Tiiu ban Khoa hgc cong nghe Biin ISBN 978 604 913 01 DAC DIEM XOI LO, BOI TU VA TIEN HOA VUNG CUA SONG LAM TRONG HOLOCEN HIEN DAI CHARACTERISTICS OF EROSION AND ACCUMULATION AND EVOLUTION IN THE ESTUA[.]
Tiiu ban: Khoa hgc cong nghe Biin ISBN: 978-604-913-01 DAC DIEM XOI LO, BOI TU VA TIEN HOA VUNG CUA SONG LAM TRONG HOLOCEN - HIEN DAI CHARACTERISTICS OF EROSION AND ACCUMULATION AND EVOLUTION IN THE ESTUARINE REGIONS OF LAM RIVER IN HOLOCENE Nguyen Tien Hai*, Do Canh Duong ** * Vien Dja ch^t va Dja vat ly bien, ** Tmdng Dai hgc Md - Dja chat Tom tat: Vimg cira sdng Lam (Cira Hdi vd Idn can) thudc dai ven biin Vimg cira sdng ndy dugc hinh thdnh mdi tuang tdc giira thgch quyin - thiiy quyen - quyen Trin ca sa tdi lieu khao sdt thue ti (2007 - 2008),^ tdi lieu dia chdt vd mot sd tdi lieu khdc, bdi viit Idm sdng td cdc dgc diim dia chdt - dia mgo, hogt ddng xdi labdi tu ciia vimg cira sdng Lam vd sir phdt triin- tien hda cua khu vuc Holocen - hien dgi Bdi viit cung di cap mot sd nguyin nhdn gdy vd tdc ddng din xdi la, bdi tu vd phdt triin ciia viing cira sdng Lam Abstract: The estuarine of Lam River (Cua Hoi and adjacent area) in the coastal zone.This regions are products of Land - Ocean - Atmospheric interactions Based on results collected from field investigations (2007-2008), geological data and other data to contribute to determine the geologicalgeomorphological characteristics and erosion - accumulation of the estuarine regions of Lam River and adjacent and their evolution in Holocene The paper also analyses the role of Sea- level change, human and causes which impacted to natural hazards in the study area \ Md dau Sdng Lam la mot ddng sdng Idn dd vao bien qua Cira Hdi Ddng sdng cd vai trd quan trgng ddi vdi khu vuc Bac Trung Bd ndi chung, hai tinh Nghe An va Ha TTnh ndi rieng Trong qua trinh phat trien ciia sdng, so vdi nhieu sdng khac dd vao bien d Viet Nam, viing cira sdng Lam cd nhieu bien ddng, dac tmng ve hinh thai cau true, che ddng lire, xdi Id - bdi til De cd the khai thac, sir dung hgp ly, hieu qua viing cira sdng nay, can nam bat dugc cac thdng tin ve dac diem va su phat trien cua khu vuc ndi chung, cira song ndi rieng Nhirng thdng tin cdn la co sd khoa hgc giiip de xuat cac bien phap giam thieu nhirng tieu cue sir phat trien eiia sdng gay Vdi vimg cua sdng Lam, nhin chung miie nghien cim chua nhieu Ve dja eh4t - dja mao khu vuc ed cac cdng trinh cua Le Duy Bach va nnk (1976-1980), Tr4n Tinh va nnk (1974-1978), La Van Xuan va nnk (1996); nghien cuu ddng lire va phan loai cira sdng cd Hoa Manh Hiing va nnk (1991), Nguyen Van Cu (1991) Nhirng nghien ciru tren da cung c^p nhiSu thdng tin v6 dja ch4t-dja mao eiia viing cua sdng Lam Tuy nhien, ddi vdi kliu vuc nay, cdn tdn tai nhieu van de can dugc lam sang td, dd cd van de xdi Id - bdi tu va phat trien - tien hda viing cira sdng 110 Hgi nghi Khoa hgc ky niem 35 ndm Vien Khoa hgc vd Cong nghe Viet Nam - Hd Ngi 10/2010 Tai lieu va phu-ffng phap Cua cua cac ddng sdng (chinh xac la viing cira sdng) dd vao bien thudng cd cau tnic kha phire tap dugc nhilu nha nghien cim chia