Bao Cao SVNCKH-Nguyen Thanh Ngan (Word)

8/3/2019 Bao Cao SVNCKH-Nguyen Thanh Ngan (Word)

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SINH VIN NGHIN CU KHOA HC 2009-i-

ABSTRACT

River basins have key role in the development and use water resource as

well as other natural resources for human being. The natural processes take

place in the river basins impact to human life activities. Therefore, the studies on

river basins are necessary. Especially the detailed studies in identification and

classification of basins which is concerned in environment aspects to develop the

resource currently are imperative research.

In the research, the GIS tools were used to classify the fifth-order

watersheds that consist of the basins of La Nga River, Be River, the middle andupstream areas of Dong Nai River. The classification was done based on

morphology and topography of the basins. In addition, the risk of flood of rain

(flash flood) that could be occurred in the classified watersheds was identified.

The results show that the fifth-order watersheds in the study area were

arranged into seven groups. Each group is described by specific characteristics

of morphology and topography. Then these characteristics were applied for

determination of risk of flood of rain (flash flood).

NG DNG H THNG THNG TIN A L PHN LOI CC TIU LU VCTRONG LU VC SNG NG NAI


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SINH VIN NGHIN CU KHOA HC 2009-ii-

GII THIU

Lu vc sng ng Nai l mt trong nhng lu vc sng ln ca Vit

Nam. y l ni tp trung dn c ng c, nhng thnh ph ln, nhng khu

cng nghip trng im ca khu vc ng Nam B. Ngy nay, do s gia tng

dn s nhanh chng, con ngi khai thc v s dng ngun ti nguyn nc

ti lu vc sng ng Nai mt cch ba bi. iu lm cc tai bin l qut

v xi mn t xy ra rt thng xuyn vi cng ngy cng mnh hn gy

ra nhng thit hi ln v ngi v ca cho c dn sng trong khu vc ny. Nhvy, vic nghin cu mt cch y v cc lu vc sng, c bit l nhn din,

phn loi c im cc lu vc c lin quan n tai bin mi trng l v cng

cn thit i vi lu vc sng ng Nai. Chnh v l do , tc gi quyt nh

thc hin ti ng dng H Thng Thng Tin a L phn loi cc tiu

lu vc trong lu vc sng ng Nai.

Trong ti ny, t d liu SRTM DEM, tc gi s dng cc cng c GIS

v vin thm xc nh c im hnh dng, mng dng chy v a hnh ca 3

lu vc sng chnh v ca cc tiu lu vc cp 5 ti khu vc nghin cu. Da

vo nhng c im lu vc xc nh c, tc gi tin hnh phn loi cc tiu

lu vc cp 5 ny thnh 7 nhm. Mi nhm lu vc ny mang nhng nt c

trng v a hnh khc nhau.

ng thi, trong ti, tc gi cng tin hnh xc nh nguy c xy ra l

qut ti khu vc nghin cu t d liu SRTM DEM. T kt qu thu c, tc gis nh gi mi tng quan gia nguy c xy ra l qut vi 7 dng lu vc c

phn loi.



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SINH VIN NGHIN CU KHOA HC 2009-iii-

MC LC

ABSTRACT .........................................................................................................I

GII THIU ......................................................................................................II

MC LC .........................................................................................................III

DANH MC CH VIT TT ........................................................................VI

DANH MC BNG ........................................................................................VII

DANH MC BIU .................................................................................VIII

DANH MC HNH NH .................................................................................XI

CHNG 1 .......................................................................................................13

TNG QUAN V TI ...............................................................................13

1.1 T VN ...................................................................................................... 131.2 MC TIU CA TI ..................................................................................... 141.3 KHU VC V I TNG NGHIN CU ..................................................... 141.4 NI DUNG THC HIN TI ....................................................................... 15

1.5 PHNG PHP NGHIN CU S DNG TRONG TI .......................... 161.6 D LIU S DNG .............................................................................................161.7 PHN MM S DNG ....................................................................................... 171.8 NGHA KHOA HC V THC TIN ............................................................ 17

CHNG 2 .......................................................................................................18

TNG QUAN V NGHIN CU LU VC ................................................18

2.1 GII THIU V HOT NG NGHIN CU LU VC SNG .................. 182.2 MT S K THUT KHC S DNG TRONG KHA LUN .....................20

2.2.1 Nn chnh hnh hc nh ...........................................................................202.2.2 Lc nh bng ma trn l ..........................................................................212.2.3 K thut ti phn loi nh ........................................................................212.2.4 K thut tnh ton trn d liu raster .......................................................212.2.5 K thut thng k d liu raster .............................................................21

2.3 NH HNG PHNG PHP THC HIN TRONG KHA LUN ...........22

CHNG 3 .......................................................................................................23

KT QU XC NH C IM CC LU VC ..................................23

TRONG KHU VC NGHIN CU ...............................................................23

3.1 THNG K C IM 3 LU VC SNG CHNH ....................................... 233.1.1 c im v hnh thi ca 3 lu vc sng chnh ......................................23



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SINH VIN NGHIN CU KHOA HC 2009-iv-

3.1.2 c im mng dng chy ca 3 lu vc sng chnh ..............................233.1.3 c im a hnh ca 3 lu vc sng chnh ............................................24

3.2 THNG K C IM TIU LU VC CP 5 TRONG KVNC ......... .........333.2.1 c im hnh thi ca cc tiu lu vc cp 5 .........................................333.2.2 c im mng dng chy ca cc tiu lu vc cp 5 ............................35

3.2.3 c im a hnh ca cc tiu lu vc cp 5 ..........................................36

CHNG 4 .......................................................................................................38

PHN LOI CC TIU LU VC CP 5 ..................................................38


4.1 PHN LOI CC LU VC CP 5 TRN KVNC .......................................... 384.1.1 Nguyn tc chn i tng lu vc cn phn loi....................................384.1.2 Nguyn tc xc nh c im phn loi.................................................394.1.3 Kt qu phn loi cc tiu lu vc cp 5 ..................................................41

4.2 XC NH MI LIN QUAN GIA DNG LU VC VI TAI BIN LQUT ........................................................................................................................... 474.2.1 Xy dng bn nguy c xy ra l qut ti khu vc nghin cu .............474.2.2 Xc nh mi lin h gia cc nhm lu vc vi nguy c xy ra l qut . .52

CHNG 5 .......................................................................................................53

KT LUN V KIN NGH ...........................................................................53

TI LIU THAM KHO ................................................................................55

PH LC

PH LC 1: BN TH HIN V TR CA KHU VC NGHIN CU.

PH LC 2: BN TH HIN CAO A HNH CA KHU VC NGHIN

CU.

PH LC 3: BN TH HIN MNG LI DNG CHY CA KHU VC

NGHIN CU.

PH LC 4: BN TH HIN DC A HNH CA KHU VC NGHIN

CU.

PH LC 5: BN TH HIN HNG SN CA KHU VC NGHINCU.

PH LC 6: BN TH HIN PHN CT SU A HNH CA KHU VC

NGHIN CU.

PH LC 7: BN TH HIN CC TIU LU VC CP 5 TRONG KVNC.

PH LC 8: BN MNG DNG CHY CC TIU LU VC CP 5

TRONG KHU VC NGHIN CU.

PH LC 9: BN TH HIN KT QU PHN LOI CC TIU LU VCCP 5.



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SINH VIN NGHIN CU KHOA HC 2009-v-

PH LC 10: BN TH HIN NGUY C L QUT XT TRN YU T

A HNH.

PH LC 11: C IM HNH THI CC TIU LU VC CP 5 TI KVNC.

PH LC 12: C IM MNG DNG CHY CC TIU LU VC CP 5

TI KVNC.

PH LC 13: C IM A HNH CC TIU LU VC CP 5 TI KVNC.

PH LC 14: KT QU TNH TON GI TR NGUY C L QUT TRN CC

TIU LU VC CP 5 TRONG KVNC.

PH LC 15: HNH NH TI MT S V TR KHO ST THC A.



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SINH VIN NGHIN CU KHOA HC 2009-vi-

DANH MC CH VIT TT

DEM : Digital Elevation Model - M hnh s cao.

GIS : Geographical Information System - H Thng Thng Tin a L.

KVNC : Khu vc nghin cu.

LV : Lu vc.

TLV : Tiu lu vc.

NASA : U.S. National Aeronautics and Space Administration - C quan Hng

Khng V Tr M.NGA : U.S. National Geospatial-Intelligence Agency - C quan Tnh Bo

a Khng Gian M.

SRTM : Shuttle Radar Topography Mission D n xy dng m hnh cao

s cho Tri t bng h thng radar t trn tu con thoi.



