VNU Ji>umal of Science, Earth Sciences 25 (2009) 223-231
A nalyse the íluctuation and w ater level trend in Saigon - Dong Nai river system
Luong Van Viet*, Pham Dang Manh Hong Luan, Le A nh Tuan
Sub-Institute o f H ydro- M etcoroỉogy an d Environm ent o f S o u th Vietnam Received 17 November 2009
A bstract. Beside the eíTcct o f gravitational íòrces, the vvater level in Sai Gon-Dong Nai River System is also aíĩected by non gravitational ĩorces such a wind, air pressure, rainfall and sea ỉevel risc. The purpose o f this papcr is to simulate the vvater ỉevel o f these river based on the tidal and non-tidal constituents, from that assess the roỉe o f non-tidaỉ constituents to w ater variation. In this study, the none-tidal data used includes the wind fíeld at surface, sea ỉevel prcssure and the rainíaỉl in Sai Gon - Dong Nai Basin. VVith the analyzed data series from 1980 to 2007, the resuỉls show thai after supplementing the non-tidal elements, the water leveỉ simulation quality is increased, the wind and rainíaỉl have an important role lo water ỉevel. The results also show that near river mouths, the vvater level raised 13 cm from 1980-2007 duc to the global clim ate change.
Keywords: tidaỉ harmonic analysis, non-tidal constituents, sea lcvel rise
1. C e n e r a liz a tio n
T h e D ong N ai - Sai G o n riv er system vvhosc w atersh ed area is ap p ro x im ately 45,0 00 k m is the seco n d largest riv er sy stem in the S o u th ern p ro v in ces. T h ese riv er system c o m p rise s o f m a in riv ers in clu d in g La N ga, Be, D o n g N ai, Sai G o n , N ha Be and rivers ending u p in G anh R ai bay. It is th e w atershed c o v e rin g m ain eco n o m ic zo n e in the South w h ich has m a n y activ ities relaíed to w ater reso u rces, th e d o w n sư e a m o f th e area is low an d v u ln e ra b le to sea level rise eíĩe c ts.
T h e re ío re , sh o rt - term and lo ng - term forecast o f w ater level in this area is a sig n iíìcan t d em an d .
•---
Corresponding author. Tel.: 84-4-38275971 E-mail: lgviet@yahoo.com
T id e reg im e o f riv e r sy stem in the research ed a re a is se m i-d iu m a l ty p e w ith tide a m p litu d e p re tty h ig h . A p a rt fro m th e eíTect o f tid e, w ater level v a ria tio n in th e area is also aíTected by ra in fa ll, w in d íìeld and a ir pressure.
T h e y e a rly a v e ra g e rainfall o f this vvatershed is 2 0 2 8 m m an d co ncen trates m ainly from M ay to N o v e m b e r w ith ab ove 90% [1].
T h e rain fall w h ich is n o t e q u ally distrib u ted and m a in ly c o n c e n tra te s in rain y season caused sig n iíìc a n t e íĩe c t o n w a te r level. In addition, dry season a n d lo n g - lastin g h eav y rain s are also íacto rs th a t g re a tly affect w a te r level variatio n.
T h e effect o f w in d o n w ater level rise in the area c an b e c le a rly seen in d ry season. In this p eriod, th e vvind a t th e sea su rface has m ain d irection from E a st to S o u th East. D ue to the
224 L.V. Viet et al. / VN U Ịournaỉ o f Science, Earth Sciences 25 (2009) 223-231
land - sea interactio n, th ere is sh arp d aily ch ang e o f d aily w in d directio n. F rom 5 am to 12 am , the p rev alen t w in d d irection is usually betw een E ast and E ast N o rth E ast w h ich n early m atches th e vvind d irection on th e sea. From 2 pm to 2 am , d u e to th e e íĩe c t o f sea - land w ind, the p rev alen t w ind d irectio n is S outh E ast [1]. T his vvind d irection m atches the directio n o f riv er m o u th s in G anh Rai bay, co n trib u tin g to th e tran sp o rtin g o f salinity d eep in the land as vvell as raisin g w a te r level. C o m p ared w ith daily av erag e w in d sp eed , the S outh East w ind speed can in crease from 1.5 to 2 tim es [2]. A t areas near th e sea, the w ater level can in crease sig n iíìca n tly w hcn th is w in d zo n e is strong.