lam nhieu ddi dua vao mdi tuong quan giiia yeu td ddng lire sdng va bien Vk vj tri dja ly, viing cua sdng chii yeu thudc dai ven bien - khu vuc dugc hinh mdi tuong tac giua thach quyen, thiiy quyen, quyen va sinh quyen) Sir phat trien, tien hda cua sdng ndi chung, viing cira sdng ndi rieng dugc the hien bdi sir thay ddi hinh dang sdng, dac diem hinh thai cau tnic day sdng Nhiing thay ddi tren ciia sdng chii yeu dugc thdng qua cae hoat ddng xdi Id - bdi tu bd va day ciia sdng dudi tac ddng ciia cac yeu td ddng lire bien, sdng, hau Nhu vay, thdng qua mdi tuong quan giiia hoat ddng chinh dien d viing cira sdng la xdi Id va bdi tu, cd the nam bat dugc sir phat trien ciia viing cira sdng Tai lieu chinh sir dung cho bai viet la nhiing sd lieu dac tac gia true tiep tien hanh (thang 7/2007, thang va 4/2008) qua trinh thue hien thue hien mot sd de tai, de an khoa hgc Ket qua nghien ciiu a) Mot vdi ddc diem chung viing cira song Lam vd ba bien Idn can Doan sdng Lam tir cau Ben Thiiy den Ciia Hdi cd dang chir S, dd doan giua dai ~ 7,5km keo chay gan nhu song song vdi dudng bd bien Chieu rdng sdng Lam dao ddng 600-^ 1.300m vdi xu the md rdng dan theo hudng di bien Ve mat kien tao, doan sdng nam d phia Ddng Nam ciia ddi sut Nghi Ldc Theo quan diem phan chia viing cira sdng ciia Nichols va Bigg (1985, dua vao tuong quan ddng lire sdng/bien), cd the coi doan sdng Lam tir cau Ben Thiiy den Ciia Hdi la viing cira ciia sdng Lam, gdm cac ddi cira (tinh theo bd Nam): i) Ddng sdng (cau Ben Thiiy - xa Xuan Giang); ii) Cira sdng (tiep ddi den khoang ranh gidi xa Xuan Tmdng/Xuan Hdi); iii) Sdng-bien (tiep ddi den ciia hd Hdi Thuy) va iv) Bien - sdng (tiep ddi phia bien) Tren thue te, rat khd tach biet dugc rd rang ranh gidi giiia cae ddi cira sdng; mat khac, ranh gidi cd the thay ddi theo miia nude lii (tham chi theo hoat ddng eiia thiiy trieu) viing cira, day sdng Lam cd trac dien ngang co ban la dang chii V khdng can ddi, noi sau nhat ciia day thudng lech ve phia bd bac hoac bd nam tiiy tirng doan sdng (hinh 2) Be mat day sdng kha phire tap, khdng bang phang, cd nhieu khdi nhd (nhieu chd tao bai bdi ngam) vdi kich thudc khac vai hudng keo dai chii yeu dgc theo long sdng Trong mot sd doan sdng, bai bdi long sdng phat trien manh theo chieu cao ciing vdi sir thay ddi ciia muc nude, tao dao ndi da chia day sdng Idng khac (hinh 1) Ve sau day sdng, sau Idn nhat dgc theo day viing cira sdng Lam (tir cau Ben Thuy den Cira Hdi) dao ddng khoang 5^ 13m, do sau day dat Idn nhat d ddi cira sdng/bien vdi mirc 12,2m each bd Bac khoang 120m (mc.CH2) Tir vj tri mat cat nay, sau Idng sdng giam dan theo hudng phia bien (d vj tri mc.CHl, Idng sdng sau nhat la 10,5m) b) Hien trang xdi la - boi tu vimg cira song Lam vd ki can - Hoat ddng xdi Id bd: Phia bd Nam, doan bd tir du Ban Thuy dSn xa Xuan Giang, hoat ddng xdi Id dien vdi mirc thap va chii yeu d phan bd cao vao miia nude lu ciia sdng Doan bd tir Xuan Hai den Ciia Hdi, tmdc nam 1978 (chua cd ke da ven bd Xuan Hai 111 Tieu ban: Khoa hgc cong nghe Bien ISBN: 978-604-913-015-1 Xuan Hdi) hoat ddng xdi Id dien manh d doan