bui minh hoa

i

MC LC

MC LC ................................................................................................................... i

DANH SCH CC BNG ..................................................................................... iii

DANH SCH CC HNH....................................................................................... iv

LI CM N ........................................................................................................... vi

M U .................................................................................................................. vii

CHNG 1. IU KIN A L T NHIN V X HI KHU VC

NGHIN CU LIN QUAN N NGP LT .................................................. 10

1.1. IU KIN T NHIN LU VC NGHIN CU ................................... 10

1.1.1. iu kin t nhin [6] .............................................................................. 10

1.1.2. c im mng li sng ngi [6] .......................................................... 15

1.1.3. c im kh tng kh hu [6] ........................................................... 19

1.1.4. c im thy vn [6] ............................................................................. 27

1.2. IU KIN KINH T X HI [6] .............................................................. 29

1.2.1. c im dn sinh kinh t ....................................................................... 29

1.2.2. c im kinh t ...................................................................................... 29

1.3. TNH HNH NGP LT H LU SNG BA [6] ...................................... 30

1.3.1. Tnh hnh ngp lt .................................................................................... 30

1.3.2. Thit hi do ngp lt ................................................................................ 30

1.3.3. Hin trng cng trnh phng chng l v tiu ng.................................. 32

1.3.4. Mc tiu phng chng l trn lu vc ..................................................... 33

1.3.5. Phng n quy hoch phng chng l .................................................... 34

CHNG 2. C S L THUYT XY DNG BN NGP LT .......... 36

2.1. TNG QUAN CHUNG ................................................................................. 36

2.1.1. Khi nim v bn ngp lt [1, 3] ........................................................ 36

2.1.2. Cc phng php xy dng bn ngp lt .......................................... 36

2.2. TNG QUAN V CC M HNH THY VN, THY LC TNH TON

NGP LT [3] ...................................................................................................... 37

2.2.1. Cc m hnh ma dng chy: .................................................................. 37

ii

2.2.2. M hnh thy lc: ..................................................................................... 38

2.2.3. La chn m hnh din ton .................................................................... 45

2.2.4. C s l thuyt ca m hnh .................................................................... 46

2.2.5. Cc bc trin khai m hnh ................................................................... 61

2.3. GII THIU QUY TRNH XY DNG BN NGP LT ................ 62

2.3.1. Khi nim h thng thng tin a l ........................................................ 62

2.3.2. Cc phng php GIS xy dng bn ngp lt [1, 2, 3, 5] ................. 64

CHNG 3. XY DNG BN NGP LT KHU VC NGHIN CU 66

3.1. XY DNG C S D LIU ..................................................................... 66

3.1.1. Ti liu a hnh ....................................................................................... 66

3.1.2. Ti liu thy vn ...................................................................................... 69

3.1.3. Ti liu iu tra vt l .............................................................................. 70

3.2. NG DNG M HNH THY LC TNH TON NGP LT KHU VC

NGHIN CU ...................................................................................................... 71

3.2.1. M hnh ma ro dng chy NAM [2] .................................................... 71

3.2.2. M hnh EFDC [7, 8, 9, 10] .................................................................... 74

3.2.3. Kt qu m phng qu trnh ngp lt bng m hnh EFDC ................... 79

3.3. TNH TON NGP LT THEO TN SUT 1%, 2%, 5% V 10% ......... 87

3.4. XY DNG BN NGP LT .............................................................. 89

3.4.1. Quy trnh chuyn kt qu ca m hnh EFDC sang GIS v xy dng bn

ngp lt ......................................................................................................... 89

3.4.2. Kt qu xy dng bn ngp lt ........................................................... 93

KT LUN V KIN NGH .............................................................................. 101

TI LIU THAM KHO .................................................................................... 103

iii

DANH SCH CC BNG

Bng 1: Cc c trng chnh ca sng Ba v mt s sng trong lu vc ............... 16

Bng 2: Tc gi trung bnh thng v nm (n v: m/s) .................................... 20

Bng 3: Nhit trung bnh thng v nm (n v: 0C) ......................................... 22

Bng 4: Mt s c trng ma nm (n v: mm) .................................................. 24

Bng 5: Lng ma trung bnh nhiu nm cc thng (n v: mm) ....................... 25

Bng 6: m tuyt i trung bnh thng v nm (mb) .......................................... 26

Bng 7: m tng i trung bnh thng v nm (n v: %) ............................ 27

Bng 8: Lu lng l ln nht ti mt s trm trn lu vc sng Ba ..................... 28

Bng 9: Thit hi mt s nm do ngp l vng h lu sng Ba .............................. 31

Bng 10: c trng mt ct ngang sng trong s tnh ton thy lc ................. 66

Bng 11: Thng s chnh p ng ng Cam [6] ................................................. 68

Bng 12: Bng nh gi kt qu hiu chnh m hnh NAM ..................................... 73

Bng 13: B thng s m hnh NAM ........................................................................ 74

Bng 14: V tr cc mt ct thc o [6].................................................................... 77

Bng 15: Ch tiu nh gi sai s thc o v tnh ton ti trm Ph Lm .............. 80

Bng 16: Kt qu m phng mc nc l ti cc v tr iu tra vt l .................... 80



Bng 19: Thng k din tch ngp theo x - phng h lu sng Ba trn l thng 11/2009

................................................................................................................................... 85

Bng 20: Tn sut l thit k ti trm Cng Sn - Sng Ba .................................... 88

Bng 21: Din tch lu vc ti Cng Sn v cc v tr nhp lu ............................. 89

iv

DANH SCH CC HNH

Hnh 1. Bn khu vc tnh Ph Yn (T l 1:600 000) .......................................... 11

Hnh 2. Bn mng li sng lu vc sng Ba ..................................................... 18

Hnh 3. S vng h lu sng Ba t Cng Sn n ca Rng ............................ 19

Hnh 4. Bn phn b lng ma ma ma (t l 1: 100 000) ............................. 25

Hnh 5. Bn phn b lng ma ma kh (t l 1: 100 000) .............................. 25

Hnh 6. Cu trc m hnh NAM [2] ......................................................................... 47

Hnh 7. Cu trc c bn m hnh EFDC [7, 10] ..................................................... 48

Hnh 8. Cu trc m hnh thy ng lc hc EFDC [7, 10].................................... 49

Hnh 9. Min li dng Uniform Grid ..................................................................... 50

Hnh 10. Min m hnh to dng Expanding Grid ................................................... 51

Hnh 11. Min m hnh to dng Centerline Dominant ........................................... 52

Hnh 12. Li cong c to theo ty chn Equi-Distance Widths ........................ 52

Hnh 13. Bng tnh thi gian s dng m hnh [7] .................................................. 53

Hnh 14. S xy dng bn ngp lt bng phng php GIS ......................... 64

Hnh 15. S ha v tr mt ct t trm Cng Sn ti ca Rng ......................... 67

Hnh 16. Mt ct ngang ph bin sng Ba ............................................................... 68

Hnh 17. Bn cao s cao DEM 30m x 30m khu vc nghin cu ............... 69

Hnh 18. S ho v tr iu tra tra vt l thng 10/1993 .......................................... 70

Hnh 19. Biu lu lng ti Cng Sn thc o v tnh ton thng 10/1993 ...... 71



Hnh 22. S ho phm vi m phng h lu sng Ba ............................................... 75

Hnh 23. Phn mm Delft 3D ................................................................................... 75

Hnh 24. Giao din lm vic chnh ca Delft 3D ..................................................... 76

Hnh 25. Ct cao a hnh khu vc tnh ton ........................................................... 77

Hnh 26. Li tnh ton v bin u vo cho m hnh ............................................. 78

Hnh 27. Biu ng qu trnh mc nc thc o v tnh ton trn l 10/1993 79

Hnh 28. Mc nc ti thi im ngp ln nht ...................................................... 81

Hnh 29. Trng vn tc ti thi im ngp ln nht trn l thng 10/1993 ......... 81

v


Hnh 31. Trng vn tc ti thi im ngp ln nht trn l thng 11/2003 ......... 83


Hnh 33. Trng vn tc ti thi im ngp ln nht trn l 11/2009 ................... 85

Hnh 34. nh v tinh hin trng ngp lt khu vc sng Ba thng 11/2009 ............. 87

Hnh 35. Lu lng ln nht ti trm Cng Sn qua cc nm ................................ 88

Hnh 36. ng tn sut l trm Cng Sn ............................................................. 89

Hnh 37. Trch xut kt qu su ngp ln nht t m hnh EFDC ..................... 90

Hnh 38. Ni-ngoi suy su ngp lt ln nht bng cng c Vertical mapper .. 91

Hnh 39. Nn DEM c to ra t php ni-ngoi suy su ngp lt ln nht ... 91

Hnh 40. Xy ng ng contour phn cp ngp lt t cng c ca vertical

mappper ..................................................................................................................... 92

Hnh 41. Bn ngp lt h lu sng Ba ng vi thi im ngp lt ln nht thng

10/2003 ...................................................................................................................... 94

Hnh 42. Bn ngp lt h lu sng Ba ng vi thi im ngp lt ln nht thng

11/2009 ...................................................................................................................... 95

Hnh 43. Bn ngp lt h lu sng Ba_ng vi tn sut 1% ............................. 96



Hnh 46. Bn ngp lt h lu sng Ba_ng vi tn sut 10% ........................... 99

vi

LI CM N

Lun vn thc s khoa hc: Nghin cu xy dng bn ngp lt h lu

lu vc sng Ba c hon thnh vo thng 12 nm 2012 di s hng dn ca

TS. Hunh Th Lan Hng. Tc gi xin by t s cm n chn thnh ti TS. Hunh

Th Lan Hng tn tnh hng dn trong sut qu trnh nghin cu v hon

thnh lun vn ny, qua y tc gi cng by t s cm n chn thnh ti PGS. TS

Nguyn Hu Khi c nhng nh hng bc u khi tc gi bt u thc hin

lun vn ny.

Tc gi cng xin gi li cm n ti cc thy, c gio trong khoa Kh tng

Thy vn Hi dng hc gip , to iu kin tt nht cho tc gi trong qu

trnh hc tp v nghin cu lun vn.

Trong khun kh ca lun vn, do thi gian v iu kin hn ch nn khng

trnh khi nhng thiu st. V vy, tc gi rt mong nhn c nhng kin ng

gp qu bu ca c gi v cc ng nghip.

H Ni, Ngy thng 12 nm 2012

Tc gi

vii

M U

i. t vn

T xa ti nay l lt lun l mi e da hng u v gy ra nhiu thit hi

v ngi v ca. Cng vi s tng trng ca cc ngnh kinh t v s pht trin ca

x hi, i hi cng tc qun l, phng chng thin tai c bit l l lt nhm m

bo mc an ton ngy cng cao v hn ch n mc thp nht v thit hi.

Trong qu trnh pht trin kinh t - x hi, vic khai thc tng hp ti nguyn

nc cho cc mc ch khc nhau trn cc h thng sng thuc min Trung ni

chung v lu vc sng Ba ni ring em li nhng gi tr to ln v ca ci x hi

ng vai tr quan trng cho cc ngnh kinh t trong tnh nh: du lch, cng nghip,

thy li, nng lng, thy sn, nng nghip...

Sng Ba l mt trong nhng con sng ln min trung Trung B Vit Nam

vi tng din tch lu vc 14.132 km2 nm trn a phn 3 tnh Gia Lai, akLak v

Ph Yn. Hng nm, v ma l, nc sng Ba dn t thng lu v gy ngp lt

nghim trng cho h lu sng Ba. L gy ngp lt, thit hi kh ln v ngi v

ti sn trn lu vc. Ma l gy cht ngi, nh ca b ngp, b sp, cc cng trnh

h tng c s nh trng hc, bnh vin b h hng, ng s cu cng cng trnh

thu li b st l, b v v bi lp. Din tch t trng trt b ngp lu ngy lm cho

la, hoa mu v cc loi cy trng khc b cht gy tht thu. Theo thng k mt s

nm gn y cho thy tnh hnh l lt trn lu vc ngy cng nghim trng vi mc

thit hi c xu th ngy cng tng:

L nm 1990 thit hi 21,6 t ng; L nm 1992 thit hi 51,5 t ng; L

nm 1993 thit hi 394 t ng; L nm 1995 thit hi 17 t ng; L nm 1999

thit hi 50 t ng. Nm 2009, lu lng nc v sng Ba do Trung Tm D bo

Kh tng Thy vn tnh Ph Yn ny o c gn 15.000 m3/s nhng lm c h

du ngp trng, thit hi nng cho vng h du lu vc sng Ba. [6]

Do tnh cht nghim trng ca l i vi vng h lu sng Ba, ng thi

hin nay quy hoch phng chng l ring cho lu vc cha c xy dng nn vic

cn thit hin nay l phi xy dng c s khoa hc v thc tin nhm a ra c

viii

phng n phng chng l bo v cho vng h lu sng Ba ng thi phc v pht

trin kinh t x hi trong vng.

Nhm mc tiu gim thiu cc thit hi do l lt gy ra, xut cc phng

n phng chng thng qua cc cnh bo v kh nng v din tch ngp lt ng vi

cc trn l khc nhau, nghin cu ny tin hnh: Nghin cu xy dng bn

ngp lt h lu lu vc sng Ba. Kt qu nghin cu s l c s quy hoch

phng chng l cho c khu vc cng nh lm ti liu tham kho cho cc nh hoch

nh chnh sch v ra quyt nh a phng.

ii. ngha ca bn ngp lt

Bn ngp lt l mt cng c trc quan cho php nm bt c kh nng

ngp lt khi d bo c din bin mc nc mt v tr c trng no trong khu

vc ngp. iu ny rt cn thit cho cc nh qun l khi quyt nh x l tnh hung

khn cp. Bn ngp lt nhm:

1. Cho bit trc din tch ngp, mc ngp ti bt k im no trong vng ngp khi

bit c cp mc nc l ti im cht.