D ue to the íre q u e n t a p p e a ra n c e o f w ind w ith directio n froirì N E to S E in dry season s (fro m the end o f O c to b e r an d la stin g till the end o f A pril), the w a te r level rises and salinity in tru des to the land, w h ich c an b rin g on the e íĩe c ts on ag ric u ltu re p ro d u ctio n so th at the vvind is also n a m e đ “C h u o n g W ind ” in tradition. Hovvever, th e m o st sig n ific a n t w ind is still S E w ind b eca u se o f its h ig h v elo cily and d u e to the fact th at it run s p arallcl to th e river m ouths. A parl from th e e d g e o f A sia C o n tin e n ta l cold h ig h p ressu re sy stem , C h u o n g W ind is also o rig in a te d from b rccz e an d ed g e o f N orlh P aciiìc O cean h ig h p ressu re system .
2-3m/s 3-4m/s 5-€m/s >6m/s
f l ị .. z
0% 10%
I—I—I—I—I—l—
50%
Fig. 1. Wind rose o f February and July, Tan Son Nhat station.
B eside th e e ffe c t o f tid e - fo rm in g forces, w in d an d th e rain íall in th e area, th ere is also hu g e im pact o f sea level rise due to clim ate ch ang e on w a te r level. T h e an aly sis o f the roles o f n on-tidal factors o n w ater level is stro ng ly n ecessary in w ater level íbrecasting.
2. M eỉh o d o lo g y and d ata used
2 .1 M ethodology
T h e an aly sis o f w ater level A uctuation and trend is bascd on h am io n ic an aly zin g m cthod su p p lem en ted w ith no n-tidal elem ents. W ater
level at a certain tim e is co n sid cre d th e su m o f tidal vvater level an d the affected p art o f n o n - tidal elem en ts:
Z , = z , + f , (1)
In w hich z , is th e sim ulatcd w ater level at tim e t, z, is the tidal w ater level, z \ is v ariation part o f the w ater lev el d u c to non-tidal factors.
T h e tidal vvater level z t , a c c o rd in g to harm o nic a n a ly z in g m cth o d , was:
n
z , = z n + c o s ( + ( K + u ) i - g i ) (2)
i - 1 . n
F c b r u a r y
L.v. Vict ct ứ/. / V N U Ịournưl o f Science, Earth Sciences 25 (2009) 223-23ĩ 225
H e re , Zois U c c o n s ta n t; H „ q „ g„ fh (Vo+u)i are am p litu d e, >peed and initial phase angle, am p litu d e s c a ln g íacto rs and phase ang le o ffse ts o f ilh co n ititu en t, w ith i = 1, 2, . . n and n is th e n u n ib e ro f con stitucnts. T h e values o f f, an d (V 0 + u), depend on tim e and can be look up fro m ta b le o r calcu lated by astron om ical functions.