Xuan Tmdng - Xuan Hdi, o phia bd Bac ddi dien, xdi Id dien chu yeu doan cau BSn Thiiy - Hung Hda (Nghi Ldc) va cang ca Cira Hdi Tir nam 1978 den nay, hoat ddng xdi Id lai dien g4n nhu ngugc lai so vdi thdi gian tmdc bd Nam, xdi Id doan Xuan Hai - Xuan Phd "chuygn thanh" xdi mdn, mai mdn bd, cdn doan Xuan Tmdng - Xuan Hdi, xdi Id dugc thay bang bdi tu va doan bd Xuan Hdi lai 'chuyen' tir bdi tu sang xdi Id bd Bac, xdi Id dien manh vdi tdc ed xu th^ tang, nhat la doan bd tir Xuan Khanh den cang ca Cua Hdi (tdc xdi Id cao nhat khoang 2m/nam [7]) Hien tai, tren ddng sdng d khu vuc Xuan Khanh, cdn lai dau tich bd sdng cii (tmdc 1978) xdi Id bd phia da de lai doan bd sdt dai - 40m nhu mot 'bai bdi' ndi map md giua sdng vao thdi gian thuy trieu dat mire cao nhat (anh 1) IIAN ix'i t)l V MAO - 1 ( ) N ( Q l AN HOI H CI A HOI - XOI l. mc.CH2 -> mc.CH3 -> mc.CH4 -> mc.CH5 -> mc.CH6) Sau nam 1978 - den nay, nhieu yeu td (dac biet la tac ddng cua ngudi) nen 112 Hgi nghi Khoa hgc ky' mem 35 ndm Vien Khoa hgc vd Cong nghe Viet Nam - Hd Ngi 10 2010 hoat ddng xdi Id - bdi tu dien biSn kha phire tap, gia tang cudng va cd xu the ngugc lai so vdi thdi gian trudc 1978 d mot sd doan bd bd nam, xdi Id bd dien manh d doan bd Xuan Hai va giam dan phia bien Hien nay, cd ke chdng xdi Id, nen hoat ddng xdi lo tai day bj 'bien ddng' chuyen sang xdi, mai mdn Phan bd biin kk can Cira Hdi, d phia Nam bd bien tir Hdi Thuy qua Xuan Thanh dkn Xuan Yen (Nghi Xuan), bd bien bj xdi Id rat manh (anh va 3); cdn phia bd Bac, xdi Id bd (phan bd cao) vdi mirc thap, hoat ddng bdi tu tao bai bdi ngam tmdc cira sdng la kha manh (hinh I) Ddng Tdv Tay Ddng [:ir'iTi-irii-tr«wir -'^i^V ^1 M si mc.CH6 mc.CH5 Ddng Nam Tdv Bdc Tdy Bdc me.CH4 Ddng nam •f i Ddng Nam mc.CH2 Tdy bdc • *>* ^ ^ H ^ •Jfes^ nam cd tdc 0^ 9lcm/s [6].); iv) Vat chat va dia ddng lire noi sdng chay cjua (tram tich De tir bd rdi, hoat ddng tan kien tao va bieu hien kien tao hien dai kha manh: tdc sut cua bdn Nghi Ldc tir dau De tir den dau Holocen ~0,058mm/nam, Holocen mugn la -5,75mm/nam [7]); v) Vai trd eiia sinh vat (nhat la ngudi, thdng qua xay dung de, ke) Ve sir ddi hudng dot nggt ciia ddng sdng tir hudng Tay Bac -> Ddng Nam tai khu virc xa Due La, Dire Thg (noi sdng La dd vao sdng Lam) chuyen sang hudng Ddng Bac ve Bin Thiiy va dd bien tai Cira Hdi, hien chua cd quan diem nao dugc minh chirng rd rang Theo ngudi viet nguyen nhan chinh la yeu td tan kien tao va kien tao hien dai Tren binh dd kien triic kien tao hien dai, viing cua sdn^ Lam (va phu can - dd thj Vinh) phat trien cac dirt gay cd phuang Tay Nam - Ddng Bac (gan triing vdi phuang kt^o dai ddng sdng Lam d luu) la cac dirt gay tre nhat d khu vuc [7] phat trien tren viing sut Nghi Ldc Cd le chinh sir cd mat ciia cac dirt gay ket hgp hoat ddng sut kha manh cua bdn Nghi Ldc (bdn cd true sut liin keo dai gan nhu vudng gdc vdi ddng sdng Lam viing cira sdng, tdc sut liin tai day: da neu tren) da tac ddng vao khdi niii da ed Ben Thuy - niii Dang va lam cho ddng sdng Lam chuyen hudng chay eat ngang khdi niii sang hudng Ddng bac, vugt qua ddng bang cat