2. nh gi nguy c thit hi hng nm v vic phn tch chi ph - li ch ca

nhng d n cng trnh phng chng ngp lt.

3. To c s la chn v phi hp cc bin php phng lt v ngp ng.

4. Tr gip thc hin phn vng qun l s dng t trong khu vc thng xuyn

ngp ng.

5. To c s nghin cu bin php phng ngp trong xy dng c bn.

6. Thit k v vn hnh cc cng trnh khng ch ngp ng. Vic thit k v vn

hnh cc cng trnh khng ch ngp nh h cha, trm bm phi da vo nhiu

ti liu nghin cu, tnh ton thu vn, thu lc trong bn ngp lt l ti

liu khng th thiu.

Quy trnh Vn hnh h cha c nh hng rt ln n ngp lt vng h

lu, iu ny cn c nh gi y hn.

ix

iii. Mc tiu, phng php:

1. Mc tiu :

Xy dng bn ngp lt do nh hng ca trn l thc nm 2009 v cc

bn ngp lt ng vi cc tn sut l c trng nhm tr gip cho vic hoch nh

cc hot ng kinh t - x hi trong trong khu vc h lu sng Ba .

2. Phng php

Hin nay trn th gii c 2 phng php c s dng xy dng bn

ngp lt, l:

a. Xy dng bn ngp lt da vo iu tra cc trn l ln thc t xy ra.

b. Xy dng bn ngp lt da vo vic m phng bng cc m hnh thy vn,

thy lc.

Lun vn ny s dng phng php th 2, tp trung vo ng dng cc m

hnh thy vn, thy lc kt hp vi c s d liu GIS xy dng bn ngp lt.

iv. B cc lun vn bao gm

M u

CHNG 1: iu kin t nhin v x hi khu vc nghin cu lin quan n ngp

lt

CHNG 2: C s l thuyt xy dng bn ngp lt

CHNG 3: Xy dng bn ngp lt khu vc nghin cu

Kt lun v kin ngh

Ti liu tham kho

10

CHNG 1. IU KIN A L T NHIN V X HI KHU VC

NGHIN CU LIN QUAN N NGP LT

1.1. IU KIN T NHIN LU VC NGHIN CU

1.1.1. iu kin t nhin [6]

a. V tr a l

Lu vc sng Ba nm min Trung Trung B Vit Nam c hnh dng ch L.

Phm vi lu vc : 12035 n 14038 v Bc v 108000 n 109055 kinh ng.

Pha Bc gip lu vc sng Tr Khc; Pha Nam gip lu vc sng Ci v

sng Srpk; Pha Ty gip lu vc sng Ssan v sng Srpk; Pha ng gip

lu vc sng Kne, sng K L v bin ng.

Din tch t nhin ton lu vc l 14.132 km2

nm trn a phn hnh chnh

ca 15 huyn, th thuc 3 tnh Gia Lai, ak Lk v Ph Yn bao gm hu ht din

tch t ai cc huyn Kbang, An Kh, KonchR, Mang Yang, A. Yunpa, K.Rng

Pa, K.Rng H Nng, Ma Rak, Sn Ho, sng Hinh, Tuy Ho v th x Tuy Ho v

mt phn din tch cc huyn Ch S, Ea H Leo, Krng Buk, Eaka. Tng din tch

nng nghip 352.811 ha.

Ph Yn l mt tnh thuc duyn hi Nam Trung B, pha Bc gip tnh Bnh

nh, pha Nam gip tnh Khnh Ha, pha Ty gip tnh Gia Lai v c Lc, pha

ng gip Bin ng. Din tch t nhin ton tnh l 5.045km2

gii hn bi ta

12039

10

n 1304520 v bc, 10803945

n 10902920

kinh ng.

C ng Quc l 1A v ng st Bc Nam chy qua, c sn bay ng Tc, cng

bin Vng R. c bit pha Ty gip ranh vi vng Ty Nguyn rng ln, c

ni lin bng quc l 25, tnh l 645 v hng chung ngun nc sng Ba. Pha

ng gip Bin ng vi nhiu loi hi sn phong ph, tr lng ln, c th nh

bt quanh nm. B bin Ph Yn di 198km chy t C Mng n Vng R, mt

bn l ni mt bn l bin vi nhiu bi tm p, cu trc kh c bit xen k rt

nhiu m, vnh, vng, mi in hnh nh m C Mng, m Loan, Vng R v

vnh Xun i u l v tr thun li pht trin du lch v nui trng hi sn (hnh 1).

11

Hnh 1. Bn khu vc tnh Ph Yn (T l 1:600 000)

b. c im a hnh

a hnh lu vc sng Ba bin i kh phc tp, b chia ct mnh m bi s

chi phi ca dy Trng Sn. ng phn thu ca lu vc c cao t (500-

2000)m bao bc 3 pha: Bc, ng, Nam v ch c m rng v pha Ty vi cao

nguyn rng ln Pleiku, Mang Yang, Ch S. ng thi m ra bin qua vng

ng bng Tuy Ho rng trn 20.000 ha. ng chia nc pha ng Bc lu vc

thuc gii Trng Sn c cao t 600-1.300m (c bit c nh Ch Trung Ari cao

1331m) di ni ny chy theo hng Ty Bc - ng Nam cho n o An Kh sau

12

chuyn hng v kt thc thng ngun sng C Li, sng Con cao (600-

700)m. Pha Nam l dy ni Phng Hong chy st ra bin theo hng ng Bc

n Ty Nam v kt thc ti o C c cao bin i (600-2000)m. in hnh c

nh Chhmu cao 2051m. Hai dy ni pha ng v pha Nam ca lu vc to

thnh bc tng chn gi, cn tr vic hot ng ca hng gi ng v ng

Nam. Pha Ty Bc c cc nh ni cao hn pha ng, nhng b chia ct nhiu,

khng lin tc. cao cc nh ni bin ng t (700-1.700)m v chy theo hng

Bc Nam. Cc nh nh Ngc R cao 1549m, Kon Ka Kinh cao 1761m, Ch R

Pan cao 1571m. n Cheo Reo, cao cc nh ni thp dn (300-400)m. Sau

li c nng ln t (700-1.200)m v chuyn hng Ty Bc - ng Nam cho n

thng ngun sng KRng H Nng: Ch Tun cao 1215m. Do cc dy ni pha Ty

b chia ct mnh v khng lin tc hnh thnh trn lu vc cc thung lng An

Kh, Cheo Reo, Ph Tc v vng ng bng h lu.

Di tc ng ca cc yu t a hnh phc tp c th chia lu vc thnh 5

vng a hnh sau:

-Vng ni cao: chim 60% din tch lu vc. cao bnh qun trong vng

ny (600-800)m, dc a hnh t thoi n rt dc.

-Vng thung lng: ko di t An Kh n Ph Tc. Cao ph bin thung

lng An Kh (400-500)m, thung lng Cheo Reo (150-200)m v Ph Tc (100-150)m.

a hnh bng phng, tp trung thnh nhng cnh ng ln dc theo hai b sng.

-Vng cao nguyn: c cao ph bin t (300-500)m.

-Vng g i: ch yu l vng An Kh, Sn Ho, h lu sng Hinh v lu

vc sng Krng H Nng.

-Vng ng bng: tp trung h lu sng Ba, cao (5-7)m.

Ph Yn pha ng gip Bin ng, ba mt cn li u gip ni, c dy C

Mng pha Bc, dy Vng Phu - o C pha Nam, pha Ty l ra ng ca

dy Trng Sn. gia sn ng ca dy Trng Sn cng c mt dy ni thp

hn m ngang ra bin to nn cao nguyn Vn Ha l ranh gii phn chia hai ng

bng tr ph, mu m do sng Ba, sng K L bi p. Ton tnh ngoi tr vi nh

ni cao trn 1.000m nh Hn D, Hn ng, Hn Cha pha Nam huyn Tuy Ha,

13

Ch Ninh, Ch an, Ch Hle nm pha ng Nam, Ty Nam huyn Sng Hinh,

Ni La Hin, Ch Treng, Hn Rung Gia, Hn Sui Hm gip ranh huyn Sn

Ha v ng Xun. Cn li ni, i Ph Yn ch cao ph bin mc 300 n

600m phn b ri rc cc ni. Chnh v th, Ph Yn l tnh c nhiu o dc v c

tt c cc loi a hnh nh ng bng, i, ni, cao nguyn, thung lng xen k

nhau, thp dn t ty sang ng. Tuy nhin, yu t a hnh chi phi n iu kin

kh hu thy vn ch yu l hai dy ni C Mng, o C, cao nguyn Vn Ha,

thung lng sng Ba, sng K L.[6]

c. c im a cht th nhng

a tng: tham gia vo cu trc lnh th tnh Ph Yn c mt kh a dng cc

thnh to trm tch, trm tch bin cht v phun tro c tui t Proterozoi n

Kanozoi, theo th t t gi n tr gm cc phn v a tng sau: gii Proterozoi,

Paleozoi, Merozoi, Kainozoi.

Mc ma xm nhp: trong phm vi tnh Ph Yn pht trin kh phong ph v a

dng c v khng gian ln thi gian, chim trn 50% din tch t nhin v c cc

phc h Bn Ging- Qu Sn, Vn Canh, Ty Ninh, nh Qun, o C, C N-

Pha 1, Phan Rang, C Mng.

c im cu trc kin to: h thng t gy theo phng ng Bc -Ty

Nam, in hnh l t gy Vnh Long - Trung Ha. H thng t gy theo phng

Ty Bc - ng Nam gm nhiu t gy quy m nh - va, in hnh l t gy

sng Ba, sng K L. H thng t gy theo phng kinh tuyn l t gy quy

m nh -va, pht trin ch yu pha Bc.

t ai Ph Yn c hnh thnh trn mu t ph sa v ba loi chnh l:

Granit, Ba Zan, trm tch gm 8 nhm ph bin.

t ct ven bin: chim 2,6% din tch t nhin, phn b dc theo b bin t

sng Cu n Ha Hip v dc sng Rng, K L. Thnh phn c gii ch yu

l ct, kh nng gi nc v dinh dng km.

t mn phn: chim 1,4% din tch t nhin, phn b tp trung Ha Tm,

Ha Hip, Ha Xun v dc ven bin t Sng Cu n ca sng Rng.

t ph sa: chim 9,8% din tch t nhin, tp chung ch yu huyn Ph

14

Ha, huyn Tuy Ha v th x Tuy Ha, ri rc Tuy An, ng Xun, sng Cu.

t xm: chim 6,9% din tch t nhin c phn b t a hnh trung gian

ni tip gip vng ni v vng thp c a hnh chia ct trung bnh, tng i bng

tp trung Sn Ha, ng Xun, Sng Hinh v pha ty huyn Ph Ha.

t en: chim 3,5% din tch, phn b pha nam huyn Tuy An, x Bnh

Kin, huyn Sng Hinh v mt phn huyn Sn Ha.

t vng: chim 65% din tch t nhin phn b u khp vng i ni.

t mn vng chim 2,2% din tch t nhin, phn b ch yu trn ni cao t 900

-1000m. t dc t chim 0,3% din tch t nhin, phn b ri rc a hnh thp.[6]

d. Lp ph thc vt

Theo thng k ca Chi cc Kim lm tnh Ph Yn nm 2002 c 363.948,2ha

t lm nghip chim 72% t t nhin, che ph rng l 32%. Trong rng t

nhin 144.664,6ha, rng trng 18.324,3ha, t i trc l 200.959ha, cn li l t

nng nghip canh tc theo thi v. Thc vt gm hai loi chnh, thc vt t nhin

v thc vt trng.

Thc vt t nhin c phn b trn cc kiu rng vi mt v s lng loi

khc nhau gm c:

Kiu rng nhit i ni thp c din tch ln nht tnh, phn b cao di

1000m, nm trong phm vi vng ni huyn Tuy Ha, Sng Hinh, Sn Ha, ng

Xun. c im kiu rng ny l rng xanh quanh nm, t thay l ti vng c a

hnh kh cao, rng tha rng l v na rng l phn b vng thp hn.

Kiu rng trung gai, cy bi: y l kiu rng tng i c bit, hnh thnh

do cc yu t tng hp ca kh hu, t ai, a hnh, h thc vt c tc ng mnh

ca nhn t con ngi. c im kiu rng ny l phn ln cy ci gm cc loi

cy chu hn, c gai, l nh, thng sng vng c t ai rt xu, kh cng, tng

mng, xi mn mt, thiu nc nn ma h c hin tng ho l khi tri nng hn.

Loi rng ny phn b nhiu ven bin huyn Sng Cu, Tuy An, th x Tuy Ha.

Kiu thc vt trn ct c din tch khong 10.000ha, ch yu l c, vng kn

gi c mt s cy g nh Cc, M U. c bit l Chai L Cong phn b cc

huyn th ven bin, nhiu nht huyn Sng Cu v Tuy Ha. Hin nay mt s ln

15

din tch a vo canh tc, trng rng, xy dng khu cng nghip hoc quy hoch

khu cng nghip.

Thc vt trng: ngoi thc vt t nhin, thc vt trng cng rt phong ph,

phn b ch yu vng c cao di 100m gm c cc nhm chnh l cy lng

thc, thc phm, cy cng nghip, dc liu theo thi v. Cy ly g trng theo

chng trnh, d n, cy cnh v cy phn tn h gia nh.

1.1.2. c im mng li sng ngi [6]

Lu vc sng Ba c dng ch L, phnh rng trung lu v thu hp hai u

thng v h lu. Mng li sng ngi kh dy v c phn b u khp trong

vng. Chiu rng bnh qun lu vc 48,6km, c ni rng 80 km.

