i bat la sinh h9C va cac chirc nang ve sinh thai, moi trirong cua no Cac gia trt va chirc nang gAn lien voi trang thai phat trien cua hai lach cira chinh Thuan An va Tir Hien ton tai nhieu nam thong noi dam pha voibien Tuy nhien, cira lach thirong khong 6n dinh ve vi tri va trang thai dong mo, gay nhimg hau qua tieu C,!Cve sinh thai, moi trirong va kern thee nhimg thiet hai IOn ve kinh te, dan sinh Co th~ coi viec lap cira, chuyen cira dam pha la cac dang tai bien nang ne & ven be mien Trung ma khu virc Thira Thien Hue la di~n hinh Bai viet danh gia hau qua moi trirong va sinh thai cua viec lap ctra, chuyen mo' cira cua he darn pha Tam Giang Tu lieu diroc sir dung chu yeu hi cac de tai cap nha ~U6'e KT.03.11 "Nghien ciru su dung hop ly cac he sinh thai tieu bieu ven bien Viet Nam", KT.DL.95.09 "Nghien ciru khai thac, su dung hop ly tiem nang pha Tam Giang" va "Danh gia tiem nang va de xuat lira chon khu bao v~ dat ngap mroc he dam pha Tam Giang-Cau Hai" Phan vien Hai dirong h9C tai Hai Phong phoi hop voi SO'Khoa h9C, Cong nghe va Moi trirong Thira Thien Hue thirc hien cac nam 1991-1999 ll Qua trinh hinh thanh, phat tri~n dfun pha va s,! dOi cua cac cira tic nam c chfnh 84 Dieu kifn hinh tluinh Cac dam pha duoc hinh & khu bo cat co nang hrong song manh Qua trinh hinh va phat trien cac darn pha da diroc nhieu nha khoa h9C n6i tieng the gioi nghien ciru nhu: Zenkovich (1962), Phleger (1967, 1981), Emery (1967), Nichols (1981) 1.1 Vai tro ctia kien true ua ch.uyen d(Jng kien tao hien dai Pha Tam Giang nam & ria dong bang Hue, phat trien tren nen kien tao hien dai nang yeu va chuyen tiep voi cac dOi sut tren them luc dia, So voi cac khoi nang manh tay Hue va Bach Ma, no tro' vung sut tirong doi Tren nen nang yeu xuat hien cac bon trung C1;lC b (Cau Hai, cira song Huong) co ã Phan vien Hai duonq hoc tai Hai PhOng T'.Ip chi Thong tin Khoa h9C va Cong ngh$ SO' Khoa h9C, Cong ngh$ va Moi trvong Thira Thien Hue 32 vai tro thu mroc tu cac song va cac vom nang cue b9 (Thuy Thanh, An Hoa, Phu Vang) co kha nang lam dich chuyen suy tan cac nhanh song VaGdam pha H~ dtrt gay quoc 19 phirong tay hac-dong nam co y nghra ph an dinh hirong chinh cua dam pha, Cac he dut gay phirong gan a vi tuyen Pho Trach, Hirong Long, Rao Trang co vai tro phan dinh va phan di dam pha theo chieu d9C Cuci cung, chinh s,! nang yeu cua dong bang Hue dieu kien dang cham dan cua mire mroc chan tmh VaG mra sau bien tien Flandrian da tao nen sir binh on tuong doi hoac nang rat cham cua mire bien khu vue, tao tien de hinh can cat chan va dam pha 1.2 Vai tro yeu to dia hinh ke tliua Dam pha va he can dun chan khong th~ hinh & vung bien ven be sau va doc Chinh be mat dong bang aluvi co Pleitoxen thoai va rong & ven bo Hue la tien de quan d~ hinh cac dam pha co va pha Tam Giang dang ton tai V6'i dieu kierinhu vay, hau nhir khong kha nang xuat hien dam pha moi phia ngoai dam pha hien Ngoai ra, dirong nhir la dam Thuy Tu phat trien ke thira tren nen long song co (Pleitoxen) dam Cau Hai thi phat trien tren nenmot vinh bien nho bi de cat khep kin 1.3 Nguon b6i tich cat tao h~ dun chiiri ngotii D~ co dam pha, phai co can dun chan ngoai tao nen tu boi tich cat Khong k~ den.cac can cat S9 phia bac cira song