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SINH VIN NGHIN CU KHOA HC 2009-vii-

DANH MC BNG

ABSTRACT .........................................................................................................I

GII THIU ......................................................................................................II

MC LC .........................................................................................................III


DANH MC BNG ........................................................................................VII

DANH MC BIU .................................................................................VIII

DANH MC HNH NH .................................................................................XI

CHNG 1 .......................................................................................................13

TNG QUAN V TI ...............................................................................13



CHNG 2 .......................................................................................................18





CHNG 3 .......................................................................................................23



3.1 THNG K C IM 3 LU VC SNG CHNH ....................................... 233.1.1 c im v hnh thi ca 3 lu vc sng chnh ......................................23



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SINH VIN NGHIN CU KHOA HC 2009-viii-

3.1.2 c im mng dng chy ca 3 lu vc sng chnh ..............................233.1.3 c im a hnh ca 3 lu vc sng chnh ............................................24

3.2 THNG K C IM TIU LU VC CP 5 TRONG KVNC ......... .........333.2.1 c im hnh thi ca cc tiu lu vc cp 5 .........................................333.2.2 c im mng dng chy ca cc tiu lu vc cp 5 ............................35

3.2.3 c im a hnh ca cc tiu lu vc cp 5 ..........................................36

CHNG 4 .......................................................................................................38




4.2 XC NH MI LIN QUAN GIA DNG LU VC VI TAI BIN LQUT ........................................................................................................................... 474.2.1 Xy dng bn nguy c xy ra l qut ti khu vc nghin cu .............474.2.2 Xc nh mi lin h gia cc nhm lu vc vi nguy c xy ra l qut . .52

CHNG 5 .......................................................................................................53

KT LUN V KIN NGH ...........................................................................53

TI LIU THAM KHO ................................................................................55

DANH MC BIU

ABSTRACT .........................................................................................................I

GII THIU ......................................................................................................IIMC LC .........................................................................................................III


DANH MC BNG ........................................................................................VII

DANH MC BIU .................................................................................VIII

DANH MC HNH NH .................................................................................XI

CHNG 1 .......................................................................................................13

TNG QUAN V TI ...............................................................................13



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SINH VIN NGHIN CU KHOA HC 2009-ix-



CHNG 2 .......................................................................................................18





CHNG 3 .......................................................................................................23



3.1 THNG K C IM 3 LU VC SNG CHNH ....................................... 233.1.1 c im v hnh thi ca 3 lu vc sng chnh ......................................233.1.2 c im mng dng chy ca 3 lu vc sng chnh ..............................233.1.3 c im a hnh ca 3 lu vc sng chnh ............................................24

Biu 3.1 th tn sut cao a hnh lu vc sng La Ng .................26Biu 3.2 th tn sut cao a hnh lu vc sng ng Nai.............27Biu 3.3 th tn sut cao a hnh lu vc sng B .......................27Biu 3.4 Biu trn th hin c cu dc a hnh lu vc sng LaNg ............................................................................................................. 29Biu 3.5 Biu trn th hin c cu dc a hnh lu vc sng ngNai............................................................................................................... 29Biu 3.6 Biu trn th hin c cu dc a hnh lu vc sng B . .30Biu 3.7 Biu radar th hin hng sn ca lu vc sng La Ng ....31Biu 3.8 Biu radar th hin hng sn ca lu vc sng ng Nai 31Biu 3.9 Biu radar th hin hng sn ca lu vc sng B ...........32

3.2 THNG K C IM TIU LU VC CP 5 TRONG KVNC ......... .........333.2.1 c im hnh thi ca cc tiu lu vc cp 5 .........................................333.2.2 c im mng dng chy ca cc tiu lu vc cp 5 ............................353.2.3 c im a hnh ca cc tiu lu vc cp 5 ..........................................36

CHNG 4 .......................................................................................................38





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SINH VIN NGHIN CU KHOA HC 2009-x-


4.2 XC NH MI LIN QUAN GIA DNG LU VC VI TAI BIN L

QUT ........................................................................................................................... 474.2.1 Xy dng bn nguy c xy ra l qut ti khu vc nghin cu .............474.2.2 Xc nh mi lin h gia cc nhm lu vc vi nguy c xy ra l qut . .52

CHNG 5 .......................................................................................................53

KT LUN V KIN NGH ...........................................................................53

TI LIU THAM KHO ................................................................................55



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SINH VIN NGHIN CU KHOA HC 2009-xii-

3.1.1 c im v hnh thi ca 3 lu vc sng chnh ......................................233.1.2 c im mng dng chy ca 3 lu vc sng chnh ..............................233.1.3 c im a hnh ca 3 lu vc sng chnh ............................................24

3.2 THNG K C IM TIU LU VC CP 5 TRONG KVNC ......... .........333.2.1 c im hnh thi ca cc tiu lu vc cp 5 .........................................33

3.2.2 c im mng dng chy ca cc tiu lu vc cp 5 ............................353.2.3 c im a hnh ca cc tiu lu vc cp 5 ..........................................36

CHNG 4 .......................................................................................................38



4.1 PHN LOI CC LU VC CP 5 TRN KVNC .......................................... 384.1.1 Nguyn tc chn i tng lu vc cn phn loi....................................384.1.2 Nguyn tc xc nh c im phn loi.................................................39

4.1.3 Kt qu phn loi cc tiu lu vc cp 5 ..................................................414.2 XC NH MI LIN QUAN GIA DNG LU VC VI TAI BIN LQUT ........................................................................................................................... 47

4.2.1 Xy dng bn nguy c xy ra l qut ti khu vc nghin cu .............474.2.2 Xc nh mi lin h gia cc nhm lu vc vi nguy c xy ra l qut . .52

CHNG 5 .......................................................................................................53

KT LUN V KIN NGH ...........................................................................53

TI LIU THAM KHO ................................................................................55



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SINH VIN NGHIN CU KHOA HC 2009-13-

Chng 1

TNG QUAN V TI

1.1 T VN

i sng loi ngi lin quan mt thit vi cc lu vc sng. Trn cc lu

vc sng con ngi thc hin cc hot ng sn xut, khai thc ti nguyn (khai

khong, khai thc rng, s dng t...) phc v cho cc nhu cu kinh t, x hi.

Nhng hot ng ny din ra cng nhiu s cng nh hng ti ngun ti nguyn

nc v cng quan trong ny.

Do s gia tng dn s nhanh chng, con ngi khai thc v s dng

ngun ti nguyn t cc lu vc mt cch ba bi. Nhng hot ng khai thc

khng hp l tc ng trc tip n cc lu vc, lm thay i cc qu trnh t

nhin din ra bn trong mi lu vc. Kt qu tt yu ca vic ny chnh l cc tai

bin t nhin (l qut, ngp lt, xi mn t) din ra ngy mt nhiu hn,

mnh hn, gy nn nhng thit hi v cng to ln cho con ngi.

Lu vc sng ng Nai l mt trong nhng lu vc sng ln ca Vit

Nam. y l ni tp trung dn c ng c, nhng thnh ph ln, nhng khu

cng nghip trng im ca khu vc ng Nam B. Ngy nay, vic khai thc

lu vc khng hp l lm cc tai bin l qut v xi mn t xy ra rt thng

xuyn v vi cng ngy cng mnh hn gy ra nhng thit hi ln v ngi

v ca cho c dn sng trong khu vc ny.

Nh vy, vic nghin cu mt cch y v cc lu vc sng, c bitl nhn din, phn loi c im cc lu vc c lin quan n tai bin mi trng

l v cng cn thit i vi lu vc sng ng Nai. Chnh v l do , sinh vin

quyt nh thc hin ti ng dng H Thng Thng Tin a L phn loi

cc tiu lu vc trong lu vc sng ng Nai.



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1.2 MC TIU CA TI

Nghin cu tnh ton cc c im hnh thi v a hnh ca cc tiu

lu vc trong lu vc sng ng Nai v phn loi cc tiu lu vc cp 5 ti

khu vc ny.1.3 KHU VC V I TNG NGHIN CU

- Khu vc nghin cu:Khu vc nghin cu trong ti ny l mt phn

ca h thng lu vc sng Si Gn ng Nai, v tr a l ca khu vc

vo khong t 10603424 n 10804341 kinh ng v t

1005014 n 1202203 v Bc. Khu vc ny thuc a gii hnh

chnh ca 6 tnh: Bnh Dng, Bnh Phc, Bnh Thun, ng Nai, Lm

ng v k Nng.

Ton b khu vc nghin cu bao gm 3 lu vc sng chnh sau:

Lu vc sng La Ng: c v tr a l t 10700950 n 10800921

kinh ng v t 1005014 n 1104657 v Bc, thuc a

gii hnh chnh 3 tnh ng Nai, Bnh Thun, Lm ng.

Phn thng lu v trung lu sng ng Nai: c v tr a l t

1060

5751 n 1080

4341 kinh ng v t 100

5748 n1202014 v Bc, thuc a gii hnh chnh 5 tnh Bnh Phc,

Lm ng, ng Nai, k Nng, Bnh Thun.

