DSpace at VNU: Simulation of changes of red river system profile using hec-6 model (Da river reach from Hoa Binh to Thao-Da confluence and red river reach from Thao-Da confluence to Ha Noi)

VNU JO U R NAL 0 F S C IE N C E , Nat , Sci.. & íe c h , T XIX, N ọ l. 2003

SIMƯLATION O F C H A N G E S OF RED RIVER S Y ST E M P R O F IL E
ƯS1NG HEC-6 M ODEL
(Da r i v e r r e a c h from Hoa B in h to T h a o - D a c o n A u e n c e
and Red r i v e r r e a c h from T h a o -D a c o n A u e n c e to Ha N o i)
N g u ye n T h i N ga

D epartm ent ofHyd.ro Meteorology a n d Occanoỉogy
Collcge o f Science, V N U
A b s tr n c t . ỉ loa B in h re s e rv o ir was b u ilt in
ìm p o rta n t

d u tic s th a t

are g c n c ra tio n

ỉ)a r iv c r to c a r r y o u t tw o top

e le c tr ic ity

and

flo o d

p re v e n tio n

for

ìow ]ands. S incc o p o ra tio n , Hoa B in h re s c rv o ir has bcen b r in g in g about v c ry big
uscíuỉnesses,

but

also

has

bcen

c a u sin g

u n fa v o u ra b lo

ch a n g e s,

such

as

d e p o sitio n in th e ro s e rv o ir, local scour in lo w e r o f th o dam and (lis s e m in a te d
scour to w a rd s lovvcr. K s tim a tio n , s im u la tio n and p re d ic tio n th c s c rh a n g e s to
lim it dam ages a lw a y s are pressing and necessary p ro b le m s.

M a th o m a tic a l

models a rc e ffe c tiv e and eco n o m ir tools to solvp these p ro b lo in s.
I1EC-G is a o n o -đ im iỉn s io n a l m ovable b o u n d a ry opon c h a n n e l flo w n u m tíric a l
m odcl dosigned to s im u la te and p r iid ic t changcs in r iv o r p ro íìlc s ro K u ltin g from
scour a ru l/o r d o p o s ilio n ovcr m o d c ra tc tim c pcriods.
T liis p a p cr s tu d ie s and a p p ỉio s 11KC-G

lo s im u la tc ch a n g e s o f D a r iv o r

p ro lìlc (reach from ỉ loa Binh t.o Thao-Da roníluencc) and Red riv e r p ro íílc
(reach from T h a o -D u conílu ence to ll a N oi). T h o r c s u lts (>f m odel c a lib r a tio n and
v e rific a tio n show th rtt IIE C -6 m odel vvith th o selected sot o f o p tim a l p a ra m e te rs
can use to s im u lu to changes o f Red r iv c r system p ro íìlc in th o ĩu tu ro w ith
accoptahỉo accuracy. T h e rc s u lts o f Red r iv c r bed chang!! s im u la tio n u s in g the
s o i o f solccteđ p a ra m e to rs ; in it ia l c o n d itio n is Red r iv e r bcul, w h ic h s u rv e y e d in
1992; u p stro a m co n ciitio n s a rc ty p ic a l discharge proccss (avcĩragc ty p o o f periocl
1988

1998) a i h y d ro lo g ic a l s ta tio n s : Hoa B in h , Y en B a i, V u Q u a n g , T h u o n g

C a t and đ o w n s tre a m c o n d itio n s is ty p ic a l 8tag<‘ proccss (a vo ra g o typcĩ o f p erio d
1988

1908) a t H a n o i h y d ro lo g ic a l s ta tio n show th a t:

Dcĩíìp scour phonom enons r c s u ltin g fro m re g u la tin g o ffí‘c:t C)f ỉ lo a B in h ro s o rv o ir
happon almost. o n ly in Da r iv o r and tra n s m it o n ly to T r u n g ỉ la s ta tio n .
Deep scour speẹđ rodur.es g ra ciu a lly. Thcíroĩorc, Da r iv tĩr

bcuỉ w ill

bceome

g ra d u a lly s ta b ility (to ro o s ta b lis h tho new b a lancc State).

1.

In tr o d u c tio n
Red r iv e r n e tv v o rk , th e second b ig g e s t r iv e r n e tw o r k in V ie tn a m , has been

p la y in g a s ig n iíic a n t ro le in th e s o c io -e co n o m ica l đ e v e lo p m e n t o f th e c o u n tr y . Red
r iv e r ris e s fro m a h e ig h t o f 20 00 m A M S L in V a n N a m ( C h in a ) . I t h a s a to ta l le n g th
o f 1126 k m . T h e b a s in o ccu p ie s to ta l a re a o f 165794 k r r r , in w h ic h 8 2 6 3 0 k m 2 lie s
w it h in in V ie tn a m . Recỉ r iv e r acts as w a te rw a y s a n d flo o d c o n v e y a n c e to p ro te c t th e
m o st N o rth e r n p a r t o f V ie tn a m fro m flo o d in g a n d in u n d a tio n . R ed r iv e r is c re a te d

68


S i r n u ỉ a t i o n o f c h a n g e s o f R e d r i v c r systcm .

69

fro m th re e m a in t r ib u t a r ie s : D a, T h a o and L o r iv e r s .

T h a o r iv e r o rig in a te s fro m

D a i L v L a k e in V a n N a m o f C h in a , vvhere i t is c a lle d N g u y e n r iv e r . F lo w in g d o w n
fro m th e a ỉt it u d e o f 2000 m A M S L in a N o rth w e s t-S o u th e a s t d ir e c tio n , i t e n te rs
V ie tn a m - C h in a b o r d e r a t L a o c a i p ro v in c e a n d is knovvn as T h a o r iv e r . I t has a to ta l
lo n g th o f 9 0 2 k m in w h ic h 332 k m v v ith in in V ie tn a m . F ro m Y en B a i to V ie t T r i, its
w iđ th s ra n g e fr o m

100 * 150 m in a ve rag e . R iv e rb a n k e le v a tio n s v a ry belovv th e

v a lu e s o f 20 m ; th e a v e ra g e d e p th is a ro u n d 5 m c o rre s p o n d in g w it h th e b a n k - fu ll

d is c h a rg e . T h e b e d s lo p e is a p p r o x im a te ly 1%U. T o ta l c a tc h m e n t a re a o f T h a o r iv e r
in s id e V ie tn a m is 12100 k n r . Da r iv e r ris e s fro m th e h ig h ly m o u n ta in o u s area in
th e

sa m e v i c in i t y

o f Thao

r iv e r ’s source.

