VNU JO U R N A L OF S C IE N C E . N at , Sci , & Tech., T XIX, N01, 2003
ON T H K S E D IM E N T A T IO N A N D E R O S IO N O N H U O N G R IV E R S E G M E N T C R O S S IN G O V E R H U E C IT Y
N g u y ê n T h a n h S o n , T r a n N g o e A n h D e p a r t m e n t o f H y d r o M e te o r o lo g y a n d O c e a n o lo g v
C o ile g e o f S c ie n c e , V N U
A b s t r a c t : H ue City is a vvorld c u ltu r a l tre a s u re and one o f V ie tn a m 's w e ll*
known tourism centers. The unstable water flow has caused erosion and sedim entation belong to both Huong river banks, specially on the river segment C rossing over H u e City vvhich are problem s m u st to be c o n tro lle d fo r r e tu rn in g wonderful spectacle of Hue, a small pretty city in the middle of Vietnam Country.
The study is carried out with many difficulties in collection of hydrological data, it seem s that up to novv. there were almost no survey vvorks on sedimentation and erosion of tho Huong river. Thereíore ihe study results is setting up the base of continuous stud ies on the progress of the river. Base on the surveyed d a ta a n d c a lc u la tio n . the s o ftw a re to tre a t and c o n tro l a ll co lle cte d data o f elevation m easurem ent and topographical map producũon of riverbed have been built up. the present of sedimentation and erosion occurređ in tho Huong river segm en t Crossi ng o ve r Hue c ity and its consequences has been described preliminarily, then withdrawn some suggestions on the main solutions for minimizing sedim entation and erosion.
K ey w o r d s:
S e d im e n t a t io n , e ro s io n , r iv e r b e d .1. In tr o d u c tio n
T h e s e d i m e n t a t i o n a n d ero sio iì p r o c e s s e s h a v e lo n g b e e n o f i n t e r e s t in th(‘
f ie l d o f m o r p h o l o g y t o i n v e s t i g a t e t h e c h a n g e s of r i v e r b o d a n d b a n k e r o s i o n w i t h t h o flow r e g im e . S t u d i e s o f t h o s c p r o c e s s e s h a v e c o n t r i b u t e d g r e a t ly to our u n d e r s t a n d i n g o f t h e r e l a t i o n s h i p b e t w e e n rivor r e v o lu tio n p r o c c s s and w a t e r flow a s w e ll a s s o c io - e c o n o m ic a c t i v i t i e s on th e rivcr b a s in . In r e c e n t y e a r s , m a n y r e s e a r c h e s on th o m o d e l l i n g of s e d i m e n t tr a n s p o r tn t io n in t h e river h a s b ecn
composed, and most of them focuscd on the problems in th e larger river systems
su c h a s Red r iv er or M e k o n g r iv e r bu t th e r e w a s v e rv f’(ầw o n e s ĩo c u s e d on t h e rivers in th e M id d le o f V i e t n a m .A lt h o u g h m o d e l l i n g is n o w b e c o m in g th e v e ry c h e a p a n d e ffe c t iv e m eth o d to s t u d v a n d Torecast t h e h y d ro lo g ica l p r o c e s s e s but w e a ls o n e e đ to i n v e s t i g a t e tho a c t u a l s i t u a t i o n a s vvell a s to m e a s u r e r e a l d a t a u s i n g f o r c a l i b r a t i o n a n d v e r ií íc a t io n of t h e m o d e ls , a n d to p o g ra p h ic a l da ta are n e e d c d to i n p u t o f th e m od els d u r in g r u n n in g 011.
On t he s e d i n i e n t a t i o n a n d erosion on ĩ l u o n g r i v e r . 83
H u e c it y is a w orld c u ltu r a l tr o a s u r e and o n e o f V ie t n a m 's w e ll k n o w to u rism c e n tr e s . F o r a lo n g p e r io d , a n u n p la n n e d đ e v o lo p m e n t u n s u it a b lc la n d a n d w a tc r US(* o f th e c a t c h m e n t a re a a n d n in n n g e m e n t o f s o c io -e c o n o m ic a c t iv i t i e s h a s causecỉ p o llu t io n a n d đ e t r im e n t a l im p a c ts <)f’ th o c n v ir o n m e n t in v v h ic h ( le t e r io r a t io n o f H u o n g r iv o r b c c a m e s e rio u s m a t t o r o f la n d s c a p c o f Hucĩ r i ty . T h e u n s t a b le w a te r flo w h a s b e c n c a u s in g c ro s io n a n d s e c lim e n ta tio n b e lo n g l) o t li r iv e r b a n k s , s p e c ia llv o n th e s e g m e n t C ro s s in g o v e r H u e c it y vvhich a r c p r o b le m s m u s t to be c o n t r o lle d fo r r e t u r n in g vvonderful s p e c t r c l e o f H ue.