Lu vc sng B: c v tr a l t 10603424 n 10703033 kinh

ng v t 110630 n 1202203 v Bc, thuc a gii hnh

chnh 4 tnh Bnh Phc, Bnh Dng, ng Nai, k Nng.



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Hnh 1.1 Ranh gii v v tr khu vc nghin cu

- i tng nghin cu: nghin cu c im lu vc v mng dng chy

ca cc tiu lu vc cp 5, t tin hnh phn loi dng lu vc ca cc

tiu lu vc sng cp 5 trn khu vc nghin cu.

1.4 NI DUNG THC HIN TI

- Nghin cu v c im cc lu vc sng v l thuyt v phn loi mng

dng chy:

Tm hiu v cc phng php phn tch mng dng chy v lu vc sng

c s dng trong nghin cu lu vc.

Tm hiu v thut ton D8 (thut ton phn loi lu vc chnh s dng

trong phn mm RiverTools 2.4) c pht trin bi OCallaghan v

Mark (1984).

- X l d liu vin thm SRTM DEM lp bn mng dng chy v

cp lu vc ca khu vc nghin cu, xc nh cc c im lu vc, xy

dng b d liu khi qut v h thng cc lu vc ti khu vc nghin cu.

- Xy dng quy trnh phn loi dng lu vc: nghin cu cc c im ca

h thng mng dng chy ca khu vc nghin cu, t tin hnh phn

loi cc dng lu vc ca khu vc ny.



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- Nghin cu xc nh mi tng quan gia cc dng lu vc phn loi

vi hin tng l qut din ra ti khu vc nghin cu.

1.5 PHNG PHP NGHIN CU S DNG TRONG TI- Phng php tng hp ti liu:

Thu thp, tng hp, chn lc cc thng tin v khu vc nghin cu t nhiu

ngun khc nhau: t cc website chuyn ngnh, cc cng trnh nghin cu

thc hin, cc ti liu khc c lin quan n ti.

Thu thp d liu vin thm v cc bn t liu c xy dng bi

cc c quan, ban ngnh c lin quan.

- S dng cc cng c GIS thc hin ni dung nghin cu:

S dng cc cng c phn tch khng gian (spatial analysis) ca GIS:

phn tch mng dng chy v dng lu vc ca khu vc nghin cu, tnh

ton cc c im a hnh, hnh th ca cc lu vc.

Thnh lp cc bn c lin quan. H thng bn s c chun ha v

h quy chiu VN2000.

- Phng php kho st thc a: Kho st thc a chp nh so snh v kim chng ph hp ca kt

qu thc hin.

Ngoi ra, trong qu trnh thc hin kha lun, tc gi cn s dng mt s

cng c x l s liu ca Excel tin hnh phn tch, thng k, x l s liu c

lin quan phc v cho vic nghin cu.

1.6 D LIU S DNG

- D liu nh SRTM DEM (m hnh s cao) c phn gii 3 arc

second (tng ng 90 m) do NASA v NGA cung cp.

- Bn mng dng chy ca khu vc nghin cu c h quy chiu

VN2000, t l 1:250.000.



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1.7 PHN MM S DNG

- Phn mm RiverTools 2.4: s dng phn tch mng dng chy, xc

nh ranh gii cc lu vc, xc nh bn knh, chu vi, din tch lu vc.

- Phn mm IDRISI Andes: s dng trong qu trnh tin x l d liuSRTM DEM v tnh ton cc c im ca vng.

- Phn mm Global Mapper 9.0: s dng chuyn d liu SRTM DEM

t nh dng GeoTIFF sang nh dng DEM.

- Phn mm Microsoft Excel: s dng thng k cc ch s hnh thi lu

vc, cc ch s a hnh lu vc.

- Phn mm Surfer 8.0: s dng biu din m hnh DEM ca cc lu

vc.

- Phn mm MapINFO 9.0: bin tp v trnh by cc bn kt qu.

1.8 NGHA KHOA HC V THC TIN

- Thng k, nh gi c nhng nt c trng v hnh thi v a hnh ca

h thng mng dng chy v cc lu vc trong khu vc nghin cu.

- Thnh lp c mt b d liu khi qut v cc lu vc ti khu vc

nghin cu.- Bc u thnh lp cc tiu ch phn loi dng lu vc.

- Xc nh mi tng quan gia kt qu phn loi lu vc vi vic din ra

tai bin l qut ti khu vc nghin cu.

- To c s cho vic xut mc ch s dng hp l cho tng dng lu

vc ti KVNC.



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Chng 2

TNG QUAN V NGHIN CU LU VC

2.1 GII THIU V HOT NG NGHIN CU LU VC SNG

Cc lu vc sng c lin quan v cng mt thit n i sng ca con

ngi. Chnh v th, hot ng nghin cu cc lu vc sng c con ngi

thc hin t rt lu i v bng nhiu hng tip cn khc nhau.

Trc y, cc nh khoa hc thc hin nghin cu lu vc ch yu bng

phng php iu tra thc t. Phng php ny c u im l kt qu nghin cu

c chnh xc cao, tuy nhin phng php ny hn ch ch cn nhiu thi

gian thc hin. Ngoi ra, phng php ny ch ph hp khi thc hin trong

mt khu vc nghin cu nh nht nh, khng th p dng nghin cu trn

mt khu vc rng ln.

Ngy nay, s pht trin nhanh chng ca ngnh cng ngh thng tin m ra mt hng i hon ton mi trong nghin cu lu vc: nghin cu lu vc

sng vi s h tr ca H Thng Thng Tin a L (GIS).

Nm 1957, s ra i ca khi nim cp Strahler v nh lut Horton-

Strahler to c s cho vic hnh thnh thut ton xc nh mng dng chy v

phn chia ranh gii lu vc sng [6]. Cp Strahler (Strahler order) l mt thuc

tnh c gn cho mi on sng trong mt mng li dng chy. Mt chui cc

on sng c cng cp Strahler to thnh mt dng Strahler (Strahler stream).Cp ca dng Strahler c xem nh mt thc o nh gi kch c v s

phc tp v cu trc ca mt mng dng chy [9]. Theo nh lut Horton-

Strahler, gi tr c s ca cp Strahler l cp 1, khi 2 dng Strahler cng cp gp

nhau s to ra mt dng Strahler ln hn 1 cp (xem hnh 2.1) [6].



19/56


Hnh 2.1 Phng php xc nh bc Strahler

T nhng khi nim c s ban u, cc tc gi pht trin thnh nhiu

thut ton xc nh mng li dng chy khc nhau, trong s c 2 thut ton

tiu biu sau:

- OCallaghan v Mark (1984) xy dng m hnh mng dng chy D8

(hnh 2.2). Trong m hnh ny, cc dng chy s c 8 hng chnh, l

cc hng: Bc, ng Bc, ng, ng Nam, Nam, Ty Nam, Ty, Ty

Bc [9].- David Tarboton (2000) xy dng m hnh mng dng chy D-Infinity.

Khc vi m hnh D8, m hnh D-Infinity quy nh s hng dng chy l

v hn [7].

Hnh 2.2 M hnh D8 m hnh mng dng chy s dng trong ti

Trn th gii, hot ng nghin cu lu vc c thc hin rng ri,

phc v cho nhiu mc ch khoa hc khc nhau. Tiu biu c th k n mt snghin cu sau:



20/56


- Cc tc gi Zhou Lin v Takashi Oguchi (i hc Tokyo, Nht) s dng 2

tiu ch l mt dng chy v gc dc a hnh xc nh cc dng tiu

lu vc c trng ca 3 vng c cu trc a cht khc nhau: vng

Kusatsu-Shirane, vng Aka-Kuzure v vng Usu.- Cc tc gi Thomas Kohler v Thomas Breu lp mt h thng tiu

chun phn loi cc lu vc h ngun sng Mekong.

- Tc gi Andreas Heinimann (i hc Berne, Thy S) thc hin phn loi

lu vc ti nc Lo v xut cc bin php s dng hp l lu vc.

Ti Vit Nam, hot ng nghin cu lu vc sng cng rt c ch

trng, c nhiu ti nghin cu lu vc sng c gi tr c thc hin, tiu

biu c th k n:

- ti Nghin cu xy dng c s khoa hc phc v qun l thng nht

v tng hp ngun nc lu vc sng ng Nai ca Vin Mi Trng

V Ti Nguyn i Hc Quc Gia Tp.HCM.

- ti Phn tch din bin ch dng chy h lu sng B sau khi c

cng trnh thy in Thc M ca Phn vin kh tng thy vn v mi

trng khu vc pha Nam.- ti Vin Thm v GIS: kh nng ng dng thnh lp bn nguy c

tai bin trn lu vc sng B ca tc gi Trn Tun T Khoa Mi

Trng, trng i Hc Khoa Hc T Nhin Tp.HCM.