Lau va dong bang cat rong 16'nphia tay pha, dien tich cac can dun chan ngoai kha rong: 190km2• Neu tinh trung binh be day cat 20m, ta co khoi hrong cat khong 10la 3,8ty m" Trong d6, tong hru hrong cat & cac song VaGdam pha chi 120 nghin tan/nam, tirong duong 80 nghin m" C6 nghia la, neu cat trr vung nui tay Hue song mang ven bien d~ tao nen can cat thi phai can c6 47.500 nam, Trong d6, theo ket qua nghien ciru (Tran Dire Th~nh-1985, Nguyen Hiru CU-1995), tudi cac can cat nguon goc bien - gio moi chi 3.000 nam (Holoxen muon) va cac giai doan bien tien Holoxen hinh nen dong bang Hue chi 11 nghin nam Nguon cat khdng 10nay diroc Zenkovich (1964, 1967) giai thich la co nguon goc song Hong co bci dap nen dong bang day vinh Bac B9 VaGPleitoxen, rmrc mroc thap hon hien tren diroi 100m Trong qua trinh bien tien, song da di chuyen ngang boi tich cat VaGven bo Binh-Tri-Thien 4.001 mo r tich tan ( ngot hinh tao J San] voi I cha] me, hon gi2 ngo! bas Thu bAn! each dai keo ban phi 0' gil nM do? True VinE 1.4 Vai tro ciia bien tieri Flandrian doi v6i hinh thanli phii Tam Giang Phleger (1981) cho rang, hau het dam pha tren the gioi diroc hinh vong 6.000-8.000 nam qua Bidn tien Flandrian bat dau tir 17.000-18.000 nam triroc tu d9 sau 100-120m tren them luc dia Theo Shepard (1963), qua trinh bien tien, mire mroc dang cao dan den mire hien nay, den 11.000 nam truce, toe d9 dang 9mm/nam va den 6.000 nam triroc, chi 4mm/nam va sau Tap chi Thong tin Khoa hoc va Cong ngh$, s62(28).2000 qual va b Vao ken} 33 oa, Phli lrn pha, l htrong Hl1O'Ilg oc, Cuoi dan cua binh 6n anh can ven bo I ven bo Giang lat hien m Thuy Hai thi Kh6ng lon phi a ng binh ;6ng hru uong 80 bi~n d~ ket qua can cat ran bien :)ngudn en, songda 4.000 nam chi Lmm/nam Vao Holoxen gitra, khoang 6.000 nam truce, bien tien mo rong nhat ve phia luc dia, toc d¢ dang mire mroc cham him lai va co S\Jboi tu tich C\JCd~ tao nen dong bang Hue, co cac can cat co, dam pha co da tan & Quang Dien, Phu Yang, sot lai di tich va vo so cac tram, bau mroc ngot M\Jc mroc chan tlnh dang cham, lai bi triet tieu tren dOOnang yeu, dia hinh yen be co nong, thoai, lai giau nguon boi tich di chuyen ngang tir day da tao dieu kien thuan 19'ihinh roi lap day nhanh chong cac dam pha co Sang den Holoxen muon, dirong bo lui boi tu den vi trt dam pha hien va vOOcac dieu kien thuan 19'icon tri (day nong thoai, mire bien dang cham chap, giau boi tich cat) da hinh nen he can cat va pha Tam Giang Ve qui mo, pha Tam Giang 16'n hon nhieu cac dam pha co, co le cung ton tai lau dai hon khong co kha nang tao pha moo phia ngoai bien day sau, doc Qua [rinh ph.at trien Qua trmh ph at tri~n, tien hoa cua pha Tam Giang co th~ diroc chi a giai doan: 2.1 Giai doari kh&i c1du Ban dau, dam pha diroc hinh nho noi cao mot day dao cat chan ngoai vung mroc nong hep phia Qua trinh bdi tu nho dong boi tich cat doc bo sau da nci lien dan cac dao cat, chi d~ lai hai cira chinh & Thai DUO'Ilg Thirong va Vinh Hai (sat phia bac ntii Vlnh Phong) S\J hinh pha bat dau bang qua trinh boi tu noi cao cua he thong can cat Linh Thai-Phu Thuan vOOtu each la motdao cat chan (Sand Barrier Island) dan dan noi cao, mo' rong va keo dai ve phia tay bac, Trong do, dong bci tich cat doc be rat manh ph at trien keo dai can dun sat bien tir cira Viet xuong Thai DUO'Ilg'I'huong NhO' do, pha ban dau moi hinh rong, sau hon hien va co hai cira deu rong, mot cira phia nam - co Ie & Vinh Hai sat phia bac mii Linh Thai, mot cira phia bac - co le & giap phia Thai DUO'IlgThirong va Thai DUO'IleH~ da diroc Krempt A.