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)

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

SIM ƯLATIO N O F C H A N G E S OF RED RIVER S Y S T E M P R O F I L E

ƯS1NG HEC-6 M O D EL (Da r i v e r r e a c h fr o m Hoa B i n h to T h a o - D a c o n A u e n c e

a n d Red r i v e r r e a c h f r o m T h a o - D a c o n A u e n c e t o Ha N o i)

N g u y e n T h i N g a

D e p a rtm e n t ofHyd.ro Meteorology a n d Occanoỉogy

Collcge o f Science, V N U

A b s t r n c t ỉ loa B in h re s e rv o ir was b u ilt in ỉ)a r iv c r to c a r r y o u t tw o top

ìm p o rta n t d u tic s t h a t are g c n c ra tio n e le c tr ic ity and flo o d p re v e n tio n for

ìow ]ands S in cc o p o ra tio n , Hoa B in h re s c rv o ir has b cen b r in g in g a bo ut v c ry big

uscíuỉnesses, b u t also has bcen c a u s in g u n fa v o u ra b lo ch a n g e s , such as

d e p o s itio n in th e ro s e rv o ir, local scour in lo w e r o f th o dam a n d (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

li m i t dam ages a lw a y s a re p re ssin g and necessary p ro b le m s M a th o m a tic a l

m odels a rc e ffe c tiv e and e co n o m ir to o ls 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 r o íìlc s r o K u ltin g fro m

scour a ru l/o r d o p o s ilio n o v c r m o d c ra tc tim c p crio d s

T liis p a p c r s tu d ie s and a p p ỉio s 11KC-G lo s im u la tc c h a n g e s o f D a r iv o r

p ro lìlc (reach from ỉ loa B inh t.o Thao-Da ronílue n cc) and Red riv e r p ro íílc

(rea ch from T h a o -D u co n ílu e n ce to l l a N o i) T h o r c s u lts (>f m o d e l 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 so t 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 r o 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 s tro a m c o n c iitio n s a rc ty p ic a l d isch a rg e 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 e n 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 v o ra g o typcĩ o f p e rio 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 p h o nom enon s r c s u ltin g fro m r e g u la tin g o ffí‘c:t C)f ỉ lo a B in h ro s o rv o ir

h a p p o n 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 c iu a lly Thcíroĩorc, Da r iv tĩr bcuỉ w ill bceome

g ra d u a lly s t a b ilit y (to ro o s ta b lis h th o new b a la n cc State)

1 I n t r o d u c t i o 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 c o n o m ic a 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 2 0 0 0 m A M S L in V a n N a m ( C h in a ) I t h a s a to t a l le n g th

o f 1126 k m T h e b a s in o c c u p ie s t o 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 a cts 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 r th 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 t io n R ed r i v 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 s ystcm 69

fro m th r e e m a in t r ib u t a r ie s : D a, T h a o a n d L o r iv e r s T h a o r iv e r o r ig 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 r th 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 r o 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 r a n g e fr o m 100 * 150 m in a ve ra g e R iv e r b 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 D a r iv e r ris e s fro m th e h ig h ly m o u n ta in o u s a rea in

th e sa m e v i c i n i t y o f T h a o r i v 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 (iir e 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 r th , a n d

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 s t im p o r t a n t t r i b 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 r ig in a te s fro m V a n N a m m o u n ta in s

a rea lo c a te d i n C h in a Its t o t a l le n g th is 470 k m ; th e c a tc h m e n t a re 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 L o 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 T h e t o t a l b a s in o f R ed r iv e r n e tw o r k c o n s id e re d a t Son T a y is

a p p r o 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

r iv e r c o n s id e re d fr o m V ie t T r i, flo w s th r o u g h im p o r ta n t u r b 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 C a p i t a 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 r o u g h o u t o u t t h e n a tio n

H oa B in h r e s e r v o ir , lo c a te d o n 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 t o o p e r a tio n p a r t ia lly in 1990 a n d f u l ly i n 1994 T h e e ffe c ts o f th e

c o n s tru c tio n h a v e b e e n seen o b v io u s ly in D a rea ch 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 d o vvnstream

m o rp h o lo g ic a l c o n c iitio n s in d e s ig n s ta g c s E ach o f th e p re v io u s s u d ie s has m e r it

p o in ts a n d l im i t a t i o n s d u e to th e d e fic ie n c y in d a ta fo r v e r tic a tio n a n d