T h e o b j e c t iv e s o f ero sio n a n d s c d im e n t a t io n s u r v e y on H u o n g r iv er s e g m e n t
Crossing over Hue city are to prepare a report in which, it is needed to review and
c o llect d o c u m e n t s r e la t e d to v a r ia b ilit v o f flow a s vvell a s e r o s io n a n d s e d i m e n t a t i o n a s p e c t s on t h e H u o n g river. T h e n in order to g e t th e p ic t u r e o f t h e a c t u a l riverbedconditions in t h e s e g m e n t Crossing over Hue city, a n d acc ess t h e r eal State ()f
riverb a n k w e n è e d to build up a to p ograp h ic n iap o f th o s e g m e n t from V a n N ie n to Bao V in h . B a s e on t h e s e r e s u l t s a n d d is c u s s io n s w e p ro p o se a p p lic a t io n t e c h n i q u e s for m i n in iiz in g d e t r im o n t a l im p a c t s o f w a te r flow to so cial e c o n o m ic a s p e c t s o f Huo citv.2. M a t e r i a l s a n d m e t h o d s
I n s t r u m e n t a t i o n :
A s o u n d e r F U R N O 4 3 0 0 w a s u sed to aid th e m e a s u r e m e n t o f w a t e r d e p th from l . õ m to 3 5 0 m . T h e g e o g r a p h ic a l c o -o rd in a te w a s c o n d u c t e d a n d rec o r d e d u s in g th e G P S e q u i p m e n t G A R M IN II w it h th e ran d om error is a r o u n d 4 0 c m h o r iz o n ta lly . T h e s c a n n e r H P 3 2 0 0 w ith th e r e s o lu t io n o f 3 0 0 dpi w a s u s e d to t r a n s f e r t h e p a p er gra p h s i n t o d i g i t a l o n e .
P r e l i m i n a r y f i e l d s u r v e ỵ s :
This is the initial survey to select the general line for im plem entation. The
mair. f e a t u r e s to be d e c id e d are:•
Selection
o f m a inobịectives
a lo n g th e r i v e r f o r o b s e r v a tio n lin e s .• I d e n t i í i c a t i o n 3 l in e s (left, righ t and m iđ d lc o f c ro ss- s e c t io n ) up a n d dovvn
of the rive r segraent for measuring topography for longitudinal section.
• S e le c tio n o f 100
positions
f o rmeasuring river
h o r iz o n t a l s e c tio n .M e a s u rin g m e t h o d :
T h e to p o g r a p h y o f th e r iv er b e d w a s p r e s e n t e d t h r o u g h ơut t h e e l e v a t i o n of m a n / p o in t s vvithin t h e s t u d iẹ d a r e a . T h e e l e v a t i o n o f t h e r iv er b e d a t e a c h poin t w a s d e fin e d a s t h e d iffe re n c e betvveen th e w a t e r le v e l a n d t h e vvater d e p th s i i n t l t a n e o u s l y . U s i n g th e F U R N O 4 3 0 0 s o u n d e r t.0 o b s e r v e t h e w a t e r d e p t h in
84 N g u y e n T h a n h So n , T r o n N go e A n h c o m b in a tio n vvith th e w a t e r le v e l a n d m e a s u r e m e n t o f p o s itio n o f t h a t p oin t (recorded by th e G P S e q u ip m e n t ) .
D a ta t r e a t m e n t m e th o d :
T h e o u t p u t o f th e F Ư R N O 4 3 0 0 is th e p a p e r g r a p h p r e s e n tin g th e c h a n g in g o f th e w a te r d e p th w it h th e d is ta n c e fro m th e s u rv e y m a r k e r ( F ig 1.1 is a n e x a m p le ).