Dng chnh sng Ba c bt ngun t nh Ngc R (tnh Kon Tum) cao

1.544m, sng chy qua cc tnh KonTum, Gia lai, akLk v Ph Yn. Din tch

lu vc sng Ba 14132 km2

vi chiu di 374 km, mt li sng 0,22 km/km2.

T thng ngun ti gn An Kh, sng chy theo hng Ty Bc - ng Nam qua

a hnh him tr, chia ct mnh, lng sng hp, lm thc ghnh, dc lng sng

20%. Sng Ba c nhiu nhnh sng , sui nh vo trong c 36 ph lu cp I,

54 ph lu cp II, 14 ph lu cp III.

T Cheo Reo n th trn Cng Sn, sng chy theo hng Ty Bc - ng

Nam li nhn thm nc ca ph lu sng Krong H,

Nng, din tch lu vc 1750

km2, chiu di sng 130km, vo bn phi sng Ba ti ranh gii Gia Lai - Ph

Yn. Sng Hinh din tch lu vc 932km2, di 85km, bt ngun t dy ni Ch Mu

cao 2051m, vo bn phi Sng Ba ti x c Bnh ng huyn Sng Hinh, y

l vng ma ln nht trong ton lu vc sng Ba. Nm 2000 thu in Sng Hinh

bt u tch nc pht in, lm cho ch thu vn y khc bit cn bn c

bit l trong ma l.

on sng cui cng chy theo hng gn nh Ty - ng, nhng t ng

B, sng hi chuyn hng lch v pha Bc v nc ra ca Rng. on

sng ny cn nhn thm nc sng Con, sng Ci bn tri, sng ng B bn phi,

lng sng kh rng, dc nh ch khong 1. Dc theo hai bn b sng l cc bi

bi rng ln to thnh cnh ng ph nhiu, tr ph. (hnh 2)

16

Ngoi dng chnh, lu vc sng Ba c 3 nhnh sng ng ch :

Sng Ayun: bt ngun t nh ni Krong H Dung cao 1.220m, chy

theo hng Bc Nam, sau chuyn hng Ty Bc - ng Nam ri nhp vi dng

chnh sng Ba ti v tr cch th trn Cheo Reo khong 1km v pha Bc. Sng c

din tch lu vc 2.950km2, di sng 175km.

Sng Krong H'Nng: bt ngun t nh ni Ch Tung cao 1.215m.

Hng dng chy tng i phc tp song ch yu l Bc - Nam v Ty Bc -

ng Nam ri nhp vi sng chnh ti ranh gii Gia Lai v Ph Yn. Sng c din

tch lu vc l 1.840km2, di l 130km.

Bng 1: Cc c trng chnh ca sng Ba v mt s sng trong lu vc

Sng chnh Sng

nhnh

cao

ngun

(m)

Din

tch

lu vc

F(km2)

Chiu

di

sng

L(km)

rng

bnh

qun

B(km)

H

s

hnh

dng

()

H

s

un

khc

(K)

dc

sng

(J

)

Mt

li

sng

(km/km2)

Sng Ba

1500 13043 360 33,9 0,1 2,0 2,7 0,5

S. Hinh 750 932 85 33,9 0,1 1,7 6,4 0,5

S. Con 750 124 20 11,7 0,3 1,2 24,0 0,5

S.ng

B

750 144 27 6,2 0,2 1,4 17,0 0,7

S. Con 450 238 30 5,3 0,3 1,5 15,0 0,6

S. Tha 300 148 25 7,9 0,2 1,5 8,9 0,2

S. C

Li

750 190 48 5,9 0,1 1,5 10,0 0,2

Bn Thch 1400 5900 68 4,0 0,1 1,8 14,0 0,5

K L 1000 1950 105 8,7 0,2 1,5 5,8 0,6

S. Tr

Bng

470 270 35 18,6 0,2 2,2 15,0 0,5

S. C 530 348 36 7,7 0,3 1,2 11,0 0,8

Sng Cu

600 146 137 9,9 0,2 1,2 16,0 0,3

Sng Hinh: bt ngun t nh ni Ch H'Mu cao 2.051m. Hng dng

chnh l Ty Bc - ng Nam n v 1205' sng chy theo hng Bc - Nam ri

nhp vi dng chnh ti pha trn Sn Ha. Sng c din tch lu vc l 1.040km2,

di l 88km. Cc sng sui thuc lu vc sng Ba u hp v su, dc ln c

tim nng ln v thy in. a hnh b chia ct mnh, lu vc sng Ba c dng

17

lng mng chy di t thng ngun n ca sng; pha Bc, ng, Nam c ni

cao bao hc ( cao 500 - 2.000m) v ch c m rng v pha Ty Nam vi cao

nguyn rng ln Pleiku, Mang Yang, Ch S, m ra bin qua vng ng bng Tuy

Ho rng hn 2.400ha vi cao t 5-10m, cn vng ca sng v ven bin t 0,5 -

2,0m. Lng mng ca lu vc b nhng dy ni m st ra mp sng to nn nhng

thung lng c lp nh An Kh (400 - 500 m), Cheo Reo (150 - 200m) v Ph Tc

(100 - 200m). [6]

18

Hnh 2. Bn mng li sng lu vc sng Ba

19

Hnh 3. S vng h lu sng Ba t Cng Sn n ca Rng

1.1.3. c im kh tng kh hu [6]

a. Ch gi

Gi cng l mt trong nhng nhn t kh hu quan trng, n phn nh cc

iu kin hon lu kh quyn v tc ng n nhiu mt trong t nhin. Ch d gi

c nhiu ngnh nh: hng khng, hng hi, xy dng, nng nghip, nng

lng quan tm.

Hng gi

Ch gi Ph Yn th hin hai ma r rt. Ma ng thnh hnh mt

trong ba hng gi chnh l: Bc, ng Bc v ng, Ma h l thi k thnh hnh

mt trong hai hng gi chnh l Ty v Ty Nam. Nhng ty thuc vo a hnh

mi ni, hng gi thnh hnh ngay trong cng mt vng, mt ma cng c th

khc nhau.

20

Ngoi ra, trong hai ma gi ma, khi cc trung tm gi ma hot ng yu

th tn phong hoc gi a hnh chim u th vi hng c thnh phn ng kh

thnh hnh.

Tc gi

Ph Yn tc gi trung bnh nm kh nh t 1,5 -2,5m/s, hng thng

trung bnh dao ng t 0,9 - 3,1m/s (bng 2). Thng c tc gi trung bnh ln

nht vo thng V, VI t 2,8 -3,1m/s, thng nh nht vo thng XII hoc thng 1 t

0,9 -1,6m/s. Vng ven bin, tc gi trung bnh vo thi k gi ma ma ng

ln hn so vi thi k gi ma ma h v ln nht vo thng XI, thng XII. Ngc

li, cc thung lng thuc vng ni c tc gi trung bnh thng vo thi k gi

ma ma h ln hn vo thi k gi ma ma ng v ln nht vo thng VII, VIII.

Trn cao nguyn thong gi, tc gi trung bnh ln hn i vi vng thp v

thung lng kn gi. Nu cng mt cao, tc gi vng ven bin c xu hng

ln hn nhng vng nm su trong t lin. [6]

Bng 2: Tc gi trung bnh thng v nm (n v: m/s)

Thng

Trm I II III IV V VI VII VIII IX X XI XII Nm

Tuy Ha 2,2 2,0 1,9 1,8 1,7 2,5 2,4 2,5 1,6 1,8 3,0 3,1 2,2

Sn Ha 1,1 1,4 1,5 1,4 1,6 2,4 2,8 2,8 1,4 0,9 1,1 1,1 1,6

Min Ty 2,0 2,0 2,6 2,7 3,0 3,0 2,5 2,2 2,4 2,2 1,8 1,8 2,3

Ngun: i KTTV Khu vc NTB

b. Bo v p thp nhit i

Ph Yn, khng phi bo b trc tip vo tnh mi gy nhng hin tng

thi tit cc oan, m nhiu cn bo b vo nhng tnh ln cn cng gy thi tit

nguy him khng km. V nh cn bo ngy 3/XI/1978 b vo Khnh Ha, tc

gi o c Tuy Ha 20m/s, Sn Ha 10m/s v Min Ty 28m/s. Hay bo s 7

ngy 24/IX/1977 b vo Bnh nh; p thp nhit i b vo Ninh Thun

2/XII/1986 cng gy ra ma ln trong ton tnh, ma ph bin 400 - 700mm, ma

ngy ln nht t 200 - 400mm.

T nm 1956 cho n nm 2002, trung bnh mi nm cc tnh Nam Trung B

21

c hn 01 cn bo hoc p thp nhit i b vo khu vc. Nu tnh tt c cc

cn bo v p thp nhit i b vo Khnh Ha v Bnh nh u nh hng trc

tip n Ph Yn th trung bnh hng nm Ph Yn nh hng trc tip 01 cn bo

hoc p thp nhit i, trong b vo a bn tnh gn 0,4 cn bo. Theo chui s

liu t 1976 - 2002 trung bnh hng nm Ph Yn c 0,54 cn bo hoc p thp nhit

i b vo khu vc tnh.

Bo, p thp nhit i b vo Ph Yn nhiu nht l cc nm 1980, 1983,

1990, 2001 nhng cng u khng qu 02 cn v cng c nm khng c cn bo

hay p thp nhit i no b nh cc nm 1982, 1985, 1986, 1989, 1991, 1994,

1997, 1999, 2000. Nu xt trong phm vi nh hng ca bo th nm 1998 l nhiu

nht, c ti 4 cn. Thi tit do bo v p thp nhit i gy ra trong thi on ngn,

nhng nhiu khi li lm bin i c cc c trng kh hu trc , nht l yu t ma

v gi mnh. [6]

c. Ch nhit

Ph Yn, nhng vng c cao di 100m nhit trung bnh nm thng

dao ng trong khong 26 - 270C, cao t 100 - 300m nhit nm thng dao

ng t 24 - 250C. Cng ln cao nhit khng kh cng gim. cao trn 400m,

nhit trung bnh nm gim xung cn 23 - 240C, trn 1000m nhit trung bnh

nm gim xung di 210C.

Tng nhit nm gia cc vng u chnh lch tng t nh nhit trung

bnh nm. Vng ng bng ven bin, cao di 100m tng nhit nm t

95000C - 9800

0C, vng ni cao di 400m gim cn trn di 85000 -

C95000C, cao 1000m ch cn trn di 75000C.

Bin trnh nm ca nhit khng kh:

Hng nm, nhit thp nht thng xy ra vo thng I (21-230C), sau tng

dn v thng t cc i vo thng VI (26-290C) ri li gim dn n thng I nm

sau. Tuy nhin, y l tnh hnh chung ca nhiu nm. Tng nm c th thng lnh

nht trong ma ng c th l thng XII hoc thng I. Thng nng nht c th l

thng VI, thng VII hoc thng VIII. Ta c th nhn thy rng, bin trnh nm nhit

Ph Yn kh thng nht vi bin trnh nm cc ni khc thuc duyn hi

22

Trung B v c dng nhit i, t cc i vo thng VII v cc tiu vo thng I

nhng cn mang dng dp bin trnh nm dng xch o, tc l cc i hi lch v

u ma h.

Bng 3: Nhit trung bnh thng v nm (n v: 0C)

Trm Thng Tuy Ha Sn Ha H Bng Sng Hinh Min Ty

I 23,3 22,1 22,5 21,4 20,6

II 23,8 23,2 23,5 22,4 21,6

III 25,4 25,5 25,3 24,4 23,7

IV 27,3 27,7 27,2 26,5 25,7

V 28,8 28,7 28,6 27,4 26,6

VI 29,2 28,6 29,1 27,5 26,5

VII 29,0 28,5 29,1 27,4 26,3

VIII 28,7 28,2 29,0 26,6 26,1

IX 27,7 27,0 27,5 26,3 25,0

X 26,4 25,5 25,8 24,8 23,7

XI 25,2 24,1 24,5 23,0 22,4

XII 23,8 22,5 23,0 21,6 21,0

Nm 26,6 26,0 26,3 24,9 24,1


Nhit ti cao hng ngy thng xy ra vo lc sau tra (13-14 gi). Ph

Yn ni c cao di 300m nhit ti cao trung bnh nm t t 29 -320C, nhit

ti cao trung bnh cc thng dao ng t 25 - 350C. Cao nht xy ra trong thng

VII ven bin, thng V vng ni t 33 - 360C, thp nht xy ra vo thng XII

hoc thng I t 25 - 270C (bng 3).

d. Ch nng

Do nm v thp, quanh nm di ban ngy ln, li thm hng nm c

c mt thi k ma kh tri quang my ko di 5 - 6 thng, nn Ph Yn l mt tnh

c thi gian nng ln. Tng s gi nng trung bnh hng nm t 2300 - 2500 gi.

Trong sut 6 thng t thng III n thng VIII, s gi nng trung bnh mi thng

dao ng t 230 - 270 gi, mi ngy trung bnh c ti 8 gi. Thng IV, thng V l

hai thng c thi gian nng nhiu nht, trung bnh hng thng c t 250 - 270 gi.

23

Cc thng t nng l nhng thng ma ma, s gi nng trung bnh hng thng cng

trong khong 100 - 200 gi, trung bnh mi ngy 5 - 6 gi. Thng t nng nht l

thng XII, trung bnh hng thng t 100 - 112 gi nng. Nh vy, s gi nng ca

thng t nng nht ch xp x bng mt na s gi nng ca thng cc i. S chnh

lch s gi nng ny cng phn nh r nt s tng phn gia hai ma: ma kh v

ma ma m.

e. Bc hi

Tng lng bc hi nm Ph Yn tng i n nh. Nm nhiu nht v

nm t nht khng qu 30% so vi tng lng bc hi trung bnh. Hng nm tng

lng bc hi t t 1100 - 1400mm, phn b khng u trong cc thng. T thng

X nm trc n thng III nm sau, tng lng bc hi hng thng trung bnh t 50

n di 100mm, ring thung lng Sn Ha thng II dn thng III hng thng trung

bnh 120-130 mm, trong thp nht l thng X v XI ch t t 50 - 80mm thng.