In th is study, co m p o n en t z \ includes vvater level v ariatio n by w in d ( z * ), air p ressure ( z ,p ), rainfall (2* ) in the w atersh ed and the tren d o f w ater level rise due to g lobal clim ate ch a n g e (z ] r ):
7 1 = 7 R + 7 * * + 7 p ' + 7 Tr' n ì
z Zị t z ( T z , ( ó )
C o m p o n c n ts in z \ are con sid ered the total o f th e lin c a r im p a c ls a n d e q u a tio n (1 ) c a n be so lv ed b y linear regression m ethod w ith the foIlow in g step s o f assu m in g sub-unknow n:
B y a s s u m in g R l = f lH l a n d c = g , ~ ( V 0 + u ị , z t w ill b e c o m e :
n
2 , = 2 Ơ + z R iCOs(q,t - c ẽ) (4 )
Ì - /
B y assu n iin g x Ị = R lc o s(C l ) and x ‘ = R ^ i n í C ị ) , (4 ) can b c perform cd as:
z, = z0 + [cos^C, M + sinrc, )x2, ] (5)
i-l
By assu m in g a l ị = c o s ( C ị) and a 2 ị = sin (C ẳ) , eq u atio n (5) beco m es the fo llow ing lin ear equation:
z, = z 0 + Ỳ X a l i x l i
+
a2i x2i }(6)
i-1
In this stu d y , co m p o n en ts o f z ’i in equation (3 ) can be ex p ressed by the follow ing linear
function:
m
ỵ t a3j x3J ( 7 )
/=l
In this eq u atio n , m is the nu m ber o f affectin g factors, a 3 j are co n stan ts, X3 is affectin g íactors, j = 1, 2, m. W ith rainfall, the aíTecting factors in clu d e to tal rain íall on the w atersh ed accu m u lated from lh to 2 4 h , 25h - 96h, 97 h - 264 h an d 26 5h - 6 2 4 h b efo re tim e t.
W ith w ind specd and air p ressu re, aíĩe c tin g íacto rs include w in d v ccto r 10 m , sea surĩace pressure. T hese c o m p o n e n ts are av erag ed on th e ch o sen arca w ith cu m u lativ e tim e rang es Oh - lh , 2h - 5h, 6h - I4 h , 15h - 30h, 31h - 55h befo re tim e t. C o m p o n e n ts ex p ressin g w ater levcl trend d r i v e n b y g lobal c lim ate is th e last co m p o n en t o f z \ vvith v alu e o f (ỉ3mx 3 m in w h ic h x3 m is e q u a l t.
C o m b in e eq u atio n (6 ), (7), and (1 ), the fu nction p e ríb rm in g Z t is:
Z, = z 0 + Ẻ ỉa / ‘ x / < + <>2i x2i ] + zi (8) /»/
O r:
z , = Zo + Ỳ Ả aI‘xI‘ +a2ix2í] + Ỹ ềa3j x3j (9)
/=/ >-/
W ith th e se tran sfo rm a tio n s, eq u atio n (9) has lin ear form w ith fo llo w in g v ariab les: x l Ễ , x2 ị an d x 3 j . T h is eq u a tio n w ill be solved by m u ltip le linear reg ressio n m e th o d w h ich is b ased on m inim um squ are m ethod. Hovvever, in o rd e r to ch o o se su ita b le tidal as vvell as non- tidal factor, in this stu d y , o n ly m u ltiple linear reg ressio n is ap plied. T h e seq u en tial m u ltiple linear regression is sim ilar to m u ltip le linear regression in w h ich the eq u atio n qu ality gained is th e b est by ro tatin g m atrix o f affectin g íactors ch o sen from eq u atio n b u ild in g steps.
A fter solving out variables x l ẵ and x 2 ị th ro ugh interm ediate steps, R, and £ á can be
226 L .v. Viel el al. / V N U Ịournal o f Science, Earlh Sciences 25 (2009) 223-231
d eíìn ed and then H, and g, can also be deíined.
By replacing these values in to (2), tidal w ater level wil! be d eíìn ed at any g iven time.
In o rd er to im p ro ve th e q u ality o f z , m a n ip u latio n , the p ro cess to b u ild the eq u atio n follow s tw o steps belovv:
- S tep 1: B uilding a3J factors throu gh eq uation (9) for ev ery m o n th w ith w ater level o b serv ed from 1980 to 2004.