P ir s t ly , th e s e g ra p h s w e re s c a n n e d in t o th e im a g e s th e n w e re a u t o m a t ic a lly d ig it is e d a n d tr e a te d b y C o m p u te r r u n n in g in P a s c a l la n g u a g e (A p p . 1) to g e t th e a c tu a l w a te r d e p th a t e ach p o in t in th e lo n g it u d in a l a n d c ro s s s e c tio n a l. T h e n i t w a s u sed to produce to p o g ra p h ic a l m ap o f H u o n g r iv er bed by u s in g a m a p soítvvare.
T h e c o n to u r lin e o f to p o g r a p h ic a l m a p w e re d r a w n a t c o n to u r in t e r v a l o f 0 .5 m le v e l on th e b ase m a p w i t h 1 :5 0 0 0 s c a le a n d a re o b ta in e d b y in t e r p o la t io n fro m n e a re s t d e s ig n c o n to u r a n d t h e re fe re n c e c o n to u r lin e . A f t e r jo in in g a n d s m o o th in g c o n to u r lin e s w r it e it s v a lu e s o n th e r n a p a c c o r d in g to th e d e t e r n in a t e d r e g u la tio n .
3. R esults and d iscussion
T o p o g r a p h y o f h o r i z o n t a l c r o s s - s e c tio n
T o s tu d y th e to p o g r a p h y o f H u o n g r i v e r c ro s s -s e c tio n fr o m V a n N ie n to B a o V in h , b a s e d on th e v a r i a b i l i t y o f H u o n g r iv e r b e d to p o g r a p h y th e f u l l s e g m e n t w a s d iv id e d in t o 5 s u b -s e g m e n ts w i t h d iffe r e n c e s in b e tl to p o g r a p h y a n d in A u e n c e to s t a b il it y o f flo w r a te as:
1 * F r o m V a n N ie n to 1 k m u p v v a rd X u o c D u b r id g e
2 - F r o m 1 k m u p w a r d X u o c D u b r id g e to T h ie n M u p a g o d a 3 - F ro m T h ie n M u p a g o d a to p r e - s ite o f C o n H e n a re a 4 - S u b s e g m e n t p a s s in g C o n H e n a re a
5 - A f t e r C o n H e n to B a o V in h
- T h e c ro s s -s e c tio n o f t h e f i r s t s u b * s e g m e n t is p a r a b o lic fo rm v v ith th e m a in h y d r o d y n a m ic c h a n n e l is lo c a te d a t r ig h t o f th e c u r r e n t ( F ig . 1). I t is to be seem ed t h a t e ro s io n a n d s e d im e n t a tio n h a v e iV t o c c u rre d a lo n g b o th b o rd e rs as a t th o r iv e r b e d in th e su b * s e g m e n t.
- T h e
second
c ro s s -s e c tio n o f th e s u b -s e g m e n t is t r i a n g u l a r fo rm vvith its to p a t th e b o tto m , w h ic h is n e a r th e l e f t b o rd e r. T h e m a in h y d r o d y n a m ic flo w w a s d e c lin e d to le f t s id e a n d a n e d d y c u r r e n t vvas fo rm e d a ls o a lo n g th e le f t s id e (F ig . 2). H e a v y e ro s io n h a s o c c u rre đ o n th e le f t b o r d e r e s p e c ia lly in f lo o d in g a n d r a in y season. A n a n n u a l a v e ra g e o f 5 -1 0 m o f th e b a n k vvas e ro d e d . In c o m p a r is o n w it h th e c u r r e n t o f10 y e a rs ago, th e r iv e r s u b -s e g m e n t h a s tr a n s fe r r e d to th e l e f t sicỉe a d is ta n c e a b o u t 70* 8 0 m . A e ro d e u s u a lly vvas fo rm e d a lo n g le f t s id e a t w a t e r d e p th fro m l l m to 19m . T h e e ro d e d s o il w a s b r o u g h t to th e o p p o s ite s id e a n d a v e r v la r g e vvater d e p o s ite d s o il w a s ío r m e d a lo n g th e r ig h t s id e o f s u b - s e g m e n t. T h is s it u a t io n m a k e s
On the s e d i m e n t a t i o n a n d erosion otì H u o n g river. 85
th e s u b - s e g m e n t g r a d u a ll y suffered from h e a v y c u r v a tu r e a n d th e river w ill u n d e rg o g r e a t c h a n g e o f cu r re n t direction.
T h e d o w n s tre a m o f th e r iv e r m a y be beco m e a " s t a g n a n t w a te r a re a " vvhich w i l l cause a d e t r im e n t a l im p a c t on e n v ir o n m e n t a n d la n d s c a p e o f H u e C ity.