T thng IV n thng IX, trung bnh hng thng t 100 - 200mm, trong cao

nht l thng VII, thng VIII t 150 - 200mm. Cng ln cao bc hi kh nng c xu

hng gim. in hnh, ti Sng Hinh cao 200m, qua s liu kho st tng

lng bc hi nm ch cn 1100mm, thng bc hi nhiu nht cng khng vt qu

160mm v thng thp nht ch t 31mm. Tuy nhin y l vng ma ln nht tnh,

do cng cao vi cc khu vc khc, nhng nhn chung y c tng lng

bc hi kh nng nm ln hn 1100mm. Bin bc hi nm dao ng 40 - 60mm,

bc hi ngy ln nht 11 - 12mm, nh nht 0,4 - 0,5mm, trung bnh 2,5 - 4,0mm.

f. Ch ma

Lng ma trung bnh nhiu nm trong khong 1200 - 2600 mm, trung bnh

1700 mm. Trung tm ma ln l vng ni cao n gi Ch Mu, o C, trn 2000 mm.

Vng ma thp nht l thung lng sng Ba: Krng Ba 1200 mm, v tm thp

th hai l vng thung lng sng K L: Xun Phc 1330 mm. Nhn chung lng

ma tng dn t cc thung lng sng ng bng ven bin n vng ni cao v ni

cao n gi.

24

Bng 4: Mt s c trng ma nm (n v: mm)

Trm Ma trung

bnh nm

Nm ma

ln nht

Nm xut

hin

Nm ma

nh nht

Nm xut

hin Tuy Ha 2090 3092 1993 1271 1982

Sng Cu 1802 2582 1999 902 1982

Sn Ha 1780 2965 1993 1081 1982

Ph Lm 1933 2927 1981 1177 1982

H Bng 1794 2663 1998 746 1982

Ph Lc 2015 3272 1993 1044 1986

Sn Thnh 2237 3390 1993 1241 1984

Ha ng 2374 3605 2000 1042 1982

C Mng 2230 3465 1998 1015 1982


Phn phi khng gian ca lng ma Ph Yn rt khng ng u. Lng

ma nm trung bnh o c c ni nhiu ma nht v t ma nht chnh lch

nhau 579mm. Dy ni Vng Phu o C v khu vc cch chn ca dy ni ny trn

di 10km v pha Bc l vng ma ln nht tnh, vi tng lng ma nm trung

bnh t 2200 - 2600mm. Vng ma ln th hai l i ni thuc trung lu sng K L

c lng ma nm t 1900 - 2200mm, tip n l vng ng bng ven bin pha nam

t 1800 - 2100mm... Nhng vng cn li nh vng ven bin pha Bc, thung lng sng

K L v sng Ba lng ma nm trung bnh t 1600 - 1800m trong tm ma thp

nht l khu vc Ch Thnh vi lng ma nm trn di 1600mm (bng 4).

Phn b lng ma theo ma

Bn thng ma ma, lng ma trung bnh nhiu nm khong 1200 -

1900mm, chim t 69 - 84% tng lng ma nm. Ma ma vi c trng nng t,

ma nhiu, tri du mt. i lp l ma kh ko di sut tm thng cn li, tri

nng nng, li thiu nhng nhiu ng mnh nh bo, di hi t ni ch tuyn... do

, t c kh nng to cho hi m c th ngng t. Cho nn ma kh l thi k thi

tit trong sng, nhit cao, ngun m ngho nn, bc hi mnh v ch c b

sung phn no bng lng ma t i, tht thng. Ma kh mc d n nh hn ma

ma nhng khng gi nguyn sc thi m c nm di, nm ngn, nm kh nhiu,

nm kh t; ph thuc vo dao ng ma ma hng nm cng nh vo tnh cht ca

gi ma. Tng lng ma ma kh khong 300 - 700mm, chim 16 - 31% lng

25

ma nm, trong vng ni thng chim 24 - 31%, ven bin thng chim 16 -

22% lng ma nm (bng 5).

Bng 5: Lng ma trung bnh nhiu nm cc thng (n v: mm)

Trm Thng I II III IV V VI VII VIII IX X XI XII

Ph Lc 48 21 43 33 80 48 36 49 245 637 517 258

Ha ng 72 28 56 45 109 80 58 63 246 679 614 324

Sn Thnh 46 17 54 52 124 100 77 76 235 621 563 272

Sng Hinh 58 21 68 65 155 125 97 95 237 626 567 274

Min Ty 22 10 34 36 125 106 80 107 213 447 409 155

Sn Ha 23 10 36 38 132 112 84 113 209 469 402 152

Cng Sn 21 9 38 35 89 113 75 106 180 487 399 154

H Bng 31 12 26 35 112 75 63 77 225 517 462 159

Xun Lnh 43 17 36 48 155 104 87 107 239 550 491 169

C Mng 59 26 34 31 96 74 44 81 269 594 607 315

Sng Cu 26 11 13 30 83 81 34 66 244 534 487 193

Ch Thnh 20 8 10 23 62 61 26 50 226 495 452 179

Tuy Ha 47 18 35 30 94 60 42 56 288 656 549 215

Ph Lm 40 19 32 30 89 56 39 51 267 612 498 200


Hnh 4. Bn phn b lng ma ma

ma (t l 1: 100 000)

Hnh 5. Bn phn b lng ma ma

kh (t l 1: 100 000)

26

g. m

m khng kh l ch s biu th lng hi nc cha trong khng kh.

Ngi ta thng dng cc c trng m tuyt i v m tng i ch v

m.

m tuyt i

Tr s trung bnh nm c xu hng gim theo cao, vng ven bin khong

27 - 28 mb, vng ng bng di 27 mb, vng ni thp di 25 mb v cao

khong 700 - 800 m im tuyt i trung bnh nm khong 21 mb.

Thi k t thng IV n thng IX ch yu tp trung vo cc thng ma nng

v t ma, m tuyt i trung bnh thng vng thp khong 28 - 30 mb v

vng ni khong 25 - 27 mb. T thng X n thng III nm sau hu nh trng vi

cc thng ma ma nhit h xung, m tuyt i xung thp dn, vng ng

bng ven bin khong 23 - 27 mb, vng ni 20 - 25 mb v cng ln cao cng gim.

Bng 6: m tuyt i trung bnh thng v nm (mb)

Thng

Trm I II III IV V VI VII VIII IX X XI XII Nm

Tuy Ha 23,5 24,6 26,5 29,2 30,3 29,6 29,2 29,0 295 28,9 27,0 24,0 27,6

Sn Ha 22,7 23 25,2 27,8 29,5 29,0 28,3 28,5 29,0 28,7 26,4 23,4 28,8

Min Ty 20,6 20,6 23,4 25,2 26,9 27,0 26,4 27,2 26,8 25,2 22,8 21,3 24,5

m tng i

m tng i trung bnh nm Ph Yn khong 80 - 85%. Phn b

khng gian ca yu t ny th hin quy lut tng theo cao a hnh, vng ng

bng v ven bin m tng i trung bnh nm l 80 - 82%, vng ni thp 83 -

85%, trn cao nguyn n 1000 m t 85 - 90%.

Cng vi thi k kt thc ma l thi k m gim lin tc, n thng IV

m gim mnh hn do nh hng ca gi ma Ty Nam cho n thng VII t

gi tr thp nht khong di 75 vng thp v di 80% vng cao. T thng

VIII n thng IX giai don kt thc ca ma kh, bt u chuyn qua ma ma

m tng i tng vt vi bin 5 - 10% trong khi cc thng khc c bin 2 -

3%. Bin nm ca m tng i trung bnh Ph Yn khong 8 - 10%.

27

Bng 7: m tng i trung bnh thng v nm (n v: %)

Thng

Trm I II III IV V VI VII VII IX X XI XII Nm

Tuy Ha 84 85 83 82 78 75 74 75 81 85 85 83 81

Sn Ha 86 83 80 78 77 76 75 76 93 95 89 88 82

Min Ty 84 84 82 79 79 81 80 81 87 88 88 87 84

1.1.4. c im thy vn [6]

Trong v ln cn lu vc sng Ba c 15 trm o c thu vn, trong c 13

trm o c yu t lu lng v mc nc v c 2 trm ch o yu t mc nc.

Vng h lu sng Ba c trm Cng Sn v Sng Hinh o yu t Q, H, vi thi gian

quan trc t nm 1976 ti nay v trm Ph Lm ch o yu t H vi thi gian quan

trc t nm 1977 ti nay.

Lu vc sng Ba c thi gian ma l ko di 4 thng t thng 9 ti thng 12,

nhng do c im ma nn lu vc c 4 thi k l khc nhau:

- Thi k l tiu mn: thng xy ra vo thng 5, 6;

- Thi k l sm: thng xy ra vo thng 8, 9;

- Thi k l chnh v: thng xy ra vo thng 10, 11;

- Thi k l mun: thng xy ra vo thng 12, 1;

Qua thng k thy vn cho thy thi gian xut hin nh l ti cc trm thy

vn hu ht vo thng 10 v thng 11 hng nm.

a. c im dng chy l

Vng h lu luu vc sng Ba lun i mt vi bo l v mc l y

rt ln. Trong vng 60 nm trn lu vc sng Ba xy ra 3 trn l c bit ln, l

l nm 1943 (Qmax = 24000 m3/s), l nm 1964 (Qmax = 21800 m3/s) v l nm

1993 (Qmax = 20700 m3/s). ng qu trnh l trn lu vc sng Ba nu gp cc

hnh th thi tit gy ma ch do 1 trong 4 yu t bo, p thp nhit i, gii hi t

nhit i hoc gi ma ng Bc gy ra th hnh dng l nhn v ln nhanh, rt

nhanh. Nu t hp y cc hnh th thi tit nu trn th hnh dng l s c nhiu

nh k tip nhau. Phn tch kt qu o c l ln nht ti Cng Sn (Flv 12400

km2) t nm 1977 ti 1999 cho thy lu lng l ln nht trung bnh nhiu nm l

7020 m3/s, l ln nht 20700 m3/s o c vo ngy 4/X/1993 v nhng trn l ln

28

k tip vo cc nm 1988, 1981, 1992 u xy ra vo thng X v thng 11. bng 8

thng k lu lng l ln nht ca mt s con l ln ti cc trm o lu lng h

lu lu vc sng Ba Do lu vc sng Ba c dc ln, c im cc sng ngn v

dc nn thi gian l trn lu vc thng ch trong khong 3 - 5 ngy v tng lng

l 1 ngy ln nht chim ti 30 - 35% tng lng ton trn l. Tng lng l 7 ngy

ln nht ti Cng Sn t 2770.106 m3 nm 1981, t 2612.106 m3 thng 10/1993.

Bng 8: Lu lng l ln nht ti mt s trm trn lu vc sng Ba

Tn trm Qmax (m3/s) Thi gian xut hin

An Kh 2440 9/XI/81

Cng Sn 20700 4/X/1993

Sng Hinh 5310 2/XII/1986

Krng Hnng 3510 2/XII/86


b. c im thy vn ma cn

Dng chy ma cn ch yu l phn nc cn li ca ma l nm trc,

gim nhanh chng theo ng nc rt v xut hin mt cc tiu th nht vo cui

thng III hoc thng IV, chim t 2,8 - 3% tng lng dng chy nm. Sang thng

V, VI dng chy c tng ln nh ma tiu mn, nhng cha vt qu tnh cht dng

chy ma cn. Thng VII, VIII dng chy trn cc khu vc li gim chm v xut hin

mt cc tiu ph trong nm, tuy nhin khng t nm dng chy thp nht nm cng

xut hin vo thi k ny.

Tnh chung trong ton tnh, lng dng chy 8 thng ma cn ch chim

khong 25 - 30% tng lng dng chy nm, khng th p ng nhu cu dng nc

trong ma cn nu nh khng c bin php tch tr v s dng nc hp l.

Dng chy nh nht nm l c trng thu vn quan trng trong tnh ton

thit k cc cng trnh cp nc trn sng, thng c biu th di dng lu

lng nh nht Qmin (m3/s) hay Mduyn nh nht Mmin (l/s.km2) cho 1 ngy, 10

ngy, 30 ngy, 3 thng v.v...

29

1.2. IU KIN KINH T X HI [6]

1.2.1. c im dn sinh kinh t

a. T chc hnh chnh lu vc sng Ba

Lu vc sng Ba nm trong phm vi ranh gii hnh chnh ca 20 huyn th

thuc 3 tnh Ty Nguyn: Kon Tum, Gia Lai, aKlak v mt tnh duyn hi min

Trung Trung B l Ph Yn. Trong c mt s huyn thuc tnh Kon Tum l

huyn KonPlong, 10 huyn th thuc tnh Gia Lai l: Kbang th x An Kh, akP,

Konch Ro, akoa, Mang Yang, Ch S, Ayun Pa, Krng Pa. EaPa, 4 huyn thuc

tnh ak Lak l:Ea Hleo, Krng HNng, Eakar, MadRk v 5 huyn thuc tnh Ph

Yn l: Sn Ha, Sng Hinh, Ph Ha, Tuy Ha, v th x Tuy Ha.

b. Dn s

Dn s trong ton lu vc sng Ba tnh n 31/12/2004 c khong 1.391.701

ngi. Trong vng thng v trung lu thuc Ty Nguyn bao gm Nam Bc

An Kh, thng Ayun, Ayun Pa, Krng Pa, Krng HNng c dn s khong

804.364 ngui, mt dn s bnh qun 76,8 ngi/Km2, ngi kinh chim 55,57%

dn s ton vng cn li 44,23% l ngi dn tc t ngi (phn ln l ngi Gia

Lai). Dn s th trn huyn l chim 19,5% v nng thn chim 80,5%. Mt dn

s phn b khng u ch yu tp trung cc thnh th, trc giao thng v nhng

vng kinh t pht trin, mt c th t t (305-1314) ngi/km2. Cn cc huyn

thuc vng Nam Bc An Kh, thng Ayun nh huyn KBang, Kon ChRo,

koa mt dn s ch t t (20-30) ngi/km2. T l tng dn s 2,01%.

