24(3),248-2s3 Tap chi cac KHoA Hoc ve TRA oat I.a. A\ u- -a- \ rgr eua BUoc paunghgn cuu HU6NG va PHAM VI PHA]\{ TOA VAT LIEU PHU SA A \ a..,

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1 24(3),248-2s3 Tap chi cac KHA Hc ve TRA AT I.a. A\ u- -a- \ rgr eua BUc paunghgn cuu HU6NG va PHAM VI PHA]\{ TOA VAT LIEU PHU SA A \ a..,{ {. a SONG HONG O WING BIEN \1EN BO VINH BAC BO TE XUAN HONG. PHAI\ NGOC VINH. PHAM VAN NINH t. tr.lo AU Hdng ndm h0 thdng song Hdng dd ra bidn mot lung phr) sa rat l6n, vd kh6ng I l0 triou tt'n, dring vi hing thir 8-9 s vdi c6c h0 thong sdng kh6c tron thd gii. Qui trinh phdn tii vat liou phr:r sa sdng H6ng 6 vung bien ven bd ViOt Nam cn chua duc ldm s6ng t vd kh6ng gian va thi gian vd dac bict le rinh hudng cua chring ddi vi qu6 trinh bdi tu ta qu! det mdi, qu6 trinh x6i 1 vd sinh th6i m6i trung bidn... Ch d n nay c6 mot so kct qud nghion criu lion quan dcn vain dd ndy nhu bin n1u song Hdng va. pham vi 6nh hudng cria n6 trng vinh B6c B (Nguy6n Chu Hdi, 1989), vd drii bun s6t nau h6ng ven b Tay vinh Bdc B (1990) l3l, inh hrrng ciia nudc dqc sng Hdng (KT.03.07) cua Pham Van Ninh (1996) [9], vqn chuyen bun c6t song Hdng trng d6i s6ng vd ven bidn Viet Nam [4-6]. Su phan t6 vat liou phtr sa s0ng Hdng ving bien Vict Nam vd inh hudng ciia n6 don qu6 trinh dia - dqng luc [71. Sng d6 m6i chi Id cdc kdt quei s b ban ddu. Ngudn vet liou phi sa song Hdng vdi kich c bin c6t, thdnh phan vo c vi hfru c duc dua ra bidn vd phan ti trng pham vi ving bidn gay 6nh hudng ldn don hdm lung vat liu l lung, tinh chdt ly ha, him lung chal kh6ng. tcing lung chat hfu c dudc ta ra nh quang hqp trng nudc bidn. Hn nfla su c6 mdt ciia vat lieu phi sa sng rinh hung don qu6 trinh bdi x6i drii b bidn, bien dong ludng lach cua song va qu6 trinh sa I6ng bioir ddi dia hinh d6y bidn, tn ta c'ac thung l0ng ngdm hdc ta ra c6c c6n, gd ngdm. C6c ddng vat liou bin c6t s6ng Hdng cn d6ng vai tr rat ldn ddi vdi rni trung sinh thai. Vd thdnh phan vat chai, trng vat liou phi sa song Hdng chita hdm lung silic nhdt dinh 6 dang dyxit silic (SiO2) vd silicat (SiO+) va hdm lung d6ng kd chdt mrin hfu c. C6c khing chdt vi min hiru cd hen li ngudn thric dn truc tiep hac gi6n ti6p ch nhidu lii sinh vat phd du (planktn) vi sinh vlt d y (benths), tri cdu d6 (ccclithphra) vd c6c sinh vat an birn (depsit feeder - detritvares). Nhtng ldi sinh vat roi neii va. di),lai ld ngudn thfc an khong the thiou duc cfa c6c ldi c6. Vai tr cria phd sa song Hdng trng su hinh thanh c6c dng vlt li0u bun c6t ld ta non c6c bdi bdi ven bien cria song, ld ngu6n c1u! ddt mdi quan trng ch con-q t6c quy hach vd ph6t tri6n n6ng nghicp, nuoi trdng thu! srin, qu6 trinh bdi-x6i cua song ldm bieh dng ludrrg lach (gia thong pha s6ng - bioh), ddng thdi phu sa c0ng la ngu6n c6 khl nang -ea1' O nhiom bidn bi cic nguyon to vi lung c6 trng vat li0u br)n c6t. Trng bdi b6 niy ch0ng tdi mdi chi dd cap t6i mot