VIEN D | A LY - VIEN KH&CN VIET NAM HOI DIA LY 'VIET NAM
P H A N
TICH DAC DIEM DIA MAO TINH LAO CAI PHUC VU DU B A O HIEN TUONG LU QUET
Kieu Qudc Lftp'
SUMMARY
Study characteristics of geomorphology in Lao Ctd province for flash flood warning For mountainouiis areas of Lao Cai province, severed kinds of natural hazards, such as flash flood, debris, mud flash flood and landslide, present a constant catastrophic rick. In order to warn of their appearance we can study geomorphological.
'This paper dicusses the necessary and sufficient geomorphologic, lithologic and tectonic conditions for flash flood which should be consider as geologo - geomorphological M-arning sings. It seems the most vulnerable sites coincide with those areas where exist tectonic .shattered belt, rocks which are easy to be crushed and shattered fomiiig weathering products heterogeneous and rich in clay material, availability of thick and abundanl cover of superficial deposits, presence of alluvial fan deposits, etc.
1. DAT V A N DE
Trong nhfrng nam gan day, ki quel xay ra ngay cang nhieu va gay ra nhfrng thid hai Idn ve ngudi va ciia. Do nai chju ki thudng la noi phan bd dan cu ddng diic nen thiet hai cang Idn. Thai gian qua, Ifi quel da xay ra d nhieu nai trong tinh Lao Cai, dac bid la cac huyen nam tren day Hoang Lien Son, nhu huyen Van Ban, Bat Xat, SaPa.
Lii qud la dang tai bien dac trung va la mgt tai bien nguy hiem ddi vdi mien mii.
Thuc chat ki q u d la mdt trang thai dac bid ciia lii cd lien quan chat che den dac diem dja hinh, dja mao. Tren ca sd nhfrng tai lieu dieu tra, khao sat, md ta cac tran Ifi quel d Vid Nam, cluing ta Ihay rang;
1 - Lfi quel thudng xay ra nhanh, bat ngd, dien ra trong thdi gian ngan, nhung sire pha buy lai rat Idn,
- Cac Iran ki quel thudng xay ra vao ban dem va vao dau miia ki, Nhfrng nam gan day, hi quel cd xu hirdng tang len mgt each rd ret,
- Noi sinh ki la dau ngudn ciia cac con sdng cd do ddc Idn. Nai chju lii thudng la cira ciia dong chay lain thdi, noi hdi luu ciia mdt vai nhanh sdng. Day thudng la noi tap Irung ddng dan cu.
- Luu vuc xay ra lfi quel thudng nhd va cd do ddc Idn, ddng chay mat cd ddng nang Idn, gay xdi mdn, sup Id phd bien.
- He thdng ddng chay bj u tac bdi dja hinh hay cac baric tu nhien hoac nhan tao.
Khi cac vat can nay bj pha buy tbi ddng hi cang hung dfr hon.
Dai hoc Thai Nguyen
Hdi nghi Klioa hgc Dia ly Todn qud'c Idn th&S - Hd Ndi, 2010 833
en ini VIEN DIA LY • VIEN KH&CN VIET NAM HOI DIA LY VIET NAM
Nlur \ a \ . ki quel co lien quan mat thiet den dac diem dja binh. dja mao d nai di ra chuiu:. Niihien ciru dac diem dja mao khu \'ii'c cd the gdp pluin phdng tranh \a gi;.,,, thieu thid hai do lu qud ga) ra. Trong khudn khd bai bao na\ lac gia xin trinh ba) dac dilin dja mao tinb Lao Cai phuc su du bao bidi lugng ki quel nham giam thieu Ibid hai do chung ga\ ra.
2. D.AC DILM DIA MAO TINH LAO CAI
Dia mao linh Lao Cai la mgi birc tranh phan anh kha rd n d mdi tuang tac gifra cac qua trinh ngi lire \a ngoai luc trong sudt Kainozoi tren nen cau tnic dja cluil c6.