- T h e t h i r d s u b -s e g m e n t is o b s e rv e d in to 15 c ro s s -s e c tio n s (F ig . 3). T h e flo w is s te a d y . A v v a te r d e p th (Vorn 5 m to 1.0m is ĩo u n d a c ro s s th e s e c tio n o f r iv e r . N o b ed e ro s io n a n d s e d im e n t a tio n a re fo u n d th e re . B u t th e G ia V ie n fix e d d u n e h a s e m e r g e i a t r i g h t b o r d e r , n e a r B a ch H o b rid g e a n d b y v v h ic h th e flo w r a te is a r re s te d a n d a c c u m u la te d s e đ im e n t a tio n at th e r iv e r bed is fo u n d . T h e s u b -s e g m e n t r u n s a c ro s s H u e C i t y \v ith b o th s id e s w e re b u i l t u p w it h s to n e t h u s n o b o r d e r e ro s io n w a s fo u n d . 3 u t r u n o f f d is c h a r g e d fro m s m a lle r in flo v v a t th e le f t s id e o f th e r iv e r in t o t h is s e ^ m e n t, w h ic h h a s b r o u g h t a lso s e d im e n ta tio n m a te r ia ls . I t ca n be seem ed c le a r ly : h a t t h e m o s t c ro s s -s e c tio n a re r a th e r f la t w i t h a v e ra g e vv a te r d e p th o f 4- 5 m a n d s e d im e n ta tio n vvas d is t r ib u t e d o n a ll a re a o f t h e r iv e r b o tto m . B u t a t th e c ro s s -s e c tio n b e fo re a n d a f t e r B a ch H o, T r a n g T ie n , P h u X u a n b rid g e , th e r e a re a bed slope fr o m le f t to r i g h t s id e v v ith d e p th w a te r o f 7 -8 m . I n g e n e ra l, r iv e r b o tto n i e ro s io n does n o t h a p p e n a n d s e d im c n t a v a ila b ilit y on t h is s e c tio n is v e ry h ig h a n d th e m a in h v d r o d y n a m ic ílovv o c c u rre d u n c le a r ly .
• AỈ1 c ro s s -s e c tio n s o f th e f o u r th s ư b -s e g m e n t is r a t h e r f l a t (F ig . 4) w it h d e p th w a t e r o:‘ 3 -4 m . T h is is a n a re a h a v in g h e a v y s e d im e n ta tio n c a u s e d b y th e b r a n c h in g f lo w o ff a n d s m a ll f lo w r a te . I n a d d itio n , in d r y se a so n , th e s e g m e n t is tid e d u p ,
salt waier also created favourable condition for sedimentation on the river bottom.
- C ro s s -s e c tio n s o f th e la s t s u b -s e g m e n t h a s th e a v e ra g e (lo p th o f 3 -7 m a n d its b o tto m slope r u n s lo f t to r i g h t b o rd e r v v ith th e w a te r d e p th v a r ie s fro m 3 to 6- 7m . T h is s e ^ m e n t h a s th e cro s s - s e c tio n w a s v e ry n a r r o w t h u s th e flo w r a te in c re a s e d a n d b e ò s c o u r in g w a s o c c u r r e d . A t dovvn s tre a m o f th e b e n d , th e r e is a b o u t 6 0 0 m o f le n g t h )f th e r i g h t s id e vvas s tr o n g ly e ro d e d c a u s in g b y h y d r o d y n a m ic c h a n n e l p a s s in g b e n d a re a . I t c a n be seen on cro ss- s e c tio n s in F ig . 5, F ig . 6.