bien Holocen giiia - mugn va dd Cira Hdi nhu Day ciing la quan diem ciia La Van Xuan va nnk [7] Thay cho ket luan - Doan sdng Lam tir cau Ben Thiiy den Cira Hdi la phan dien tich chinh eiia viing cira sdng Lam, gdm cae ddi cira: ddng sdng, cira sdng, sdng-bien va bien-sdng Trac dien ngang long sdng d viing cira cd hinh thai dac tmng dang chir V lech ve phia bd Nam hoac Bac O mot sd doan, ldng sdng cd day Do sau day d viing cira sdng dao ddng 5^13m Tai noi ranh gidi ddi cira sdng-bien va bien-sdng, day sdng nhd cao hon so vdi day chung khoang 3-^5m - Hoat ddng xdi Id va bdi tu d viing cira sdng va bd bien ke can cd xu hudng cang gia tang va ed sir khac biet giai doan: tmdc 1978 va sau 1978 - Phat trien, tien hda ciia viing cira sdng va bd bien ke can kha phire tap vdi mire bien ddng cao (bieu hien qua cac qua trinh, hien tugng xdi Id, bdi tu, sut liin viing ) dudi tac ddng ciia cac yeu td thach quyen - thiiy quyen - quyen - sinh quyen Do tien hda, cau tnic hinh thai ldng sdng d viing cira sdng Lam ed the bj bien ddng vdi xu the hinh dang chir S ciia viing cira sdng cang rd net hon - Trong khai thac va sir dung viing cira sdng Lam ckn than trgn^ va cd nhirng giai phap phdng tranh, giam thieu mirc xdi Id - bdi tu bd, tron^ dd c4n phdi hgp nhilu giai phap, dd nen coi trgng giai phap cdng trinh (xay de ke) ket hgp vdi phi cdng trinh (trdng cay nude Ig d ven bd) 115 Tieu ban: Khoa hgc cong nghe Bien ISBN: 978-604-913-015- TAI LIEU THAM KHAO 116 Le Duy Bach va nnk (1995) Ban dd Dja hda chSt va khoang san ty le 1/200.000, td Vinh Cue Dja chat Viet Nam Nguyen Van Can va nnk (2008) Bao cao de tai khoa hgc "Nghien ciru xdi Id bdi tu cae cira sdng ven bien Nghe An" Tmdng Dai hgc Md - Dja eh4t Nguyen Van Cu, 1991 Ve van de nghien cim ddng lire cac viing cira sdng Viet Nam TT Bao cao khoa hgc HNKH toan qude vl biin i k thir III, tap Vien KHVN Tr.166-169 Nguyen Tien Hai va nnk (2008) Dac diem dja mao - dja chat va sir phat trien, tien hda viing cira sdng Lam Holocen Bao cao khoa hgc Vien Dja chat va Dja vat ly bien Hoa Manh Himg va nnk (1991) Phan loai cac cira sdng Viet Nam theo dac diem dja hinh va cac dau hieu dja mao ddng lire TT Bao cao khoa hgc HNKH toan qude ve biin l4n thir III, tap Vien KHVN, tr.238-243 Nguyen The Tudng va nnk (2000) Sd tay tra cim cac dac tmng tugng thiiy van viing them luc dja Viet Nam Tdng cue Khi tugng- Thuy van, Nxb Ndng nghiep La Van Xuan va nnk (1996) Dac diem dja mao dd thj Vinh Bao cao khoa hgc Cue Dja chat va Khoang san Viet Nam ... cira song Lam vd ba bien Idn can Doan sdng Lam tir cau Ben Thiiy den Ciia Hdi cd dang chir S, dd doan giua dai ~ 7,5km keo chay gan nhu song song vdi dudng bd bien Chieu rdng sdng Lam dao ddng... gan nhu vudng gdc vdi ddng sdng Lam viing cira sdng, tdc sut liin tai day: da neu tren) da tac ddng vao khdi niii da ed Ben Thuy - niii Dang va lam cho ddng sdng Lam chuyen hudng chay eat ngang... ldng sdng d viing cira sdng Lam ed the bj bien ddng vdi xu the hinh dang chir S ciia viing cira sdng cang rd net hon - Trong khai thac va sir dung viing cira sdng Lam ckn than trgn^ va cd nhirng