• K H O A H Q C C O N G N G H E •
NGHIEN CIJU
KHAOSAT CAC THONG S6 CO BAN
ANH
HU'dNG
O^N S U XOI MON L O N G S O N G SAI GONKHU v y c THANH DA
TS Liru XUAN LOC, PGS.TS NGUYEN T H O N G Khoa Kp thuat Xay dung, Bgi hpc Bdch khoa TP. HCM
Tom t i t : Hien nay chung ta chua chu trgng ddu tu va giai quyit tri$t de vao cac cong trinh chinh trf song, bao ve ba song. Vi vay vdn di sgt la ba song thuang xuyen dien ra a hdu hit cdc con song tren khdp cd nuac, gdy nhiiu thiet hgi va dnh huang khong nho den su phdt triin kinh tixS hoi cua khu vuc. Bdi bdo ndy trinh bdy kit qua nghien cuu hi?n tu^mg dong chay vd khd ndng xoi mon long song khu vj^c bdn ddo Thanh Da thugc song Sdi Gon bdng cdc sd do dgc thuc ti, thu th$p phdn tich vi thdnh phdn phdn bo hgt cua vdt li$u ddy song, thong s6 ddng chay. Bong thai cdc tinh todn gid tri van tdc xoi mdn dua tren cdc sd liiu thu thap tgi hien tru&ng cung duoc di cap.
Tw khoa: xoi mdn Idng sdng, tdc dp xdi mdn, vgt lieu dinh, khu vyc Thanh Da, song Sdi Gon
Abstract: At present, we have not paid much attention to investing and solving thoroughly th works of river management and river bank protection. As a result, river bank erosion occurs frequently in most of the rivers along the country, causing considerable damage and impact to th socio-economic development of the area. This paper presents the results of the study on flow phenomena and river bed erosion in the Thanh Da Peninsula of Saigon River by using in situ measurements, collecting analysis of the grain composition of river bed, flow parameters.
Simultaneous calculations of velocity of erosion based on field data were also reported.
1. T Q N G QUAN TINH H I N H SAT L d Id da nhdn chim 2 cdn nhd cimg dogn bd ke co TREN SONG SAI GON
Theo danh gia cua Sd Giao thdng Van tai, vdi dien bidn phiic tap cua biln ddi khi hdu, trong miia mua bao 2018, dy bdo tren dia ban todn thdnh phd Ho Chi Minh ndi chung va tren tuydn Sdng Sdi Gdn ndi rieng tmh hmh sat Id bd sdng tidp tyc gia tang. Mdt sd dilm sat Id diln hinh dugc thdng ke theo khu vuc cac quan nai cd sdng Sai Gon di qua cd the k l din nhu sau.
Qudn Thu E>irc c6 4 vi tri sat Id nim quanh tuydn sdng Sai Gdn. Trong do co vi tri sd 2 (ndm d cudi dudng so 7, khu phfi 5, phudng Hiep Binh Phudc, each cdu Bmh Phudc khoang 1.000 vl phia ha luu), xdp loai dac biet nguy hidm. Nam 2015, ciing d ngay khu vyc nay, sat
didn tich khoang 2.000 m xudng sdng Sdi Gon.
Hinh 1: Cdc diem sgt la tgi khu vuc Quan Thu Due
50 TAP CHfTAl NGUYEN NU<5C SO -2019
Qudn Binh Thanh cd 3 dia d i l m sat Id, ndm rdi rac d phudng 27 va 28, thudc tuyln sdng Sdi Gdn, tiic la khu vyc ban dao Thanh Da. Cd 3 diem nay ddu xdp loai dac bidt nguy hilm. Cach ddy nhidu nam, phudng 27 timg da xay ra 4 vu sat Id ldm mdt han 1.000 m^ ddt, ti-ong do cd 4 can nhd dd dp xudng ddng sdng trong ddm.
Hinh 2: Cdc diem sgt la tgi khu vuc Qudn Binh Thanh
Quan 2 cd 5 diem sgt Id. Trong dd, vi tri sd 12 {nam d bd trai sdng Sai Gdn, cdch cdu Sdi Gon 4,5 km ve phia thugng luu, khu vyc khu ddt sd 61 Tran Ngoc Dien, phudng Thdo Diln) la vi tri sgt Id mdi, miic dp sgt Id dac bidt nguy hidm. Noi day dang dugc thyc hidn cdc thii tyc vd dy dn dau tu xay dimg bd ke.
Hinh 3: Cdc diem sgt la tgi khu vuc Qudn 2
hgng dgc biet nguy hiem. Nam 2017, mpt vy sgt Id nghiem trgng da xay ra d khu vyc ven sdng Kinh Ld, dogn gan cdu Kinh Ld thuoc xa Hiep Phudc, khidn 5 can nha bi hu hgi nghiem trpng, hang chuc ngudi phai sa tan khan cdp.
