HOI NGH! KHOA HQC TOAN QUOC V £ SINH THAI VA TAI NGUY£N SINH VAT U N THU BA LI/A CHON PHU''''ONG PHAP NGHEEN ClTU DANH GIA XOI MON DAT PHU HOP C H O HUYEN SON DQNG TINH B A C GIANG HOANG TIEN HA Sa Nong[.]
Trang 1HOI NGH! KHOA HQC T O A N Q U O C V £ SINH THAI VA TAI NGUY£N SINH VAT U N THU BA
LI/A CHON PHU'ONG PHAP NGHEEN ClTU DANH GIA XOI MON DAT PHU HOP
C H O H U Y E N SON D Q N G - T I N H B A C GIANG
HOANG TIEN HA
Sa Nong nghiep vd Phdt trien nong thon Bdc Giang
Xdi mdn dit Ii qui trinh phi buy lcip thd nhudng (bao gom c i phi buy thinh phin co, Iy, hoa, chit dinh dudng v.v cua dit) dudi tic dgng ciia cic nhin td ty nhien va nhan sinh lam giam do phi nhieu ciia dit, giy rabac miu, thoii hoi dit, laterit hoi, tro sdi di v.v , inh hudng fryc tilp tdi sy sdng vi phit friln ciia thim thyc vat rimg, thim ciy trong khic
Cic nha khoa hgc d tren thi gidi ciing nhu d Viet Nam di neu ra nhilu phuang phap de tinh toin, dinh gia xdi mdn dit Tuy nhien, vifc lya chgn phucmg phip nghien cim, danh gii xdi mdn dit phii hgp cho huyfn Son Dgng - tinh Bic Giang vi vd ciing can thilt
Scm Ddng Ii huyfn miln nui vimg cao cua tinh Bic Giang cd difn tich ty nhien la 84.432,4ha, trong dd difn tich dit lam nghiep Ii 65.528,8ha chilm 77,6% [8] Dia hinh Son Dgng gom ci miln nui va dong bing xen ke, manh miin Die dilm chii ylu cua dja hinh viing niii Ii chia cit manh, phuc tap, chenh Ifch vl dg cao ldn Trong nhirng nim qua, vifcijuin ly va sir dyng bin vtrng dat canh tic, die bift Ii viing dit ddc chua dugc cac cip, cac nganh quan tam diing mirc Hing nim, hang trim hecta rimg ty nhien bi tan phi lim cho_ difn tich dit frong, dong nui trgc ngay cang ting hoic thay vio do la nhtmg difn tich rimg trong kem^chit lugng, khi ning bao vf dit thip Chinh vi vay, hifn tugng xdi mdn dang xiy ra manh, mdi nim hang nghin tin dit miu md bi xdi mdn, rira trdi Thyc frang niy dang lim cho dit dai ciia huyfn mit din khi ning canh tic
I M y c DICH VA PHU^ONG PHAP
Tren co Sd phin tich dinh gii cic phuomg phip dinh gii xdi mdn dit da dugc thyc hifn trong vi ngoai nude, lya chgn dugc phuang phip nghien ciiu, dinh gii xdi mdn dit phii bgp cho huyfn Son Dgng - tinh Bic Giang, lim co sd cho cac dl tii nghien cuu sau niy lien quan den xdi mdn dit tren dia bin huyfn Som Dgng
' IL KET QUA NGHIEN CUtl
" 1 Cac nhan to anh hud'ng den xdi mdn dat: Cac nhan to chinh inh hudng din qui trinh xdi mdn dit bao gdm: khi hau, dia hinh, ldp phu thyc vat, dang dit, con ngudi
1-1 Anh hudng cua cac nhan to khi hau den xdi mdn dat: Xdi mdn chu ylu do ddng chiy bl mit giy ra, nhung ddng chay lai do cic ylu td khi hiu quan frgng quyet dinh do la: Tdng lugng mua va tinh chit ciia mua, thdi gian vi cudng do mua Thdi gian mua cang Ion, cudng dg mua cing cao thi qui trmh xdi mdn cing xiy ra manh me
Q Vift Nam ndi chung va d huyfn Son Dgng - tinh Bic Giang ndi rieng, mua phan hda theo miia rd rft Lugng mua cue dai vio cic tiling miia he vi rat it trong nhung thang mua dong Vi vay vifc bao vf dit chong xdi mdn die bift trong miia mua Ii vo cung can thiet
1 2 Anh hudng cua dja hinh din xdi mdn dit: Dja hinh cung Ii nhan td ty nhien anh hudng Idn din xdi mdn dit NIU xet tren difn rgng, dia hinh cd tac dung lam thay do, sy phan
bd nhift vi lugng mua roi xudng Sy thay ddi ve dg cao d Vift Nam keo theo sy tjay <3°' ca ban
vl nhift dd mua im Cic ylu td ciia dia hinh nhu dg ddc, chieu dai suan doc, hinh dang (loi, 15m, thLg bic thang v.v ) muc dg chia cit ngang cua dia hinh anh hudng tryc tiep den xo, mdn dit
Trang 2HOI NGH! KHOA HQC T O A N Q U O C V £ SINH THAI V A TAI N G U Y £ N SINH VAT L^N THU' BA