- Step 2: B uild in g v alu es o f H, an d g, th ro ug h o n e - y e a r d ata o f o b serv ed w ater level ch o sen ran d o m ly from data series o f tim e perio d from 1980 to 2004 th rou gh eq u atio n (8) w h en the v alue o f
z ' f is s o l v c d o u t from v alu es o f a 3 j . T h e assessm cn t o f the qu ality o f the eq u atio n is th ro u g h statistical ĩa cto rs includ ing F ish er statistical index, th e d ev iatio n o f reg ressiv e factors, d efin in g facto rs, m ean erro r and m ax crror. T h ese facto rs are also d eterm in in g facto r for th e n u m b e r o f w av e to be cho sen. T he n u m b e r o f w av e w ill be d epen dent on th e length o f an aly zin g series and the featu res o f every area. F or th e stu d ied area , if
the length o f d ata series is lo n g en o u g h , the nu m b er o f w av e ch o sen w ill ra n g e from 18 for on an d near- sea locations to 22 for lo catio n s lying d e e p in the land.
B esides, th e qu ality o f sim u la tin g w ater level is also assessed by o b se rv e d w ater level data w hich is no t included to b u ild , H, and g, factors. T h is data is taken fro m 2005 to 2 0 07 .
2.2 D ata u sed
T h e d ata used in th is s tu d y in clu des d a ta o f ob serv ed vvater level, rain fa ll, w in d a n d air pressure. T im e rang e o f th e se d ata se rie s is from 1980 to 2007. T h e w a te r level d a ta is hou rly o b serv ed data. T he ra in ía ll d a ta is d aily data, th e w in d an d air p re ssu re d a ta ty p e are taken 4 tim es a d ay. In o rd e r to tra n síb rm th e se data to th e sam e tim e reso lu tio n w ith w ater level d ata, th cy w ill bc be in terp o lated by u sin g linear m ethod
T h e w ater level m o n ito rin g sta tio n s th a t are used in the an aly sis in clude V u n g T a u , N h a B e, Phu A n, H oa A n, Ben Luc and T an A n. T h e lo catio n s o f these statio n s are illu stra te d in F igure 2.
Fig. 2. Localion o f water level stations.
L . v . Viet et al. ỉ V N U lournal o f Science, Earth Sciences 25 (2009) 223-231 227
T h e w ind a n d a ir p re s s u re d a ta a re fro m g lo b al re a m ly z e d d ata o f N C E P in the
fo llo w in g link
h ttp ://w w w .cJc.n o aa.g o v /d ata/g rid d c d /d ata.n ce
p .rean aly sis.su rface.h tm l, these d ata h av e the reso lution o f 2.5 X 2.5 d egree. T he ch o sen area from 102.5° to 112.5°E and 5° to I5°N is illustrated in Figure 3.
Fig. 3. Surface wind field o f the studied arca.
T h e rainfall m o n ito rin g data is taken from statio n s lying in the stu d ied area, in o rd e r to im prov e the q u a lity o f sim ulatio n, som e statio ns n earb y are also included. T h e area for ch o o sin g rainfall m o n ito rin g statio ns is from 106° to 108°E and 10° to 12°N. T h ere are to tally 13 rain fall m o n ito rin g statio ns taking p art in the calcu latio n in c lu d in g Bao Loc, B icn H oa, Dac N o ng , D ong P h u, M oc H oa, Phuoc Long, So S ao, T an A n, T a n Son H oa, T ay N in h , T ri A n, V u n g T au , X u an L oc. A part from these statio n s, d ata fro m 12 rainfall g au g in g site in the studied a re a are also used. T h e d ata form to be used is th e av erag e rain fall in pixel w ith reso lutio n o f 0.5 X 0.5 degree.
3 . R e s u lts a n d D iscu ssio n
3 .1 The q u a ỉity o f sim ulation o f w ater level with the sup plem enta tion o f n o n -tid a l com ponents
A fter su p p le m c n tin g non - tidal co m p on ents, th e v alu es o f am p titu te (H ,) and
initial p h ase (g.) o f tidal w ave in vvater level sim u latio n are chang ed . T h e illu stration o f this c h an g e at V un g T au statio n is shovvn in table 1, here, ch an ge m ain ly o ccu rs in tid al w ave ssa, sa an d k l . In ad d itio n , there ex ist ch ang e in co m p o n en t Zo, in V u n g T au statio n , the values o f Zo b efo re and afte r ad d in g no n - tidal co m p o n en ts are -2 4 cm an d -22 cm respectively .