R u n n in g

in

a N o rth w e s t-S o u th e a s t

(iire c tio n to H o a B in h , i t th e n c h a n g e s th e flo w in g d ir e c tio n to S o u th -N o rth , and
jo in ts T h a o r i v e r a t T r u n g H a , 12 k m u p s tre a m fro m V ie t T r i to w n . T h e to ta l le n g th
fro m b o rd e r t o V ie t T r i is a b o u t 5 7 0 k m w it h th e c a tc h m e n t a re a o f 2 6 8 0 0 k m 2. I t is
th e m o st im p o r t a n t t r ib u t a r y o f Red r iv e r n e tvvo rk a n d n o r m a lly c o n tr ib u te s up to
50% t o t a l in f lo w fo r R ed r iv e r . L o r iv e r also o rig in a te s fro m V a n N a m m o u n ta in s
a rea lo ca te d i n C h in a . Its to t a l le n g th is 470 k m ; th e c a tc h m e n t are a is 136900 k m 2.
In V ie tn a m t e r r i t o r y , th e b e d slo p e o f Lo r iv e r is 2 6 %0. In th e d o vvn stre a m course
fro m T u y en Q u a n g to V ie t T r i, it s v v id th is a b o u t 200 m a t flo w d e p th ra g in g fro m
1.5 to 3 m .

The

to t a l b a s in o f R ed r iv e r

n e tw o rk

c o n s id e re d

a t Son T a y

is

a p p ro x im a te ly 7 0 7 0 0 k m 2, o c c u p y in g 45% o f N o r th e r n p a r t a re a o f V ie tn a m . Red
riv e r c o n s id e re d fro m V ie t T r i, flo w s th ro u g h im p o r ta n t u rb a n c e n te rs , Son T a y
p ro v in c e a n d

H a n o i Capi ta l w h e re

th e

p o p u la tio n s

a re th e

h ig h e s t c o m p a rin g

th ro u g h o u t o u t th e n a tio n .
H oa B in h r e s e r v o ir , lo c a te d on D a r iv e r , 50 km fa r fro m T h a o -D a c o n ilu e n c e ,
was p u t in to

o p e r a tio n p a r t ia lly in

1990 a n d f u lly i n

1994. T h e e ffe cts o f th e

c o n s tru c tio n h a v e b e en seen o b v io u s ly in D a reach a fte r o f c lo s u re . P re v io u s ly , th e re
vvere som e re s e a rc h e s p r e d ic tin g th e im p a c t o f H oa B in h re s e rv o ir o n dovvnstream
m o rp h o lo g ic a l c o n c iitio n s in d e s ig n sta g c s . Each o f th e p re v io u s s u d ie s has m e rit
p o in ts

and

lim it a t io n s

due

to

th e

d e fic ie n c y

in

d a ta

fo r

v e r tic a tio n

and

c o m p u ta tio n a l m e th o d s .

In

re c e n t

y e a rs ,

d a ta

and

o b s e rv a tio n s

o b ta in e d

by

D e p a rtm e n t

of

M a n a g e m e n t & F lo o đ C o n tro l a n d R ese a rch In s t it u t e o f W a te r R esources sh o w th a t
th e d e g ra d a tio n o f D a riv e rb e đ h a s been p ro p a g a tin g to th e d o w n s tre a m . B a n k
erosions a n d a v u ls io n s d ư rin g re s e n t y e a rs in d o w n s tre a m h a ve been s e rio u s ly
o c c u rrin g a t

a la r m in g

ra te s . T h e

riv e rb e d s in o u te r b a n k

a re b e in g deepened

ra p id ly , th e flo w p a th a p p ro a c h in g th e r iv e r b a n k c r e a tin g s e rio u s a v u ls io n s in both
flood a n d t r a n s it io n a l sta g e s. T h is s itu a tio n th re a te n s th e s a fe ty o f n a tio n a l d ik e
system a n d v v ill c a u s e b ig d a m a g e s i f th e re is no in - tim e a c tio n to p re v e n t th e
erosion.


N g u y en T h i N g a

70

T h is reseach a p p lie s H E C -6 m o d e l to s im u la te a n d p re d ic t c h a n g e s o f Da r iv e r
p ro file s (re a c h fro m H oa B in h to T h a o -D a c o n flu e n c e ) a n d Red r iv e r p r o file s (re a ch
fro m T h a o -D a c o n ílu e n c e to H a N o i).

2. Theoretical basis o fm o v a b le boundary calculation of IIEC-6
HEC-6 is a one-dimensional movable boundary open channel flow numerical
m o d e l. I t is đ e s ig n e d b y U S A H y d ro lo g ic a l E n g in e e rin g C e n te r to s im u la te a n d
p re d ic t cha ng e s

in

r iv e r

p ro íĩle s

r e s u ltin g

fro m

scour

a n d /o r

d e p o s itio n

o ve r

m o d e ra te tim e p e rio d s ( ty p ic a lly m o n th s o r y e a rs , a lth r o u g h a p p lic a tio n s to s in g le
flo o d e v e n ts a re p o s s ib le ). H E C -6 used in

th is re s e a rc h

is H E C - 6 v e rs io n

4.1

p u b lis h e d in 1993.
In H E C -6 m ocỉel, a c o n tin u o u s flo w re co rd s is p a r titio n e d in t o a s e rie s o f
s te a d y flo w s o f v a r ia b le d is c h a rg e s and d u ra tio n s . F o r each flo w , a w a te r s u rfa c e
p ro íile is c a ỉc u la te d th e re b y p r o v id in g e n e rg y slope, v e lo c ity , d e p th , etc. a t each
cross s e c tio n . P o te n tia l s e d im e n t tr a n s p o r t ra te s a re th e n c o m p u te d a t each se ctio n .
T h ese ra te s , c o m b in e d w it h th e d u r a tio n o f th e flo w , p e r m it a v o lu m e tr ic a c c o u n tin g
o f s e d im e n t w it h in each re a c h T h e a m o u n t o f SCOU1* o r d e p o s itio n a t e a ch s e c tio n is
th e n c o m p u te d a n d th e cro ss s e c tio n a d ju s te d a c c o rd in g ly . T h e c o m p u ta tio n s th e n
proceed to th e n e x t flo w in th e sequence a n d th e c y c le is re p e a te d b e g in n in g vvith
th e u p d a te g e o m e try . T h e s e d im e n t c a lc u la tio n s a re p e rfo rm e d b y g r a in size fr a tio n

thereby allowing the sim ulation of hydraulic sorting and amoríng Features of HEC6 in c lu d e : c a p a b ility to a n a ly z e n e tw o rk s o f s t*e a m s , c h a n n e l d r e d g in g , v a rio u s

levee a n d e n c ro a c h m e n t a lte r n a tiv e s , a n d to use s e v e ra l m e th o d s fo r c o m p u ta tio n o f
s e d im e n t tr a n s p o r t ra te s .