2.2 MT S K THUT KHC S DNG TRONG KHA LUN

2.2.1 Nn chnh hnh hc nh

Nn chnh hnh hc l k thut c thc hin loi b nhng bin dng

hnh hc trn nh bng cch thit lp mi quan h gia h ta nh v h ta

a l ca cc im khng ch [4].

Trong kha lun, k thut nn chnh hnh hc s c thc hin chuyn

d liu SRTM DEM t h quy chiu Latitude/Longitude sang h quy chiu

VN2000.



21/56


22/56


2.3 NH HNG PHNG PHP THC HIN TRONG KHA

LUN

Trong phm vi kha lun, tc gi s s dng cng c GIS phn chia

ranh gii lu vc, xc nh mng dng chy, cc yu t hnh thi v a hnh cacc tiu lu vc nm trong khu vc nghin cu, m c th l cc tiu lu vc cp

5 trong lu vc sng La Ng, lu vc sng B, vng thng lu v trung lu

sng ng Nai.

T kt qu phn tch lu vc thc hin, tc gi s tin hnh phn loi

cc dng tiu lu vc trong vng da trn cc c im c trng ca chng

(xem hnh 2.3).

Hnh 2.3 Khi qut cc bc thc hin phn loi dng lu vc (watershed classification)



23/56


Chng 3

KT QU XC NH C IM CC LU VCTRONG KHU VC NGHIN CU

Trong chng ny, tc gi s trnh by 2 ni dung chnh:

- Kt qu phn tch cc c im hnh thi, mng dng chy v a hnh ca

3 lu vc sng chnh: lu vc sng La Ng, phn thng lu v trung lu

sng ng Nai v lu vc sng B.

- Kt qu tnh ton thc hin trn cc tiu lu vc cp 5 thuc KVNC.

3.1 THNG K C IM 3 LU VC SNG CHNH

3.1.1 c im v hnh thi ca 3 lu vc sng chnh

Thc hin tnh ton din tch, ng knh, chu vi v ch s hnh dng lu

vc t lp d liu lu vc va to thnh, ta c kt qu nh bng 3.1 sau y:

Bng 3.1: c im hnh thi cc lu vc chnh

LU VCDIN TCHLU VC

(km2)

NG KNHLU VC (km)

CHU VILU VC

(km)

CH S HNHDNG LU

VCSng La Ng 4.084,18 128,136 559,349 0,4987Sng ng Nai 10.598,78 224,5 1.095,85 0,4586Sng B 7.770,648 149,992 587,382 0,588

Trong 3 lu vc trn, lu vc sng ng Nai c din tch v chu vi ln

nht, cn lu vc sng La Ng l lu vc c din tch v chu vi nh nht.

Xt trn yu t hnh dng lu vc, ta thy 2 lu vc sng ng Nai v LaNg c hnh dng ko di theo hng ng Bc Ty Nam, cn lu vc sng

B li c xu hng tri di theo hng Bc Nam.

3.1.2 c im mng dng chy ca 3 lu vc sng chnh

Sau khi s dng m hnh D8 xc nh mng dng chy t d liu

SRTM DEM, ta c kt qu nh trong hnh 3.1.



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Hnh 3.1 H thng mng dng chy ca cc lu vc chnh

Thc hin tnh ton tng chiu di dng chy, mt dng chy v thng

k cc c im hng dng chy, dng mng dng chy, ta c kt qu nh bng

3.2 sau y.

Bng 3.2: c im mng dng chy trong cc lu vc chnh

LU VC

TNGCHIU DIDNGCHY

TRONG LUVC (km)

HNG DNG CHYCHNH

DNGMNG LI

DNGCHY

MT DNGCHY

TB(km/km2)

Sng La Ng 2.019,8 ng Bc - Ty NamDng nhnhcy 0,4945

Sng ng Nai 5.164,17 ng Bc - Ty NamDng nhnhcy 0,4872

Sng B 3.916,276 ng Bc - Ty Nam

Dng nhnh

cy 0,504Da vo kt qu thng k, ta thy c 3 lu vc u c dng mng li

dng chy dng nhnh cy v u c hng dng chy chnh l hng ng Bc

Ty Nam. Trong 3 lu vc, lu vc sng B l lu vc c mt dng chy

ln nht (0,504 km/km2).

3.1.3 c im a hnh ca 3 lu vc sng chnh

3.1.3.1 c im cao a hnh ( cao tuyt i)



25/56


Biu din d liu SRTM DEM ca khu vc nghin cu bng phn mm

MapINFO, ta c kt qu nh hnh 3.2 sau y:

Hnh 3.2 Bn cao a hnh ca khu vc nghin cu

Thc hin k thut thng k raster trn lp d liu cao a hnh ca

khu vc, ta c kt qu nh trong bng 3.3.

Bng 3.3: c im cao a hnh ca cc lu vc chnh

LU VCGi tr

cao nh nht(m)

Gi tr cao ln nht

(m)

Gi tr cao trungbnh (m)

lchchun

Sng La Ng 53 1.787 457,912 367,958Sng ng Nai 13 2.285 720,256 447,232Sng B 13 983 230,234 198,693

* Nhn xt:

Lu vc sng La Ng:

Da vo bn th hin cao (hnh 3.2) v th tn sut (biu 3.1),

ta thy cao a hnh ca lu vc sng La Ng tp trung ch yu trong 2

khong: mt khong t 53 200 m, mt khong t 200 m n trn 2000 m.

Khu vc c cao a hnh thp (53 200 m) tp trung ch yu phn

trung tm v phn pha Ty Nam ca lu vc, ng vi vng ng bng. Cn khu

vc c cao a hnh ln (200 m n trn 2000 m) th li tp trung phn ng

Bc ca lu vc. Gia 2 khu vc ny c s chnh lch v cao kh ln.



26/56


Xt trn tng th ton lu vc, ta thy cao a hnh ca lu vc sng

La Ng c xu hng cao ng Bc, v gim dn theo hng t ng Bc n

Ty Nam.

Biu 3.1 th tn sut cao a hnh lu vc sng La Ng

Lu vc sng ng Nai:

Da vo bn th hin cao (hnh 3.2) v th kt qu (biu 3.2),

ta thy cao a hnh ca vng thng lu v trung lu sng ng Nai chia

thnh 3 khong cao r rt: t 50 250 m, t 250 800 m, t 800 m n trn

2000 m.

3 khong cao trn ng vi 3 b phn a hnh c trng ca vng:

- Vng c cao a hnh thp (50 250 m): tp trung ti pha Ty Nam

ca khu vc, c trng cho a hnh vng ng bng.

- Vng c cao a hnh trung bnh (250 800 m): tp trung ti vng

trung tm ca khu vc, c trng cho a hnh vng cao nguyn v

chuyn tip ng bng cao nguyn.

- Vng c cao trung bnh ln (800 m n trn 2000 m): tp trung tipha ng Bc ca khu vc, c trng cho a hnh vng i ni cao.

Cng nh lu vc sng La Ng, ta thy cao a hnh ca vng thng

lu v trung lu sng ng Nai c xu hng cao ng Bc, v gim dn theo

hng t ng Bc n Ty Nam.



27/56


Biu 3.2 th tn sut cao a hnh lu vc sng ng Nai

Lu vc sng B:

Qua th tn sut (biu 3.3), ta thy cao a hnh ca lu vc sngB cng chia thnh 3 khong r rt: t 10 200 m, t 200 500 m, t 500 m n

trn 900 m. Trong , khong cao t 10 200 m chim phn ln din tch

vng (pha Nam), tip n l khong cao t 200-500 m (khu vc trung tm

lu vc), cn khong cao t 500 900 m chim din tch kh nh (pha Bc

v ng Bc).

Cng nh 2 lu vc La Ng v ng Nai, cao lu vc sng B cng c

xu hng gim dn t ng Bc xung Ty Nam.

Biu 3.3 th tn sut cao a hnh lu vc sng B

3.1.3.2 c im dc a hnh



28/56


Tin hnh tnh ton v thng k dc a hnh da vo d liu SRTM

DEM ca khu vc nghin cu, ta c kt qu nh trong hnh 3.3 v bng 3.4 sau

y:

Bng 3.4: c im dc a hnh ca cc lu vc chnh

LU VCGi tr dc nh

nht (deg)

Gi tr dc ln nht

(deg)

Gi tr dc trungbnh (deg)

lchchun

Sng La Ng 0 48,530 6,354 7,424Sng ng Nai 0 55,243 8,599 6,902Sng B 0 52,873 4,615 4,353

Hnh 3.3 Bn dc a hnh ca khu vc nghin cu

* Nhn xt:

Lu vc sng La Ng:

dc ca lu vc sng La Ng ch yu tp trung trong khong t 0-5

(61%). Cc khu vc c dc thp tp trung ch yu ti vng ng bng gn h

Tr An. Cn cc khu vc c dc cao li tp trung cc khu vc chuyn tip

gia vng ng bng v cao nguyn trung tm lu vc sng La Ng v vng

chuyn tip gia cao nguyn v ni cao trn pha ng Bc lu vc sng La

Ng.