Nhfrnu nel dac irung co ban cua dia mao Lao Cai cd lien quan vdi lfi quel dugc ihc hien dudi da);
2.1. Binh do son van phu hop vdi cau true dja chat cd vol phuong thong trj \h Tay Bac - Dong Nam
Neu dem ban d6 dja hinh linh Lao Cai dat chdng len ban dd dja chat, ban d6 kiln tao cluing ta se thay c6 mgt sii triing hgp den ngac nhien gifra dja binh va dudng net cau tiiic dia chat. Dudng nlur loan bg cac )cii td cau tnic dja chat Idn deu dugc phai ba)' trdi dja hinh hidi dai. Dicu do da khang djnh cac qua trinh ndi lire xa)' ra tren v6 Triii Dal a da) co su boat dgng manh me, chimg thang the va qu)' djnh hudng ciing nhir ciiiing do cua qui trinh ngoai sinh trong \ iec thanh tao dja hinh,
liuing king S6ng H6ng phat trien tren mgt ddi dirt gay cimg ten, la ranh gidi phan chia gifra hai midi dja mao va dja chat khac nhau: mien Ddng Bac va mien Tii) Biic.
Thugc pham vi linh Lao Cai, dja hinh a Ddng Bac thung king Sdng Hdng cd dang Uivdi theo phuong Tay Bac - Ddng Nam, pbii hgp vdi cac can tnic dja chat phat trien trdi cac da tram tich Ui6i Paleozoi. Cac thanh lao dja hinh d Tay Bac lai cd dang tuyin theo phuang Ta) Bac - Ddng Nam - phuong th6ng trj ciia cac cau tnic dja chat Ircn cac dii tu6i lir Prolcrozoi den Mesozoi. Tai vimg cue Tay Nam ciia tinh, cac day mii ihip co dang lu)en vdi sudn bat ddi xirng dugc phat triln tren cac trim tich luc nguyen tuoi Mesozoi. Ciing vdi cac day mii, hinh thai mang sdng sudi trong khu vuc cfnig cd dang thang, \dng cung lbeo cau tnic dja chat. He thong sdng sudi dang loa lia (ly lam) ciing dugc phat trien lai cac khdi xam nhap axil.
2.2. Sir phan di >c do cao dja hinh phiin anh dac trung ciia hoat dgng tan kicii tao manh me
Dja hinh ngay nay da phan anh kha trung thuc va sinh ddng cac boat dgng tan kien tao. Cac he thdng dirt gay phuong Tay BIC - Ddng Nam da boat ddng lich cue Irong Tan kicn tao, keo theo cac chu)'en ddng khdi tang. Dang clui y la khoi nang dang dia kl) \di bien do Idn da binh thanh da) niii Hoang Lien Son - day mii dd so cd do cao Ion nhai Vid Nam. Day la day mii cd anh hudng dang kl tdi cac dac trung khi hau ciia Lao Cai, \a do dd ciing lien quan chat che vdi hidi tugng ki kit, lu quel. Day mii Con Vol - mgt bg phan ciia phirc nep I6i s6ng Hong cung cd dang mdt day mii dja luy. kep gifra hai ddi dirt gay Sdng Hong va Sdng Chay.
Dong thdi vdi su nang manh dl tao cac day mii cao, dgc ddi dirt gay Song Hong, qua trinh sut kin kien tao tuang doi da dan tdi hinh thanh thung lung vdi tang trim lich
K I " • • • X • , o o o ^
^cogcn, \ai cac be miil them sdng. cac bl mai pediment thung king bj phan clt manh lao dja hinh go doi thoai.
VIEN DIA LY - VIEN KH&CN VIET NAM HOI D!A L'r VIET NAM
2.3. Dja hinii Lao Cai cd tinh phiin biic rd riing
1 inli phan bac dia hinh phan anh klui rd diic trirng ciia hoai dgng tan kidi tao trong vice thanh lao dia hinh. da la linh clui ky. Cac be mat san bang dugc hmh ihanh d cii6i mdi chu ky tan kiiin lao bidi cdn dugc bao ton kbi rd Iren dja pluin linh Lao Cai, do la cac be mill hidi dang phan bd iren cac bac do cao 150 - 250ni, 400 - 600m, 900 -
1200m, 1400 - 1600m, 1800 - 2000m, 2200 - 2400m, va 2800 - 3000m.