so kei quri ban ddu vd hu6ng van chu),ein bun c6t song Hdng vi pham vi lan td cua ch0ng trng ddi bd bien vinh B6c B bang phung ph6p nghion cuu thuy thach dong luc vd mo phng t6n hc. [. var NET vi van chlar BL]N cat Nhu chfing ta dd bioi, sq van chuyen bin c6t trng sng thung 6 du6i hai dang t lring vd lan s6t d6y. Dang bun c6t van chul,sn l lung thudng c6 kich thudc hat cd nh, dudng kinh hat b6 hn 0,01mm (bot, s6t), cn bin cht the lan c6 dudng kinh hat l6n hn 0,0lmm (c6t, san, si, cuoi). Hudng van chuydn bin c6t 6 trng song thung dn gidn vi chri yeu mot hudng tu thttng ngu6n vd ha ngu6n (cua s6ng). DOi vdi bun cdt dr-rc van chuydn td cria sdng ra bidn thi rait ph0c tap, c nhidu hudng khac nhau, phu thuoc va nhidu ycu 248

2 m?nh, phu sa s0ng c6 thd dud. c phan tii ra xa bd hn. Sr; v{n chuy 'n the c6c hudng khac nhau phr; thuoc vl chinh hudng s6ng tdi bd (hudng gi6), ddng tri u, dia hinh diy vi dung bd... [7], Tr n cd s nghion cfu thinh phdn vat chdt phti sa s0ng Hdng md chti ydu li thinh phdn kh6ng vat n+ng (KVN) 6 cdp h4t s4n c6t vi rrng s6t, cing vdi viqc m0 ph6ng t6n hgc su lan truy n phi sa l lung s0ng Hdng ciira Ba +t (crla song Hdng), chfing toi dua ra mot sd nhfln x6t budc ddu v hu6ng vd su lan tii ciia chfing. SU v4n chuytln btn c6t ven the bd bidn rdt phfrc tap. C6c vat li u van chuytln dc bd bidn phu thuoc vd. mria vd hu6ng gi6 hang ngdy tron bidn. C6c v4t chdt trdm tich ven bd bi but I n bdi s6ng luon lu0n & trang th6i chuydn dng khi c6 s6ng dei vi bd, Hung s6ng thay ddi sc den tdi su thay deii cria hudng v6n chuydn trdm tich. B6i vay s{ van chuydn ciia c6c vat chdt & ven bd bidn lu6n luon bion d6ng vd phu thu0c vi thi gian. Hudng van chuydn bin c6t c6 thti td hudng tric thi vi hu6ng van chuydn trdm tich Id lau ddi. Ndu trudng hgp s6ng dei thing g6c vdi dudng bd, bdn cdt chi dich lon xudng the mat sudn bd. C6c hat c6 kich cd ldn du.c dua lon bd, c6c hat c6 kich cd nh6 chuydn dich ra xa bd. NOu trudng hqp s6ng dd vd bd dudi m6t g6c nhn thi brln c6t dich chuydn the hu6ng dc bd. Chfng c6 thd dich chuyiln sang phia phdi hac trai tuj' thuc vi hudng s6ng dd vd bd. Qu6 trinh dich chuydn br)n c6t d d6i bd rdt phirc tap vd phu thudc vi. ddng chdy s6ng ven bd (dng ven). Sr1 vln chuydn bin c6t Id qud trinh lion hgp ciia s6ng vi c6c lai dng chdy ven bd kh6c. Tdc d vd khdi lung bin c6t van chuydn dc bd thung ln nhdt khi hung tia s6ng tdi bd dudi mot g6c nhn 45 tung doi vdi dudng bd. NCu tia s6ng tdi bd dudi mr g6c khing 90'rhi budc di cia c6c hat bin c6t le nh6 nha/t. Su van chuydn trdm tich dc bd phu rhuc vd hudng van chuydn bin c6t c6 lung troi hn : xdy ra the tung mia kh6c nhau, tham chi the tdng ngay, tung gid. O nudc ta c6 hai hudng gi6 mr)a 16 r0t, hudng gi6 mia D0ng B6c vi hudng gi6 mr)a TAy Nam. Sg vfln chuydn btin c6t dc bd phu thuc vd hai mda gi6 chinh dy. Ket quri nghion criu v1n III CAC PH PHAPNGHIET.T CT1U VA QUA 1, Phung phip