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Biu 3.4 Biu trn th hin c cu dc a hnh lu vc sng La Ng

Lu vc sng ng Nai:

Da vo biu trn, ta thy dc ca vng thng lu v trung lu

sng ng Nai ch yu tp trung trong 3 khong t 0-5 (37%), t 6-10

(27%), t 11-20 (28%). Nhng ni c dc thp tp trung ch yu ti khu

vc ng bng pha Ty Nam, nhng ni c dc cao tp trung ti nhng vng

chuyn tip gia ng bng vi cao nguyn ti khu vc trung tm ca vng.

Biu 3.5 Biu trn th hin c cu dc a hnh lu vc sng ng Nai

Lu vc sng B:

Nhn chung, lu vc sng B c dc thp hn 2 lu vc La Ng vng Nai, trong phn din tch c dc t 0 5 chim n 66%, tip

theo l phn din tch c dc t 6 10 chim 23%, phn din tch cn li

c dc t 11 30 ch yu tp trung pha Bc ca vng.



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Biu 3.6 Biu trn th hin c cu dc a hnh lu vc sng B

3.1.3.3 c im hng sn

Tin hnh tnh ton v thng k hng sn da vo d liu SRTM DEM

ca khu vc nghin cu, ta c kt qu nh trong hnh 3.4 v bng 3.5 sau y.

Hnh 3.4 Bn hng sn ca khu vc nghin cu

Bng 3.5: c im hng sn ca cc lu vc chnh

HNGSN

(%)

Lu vcsng La

Ng

Lu vcsng ng

Nai

Lu vcsng B

Bc 12,03% 11,22% 11,66%ng Bc 10,81% 9,96% 9,17%

ng 12,93% 12,95% 11,82%



31/56


32/56


Biu 3.9 Biu radar th hin hng sn ca lu vc sng B

3.1.3.4 c im phn ct su a hnh

S dng phng php lc ma trn v tnh ton trn raster, ta tnh c gi

tr phn ct su ca khu vc nghin cu nh hnh 3.5 v bng 3.6 sau y:

Hnh 3.5 Bn phn ct su ca khu vc nghin cu

Bng 3.6: c im phn ct su ca cc lu vc chnh

LU VCGi tr nh

nht(m/km2)

Gi tr lnnht (m/km2)

Gi trtrung bnh

(m/km2)

lchchun

Sng La Ng 0 552 66,21 76,23Sng ng Nai 0 528 85,33 63,43Sng B 0 359 44,54 36,65

* Nhn xt: Lu vc sng La Ng:



33/56


Da vo bn th hin gi tr phn ct su, ta thy khu vc c gi tr

phn ct su ln tp trung ch yu ti khu vc chuyn tip gia vng ng bng

vi vng ni v cao nguyn (khu vc trung tm ca lu vc sng La Ng), kt

qa ny ph hp vi kt qu phn tch dc thc hin. iu chng t, ticc khu vc chuyn tip, mc phn ct a hnh ln.

Lu vc sng ng Nai:

Da vo bn th hin gi tr phn ct su, ta thy khu vc c gi tr

phn ct su ln tp trung ch yu ti khu vc trung tm v khu vc pha ng

Bc ca vng thng lu v trung lu sng ng Nai. Khu vc c gi tr phn

ct su nh tp trung ti khu vc gn h Tr An.

Lu vc sng B:

Khu vc c gi tr phn ct su ln ch yu tp trung ti pha Bc v ng

Bc lu vc sng B, chim din tch kh nh so vi din tch ton vng. Khu

vc trung tm vng c gi tr phn ct su dao ng t 30 80 m/km2. Khu vc

pha Nam ca vng c phn ct su tng i nh (t 0 20 m/km 2).

3.2 THNG K C IM TIU LU VC CP 5 TRONG KVNC3.2.1 c im hnh thi ca cc tiu lu vc cp 5

Tin hnh xc nh cc tiu lu vc cp 5 trong KVNC bng phn mm

RiverTools, ta c ranh gii v hnh thi cc tiu lu vc cp 5 nh trong hnh 3.6.



34/56


Hnh 3.6 Kt qu xc nh cc tiu lu vc cp 5 trong khu vc nghin cu

Lu vc sng La Ng:

Da kt qu thng k, ta thy mc dao ng v din tch ca cc tiu

lu vc cp 5 ti lu vc sng La Ng trong khong t 34,8452 km2 (LN5_01)

n 273,884 km2 (LN5_08). Da vo ch s hnh dng, ta nhn thy hnh dng

ch yu ca cc tiu lu vc cp 5 trong lu vc sng La Ng c dng trn (11

tiu lu vc), cc tiu lu vc cp 5 dng ko di ch c 8 tiu lu vc. Ngoi ra,

ta cn nhn thy cc tiu lu vc cp 5 c din tch ln tp trung ch yu phn

thng lu sng La Ng.

Lu vc sng ng Nai:

Mc dao ng v din tch ca cc tiu lu vc cp 5 ti lu vc sng

ng Nai trong khong t 26,68 km2

(DN5_26) n 385,794 km2

(DN5_37).Da vo ch s hnh dng, ta nhn thy hnh dng ch yu ca cc tiu lu vc

cp 5 trong lu vc sng ng Nai c dng trn (24 tiu lu vc), cc tiu lu

vc cp 5 dng ko di ch c 14 tiu lu vc.

Lu vc sng B:

Qua kt qu thng k, ta thy mc dao ng v din tch ca cc tiu

lu vc cp 5 trong lu vc sng B l kh ln, t 29,48 km2 (SB5_27) n

791,66 km2 (SB5_09). Cc tiu lu vc cp 5 c din tch ln tp trung ch yu



35/56


vng thng lu sng B, cn cc tiu lu vc cp 5 c din tch nh tp trung

ch yu ti phn trung lu sng B.

Cc tiu lu vc cp 5 ti lu vc sng B c hnh dng ch yu l dng

ko di theo hng ng Bc Ty Nam.(Kt qu tnh ton chi tit cc ch s c im hnh thi ca tng lu vc cp 5

c th hin trongph lc 11)

3.2.2 c im mng dng chy ca cc tiu lu vc cp 5

Kt hp d liu cc tiu lu vc cp 5 thnh lp v d liu bn

mng dng chy ti KVNC, ta xy dng c bn mng dng chy ca cc

TLV cp 5 ti KVNC nh hnh 3.7 sau y.

Hnh 3.7 c im mng dng chy cc tiu lu vc cp 5 trong khu vc nghin cu

Lu vc sng La Ng:

Mt dng chy ca cc tiu lu vc cp 5 thuc lu vc sng La Ng

dao ng trong khong t 0,39107 km/km2 (LN5_05) n 0,63596 km/km2

(LN5_04). Hng dng chy ch yu ca cc tiu lu vc cp 5 trong lu vc

sng La Ng l hng ng Bc - Ty Nam, cn dng dng chy ch yu ca

cc tiu lu vc ny l dng nhnh cy (xem hnh 3.7).

Lu vc sng ng Nai:



36/56


Mt dng chy ca cc tiu lu vc cp 5 thuc lu vc sng ng

Nai dao ng trong khong t 0,3944 km/km2 (DN5_37) n 0,63268 km/km2

(DN5_11). Hng dng chy ch yu ca cc tiu lu vc cp 6 trong lu vc

sng ng Nai l hng ng Bc Ty Nam, cn dng dng chy ch yu cacc tiu lu vc ny l dng nhnh cy (xem hnh 3.7).

Lu vc sng B:

Da vo kt qu thng k, ta thy c ton b cc tiu lu vc cp 5

trong lu vc sng B u c mng dng chy dng nhnh cy. Mt dng

chy ca cc tiu lu vc cp 5 dao ng t 0,417 km/km2 (SB5_24) n 0,629

km/km2 (SB5_27). Kt qu thng k cn cho thy cc tiu lu vc cp 5 vng

thng lu sng B c hng dng chy l ng Bc Ty Nam, mt s tiu

lu vc cp 5 vng trung lu v h lu sng B li c hng dng chy Bc

Nam theo hnh vng cung rt c bit. Ngoi ra cn c mt s tiu lu vc cp 5

c hng dng chy l Ty Bc ng Nam v Ty ng nhng s lng rt

t (xem hnh 3.7).

(Kt qu tnh ton chi tit cc ch s c im mng dng chy ca tng lu vc

cp 5 c th hin trongph lc 12)

3.2.3 c im a hnh ca cc tiu lu vc cp 5

Lu vc sng La Ng:

Trong lu vc sng La Ng, ta thy gi tr cao trung bnh ca cc tiu

lu vc cp 5 dao ng t 108,4 m (LN5_19) n 1019,188 m (LN5_10), gi tr

dc trung bnh dao ng t 1,275 (LN5_03) n 17,913 (LN5_05), gi

tr phn ct su trung bnh dao ng t 12,366 m/km2 (LN5_16) n 204,033

m/km2 (LN5_05). Kt qu thng k cho ta thy c s chnh lch r nt v cao

a hnh ca cc tiu lu vc cp 5 trong lu vc sng La Ng.