T c o o g r a p h y o f l o n g i t u d i n a l s e c tio n
w * h a v e in v e s tig a t e d 3 lo n g it u d in a l s e c tio n s o f t h e r iv e r s e g m e n t. T h e f i r s t is fro m B ỉo V in h to V a n N ie n (1 6 .2 7 .7 1 I N a n d 1 0 7 .3 4 .6 6 9 E to 1 6 .2 5 .7 3 N a n d 1 0 7 .3 3 3 2 8 8 E ) a lo n g le f t s id e t h a t is f a r fro m th e b o r d e r a b o u t 2 0 -3 0 m . T h e second s e c tio n vvas đ e c e r m in e d in th e m id d lè of the c u r r e n t a n d b e g in from V an N ien (1 6 .2 5 .7 J 0 N a n d 1 0 7 .3 3 .2 6 4 E ) to B a o V in h (1 6 .2 9 .7 6 0 N a n d 1 0 7 .3 4 .6 4 0 E . T h e t h ir d s e c tio n v a s d e íin e d a lo n g th e r ig h t s id e fa r fr o m t h e s h o re a b o u t 2 0 -3 0 m fro rn Bao V in h ( li. 2 9 . 7 4 0 N a n d 1 0 7 .3 4 .6 7 5 E ) to V a n N ie n ( 1 6 .2 5 .7 6 1 N a n d 1 0 7 .3 3 .6 2 0 E ). H h e r e s u lt s ro m t h e w a tẽ r c ie p th rn e a s u re đ lin e on th e lo n g it u d in a l s e c tio n h a v e s h o w n t h a t d if e r e n t s e d im e n t a tio n a n d e r o s i o n l e v e l w ere o c c ư rre d in th e d r y e r
s e g m e n t .
86 N g u y e n T h a n h S o n , T r a n N g o e A n h
500 200 300 400 500
Fig. 1.
T ypical c ro ss-sectio n of th e íìrst sub-Fig. 2.
T yp ical cro ss-section o f th e secon ds e g m e n t s u b s e g m e n t
400 500
Fig.3.
T ypical cro ss-se c tio n o f th e third sub-Fig.4
T yp ical cross-sectio n of th e íourths e g m e n t s u b s e g m e n t
500 500
Fig.5
T ypical c ro ss-sectio n of th e la st sub-Fig.6
T ypical cro ss-se c tio n of th e l a s t sul)s e g m e n t s e g m e n t
On t h e b a s e o f 3 l o n g i t u d i n a l s e c t io n s and froiiì d e p th m e a s u r i n g d a t a , s o m e r e m a r k s o f to p o g r a p h ic a l c h a n g e s could be p r e s e n t e d a s follows:
• S c c t io n from V an N i c n to Xuoc Du B rid ge. T h e bed t o p o g r a p h y d o e s not c h a n g e a c c i d e n t a l l y on t h e 3 v e r t ic a l c r o s s - s e c t io n s . T h e d e p t h o f r iv er v a r i e s from 3 to 6 m vvith t h e d e e p e s t r u n n e l in t h e m id d le. It vvas fou nd a t t h e b o tto m s o m e sh o r t s a n d w a v e .
• S e c t io n from X u o c Du brid ge to T h ie n Mu p a g o d a . It is th e m o s t ty p ica l
eroded section of t h e s e g m e n t . For exam ple a t lcft side t h e r e is a n unstn bl o
0 /1
//ỉ<? s c d i m c n t a t ỉ o n a n d crosion 0/1 H u o n g river. 87
l o n g i t u d i n a l s e c tio n , th o vvater <l(‘Ị)th. vvhieh is far from th e bordcr ()f 2 0 - 3 0 m v a r ie s from 5 to 8 m and a t X uoc Du b r id g e up to 17m. It is s h o w e d t h a t s c o u r in g p r o c e s s is h a p p e n i n g and w ill b e c o n t i n u e a t s e r io u s lc v el. Tho bed to p o g ra p h y is r o u g h a lo n g
tho r i g h t side a n d t h e middle of vertical cross-sections. So, t h e left side of t h e r i v e r
s e c t i o n m u s t be p aid m a n y a t t c n t i o n of in v e s t i g a t i o n in d e t a il to find ou t th e b e s t s o l u t i o n s .- S e c t io n from T h ie n Mu pagod a to Con H en . T h e lo n gitu cỉin al s e c t i o n
varies
v v ith t h e d e p tlì fr o m 4 to I m . H o w e v e r, th e r e a re a n im m e r g e d d u n e a t b o tto m before B ach Ho b r id g e a n d a b ig d u n e im m e r s in g betvveen P h u X u a n a n d T r a n g T ie n B r i d g e and do n ot find o u t th e m a in h y d r o d y n a m ic c h a n n e l of th e c u r r e n t.