1.2.2. c im kinh t

C cu pht trin kinh t t trc n nay vn ly Nng - Lm - Nghip l

chnh cho nn gi tr GDP trong nng nghp vn chim t trng cao trong tng gi

tr cc ngnh nm 1998 chim 52,6%, nm 2000 chim 48,5%, nm 2004 gim cn

46% trong tng gi tr cc ngnh kinh t trong lu vc. Tuy vy nn kinh t nng

lm nghip ang c chiu hng gim dn tng gi tr c cu cng nghip - dch

v du lch cho ph hp vi xu th pht trin kinh t chung ca t nc nhm thc

y v p ng nhu cu hin i ho v cng nghip ho t nc. Nhn chung c

cu kinh t gia cc vng trong lu vc sng Ba bin ng khng ng u.

30

i vi vng thng v trung lu c cu kinh t nng lm nghip chim

69,6% nm 1998 v nm 2004 chim 65%. Nhng gia cc huyn bin ng cng

khc nhau. Nm 1998 c cu Nng lm nghip huyn An Kh, Krng Pa l (45,9

46,9%) trong khi cc huyn lin k nh KBng, Kon Chro, k oa, Ayun Pa c

cu kinh t nng lm nghip chim ti (68 -95,8%) tng c cu kinh t cc ngnh.

Hin nay bnh qun thu nhp u ngi trn lu vc sng Ba t khong 335

USD/ngi/nm. Khu vc thng trung lu thuc vng Ty Nguyn c li th v

mt hng nng lm sn c gi tr kinh t cao nh cao su, cafe, tiu, iu nn mc

thu nhp bnh qun u ngi t khong 324 USD/ngi/nm. Cn khu vc h lu

thuc ng bng Duyn Hi ven bin min Trung c nhiu li th v iu kin t

nhin, x hi nht l dch v du lch, thu hi sn nn mc thu nhp bnh qun u

ngi c phn cao hn vng thng trung lu mt cht v mc thu nhp t khong

350 USD/ngi/nm. [5, 6]

1.3. TNH HNH NGP LT H LU SNG BA [6]

1.3.1. Tnh hnh ngp lt

Theo thng k ca chi cc phng chng lt bo tnh Ph Yn, hng nm khi

ma ma l v, l ngoi sng cng ma trong ng gy ngp lt trn din rng cc

huyn Tuy Ho, th x Tuy Ho. Trong thi k l chnh v t thng X n thng XI

phn ln din tch h lu sau p ng Cam b ngp chm trong nc. c bit l

c bit ln thng 10/1993 xy ra do 3 t bo lin tip b vo Ph Yn gy ma

ln trn din rng lm l sng Ba ln rt nhanh gy ngp hu ht ton b vng

h lu sng Ba. Nc l trn qua knh Bc, Nam ng Cam gy ngp ton b

vng la ca huyn Tuy Ho thuc a phn cc x Ho Phong, Ho Thnh, Ho

M ng, Ho ng, Ho Tn Ty. Trn l ny cng gy ngp rt su cho

ton b vng h lu sng Bn Thch.

1.3.2. Thit hi do ngp lt

Mi nm khi ma ma bo v, l gy ngp lt, thit hi kh ln v ngi

v ti sn tren lu vc. Ma l gy cht ngi, nh ca b ngp, b sp, cc cng

trnh h tng c s nh trng hc, bnh vin b h hng, ng s cu cng cng

31

trnh thu li b st l, b v v bi lp. Din tch t trng trt b ngp lu ngy lm

cho la, hoa mu v cc loi cy trng khc b tht thu.

L thng 10/1993 l l ln nht tng xy ra trn lu vc sng Ba t nm

1976 ti nay. Theo bo co thit hi do l gy ra ca cc huyn Tuy Ho, Ph Ho

v th x Tuy Ho, l thng 10/1993 lm 72 ngi cht, 4 ngi mt tch, 464

ngi b thng, 10902 ngi nh b sp hon ton tri i mt, 138 kho tng, tr

s c quan, 264 trng hc b sp hon ton, gn 20000 ha din tch cy trng

cc loi b ngp v h hi. Gia sc gia cm b cht tri khong 370 nghn con.

Ngoi ra cc thit hi v giao thng, thu li cng rt ln, ti 105 cu cng b sp

tri, cc tuyn ng giao thng b st l v ngp ti hng trm km. c tnh tng

thit hi ca trn l ny ln ti 394 t ng. Tng hp thit hi do ngp lt mt s

nm vng h lu sng Ba c thng k trong (bng 9). [6]

Bng 9: Thit hi mt s nm do ngp l vng h lu sng Ba

Hng mc n v 1993 1998 1999 2000 2001 2002 2003

Thit hi v

ngi

Cht Ngi 72 38 32 14 21 9 13

B thng Ngi 464 6 1 88 7

Mt tch Ngi 4

Nh ca, kho

tng trng hc

Sp , tri hon

ton

Ci 10902 263 215 54 2457 9 64

Nh b h hng Ci 14587 1900 455 235 23197 2 727

Nh phi di di Ci 14436

3

119

Trng hc sp

hon ton

Ci 264 13 6 4 90 5

Trng hc b h

hng Ci 797 77 23 1072

Trm x sp hon

ton

Ci 69

Trm x b h

hng Ci 223 10 25 1 36 5

Nng nghip

Din tch la mt

trng

Ha 20083 5600 2054 60 6152 1201

Din tch la h

hi

Ha 1500 7200 3023 638 3815

Din tch mu

mt trng

Ha 4000 445

32

Hng mc n v 1993 1998 1999 2000 2001 2002 2003

Din tch hoa

mu h hi

Ha 971 2150 4619 149 9817

Din tch NN b

bi lng Ha 250 189 209 10 186

Gia sc cht tri Con 27325 291 11 148 81

Gia cm cht tri Con 31000

0

10000 370 1077 17069 1492

0 Giao thng

ng x b h

hng

103m3 139.9 930 382.4 318.8 222.6 15.6 914.

8 Cu cng sp

tri, h hng

Ci 105 64 22 87 2 7 33

ng st b

cun tri

m3 130

Thy li

Knh mng st

l bi lp

103m3 187.2 295.2 15284

0

10040

3

14521

4

14476 2914

01 k st l m3 1287 19000 13600 6550 11000 60 1043

80 Cng trnh thy

li h hng

Ci 44 16 26 2 10

Cng trnh ni

ng h hng

ci 87 19 1

Thy sn

Ghe thuyn chm

tri h hi

Ci 130 111 110 3 509 82 7

in tch ao m

v

Ha 390 1160 846 1154 1523

in lc

Trm bin th

ngp h hi

Trm 4 4

Ct in gy Ct 3081 41 4 1171 29

Dy in t, mt Km 1259 1.1

Tng thit hi

c tnh

109 394 120 54 24 405.6 4.2 103

Ngun: Vin Quy hoch Thy li

1.3.3. Hin trng cng trnh phng chng l v tiu ng

Do c im l sng Ba ln nhanh v rt cng rt nhanh, thi gian ngp lt

ngn nn vng h lu sng Ba khng c h thng iu chng l. Ch c mt s

on chng xm nhp mn, ngn ct, bo v cc khu dn c mt s khu vc

nh Ph Cu, ng Tc, Bi Gi, Nng. Ngoi ra pha b t ca Rng

cn c 7 m hn bng chng xi l b sng.

33

Hin ti trn ton lu vc xy dng c 147 h cha, trong s ch c 2

cng trnh c kh nng ct gim l cho h du sng Ba l h Ayun h v h Sng Hinh.

H Ayun h c xy dng nm 1999 - 2000 trn nhnh Ayun ti v tr c

din tch lu vc 1670 km2. H c nhim v ti l chnh vi din tch ti thit k

13500 ha, ngoi ra h cn c nhim v phng l h du vi dung tch phng l

153.106m3.

H Sng Hinh c xy dng t nm 1995 trn nhnh sng Hinh v tr c

din tch lu vc 772 km2. H c nhim v pht in l chnh. Ngoi ra h cn c

nhim v phng l cho h du vi dung tch 250.106m3.

Nh vy, tng dung tch phng l ca 2 h cha Ayun h v Sng Hinh t

403.106m3. Trong khi tng lng l 7 ngy ln nht ti Cng Sn nm 1981 t

2,77 t v nm 1993 l 2,6 t. Nh vy 2 h Ayun h v Sng Hinh mi ch ct

c khong gn 15% tng lng l 1993. i vi l tn sut 10%, hai h Ayun h

v Sng Hinh cng ch ct c khong 20% tng lng 7 ngy ti Cng Sn.

Tm li, hin trng cc cng trnh phng chng l trn lu vc sng Ba hin

ti cn qu t, trong khi gn nh nm no vng h du cng b thit hi rt ln bi

ngp lt. Bi vy vic nghin cu cc gii php nhm gim thit hi do bo l gy

ra trn lu vc thc s l vic lm cn thit. [6]

1.3.4. Mc tiu phng chng l trn lu vc

Mc d vng h lu sng Ba l thng gy ngp trn din rng nhng qu

trnh l ln nhanh v rt cng nhanh. Ma l h du sng Ba thng ko di 3 thng

t 15/9 ti 15/12, mi nm thng xy ra t 1 ti vi ba trn l. Vo ma ma l

chnh v, ton b vng h lu sng Ba b ng khng sn xut nng nghip tr

thnh tp qun canh tc tn ti lu i. V vy, mc tiu chng l cho h lu sng Ba

nh sau:

- L chnh v: do tng lng l ln gy cho vng su b ngp ln, din

tch ngp rng v di ngy nn khng th phng chng c mt cch trit m

ch c gng phn u gim bt tc hi ca l, m bo an ton tnh mng v ti sn

cho ngi dn trong vng, hn ch ti mc thp nht thit hi v ngi v ti sn do

l bo gy ra.

- L sm, l mun v l tiu mn: cc thi k l ny c cng l nh,

lng ma ni ng khng ln nn c kh nng phng chng c. Mc tiu l

34

nghin cu cc gii php chng l l sm, mun v tiu mn, m bo cho sn

xut nng nghip nhm nng cao sn lng lng thc thc y s pht trin kinh

t x hi v n nh i sng nhn dn trong vng.

Tuy nhin hin nay cha c quy hoch phng chng l ring cho lu vc

cha c xy dng nn vic trc tin l cn thit phi xy dng c s khoa hc v

thc tin nhm a ra c phng n phng chng l phc v pht trin KTXH.

1.3.5. Phng n quy hoch phng chng l

a. Quan im chng l

Quan im v chng l cho h du sng Ba c cp ti trong cc kt

qu nghin cu nh "nh hng quy hoch l min Trung" (Vin QHTL 1998-

2000), "Hiu qu chng l h du cng trnh thu in sng Ba h"... Do c im

a hnh, l trn sng Ba ln nhanh v xung cng nhanh. Nhng nm l ln

(10/1993) l v gy ngp trn lan khp vng h lu vi ngp su ln (2m n

3m), nhng nm l nh thng gy ngp t 01,5 n 1m nhng do di t ng

bng hp, dc, chy st bin nn nc rt nhanh ra bin. V vy m vng h lu

sng Ba ni ring cng nh cc vng duyn hi min Trung Trung B khng xy

dng h thng ngn l nh cc lu vc sng khc thuc min Bc. Do quan

im phng chng l cho h du sng Ba ch yu vn l thch nghi, sng chung vi

l l chnh. Tuy nhin cng cn xem xt nhim v ct l ca mt s cng trnh h

cha c quy m ln trn dng chnh sng Ba gim thiu thit hi do l gy ra i

vi vng h lu sng Ba.

Qua phn tch lit thng k cc trn l ln thng xy ra trong nm cho thy

l sm mc d xut hin sau l tiu mn nhng cng l ln cng nh ln

ca lu lng nh l, tng lng l ln hn so vi l tiu mn. V vy s tp trung

chng l cho l sm, bi nu chng c l sm cng c ngha l s chng c l

tiu mn. Cn vi l chnh v, do mc ngp lt ca h du rt ln, nn vic chng

l chnh v l kh c th. Hn na tp qun canh tc ca ngi dn vng thng

xuyn ngp lt thch nghi vi l chnh v, trong ma l chnh v vng ngp

trng thng b ng. V vy, vic tnh ton l chnh v ch c tnh cht kim tra.

b. Vng bo v

35

Vng h lu sng Ba l vng thng xuyn i mt vi ma bo l lt, trong

ton b t ai, c s h tng v dn c nm trong phm vi ng 25 kt hp vi

knh chnh Bc ng Cam, ng lin huyn ln Sng Hinh kt hp vi knh

chnh Nam v vng ca sng Rng ch yu thuc a phn cc huyn Ph Ho,

Tuy Ho v th x Tuy Ho cn bo v.

c. Tiu chun chng l

- Cn c vo tiu chun xy dng Vit Nam TCXDVN 285-2002: cc quy

nh ch yu v thit k.

- Cn c vo tiu chun phn cp ban hnh theo ngh nh 429-HBT.