Lu vc sng ng Nai:

Trong vng thng lu v trung lu sng ng Nai, ta thy gi tr cao

trung bnh ca cc tiu lu vc cp 5 dao ng t 126,304 m (DN5_38) n

1604,937 m (DN5_14), gi tr dc trung bnh dao ng t 2,226 (DN5_38)n 16,29 (DN5_37), gi tr phn ct su trung bnh dao ng t 23,878



37/56


m/km2 (DN5_38) n 183,844 m/km2 (DN5_37). Mc chnh lch v cao

gia cc tiu lu vc ti ni y l rt ln.

Lu vc sng B:

Ti lu vc sng B, ta thy gi tr cao trung bnh ca cc tiu lu vccp 5 dao ng t 56,12 m (SB5_02) n 628,65 m (SB5_12), gi tr dc

trung bnh dao ng t 1,322 (SB5_02) n 10,665 (SB5_12), gi tr phn

ct su trung bnh dao ng t 12,441 m/km2 (SB5_02) n 108,045 m/km2

(SB5_12). Kt qu thng k cho ta thy c s chnh lch v cao a hnh ca

cc tiu lu vc cp 5 trong lu vc sng B, nhng s chnh lch ny khng

ln. iu chng t mc phn ct a hnh ti lu vc sng B nh hn lu

vc sng La Ng v ng Nai.

(Kt qu tnh ton chi tit cc ch s c im a hnh ca tng lu vc cp 5

c th hin trongph lc 13)



38/56


Chng 4

PHN LOI CC TIU LU VC CP 5TRONG KHU VC NGHIN CU

Trong chng ny, tc gi s trnh by 3 ni dung chnh sau:

- Kt qu phn loi cc tiu lu vc cp 5 trong khu vc nghin cu.

- Kt qu nh gi nguy c xy ra l qut da vo cc yu t a hnh ca

khu vc nghin cu.- Kt qu nghin cu mi lin h gia cc dng lu vc phn loi vi

nguy c xy ra l qut.

4.1 PHN LOI CC LU VC CP 5 TRN KVNC

4.1.1 Nguyn tc chn i tng lu vc cn phn loi

Trong kha lun ny, tc gi s thc hin phn loi dng lu vc trn i

tng l cc tiu lu vc cp 5 nm trong khu vc nghin cu. S d tc gi chn

cc tiu lu vc cp 5 v cc tiu lu vc ny th hin c nhng c trng c

bn ca a hnh v mi trng ca khu vc nghin cu v ph hp vi phn

gii ca d liu SRTM DEM s dng.

Cc tiu lu vc c cp nh hn 5 khng c chn phn loi l bi l

do sau:

- Cc tiu lu vc ny c din tch kh nh, li nm trn 1 phm vi hp nnnhng c im ca cc tiu lu vc ny kh cc b, khng th hin c

mt cch khi qut cc c trng a hnh v mi trng vng.

- Vic phn chia cc tiu lu vc cp 1, 2, 3, 4 s gy ra sai s ng k,

khng m bo kt qu phn loi.

- Ngoi ra, tc gi khng thc hin phn loi cc tiu lu vc c cp nh

hn 5 cn v hn ch ca thi gian thc hin kha lun. Cc tiu lu vc

c cp nh hn 5 c s lng rt ln, khong trn 2000 tiu lu vc.



39/56


c th tin hnh phn loi chng cn c mt khong thi gian thc hin

di.

Bn cnh , cc tiu lu vc c cp ln hn 5 cng khng c chn

phn loi l do:- Cc tiu lu vc cp 6, 7 c din tch ln, nm trn 1 phm vi rng, tri

di trn nhiu dng tiu a hnh ca vng, chu s chi phi ca rt nhiu

yu t mi trng, nn vic xc nh c trng ca cc tiu lu vc ny l

rt kh.

- S lng cc tiu lu vc c cp ln hn 5 nh (ton vng ch c 22 tiu

lu vc), nn kh xc nh c s lin quan gia cc c im phn loi

vi tng dng tiu lu vc.

4.1.2 Nguyn tc xc nh c im phn loi

ph hp vi mc tiu phn loi dng lu vc, trong kha lun ny, tc

gi s s dng 2 yu t chnh (kha chnh) ca vic phn loi l cao a hnh

trung bnh v dc a hnh trung bnh ca cc tiu lu vc cp 5.

Vi kha phn loi l a hnh trung bnh, tc gi s chia cc tiu lu vccp 5 trong khu vc nghin cu thnh 4 nhm sau (xem hnh 4.1):

- Nhm c cao trung bnh t 50 150 m.




Vi kha phn loi l dc trung bnh, tc gi s chia cc tiu lu vc

cp 5 trong khu vc nghin cu thnh 3 nhm sau (xem hnh 4.2):- Nhm c dc trung bnh t 1,2 4,5 .

- Nhm c dc trung bnh t 4,5 10 .

- Nhm c dc trung bnh t 10 18 .



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Hnh 4.1 Cc tiu lu vc cp 5 phn theo 4 nhm cao trung bnh

Hnh 4.2 Cc tiu lu vc cp 5 phn theo 3 nhm dc trung bnh

Trong qu trnh phn loi, c 2 yu t cao trung bnh v dc trung

bnh s cng c s dng quyt nh xem 1 tiu lu vc thuc dng no.

Tin hnh kt hp 2 yu t cao v dc a hnh, ta s c bng tiu chun

phn loi sau:



41/56


42/56


Hnh 4.3 Kt qu phn loi cc tiu lu vc cp 5

* Nhm I (31 tiu lu vc):

Cc tiu lu vc ny tp trung ch yu phn h lu ca sng La Ng, h

lu sng B v trung lu sng ng Nai. Nhm lu vc ny xut hin vng

ng bng bng phng, c dc v gi tr phn ct su nh. y l nhm lu

vc c s lng ln nht (31 tiu lu vc) trong khu vc nghin cu.

Ti phn h lu sng B cc tiu lu vc nhm I c hnh dng ko di lch yu. Tuy nhin, ti phn h lu sng La Ng v trung lu sng ng Nai th

cc tiu lu vc ny li c hnh dng chnh l hnh trn.

Hng dng chy chnh ca cc tiu lu vc nhm I kh phc tp. Ti

phn trung lu sng B, trung lu sng ng Nai v h lu sng La Ng, hng

dng chy chnh ca cc tiu lu vc nhm I l hng ng Bc Ty Nam. Ti

phn h lu sng B, hng dng chy chnh ca cc tiu lu vc ny li c

dng rt c bit, dng vng cung theo hng Bc Nam.



43/56


Hnh 4.4 Hnh dng mt s tiu lu vc nhm I

* Nhm II (6 tiu lu vc):

S lng tiu lu vc nhm II rt t, ch c 6 tiu lu vc tp trung ti

trung lu sng B v h lu sng La Ng. Hnh dng ch yu ca chng l dng

ko di, hng dng chy ch yu l 2 hng Bc Nam v ng Bc Ty

Nam. Nhm lu vc ny xut hin ch yu khu vc chuyn tip gia vng

ng bng v cao nguyn.

Hnh 4.5 Hnh dng mt s tiu lu vc nhm II

* Nhm III (12 tiu lu vc):

Cc tiu lu vc nhm III nm ri rc ti phn trung lu sng B, trung

lu sng ng Nai v trung lu sng La Ng. Hnh dng ch yu ca chng l

dng trn, hng dng chy ch yu l hng Bc Nam v Ty ng.

nhm lu vc ny, ta nhn thy bt u xut hin s phn ct a hnh ln.



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Hnh 4.6 Hnh dng mt s tiu lu vc nhm III

* Nhm IV (12 tiu lu vc):

Cc tiu lu vc nhm IV tp trung ch yu ti thng lu sng B v

khu vc tip gip gia lu vc sng B v lu vc sng ng Nai. C 12 tiu

lu vc nhm IV u c hnh dng ko di. im c bit ca cc tiu lu vc

nhm IV ny l ti phn tip gip gia thng lu sng B v lu vc sng

ng Nai c s i nhau v hng dng chy: cc tiu lu vc nhm IV nm

bn phn thng lu sng B c hng dng chy l ng Bc Ty Nam, cn

cc tiu lu vc nhm IV nm bn phn lu vc sng ng Nai li hng dng

chy l Ty Bc ng Nam. iu ny cho bit ti phn tip gip gia thng

lu sng B v lu vc sng ng Nai c th c t gy a cht. Mc phn

ct a hnh trong nhm lu vc ny kh ln.