2.1 T h e o r e tic a l l i a s i s f o r H y d r a u l i c C a l c u l a t io n s
T h e h y d r a u lic p a ra m e te rs needs to
c a lc u la te s e d im e n t tr a n s p o r t p o te n tia l a re
x—

v e lo c ity , d e p th , w id th a n d e n e rg y s lo p e -a ll

^ -1'
-Ị”
Croó* Un«
Wo4»' S«ftoc«

a re

c a lc u ỉa te d

u s in g

th e

ws?

o n e -đ im e n s io n a l

(E q u a tio n

2.1)

and

1

* 'v *

ws,

s ta n c ỉa rd -s te p

m e th o d to so lve th e c o n tin u itv e q u a tio n
and

°

l1ĩ s
9

o f w h ic h a re o b ta in e d fro m vvater s u rfa c e
p ro file c a lc u la tio n s . W a te r s u ría c e p ro fíle s

_

e n e rg y

e q u a tio n

th e

h y d r a u lic

0 o tu » T >

Figure 2.1

p a ra m e te rs a re c a lc u la te d a t each cross s e c tio n fo r succe ssive d is c h a rg e . F ig u re 2.1
show s a re p re s e n ta tio n o f th e te rm s in th e e n e rg y e q u a tio n .

ws,

2g

= w s ,+ ^ ỉ - + he.
2g

(2.1)


71

S i m u l a t i o n o f c h a riỊỊc s o f R e d r i v c r systcm .

vvhere: g = a c c e le ra tio n o f g r a v ity ; h c = e n e rg y loss; V j, V , = a v e ra g e v e lo c itie s (to ta l
d is c h a rg e - r t o t a l flo w a re a ) a t ends o f re a c h ; W S j, W S 2 = w a te r s u rĩa c e e le v a tio n s
a t e n d s o f re a c h a n d a | t a , = v e lo c ity d is tr ih u ta tio n c o e ffic ie n ts fo r flo w a t c n d s o f
re a ch .
T h e e n e rg y loss te r m , h,., in e q u a tio n 2 . 1 is com posed o f í r ic tio n loss, hf, and

fo rm losses, h ot as shovvn in e q u a tio n 2.2. O n ly c o n s tra c tio n a n d e x p a n s io n losses in
th e g e o m e tric fo rm loss te rm .
he = h i + h0 .

( 2 .2 )

To a p p r o x im a te th e tra n s v e rs e d is tr ib u tio n o f flo w , th e r iv e r is d iv id e d in to
s tr ip s h a v in g s im ila r h y d r a u lic p ro p e rtie s in th e d ir e c tio n o f flo w . Each cross
se c tio n is s u b d iv iđ e d in to p o rtio n s th a t a re re íe rre d to as s u b s e c tio n s . F r ic tio n , h f>
loss is c a lc u la te d as shovvn b e lo w :

(2.3)

hí

in w h ic h :

NSS

k;

w h e re : A j, Á ,

-

z

J 1

( ả 2 + Ạ j).

r 2 + r,"

2

->

1 49

2 l
J

(2.4)

LV2

",

= d o w n s tre a m a n d u p s tre a m area, re s p e c tiv e ly , o f th e flo w n o r m a l to

th e cro ss s e c tio n ; N S S = to ta l n u m b e r o f s u b s c c tio n s across each cro ss s e c tio n ;
le n g th * w e ig h te d

s u b s e c tio n

conveyance;

1^

=

le n g th

o f th e

j lh s t r ip

Kị =

b e tw e e n

s u b s e ctio n s; n = M a n n in g 's ro u g h n e s s c o e ffic ie n t; Q = w a te r d is c h a rg e a n d H ;. R 2

=

d o w n s tre a m «ancỉ u p s tr e a m h y d r a u lic ra d iu s , re s p e c tiv e lv .
E n e rg y

losses due to c o n s tra c tio n s and e x p a n s io n s a re c o m p u te d b y th e

fo llo w in g e q u a tio n :

h o = C ,.

a2VỈ

q,v,

2

(2.5)

2g

w te re : C( = lo»ss c o e ffic ie n t fo r e x p a n s io n o r c o n s tra c tiơ n .

2.2 T h e o r e t i c a l B a s is f o r S e d irn en t C a lc u la tio n s
S e d im e n t tr a n s p o r t ra te s a re c a ic u la te d fo r cach flo w in th e h y d ro g ra p h fo r
e a ;h g r a in s iz e . T h e tr a n s p o r t p o te n tia l is c a lc u la te d fo r each g r a in s iz e class i n th e
beJ as th o u g h t h a t a re c o m p ris e d

1 0 0 °o

o f th e bed m a te r ia l. T r a n s p o r t p o te n tia l is


72

N g u y en T h i N g a

th e n m u lt ip lie d b y th e ír a c tio n o f each size class p re s e n t in th e b e d a t t h a t tim e to
y ie ld

th e tr a n s p o r t c a p a c ity

fo r t h a t size class. T h e se ÍY a c tio n s o fte n ch a n g e

s ig n ific a n t ly d u r in g a tim e s te p , th e re fo re an ite r a c tio n te c h n iq u e is used to p e r m it
th e se ch a n g e s to c ffe c t th e tr a n s p o r t c a p a c ity .
T h e s e d im e n t tr a n s p o r t íu n c tio n fo r becỉ m a te r ia l lo a d is s e le c te d by u se r.

T r a n s p o r t íu n c tio n s a v a ila b le in th e p ro g ra m a re th fo llo w in g :
T o ff a le ti’s (1 9 6 6 ) tr a n s p o r t íu n c tio n
M a d d e n 's (1 9 6 3 ) m o d iíic a tio n o f L a u rs e n 's (1 9 5 8 ) r e la tio n s h ip
Y a n g 's (1 9 7 3 ) s tre a m povver fo r sands
D u b o y s ' t r a n s p o r t fu n c tio n (V a n o n i 1975)
A c k e rs -V V h ite (1 9 7 3 ) tr a n s p o r t fu n c tio n
C o lb y (1 9 6 4 ) tr a n s p o r t fu n c tio n
T o ffa le ti (1 9 6 6 ) a n d S c h o k lits c h (1930) c o m b in a tio n
M e y e r-P e te r a n d M u lle r (1948)
T o ffa le ti a n d M e y e r-P e te r a n d M u lle r to m b in a tio n
M a d d e n 's