thai thqch dqng tu. c Dd x6c dinh hudng van chuydln trdm tich song Hdng vl ving inh hung ciia ch0ng blng phung ph6p diama - thuj th4ch dong luc,th0ng qua thanh phdn KVN d6c trung, trudc ti n phrii x6c dinh "BQ md kh6 c6c KVN d6c trung" ciia tram tich song Hdng. Tr0n c sd x6c dinh cdc KVN dac trung d6, du xem x6t c6c thdnh phdn ciia chirng van vd nhan bidt qua su dich chuytln KVN ven bd den dau the mia. Vtng rinh hung ciia trdm tich song Hdng ddn dau, chinh ld ni c6 mdt ciia cdc KVN ddc trung ciia trdm tich song Hdng du. c dich chuydn d 'n. Nghicn criu KVN ld mot trng nhfing hgp phdn cria trdm tich. Vi0c nghi n cfru K ciing nhu nghi n criu c6c hqp phdn kh6c ch ph6p di6n girii nhidu van dd quan trng lion quan ddn qu6 trinh thdnh ta trdm tich, ciing nhu ngudn cung cdp vat li6u, hudng van chuydn cria ching, vd ving :inh hung cria moi trudng tram tich. KVN li c6c kh6ng vat c6 tj trng nang tt 2,9 trb lon nhu Inmenit, Ziacn, Rutin,... Mt dec thi khac ld m6i tci hqp KVN chi phrl bion vi mang tinh ch{t dec fiung ch rring khu vuc dia chdt kh6c nhau, chi thi ch ngudn vat liou tram tich. Tr n c sii ciia KVN ti6u bidu li n quan rdi su dich ngudn gdc cung cdp, nhan bi6l d chuydn ciia chrlng (vdnh phan t6n). Trng qu6 rrinh nghi n cuu KVN cdn luu! ddn kich thudc, hinh th6i cria c6c td hqp c6c KVN. C6c K d6 c6 y nghia ldn deii vdi su lj, gi6i vd c chd v4n chuydn vd qudng dudng van chuydn ciia chtng. Dd x6c dinh c6c KVN dac trung ciia tram tich s6ng Hdng, cilc ticgid, dd lua chn cec td hqp KVN dac ffung c6 trng c6.c m6u l{y 6 c6c 16 khan D0 Tir, ddng bang Bic B0 ven song Hdng trng tdng ddt Hlcen (Qa), v6i 4 vi tri kh6c nhau : Hd N6i, Hung Ydn, Hi Nam, Th6i Binh vi ldy ket quri thdnh phdn KVN tron ldng sdng Hbng hion dai Hd NOi, Hung YOn vd Hd Nam. C6c K s6ng Hdng phdn l6n thuoc ngudn geic bi6h chavt - gnei. DOi chidu c6c thdnh phan K c6 rrng cdc

3 khan, trng bd mat lng song Hdng, v) KVN c6 trng tram tich tang mlt ving ven bidn cua c c cua song TrA Lj', Ba l,at ve ThAi Binh dd tim ra b0 khl chung ch bdn clt song Hdng [6' 71. TrOn c s kct qua thdnh phdn KVN c6 trcn Idng song Hdng hion dai' cua song Hdng vi c[c bai bdi cua chring, th6ng qua tan suat xuat hion vi hirn lugng phdn trim (a/) chta trng c6c mau ' chfing ta rfit ra duc c6c nh6m tci hp KVN rieng dac trung ciia trdm tich song Hdng vd c6c nh6m t hgp KVN kh6c nhau. Dd drirn bri d tin cay ch b kha chuan KVN cija trdm tich song Hdng, chfing toi de tieh hinh khri 5u phan tich bun cdt hai cua s6ng chinh ai khi dia chdt khlc nhau kd can. OO ta ThuAn An 6 trua ThiOn Hu n (B6c Trung Phng) thuoc PhAn tich nd1' phdn vat chit bun c6t song Hdng vi thanh phdn vat chdt (KVN) cila cac khi dia chdt lan can [71. NgAi ra cdn tion h)nh nghion cfu thdnh phin KVN trng s6t l), kich cd hat nh6 hn vd c6 khii nang van chuydn di xa hn. C6c kct quii phan tich th)nh phdn KVT\ cua c6c mau sa kh6ng ldy trng vung thung ling song Hdng