- Cn c vo quy phm thu li QPTL A.6.77. p dng cho lu vc sng Ba

c vng cn bo v l h lu sng Ba nm trn a bn cc huyn Tuy Ho, thnh

ph Tuy Ho, huyn Ph Ho, hng nm thng c khong hn 5000 ha b ngp.

- Theo Ngh nh 429 HBT tiu chun thit k cp III.

- Theo QPTL A.6-77 tiu chun thit k cp IV Do vy, chn tn sut l

thit k ca cng trnh cp IV: 10 %.

d. Cc phng n quy hoch phng chng l v tiu ng

Xy dng cc hnh lang thot l kt hp cng trnh iu tit l thng lu l

bin php chng l c bn i vi vng h lu sng Ba. Hin nay trn lu vc

hnh thnh 2 p chn l l Quc l 1A v ng st thng nht Bc Nam. Pha h

lu hai bn t hu c knh chnh Bc Nam p ng Cam kt hp giao thng l

ng lin tnh 7B (Bc) v 436 (Nam) nhng nhiu on khi c l ln nc vn

trn qua. Trn lu vc hin ti ch c 2 h cha a mc tiu trong c nhim v

phng l l h Ayun h v h Sng Hinh. Ngoi ra cn c h cha sng Ba h ang

c xy dng. Trong tng lai quy hoch ngh xy dng bc thang cc cng

trnh h cha a mc tiu pha thng ngun c tc dng ct l cho h du bao gm

h Krng Hnng, h An Kh Kanak. [6]

36

CHNG 2. C S L THUYT XY DNG BN NGP LT

2.1. TNG QUAN CHUNG

2.1.1. Khi nim v bn ngp lt [1, 3]

Bn nguy c ngp lt l ti liu c bn, lm c s khoa hc cho vic quy

hoch phng trnh l lt, la chn cc bin php, thit k cc cng trnh khng ch

l, l thng tin cn thit thng bo cho nhn dn v nguy c thit hi do l lt

ni hc c tr v hot ng.

Bn ngp lt thng th hin cc ni dung sau:

Vng ng ngp thng xuyn.

Vng ngp lt ng vi tn sut ma, l khc nhau.

Khu vc nguy him khi c l ln.

Khu vc c nguy c b trt l, st l.

Vt xi l b sng, st l b bin, trt l sn.

Ngoi ra cn th hin h thng thy li: h cha, trm bm, p dng, cng

v cc yu t nn a l.

Bn ngp lt phi xc nh r ranh gii nhng vng b ngp do mt trn

ma l no gy ra trn bn . Ranh gii vng ngp lt ph thuc vo cc yu t

mc nc l v a hnh, a mo ca khu vc ; trong khi nhn t a hnh t thay

i nn ranh gii ngp lt ch cn ph thuc vo s thay i mc nc l. [1, 3]

2.1.2. Cc phng php xy dng bn ngp lt

Hin nay trn th gii c 2 phng php c s dng xy dng bn

ngp lt, l:

1. Xy dng bn ngp lt da vo iu tra cc trn l ln thc t xy ra.

2. Xy dng bn ngp lt da vo vic m phng bng cc m hnh thy vn, thy lc

Mi phng php trn u c cc u nhc im ring trong vic xy dng

v c lng din tch ngp lt. Bn ngp lt xy dng theo phng php iu

tra cc trn l ln xy ra ch ti hin li hin trng ngp lt, cha mang tnh d bo

nhng n vn mang ngha to ln v nhiu mt trong cng tc ch huy phng

chng l lt cng nh lm c s nh gi, so snh cc nghin cu tip theo. Tuy

37

vy phng php ny tn cng, mt nhiu thi gian, khng p ng nhu cu thc t

v c nhng im ngi nghin cu khng th o c c hoc khng thu thp

c s liu.

S dng cng c m phng, m hnh ha bng cc m hnh thy vn, thy

lc l rt cn thit v c hiu qu hn rt nhiu v cng l cch tip cn hin i v

ang c s dng rng ri trong thi gian gn y trn c th gii v Vit Nam

trong s kt hp vi c cc li th ca phng php truyn thng.

Mt khc, vi s pht trin ca my tnh v cc h thng thng tin, c s d

liu ngy cng c nhiu ng dng pht trin da trn nn h thng tin a l (GIS),

m xy dng bn ngp lt l mt trong nhng ng dng quan trng mang li

nhiu li ch thit thc trong thc tin cng tc phng chng lt bo v gim nh

thin tai.

Do vy lun vn ny s tp trung gii thiu v phn tch cc nhm m hnh

thy vn, thy lc c kh nng ng dng trong xy dng bn ngp lt, nhm lm

c s la chn phng php s dng cho khu vc nghin cu cng vi vic gii

thiu cc quy trnh v cng c xy dng bn ngp lt tch hp kt qu m phng

bng m hnh thy ng lc vi h thng c s d liu GIS.

2.2. TNG QUAN V CC M HNH THY VN, THY LC TNH TON

NGP LT [3]

2.2.1. Cc m hnh ma dng chy:

M hnh Ltank: do PGS.TS Nguyn Vn Lai xut nm 1986, l mt phin

bn ci tin t m hnh Tank gc ca tc gi Sugawara (1959). M hnh ton ma

ro dng chy da trn qu trnh trao i lng m gia cc tng mt, ngm lu

vc, v bc hi. ng dng tt cho lu vc va v nh.

M hnh HEC-HMS: l m hnh ma dng chy ca trung tm thy vn k

thut qun i Hoa K c pht trin t m hnh HEC-1, m hnh c nhng ci

tin ng k c v k thut tnh ton v khoa hc thy vn thch hp vi cc lu vc

sng va v nh. L dng m hnh tnh ton thy vn c dng tnh dng chy

t s liu o ma trn lu vc. Trong cc thnh phn m t lu vc sng gm

cc cng trnh thy li, cc nhnh sng.

38

Kt qu ca HEC-HMS c biu din di dng s , biu bng tng minh

rt thun tin cho ngi s dng. Ngoi ra, chng trnh c th lin kt vi c s d

liu dng DSS ca m hnh thy lc HEC-RAS.

M hnh NAM: c xy dng nm 1982 ti khoa thy vn vin k thut

thy ng lc v thy lc thuc i hc k thut an Mch. M hnh da trn

nguyn tc cc b cha theo chiu thng ng v h cha tuyn tnh. M hnh tnh

qu trnh ma dng chy theo cch tnh lin tc hm lng m trong nm b cha

ring bit tng tc ln nhau. NAM m phng qu trnh ma - dng chy bng vic

m t lin tc cho cc thnh phn trong 4 vng tr lng tng tc ln nhau bao gm:

tr lng tuyt; Tr lng nc mt; Tr lng nc st mt; Tr lng nc ngm.

Cc m hnh thy vn trn y cho kt qu l cc qu trnh dng chy ti cc

im khng ch (ca ra lu vc) v vy t thn chng ng c lp cha kh

nng a ra cc thng tin v din tch v mc ngp lt m phi kt hp ci

mt s cc cng c khc nh GIS, hoc l bin cho cc m hnh thy ng lc 1-2

chiu khc. [3]

2.2.2. M hnh thy lc:

M hnh VRSAP (Vietnam River System And Plains): tin thn l m hnh

KRSAL do c PSG.TS Nguyn Nh Khu xy dng t 1965 n 1993 v c s

dng rng ri nc ta trong khong 25 nm tr li y.

y l m hnh ton thy vn - thy lc ca dng chy mt chiu trn h

thng sng ngi c ni vi ng rung v cc khu cha khc. Dng chy trong cc

on sng c m t bng h phng trnh Saint-Venant y , khng b bt mt

vi s hng nh trong mt s m hnh khc. Dng chy qua cc cng trnh c m

t bng cc cng thc thy lc bit v c a vo cng mt s hng nh

phng trnh ca cc on sng. Dng chy trn vo cc rung hay khu cha

c m phng theo t tng chung ca m hnh SOGREAH. Cc khu cha nc

v cc ng rung trao i nc vi sng v trao i nc vi nhau qua cc trn hay

cng iu tit. Do , m hnh chia cc khu cha v cc ng rung thnh hai loi

chnh. Loi kn trao i nc vi sng qua cng iu tit, loi h trao i nc vi

sng qua trn mt hay trc tip gn vi sng nh cc khu cha thng thng.

39

M hnh VRSAP cng xt n s gia nhp ca ma trong tnh ton thy lc

dng chy trong cc h thng sng khi din ton l hay tnh tiu nc cho h thng

thy nng. M hnh c ng xt n kh nng truyn mn trn h thng sng v ng

rung. S tnh trong VRSAP l s sai phn n li ch nht c xt n trng

s i vi cc bc sai phn theo thi gian t v khng gian x.

M hnh VRSAP ph hp vi iu kin Vit Nam, c th s dng :

+ Tnh ton v tm ra quy lut thay i ca lu lng Q v mc nc Z ti

tng mt ct trn h thng sng v cha k c vng b nh hng ca thy triu.

+ Gii bi ton tiu ng, thot l v cp nc trn cc h thng cng trnh

thy li vng ng bng v ven bin.

+ Lp cc phng n quy hoch qun l v khai thc thy li trn lu vc

sng ln nh v cc h thng cng trnh thy li.

+ Tnh truyn triu v truyn mn trn cc h thng sng v.v...

M hnh VRSAP l m hnh m ngun m, nn t nhiu tc gi ci tin

m hnh c th tnh c truyn ti ph sa, tnh tiu thot nc th. Cc loi

m hnh ton ny hin cng ang c ng dng nc ta v cho kt qu tt. Mt

s ng dng ca m hnh cho h thng sng Hng, sng Thi Bnh, sng C, sng

Nht L, sng Hng, sng Thu Bn, sng Cu Long... t cc kt qu tin cy.

M hnh VRSAP ng dng rt c hiu qu i vi vic tnh ton thy lc ti, tiu

cc h thng thy nng, quy hoch v lp cc d n qun l, khai thc h thng

thy nng, tnh ton quy m cc cng trnh trn h thng, qun l lu vc v ti

nguyn nc ta.

Chuyn ng ca cht lng trong lng dn h c th m t bng h phng

trnh Saint - Venant. Trong m hnh VRSAP, h phng trnh Saint - Venant ca

dng chy mt chiu l h phng trnh thy ng lc vit cho dng chy mt

chiu trong lng dn h:

Phng trnh lin tc:

Phng trnh ng lc:

40

( )

M hnh VRSAP ch gii quyt c bi ton m dng chy c s

(tc l dng chy m).

Hai h phng trnh trn l h phng trnh Saint Venant c hai n s l :

+ Q=Q(x,t) l lu lng trung bnh mt ct ph thuc vo trc x v thi im t.

+ Z=Z(x,t) l mt nc ti mt ct x, thi im t.

Trong , bin khng gian x v thi gian t l hai bin c lp.

ngha ca cc i lng trong h phng trnh Saint - Venant:

Bc - chiu rng ton mt ct ngang sng, Bc = B + Bb;

B - chiu rng lng sng;

Bb - chiu rng bi sng;

q - lu lng dng chy gia nhp trn mt n v di theo on sng;

J - dc thy lc, c tnh theo cng thc tn tht ca dng chy n nh,

R- l bn knh thy lc,

A - din tch mt ct t;

P - chu vi t;

C - h s Chezy. Nu tnh theo cng thc Manning, C=

R

1/ 6

n - h s nhm Manning;

h s ng lng;

h s sa cha ng nng

Tuy nhin m hnh VRSAP khng phi l mt m hnh thng mi, m l

m hnh c m ngun m ch thch hp vi nhng ngi c s am hiu su rng v

kin thc m hnh; cn i vi cng tc d bo, cnh bo nhanh cho mt khu vc

c th, nht l khu vc min Trung th m hnh t ra cha ph hp.

41

M hnh KOD-01 v KOD-02 ca GS.TSKH Nguyn n Nin dng tnh

thy lc dng chy h mt v hai chiu trn h thng sng c cng trnh iu tit v

ng rung. H phng trnh Saint - Venant c s dng dng rt gn. S

tnh l s hin tam gic hn hp. S tnh cho php gii cc bi ton dng

khng n nh mt chiu nh tnh ton truyn triu, truyn l, phn phi nc, tiu

nc... cho mng li sng, cha, cng trnh iu tit vi phc tp bt k. S

tnh c th phc v tnh ton quy hoch d bo l v phn phi nc, phc v

thit k v qun l h thng knh ti tiu v cc mc ch khc trong cng tc thy

li nc ta.

M hnh WENDY: do Vin thy lc H Lan (DELFT) xy dng cho php

tnh thy lc dng chy h, xi lan truyn, chuyn ti ph sa v xm nhp mn.

M hnh HEC-RAS: do Trung tm Thy vn k thut qun i Hoa K

(Hydrologic Engineering Center of US Army Corps of Engineers) xy dng. M

hnh c u im l cho kt qu r rng, c s mng li sng, mt ct ca tng

nt sng. Cc quan h Q ~ t v Z ~ t c trnh by dng biu bng v th,

ng mt nc trong sng c m t chi tit. M hnh HEC-RAS l m hnh tnh

dng chy mt chiu ca h thng sng, dng chy trong sng c m t bng h

phng trnh Saint - Venant y v c xy dng theo s sai phn n c xt

n trng s i vi cc bc sai phn theo thi gian t v chiu dc theo dng chy x.

M hnh c hn ch l khng xt n lng ma ri xung cc khu cha sau gia

nhp dng chy. Trong nhng nm gn y HEC-RAS c s dng nc ta

trong cc nghin cu v l, c bit l trong cng tc o to ti cc trng i hc.

