VNU JO U R N A L OF SC IEN 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 Son, T ran N goe A nh
D e p a r tm 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 su re and one o f V ie tn a m 's w ell*

known tourism centers. The unstable water flow has caused erosion and
sedimentation belong to both Huong river banks, specially on the river segment
Crossing over H ue City vvhich are problem s m ust to be c o n tro lle d fo r re 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 studies on the progress of the river. Base on the surveyed
d a ta a n d c a lc u la tio n . the so ftw a re to tre a t and c o n tro l a ll collected data of

elevation m easurement and topographical map producũon of riverbed have been
built up. the present of sedimentation and erosion occurređ in tho Huong river
segm ent Crossing over Hue c ity and its consequences has been described
preliminarily, then withdrawn some suggestions on the main solutions for
minimizing sedimentation and erosion.

K ey w ords: S e d im e n ta tio 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 im e n t a t io n and erosioiì p ro cesses h a v e long b e e n o f in t e r e s t in th(‘
field 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 th o

s tu d v an d Torecast th e hyd ro log ical p r o c esses but w e a lso n e e đ to in v e s tig a te tho
actual

situation

as

vvell a s

to

m easure

real

data

using

for calib ratio n

and

v e r iííc a tio n of th e m o d e ls , and top ograp hical da ta are n e e d c d to in p u t o f th e m odels
d u r in g r u n n in g 011.


On the s e d i n ie n ta t i o n a n d erosion on ĩ lu o n g ri v e r .

83

A s o u n d e r F U R N O 4 3 0 0 w a s used to aid th e m e a s u r e m e n t o f w a t e r depth
from l.õ m to 3 5 0 m . T h e g e o g r a p h ic a l co-ordinate w a s c o n d u c te d a n d recorded u sin g
the GPS e q u ip m e n t G A R M IN II w ith the random error is a r o u n d 4 0 cm h o riz o n ta lly .
T he sca n n e r H P 3 2 0 0 w ith th e r e so lu tio n o f 3 0 0 dpi w a s u s e d to tr a n s fe r th e paper
graphs in to d ig ita l o n e .
P r e lim in a r y fi e ld su rv eỵs:

This is the initial survey to select the general line for im plem entation. The
mair. fe a tu r e s to be d ec id e d are:
•

Selection

•

I d e n tiíic a t io n 3 lin e s (left, right and m iđ d lc o f cross- sec tio n ) up a n d dovvn

o f m a in

obịectives 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 .

of the river segraent for measuring topography for longitudinal section.
•

S e le c tio n o f 100

positions fo r measuring river h o r iz o n t a l s e c tio n .

M ea su rin g m e th o d :
T he to p o g r a p h y o f th e riverbed w as p r e se n te d th r o u g h ơut th e e le v a t io n of


scanned

in t o

th e

im a g e s

th e n

w e re

a u to m a t ic a lly

d ig itis e d a n d tre 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 each 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 used to produce top og ra p h ical m ap o f H uong riv er bed by u s in g a m ap 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 base m a p w it h

1 :5 0 0 0 sca 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 rd in g to th e d e te r n in a te d r e g u la tio n .

3. R esults and discussion
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 iv e r c ro s s -s e c tio n fr o m V a n N ie n to B ao

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

llm

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 rg e vvater
d e p o s ite d s o il w a s ío rm 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 ke s


85

On the s e d i m e n t a t io n a n d erosion otì Huong river.

th e s u b - s e g m e n t g r a d u a lly suffered from h e a v y c u r v a tu r e an d th e river will
un dergo g r ea t c h a n g e o f current direction.
T h e d o w n s tre a m o f th e r iv e r m a y be becom e a " s ta 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 iro 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 se rve 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 cro ss th e s e c tio n o f r iv e r . N o bed
e ro s io n a n d

s e d im e n ta tio n

a re

fo u n d

th e re .


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 ha 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 vvith 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 ss- 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 rre 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 th

)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 cross- 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 itu d in a l s e c tio n s o f th 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

Van

N ie n

(1 6 .2 7 .7 1 I N

and

1 0 7 .3 4 .6 6 9 E


500

Fig. 1. Typical cross-section of th e íìrst sub- Fig. 2. T ypical cross-section of the second
segm ent

su b s e g m e n t

400

500

Fig.3. Typical cross-section of the third sub-

Fig.4 T ypical cross-section of the íourth

segm ent

su b s e g m e n t

500

500

Fig.5 Typical cross-section of the last sub-

Fig.6 Typical cross-section of th e la s t sul)

segm ent