va 6 ving ctra s6ng Thdi Binh, Tri L! vi Ba Lat, ta thdy trng phdn luc dia c6 khting 20 KVN' trng d6 c6 l5 KVN thung gip li Inrrenit, pyrxen' leicxen, granat, tuamalin, ar-nfibn, Iimnit, caslterit, clrit, manhetit, mnazit. rutin' ziacn' epidt, silimanit. Di vi chc KVN c6c vung cua Ba Lat, Tri Lj' vi Th6i Binh c6 khring 28 KVN c6 tan sudt xudt hion va him lung d6ng ke. NgAi c6c KVN gip trng phin luc dia cua thuttg lting sng H6ng cn c6 clc KVN khlc nhu : staurlit, hernattt, sphen, crrrspinen, siderit, allata' silimanit, apatit' ziatlit, disten, thdn sa, makzit vd macttt' Dac didrn c6c KVN vung bidn ven b vinh Bac BO c thd chia ra lim ba rrh6m chinh : - Nh6m tu crim : manhetit, mactit. hematit' - Nh6m KVN dien tu : inmenit. mnazlt, limnit, granat, epidt, clrit, tuamalin, bitit' amfibl, staurlit, pirxen' siderit. - Nh6m K\4] : ziactr, rutin, mackazit, disten, crmspinel, silirnanit, leicxen, xerixit, anaraz, rubi, spinel, apatit, thdn sa, ziatlit, pyrrncfit, phion rnica, casiterit,cridn, bruckit, galen Il l. Trng s cac KVN tron c6 ci ngu6n cung cap cria s0ng H6ng vi c6 cri tu ni kh6c mang d n' KVN gidu nhm ld iumenit-ziac Dac ffung KVN cria tram tich song Hdng c ngudn gc bicn chdt khi sdng thanh phdn ctia chirng giau kim lai n p cac iteritsiliuranit-hematit-stauri it-epidt [7 I' DOi s6nh c6c kct quri nghion ciru, trng ddi bidn cua ThuAn An cdn gip mot so khang vat g. udng r') an ch song bi i n HuO hay khng dang crr duc tiep tuc nghi n cfu' 2. Phung phip nto hinh tin hc [9-I0J Sng sng r'6i phung phirp nghien cuu dia ma thuy thich dong luc (KVN), phung ph6p mo ph<3rrg tln hc drrtvc tion hlnh, v6i su Ap dung m0 hinh ngau hinh de tinh tdn hu6ng va pham vi lan ta vat chdt phu sa l lung s6ng H6ng trng hai mira gi6 chinh : mda gi6 DOng Bdc vi rnua gi6 Nam' The mo hinh ngau hinh' khi lung chdt ban ttr sng dei va bien duc bicu dien nhu tap hp N hat bari riong biot. Du6i trudng van t6c trung binh r,) rdi, m6i hat bdn chuycn dong the 3 chi u kh6ng gian vdi phung trinh chuyen dong cria tam cluln tinh cua hat thti i c6 dang : dr, :. - =Ui-ftti AT (i = 1,2...N) (l) Trng d6: R, - vect birn kinh cila vi tri hat bln th(r i tai thi dicm r, A, - vect varl toc ttung binh, rr, - vect chuyen d6ng r'oi. Bict hai vect van tc d6 c6 thd biet vi tri cia hat bdn i tai thi didm bdt ky' S luitg hat ri va m6t the tich hinh hc co dinh nd d6 se li hdm lung cua chat bdn tai d6' Ldy trung binh hlm lung nhan duc the chidu sau ta so c6 phln b n6ng do chdt ban the chidu.ngang. De giai phucrng trinh ( l) cdn tinh U, r'i t7, ' Thinh phdn van toc trung birth d, c the duc tinh 250