T h e quality o f th e sim u latio n o f w ater level ílu ctu atio n w ith th e su p p lem en tatio n o f non- tid al co m p o n en ts is acc essed th ro u g h the d eterm in e d c o c tĩic ie n t an d th e m ean error.
T im e o f assessm en t is th e tim e ran g e th at w as no t inclu d ed in b u ĩld in g the íacto rs a3j, H, and g , , from 2005 to 2 00 7 . T h ere are tw o ty p es o f assessm en t including:
- D etcrm in ing the qu ality o f th e sim ulation o f tidal w ater level by eq uation (2 ) w ith values o f H, and g, built fro m step 2.
228 L .v. Viet ct aỉ. / V N U lournal o f Science, ía rth Saence> 25 <2iH)9> 223-2
- D eterm ining th e q u ality o f th e sim u lation calib rate the w a te r level v ariatio n d u e to non- ta k in g in acco u n t co m p o n en t z \ used to tidal íactors.
Table 1. The amplitude and initial phase values o f tidal wave in Vung Tau station
No. Symbol Phase (°/h) VVithout non-tidal Element With non-tidal Element
H, (cm) g, (°) H, (cm) g,(°)
1 m2 28.9841042 76.07120 63.76976 76.06539 63.76058
2 kl 15.0410686 59.36825 -33.73985 59.46649 -33.08949
3 ol 13.9430356 44.57975 -82.60097 44.57684 -82.59804
4 s2 30.0000000 30.09205 107.23598 30.06174 107.52096
5 sa 0.0410686 20.67649 -86.21850 20.00824 -86.52581
6 pl 14.9589314 18.86379 -36.50550 18.84166 -36.13764
7 n2 28.4397295 15.93458 40.51535 15.90711 40.57601
8 k2 30.0821373 9.27898 115.71067 9.33931 116.03352
9 qi 13.3986609 8.52208 -104.10203 8.49669 -104.27054
10 ssa 0.0821373 6.15398 91.27816 3.27434 105.56152
11 ml 14.4920521 2.02516 -71.72914 2.02822 -71.59688
12 j l 15.5854433 2.30905 6.97230 2.30199 6.40569
13 mk3 4 4,0251729 2.82627 -120.98422 2.82923 -120.94674
14 mu2 27.9682084 2.48928 -2.44140 2.48340 -2.40553
15 op2 2 8.9019669 2.07748 -94.18789 2.08401 -94.22076
16 2n2 27.8953548 2.43837 14.16457 2.44413 14.12801
17 ool 16.1391017 1.73745 33.41912 1.72919 33.24114
18 mo3 42.9271398 1.94380 179.61837 t.94238 179.56725
Time
Fig. 4. The observed and simulated vvatcr level in Jan/2007 o f Vung Tau station.
A ssu m in g R2|, E ĩ| a re d e fin in g co efficien t and m ean error w hen sim u latin g th e tidal w ater level b y equation (2 ), w h ich m ean s n o t taking into acco u n t the v ariatio n b y w in d , a ir force and rain o f w atcr level; R 22, E r2 are d efin in g co efficien t and m ean e rro r w hen s in iu la tin g the
tidal vvater lev el by equation (2 ) in case th e v alu es o f H, an d g, alread y tak e in to a c c o u n t the e íĩe c t o f w e a th e r elem en ts; R23, E r3 are d e íìn in g c o e ffic ie n t and m ean e rro r w h en sim u latin g the w a te r level w ith the e ffe c t o f vveather elem en ts is already taken into a c c o u n t
L.V. Viet et a i / V N U lournal o f Science, Earth Sciences 25 (2009> 223-231 2 2 9
(in equation (8)). T h e assessm en t resu lt is based o n the d iíĩe re n c e b e íb re an d after
su p p lem en tin g th e aíĩe c tin g disp lay ed on T ab le 2.