(1 9 8 5 ,

u n p u b lis h e d )

m o d iíic a tio n

of

L a u rs e n 's

(1958)

r e la tio n s h ip
M o d ific a tio n

b y A r ia t h u r a i

a n d K ro n e

(1 9 76 ) o f P a rth e n a iđ e s ' (1965)

m e th o d fo r s c o u r a n d K ro n e 's (1962) m e th o d fo r d e p o s itio n o f co h e sive
s e d im e n ts .
C o p e la n d 's

(1 9 9 0 ) m o d iíìc a tio n o f L a u rs e n 's r e la tio n s h ip (C o p e la n d a n d

T h o m a s 1989)
U s e r s p e c ific a tio n o f tr a n s p o r t c o e ffic ie n ts based u p o n o b s e rv e d d a ta .
T h is re s e a rc h is c h o s e n Yang*s s e d im e n t tr a n s p o r t fu n c tio n to c a lc u la te th e
u n m e a s u re d s e d im e n t in p u t fo r H E C -6 m o d el. T h is is h is

u n i t s tre a m

power

e q u a tio n (Y a n g , 1973), n a m e ly :

V

(0

( 2 .6)

w h e re : C t8 = to t a l s a n d c o n c e n tra tio n (in ppm by w e ig h t);co = t e r m in a l fa ll v e lo c ity ;
d

=

m e d ia n

s ie ve

d ia m e te r

o f s e d im e n t

p a rtic le s ;

V=

k in e m a tic

v is c o s ity ;

g = g r a v it a t io n a l a c c e le ra tio n ; v s = u n it s tre a m povver a n d V crS = c r itic a l u n it
s tre a m p o w e r r e q u ir e d a t in c ip ie n t m o tio n .


S i r n u l a t i o n o f c h a n g c s o f Red r i v c r systcm .

73

T h e b a sis fo r a d ju s tin g bed e le v n tio n s fo r sco u r o r d e p o s itio n ( s im u la tin g
v e r tic a l m o v e m e n t o f th e bed) is th o c o n tin u ity e q u a tio n fo r s e d im e n t m a te r ia l
( E x n e r e q u a tio n ):

(2.7)

0

2 . , B r •
cĩ

w h e re :B u = w id th o f m o v a b le bed; t = tim e ; G = average s e đ im e n t d is c h a rg e ( ft Vsec)
r a te d u r in g tim e s te p

A t ; X = đ is ta n c e a lo n g th e c h a n n e l a n d Y s

= d e p th o f

s e d im e n t in c o n tr o l v o lu m e .
E q u a tio n s 2 . 8 a n d 2 .9 re p re s e n ts E x n e r e q u a tio n e x p re s s e d in f in it e d iffre n c e
fo rm fo r p o in t p u s in g th e te rm s sh o w n in F ig u re 2.2
G ,, ~- GG.u
G

t Bsp(Ysp- Y sp)

0.5fLt + L„) r
Y

sp

w here:B*p =

w id th

of

--------—

(0.5)B 5P

=0.

( 2 .8 )

At

Gạ-G,

(2.9)

+ Lu

m o v a b le

bed a t p o in t P; G U1 G d = s e d im e n t
loacis

at

th e

d o w n s tre a m

u p s tre a m

cro s s

and

se c tio n s ,

re s p e c tiv e ly ; L u, L d = u p s tre a m
a n d d o w n s tre a m
re s p e c tiv e ly ,
se ctio ns;

re a c h le n g th s ,

betvveen

Y sp,Y jp =

cross

d e p th

of

s e d im e n t b e fo re a n d a f t e r tim e
step, re s p e c tiv e ly , a t p o in t P; 0.5
=

th e

"v o lu m e

shape

fa c to r"

w h ic h w e ig h ts th e u p s tr e a m a n d d o w n s tre a m re a ch le n g th s a n d At = c o m p u ta tio n a l
tim e step.

3. Simulation of changes of red river system proílles usin g HEC-6 model
3.1 Collectecl d a t a
R esearch r iv e r re a c h is D a r iv e r re a c h (fro m H oa B in h to T h a o -D a c o n flu e n c e )
an d Red r iv e r re a c h ( fr o m T h a o -D a c o n flu e n c e to H a n o i). T h e fo llo w in g d a ta has
been c o lle c te d to s im u la te ch a ng e s in th c p ro íĩle o f th is r iv e r re a c h :
•

G e o m e tric d a t a :
47 cro ss s e c tio n s (fro m 1 to 47) in Da r iv e r re a c h ( fr o m H o a B in h to T h a o Da co n A u e n c e ) so u n d e d in 1992.


74

N g u y en T h i N g a
17 cross s e c tio n s

(fro m

48 to

64) in

R ed

r iv e r

re a c h

fro m

T h a o -D a

c o n ílu e n c e to H a n o i so u nd e d in 1992.
10 cro ss s e c tio n s in T h a o r iv e r (fro m Y e n B a i to T h a o -D a c o n flu e n c e )
so u nd e d in 1992
6 cross s e c tio n s in L o r iv e r (fro m V u Q u a n g to V ie t T r i) s o u n d e d in 1992

2 cross s e c tio n s in D u o n g r iv e r so u nd e d in 1992
Thalvveg p ro íìle s o f Red r iv e r (fro m

H oa B in h to T h a o -D a conA uence)

so u nd e d in 1992, 1994, 1997

Hydrological d a t a :

•

- F lo w d a ta : d a i ly a v e ra g e w a te r d is c h a rg e s in y e a rs fro m 1988 to 1998 a t H a
N o i a n d Son T a y s ta tio n s in Red r iv e r , T h u o n g C a t s ta tio n in D u o n g r iv e r , Y en B a i
s ta tio n in T h a o r iv e r , H oa B in h s ta tio n in D a r iv e r a n d V u Q u a n g s ta tio n in Lo
r iv e r .

- W a te r le v e l: d a ily a ve ra g e vvater le v e l in 1993 y e a r a t Son T a y s ta tio n a n d in
y e a rs fro m 1988 to 1998 a t H a n o i s ta tio n .
- W a te r te m p e ra tu re : m o n th ly a v e ra g e vvater te m p e r a tu re o f p e rio d fro m 1988
to 1998 a t G s ta tio n s : H oa B in h , Y e n B a i, , V u Q u a n g , Son T a y , H a n o i, T h u o n g C a t,
s ta tio n s .