- S e c tio n p á s s i n g C o n H e n a r c a . 3 lo n g it u d in a l s e c t i o n s o f C o n H e n a re a a re s im ila r . T h e shallcnv w a t e r d e p th o f 2-3m is m u ch lo w er th a n th a t of u p a n d dovvn river s e c t i o n . ỉt is p roved t h a t th e sec tio n h a v in g th e ĩa v o u r a b le c o n d i t i o n s for s e d i m e n t a t i o n . It c a n be found t h a t íầ cto rs c a u s i n g s e d i n i e n t a t i o n w e r e a c t e d in th e s a m e t y p e and spread ecỉ o v er th e r iv er bed s e c tio n .
- S e c tio n a f t e r Con H en to B ao V inh . T o p o g r a p h y o f
lo ng itudin al
s e c t i o n v a r ie s w ith w a t e r d e p th ÍVoni 5 to l l m and th e bottorn s lo p e to tho dovvn s t r e a m . H y d r o d y n a m ic c h a n n e l is in th e m id d le of th e c u r r e n t. T h e vert ical c r o s s - s e c t i o n of r ig h t s id e is u n s ta b le d u e to l i t t l e e ro s io n h a s o c c u rre d a lo n g t he side.B o t t o m to p o g r a p h y
A c co r d in g to H u o n g R iver b o tto m to p o g ra p h ic a l m ap w ith s c a le 1 :5 0 0 0 th e r e a re a b o u t 70 % o f th e r iv e r b ed a re a fro m V a n N ie n to B a o - V in h a t a n e le v a t io n o f 3-5m vvater d ep th . T h e m a x im u m d ep th is 19.8m a t t h e c r o s s -s e c tio n M C 1 9 (n ea r
Xuoc Du bridge). Gencrally in the studicd river area, the deposition of sediment was
d o m in a n t . It could be d iv id e d in to 4 a r e a s for t h is river s e g m e n t .T h e first is from V an N i e n to lk m u p w a rd X uoc Du bridge. T h o b o tto m to p o g ra p h ic a l m a p s h o w e d t h a t th o riverbed is s t e a d y . T h e w a t c r lin e o f m a x im u m d epth is d is t r ib u t e d n e a r th e m id d le of th e c u r re n t. T h o g c o lo g ic a l f o u n d a t io n o f t h is se c tio n is q u it e d u r a b le . T h e r e ío r e , t h e r e a r e h ig h s t a b i l i t y o f flow ra te.
T h e s ec o n d is from l k m u p w a r d Xuoc D u b rid g e to T h ie n M u p a g o d a . It is th e d e e p e s t a r e a and i t s b o tto m to p o g ra p h y g r e a t lv s p e c ia l ly in th e c u r v a t u r e s e c tio n n e a r Xuoc Du b r id g e . (b efore Xuoc Du bridge 1.5 kin a n d b c h in d 1 km ). T h e b o tto m top og ra p h y of th e a r e a v a r ie s from 2.9 to 19m . T h e r c f o r è t the h y d r o d y n a m ic c h a n n c l g o e s to th e l e f t s id e a n d c a u s e h e a v y e ro sio n a t t h e s id e vvith d i s t a n c e o f more th a n 2 k m . E roded soil w a s b r o u g h t to t h e o p p o s it e s i d e and a v e r y la r g e a llu v ia l grou n d w a s form ed a lo n g t h e right s id e w h ic h h a s c a u s e d t h e c h a n g e o f
direction current of this river segment. A erođed gully was formed along the left side at w a t e r d e p th from 11 to 19m. It can be seen t h a t t he c u r r e n t of t h is s e g m e n t
h a s tr a n s íẹ r r e d to th e h»ft s id o a b o u t 7 0 -8 0 m w h e n c o n ip a r in g w ith t o p o g r a p h ic a l
8 8
N g u y en T h a n h So n , T r a n Ngoe A n h
m a p e s ta b lis h e d in 1986. T h e s e c tio n a lo n g T h ie n M u pagocỉa a re a is in í lu e ic e d b y m o u n ta in s s v s te m a t le f t s id e o f th e r iv e r , so t h a t th e h y d r o d y n a m ic c h a n n e l h a s g o n e to l e f t s id e a n d th e r e a re a ls o a r u n n e l a t r iv e r b o tto m w it h d e p th u p to 8 .Ồm.
F ro m t h e r e to th e dovvn s tre a m o f t h is s e c tio n th e r iv e r flo w is m o re a r d m o re s te a d y .