ía cto rs and
Table 2. Change o f defming coetĩicient and mean error
Coefficient Vung Tau Nha Be Phu An Bien Hoa Thu Dau Mot Ben Luc Tan An
r22-r2, 0.002 0.007 0.009 0.010 0.012 0.013 0.013
rV r2, 0.007 0.024 0.022 0.032 0.026 0.029 0.028
Erl-Er2 (cm) 0.5 1.1 1.4 1.2 1.5 1.3 1.3
E rl-E r3 (cm) 2.2 4.8 4.1 3.5 3.4 3.4 3.2
R esult from T ab le 2 shovvs th at w ith the su p p lem cn tin g o f w eath er elem en ts in b u ild in g harm onic constants, the q u ality o f sim u latin g the tidal level is im proved w ith the m ean error red u ced ab o v e 1 cm from o n -riv e r stations. T h e m axim um m ean e rro r for all statio n s đ ecreases 5 cm w h ich is p retty m eaningfiil in bu ild ing tid al w ater level tables. T ab le 2 also su g g ests that vvhen sim u latin g w ater level w ith the su p p lcm cn tin g o f vveather ía cto rs, the q u ality o f sin iu latio n is im proved sig n ifican tly . E x cep t for V ung T a u station w h ich has m ean error d e c re a sin g 2.2 cm , the in riv e r statio n s h av e the d e c re a sin g level o f 3 cm . T he m ax im u m error avcrag ed fro m statio ns d ecreases 14 cm.
3.2 A nalyzing the ro le o f non-tidal com ponenís T o see the e íĩe c t o f rain fall, w in d and air pressure on the v aria tio n o f gau ged w ater level, these co m p o n en ts are sep arated from c o e íĩic ie n t o f s im u la tin g eq u atio n . in general, the sim u latin g re su lt o f the w ater level variation d u e to n on-tidal e lem en ts has p retty good relatio n sh ip w ith th e d ifference o f th e ob served w ater level an d th e tid al vvater level. T he nearer th e station is to th e riv er m outh, th e b etter this relatio n sh ip is. F ig u re 5 is th e illu stratin g resu lt for V un g T au sta tio n in 2005.
£ o
■*—' - C
ơ>
X03
Dỉfference o f the observed water level and the tidal water level VVater level variation due to wind and air pressure
Vung Tau statio n , 2005 '
-t---1---1---1---1— —I--- r~
p O
1*^
§ 5
9 9
ỏ ỏ
V—
5 r — •r- _ T— T—
p p o Ò p O p p Ọ p o Ọ
oc
“ 5
Ò CN CNÍ r— T— T - o Ò Ò Ò> ó»
O ic
“ĩ(TJ
£3 u .
2 t ì L
ế 5 .■ 2
CN3k to 2
c
—>3 coc
—ì3 CN
—>3 0
cn 1
(N ờ)
I co
Fig. 5. The resuỉt o f simulating water level variation due to wind and air pressure.
T h e ro le o f th e no n -tid al co m p o n en ts on vvater level v ariatio n is sh ow ed th ro ug h Standard d ev iatio n (S ) o f w ater level sim u latin g d ata s e rie s o f these co m po nents. T h e result is
sh ow ed in T a b le 3. T h e statistical resu lt su g g ests that at sta tio n s on th e sea (V u n g Tau station),
s
in dry season has v alu es g reater than in rainy season . T h is íe a tu re is due to the230 L.v. Vict et aỉ. / V N U ịoum al o f Science, Earth Sciences 25 (2009) 223-231
d iíĩe re n c e o f N o rth E ast and S outh W est seasonal w in d in term o f w in d v elo city and d irectio n as w ell as w ind period. A t N ha B e and Phu An statio n s has sim ilar ch aracteristics, hovvever, a t statio n s lying d eep in to the land,
th e eíTect o f rainfall on
s
is m ore clearly. At th e s e statio n s, the v alu e o fs
is p re tty high in th e en d o f d ry seaso ns (M arch and A pril) and esp e c ia lly in the m id o f rainy seaso n s (from J u ly to S eptem ber).T ab le 3. Standard deviation o f non -tid al w a tc r level
M onth V u n g T au N ha Be Phu An B ien H oa T h u Dau Ben Luc T an An
1 7.9 6.1 5.2 4.0 3.8 3.1 2.8
3 7.2 6.6 5.5 4.2 4.3 3.8 3.5
5 5.1 5.9 4.7 4.4 3.4 3.4 3 .0
7 4.0 4.6 3.4 5.4 2.5 2.1 1.8
9 5.7 6.5 5.4 7.4 4 .3 4.5 4 .4
11 7.2 6.7 5.3 4.2 3.7 2.9 2.8
T able 4. T rcn d o f w ater levcl ai o bservation statio n s d u rin g p eríod 1981-2007
S tation V u n g T au N ha Be P hu A n B icn Hoa T hu Dau B en Luc T a n An T re n d o f w a te r lcvel
(cm ) 13 12 11 9 8 11 11
ta k in g into acco un t n on-tidal c o m p o n en ts. The im pact o f w ind on w ater levcl v arialio n is T h e w ater level trenđ at ob scrv atio n stations
is d e íin e d from a 3 m coefTicient, the calculation resu lt is show n in T ab le 4. D ue to calculation m ethod, th is resu lt is m ean vvater level increase.