(1931) nhac den Cira sau bi can cat vun cao tren 20m chay dai, lap thang Giai dean khoi dau ket thuc dai cat keo dai gap hmh nen Dai 'I'ruong Sa chay doc ttr cira Viet xuong Linh Thai Ca hai cira Thai DUO'Ilgva Vinh Hai bi lap, dong thai mo cira 'I'ir Hien 2.2 Giai doan tre sang 1-18.000 ), 100 nam l va sau Pha chi co mot cira nhat & phia nam la cira Tir Hien, Vao doi Tran, quan Nguyen danh Chiem Thanh van phai qua cira nay, hai cira co Thuan An va bac Linh Thai bi lap - Pha 1: Tir Hien la cira chinh va Phu Cam la song 16'ndo dam Cau Hai Vao pha 1, song HUO'Ilgchi a lam hai nhanh ttr Hue, nhanh chinh theo kenh Phii Cam, Dai Giang (von la long mot pha tan) van tay bac Cau Hai Tap chi Thong tin Khoa hoc va Cong ngh~, so 2(28).2000 34 Nhanh phu, co le d6 van khu dam Sam-An Truyen V\Jc mroc dam Cau Hai co Ie Ian sau van cira Dai Giang den nga basong Nong Tir Hien la cira nhat cua pha, sau, rong - Pha 2: Tu Hien la cira chinh, song Phu Cam tan, song Hirong la dong chinh d6 van dam pha Vao pha 2, qua qua trinh phat trien, cira song Hirong hie la Dai Giang bi bdi tu manh gay tiic thoat mroc Hoat dong cua vom nang hien dai Thuy Thanh lam song Huang doan Phu Cam bi tan di Song Huang tho at dong chinh bien theo huang dong-hac va co vi tri gan nhu vom nang Phu Vang dAy lech no ve phia bac va nhan hop hru song B6, d6 ve bon sut cira song Huang hien va b6i tu manh chau th6 dam pha - Pha 3: S\J ach tac thoat lu phat tridn delta trieu xu6ng & phia nam dam Thuy Tu dan den mo' cira Thuan An Do khong co 16i thoat true tiep vi tri cira Thuan An bay gio, to an bo dong chay song Huang theo dam Thuy Tu co vai tro nhir kenh dan d6 mroc van dam Cau Hai Vao mila 111, dong hi song Huang tran bo Thuy Tii tao nen cac bai dao dinh huang dong chay, xam thirc hai bo cat va tao nen cac bai boi ngap lu hai ben bo, lam thu hep dang k~ long dan Thuy Tu Mat khac, dieu kien dac biet thuan loi, dong trieu xu6ng va dong hi thoat da: tao nen cac delta trieu xu6ng duoi dang ac bai chim, dao ndi chan dau cira phia nam Thuy Tu Chinh cac bai dao can tro' nghiem thoat lu song Huang va dam pha, dong lu song Huang cong pha cat d6i dien d~ tao l6i thoat moo ngan nhat Vi the cira Thuan An da mo van nam 1404 cham dirt giai doan tre cua pha 2.3 Giai doari truong thanli Thirc day 18.giai doan suy tan cua pha, giin lien voi viec mo' cira moo Thuan An va sir phan di V\JCmroc phan: Tam Giang (tay-bac), Thuy Tu (& giira) va Cau Hai (dong-nam), khac ve hinh dang, hoan hru mroc, qua trinh tram tich va dac diem sinh thai V\JCmroc Tir dau the ky 15 den nay, cira Thuan An tro' cira chinh va l6i thoat mroc chu yeu cua song Huang; Tu Hien cira phu va bi lap, mo' vOOnhip dieu mau dan Trong giai doan co nhirng S\Jkien quan nhir song Phu Cam gan nhir tan han phai khoi dao, song B6 nhap hc1nvan song Huang, song Lau u6n dong vuong goc chay thuan huang van dinh pha Tam Giang, cira Thuan An dich vi