Dng chy trong sng thin nhin c coi l dng khng n nh bin i

chm chy mt chiu, thay i theo khng gian v thi gian. Cc yu t c m t

bng h phng trnh Saint - Venant, gm phng trnh lin tc v phng trnh

ng lc. H phng trnh Saint - Venant trong m hnh ny c dng:

Phng trnh lin tc:

42

Phng trnh ng lc:

gii h gm hai phng trnh lin tc (2.3) v ng lc (2.4) dng

phng php sai phn hu hn thay cc o hm ring bng t s cc sai phn.

Ging nh m hnh VRSAP, trong m hnh HEC-RAS cng s dng s n (li

sai phn ch nht) gii h phng trnh Saint-Venant.

H m hnh MIKE: do vin thy lc an Mch (DHI) xy dng c tch

hp rt nhiu cc cng c mnh, c th gii quyt cc bi ton c bn trong lnh vc

ti nguyn nc. Tuy nhin y l m hnh thng mi, ph bn quyn rt cao nn

khng phi c quan no cng c iu kin s dng.

MIKE 11: l m hnh mt chiu trn knh h, bi ven sng, vng ngp l,

trn sng knh c kt hp m phng cc rung m kt qu thy lc trong cc rung

l gi hai chiu. MIKE 11 c mt s u im ni tri so vi cc m hnh nh:

i. Lin kt vi GIS;

ii. Kt ni vi cc m hnh thnh phn khc ca b MIKE v d m hnh ma ro

- dng chy NAM, m hnh thy ng lc hc 2 chiu MIKE 21, m hnh dng chy

nc di t, dng chy trn b mt v dng bc thot hi thm ph (MIKE SHE);

iii. Tnh ton chuyn ti cht khuych tn;

iv. Vn hnh cng trnh;

v. Tnh ton qu trnh ph dng;

H phng trnh s dng trong m hnh l h phng trnh Saint - Venant

mt chiu khng gian, vi mc ch tm quy lut din bin ca mc nc v lu

lng dc theo chiu di sng hoc knh dn v theo thi gian.

M hnh MIKE 11 c ng dng rng ri ti Vit Nam v trn phm vi

ton th gii. Tuy nhin MIKE 11 khng c kh nng m phng trn bi nn trong

cc bi ton ngp lt MIKE 11 cha m phng mt cch y qu trnh nc

dng t sng vo trn bi vo rung v ngc li ci thin vn ny b MIKE

c thm m hnh thy lc hai chiu MIKE 21 v b kt ni MIKE FLOOD.

43

MIKE 21 & MIKE FLOOD: l m hnh thy ng lc hc dng chy 2 chiu

trn vng ngp l c ng dng tnh ton rng ri ti Vit Nam v trn phm vi

ton th gii. M hnh MIKE 21 HD l m hnh thy ng lc hc m phng mc

nc v dng chy trn sng, vng ca sng vnh v ven bin. M hnh m phng

dng chy khng n nh hai chiu ngang i vi mt lp dng chy.

Mike 21 HD c th m hnh ha dng chy trn vi nhiu iu kin c

tnh n, gao gm:

i. Ngp v tiu nc cho vng trn

ii. Trn b

iii. Dng chy qua cng trnh thy li

iv. Thy triu

v. Nc dng do ma bo

Phng php m phng bao gm phng trnh lin tc kt hp vi phng

trnh ng lng m t s bin i ca mc nc v lu lng. Li tnh ton s

dng trong m hnh l li hnh ch nht.

Tuy nhin MIKE 21 nu c lp cng kh c th m phng tt qu trnh

ngp lt ti mt lu vc sng vi cc iu kin ngp thp. c th tn dng tt

cc u im v hn ch nhng khuyt im ca c hai m hnh mt chiu v hai

chiu trn, DHI cho ra i mt cng c nhm tch hp c hai m hnh trn; l

cng c MIKE FLOOD.

MIKE FLOOD l mt cng c tng hp cho vic nghin cu cc ng dng

v vng bi trn v cc nghin cu v dng nc do ma bo. Ngoi ra, MIKE

FLOOD cn c th nghin cu v tiu thot nc th, cc hin tng v p,

thit k cng trnh thy li v tnh ton cho cc vng sng ln.

MIKE FLOOD c s dng khi cn c s m t hai chiu mt s khu vc

(MIKE 21) v ti nhng ni cn kt hp m hnh mt chiu (MIKE 11). Trng

hp cn kt ni mt chiu v hai chiu l khi cn c mt m hnh vn tc chi tit

cc b (MIKE 21) trong khi thay i dng chy sng c iu tit bi cc cng

trnh phc tp (ca van, cng iu tit, cc cng trnh thy li c bit) m phng

44

theo m hnh MIKE 11. Khi m hnh mt chiu MIKE 11 c th cung cp iu

kin bin cho m hnh MIKE 21 v ngc li.

B m hnh MIKE 11 v MIKE 11-GIS ca vin thy lc an mch (DHI)

s dng xy dng bn ngp lt cho vng h lu sng. MIKE 11-GIS l b

cng c mnh trong trnh by v biu din v mt khng gian v thch hp cng

ngh m hnh bi ngp v sng ca MIKE 11 cng vi kh nng phn tch khng

gian ca h thng tin a l trn mi trng ARCGIS 9.1.

MIKE 11-GIS c th m phng din ngp ln nht, nh nht hay din bin t

lc nc ln cho ti lc nc xung trong mt trn l. chnh xc ca kt qu

tnh t m hnh v thi gian tnh ton ph thuc rt nhiu vo chnh xc ca

DEM. N cho bit din ngp v su tng ng tng vng nhng khng xc nh

c hng dng chy trn .

M hnh MIKE SHE: m hnh ton vt l thng s phn b m phng h

thng tng hp dng chy mt, dng chy ngm lu vc sng. M phng bin i

v lng v cht h thng ti nguyn nc. Bao gm dng chy trong lng dn,

dng chy trn b mt, dng chy ngm tng khng p, dng chy ngm tng c p,

dng chy tng ngm chuyn tip gia tng c p v tng khng p, bc thot hi t

tng thm ph, truyn cht, vn chuyn bn ct. ng dng thc tin: c ng

dng tnh ton rng ri trn phm vi ton th gii. Vit Nam MIKE SHE c

ng dng m phng dng h thng dng chy ngm, mt lu vc.

Qua thc t vic s dng cc m hnh thy vn, thy lc hin nay trn th gii

v ti Vit Nam; vi mong mun m phng mt cch chnh xc nht qu trnh ngp

lt trong khu vc nghin cu, tc gi nhn thy b m hnh MIKE-FLOOD ca

Vin thy lc H Lan c th p ng c yu cu xy dng bn ngp lt cho

khu vc nghin cu vi cc l do sau:

B m hnh MIKE bao gm: m hnh thy vn MIKE NAM, dng

tnh ton cc bin u vo cho m hnh thy lc 1 chiu MIKE 11, cng nh bin

gia nhp khu gia cho m hnh thy lc hai chiu MIKE 21. M hnh thy lc mt

chiu MIKE 11 m phng dng chy mt chiu trong sng v m hnh hai chiu

MIKE 21 m phng dng chy hai chiu ngang bi trn. B m hnh ny rt ph

45

hp m phng ngp lt h lu lu vc sng Ba ni thng xuyn xy ra cc

trn l t nh n ln.

iu kin s liu o c trong khu vc hn ch do nhiu nguyn nhn khc

nhau nn vic s dng m hnh MIKE-NAM tnh ton dng chy t ma

lm bin u vo cho m hnh thy lc l cn thit.

M hnh MIKE FLOOD l mt cng c tng hp cho vic nghin cu cc

ng dng v vng bi trn ph hp cho vng trng nghin cu, c th th

hin c c mc ngp lt ln tc v hng dng chy l trong vng

ngp lt.

M hnh EFDC

M hnh EFDC (Environmental Fluid Dynamics Code) l mt phn mm m

hnh ton c kh nng d bo, tnh ton v m phng cc qu trnh dng chy, lan

truyn c tnh n cc qu trnh sinh - a - ha trong sng, h, h cha, cc vng

ca sng M hnh c c quan bo v mi trng M US EPA pht trin t

nhng nm 1980 n 1994 c cc nh khoa hc vin khoa hc bin Virgina tip

tc xy dng. M hnh c xy dng da trn cc phng trnh ng lc, nguyn

tc bo ton khi lng v bo ton th tch. M hnh l m hnh a chiu (1 chiu,

2 chiu, 3 chiu) nn c kh nng t chnh xc cao trong vic m hnh ha cc

h thng m ly, t ngp nc, kim sot dng chy, cc dng sinh song gn b

v cc qu trnh vn chuyn trm tch. [3]

2.2.3. La chn m hnh din ton

Vi nhng c trng, tnh nng, ca cc m hnh ton thy vn, thy lc

trn, ng thi qua tnh hnh s dng c th cc m hnh ny hin nay trn th gii

cng nh Vit Nam. Vi mong mun m phng mt cch chnh xc nht qu trnh

tp trung nc, din bin qu trnh ma ro - dng chy v c bit l m phng

chnh xc qu trnh ngp lt trong vng nghin cu tc gi nhn thy phn mm

EFDC c th p ng c yu cu nh gi mc ngp lt cho mt h thng.

La chn m hnh thy vn :

Do iu kin s liu thc o u vo cho m hnh, c bit l s liu ma

cng nh s liu gia nhp khu gia ca mng sng nghin cu l rt hn ch c v

46

s lng trm o v ch o. Chnh v vy, vic s dng MIKE - NAM tnh

ton dng chy t ma lm bin u vo cho m hnh thy lc l rt cn thit v

ph hp.

La chn m hnh thy lc:

Vi mc ch ca ti lun vn l xy dng bn ngp lt, nh gi mc

ngp lt trn mt khu vc. Yu cu t ra l phi tnh ton, m phng c

lng v din ngp lt trn ton b khu vc . Do vy cn phi s dng m hnh

c kh nng m phng dng chy 2 chiu, dng chy trn trn rung ng trong

khi thi gian m phng khng ln. Trong ni dung lun vn ny tc gi la chn

v s dng phn mm EFDC xc nh mc ngp lt cho vng h lu sng Ba

tnh Ph Yn.

2.2.4. C s l thuyt ca m hnh

M hnh ma dng chy MIKE-NAM

Gii thiu m hnh NAM

tnh ton qu trnh hnh thnh dng chy t ma trn cc lu vc sng th

m hnh NAM l mt cng c kh mnh. M hnh quan nim lu vc l cc b

cha xp chng nhau, trong mi b cha c trng cho mt mi trng c cha

cc yu t gy nh hng n qu trnh hnh thnh dng chy trn lu vc, v cc

b cha nc lin kt vi nhau bng cc biu thc ton hc. Trong m hnh NAM,

mi mt lu vc c xem nh mt n v x l vi cc thng s l i din cho

cc gi tr c trung bnh ha trn ton lu vc. M hnh NAM tnh ton qu trnh

ma dng chy theo cch tnh lin tc hm lng m trong cc b cha ring bit

tng tc ln nhau (hnh 6). M hnh NAM c tng cng 19 thng s gm cc

thng s v dng chy mt, thng s bc hi, thng s ti... V theo thc t tnh

ton cho thy ch c 5 thng s chnh nh hng n qu trnh hnh thnh dng

chy l Umax; Lmax; CK1,2; CQOF; CQIF. [2]

47

Hnh 6. Cu trc m hnh NAM [2]

u vo ca m hnh NAM

M hnh NAM l mt m hnh ma ro - dng chy nn d liu u vo ca

m hnh s l s liu ma gi hoc ma ngy thc o ca trm kh tng v s liu

bc hi trung bnh cng vi din tch ca lu vc m ma ri xung.

u ra ca m hnh

Kt qu ca m hnh c biu din qua ng qu trnh lu lng

theo thi gian (thi gian tnh bng gi hoc bng ngy ty thuc vo thi gian ca

ma thc o).

48

M hnh EFDC [7, 8]

1. gii thiu chung v m hnh

M hnh EFDC (Environmental Fluid Dynamics Code) l mt phn mm m

hnh ton c kh nng d bo, tnh ton v m phng cc qu trnh dng chy, lan

truyn c tnh n cc qu trnh sinh - a - ha trong sng, h, h cha, cc vng

ca sng M hnh c c quan bo v mi trng M US EPA pht trin t

nhng nm 1980 n 1994 c cc nh khoa hc vin khoa hc bin Virgina tip

tc xy dng. M hnh c xy dng da trn cc phng trnh ng lc, nguyn

tc bo ton khi lng v bo ton th tch. M hnh l m hnh a chiu (1 chiu,

2 chiu, 3 chiu) nn c kh nng t chnh xc cao trong vic m hnh ha cc

h thng m ly, t ngp nc, kim sot dng chy, cc dng sinh sng gn b

v cc qu trnh vn chuyn trm tch.

2. Cu trc m hnh

M hnh EFDC gm 4 modul chnh (hnh 7)

i. M hnh thy ng lc hc

ii. M hnh cht lng nc

iii. M hnh vn chuyn trm tch

iv. M hnh lan truyn, phn hy cc cht c trong mi trng nc mt

Hnh 7. Cu trc c bn m hnh EFDC [7, 10]

M hnh thy ng lc hc EFDC gm 6 modul lan truyn vn chuyn, bao

gm: ng lc hc, mu sc, nhit , mn.(hnh 8)

M hnh EFDC

M hnh thy ng lc hc

MH cht lng nc

MH vn chuyn bn ct

MH lan truyn cht c

49

Hnh 8. Cu trc m hnh thy ng lc hc EFDC [7, 10]

3. Mt s c im tnh nng ca phn mm [7, 10]

Giao din s dng: giao din s dng m hnh EFDC cu trc trn tp hp

cc phn mn x l ring . Ta c th chnh sa tng phn ring bit m khng nh

hng n kt qu ca cc phn khc. Tuy l x l ring bit nhng gia cc phn

ny c tnh hp to nn mt s thng nht trong m hnh. Giao din ny m bo

tnh kh chuyn gia cc phn my tnh v cho php ngi s dng m hnh c th

d dng qun l cc s liu u vo ca m hnh ny. V vy vic chnh sa cc tp

s liu u vo ny l tng i d dng.

c bit ca s xem m hnh cho ta bit c cc thng s ca tng im

li trn min m hnh: kch thc li, cao trnh a hnh, mc nc, su ct

nc, h s nhm hn na m hnh cho php iu chnh tt c cc thng s tng

im li ngay trn giao din min m hnh.