Be mill san bang dien hinh lai Lao Cai la cac be mai cd do cao 1400 - 1600m phan bd a Bac Ha vi Sa Pa. Dd la cac be mat rgng, bj cac muong xdi va khe su6i pluin cat, tao dja hinh ddi tren luii.
Ircn cac be mat san bang thudng bao tdn ldp vd phong boa cd be day kha Idn.
cac khe sudi pluin cat sau vao cac be mat na) tao sudn vach ddc tren tang phong hoa de phat sinh cac khdi trugt, lain gia lang boat ddng ciia cac ddng biin da.
2.4. Dia hinh karst d Liio Cai phan anh cac dac trung ciia karst nhiet ddi
I bugc pham vi linh Lao Cai cd ba tlianh tao dja chat chira carbonal cd mirc dja Uing khac nhau, do hi cac trini lich bien chat tudi Proterozoi thugng - Cainbri thudc he Uing Sa Pa phan bd tai khu vuc day Hoang Lien So'n, tram tich tudi Cambri phan bd tren cac son nguyen Bac Ha - Mirdng Khuong va tram lich thudc he tang Ddng Ciiao liioi Trial phan bd d khu virc Than Uyen. Cd sir kluic bid ve dja hinh tren cac thanh tao da gdc khac nhau.
Cac tram tich carbonal cd ludi co thirdng da bj bien chat, trong mat cat lai cd sir xen ke dang ke ciia thanh phan kh6ng boa tan, do vay mirc do karst kem hon. Dja binh mii vdi cac dinh dang thap, dang chudng vdi cac sirini thoai vdi ldp dcluvi da) la diic trung cho karst pluil trien tren da luiy. Mac dii tren cac Idp sudn tich vdi thanh phan giau Viit lieu set de bj xdi mdn, trugt Id dat, tao dieu kien cho hi bim di, song chinh cac viit lidi khdng boa tan lai giiip cho viec binh thanh cac tang each nirdc, tao lien de cho hinh thanh cac tang nude ngam.
Cac thanh lao carbonal thudc he Uing Ddng Giao tai Than U)'eii cd mirc do ddng nhat cao, chimg bj karst boa numb tao dia hinh niii sdt co sudn vach ddc dirng xen gifra cac tilling king karst rgng. Tren be mat lining lung niy cdn phat trien nhieu phdi thu nirdc karst, tao dicu kidi cho viec nuil nude mat tai Than Uyen.
2.5. He thong thuy viin da dang dugc djnh hudng kha ro theo cac diit gay vii vimg sut kicn tao
Cac dirt gay Idn tao dieu kidi cho qua trinh ngoai sinh tao nen cac thung king song Idn ma dien hinh la thung lung kien lao Sdng Hdng, Sdng Chay. Dac diem binh tbai va phat trien ciia cac thung king sdng tren khu vuc la birc tranh the hien rd nhai can Inic dja hinh va tan kien tao khu vuc. Sdng Hdng chay lbeo hudng Tay Bac - Ddng Nam la sir khdng che ciia be thdng dirt ga) cimg plurong va sau vi the sdng cd thung king rat hep dang dja hao. Tren lanh thd Lao Cai hau nhu khdng cd sdng nhanh do vao lir ben trai, cdn ben phai tbi sudi deu ngan. Dieu dd ndi len tinh chat tie ciia thung king, lidi quan den tinh tich cue ciia tan kien tao.
Cac dirt gav cap nhd tbi tao nen cac tluing king cap nho lion. Cac dirt gay va khe nirt kiem tao khdng the hidi Ircn dja hinh thi lai ddng vai trd bet sire quan trgng trong ihanh lao dja hinh bicn dai lien quan ldi cac lai bien thien nhicn dac bid ki tai bidi irugt Id dai va ki quel dang phat trien manh tren lanh thd Lao Cai.