S e d im e n t d a t a :

•

- D a ily a ve ra g e s u s p e n d e d s e d im e n t c o n c e n tra tio n s a n d d is c h a rg e s y e a rs fro m
1988-1996 a t 7 s ta tio n s : H o a B in h , Y e n B a i, V u Q u a n g , Son T a y , H a n o i, T h u o n g

Cat.
•

M o n th ly a v e ra g e g r a in size c o m p o s itio n o f su sp e n d e d s e d im e n t a t 7 s ta tio n s :

H oa B in h (64-70, 7 2-75, 7 7 -7 8 ), Y e n B a i (64-70, 72-75, 77), V u Q u a n g (6 5 -7 0 , 72-75,
7 7 -78 ) , Son T a y (6 5 -7 0 , 72-75, 7 7 -78 ), H a N o i (6 5 -7 0 , 72-75, 7 7 -7 8 ), T h u o n g C a t
(6 5 -7 0 , 74, 77).
- G ra in

size g r a d a tio n

c u rv e o f su sp en d e d s e d im e n t a n d ta b le

o f g ra in

c o m p o s itio n p e rc e n ta g e s c o rre s p o n d in g to g r a in d ia m e te rs a t cro ss s e c tio n s : 2 in Lo

r iv e r ; 10 a n d 37 in Da r iv e r ; 1 in T h a o r iv e r ; 54, 63, 70 in Red r iv e r a n d 2 in D u o n g
r iv e r (s u rv e y e d in O c to b e r 1996).
- G r a in size g r a d a tio n c u rv e o f bed s e d im e n t a n d ta b le o f g r a in c o m p o s itio n
p e rce n ta g e s (%) c o rre s p o n d in g to g r a in d ia m e te rs (m m ) s u rv e y e d i n M a y 1996 a t
cross

se ctio n s

63, 65,

67

in

R ed

(d o vvnstrea m o f T h u o n g C a t s ta tio n ).

r iv e r

and

cross

s e c tio n

4

in. D u o n g

r iv e r


S i m u l a t i o n o f c h n n g e s o f R ed r i v e r systern.

75

3.2 C o in p iita lio n a l scheine
D e p e n d in g

on

th e

d a ta
V e o tỉai

a v a ila b ilit y , h y d ro lo g ic s ta tio n s and

H o a Điỉtb

- -

w h o le

re s e a rc h

s c h e n iă tic a lix e d
U p s tre a m

r iv e r

n e tvvork

in

íìg u re

b o u n d a rie s

used

and

Thuong

D o vvn stre a m
s ta tio n .

C at

b o u n đ a rie

10 -

^ F ỉ . i a Biob

© ::5
I.uoogLo

-

°T ©
Ptu Tbo^^1~
38
47 " -+-I0
24 30
4 - 4 - 1-1 - u
26
<1la .4K
ĩ ỉuaạ
Da nvcr

H anoi

C o m p u ta tio n a l schem e fo r
50

th e r iv e r n e tv v o rk c o n s is ts o f 1 m a in
se ctio n s.

M a in

r iv e r

51 -Ị-V.CI Tri

o f th e
< ^ | H y đ ro ío g ic a l ỉta iio u

H anoi

m Dc*usí/r»m hoim<Jar>

u p s tre a m is H o a B in h
s ta tio n .

The

and

h y d ro lo g ic a l

fir s t

I I

t r ib u ta r y

c o m p u ta tio n a l

schem e

is

^

b o u n d a ry

is

ỉcflow ịxxn!

o

Duoo* rivcr

a

Ou

+ 63Pcsitiaa vt SCCỈH»

r iv e r re a ch w it h u p s tre a m b o u n d a ry

dovvnstream

- -60
;:m ©

ưpstrtam bouodary

64

D uong

is flo w d iv is io n a l p o in t betvveen Red
r iv e r
and
D uông

r iv e r
and

57

O u íflo w p oiot

( tr ib u t a r y o f d iv is io n w a te r) o f th e

Vu Quang

54■^ SonTay

re a ch w ith d o v v n s tre a m b o u n d a ry is
s ta io n

0

52-

Lcgcud

c o m p u ta tio n a l s c h e m e is Red r iv e r
h y d ro lo g ic a l

L o nvcr

I"IT' rỉ ' 11 ỉ A - ũ
A T

r iv e r a n d 3 t r ib u t a r ie s vvith to ta l 82
cross

]

ỉh *» n % rr

th e

s ta tio n s .
is

- -

1 2 -4-

m o d el a re H o a B in h , Y en B a i, V u
Q uang

l

--5

is
3.1.

in

□

□

p rin c ip le s used in H E C -6 m o đ el, th e

Fiẽure 3.1. C o m p u ta tio n a l schem e o f Red

Thuong

r iv e r n e tw o rk (re se arch reach)

C a t h y d ro lo g ic a l s ta tio n . T h e seconti
tr ib u ta r y o f th e c o m p u ta tio n a l s c h e m e is L o r iv e r re a ch w it h d o w n s tre a m b o u n d a ry
is ju n c tio n

o f R ed r iv e r a n d

L o r iv e r

a n d u p s tre a m

b o u n d a ry

is V u

Q uang

h y d ro lo g ic a l s ta tio n . T h e t h ir d t r ib u t a r y o f th e c o m p u ta tio n a l schem e is T h a o r iv e r
reach vvith u p s tre a m b o u n d a ry is V u Q u a n g h y d ro lo g ic a l s tá tio n a n d d o vvnstream
b o u n d a rv is T h a o -D a c o n flu e n c e .
3.3 I n p u t d a t a

In p u t d a tn
g e o m e tric

d a ta ,

file
th e

o f H E C -6 is o rg a n iz e d in to
fo llo w in g

g ro u p

3 g ro u p s : th e

is s e d im e n t d a ta

and

th e

f i r s t g ro u p

is

la s t g ro u p

is

h y đ ro lo g ic a l d a ta . G e o m e tric d a ta is a rra n g e d in fo llo w in g o rd e r: th e p o s itio n o f

local ju n c tio n

a n d d iv e rs io n p o in ts in th e r iv e r n e tv v o rk , th e p o s itio n o f cross

sections in th e r iv e r n e tv v o rk , th e g e o m e trv o f cross s e c tio n s (c o o rd in a te p o in ts o f
crcss se ctio ns a n d th e d is ta n c e s be tw ee n cross s e c tio n s ), th e v a lu e s o f M a n n in g 's
roughness n in c ro s s s e c tio n s (in c lu d e M a n n in g ^ n v a lu e s o f th e m a in c h a n n e l and
o ve rb a n k a re a s) a n d c o n v e y a n c e lim its o f c h a n n e l a t cro ss se ctio n s. S e d im e n t d a ta