Do doc va chilu dai ciia sudn la ylu to dia hinh cd anh hudng ldn nhat den qui trinh xdi inbn Dg ddc ldm lam tang cudng dg ddng chiy va do do day nhanh qua trinh rira trdi, xdi mdn dit, gay nen xdi mdn manh hem Nguyin Quang My da nghien ciru anh hudng ciia dg ddc din xdi mdn dit tai Tay Nguyen tir nim 1978 den 1982 tren dit bazan, trdng che mdt tudi, kit qua cho thiy: NIU do doc tang 2 lin thi cudng do xdi mdn tang hon 4 lan; neu tang chieu dii sudn doc len 2 lin thi xdi mdn dat tang tir 2 den 7,5 Ian
1.3 Anh hud'ng ciia Idp phu thyc vat den xdi mdn dat: Ldp phii thyc vat cd anh hudng ldn din qui trinh xdi mdn dit, nlu Idp phu thyc vat cang ting thi qui frinh xdi mdn cing giam Vai trd chong xdi mdn ciia Idp phii thyc vat phu thugc vao tudi va do che phu ciia no Thyc vat
cd kha nang bio vf dit chdng xdi mdn qua vifc lim giam anh hudng cua hat mua xuong mat dit bdi tin Ii vi lam cho nude cd khi nang chay xudng den 50-60%) theo chieu thing dirng ciia bd
re Khdng nhiJng thi, vat roi ryng ciia thyc vat nhu canh khd, la ryng cdn tao ra lugng miin lcin trong dit, giir dit toi xdp, chdng xdi mdn
1.4 Anh hudng ciia dat den qua trinh xoi mdn dat: Nhung yeu td chinh cua dit inh hudng din xdi mdn dit Ii thinh phin co gidi, ciu true va dg tham nude cung nhu him lugng miin trong dit Nhirng ylu td dd inh hudng din kha nang hinh thinh ddng chiy khi mua rao 1.5 Anh hudng cua con ngudi den xdi mdn dat: Con ngudi anh hudng true tiep den qui trinh xdi mdn dat thdng qua boat ddng sdng nhu canh tic tren dat ddc khdng khoa hgc, du canh
du cu, phi rimg lam nuomg, phi rimg ty nhien de trdng rimg Ii nhiing tic nhin gia ting xdi mdn dat
2 Cac phuo'ng phap nghien ciru, danh gia xdi mdn dat
Cd the ndi ring con ngudi da quan tim den hifn tugng xdi mdn tir rat sdm, tir thdi Hy Lap vi La Ma cd dai da cd nhung tic gii de cap den xdi mdn cimg vdi vifc bao vf dat Qui trinh xdi mdn hifn dai dugc gin lien vcii cac boat ddng ndng nghifp Nhieu ngudi da cho ring dat dai bj khai thic can kiet cd the Ii nguyen nhin khien cac nen van minh qui khii mat di Vi viy, cimg vcii thoii hoi dat, xdi mdn tdn tai nhu mgt van de trong sudt qui trinh phit trien ciia toan nhan loai 2.1 Cac phuong phap danh gia xdi mdn dat: Cho den nay, cac cdng trinh frong va ngoai nude nhim nghien cuu tiep can qui trinh xdi mdn da dugc tien hanh theo cic hudng chinh sau:
- Danh gia tdng hgp anh hudng ciia cac dieu kifn ty nhien den xdi mdn Theo hucing nay, miic dg xdi mdn dugc dinh gia theo cap Mgt cap cudng do xdi mdn se Ii tap hgp ciing cap tuomg ling cua cic yeu td gay xdi mdn Vifc phan vimg lanh thd theo do nguy hiem xuit hifn cac qui trinh xdi mdn hoic theo miirc do xdi mdn thyc hifn tren co sd tdng hcjrp cic bin dd phan cap cua timg nhin td anh hudng den xdi mdn bing ky thuat chdng xep ban dd Theo phuong phip niy, vifc tiep can qui trinh xdi mdn gin lien vdi phin viing xdi mdn
- Danh gia mirc dg xdi mdn hifn tai dya tren dai lugng modul ddng chay ran ciia cac luu vuc Dai lugng modul ddng chiy rin die trung cho lyc xdi mdn ciia ca mgt luu vyc lcin, la nhtrng sd lieu ding tin cay chinh xic, tuy nhien cd han chi la khdng phan anh dugc day dii toan
bd lugng xdi mdn, bd qua mdt lugng dat xdi mdn ty lai d nhtmg chd triing va ling dgng tai diy ddng chiy sdng ngdi Hon nua d Vift Nam, cic sd lifu quan trie nay ciing khdng dii, vi the hucing nay chi diing de so bg phan vimg xdi mdn hifn tai tren lanh thd Idn
- Td chuc cac diem thyc nghifm nghien cii'u qua trinh xdi mdn Theo hudng niy, nhieu cdng trinh da danh gii dugc inh hucing cua timg yeu td (cic yeu td dia hinh, mua, dat, Icip
phu thyc vat v i cac bifn phip canh tic) den qui trinh xdi mdn Tdng hgp lai da xay dyng dugc