Hdi ng-hi Khoa hgc Dia ly Todn qud'c la'n th&S - Hd Ndi, 2010 835
VIEN DIA LY - VIEN KH&CN VIET NAM HOI DIA LY VIETJ<AM
3. NHUNG DU B A O N H A M G I A M T H I E U THIET H.4I DO LU QUET G A Y RA
Khi xa\ ra ki quel, khu vuc chju ki thirdng la ndn phdng vat ciia cac ddng chay tam thai. Tai ndn phdng viit, do do ddc giam dot nggt. ddng ki giai phdng nang krgng va nauon \al lieu chimg mang theo. lam pha buy cac cdng trinh va cay trdng tren non phdng \'at. Do dd. viec xay dung cac diem dan cu tren ndn phdng vat la khdng an loan, Tu\ nhien mirc do tac d6ng cua dong ki tren be mat cua ndn phdng vat la khdng gilng nhau, do do do an toan ciia cac diem tren ndn phdng \at cung khac nhau.
Nhfrna Iran lfi quel xay ra tren cac song sudi cd do ddc Idn va hudng thay doi, kl ca tren cac suoi nho cd luu vuc tu vai 3 km" cfmg cd the xay ra lii quel dot nggt nhanh chdng (Iran lu thang 8/1993 tai Ta Giang Phinh Sa Pa xa)' ra tren kru vuc 3knr gay thid nghiem trgng ve ngudi va nha cira), day la mdt dang ki q u d nghen ddng, Cac thuna lung s6ng su6i phan cat sau manh, lai cat qua cac be mat san bang vdi ldp v6 phonti boa day la dieu kidi de phat sinh khoi trugt Id dat. bd sung ngudn vat lieu Idn gay ra lfi qud.
Lii quel thudng cudn theo cac N'at can, do kru tdc ciia ddng chay rat Idn. sire cong pha manh. bien do dinh lfi tir 3 - 5ni, ddng lu mang dam dac bim da (Iran ki thang 8/2008 Bat Xat), day la dang ki quel sudn xay ra tren pham vi Idn d cac sudn mii co do die Idn, phia dudi la nen da phia tren la Idp dat tir 2 den 4in (Iran lu ngay 15/7/2000 lai 7 xa phia Nam lun'di Sa Pa),
Theo khong gian. nhfrng Iran lfi xay ra d phia Tay ciia Sdng Hdng cd nuic do ac lid hon phia D6ng, dac diem nay do krgng mua quyet djnh, mat khac lfi quel xay ra
\anh dai thap dudi 700ni mirc do nhieu hon va gay thiet hai Idn hon, do yeu td dja hinh tao len.
Su xuat hien ciia IQ quel cd cudng suat Idn va gay thiet bai Idn d Lao Cai cd xu the gia tang, nguyen nhan la do cac boat dgng dan sinh, kinh te gay anh hudng Idn tdi mat ddn. pha vd can bang sinh thai. Qua sd lieu dieu tra d cac vj tri mat cat song suoi nhung nam gan da)' da bj bien dang rat Idn cd nai mat cat bj md rdng den 3 kin do khdng tai dugc kru krgng lii.
Nhung thid bai thudng gap do lu quel gay ra; Thiet hai chinh la viii lap dong rugng. xoi Id dat canh tac gay thid hai vc kia va hoa mau. Tru'dng hgp nay thudng xay ra a nhfrng canh ddng ven sudi cd chenh lech do cao so vdi ddng sudi rat it, hoac dudi chan nhfrng sudn mii doc, thudng bj ngap nude va ddng bim da tran qua ddng rudng, lang mac mang theo ldp dit da day tir 0,5 - 4in (tran lu thang 8 /1969 tai Bat Xat va Iran ki thang 7/2008 tai Sa pa - Lao Cai). Lu qud cudn trdi ngudi va nha cira, pha buy cac cdng trinh. thudng xay d nhfrng thung lung cd do doc Idn, cd do che phii it.
Tu nhung nhan djnh tren, de giam thilu thiet hai do lu quel gay ra can thuc hien cac bien phap sau;
- Tien hanh trdng rirng phii xanh dat trong doi trgc. Bien phap nay nham lang cudng kha nang bao ve dat ciia tham tlurc vat, chong lai cac qua trinh ddng luc hien lai dicn ra tren dja hinh, ke ca qua trinh sdi Id. trugt Id hay xam thuc, Phu xanh dll trong d6i troc cdn CO lac dung lam chain qua trinh tap trung nude, giam kha nang hinh thanh ki.