76

N guyen T h i Nga

in c lu d e s flu id

a n d s e d im e n t p ro p e rtie s , th e

in flo w in g

s e d im e n t lo a d d a ta , th e

g ra d a tio n o f m a te r ia l in th e s tre a m bed, th e tr a n s p o r t c a p a c ity r e la tio n s h ip a n d
u n it vveights o f d e p o s ite d m a te r ia l. H y d ro lo g ic a l d a ta in c lu d e s vvater d is c h a rg e s ,
te m p e ra tu re s , d o w n s tre a m w a te r s u rĩa c e e le v a tio n s a n d flo w d u r a tio n .
3 .4 I n i t i a l a n d b o u n d a r y c o n d i t i o n s
I n i t i a l c o n d itio n is cro ss s e c tio n g e o m e try o f r iv e r s e g m e n ts i n c o m p u ta tio n a l
schem e a t th e tim e t h a t c o m p u ta tio n is s ta rte d . M e a s u re d g e o m e tric d a ta o f 82
cross s e c tio n in c o m p u ta tio n a l schem e in 1992 is used as th e i n i t i a l c o n d itio n . T h is
d a ta is re p re s e n te d in c o o rd in a te p o in t fo rm (s ta tio n s , e lv a tio n s ) o f p o s itio n s in

cross se ctio n s in th e o rd e r fro m th e le f t to th e r ig h t (d o v v n s tre a m ). T h e e le v a tio n s
m ay be p o s itiv e , zero o r n e g a tiv e . T h e cross se ctio ns a re a rra n g e d fr o m d o w n s tre a m
to u p s tre a m , s ta r tin g fro m cro ss s e ctio n s o f th e m a in r iv e r , th e n to cross s e c tio n s o f
th e t r ib u t a r y r iv e r .
I n a r iv e r s y s te m th e re are th re e ty p e s o f b o u n d a rie s : u p s tre a m , d o vvn stre a m
and in te r n a l. T h e u p s tre a m a n d dovvnstrea m b o u n d a rie s a re a t th e cross s e c tio n s
th a t a re m o s t u p s tre a m a n d m o st d o vvnstrea m , re s p e c tiv e ly , o n a s tre a m s e g m e n t.
T h e re a re th re e ty p e s o f in te r n a l b o u n d a rie s : a lo c a l in flo w , a t r ib u t e r y ju n c tio n ,
and a h y d r a u lic c o n tro l p o in t. T h e re a re also th re e b o u n d a ry c o n d itio n s t h a t ca n be
p re s c rib e d by H E C - 6 : w a te r d is c h a rg e , s e d im e n t d is c h a rg e , a n d s u rfa c e e le v a tio n
(sta g e ). T h e w a te r a n d s e d im e n t d is c h a rg e s m u s t be d e íìn e d a t each u p s tre a m
b o u n d a ry

and

at

each

lo c a l

inílovv

p o in t.

S ta g e

m ust

be

p re s c ib e d

at

th e

do vvnstream b o u n d a ry o f th e p r im a r y s tre a m s e g m e n t; a n d i t c a n be p re c rib e d a t
h y d r a u lic c o n tro l p o in ts . In s tu d y r iv e r n e tvvo rk th e u p s tre a m b o u n d a ry c o n d itio n s
in c lu d e w a te r d is c h a rg e , s e d im e n t d is c h a rg e a n d d a ily a v e ra g e te m p e r a tu r e a t H oa
B in h , Y e n B a i, V u Q u a n g a n d T h u o n g C a t s ta tio n s . T h e d o v v n s tre a m b o u n d a ry
c o n d itio n is d a ily a v e ra g e sta g e (vvater s u ría c e e le v a tio n ) a t H a n o i s ta tio n . T he
c o m p u ta tio n a l tim e s te p is one day.
3 .5 M o d e l c a l i b r a t i o n
H E C -6 m o d el s im u la te s changes o f r iv e r p ro file s c o m b in e d u s in g th re e m odels:
h ycừ aư lics m o d el, s e d im e n t tr a n s p o r t m odel and m o rp h o lo g ic m o d c l. H y d r a u lic s
m odel is used to c o m p u te

w a te r s u ría c e p ro íìle

a t each

tim e

step. S e d im e n t

tr a n s p o r t m o d e ỉ is used to c o m p u te s e d im e n t tr a n s p o r t d is c h a rg e across each cross
se ctio n in c o m p u ta tio n a l schem a

a t each tim e step. M o r p h o lo g ic a l m o d el is used to

c o m p u te cha ng e s o f r iv e r bed e le v a tio n s fo r s c o u r o r d e p o s itio n . P a ra m e te rs needed
c a lib ra tio n

in

H E C -6

a re

m a in ly

p a ra m e te rs

of

h y d r a u lic s

m o d e l,

th a t

are

M a rm in g ’s ro u g h n e s s c o e ffic ie n ts o f r iv e r bed, le ft a n d r ig h t o v e r b a n k s .
T h e s tu d y used h v d ro lo g ic a l a n d s e d im e n t tr a n s p o r t d a ta in 1993 to c a lib ra te
h y d ra u lic a n d s e d im e n t tr a n s p o r t m o d el.


77

S i m u l a t i o n o f c h a n g e s o f R ed rivcr systcm.
T h e c a lib r a t io n process o f h y d r a u lic m o d e l is c a r r ie d o u t as fo llo w s :
*

Preliminary selection a set of roughness coefficients at all

C )f

cross sections in

c o m p u ta tio n a l s ch cm e. T his prelim inary selection is carried out on experience:
s e le c tio n r o ư g h n e s s coefficien ts fronì 0.1 to 0 .1 5 for over bank part an d from 0.02 2
to 0 .0 4 2 for riv er bed part.

- U sing H E C -6 model, in turn smulation hydraulcs with the selected set of
h y d r a u lic s p a r a m e te r s in con d ition that th e ch a n n el is rega rd ed fixed chann el.
In p u t d a ta o f h y d ra u lic s are daily average w a te r d isc h a r g e of Hoa Binh, Yen Bai,
Vu Q u a n g , T h u o n g C at s ta tio n s and daily average s ta g e (w a te r su r ía ce e lev ation ) at
Ha noi s t a t io n in 1993. R e su lts of hvdraulics sim u la tio n are th e s ta g e at all o f cross
se c tio n s in th e c o m p u ta tio n a l s c h e m e at each tim e step.
- T ak e Son T a y

sta tio n in R ed river (section 54) to make control s e c tio n . From

hyciraulics s im u la t io n r e s u lts w ith th e selected set of p a r a m e te r s , extraction and
d r a w in g 021 g ra p h c o m p u te d d a ily a v e ra g e s ta g e Ị)rocess a t Son T a y s ta tio n 1993.