Trang 3HOI NGH! KHOA HQC T O A N Q U O C Vg SINH THAI VA TAI N G U Y £ N SINH VAT LAN THQ- BA
nhihig md hinh toin hpc tilp can qua trinh xdi mdn tiieo timg dia phuong nhim tinh lugng dit mat do xdi mdn de thiet kl ky thuat canh tic ndng nghifp tren dit ddc
2.2 Cac phuong phap nghien ciru xdi mdn dat
- Phuong phap phan loai, phan viing lanh tho theo mirc dg xdi mon Phuang phap nay da dugc ip dung d nhieu nude de phin chia khii quit ra cic vimg Icin cd miic do nguy hilm xdi mdn tiem nang khic nhau tren toin lanh thd mdt qudc gia Tuy nhien han chi ciia phucmg phap nay la thien ve dinh tinh, mang die trung ciia phucmg phip chuyen gia, cd khd khin trong vifc giai quyet chinh xic ranh gidi giira cac viing v i khi di vio cic pham vi hep Phuang phip nay da dugc cac tic gii Lien Xd (cii) vi Trung Qudc ip dyng Cic ban dd phan vimg theo do nguy hiem tiem nang xuat hien xdi mdn dugc xay dyng tren ca sd tdng hgp cic ban dd phan cip cic dieu kifn ty nhien tham gia qua trinh xdi mdn: dia hinh, khi hau, Icip phii thyc vat Trong cic yeu td dd, cac tic gii chii y nhieu nhit den cic yeu td dia hinh va khi hau
- Phuong phap md hinh hoa Phuang phip md hinh hoi sir dyng cic md hinh dl dien ti qui trinh xdi mdn Cic md hinh niy cd the la cic md hinh thyc nghifm hoic md hinh Iy thuyet
Uu diem quan trgng ciia phuong phip niy so vdi cic phuong phip nghien ciiu khic Ii da phin nio lugmg hoi dugc vai trd ciia timg yeu td inh hudng tdi qui trinh xdi mdn, cd nghTa la lim ro ban vai trd ciia chiing trong toin bg hf thdng Phuang phip nay ciing cho phep img dyng cic cong nghf hien dai vio nghien cim tinh toin Han che quan trgng ciia phuang phip nay Ii do qua trinh xdi mdn dien rat da dang, thay ddi theo dieu kifn cu the cua timg dia phuang nen md hinh cd the diing tdt cho dia phuang niy nhung khdng dung vdi dia phuang khic Vi viy, khi van dyng cic md hinh can phii chu y tdi cic dieu kifn die thii tai dia phucmg, hay diing ban, Ii sir dyng cac thdng sd ciia md hinh da dugc kiem chumg cho dia phuang
2.3 Cac md hinh danh gia xdi mdn dat: Vifc md hinh hoi qui Jrrinh xdi mdn bit dau manh vio thip nien 80 thi ky 20, gdp phin tinh toin vi dy bao xdi mdn Theo Pham Hiing, cd thi chia cic loai md hinh ra lim hai loai chinh Ii md hinh kinh nghifm va md hinh nhin thirc Cac md hinh dugc xiy dyng tren co sd ciia ly thuyet hf thdng vdi gii thiet Ii lugng vao vi ra ciia hf thdng la da xic dinh
, 2.3.1 Md hinh kinh nghifm: Md hinh kinh nghifm la cic md hinh dugc xiy dyng dya vio cac tdng kit tir cic quan sat thyc tl Ndi theo nghTa hgp ban, hiu het cic md hinh niy deu dya vao phuong trinh mit dit tong quit cua Wischmeier vi Schmid hoac cic tu duy tuong ty Cd thi kl ra day cic md hinh: Phuong trinh Musgrave ciia Musgrave, 1947; Phuang phip ti If phin chia biin cit, Renfro, 1975; Phuong phip Dendy - Boltan, Dendy va Boltcn, 1976; MUSLE (modified universal soil loss equation, ciia Auerswwald, 1990
Myc dich cua cic md hinh niy khdng nhim md phdng qua trinh xdi rndn ma diing de tinh
toin lugng dit tdn thit trung bmh hang nim cung nhu dy bio xdi mdn dit binh quin tren dit
doc Ngoai ra, vifc su dyng cic md hinh nay cung cho phep dy bao nhiimg thay ddi ve xdi mdn dit do nhumg biln ddi trong hf thdng canh tic va dl xuit cung nhu udc doin hifu qui ciia cic bifn phip phdng chdng xdi mdn
Md hinh kinh nghifm cd nhumg ban chi sau:
- Pham vi ung dung mang tinh dia phuong, cd dg chinh xic ban chi khi ip dyng d nhumg khu vyc khic nhau
- Chua dl cap din qui truth bdi ling vi chuyin tii hat dit
- Khdng cd khi nang tinh toan cho timg t r ^ mua hay cac budc thdi gian ngin ban