Hnh 4.7 Hnh dng mt s tiu lu vc nhm IV

* Nhm V (10 tiu lu vc):



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Cc tiu lu vc nhm V tp trung ti 3 khu vc chnh: phn thng lu

sng B, trung lu sng ng Nai v sng La Ng. c im ni bt ca cc tiu

lu vc dng ny l chng nm ch yu ti vng chuyn tip gia ng bng v

i ni nn tt c cc tiu lu vc nhm V c gi tr phn ct su ln. Hnh dngca cc tiu lu vc ny c c dng di v dng trn.

Hng dng chy chnh ca cc tiu lu vc nhm V ch yu l ng

Bc Ty Nam. Tuy nhin ti lu vc sng La Ng, cc tiu lu vc ny li c

hng dng chy chnh l hng Bc Nam.

Cc tiu lu vc nhm V c xem l mt trong nhng dng tiu lu vc

c nguy c ri ro v mi trng cao do c gi tr phn ct su kh ln.

Hnh 4.8 Hnh dng mt s tiu lu vc nhm V

* Nhm VI (13 tiu lu vc):

Cc tiu lu vc nhm VI ch c trung lu sng ng Nai v thng

lu sng La Ng. Nhn chung, cc lu vc ny u nm trn khu vc c cao

a hnh ln. Cc tiu lu vc ny c 2 hng dng chy chnh, l hng Ty

Bc ng Nam v ng Bc Ty Nam. Hnh dng lu vc ca chng ch

yu l dng ko di.

Cc tiu lu vc nhm VI cng c xem l mt trong nhng dng tiu

lu vc c nguy c ri ro v mi trng cao.



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Hnh 4.9 Hnh dng mt s tiu lu vc nhm VI

* Nhm VII (11 tiu lu vc):

Cc tiu lu vc nhm VII phn b ch yu phn thng ngun sngng Nai. Cc tiu lu vc nhm ny ch xut hin ti khu vc c i ni cao,

him tr, phn ct a hnh rt mnh. y l dng lu vc c cao trung bnh

v dc trung bnh ln nht. Cc tiu lu vc ny c hnh dng ch yu l dng

ko di theo hng ng Bc Ty Nam, hng dng chy chnh cng l hng

ng Bc Ty Nam.

y chnh l dng lu vc c nh gi l c nguy c ri ro v mi

trng cao nht trong 7 dng lu vc c phn loi.

Hnh 4.10 Hnh dng mt s tiu lu vc nhm VII



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4.2 XC NH MI LIN QUAN GIA DNG LU VC VI TAI

BIN L QUT

4.2.1 Xy dng bn nguy c xy ra l qut ti khu vc nghin cu

L qut l mt hin tng thin tai c tnh cht v c im khc bit vil sng l l din bin nhanh, mang tnh bt thn v khc lit, mi trn xy ra

trn mt din hp v phm vi tc ng cng hp hn l sng [1]. L qut thng

xy ra vng ni, ni c a hnh i ni cao xen k vi thung lng v sng sui

thp [1].

L qut c hnh thnh do nh hng ca nhiu nhn t: cao ln,

dc ln, phn ct a hnh mnh, ma ln, mt m lu vc (mt li sng,

t, lp ph.v.v) v hot ng ca con ngi trn lu vc [1]. Trong cc nhn

t gy l qut c cc yu t thay i nhanh, c yu t thay i chm v c yu t

hu nh khng thay i. Cc yu t ny lin quan vi nhau v s kt hp mt

mc nht nh s gy ra l qut [1].

Trong phm vi kha lun ny, do hn ch v d liu nghin cu, tc gi s

ch tin hnh nh gi nguy c tai bin l qut da trn cc yu t a hnh. Cc

yu t a hnh c chn nh gi v xy dng bn nguy c l qut l 3yu t sau: cao a hnh, dc a hnh v phn ct su.

Bn nguy c l qut s c thc hin bng phng php chm im

cc yu t lin quan da trn k thut ti phn loi d liu (reclass) [5].

* Bc 1: Chm im yu t cao a hnh

S hnh thnh l qut c lin quan mt thit n cao a hnh ca khu

vc. Nhng khu vc c cao ln th tim nng xy ra l qut cng cao [1]. Mc

im nguy c l qut xt trn yu t cao a hnh c xc nh nh trong

bng sau:

Bng 4.3: Mc im ng vi yu t cao a hnh

STT Gi tr cao im1 < 50 m 12 50 - 100 m 23 100 - 200 m 34 200 - 300 m 4

5 300 - 400 m 56 400 - 800 m 6



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7 800 - 1000 m 78 1000 - 1500 m 89 1500 - 2000 m 9

10 >= 2000 m 10Kt qu chm im yu t cao a hnh c th hin qua hnh 4.11 sau

y:

Hnh 4.11 Kt qu phn loi cao theo mc im ca KVNC

* Bc 2: Chm im yu t dc a hnh

S hnh thnh l qut cn c quyt nh bi yu t dc a hnh ca

khu vc nghin cu. Mc im nguy c l qut xt trn yu t dc a hnh

c xc nh nh trong bng sau:

Bng 4.4: Mc im ng vi yu t dc a hnh

STT Gi tr dc () im1 < 5 12 5 10 2

3 10 15 34 15 20 45 20 25 56 25 30 67 30 35 78 35 40 89 40 45 9

10 >= 45 10Kt qu chm im yu t dc a hnh c th hin qua hnh 4.12

sau y:



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Hnh 4.12 Kt qu phn loi dc theo mc im ca KVNC

* Bc 3: Chm im yu t phn ct su a hnh

Nguy c xy ra l qut cn c xc nh bi mt yu t quan trng na

l c im phn ct su ca khu vc nghin cu. Mc im nguy c l qut xt

trn yu t phn ct su a hnh c xc nh nh trong bng sau:

Bng 4.5: Mc im ng vi yu t phn ct su

STTGi tr phn ct

su (m/km2)im

1 < 10 12 10 20 23 20 40 34 40 60 45 60 80 56 80 100 67 100 200 7

8 200 300 89 300 400 910 >= 400 10

Kt qu chm im yu t phn ct su a hnh c th hin qua hnh4.13 sau y:



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Hnh 4.13 Kt qu phn loi gi tr phn ct su theo mc im ca KVNC

* Bc 4: To bn nguy c l qut ca khu vc nghin cu

Sau khi c c d liu raster ti phn loi t cc yu t cao, dc

v phn ct su, ta s dng k thut cng raster cng cc lp d liu thc hin

li vi nhau, ta s c c bn nguy c l qut xt trn cc yu t a hnh ca

khu vc nghin cu. Gi tr nguy c xy ra l qut c gii hn t 0 30, gi tr

cng ln biu hin nguy c xy ra l qut cng cao (xem hnh 4.14).

Da vo bn nguy c l qut thnh lp c, ta thy cc khu vc c

nguy c xy ra l qut cao ch yu tp trung ti: vng thng lu ca lu vc

sng B, vng thng lu ca lu vc sng ng Nai, vng thng lu ca lu

vc sng La Ng v nhng khu vc c a hnh tip gip gia i ni v ng

bng tp trung ti trung tm ca khu vc nghin cu.

Tin hnh so snh bn nguy c l qut va xy dng vi bn Cckhu vc xy ra l qut Vit Nam giai on 1953 2005 do Vin Khoa Hc

Kh Tng Thy Vn V Mi Trng thnh lp [15], ta thy nhng khu vc c

nguy c l qut cao trng vi nhng khu vc thng xuyn xy ra l qut trong

giai on 1953 2005 (so snh hnh 4.14 vi hnh 4.15). iu chng t bn

nguy c l qut va xy dng c c tnh ph hp vi thc t.



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Hnh 4.14 Bn nguy c l qut ca khu vc nghin cu (xy dng t yu t a hnh)

(Bn t trang web ca Vin Khoa Hc Thy Vn v Mi Trngwww.imh.ac.vn)

Hnh 4.15 Cc khu vc xy ra l qut Vit Nam giai on 1953 2005

http://www.imh.ac.vn/http://www.imh.ac.vn/http://www.imh.ac.vn/


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4.2.2 Xc nh mi lin h gia cc nhm lu vc vi nguy c xy ra l qut

xc nh mi lin h gia cc dng lu vc c phn loi vi nguy c

xy ra tai bin l qut, chng ta s tnh gi tr trung bnh biu hin nguy c l

qut ca tng nhm lu vc c phn loi da trn lp d liu nguy c l qut xy dng trn. Kt qu tnh ton gi tr nguy c l qut trung bnh cho cc

nhm lu vc c th hin trong bng sau:

Bng 4.6: im nguy c l qut theo dng lu vc

DNG LU VC Nhm INhm

IINhm

IIINhm

IVNhm

VNhm

VINhm

VIIIM NGUYC L QUT 6,18 8,01 9,46 12,36 15,05 13,98 17,19

(Kt qu tnh ton nguy c l qut c th trn tng tiu lu vc cp 5 c th

hin trongph lc 14)

Da vo kt qu thc hin c, ta thy c 3 nhm lu vc c nguy c

xy ra l qut cao, l cc nhm lu vc V, VI, VII. Trong s 3 nhm trn,

nhm VII l nhm c nguy c xy ra l qut ln nht (17,19), tip theo l nhm

V (15,05).