C o m p a r iso n it vvith m e a su r e đ daily average s ta g e p ro cess at Son Tay s ta tio n 1993
and e s t i m a t i o n a g r e e lev el by N a sh norm.

After a lot o f try and error tim es with many different couples of river bed and
over bank r o u g h n e s s coeĩricients, th e study selected a couple of river bed and over bank
roughness coefficients th at results in the best hvdraulics sim u la tio n result: river bed
roughness coefficien t is 0.029, left and over bank roughn ess coeííicients is both equal
0.10. With th is set of hydraulic parameters, effective level o f the model com puted on
Nash norm is th e h ig h est (98.9%) and the forms of com pu ted and m easured water
suface e le v a tio n process graph agree highly each other (F igure 3.2).

Stage (m)

Kigurc 3.2
Compiitcd and meastiriđ dail Vslage proccss al Son Tav station ỉn 1993


78

N g u y ên Thi N g a
A ccuracy o f s e d im e n t transport s im u la tio n of river netw ork

d epend s

on

accuracy of h y d ra u lic s im u la t io n r e su lts, on accuracy o f d e fin itio n p a r a m e te r s of
s e d im e n t tr a n s p o r t m ođ el and se le c te d s e d im e n t tr a n sp o r t fu nction. T he stu d y
d e ĩin e d c a r e fu lly

p a r a m e te r s o f se d im e n t

tra n sp o rt

m od el

b a s in g

o n e s e lf

on

co lle cte d d a ta , s e le c t e d Y ang's s e d im e n t tra n sp o rt fu n ctio n an d ran s e d im e n t
tr a n sp o r t

m odel

u s in g

th e

set

of hydraulic

p a r a m e te r s

th at

se le c te d

vvhen

c a lib r a tio n h y d r a u lic m o d el. The sim u la tio n r e su lts are d a ily s e d im e n t d isc h a r g e s
a cross each c ro ss s e c t io n in co m p u ta tio n a l s c h em e in 1993. From t h e s e resu lts, th e
stuciy e x tr a c te d da ily s c d im e n t d isc h a r g e process d a ta a c r o s s cro ss se c tio n of S o n
T ay s ta tio n , drew c o n ìb in a tiv e lv co m p u ted an d m e a su r ed d a ily s e d im e n t d isc h a r g e
process g r a p h s at S o n T ay sta tio n in 1993 on th e s a m e c o o r d in a te sy ste m , a n d
estim a tecl e ffe c tiv e le v e l o f se d im e n t tra n sp o rt model on N a s h norm . T h e s e r e s u lt s
s h o w e d t h a t c o m p u te d a n d m ea su red se d im e n t d isc h a r g e s a g r e e r a th e r each o th e r
(F ig u r e 3.3), e ffe c tiv e le v el co m p u ted on N a sh norm r ea ch s 0 .7 6 .

Sedim cnt d isch arg c R (kg /s)

F ig u re 3.3. C o m p u te d and m easured d a ily se d im e n t disch a rg e process graph s a t Son
T ay s ta tio n in 1993

3.6 M o c ỉc l v c r i f i c a t i o n

M orp hological m o d el is s im u la te d b ased on c o m p u ta tio n a l s c h e m c e sta b lis h e d
for h y d ra u lic m odel w it h

u ltim a te hydraulic an d s e d im e n t

p a r a m e te r s . River

thalvvegs m e a s u r e đ in 1994 o f reach from Iioa B inh to T r u n g Ha. a n d in 1997 of
reach from ỉ lo a B inh to Ma Noi are u sed to verifv th e m od el. In p u t d ata is daily
a v e r a g e d is c h a r g e from 1992 to 1997. T h e rcsu lts include: to ta l s e d im e n t d isch a rg e


S i m l i l a t i o n o f c h a n g c s o f R ed rivcr s ỵ s t c m .

79

inílovv and o u tflow e a ch river reach for each g rain tvpe a t each tim e s te p , q u a n tity
o f s c o u r or d e p o sitio n se d im e n t on each river reach at ea ch t im e s te p , w a te r su r fa c e
a n d river ỉ)ecỉ e le v a t io n s at cross sec tio n s o f c o m p u ta tio n a l s c h e m e a t each tim e
s te p . totnl s e d im e n t d isc h a r g e from trib u ta ries inflow m a in riv er and ou tflow m ain
river, total scour and d eposition s e d im e n t qu an tity over s tu d y river reach.

Zi m)

15.00
m.(M)
5.00
1.00

<

1:

-5.00
10 00

ị

••
: , 9

••
ề1
* 1(M)0(»

■

* 1
** 9ệ
* ;
.f

, • <*
• .■

201)00

30000

Computeđ z (m)

ỉ
\ !
.0

»

/40000

\
i
y ỉ
ầ
. •'

‘.;-

V; "
V
50000

Disian :c

(m )

6(H )()

........ Measurcd z (m)

15.00

PiỊỊure 3 4 Computed and measurcd Da river thalweg of rcach from Hoa Binh to Trung Ha in
1994

Z(m)
10.00 1

Figure 3.5. C om pu ted and m easured river th a lw eg of reach from Hoa B inh to Ha Noi
in 1997


80

N guyên Thi Nga

R e s u lts o f c o m p a r is o n betvveen c o m p u te d and m e a su r e d thalvvegs o f D a river

r ea c h from Hoa B in h to T r u n g Ha in 1994 a n d Red river reach from Hoa B in h to Ha
N oi in 1997 are s h o w n in F ig u r e s 3.4 an d 3.5. T h e se fig u res shovv th a t c o m p u te d
river t h a lw e g a g r e e r a th e r vvith m ea su red river th a lw e g . E ffe c tiv e le v e l of th e
m od el c o m p u te d on N a s h n o r m o f 1994 r ea c h s 0.93 an d o f 1997 r e a c h s 0.87.
3 .7 S i m u l a t i o n c h a n g e s o f R e d r i v e r b e d to 2 032

T h e r e s u lt s o f m o d el c a lib r a tio n and v erifica tio n sh o w t h a t H E C -6 m o d el w ith
t h e s e t o f s e le c te d o p t im a l p a r a m e te r s can u s e to s im u la t e c h a n g e s of Red riv er bed
in th e fu tu re.
W ith in tin ia l c o n d itio n is m e a su r e d river bed proíìle in 1992, th e Symbol ic
w a te r d is c h a r g e p r o c e s s e s (a v e r a g e o f 11 y e a r s fom 1988 to 1998) at Hoa B inh , Y en
B ai, Vu Q u a n g , T h u o n g C a t s ta tio n s are t h e u p str e a m b o u n d a r ie s and th e sym bolic
s t a g e p r o c e s s e s ( a v e r a g e o f 11 y e a r s fom 1988 to 1998) at H a N oi s ta tio n is th e
dovvnstream b o u n d a ry , t h e s tu d y s im u la t e d c h a n g e s o f Red r iv e r bed to 2 0 3 2 . T he
r e r s u lts are shovved in F ig u r e 3.6. T h e se r e s u lt s sh o w that:
Deep scour phenom enons resulting from regulating eíTect of Hoa Binh reservoir
happen alm ost only in Da river and transmit only to T rung H a station.
T he deep scour sp eed in Da river reduces gradually (S ee ta b le 3.1). Da river
bed w ill b ecom e gradually stability (to reestablish th e n e w balance State).