Trang 4- Ddi vcii cic luu vyc Icin, dd chinh xac chua cao do tinh phiic tap cua lim vyc Nhugc dilm niy cd thi dugc khic phyc bang cich chia luu vyc thanh cac luu vyc nhd hon
Mo hinh thyc nghifm A D Ivanovski va I A Kornev (1952)
Md hinh nay dugc xay dyng tai cac tram thyc nghifm Novosilski Phuong frinh cua mo hinh cd dang: M = AI^'^^L'^'X'''" ' ' , •
Trong do: M: lugng dat nia trdi
I: Dg ddc sudn (tang gdc ddc)
L: Khoang each tir dudng chia nude (chieu dai sudn m)
X: Cudng dg mua hoac myet tan (mm/ph)
A: Hf so tinh den cac nhan td khic
Md hinh niy chua de cap tdi vai trd cua tham thyc vat cQng nhu vai frd cua cic loai dit, chi dua vao dudi dang mgt hf sd Tuy vay, md hinh thyc nghiem nay dugc mdt so nha khoa hgc Viet Nam umg dung trong cic tinh toan cua minh de phan cap tiem ning xdi mdn cho cic khu vyc khic nhau Do Hung Thinh da cii bien cdng thirc tren:
Y = A I ° • ' ^ L ' ' • ^ x • • ^ T Y: Lugmg dit nia trdi fren mgt don vi difn tich
1: Do ddc sudn tinh binh quan cho mdi d vudng 4 km^
(bing phuang phap tinh gan dung tren bin do ty If 1/100.000)
L: Do dai sudn tinh tmng binh cho mdi d vudng tren
X: Lugmg mua xdi mdn (mua cd cudng dg > 0,2 mm/phiit)
T: Thdi gian tuong iing lugng mua xdi mdn
A: Hf so the hifn die tinh xdi mdn cua dat, vdi 2 nhdm dat chinh ciia tay bic cd he so la 2
vi 1
Mo hinh USEE
USEE (Universal soil loss equation) - Phuong trinh mit dat tdng quit (hay phuang trinh mat dat phd dyng) dugc Wischmeier v i Schmid hoan thifn vio nim 1978 tir ket qui ciia mgt nd lyc thdng ke Icin (dtr lifu tii hon 5000 plot hang nam) Phuong trinh dugc thiet kf ban dau nhu la mdt cdng cy qui hoach de kiem soat van de xdi mdn cho cic cinh ddng d vimg trung tay v i "vinh dai ngd" nude My Phuong trinh mit dit tdng quit cho phep danh gia d ty If tiing cinh ddng lugmg dat mit do xdi mdn khe ranh va xdi mdn hen ranh Trong khung cinh ciia phuong trinh mat dat tdng quit, xdi mdn dugc djnh nghTa la tdng lugng dat dugc chuyen tcii chin sudn ddc noi hoic la cic qui trinh ling dgng (deposit) quan trgng bit dau difn ra hoac cic ddng chiy bit diu dugc tap trung lai
Vifc ip dyng cich tifm can md hinh hoi phin tich thdng ke hdi qui da bien de xiy dyng phuong trinh d i cho phep phan tich ra cac nhan td trgng sd cua mgt loat bien dgc lap (mua, dat, dia hinh, ldp phu thyc v^t v i phucmg thurc canh tic) Hon nira, viec sir dung cic tham
sd do ludng lugng mat dat hang nim cho phep phucmg trinh niy cd the diing dugc trong dinh gii lugng mat dat trung buih hang nam Phuomg trinh cd dugc tir sd lugng lcin cic thira dat dugc quan sit hiem khi qua 90m chilu dii v i ddc qui 18%
Trang 5HQI NGH! KHOA HQC T O A N Q U O C V £ SINH THAI V A TAI N G U Y £ N SINH VAT LAN THU BA
Phucmg trinh mat dat tdng quit cd dang nhu sau:
A = RKLSCP (Phuong frinh: Wischmeier WH - Smith DD) Trong dd: A: Lugngdit mat tmng binh hang nam chuyin tdi chan sudn (kg/m^nim)
R: He sd xdi mdn do mua (thang do do xdi mdn dugc lap tren co sd EI30) (KJ.mm/m^.h.nim)
K: Hf sd khing xdi ciia dit (dugc xic dinh bing lugmg dit mit di cho mgt don vi x(5i mdn ciia mua trong dilu kifn chuin, nghTa la chilu dii sudn la 22,4m, do ddc 9%, trdng ludng theo chieu tir fren xudng sudn ddc) (kg.h/KJ.mm)
L: Hf sd chieu dii sudn ddc, ty If dit mit di ciia thira dit so vdi lugng dit mit di ciia thira dat chuan (khdng thir nguyen)
S: Hf sd dg ddc (ty If dat mat di cua thira dit so vdi lugng mit dit ciia thua dit chuin) (khdng thu nguyen)
C: Hf sd cay trdng hoic lcip phii (khdng thii nguyen) ty If lugng dit mit ciia thira dat so vdi lugng dat mat di ciia thira dit chuin (bd hoi cich nim)
P: Hf sd canh tic bio vf dat (khdng thir nguyen) ty If lugng dit mit di cua thua dit