- Chii)'en doi ca cau cay trdng theo hudng ndng - lam kit hgp. de cd the giam ap lire do cac boat ddng canh tac ciia con ngudi gay ra tren dja binh. dac bid la boat dgng canh tac kia tren sudn ddc.
VIEN DIA LY - VIEN KH&CN V I E T N A M HOI DIA L'Y VIET NAM
- Tien hanh khai thdng ddng chiiy, ddi vdi cac cdng trinh gifr nude ciia nhan dan trong xa nen thiet ke bgp li, tranh anh hudng den qua Irinh thoat ki, nhung phai dam bao dugc ngudn nude cung cap trong miia can, Khdng cho phep xay dung cac cong trinh d viing dc cd lu quel,
- llurc bien tdt cac bien phap cdng trinh; xay dung cac be thdng du bao, canh bao hi; khao sat, dieu tra tim kiem nhfrng vimg cd nguy ca lu qud; lap ban dd lu qud;
quy hoach sir dung dat va khu dan cu.
4. KET LUAN
Dja binh - dja mao la mdt thanh phan quan trgng ciia ldp vd dja li. Lao Cai la mgt tinh mien mii cd diic diem dja mao bet sire pbiic tap. Dac trung ca ban la cau triic dja chat cd vdi phuang thdng trj ki Tay Bac - Ddng Nam, cd sir phan dj ve dja hinh do lac dgng manh me ciia boat dgng Tan kien tao; dja hinh cd sir phan bac rd rang phan anh tinh chat dja mao ciia mien nbid ddi; dac trung ciia dja mao cdn the bien d he thong thuy van da dang dugc djnh hudng kha rd theo cac dut gay va vimg sut kien tao.
Dac diem dja mao cd anb hudng rat ldi den hien tugng 15 qud. Cau triic dja chat, mirc do phan dj dja hinh, hudng sudn deu anb hudng den cudng do tac ddng ciia cac Iran lfi quel. Dac b i d tai Lao Cai, dac diem dja mao phan anh va du bao mirc do boat ddng ciia cac Iran lu qud. Nghien ciru dac diem dja mao cd the dir bao dien bien, boat ddng ciia IQ quel tir dd cd bien phap phdng tranh, giam thieu thiet bai do ki qud gay ra.
TAI LIEU THAM KHAO
1. Le Du'c An, Lai Huy Anh, 2000. Ket qud nghien cim dia mgo dai dirt gay .Sdng Hdng.
Tap chi cac khoa hgc vl Trai dat, sd chuyen de ve dirt gay Sdng Hdng T22 (4), tr 253 - 258.
2.Lai Huy Anh, 2000. Ddnh gid mirc do dn dinh vimg tdy bdc dai dirt gay Sdng Hdng tren ca sd phdn vimg dia ddng lire. Tap chi cac khoa hgc ve Trai dat, so chuyen de ve dut gay Sdng Hong T22 (4), tr 429 - 436, 12 - 2000.
3.Dao Dinh B3c, Hoang Thj Thu Huang, 2008. Ddu hieu dia mgo cdnh bdo nhimg tai biin thien nhien thudng gap tgi dia bdn cdc diem ddn cu mien nid Tdy Bdc. Tuyen tap cac bao cao khoa hgc, Hdi nghj khoa hgc Dja li toan qudc Ian thu 3, tr 46 -55.
4.DaG Dinh BIC va nnk, 2006. Van di cdnh bdo - du bdo ted bien thien nhien clam bao do an todn cho cdc diem ddn cu mien niu. Tap chi khoa bgc DHQG Lla Ndi, No 4, tri -
12,
5,UBND tinh Lao Cai, Sd KHCN&MT, Bdo cdo hien trgng mdi trirang tinh Lao Cai ndm 2009. Lao Cai, 3/2009.
6,Nguyen Trong Yem (chu bien), 1996, Dia chdt - Tdi nguyen Tl, T2. NXB Khoa hgc va Ky thuat.
Hdi nghi Klioa hgc Dia ly Todn qudc lan th&S - Hd Ndi, 2010 837