T h e t h ir d is fro m T h ie n M u p a g o d a to Con H e n a re a . T h e b o t t o m to p * g r a p h y o f th e s e c tio n is q u ite f la t . M o s t b o tto m to p o g r a p h y h a s e le v a tio n d iff e r e n c e ) f 2 -4 m . W it h th e le n g th o f 5 0 0 m b e fo re G ia V ie n d u n e , th e d iffe r e n c e o f b o t t o m to p > g ra p h y is fr o m 2 -3 m , w h ic h is e a s y to c re a te A o a tin g d u n e in d r y se a s o n . A t le f t s de n e a r B a c h H o b r id g e h a s a r u n n e l v v ith d e p th o f õ to 7m . H o v v e v e r, a s m a ll s a n d dan e h a s b e e n e s ta b lis h e d a n d is r u n n in g g r a d u a lly to th e N o r t h . S e d im e n t a t io n alsc fo rm e d in a re a s u r r o u n d in g P h u X u a n b r id g e . 11 c re a te d im m e rg e d d u n e a t th e b o tto m v v ith s iz e as la rg e as G ia v ie n d u n e . In g e n e ra l, t h is a re a n e e d s s c ra p e fo r : r e a tin g th e h y d r o d y n a m ic c o r r id o r w h ic h is n e c e s s a ry f o r p r o te c tio n o f s e d im e n ta ù o n a n d m a in t a in in g s t a b il it y o f th e f lo w ra te , fo r p u s h in g u p e ro d e d m a t e r ia l at b o tto m r iv e r to th e d o w n s tre a m a n d m a in t a in in g th e n a v ig a t io n c h a n n e l f o r s h ip s a n d o t h e r s o c io -e c o n o m ic a l a c t iv it ie s o n th e r iv e r in d r y se a so n .
T h e a re a fr o m C o n H e n to B a o V in h h a s a to p o g r a p h ic a l d iffe r e n c e o f th e b o tto rn w h ic h f lu c t u a t e betvveen 4 .5 a n d 8 m o f v v a te r d e p th . B e c a u s e oí n a r r o w h o r iz o n t a l c ro s s -s e c tio n in t h is c u r v a t u r e s e c tio n th e fio w ra te is in c re a s e d a n d th e r iv e r b o tto m w a s e ro d e d . 'T h e h v d r o d y n a m ic c h a n n e l in th e m id d le o f th e c u r r e n t a n d flo w r a te is q u ite s te a d y .
S o m e m a ỉ n s o l u t i o n s to m i n i m i z e s e d i m e n t a t i o n a n d e r o s i o n o f th e r iu e r s e g m e n t
H u o n g r iv e r h a s r e la te d w i t h H u e o ld c it y d u r in g it s d e v o lo p in e n t p e rio d . T h e p r o t e c tio n o f H u o n g r iv e r is a ls o th e p r o te c tio n o f H u e c it y , so t h a t i t is e s s e n tia l to d e v e lo p e ffe c tiv e p r a c tic e s in o r d e r to p r e v e n t a n d o v e rc o m e e n v ir o n m e n ta l c o n s e q u e n c e s . In te g r a te d p r a c tic e s o f a l l a s p e c ts s u c h a s Science a n d te c h n o lo g y
m anagement options, environmental
e d u c a tio nare necessary Ểor solving this
p r o b le m . In t h is r e p o r t, som e m a in s o lu tio n s vvere p ro p o s e d to s o lv e s e d im e n ta tio n a n d e ro s io n in th e s t u d y in g r iv e r s e g m e n t, s u c h as:
- R e b u ild in g th e flow d ir e c t io n o f c u r v a t u r e s e c tio n a t X u o c D u b rid g e for r o h a b ili t a t i n g s te a d y
State
o f th e c u r r e n t h y b u ild in g s to n e s p u r s y s te m s a t th e le f t s id e o f th e r iv e r a t th e s ite o f 2 -3 k m b e íb re X u o c D u b r id g e . I t is n«ecessary to b u ild s to n e s p u r s y s te m s w i t h th e s p u r le n g th o f 30- 4 0 m a n d s e p a r a tin g e a ch o th e r a b o u t 5 0 - 7 0 rn . T h e s p u r m u s t be h ig h e n o u g h to p r e v e n t w a te r le a v in g 0'f H u o n g r iv e r in th e flo o d in g se a so n . T h e s to n e s p u r s y s te m s m a in t a in th e s te a d y flc -w fo r p r e v e n tin g a c o m p le te c h a n g e o f c u r r e n t d ir e c t io n vvh ich m a y c a u s e H u o n g r i v e r d o w n s tre a m b e c o m in g "a s ta g n a n t w a te r a re a ".O n the s e d i m e n t a t i o n a n d erosion on Hĩiong river. 89
- S t r e n g c h e n i n g scra p e off tho rivcr bed in th e a rca from G ia V ien to Con Hen f o r c r e a t in g a g r e a t h y d r o d y n a m ic c o r r iđ o r a n d m a in t a in in g a h ig h flo w ra te fo r s c o u r in g s te p b y s te p s e d im e n ta tio n a t th e r iv e r b e d a re a . G e n e ra l s c ra p e n e e d s to be don e in s h o r t tim e a n d s u p p le m e n ta r v s c ra p e is n e c e s s a ry fo r S 0 Ỉ 1 1 0 y e a rs .