• so vdi lugmg dit mat di cua thua dit chuin (trdng ludng theo chieu tir tren xudng sudn doc)
Phuang trinh ban diu dugc thanh lap d hf do ludng Anh - My nhung ngay nay da dugc chuyen sang hf SI de tifn cho vifc tinh-toin vdi cac dtr lifu thu thip dugc ciing nhu dinh gii so sanh USLE vdi cic md hinh xdi mdn khic Phuang trinh mat dit tdng quit cd the dugc coi la cong cu dy bio cd the "dinh gii tdt nhat" vi chinh xic dudi cac dieu kifn ve khi hiu, dit, dia hinh da dugc Wischmieier vi Smith chi rd Ciing cd the nhan thay ring vifc su dyng phuang trinh nay de tinh toin hoic dy doan cho cic hifn tugng xdi mdn xiy ra trong thdi gian ngan hon
se khong chinh xic vi khi ip dyng phuong trinh eho cic ty If khic (qui md ve khdng gian) cung can het sire than trgng Tuy nhien, vifc phin tich qui trinh xdi mdn thanh cic bien dgc lap cung mang lai khi nang to lcin trong tinh toan dy doin xdi mdn vi tu duy niy, cung nhu ban thin phuang trinh USLE cd thi dugc sira doi dl thich hgp vdi nhirng hoan cinh cy the ve ty If khdng gian, dilu kifn khi hiu ciing nhu cic dieu kifn dia - vit Iy khic bing cich thay ddi cic hf sd ciia phucmg trinh Vi Iy do tren, phuang trinh USLE da dugc thay ddi cho phii hgp vdi cic dieu kifojchic nhau, vi dy:
- USLE cho dit canh tie ndng nghifp (chinh Ii phuang trinh gdc ciia Wischmeier va Smith)
- USLE cho dit xay dyng (Wischmeier, Jonson va Cross, 1971)
- USLE cho dit rimg (Dissmeier va Foster, 1981)
- USLE trong dilu kifn bao (Onstad v i Foster, 1974)
- USLE cho danh gii lugng trim tich ciia luu vyc (Williams, 1975)
Mo hinh SEIM
Dk dinh gii dugc mirc dg xdi mdn tren linh tiid Icm (toin bg Dai Loan), cic tic gii di sir
dyng md hinh chi sd xdi mdn dit (Soil Erosion Index Model - SEIM) Md hinh niy nghien cuu
sy inh hudng cua cic chi so khic nhau tdi lugng dit xdi_ mdn ma khdng nhim tinh ra cy the lugng dit xdi mdn hing nim Vdi sy cd mat ciia Ci (chi sd ldp phu) vi Ui (chi so su dung dit),
mo hinh nay mang tdi birc franh rd rft ban vl tmh trang xdi mdn so vdi md hinh xdi mdn tilm ning tir phuong trinh USLE (loai bd hf sd C vi P) Md hinh chi sd xdi mdn dit cd dang:
Ai = Ki + Ri + Ti -f Ci + Ui Trong dd: Ki: chi sd xdi mdn cua dit
Ri: Chi sd xdi mdn cua mua Ti: Chi sd xdi mdn ciia sudn (slope) Ci: Chi sd xoi mdn ciia Icip phii Ui: Chi sd xdi mdn ciia sir dyng dati
Trang 6HOI NGHI KHOA HQC T O A N Q U O C Vfe SINH THAI VA TAI N G U Y £ N SINH VAT L^N THU' BA
Va sy lien quan giiia lugng dit xdi mdn va chi so tdng AI dugc bieu dien:
SE = d.lC'Al''^ vdi Ai < 50 (1)
SE = 0.233AI'" vdi Ai >50 (2)
Hf so tuong quan R^ cua cac phuong truih quan hf tren dat 0.88 (ptl) va 0.94 (pt2)
D I cd thi thiy ro hon vai frd ciia cac chi sd tdi tiem ning xdi mdn, cac tic gia da phan
tich dya tren co sd chia 5 loai chi sd tren thanh 2 ITnh vyc: cac chi sd dieu kien ty nhien vi cac
chi sd nhin tao (artificial index) gdm Ci vi Ui, tir dd cd dugc ket luan vl nhirng noi mi con
ngudi cin cd tic dgng de giim thieu xdi mdn
2.3.2 Mo hinh nhan thirc: Khic vdi md hinh kinh nghiem, cac md hmh nhan thiic dugc
phit triln dya vio hieu biet ve cac qui luat van ddng va co che vat Iy cua qui trinh xdi mdn,
nghTa Ii dya vio cac hieu biet da dugc Iy thuylt hoi dudi dang cic dinh luat hay phuong trinh
vat Iy Cac qui trinh vat ly cua xdi mdn cd the dugc ke ra gdm: qua trinh bdc tich hat dat (do
ning lugng cua hat mua roi hoac mgt dang nang lucTng khic); qua trinh chuyen tai (vdi cac djnh
luat ve ddng chay ma qui trinh niy man thu) vi qui trinh sa ling cua cac hat dit Vi till, co sd
ly thuyet cua md hinh nhan thiic Ii ly thuyet co hgc chat ran, chat ldng vi phan tich md hinh
kinh nghiem