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

In r e c e n t y e a rs , d a ta a n d o b s e rv a tio n s o b ta in e d by D e p a r tm e n t o f

M a n a g e m e n t & F lo o đ C o n tr o l a n d R e se a rch I n s t it u t e o f W a te r R esources sh o w t h a t

th e d e g ra d a tio n o f D a r iv e r b e đ h a s been p r o 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 r in g re s e n t y e a rs in d o w n s tre a m h a v e 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 bo th flood a n d t r a n s i t i o n a l s ta 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 - t im e a c tio n to p re v e n t th e erosion

T h is re seach 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 r o file s (re a c h fr o m H o a B in h to T h a o -D a c o n flu e n c e ) a n d Red r i v e r p r o file s (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)

2 Theoretical basis o f m o v a b l e 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 r e d ic t ch a ng e s in r iv e r p ro íĩle s r e s u ltin g fro m s c o u r a n d /o r d e p o s itio n o v e 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 lt h r o u g h a p p lic a t io 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 i n 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 a n d d u ra tio n s F o r each flo w , a w a te r s u rfa c e

p r o íile is c a ỉc u la te d th e r e 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 t r 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 s e c tio n

T h e se 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 t r 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 c h s e c tio n is

th e n c o m p u te d a n d th e cro s s 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 HEC-

6 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 t i c 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 i o n s

T h e h y d r a u lic p a r a m e te rs needs to

c a lc u la te s e d im e n t t r a n s p o r t p o te n tia l a re

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

o f w h ic h a re o b ta in e d fr o m vvater s u rfa c e

p r o file c a lc u la tio n s W a te r s u ría c e p ro fíle s

a re c a lc u ỉa te d u s in g th e s ta n c ỉa rd -s te p

m e th o d to s o lve th e c o n t in u it v e q u a tio n

a n d o n e -đ im e n s io n a l e n e rg y e q u a tio n

( E q u a tio n 2.1) a n d th e h y d r a u lic

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 su cce ssive d is c h a r g e F ig u re 2.1 show s a r e p re s e n ta tio n o f th e te r m s in th e e n e rg y e q u a tio n

ws?

_ °

^ -1' -Ị” l ĩ s

Wo4»' S«ftoc« 1 * ' v *

9

ws,

0 o t u » T >

Figure 2.1

S i m u l a t i o n o f c h a r iỊ Ịc s o f R e d r i v c r systcm 71

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 t r 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 c h

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 t io n loss, hf, an d

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 r m

To a p p r o x im a t e th e tra n s v e rs e d is t r 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 E ach cross

s e c tio n is s u b d iv iđ e d in to p o rtio n s th a t a re r e 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 :

in w h ic h :

NSS

k ; - z

J 1

( ả 2 + Ạ j) r 2 + r , " 2 l

J

(2.4)

w h e re : A j, Á , = d o w n s tre a m a n d u p s tre a m a rea, re s p e c tiv e ly , o f th e flo w n o r m a l to

th e cro s s 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 ; Kị =

le n g th * w e ig h te d s u b s e c tio n co nveyance; 1^ = le n g th o f th e j lh s t r ip b e tw e e n

s u b s e c tio 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 r a d iu s , re s p e c tiv e lv

E n e rg y losses d u e to c o n s tra c tio n s an d 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 :

2

h o = C , a2VỈ q,v,

2 g

(2.5)

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 i s f o r S e d ir n e n t C a l c u l a t i o 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 r o g r a p h fo r

e a ;h g r a in s iz e T h e t r 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 cla ss i n th e beJ as t h 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

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 s e ÍY a c tio n s o fte n c h a n g e

s ig n if ic 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 s e c h 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 t r 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 s e 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 f f a le t i’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 t io n s h ip

Y a n g 's (1 9 7 3 ) s tr e 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 f f a le t i (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 f f a le t i 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 o f L a u r s e n 's (1958)

r e la t io n s h ip

M o d if ic a tio n b y A r ia t h u r a i a n d K ro n e (1 9 7 6 ) o f P a r th 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 s iv e

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 t io 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 f u n c t io 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 p o w e r

e q u a tio n (Y a n g , 1 973), n a m e ly :

w h e re : C t8 = t o 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 v e 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 it ic 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

( 2 6 )