Phn mm tin x l: trc giai on tnh ton m phng phn mm m hnh

EFDC c b m tin x l to li vi tn gi GEFDC. B m tin x l ny cho

php xy dng li m hnh, a vo cc s liu o c su cng nh cc thng

s ban u nh cao mt nc, mt bn ct cho c min m hnh. Qua qu

trnh x l ca b m tin x l ny, cc file s liu u vo v cc thng s ban

u ca ng mt nc cng nh cc iu kin bin ca m hnh c to ra.

c th m phng mt cch ph hp nht vng nghin cu b m tin x l ca phn

mm EFDC c kh nng cho php to ra cc li ta m hnh dng Cc hoc

dng li cong trc giao.

MH thy ng lc hc

ng lc hc ( vn tc, cao..)

Mu sc Nhit mn Lan truyn

cht

Vn chuyn bn ct

50

Trong phn tin x l ny m hnh cho php la chn cc cch to ra li

cho lu vc nghin cu nh sau:

Cartesian: to li dng Cc, min li c to nn bi cc phn t li dng

vung kch thc dx, dy. Vi loi li ny ta c nhiu cch la chn loi khc

nhau min nghin cu l ph hp nht.

+ Uniform Grid, kiu ny to li dng hnh ch nht cho vng nghin cu khi bit

ta khng ch ca vng to li v kch thc ca mi . y cc li c

kch thc l nh nhau, s lng li trn ton min c m hnh t ng tnh

ton ra trn c s s liu nhp vo (hnh 9).

Hnh 9. Min li dng Uniform Grid

+ Expanding Grid, khc vi Uniform Grid kiu to li ny to ra cc li c

kch thc khc nhau. Kiu ny cho php to ra li vi cc li nh dn cc

khu vc min to li c dng khng ng nht. Vi cch to li ny ngi s

dng phi khai bo kch thc ln nht v nh nht ca li mun to trong m

hnh v ta im m ti li c kch thc l hp nht (hnh 10)

51

Hnh 10. Min m hnh to dng Expanding Grid

+ Curvilinear (EFDC) To li dng cong trc giao. Cc phn t li l cc cong

theo chiu dc sng. Vi kiu to li ny i hi s liu nhiu hn so vi

Cartesian. Tuy nhin loi ny ph hp hn khi nghin cu nhng khu vc c dng

cong. Trong kiu ny cng c nhiu ty chn s dng:

+ Centerline Dominant: ty chn ny cho php ngi s dng to ra li cong c

tnh cht tp trung dng ch lu ngha l cc ng cong chia dc sng c to

ra mau dn t hai bin vo dng chnh (hnh11)

52

Hnh 11. Min m hnh to dng Centerline Dominant

+ Equi-Distance Widths: ty chn ny xy dng li m hnh cho php ngi s

dng quyt nh s phn t ngang sng (tng ng vi dng tnh ton). Ch cn

nhp s phn t mun to theo chin ngang sng th m hnh t xc nh b rng

ca li sao cho va vn vi chiu rng ca sng.

Hnh 12. Li cong c to theo ty chn Equi-Distance Widths

53

+ Uniform (Ficxed): ty chn ny xy dng ln li m hnh vi b rng cc

phn t do ta quyt nh. Khi a b rng li vo th m hnh xy dng min

li sao cho ph hp nht vi chiu rng sng. Tuy nhin min m hnh trong

trng hp ny ch phn nh gn ng hnh chiu rng sng.

Import Grid: phng php ny cho php xy dng li trong m hnh bng cch

a file d liu s ha ca min m hnh di dng ECOMSED.

Tnh ton thi gian chy m hnh: m hnh EFDC c kh nng tnh ton chun on

thi gian chy m hnh ti u t nhng d liu, thng tin u vo cho ngi s

dng m hnh thit lp. Cc d tnh bao gm s lng bc thi gian ti a (CFL),

thi gian v v tr cc im c su m, cc kim tra v cn bng th tch v khi

lng kh nng ny gip ngi dng c th d dng xc nh bc thi gian ti

u m hnh t kt qu tt (hnh 13).

Hnh 13. Bng tnh thi gian s dng m hnh [7]

Truy sut kt qu: kt qu m hnh c hin th cho tng im li v ti mi

bc thi gian m ngi s dng chn. Kt qu m hnh c th c truy xut

di dng cc file nh trn c hin th cc c tnh cn xem xt. Ngoi kt qu

dng file nh m hnh cho php xut d liu di dng Tecplot. Kh nng xut ra

dng Tecplot gip cho vic x l kt qu c thc hin tt hn.

54

4. C s l thuyt m hnh EFDC [7, 9, 10]

Thy ng lc ca m hnh EFDC da trn h phng trnh thy tnh 3

chiu m phng theo phng thng ng v phng nm ngang trc giao cong.

Phng trnh ng lng l:

- Theo phng X:

- Theo phng Y:

Phng trnh lin tc 3 chiu trong h ta ngang trc giao cong theo

phng thng ng l:

Trong a mo th phng trnh lin tc ca dng nc lin quan ti phng

trnh cn bng bn ct y:

Trong :

x, y: l ta nm ngang trc giao

u, v: tng ng l vn tc ngang trong li ta cong trc giao x, y

55

mx, my : h s t l theo trc x, y

H: su ct nc

z: ta cao thng ng

w: vn tc thng ng

p: thnh phn p sut

f: thng s lc Coriolit

Av: ri thng ng hoc tnh nht xoy

Qss: lu lng bn ct n

Qsw: lu lng nc n

QGW: lu lng nc ngm chy vo di y lp bn ct

B: tng chiu dy lp bn ct y (lp bn ct c kh nng b xi)

QH: gm lng tr ban u, lng nc do ma ri xung, lng dng bn gia

nhp v chy ra khi on knh.

y h s ri lon nht lin quan n ng sut tip, p sut kh ng lc

hc lin quan n mt nc. p sut ng lc nc c vit bi phng trnh

sau:

Cao trnh y sng c xc nh bi phng trnh:

Vi l cao trnh y tnh ton vn chuyn bn ct y

Cao trnh mt nc c xc nh nh sau:

5. Cch gii quyt bi ton trong m hnh EFDC

M hnh EFDC gii quyt c cc phng trnh thy tnh theo chiu ng,

mt nc thong, chy ri trong khng gian 3 chiu i vi dng chy c t trng

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thay i. n cng gii quyt c phng trnh lan truyn vt cht i vi trng

hp truyn nhit ng ri theo chiu dc, lan truyn mn v nhit. M hnh EFDC

s dng h ta bin dng hoc sigma thng ng vi h ta Cc, hay cong

trc giao.

T phng trnh (10) v (12) ta c :

Thay 5 vo 10 ta c phng trnh

gii phng trnh ng lng m hnh s dng phng php sai phn

hu hn khng gian chnh xc bc 2. Vic kt hp thi gian trong m hnh s dng

phng php sai phn hu hn 3 cp thi gian chnh xc bc hai vi kiu tch ring

qu trnh chuyn ng do cc yu t chnh trong cc lp nc to ra v cc qu

trnh do cc yu t trn b mt nc (sng, gi..). Kiu ngoi l bn n v tnh ton

ng thi trng cao hai chiu bng bc gradient lin hp c iu kin. Kiu

ngoi kt thc khi tnh ton vn tc trung bnh theo su. Cn kiu trong c

thc hin ng thi vi kiu ngoi v hon ton ch lin quan n khuch tn theo

chiu thng ng do ng sut ct v ct do dng chy.

M hnh ng dng s gii theo khng gian v thi gian c chnh xc

bc 2 theo s bc gii phn on bo ton khi lng i vi cc phng trnh

lan truyn mn, truyn nhit, cht l lng, cht lng nc v cc cht nhim

trong nc.

Vi phng trnh (15) m hnh gii bng cch s dng moduyn gm 2 bc

tnh ton. Bc th nht gii theo phng php ng lc vi s n nh sau:

y l bc thi gian tnh ton gia n v n+1 v n c vit nh sau:

Kt hp phng trnh ca hai bc tnh ton trn ta c phng trnh:

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Khi chiu su mc nc c tnh ton theo phng trnh:

M hnh EFDC gii cc phng trnh thy tnh theo phng thng ng, mt

thong nc, chy ri khng gian 3 chiu i vi dng chy c t trng thay i.

EFDC s dng h ta bin dng hoc sigma thng ng, h ta Cc, h ta

cong trc giao. gii cc phng trnh ng lng EFDC s dng phng

php sai phn hu hn khng gian chnh xc bc 2. Vic kt hp thi gian trong m

hnh s dng phng php sai phn hu hn 3 cp thi gian chnh xc bc 2 vi

kiu tch ring qu trnh chuyn ng do cc yu t chnh trong cc lp nc to ra

(internal model kiu trong) v qu trnh do cc yu t trn b mt nc nh sng,

gi to ra (external model - kiu ngoi). Kiu ngoi l kiu bn n v tnh ton ng

thi trng cao hai chiu bng bc gradient lin hp c iu kin. Kiu ngoi

kt thc khi tnh ton vn tc trung bnh theo su (s dng mc nc mi c

tnh). Kiu trong c thc hin ng thi vi kiu ngoi v ch hon ton lin quan

n khuych tn theo chiu thng ng do ng sut ct v ct theo dng chy. [9]

6. Qun l cc file trong model

M hnh EFDC s dng tn file ty theo thng tin m file lu tr. Trong

file iu khin chnh cho mi ng dng m hnh l file EFDC.INP, trong file ny c

cu trc nhiu phn mi phn cha ng nhng i tng c bn ging nhau.

Cc file u vo m hnh c s dng phn ra cc loi:

- File m t khng gian: cell.inp, dxdy.inp, lxly.inp

- File m t chui thi gian: qser.inp, wser.inp

- File iu kin ban u;

- Cc file x l: Qctl.inp, gwater.inp, wavebl.inp, wavesx.inp;

Cc file u ra trong m hnh

- SURFCON.OUT: file cha su ct nc;

- VELVECH.OUT: file cha trng lu tc;

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- BED_TOP.OUT: file cha thng tin vt cht trn b mt;

- BED_LAY.OUT: file cha d liu vt cht y ca mi lp;

Phng php sai phn hu hn ng dng cho gii bi ton

m phng, tnh ton din bin dng chy trong sng v vng ca sng th

cng vic ny ng ngha vi vic phi gii h phng trnh ng lng theo cc

phng ca m hnh. Cc nh khoa hc nghin cu v a ra cc cch gii khc

nhau trong c phng php gii bng phng php gii tch v bng phng

php s.

V phng php gii tch: vi phng php ny th bi ton gii c v tm

c nghim chnh xc, nhng n ch c th p dng c trong mt s trng hp

nht nh v iu kin bin nh: thng phi n gin v hnh dng, khng thay i

theo thi gian tnh ton, mi trng l ng nht c ngha l cc thng s ca lu

vc tnh ton l khng thay i theo khng gian v thi gian. Nhng trong thc t

th cc yu t trn u c th thay i v khi c mt trong cc yu t ny thay i

th bi ton khng th gii c do khng tm c nghim.

khc phc c nhng hn ch ca phng php gii tch v khng phi

bi ton no cng tm c nghim chnh xc thay vo cc nh khoa hc

nghin cu bin php tm ra nghim gn ng ca bi ton bng phng php s,

y l phng php gii gn ng. Nghim ca bi ton c th l nghim xp x vi

nghim chnh xc hoc n c th biu din bng nhng biu thc ton hc ng vi

cc bin ban u gii ra nghim kh st so vi nghim gii tch.

C nhiu phng php s khc nhau nh phng php sai phn hu hn,

phng php ng c trng, phng php phn t bin, phng php phn t

hu hn trong phng php sai phn hu hn l phng php c s dng

kh ph bin gii h phng trnh ng lng gip gii quyt bi ton din bin

dng sng v vng ca sng kh ph bin v hu hiu. y model EFDC s dng

phng php sai phn hu hn gii phng trnh ng lng do bi ton t ra.

Cc h phng trnh ng lc theo cc phng nh trnh by trong phn

c s l thuyt ca m hnh EFDC u l cc phng trnh vi phn o hm ring

ca mc nc, lu tc theo cc phng ngang sng, dc chiu di sng, theo chiu

59

su dng chy v theo thi gian. o hm ca cc hm s ny theo khng gian v

thi gian c th c th hin bng cc cng thc gn ng. Nu ta chia min m

hnh mt li cc nt, vit gi tr gn ng ca cc o hm ca cc bin s cho

mi im li, thay o hm gn ng ny vo cc phng trnh vi phn o hm

ring ta s c h phng trnh v gii h phng trnh ny ta c c nghim ca

cc bin s cn tm. y l c s ca phng php sai phn hu hn.

Gi s ta cho cc bin nh mc nc, lu tc c k hiu chung l C, ta

xc nh o hm gn ng ca C nh sau:

Theo thuyt Taylor v s d ta c th vit cho im c ta

theo hng x ca ta cong:

Vi vi l mt s c gi tr trong khong 0 1

Ta s s dng thay cho C( ) t ta c:

Gi

suy ra:

vi

bui minh hoa

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