tri Ian tren cung bo dai 7km vOOchu ky 100-200 nam, vung To Da & cira Dai Giang bi boi lap tan han Pha da bi nong va hep dang k~, iroc tinh boi nong 2,4mmlnam, bei nong gan 1,5m giai doan nay, tire la d('>sau trung binh cua pha khoang gan 600 nam qua bi giam di mot mra Rieng dam Cau Hai bi b6i nong 1-1,4mmlnam, tirong img 0,6-0,8m k~ tir Tir Hien Tap chf Thong tin Khoa h9C va Cong ngh$, so 2(28).2000 la ell den Vin~ (can] thuo chin nlla cua' li~u toan cac (198 cua Thu cua cua de c qua pha] ton don] sat dan tron chin d9n~ nhm 199 dao 35 Hai co le nhat ~la dong hrong hie cua vom t tan di gan nhir hru song h6 hia nam iep vi iy Tti co hi song am thirc r k~ long mong va dao noi lm doi dien P4 cham cua moo [huy ru l16'c, qua oi thoat oi nhip DngPhti ,song lng, cua , vung k~,u6'c a d(J sau r, Rieng ru Hien a la cira phu giai doan trirong thanh, tac dong nhan sinh da anh hirong sau sac den tien hoa tlJ' nhien cua pha, Vi du: thi hoa ven song Hirong, dao kenh Vinh Te (doi Le) noi Lau-cira Viet, vet song Phil Cam, lap cang Thanh Ha (cang c6 gan Bao Vinh), Tan My (hien nay), diip de Q~P ngan man, ho chua thirong ngudn, tan pha rung Trong qua trinh phat trien cua pha Tam Giang, nguoi luon muon chinh tri hai cira nhirng deu that bai Hai Ian dap dap lap cira Thuan An vao mra the ky 15 va mra dau the ky 20 nhung dap deu bi va Nhieu Ian khoi thong cira Tu Hien ctra hi lap deu khong congo III Bien dc?ng cua cac ctra K~ tu cira Thuan An doi, cira Tir Hien tr6' cira phu va ca hai cira deu khong 6n dinh Tinh khong 6n dinh bieu hien qua cac trang thai chuyen d6i vi tri cira, dich cira, mo' cira, lap cira, thu hep mat cat uct hoac bien dang luong cira nhieu Ian Itch su.· Dien bien cua qua trinh chuyen lap cira dam pha duoc theo doi qua cac tir lieu c6 nhir cluui can luc cua Duong Van An (tir the ky XVI), DCJ.-iVi~t szi: kj toari thu: (tir the ky XVII), Phii bien tCJ.-Pluc cua Le Quy Don (ttr the ky XVIII) va cac nghien ciru cua Krempt A (1931), Son Hong Dire (1974), 'I'ran Dire Thanh (1985) va nhimg dieu tra nhan dan gan day Ctia Tu ttu« Nhir da trinh bay, tu nhieu the ky triroc, he dam pha TG-CH chi co mot cira nhat goi la cira Tir Dung (nay la cira Tu Hien), Chi tir nam 1404, cira Thuan An mo, he dam pha moo co hai cira Tren thirc te, cira Tir Hien gem cira, cira chinh dong hi mo' thong true tiep bien 6' Vinh Hien (thon Phil An), va cira phu 6' Loc Thuy (sat mui Chari May Tay) Hai cira ngan each qua mot de cat dai km, cao khoang 2-2,5m chay doc bo Dong mroc tir dam pha bien qua cira phu phai chay vong theo mot lach nong nam sat sau de cat chan Theo ph an tich dien bien Itch su va dc}cdi~m hinh thai dong lire thi cira Vinh Hien ton tai truce, K~ tir cira Thuan An mo, dong hrc dong qua cira yeu di va dong boi tich doc bo tao nen mot doi cat phat trien day Ian cira v~ phia nam den sat mui Chari May Tay Khi cira Loc Thuy 6' Chari May 'I'ay bi tan boi lap dan thi dong III mo' lai cira chinh Vinh Hien Trang thai cira Tir Hien luon 6''mot bon trirong hop: cira chinh mo, cira phu dong; ca hai cira d~u dong kin; cira chinh dong, cira phu mo; va ca hai cira d~u mo Truong hop va hoan toan dong lire tu nhien tao Da nhieu Ian cira chinh bi dong, nhan dan t6 chirc dao nhirng sau bi lap