S i r n u l a t i o n o f c h a n g c s o f R ed r i v c r systcm 73

T h e b a s is fo r a d ju s tin g bed e le v n tio n s fo r s c o 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 , B r •

w h e re :B u = w id t h o f m o v a b le bed; t = tim e ; G = ave rag e s e đ im e n t d is c h a rg e ( f t Vsec)

r a te d u r in g t im 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 i n 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 s h o w n in F ig u re 2.2

G , ~ G Bsp(Ysp- Y sp)

G , - G u t

sp Y -—

(0.5)B 5P

G ạ - G , + L u

(2.8)

(2.9)

w here:B *p = w id th o f 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 a t th e u p s tr e a m a n d

d o w n s tre a m c ro s s s e 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 a c h le n g th s ,

re s p e c tiv e ly , betvveen cross

se ctio n s; Y sp,Y jp = d e p th o f

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 s h a p e 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 c h a n g e s o f red river system proílles u s in g HEC-6 model

3.1 Collectecl d a t a

R esearch r i v 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 )

a n 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 t e ch a n g 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 s s 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 c o n A u e n c e ) so u n d e d in 1992

17 cross s e c tio n s (fro m 48 to 64) in R ed r iv e r re a c h fr o m T h a o -D a

c o n ílu e n c e to H a n o i so u n d 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 n d 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 n d e d in 1992

T ha lvveg 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 co nA uence)

so u n d e d in 1992, 1994, 1997

• H ydrological 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 L o

r iv e r

- W a te r le v e l: d a ily a v e ra g e vvater le v e l in 1993 y e a r a t S on 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 r a tu re : m o n th ly a v e ra g e vvater te m p e r a tu r e o f p e r io d fro m 1988

to 1998 a t G s ta tio n s : H o a B in h , Y e n B a i, , V u Q u a n g , S on 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 v e 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

19 88 -1 9 96 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 s p 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 (64-7 0 , 7 2 -75 , 7 7 -7 8 ), Y e n B a i (64-7 0 , 7 2 -75 , 77), V u Q u a n g (6 5 -7 0 , 72-75,

7 7 -7 8 ) , Son T a y (6 5 -7 0 , 7 2 -75 , 7 7 -7 8 ), H a N o i (6 5 -7 0 , 7 2 -75 , 7 7 -7 8 ), T h u o n g C a t (6 5 -7 0 , 74, 77)

- G r a 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 r a 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 s s s e c tio n s : 2 in Lo

r iv e r ; 10 a n d 37 in D a 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 b e d 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 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 (m m ) s u rv e y e d i n M a y 1996 a t cross s e c tio n s 63, 65, 67 in R ed r iv e r a n d cross s e c tio n 4 in D u o n g r iv e r (d o vvn stre a m o f T h u o n g C a t s ta tio n )

S i m u l a t i o n o f c h n n g e s o f R e d 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 o n th e d a ta

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

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

w h o le re s e a rc h r i v e r n e tvvo rk is

s c h e n iă tic a lix e d in íìg u re 3.1

U p s tre a m b o u n d a rie s used in th e

m o d e l a re H o a 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

D o v v n s tre a m b o u n đ a r ie is H a n o i

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

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

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

cross s e c tio n s M a in r iv e r o f th e

c o m p u ta tio n a l s c h e m e is Red r iv e r

re a ch w it h d o v v n s tre a m b o u n d a ry is

H a n o i h y d r o lo g ic a l s ta io n and

u p s tre a m is H o a B in h h y d ro lo g ic a l

s ta tio n T h e f i r s t t r ib u t a r y

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

c o m p u ta tio n a l s c h e m e is D u o n g

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

is flo w d iv is io n a l p o in t betvveen Red

r iv e r a n d D u ô n g r iv e r a n d Fiẽ u re 3.1 C o m p u ta tio n a l schem e o f Red

dovvnstrea m b o u n d a r y is T h u o n g r iv e r n e tw o rk (re se a rch reach)

C a t h y d ro lo g ic a l s ta tio n T h e seconti

tr ib u t a 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 c h 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 u a n g

h y d ro lo g ic a l s ta tio n T h e t h i r d t r ib u t a r y o f th e c o m p u ta tio n a l sch e m e is T h a o r iv e r reach vvith u p s tr e 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 vvnstrea m