- C a r e ĩ u l n ia n a g e m e n t o f e n g in e e r in g w o rk s o f s a lt y p r e v e n tio n fr o m tid e p r o p a g a tin g t o C o n H e n a re a w h ic h c a u s e d h e a v y s e d im e n t a tio n a t r iv e r b o tto m o f th o s e c tio n .
- C o n s o lid a t in g íb re s t e c o s y s te m in u p s tr e a m a r e a fo r r e g u la t in g w a te r a v a ila b ilit y o f th e c a tc h m e n t a n d flo w r a te in th e flo o d in g se a so n , in c r e a s in g w a te r H o ld in g c a p a c ity in th e s o il a n d c o n tr o l s u rfa c e e ro s io n o f th e slo p e a re a .
References
1. F i n c l R e p o r t o f P r o ịe c t K C - 1 2 , M in i s t r y o f W a t e r R e s o u rc e .
2. N g u ỵ e n T r o n g H ie u , D a ta s e ts a n d c l i m a t o l o g i c a l a t l a s o f V i e tn a m , P r o je c t 4 2 A 0 1 .0 1 . H y d ro - M e te o r ơ lo g ic a l S e rv ic e o f V ie tn a m
TAP CHỈ KHOA H Ọ C Đ HQ G H N. KHTN & CN, T XIX, No1 ,2 0 0 3 _________
VỂ BỔI, XÓI ĐOẠN SÒNG HƯƠNG CHẢY Q U A THÀNH PHỐ H ư Ế VÀ CÁC GIẢI P H Á P GIẢM T H IÊ U
N g u y ễ n T h a n h S ơ n , T r ầ n N g ọ c A n h
Khoa Khí tượng Thủy văn & Hải dương học Đại học Khoa học Tự nhiên
,ĐHQG Hà Nội
Huè là m ộ t t h à n h phô'du lịch và là di s ả n v ă n hoá t h ế giới đã được U N E S C O c ô n g n h ệ n . S ô n g H ư ơ n g là m ộ t c ả n h q u a n q u a n t r ọ n g c ủ a H u ế , h iệ n n a y đ a n g b ị s u y th o á i trể m t r ọ n g do t ì n h t r ạ n g b ổ i xó i lò n g sông. N g h iê n cứ u b ồ i, x ó i và t ìm ra các g iả i p h á ĩ g iả m th iể u là m ộ t n h iệ m v ụ c ấ p b á c h n h ằ m b ảo vệ th à n h p h ô và các c ả n h q u a n m ô tr ư ờ n g củ a nó.
Dựi t r ê n các k ế t quả k h ả o s á t lò n g sô n g H ư ơ n g b ằ n g m á y đo sâ u hồi âm F Ư R N O 1300, đ o ạ n c h ả y q u a t h à n h H u ế từ V ạ n N iê n đ ế n B a o V in h , các tá c g iả đ ã th ự c h iệ i được m ô t sô" n ộ i d u n g sa u :
- X iy d ự n g p h ầ n m ề m xử lý tín h to á n sô liệ u k h ả o s á t, lậ p b ìn h đồ đ o ạ n s ô n g t ỷ lệ 1: 5 )0 0 p h ụ c v ụ c ô n g tá c q u y h o ạ c h t h u ỷ lợ i, g ia o t h ô n g và các lĩ n h vự c k in h tê quốc dâr k h á c .
- Mô tả c á c đ o ạ n s ô n g có h iệ n tư ợ n g b ồ i, x ó i đ ặ c b iệ t n g u y h iể m và đề x u â 't m ộ t sô g iả i p iá p n h ằ m h ạ n ch ế c h ú n g .