Figure 3.6. P redited resu lt of Rccỉ river bed c h a n g e s to 2032
(reach from Hoa B inh to Ha Noi)
T a b l e 3.1 A v era g e deep scour speed at so m e cross section in d e í ử e n t period (m/year)
Cross section

1992 - 2002

2002 - 2012

2012 - 20 22

2022 - 2032

Section 5

0 .3 8 0

0.168

0.062

0.0 00

Section 18

0.061

0.003

0.001

0.0 00

Section 48

0.021

0.017

0.014

0.013


81

S i m u i a t i o n o f c h a n g c s o f R e d rivcr systern.
T ài liệ u th a m k h a o
1.

C h ih T e d Y a n g , S e c lim e n t T r a n s p o r t - T h e o r y a n d

P r a c t ic c , M c G ra v v - H i l l

C o m p a n ie s, Inc. 1996.
2.

N g u y ề n T h ị N g a , T r ầ n T h ụ c , D ộ n g lự c h ọ c d ò n g s ô n g , G iá o t r ì n h T rư ờ n g Đ ạ i
h ọ c Khoa học Tự n h iên , Đ H Q G H N . Hà Nôi, 2001.

3.

T r a n T u ấ t và n n k , Đ ặ c tr ư n g h ì n h th á i

lưu v ự c s ô n g V iệ t N a m ,

V iệ n K h í tư ớ n g

T h ủ y v ã n , H à N ộ i, 1985.
4.

u . s A r m y C o rp s o f E n g in e e rs , 1 IE C -6

version 4 .1 . U s e r 's M a n u a ỉ , H y d r o lo g ic

E n g in e e r in g C en ter, 1993.
ĨA P CHÍ KHOA HỌC ĐHQGHN. KHTN & CN, T XIX, Nọ1, 2003________

M Ỏ P H Ỏ N G D IỄ N B IẾ N L Ò N G D A N H Ệ T H Ố N G S Ô N G H ồ N G
B Ằ N G M Ỏ H ÌN H H E C -6
(Đ o ạ n s ô n g Đ à từ H oà B ìn h đ ế n n g â ba T h a o Đ à
v à đ o ạ n s ô n g H ổ n g từ n g ả ba T h a o -Đ à đ ế n H à N ô i )
Nguyển T hi Nga
K h o a K h í tượng T h ủ y v ă n & Hải d ư ơ n g h ọ c
Đ ạ i h ọ c K h o a học T ự n h iê n , Đ H Q G H à N ộ i

v ỏ i hai n h iệm v ụ q u an trọ n g hà n g đầu là p h á t đ iệ n v à p h ò n g lù cho hạ du, từ
khi v ậ n h à n h , hồ H oà Bình đà v à đan g đem lại n h ử n g lợi ích h ế t sứ c to lớn n h ư n g
c ủ n g đă và đ an g gãy ra n h ữ n g th a y đổi khá bất lợi n h ư bồi la n g lòn g hồ, xói cục bộ
hạ lưu đập và xói lan tr u y ề n v ê hạ du... Đ ánh giá, mô p h ỏ n g và dự báo các th a y đỏi
sau khi xây dựng các công trìn h trên s ô n g đê c!ê x u ấ t các b iện pháp h ạ n ch ê các
th iệ t hại luôn là đề tài cấp th iế t và có ý ng h ĩa th ự c t iễ n lốn. C ô n g cụ hữu h iệu và
kinh tê (lể giải q u yết c á c dể tà i n à y là mô hình to án .
H E C -6 là mô h ìn h sô th ủ y động lực một c h iề u tr o n g lò n g d ẫ n hở có biên di
động được T ru ng tâm Kỹ t h u ậ t Thủy v ă n Hoa Kỳ t h iế t kê đ ể mô p h ỏn g và dự báo
các th a y đôi trong trắc diện dọc sô n g do xói hoặc bồi trong các thời đoạn vừa.
Bài báo này n g h iê n cứu ứng dụ ng mô hình H E C -6 để m ô p h ỏn g d iễn b iến lòng
sôn g Dà phía hạ lưu đá p Hoà B ình (đoạn từ Hoà Bình đ ên n g ã ba T h a o -Đ à ) và lòng

sô n g H ồng (đoạn từ n g ã ba T h a o-Đ à đến H à Nội). K ết quả h iệ u c h ỉn h và kiểm định
mỏ hình cho th ấ y mô h ìn h H E C -6 vói bộ th ô n g s ố tôi ưu đà lựa chọn có th ể sử d ụ ng

dể mô phòng diẻn biên lòng sông Hổng tron g tương lai VỚI mức độ chính xác có the
chấp n h ận được. K ết quả mô ph ỏng (liền biến đáy s ô n g H ồn g b ằ n g mô h ìn h H E C -6
vối bộ th ông sô đả lự a chọn vỏi điểu k iện ban đầ u là lòn g s ô n g H ồ n g đo đạc nă m
1992, điêu k iện biên tr ê n là đường quá trình lưu lượng đ iể n hìn h (d ạn g tru n g bình
n h iề u n ă m th ờ i kỹ 1 9 8 8 -1 9 9 8 ) c ủ a các t r ạ m H ò a B ìn h , Y ê n B á i, V ụ Q u a n g , T h ư ợ n g

Cát và điếu kiện biên dưới là đường quá trình mực nước đ iể n h ìn h (ciạng tr u n g bình
n h iê u năm th ờ i k ỳ 1 9 8 8 -1 9 9 8 ) c ủ a tr ạ m H à N ộ i c h o th à y :

• H iện tượng xói sâ u do ản h hưỏng điêu t iế t c ủ a hồ H oà B ìn h c h ủ y ê u chỉ xảy
ra trên sông Đà và chỉ lan tr u y ề n đên trạm th ủ y v ă n T r u n g Hà.
■ Tốc độ xói có xu hướng g iả m dần. Lòng s ô n g Đ à d ầ n d ầ n
trở n ê n ổn địn h (lập
lại trạng th ái cân bằn g mói).