T h is resu lt sh o w th a t in the p erio d 1978 - 2007, th e averag e w ater level at ob serv atio n station s had increased sig n iíica n tly . T he m axim um increase is 13 cm at o b serv atio n statio ns on the sea (V u n g T au statio n ), w h ich is app ro xim ately equal to the risin g o f w ater level at inshore statio ns o f V ietnam [3-5]. A t statio n s on the river, th e risin g level is low er and has values rang in g from 8 cm to 12 cm . D ue to the fact th at th e accu racy o f the result o f w ater level sim u latin g is n o t really high for th e statio ns on the rivers, th is is o n ly co nsidered the referencin g data.
C o n c lu sio n s
c o n sid era b le, esp ecially in dry seaso n . T he rainfall also play s an im portant role to the vvater level v ariatio n on thc riv ers w h ich is revealed m ost c le a rly in th e m id d le o f m o n th s o f rainy season. T h e su p p lem en tin g o f w ater lev el trend c o m p o n en t into an aly sis im p ro ves th e q u a lity o f the sim u latio n and sh o w s o f f a rise a t a lert lcvel o f w a te r level d u e to global c lim a te c h a n g e in Sai G o n - D o n g N ai riv er system .
In o rd e r to im p ro ve th e q u a lity o f sim u latio n , it is n ece ssary to im p ro v e the affectin g facto rs esp ecially th e d a ta o f flo w in the u p p er stream . T h e ap p licatio n o f this m eth o d in íò rec astin g w ater level in th e stu d ied area is feasible w h en it is c o o p e ra te d w ith P ro du cts from w cath cr m odels.
T he assessm en t sh o w that the q u ality o f w ater level sim u latio n on Sai G on - D ong N ai riv er system is im p ro v ed co n sid erab ly and m ax im u m error d ecre ase s sig n iĩica n tly w hen
R eíeren ces
[1] Luong Van Viet, Research to create h y d ro - m eteorological database 10 serve inundation
L.V. Vict et ứ/. / V N U Ịournaỉ o f Science. Earth Sciences 25 (2009) 223-232 231
prevcntion in Ho Chi Minh city, Scientifìc research - Center o f Managing ỉnundation Preveniion Program Ho Chi Minh City, 2008.
[2] Luong Van Viet, Building H ydrology M cteorology database in conịunction vvith land use planning till 2020 at Nhon Trach D istrict, SEM LA prọịect, Dong Nai Ministry' o f Resources and Environment, 2008.
[3] M inistry o f Resources and Environmení, D evelopm ent o f National target program on clim ate change adaptation, 2008.
[4] M inistry o f Resources and Environmenty C lim ate C hange and Sea Lcvel Rise Scenarios for Vietnam , 2009.
[5] N guycn Duc N gu, C lim ate C hange and C oping Sưategy, T he H ydro m eteorological jo u m al' 567(2007), p. 9 - !3th.