* Mo hinh nhan thirc don gian: Bin chit ciia cac md hinh nhan thiic dom gian Ii qui trinh
xdi mdn dugc chia ra lam hai budc, budc dat bj bdc tach vi budc dat dugc chuyen tai tdi ciia ra
Lugng dit bi bdc tich thudng dugc tinh theo phuomg trinh mat dat tdng quit USLE, qui trinh
chuyen tii dugc tinh toin qua cic ham dien toin thinh phin chuyen tai Cic md hinh thugc loai
niy cd the ke ra Ii Md hinh dien toan bim cit theo Muskingum, Sign vi Qufroga, 1986; Ket hgp
md hinh md phdng mua, ddng chiy v i bim cit, Franchini vi Schipa, 1993
Md hinh nhan thirc don gian cd cac uu diem va nhugc diem sau:
- Uu diem:
+ Md t i va tinh toin kha chi tiet qui trinh chuyen tai hat dat tren sudn doc thdng qua
vifc phan chia luu vyc
+ Khdng bat budc phy thugc vio hinh dang xac dinh
- Nhugc diem: Khdng hoin toan dya vao qui trinh vat Iy cua hifn tugng xdi mdn ma
mdi chi de cap den lugng dit tdn that hing nim Vi vay, cin nghien ciru hoan thifn ciu tnic ciia
md hinh de cd the cho phep md phdng lugng dat mit vdi thdi gian tinh toin nhd hon mdt nim
* Md hinh nhan thirc phiic tap: Cic md hinh loai niy dugc xay dyng dya vio bin chat
vat ly ciia hifn tugng xdi mdn luu vyc Qua trinh xdi mdn luu vyc dugc md t i qua ba qui trinh
chinh: qui frinh bdc tich cic hat dat do ning lugng cua hat mua; qui trinh chuyen tii hat dit do
ddng chay mat gay nen v i qui trinh bdi ling do kha nfing chuyen tai ciia be mat lim vyc nho
hon ndng do tap trung cic hat Mdi qua trinh dfu tuan thu nhirng djnh luat vat ly nhat djnh va cd
the md phdng dugc Toan bg ba qua trinh tren Ii lien tyc va tao nen ddng lyc cua qui trinh xoi
mdn tren be mat luu vyc Cd the ke ra d day Ii cic md hinh phd bien sau: Dy bio xdi mdn do
nude (WEPP), Lane va Nearing, 1989; Md hinh xdi mdn Chau Au, Morgan, 1992; Chuang
trinh dy bio xdi mdn tiieo qui trinh, Schramm, 1994:
- Uu diem quan trgng nhat cin phai ke tdi ciia md hinh nhan thuc phirc tap la nd da khic phuc
nhieu nhugc diem ciia hai loai md hinh fren Cich md phdng sat vdi qua trinh xdi mdn tren be mat
luu w c , vi the, cho phep xem xet phan img cua hf thdng thuy vin khi mudn thay ddi mdt bd phan
hay toin bd cau tnic ciia he
- Nhugc diem de thay cua md hinh nhan thiic phiic tap la ddi hdi lugng thdng tin dau
Trang 76 Viet Nam tmdc day, mdt sd tic gia da nghien cim xdi mdn dit d ddng bic, tiy bic bing cic phucmg phap don gian va tryc quan nhu ddng cgc, dimg day dgi hoic md ti, danh gia djnh tinh qua trmh xdi mdn trong 4 nam (1961-1964) Sau dd, do chiln tranh (1965-1976), vin dl xdi mon
it dugc quan tam nghien cim: Sau nam 1960, cic cdng trinh nghien ciru ciia Nguyin Nggc Binh (1962), Nguyen Quy Khai (1962), Cao Vin Binh (1962) da nghien ciiu vl inh hudng cua do doc den xdi mdn dit, gdp phin dua ra cic tieu chi bio vf dit, sir dyng vi khai thac dit doc Cac tac gia Tdn Gia Huyen, Chu Dinh Hoing, Nguyin Xuin Ky, Nguyin Quy Khii, Biii Nganh (1963) v.v da tap trung nghien ciru d tay bic, Bic Thii (cu), Phu Thg (cu), Son La vi Lao Cai
vl xdi mdn khu vyc va bifn phap, cdng trinh trdng cay xanh che phii dat chong xdi mdn Cdng trinh ciia Pham Nggc Diing (1991) ve iimg dyng phucmg trinh mat dat phd quit vao dy bao tilm nang xdi mdn dat md ra trien vgng cho vifc img dung phuang trinh Wischmeier W.H-Smith D.D vio dy bio xdi mdn dit trong dieu kifn nude ta hifn nay "Nim 1996, Nguyen Nggc Lung vi Vd Dai Hii da cdng bd cdng trinh nghien cim vdi tya de "Nghien ciru tic dung phdng hg ngudn nude cua mgt sd thim thyc vit chinh vi cic nguyen tic xiy dyng rimg phdng
hg ngudn nude" Ve mat Iy luan cic tic gii da dinh gii dugc ning lyc phdng hd ciia mdt sd dang ciu triic thim thyc vit rimg ve mat chdng xdi mdn