tro' lai Lan lap cira gan day nhat vao thang 12 nam 1994 cung vay Truong hop ton tai ca hai cira d~u bi lap va phai tien hanh dao cira phu sau viec khai dao cira chinh that bai, Tren thirc te, chira Ian Tap chi Thong tin Khoa hoc va Cong ngh$, s62(28).2000 36 nao cira phu t\! mo' nhir cira chinh Truong hop it xay va ton tai thoi gian ngan vi sau dong hi mo lai cira chinh, cira phu se bi boi lap Ngay sau cira Thuan An mo, cira Tir Hien bat dau co xu the bi boi lap Vi v~y, nam Quang Thuan thir (1467), Tham nghi chau Hoa la Dang Chiem dang so xin lam viec tien loi dieu, co cac dieu lap cira Eo (Thuan An) va giu cira Ttr Dung (Tir Hien) va d~ nghi da diroc chap nhan, Dieu co nghta la sir ton tai cua cira Ttr Hien da bi de doa tir thoi va sir de doa da dan den ton tai hai vi tri: mot 0' Vinh Hien va mot 0' LQc Thuy Lich su bien dong cira Tir Hien diroc tom tiit lai nhir sau: Bang 1: Bien dQng lap, md cua Tu Hi~n ve Sl no tJ co vi Vi trf clia Thai gian Vinh Hien L9c Thuy Narn 1804 Van co Nam 1811 Ma Narn 1823 Lap danl Narn 1844 Ma nhu Narn 1953 Lap Narn 1959 Ma tran Nam 1979 Lap Narn 1984 Narn 1990 Ma Narn 1994 Lap Chva co Lap thu Ma Lap xay Ma dam rat] Moi Ian bien dong cira d~u gay kh6 khan cho doi song cong dong dan cir khu V\!C.Khi cira bi lap, ngoai viec lam ach tac giao thong va nghe khai thac bien khoi, lam thay d6i C(J cau tai nguyen va gia tri tai nguyen sinh vat dam Cau Hai bi ngot h6a Sau gan nam ke tir bi lap (12.199411.1999), mac du da diroc ke kha kien co, cira Tu Hien van bi pha mo' vao 2.11.1999 CCJnlut the ky khung khiep voi rmrc mroc dang cao 5,94m tai Hue Cling voi thoi khoang mo' nam vao 1990-1994, thoi khoang lap Ian chi nam, chtrng minh rang nhip dieu lap mo cira mau hon nhieu so voi trtroc day Ctia Th.utin An So voi cira Tir Hien, cira Thuan An co C(J che va Itch su bien dong phirc tap hon Ngoai che dQ dQng hrc bien san bang bo, su' bien dong cua cira lien quan too C(J che uon khuc cua doan hru song HUCJng,thay d6i tirong quan giira chu hru va chi hru c6 tac dung cua vom nang Phii Yang Do v~y, cira Thuan An da tirng ton tai nhieu vi tri cung nhir ten goi khac Itch suo b mal tiep hoan xu h cua Thuc An c den: tri tl Tinh 15m - Nam 1404, me cira Thuan An va tro cira chinh cua he dam pha c6 ten la cira Nhuyen bOi - Nam 1467, s6' dang cua Tham nghi chau Hoa la Dang Chiem diroc chap nhan, chinh quyen phong kien sai truyen dan binh lap tro' lai dam T'ilp chi Thong tin Khoa hoc /a Cong ngh$, s62(28).2000 chuy 37 ~ongthoi rp ~b6i lap Ig Chiem LU~n An) c6 nghla a del 811 bien - Cho too doi Canh Thong (1498-1504), cira mo tro' lai Rat co th~ hie moo mo Ian dau nam 1404 cira nho nen ngiroi thoi moo co th~ lap lai d~ han khau cho too doi Canh Thong Nhung Ian bien dong ve sau manh hon, nguoi khong du kha nang che ngu va del tim each su dung n6 the chien hroc kinh te-quan str thoi phong kien, - Trong khoang thoi gian chimg 200 nam k~ tir nam Giap Ty (1504), cira c6 vi tri & Thai DUO'IlgH~ - Trong khoang thoi gian chimg 200 nam tiep theo cho too nam 1897, cira c6 vi tri tai lang Hoa Duan, - K~ tu nam 1897 too nay, cira c6 vi tri nhir hien - cira Thuan An (Hd Tan Phan va Ho Th~ Thu Trang, 1991) Trong thirc te Itch su, ten cira "Thuan An" chinh thirc