4 t6n tu m hinh dua tren h0 phung trinh phi tuyen luc nng hai chidu trung binh h6 the chidu sau. 'Van tdc thang gi6ng Z, le mt dai ltrng ng6u nhi n. D' van tdc ndy md sau thdi dan AT hat ban se dich di duc mot d dii AXi (xi, yi, zi). Dan di ndy duc x6c dinh mt c6ch ngsu nhion the phan bd thdng kc x6c dinh. Nhu vdy, hiou irng chuydn dong r6i day duc mo ph6ng nhu ld x6c sudt dd hat bdn c thd chuydn dich duc mot dan AXl sau budc thi gian AT vi d ddi ndy duc x6c dinh bi cong thitc : Ax= * (2DLDtp ddu cria bidu thfc duc x6c nhi n. Tu d6 ta x6c dinh duc dinh ili. mot c6ch ngdu Phung trinh (l) duc gi6i vji c\c didu kion : - TrOn pi6n l6ng : thung giri thidt ring ncu tai mt thi didm ni d6 hat l6ng dlr. c x6t ri vd lan can dil nh6 crja bion l6ng thi tu thdi didm sau d6 n6 duc ci nhu ra ngdi vdng xem x6t, ncu sau budc thi gian t hat d6 khong quay tr lai vr)ng tinh. - TrOn bi6n curng vd d6y : rinh hudng cria b vd d6y dtrc x6t dn bing c6ch ci hat l6ng c6 thd thdm qua hdc m6c can tai d6. Dang cu thd ciia c6c biou thric tung ring phu thuoc vd. ddc tru4g, c ly h6a ciia bd, d6y vi clia brin than chdt bdn., - Thdi gian sdng : ndu char ban ta x6t c6 thdi gian tdn tai hiru han thi khi lung chdt d6 s6 bi gi6m di s vdi lung th6i vd'nu6c bidn vd lung girim bt di d6 du. c thuc hion bang c6ch dn girin li lai nhtng phdn tir dd qu6 thi han tdn tai ra kh6i danh s6ch c6c hat l6ng md ta the d6i. 3. Kdt qud tinh tinh tdn Cfing nhu doi vdi c6c virng cua song kh6c, pham vi rinh hudng cria ddng nltdc duc tir cua Ba L4t ddn vr)ng bidn ven bd phu thuc vi: luu lung nudc s6ng, dia hinh b va day. c6c pha tridu vd nhat ld hrr6ng vi cudng do gi6. a) Ddivaigi6 S 6,8 m/s Ket quri tinh t6n ch thdy sau khi ra khi cua, vot nu6c duc quit l n phia dong b6c the g6c 45, nhung nhan duc c6 xu thdnlm s6t dudng bd hn, k6 ddi ti ciia song den v! do 2035' vd ta thdnh m0t khu vqc nudc duc ti (20"12',106?38') dch (20"50',107'20'), tric ld vdt nudc dqc c6 thd lan t6i tan ving bidn dri Cet Be - Ha [,ng (hinh',]). Th6ng 7 Gi trung binh S 6,8 m/s <- Hinh l. Pham vi lan td bun c6t sdng Hdng th6,ng7 C.,l )

5 b) Ddi vdi gi6 NE.7,0 m/s Ke't qud tinh vdi gi6 NE 7,0 m/s (htnh 2) eh thdy vqt nu6c dr,rc sau khi ra khdi crla quflt xudng phia tay nam dgc the dudng bd, Vet nudc duc lan xa nhdt c6 thd di qu4 v! dq 1730' tfc la qu6 dia phgn tinh Quring Binh, Ving nhan dqc t{p trung chii y 'u dc the dudng bd vd c0ng hi phinh ra vdng cua sorrg Ba I4t, Ving nudc duc rinh hung ra khi xa bd nhdt cd tren 50 km, xfr luan Hudng van chuydn vd {nh hung ctia trdm tich song Hdng trng ddi s6ng v6 va ddi s6ng vd dpn bd tit M6ng C6i (Qu{ng Ninh) ddn Thr}a Thi n. Hue, bidu hign : 1) Bin c6t song Hdng c6 hudng dich chuydn vd phia bdc ng6n hn s vdi hudng dich chuydn vd phia nam, Hudng dich chuydn vd phan td bin cat s0ng Hdng phr,r thuoc va didu kiqn dia hinh dung bd va hudng gi6 (s6ng) thdng tri cd n4m, Th6ng'1 Gi trung binh NE 7,0 m/s e Hinh2. Pham vi lan ti bin c6t song H6ng th6ng I t ) Anh hung cria br)n c6t sng Hdng vd phia b6c den bd bid:n Cat Ba Hrii Phdng. 3) Anh hung cria bdn c6t song Hdng vd phia nam don qu6 b bidn tinh Quring Binh vi c6 thd rinh hudng deh bd bidn Thta Thi6n Hud. 4) Phn sa song Hdng lan td xa nhdt virng cua song Hdng, c6ch xa bd bien khd'ng 50 km. TAI LIEU THAM KHAO lli NGLJYEN van BACH vi nnk,2000 : Su phan td vat licu phi sa s6ng Hdng vinh B6c BQ. Tep chi cdc KH vd TD,2, J. Ha NOi. [2] NCr]l N Br6U, NGrJyEt.,t CHUNG HOAT, 1990 : 86 c6 d tdi nghi n ciru thuy thach dong luc bdi tridu vd bidn ven bd ThAi Binh - Hd Nam Ninh, Vien Dia chdt vi Kh6ng srin, Hd Ni. 252