3 Hf thong thdng tin dja li (GIS) va nhirng iing dung trong tinh toan xoi mdn dat 3.1 Hf thong thdng tin dja ly (GIS): Thuomg GIS hay dugc ghep vdi ban dd Tuy nhien ban dd chi li mdt each de lam vifc vdi cic du lifu dia ly trong GIS vi chi Ii mgt loai sin pham dugc GIS tao ra 6 Vift Nam, GIS dugc thdng nhit hieu chung: He thdng tin dja Iy la mgt hf thdng kit hgp giua con ngudi vi hf thdng miy tinh ciing cic thiet bj ngoai vi de luu trti', xir ly, phan tich vi hiln thj cac thdng tin dia ly dl phyc vy mgt muc dich nghien ciiu nhat djnh
DiKii tra tiiyc tii
Du lietu lj;a.j;im.JEr]k
nFCtnthj
" 1
.Hmh 1 Qui trinh GIS co ban
Mgt hf thdng tin dia ly cd cic chiic ning co bin sau:
- Nhap dir lifu
- Thao tic dir lifu
- Quin Iy dir lifu
- Tmy van vi phan tich
- Hiln thj va kit xuit dtir lifu
Qui trinh boat dgng ciia GIS dugc mieu ta trong hinh 1
Trang 8HOI NGHI KHOA HOC T O A N Q U O C V £ SINH THAI V A TAI N G U Y £ N SINH VAT LAN THU' BA
3.2 Lfng dyng GIS trong mo hinh hda danh gia xdi mdn dat
3.2.1 LTng dung GIS tryc tiep xay dyng ban do xdi mdn: Nhu trmh bay d frfn
cho thiy GIS li cdng cy manh cd kha ning tryc tiep iing dung de danh gia xdi mdn dit Sir dyng tryc tilp GIS trong danh gii xay dyng ban dd xdi mdn dat dugc thyc hifn qua 2 budc sau:
Budc 1: Xay dyng cic ban dd don tinh, can it nhat 4 loai ban do sau: Ban do thd nhudng, ban dd lugng mua, bin do dia hinh, bin dd tham thyc vat
Budc 2: Sii dyng GIS tinh toin dl dugc bin dd xdi mdn dit
- U'u dilm cua phuong phap nay: Nhanh, tdn it cdng
- Nhugc dilm: Dg tin cay khdng cao, khi t^o thanh ban do thanh qua khdng cd co sd de phan cap xdi mdn
3.2.2 LTng dung GIS va md hinh hoa tinh toan xoi mdn dat: Vdi vifc cic md hinh tinh
toin xdi mdn phong phii, da dang nhu da trinh biy d tren, viec lya chgn mdt md hinh de sir dung cin dugc quan tam can nhic dya tren nhieu yeu td:
- Tinh kha thi, bao gom c i vifc kha thi vl dtr lif u va phuong phap
- Tinh phu hgp vl thdng tin Cic thdng tin ma md hinh cd the dem lai (nghTa li ket qui tinh toin) phii diy du, phii hgp vdi yeu ciu dat ra
- Tinh chinh xic Md hinh dugc chgn phii cd dg chinh xic phii hgp vcii yeu cau
Nhtrng phan tich tren diy cho thiy USLE li mgt trong nhtrng md hinh phii hgp df dinh gii, tinh toin xdi mdn Sir dyng md hinh USLE frong dinh gii xdi mdn di l i de tii nghien curu cua nhieu tic gii khic nhau vi cho thay md hinh USLE cd the i p dyng thinh cdng cho tinh toan xdi mdn d cap dg khu vyc hoac mgt huyfn (nhu nghien ciiu cua de tii) Mgt dieu die bift thuan Igi nua ciia md hinh USLE l i de cap den cic nhan td anh hudng tdi xdi mdn mdt cich rieng bift trong mdt mdi tuomg quan chit che Dilu niy cho phep tich rieng timg ylu to de phan tich anh hudng ciia chiing den xdi mdn va tim ra bifn phip tic dgng phii hgp nhat
Vcii each tifm can van dl theo timg thdng sd anh hudng den xdi mdn, USLE cd the dugc tinh toan bing GIS Trinh ty cac budc co ban dugc thyc hifn nhu sau:
Budc I: Xay dyng cac bin do don tinh:
- Ban dd thd nhudng
- Ban dd lugng m u a
- Ban dd dia hinh
- Ban dd tham thyc vat
- Bin do canh tic sir dyng dat v.v
Budc 2: Tir cic ban do don tinh, irng dyng GIS xay dyng cic bin do he sd xdi mdn ciia phuong trinh USLE
Budc 3: Tir cac ban dd hf so xdi mdn, iing dyng GIS xay dyng ban dd tiem ning xdi mdn va xdi mdn hifn tai cua khu vyc nghien ciiu
Cac budc thyc hifn dugc md phdng theo hinh 2 dudi day Hinh 2 mieu ta vifc sii dyng
md hinh USLE trong tinh toin xdi mdn bing hf thdng thdng tin dia Iy Cic thdng sd ciia md hinh (cic he sd) dugc tinh toin fren GIS tir cac du lifu diu vio (cic ban dd) Cudi ciing, dya tren ban dd cic hf sd nay, ban dd xdi mdn v i ban dd xdi mdn tiem ning dugc tinh toan