Xt theo v tr, ta thy cc dng lu vc c nguy c xy ra l qut ln u

thuc phn thng lu sng (sng B, sng La Ng, sng ng Nai) hoc ti nitip gip gia ng bng v vng i ni nhng vng c phn bc a hnh r

nt, dc v phn ct su ln. iu ny ph hp vi iu kin hnh thnh l

qut.

Mt c im ng ch na l cc dng lu vc c nguy c xy ra l

qut ln thng c hnh dng ko di v din tch tng i nh.



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Chng 5

KT LUN V KIN NGH

* Kt lun:

Qua qu trnh thc hin kha lun, tc gi rt ra c nhng kt lun sau

y:

- Kha lun cho thy vic nghin cu, phn tch v phn loi cc tiu lu

vc trong lu vc sng ng Nai l ht sc cn thit to c s cho vic

s dng hp l cc tiu lu vc, gim thiu tc ng ca cc tai bin mi

trng din ra trong khu vc ny.

- Vic ng dng cc cng c GIS trong nghin cu lu vc mang li nhng

hiu qu r rt. N gip chng ta nhanh chng tip cn c nhng thng

tin khi qut v cc lu vc hn l phng php iu tra thc t truyn

thng. Ngoi ra, vi vic kt hp cc cng c h tr khc ca GIS, qutrnh x l thng tin khi thc hin nghin cu lu vc tr nn d dng

hn.

Tc gi bc u t c mc tiu ra ban u khi thc hin kha

lun. C th, kha lun t c nhng kt qu chnh sau:

- Xc nh v thng k c cc c im hnh thi, mng dng chy v a

hnh ca 95 tiu lu vc cp 5 (LV sng La Ng: 19, LV sng ng Nai:

38, LV sng B: 38) trong khu vc nghin cu.- Phn loi 95 tiu lu vc cp 5 trong khu vc nghin cu thnh 7 nhm

chnh da vo nhng c im cao v dc a hnh ca chng. Mi

nhm c s lin quan mt thit n tng kiu a hnh khc nhau ca

vng.

- Bc u xc nh c mi lin h gia cc dng lu vc phn loi

c vi nguy c xy ra l qut. C th nu chia theo nguy c xy ra l

qut, ta thy 2 nhm lu vc I, II c nguy c xy ra l qut t nht, cc lu



54/56


vc nhm III, IV c nguy c xy ra l qut trung bnh, cn cc lu vc

nhm V, VI, VII c nguy c xy ra l qut cao nht.

D kha lun bc u thc hin c mc tiu ra, nhng tc gi

nhn thy cn mt s im cn pht trin thm nh sau:- phn gii ca d liu SRTM DEM thp nn vic xc nh cc dng

chy v lu vc c cp nh hn 5 gy ra nhng sai s ln. tng ph

hp ca kt qu cn s dng ngun d liu c phn gii cao hn.

- Cn tng s lng cc yu t phn loi lm vic phn loi linh hot

hn. Cn xt tnh u tin ca cc yu t phn loi c c kt qu phn

loi ph hp vi mc ch ra.

- Vic tnh ton nguy c xy ra l qut khng tnh n cc yu t c tnh

thay i thng xuyn chng hn nh c im lp ph thc vt, c

im kh tng.

* Kin ngh:

Sau khi thc hin ti, tc gi xin c xut mt s kin sau:

- Cn thc hin mt cng trnh nghin cu khoa hc quy m ln nhm phnloi lu vc ti h thng sng Si Gn ng Nai da trn nhiu nhm

yu t c th hn. T , ra phng n khai thc v qun l cc dng

lu vc theo hng hp l nht va nng cao hiu qu s dng, va

bo v c ngun ti nguyn nc qu bu.

- Ti nhng ni c nguy c xy ra l qut cao, cn c nhng bin php c

th phng chng. V d nh trng rng u ngun, di di dn nhng

vng c nguy c ln.

- Cn thit lp mt h thng cnh bo l qut sm c k hoch s tn kp

thi dn c, gim thit hi v vt cht v nhn mng.



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TI LIU THAM KHO

* Ti liu tham kho ting Vit

[1] Cao ng D (1995),Nghin cu nguyn nhn hnh thnh v cc bin php

phng chng l qut, ti khoa hc cp nh nc, Vin Khoa Hc Kh Tng

Thy Vn V Mi Trng, H Ni.

[2] H Quang Hi, Trn Tun T (2007),Bn hc v h thng tin a l, NXB

i Hc Quc Gia Tp.H Ch Minh.[3] Lm Minh Trit v nnk(2000),Nghin cu xy dng c s khoa hc phc v

qun l thng nht v tng hp ngun nc lu vc sng ng Nai , ti khoa

hc cp nh nc, Vin Mi Trng V Ti Nguyn, i Hc Quc Gia Tp.H

Ch Minh.

[4]L Vn Trung (2005), Vin Thm,NXB i Hc Quc Gia Tp.H Ch Minh.

[5] Trn Tun T (2005), Vin Thm v GIS: kh nng ng dng thnh lp bn

nguy c tai bin trn lu vc sng B, Bo co khoa hc, Trng i Hc

Khoa Hc T Nhin Tp.H Ch Minh.

* Ti liu tham kho ting Anh

[6] ESRI (2008),ArcGIS Desktop Tutorial, ArcGIS 9.3.

[7] David Tarboton (2004), Terrain Analysis Using Digital Elevation Models in

Hydrology, Utah State University.[8] Clark Labs (2006), IDRISI Manual and IDRISI Tutorial, IDRISI Andes,

Clark University.

[9] Rivix LLC (2002),RiverTools Tutorial, RiverTools 2.4.

* Ti liu tham kho t Internet

[10] Trang web cung cp d liu SRTM DEM ca t chc CGIAR:http://srtm.csi.cgiar.org/

http://srtm.csi.cgiar.org/http://srtm.csi.cgiar.org/


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[11] Bi ging hng dn phng php tnh dc, hng sn t d liu DEM

ca i Hc Bang Oregon (Oregon State University):

http://dusk.geo.orst.edu/buffgis/PPT/geo580_spat_analy2.ppt

[12] Trang web ca Tng Cc Thng K: http://www.gso.gov.vn/default.aspx?tabid=427&idmid=3

[13] Trang web Wikipedia Ting Anh:

http://en.wikipedia.org/wiki/SRTM

[14] Trang web Wikipedia Ting Vit:

http://vi.wikipedia.org/wiki/L%C6%B0u_v%E1%BB%B1c

[15] Trang web ca Vin Khoa Hc Kh Tng Thy Vn V Mi Trng:

http://www.imh.ac.vn/b_tintuc_sukien/bb_tt_khkt/mlnews.2007-01-

12.5150159543

[16] Trang web v qun l Lu vc sng ng Nai ca Tng Cc Mi Trng:

http://www.nea.gov.vn/Sukien_Noibat/Luuvuc_Song/index_SG-DN.htm
http://dusk.geo.orst.edu/buffgis/PPT/geo580_spat_analy2.ppthttp://www.gso.gov.vn/default.aspx?tabid=427&idmid=3http://www.gso.gov.vn/default.aspx?tabid=427&idmid=3http://en.wikipedia.org/wiki/SRTMhttp://vi.wikipedia.org/wiki/L%C6%B0u_v%E1%BB%B1chttp://www.imh.ac.vn/b_tintuc_sukien/bb_tt_khkt/mlnews.2007-01-12.5150159543http://www.imh.ac.vn/b_tintuc_sukien/bb_tt_khkt/mlnews.2007-01-12.5150159543http://www.nea.gov.vn/Sukien_Noibat/Luuvuc_Song/index_SG-DN.htmhttp://dusk.geo.orst.edu/buffgis/PPT/geo580_spat_analy2.ppthttp://www.gso.gov.vn/default.aspx?tabid=427&idmid=3http://www.gso.gov.vn/default.aspx?tabid=427&idmid=3http://en.wikipedia.org/wiki/SRTMhttp://vi.wikipedia.org/wiki/L%C6%B0u_v%E1%BB%B1chttp://www.imh.ac.vn/b_tintuc_sukien/bb_tt_khkt/mlnews.2007-01-12.5150159543http://www.imh.ac.vn/b_tintuc_sukien/bb_tt_khkt/mlnews.2007-01-12.5150159543http://www.nea.gov.vn/Sukien_Noibat/Luuvuc_Song/index_SG-DN.htm

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