6 l3l NGulEN CHU HdI va nnk, 1990 : Vd drii brin s6t nau h6ng ven bd TAy vinh Bic BO. Tap chi KHTD. Tuyen tap cong trinh nghi n cfu ,16-50.He N6i. t4l LE XUAN udnc va nnk, 1996 : 86 c6 dd t)i ct'p c s 1996 "Hi0n trang b6i tich va hudng van chuydn bin cit tron c s phan tich c6c thdnh phdn khlng vat nang tir Dd Sn ddn Hue". l5l LE XUAN udnc va nnk, 1997 : 86 c6 dd tli cap c sb 199'7 "NghiOn ciru hudng van chuydn bun c6t ven b trcn c s6 phdn tich thdnh phdn khlng vat nf,ng cria ddng bdi tich song Hdng ti Dd Sn deir M6ng C6i". t6l LE xuan HdNc vi nnk, 1998 : K t quri budc ddu nghion citu hudng van chuydn vd inh hung cria bun c6t song H6ng 6 dc bd bidn Viet Nam. Tuydn mp be cl kha hc, HOi nghi kha hc tin quc v6 bidn ldn thf IV nam Hi ni, TAp I, I7l LE xuan r-rdnc, NGUYENVAN BACH, I999: Khii crlru su phan ti vat lieu phu sa song Hdng 6 ving bidn Vi0t Nam vd iinh hung cria n6 don qu6 trinh dia - dqng luc. Bl c6 teing ket dd tdi cdp BQ (1-fKHTN&CNQC). l3l tr., Ha Ni. I8I PHAM VA\I NINH, BUI MINH DUC, PHAM TRLING LUONG, l99l : Mathematical mdelling and remte sensing methds fr assessment riverine pllutin inputs t the sea. Secnd Westpac Sympsium, Malaysia. I9I PHAM VAN NINH, BUI MINH DUC, PHAN NGOC VINH, 1995 : M0 phng vr)ng nudc duc d cria song bang phung ph6p ngau hdnh. Tap chi C hc, tap XMI, 4, Hd noi. [1OI PHAM VAN NINH, NGLYEN W TUdNG, PH/Nr NGQC VINH, DINH VAN MANH, lgg5 : MO ph6ng tan hc 0 nhiom bidn d song tiii ra. Bl c6 dd tai KT SUMMARY Preliminary results f studying the mvement directin f the Red river's sediments and their effect dmain in the castal zne f the gulf f Tnkin In this paper, the authrs presented sme preliminary results f studying the mvement directin f the Red river's sediments and their effect dmain in the castal zne f the Gulf f Tnkin which are based n methds f the hydrdynamics (heavy minerals) and mathematical simulatin. Calculatin f Red river's susensin sediments spreading fr the tw predminant wind directin (NE and S) has been carried ut. Several cnclusins have been made as fllws : displacement f Red river's sediments is fairly cmplicated when they flux int the sea, which depends n the marine dynamics, tpgraphy, especially n the predrlinant wind directin. Red river's suspendedlsediments can spread nrth up t the castal 'rzne '( Catba island- Haiphng and suth t the castal zne f Quang Binh prvince. They can likely affect the castal zne f ThuaThien-Hue prvince. The maximum ffshre distance that they can reach is ver 50km. Ngdy nhdn bdi : Phdn vi n C hc bidn - Vien C hc 253