dman dam Cau Hai bi giam 8-11%0 so voi nen chung mo' Tap chi Thong tin Khoa hoc va Cong ngh$, so 2(28).2000 42 cira la 20-32%0 Tuy nhien qua trinh ngot hoa xay sau sac VaGmua mira qua Ian lap cira VaGthang 12.1994 Sir ngot hoa khong chi (j khu dam Cau Hai ma xay tren toan pha Tam Giang Theo so lieu VaG mua mira thang 1.1993 (khi cira Tir Hien mo) cac khu VVC cira Thuan An, Ttr Hien va An 'I'ruyen-bac Thuy TU d9 man 10%0; Cau Hai va gnra Thuy TU co d9 man 5-10%0; cac khu VVC ctra song Hirong, cira Dai Giang va mra bac Tam Giang co d9 man ttr diroi 0,5%0 den 5%0 Den mua mira, thang 11 1995 (khi cira 'I'ir Hien lap), su ngot hoa bao trum len gan toan b9 dam pha D9 man circ dai 15%0 chi ghi diroc (j mot thai di~m (j tang day tai cira Thuan An va d9 man cue dai tang mat (j day cling chi 0,7%0 cira Tir Hien, d9 man cao nhat chi 0,33%0 dam Cau Hai, d9 man phd bien diroi 0,2%0, cue dai chi 0,3%0 Cac khu virc cira song Hirong, phia bac Tam Giang, cira Dai Giang d9 man diroi 0,1%0 hiem den 0,2%0 T6ng quan lai, ve mua mira triroc lap cira Tir Hien, d9 man 1-10%0 dac trung cho toan dam phi, sau lap cira d9 man diroi 1%0 dac trung cho toan dam pha (Nguyen Chu Hoi, Do Nam va nnk, 1996) a a Su ngot hoa virc mroc dan den thay d6i cau true phan loai va cau true he sinh thai dam pha Nhirng thay d6i xay manh nhat (j khu he thirc vat Thanh phan khu h~ gom 8,93% so loai mroc ngot dien hinh; 19'va nhat 12,34%; 19' di~n hinh 0,85%; 19' man (8=15-30%0) 72,76% va man 5,10% Rieng doi vOOthuc vat phu du co 78,36% so 17110ai co nguon goc bien va 19,29% loai mroc ngot, Trong dam pha, d9 man giam den 15%0 chi 36 loai thirc vat phu du bien, d9 man 10%0 chi 25 loai va 5%0 chi loai (Ton That Phap, 1993) Vi v~y dong cira 'I'ir Hien, khu he thirc vat phu du bien bi huy hoai, thay VaG la khu he mroc ngot, thuong ngheo hon ve sinh khoi Dei vOOcac loai co mroc, duoc biet co 11 loai co vai tro quan dac biet vOOhe sinh thai dam pha Tam Giang[6] Trong co cac loai co bien ira d9 man cao (23-30%0) nhu Hylophylla ovalis, Halodule tridentata; cac loai co bien thich nghi mroc 19' (7-20%0) Ruppia maritima, Halophylla beccari; va loai ira man (1530%0) Cymmodocea rotundata co sinh khci rat cao va phan bo rong khap dam pha Khi d9 man diroi 10%0, cac loai deu suy tan, han che phat trien va bi ngot hoa chung chet hang loat, thay VaG la sir phat trien cue thinh cua Valisneria spiralis «5%0) va Najas indica (0-25%0) Sir huy hoai tham co bien ngot hoa dan den thay d6i cau true khu he, dien tich ph an bo va keo theo sir thay d6i ve phan bo cac doi tirong dong' vat (chu yeu la ca) an chung, a Ngot hoa anh hirong dac biet 16'n den khu he ca dam pha Tam Giang co too 230 loai ca, 65% la ca bien, 19,2% ca mroc 19'va 15,7% ca mroc ngot (Nguyen Nhat Thi, 1998) Da dang sinh hoc nhom ca giam han ca bien phai di cu khoi dam pha Dang chu y la 20-23% loai ca kinh te thich hop dieu kien mroc 19' Khi d(>muoi giam thap cung anh huong den san hrong thuy san Tuy nhien, mot so doi tirong ua mroc ngot va 19' nhat, dac biet la loai ca day (Cyprinus Tap chf Thong tin Khoa hoc va Cong ngh$, so 2(28).2000 ceni d6i th tha b~t I Mt Hi~ chd h6 Tu hH S1! tin} chi] eel phd den chu Tu cao v6'i di~J 77 nll) h 43 qua Ian xay cira Tu !t