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 file o f H E C -6 is o rg a n iz e d in to 3 g ro u p s : th e f i r s t g ro u p is

g e o m e tric d a ta , th e fo llo w in g g ro u p is s e d im e n t d a ta a n d th e 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 r s 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 i v 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 s e ctio n s a n d th e d is ta n c e s b e 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 rou gh n e ss 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 v e rb a n k a re a s ) a n d c o n v e y a n c e lim it s o f c h a n n e l a t cro ss s e c tio n s S e d im e n t d a ta

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in c lu d e s f lu 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 r a 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 vva te r 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 t io 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 u se d 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 s e c tio n s in th e o r d 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 n s 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 t a r tin g fro m cro ss s e c tio 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 r e are th re e ty p e s o f b o u n d a rie s : u p s tr e a m , d o v v n s tre a m and in t e r n a l T h e u p s tre a m a n d d o vvn stre a 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 s t d o vvn stre a 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 t e r n a l b o u n d a rie s : a lo c a l in f lo w , a t r ib u t e r y ju n c t io n ,

an d a h y d r a u lic c o n tr o 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 c a 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 a n d a t each lo c a l inílo vv p o in t S ta g e m u s t be p re s c ib e d a t th e

d o vvnstrea m 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 tr o 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 s ta 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 o n e d ay

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 a ư lics m o d e l, s e d im e n t tr a n s p o r t m o d el 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 r o íìle a t each t im 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 a cross each cross

s e c tio n in c o m p u ta tio n a l sch e m a a t each tim e step M o r p h o lo g ic a l m o d e l is u se d to

c o m p u te ch a 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 r a tio n in H E C -6 a re m a in ly p a ra m e te rs o f h y d r a u lic s m o d e l, t h a t are

M a r m 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 f t 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 r a te

h y d r a u lic a n d s e d im e n t tr a n s p o r t m o d e l

S i m u l a t i o n o f c h a n g e s o f R e d rivcr systcm. 77

T h e c a lib r a t io n p ro ce ss 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 :

c o m p u t a t i o n a l s c h c m e T h is p r elim in a ry sele c tio n is c a rr ie d o u t o n experience:

s e l e c t i o n r o ư g h n e s s c o e f fic ie n ts fronì 0.1 to 0 1 5 for o v e r b a n k part a n d from 0 0 2 2

to 0 0 4 2 for r iv er bed part.

h y d r a u lic s p a r a m e t e r s in co n d itio n th at th e ch a n n el is r eg a r d e d fixed c h a n n el

In p u t d a t a o f h y d r a u lic s are d a ily a v e ra g e w a te r d is c h a r g e o f Hoa B inh , Y en Bai,

Vu Q u a n g , T h u o n g C at s t a t i o n s an d daily a v e ra g e s t a g e ( w a te r s u r ía c e e le v a tio n ) at

Ha noi s t a t i o n in 1993 R e s u l t s o f h vd ra u lics s im u la t io n a re th e s t a g e at all o f cross

s e c t io n s in t h e c o m p u t a t io n a l s c h e m e at each t im e step

- T a k e S o n T a y s ta tio n in R e d river (section 54) to make control s e c tio n From

hyciraulics s i m u l a t i o n r e s u lt s w ith th e s e le c te d s e t of p a r a m e t e r s , e x tr a ctio n 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 sta g e Ị)rocess a t Son T a y s ta tio n 1993

C o m p a r is o n it vvith m e a s u r e đ d aily a v e ra g e s t a g e p r o c ess at Son Tay s t a t io n 1993

and e s t i m a t i o n a g r e e le v e l by N a sh norm.

After a lot o f try and error t im e s with many different couples o f river bed and

over bank r o u g h n e s s coeĩricients, th e stud y selected a couple of river bed and over bank

roughn ess co efficien ts th a t r esu lts in the best hvdraulics s im u la t io n result: river bed

roughn ess c o efficien t is 0.029, left and over bank r o u g h n ess c o eííicien ts is both equal

0.10 W ith t h is set o f h yd rau lic param eters, effective level o f th e m odel com pu ted on

Nash norm is th e h ig h est (98.9%) and the forms o f c o m p u te d and m easu red water

suface e le v a t io n process graph a g r ee highly each oth er (F ig u re 3.2).

Stage (m)

Kigurc 3.2

Compiitcd and meastiriđ dail V slage proccss al Son Tav station ỉn 1993