Trang 9HOI NGH! KHOA HQC T O A N Q U O C V £ SINH THAI VA TAI NGUYEN SINH VAT LAN THU" BA
- Uu diem: Phuong phap nay cho dg tin cay cao, de phan cip xdi mdn
- Nhugc diem: Can hieu ro vl GIS dl thyc hifn tdt cic budc cdng vifc
Tuy nhien, can die bift luu y ddi vdi vifc ung dung GIS trong tinh toan xdi mdn dit la
so lifu diu vio phai chinh xac thi GIS mdi cho kit qua tin cay Do dd, quan tim din viec xay
dyng mdt co sd dtr lifu dii tin cay li yeu ciu hang diu trong vifc ihig dyng GIS ndi chung va
img dung GIS trong dinh gii xdi mdn dit ndi rieng
Ban do lirgng mira trung , ^ ^ ^
binh n a m
,
Ban do
tho nhir&ng
Ban do lop phii thyc v$t ^ ^ ^
f
H | se R
T S
H^ so K
Hf so C
He so P
I ^ , - , 1 , , A ^ Ban do thanh phdn \Bdn dS kei qua GIS !>;
• i Ca sa air li^u aau VCtO '^ ; ' ' ,
Hinh 2: Sir dyng mo hinh USLE trong tinh toin x6i ni6n bang GIS
IIL KET LUAN
Tir nhtrng ket qua tdng hgp, phan tich neu fren cd the di den nhumg ket luan sau:
- Hifn nay cd nhieu phuong phip nghien ciru, dinh gii xdi mdn dit dugc cic nhi khoa hgc
trong va ngoii nude sir dyng Cic phuong phip my khic nhau nhung deu cho nhtrng ket qui
nghien ciru cd gii trj
- Phuomg trinh mit dit phd qui cua Wischmeier W.H and Smith D.D tuy da ra ddi tir rat liu
nhung van dang dugc nhieu nha khoa hgc coi la cdng cu hiru hifu trong dinh gii xdi mdn dit
- Vdi vifc phat triln manh ciia cdng nghf thdng tin, vifc nghien cim, dinh gii xdi mdn dit
tren difn rgng trd nen de ding va thuan lgi
- Ciing Iiic kit hgp phuong trinh USLE ciia Wischmeier W.H and Smith D.D vi hf thdng tin
dia Iy (GIS) frong nghien cim, danh gii xdi mdn dit vira dam bio nhanh chdng, chinh xic ma
van bdc tich dugc tung ylu td dl nghien cim rieng bift va cd nhimg khuyen cao, tic dgng hgp
Iy cho khu vyc nghien ciiu Do vay, diy la lya chgn phii hgp cho nghien cuu, dinh gii xdi mdn
dit ndi chung vi tren dja bin huyfn Son Dgng - tinh Bic Giang ndi rieng
Trang 10HOI NGH! KHOA HOC T O A N Q U O C Vg SINH T H A I V A TAI N G U Y £ N SINH VAT LAN THU" BA
TAI LIfU THAM KHAO
1 Lai Vinh Cam, 2000: "Soil erosion smdy in North West region of Viet Nam by
intergrating watersheed analysis and universal soil loss equation (USLE)" Tap chi khoa
hgc Dai hgc Qiioc gia H i Ndi, sd XI
2 Nguyen The Dang, Dao Chau Thu, Dang Van Minh, 2003: Dat doi nui Vift Nam,
N'XB Ndng nghifp Ha Ngi
3 Hgi Khoa hgc dat Vift Nam, 2000: Dit Vift Nam, NXB Ndng nghifp Ha Ngi
4 Phdng Thong ke huyfn Son Dgng, 2007: Nien giim thong ke nam 2007, Scm Dgng,
Bac Giang
5 Tran Vinh Phudc, 2001: GIS - Mgt so vin d l chgn Igc, NXB Giao dye Ha Ngi
6 Nguyen Quang My, 2005: Xdi mdn dit hifn dai va cic bifn phip chdng xdi mdn, NXB
Dai hgc Qudc gia Ha Ndi
7 Tran Van Y, Nguyen Quang My, Nguyen Van Nhung, 1999: "Sir dyng Hf Thdng tin
dia Iy xay dyng bin dd xdi mdn tiem ning Vift Nam ty If 1:1000.000", Ung dyng Vien
thim vi Hf thdng tin dja Iy trong quy hoach mdi trudng, H i Ngi »
8 UBNT) tinh Bac Giang, 2007: Kit qua theo ddi dien bien tai nguyen rimg tinh Bac Giang
nam 2007
9 Wischmeier W.H and Smith D.D, 1962: Rainfall erosion, advance in Agronomy
S E L E C T I N G AN A P P R O P R I A T E M E T H O D F O R A S S E S S M E N T O F SOIL
E R O S I O N O F SON D O N G D I S T R I C T - B A C G I A N G P R O V I N C E
HOANG TIEN HA SUMMARY
This paper presents a review on methods of assessment of soil erosion in order to choose an
appropriate method for assessment of soil erosion of Son Dong District - Bac Giang Province
As the result, the USLE with application of GIS has been selected for assessment of soil erosion
of Son Dong District - Bac Giang Province