Hinh 4: Cdc diem sgt la tgi khu vuc Huyen Nhd Be
Huyen Cdn Gid cd 6 vi tri sat Id, 4 trong sd dd dac biet nguy hiem. Gan ddy nhdt, thang 6/2018, tai du an xay dung ke bao vd khu dan cu Tac Sdng Cha (Ap Bmh My, xa Binh Khanh) dd xay ra vu sat Id nghiem trpng khien 160 m ke dpc theo bd sdng bi cudn theo ddng nudc. Vy vide khien 4 hd dan phai di ddi khan cap ra khdi vung hi anh huong.
Hinh 5: Cdc diem sgt la tgi khu vuc Huyen Cdn Gia
Huyen Nha Be la noi co nhidu vi tri sat la Trong do, doan song chay qua khu w c nhat, 12 diSm. Trong do co toi 8 noi dupc xep j h ^ ^ o a Quan Bmh Thanh co hmh thai kha
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ddc bidt, ddng thdi Id khu vyc xdy ra sat Id rat nghiem trpng, gdy tiiipt hai nang nl nhdt. Vi vgy vipc thu thap, do dac cdc sd Hdu thyc tl, tinh t o ^ cdc gia tri cua ddng chay dl hidu ro nguydn nhan sgt Id tai khu vyc ndy la hit siic cdn thilt.
2. KHAO SAT DO DAC TAI KHU V^C NGHliN CUtJ
a. f^ tri khdo sdt
Bom sdng khdo sdt ndm trong khu vyc ban dao Thanh Da diupc ha luu sdng Sai Gdn thkih phd Ho Chi Minh. Vi tri khdo sdt dugc bidu dien tren anh vp tinh Hinh 6. Doan sdng khdo sat hoi coi^ (hinh vdng cung), Idng sdng tgi doan sdng khdo sdt gIm mpt tram do khu vyc cdu Bmh Lgi, mgt trgm tren nhanh Idn cua kenh Thanh Da rdng tir 190m -^
220m, mdt trgm trdn nhdnh nhd cua kenh Thanh Da rpng tir 80 - 9(hTi. Dia chdt day sdng phan Idn la bun. Che dp nudc sdng tai tuydn do ndm trong khu vyc chiu anh hudng cua thuy trilu, Lirgng nudc tir thugng luu dd vl khdng nhilu ndn muc nudc dao dgng chii yeu dao ddng flieo con tridu.
y
Hinh 6: Vj tri cdc mat cdt khdo sdt b. Bo Of c bing thiet bjADCP
Dimg may ADCP (Mnh 7) hfii am doppler ddi rpng g5n man thuySn, diu thu ngap sau dirdd mat nudtc 30cm di chuySn qua mat cJt ngang song kSt hop cung phfin mSm thu s6 li?u t6ng hgip cac ygu t6 dong chay WinRiver Acquire Mode thong qua may tinh.
52 TAPCHfTAl NGUYEN Nl/(3C SO 1-2019
Sli dung phan mem WinRiver-Playback de giai ma cac file s6 li$u g6c. Sil dyng phin mem Microsoft Excel, Surfer va phan mSm chuySn dung &k tinh toan, trinh bay ket qua do djc. Kit qua thd hi$n trong Bang l,2,vaHinh8.
Bang 1. Dac trimg Iini lirgng, liru toe trung binh m^t c^t ngang tr^m 1 Dac trung
Trung binh Max (trieu xuong) Max (trieu len)
0 (m^/s) -143.0
2705 -2650
V(m/s) 0.57 0.99 0.79 Bang 2. B^c trung liru lirgng, lini toe trung
binh mdt cdt ngang tr^m 3 Dac trung
Trung binh Max (trieu xu6ng) Max (trilu len)
Q (m'/s) -49.6
423 -377
V(ni/s) 0.45 0.74 0.56 Bang 3. D^c trimg liru lirpng, lira tic trung binh m^t cdt ngang tram 4 Dac tnmg
Trung binh Max (trieu xu6ng) Max (trieu len)
Q (m'/s) -164.6
2546 -2414
V(m/s) 0.51 0.85 0.71
Hinh 8: Phdn bS van tic do bai ADCP tai mdt cdt diin hinh 2 c. Thu thfp miu v^t lifu ling song y^t li$u long song ciing dugc thu thap bang thiet b) liy mau cim tay kSt hgp GPS theo mjt
cdt ngang tgi dogn sdng vdi dO sau trung binh khodng 18m. Phuang phdp thu thap dugc thi hipn trong Hinh 9.
Kdt qud sau khi thu thdp dugc phan tich bdng mdy phan tich ed hgt laser SALD-3000 dugc minh hga trong Hinh 10.
Hinh 9. Phuang phdp lay mdu vdt lieu Idng sdng
Hinh 10: Mdy phdn tich thdnh phdn hgt (Laser Diffraction Particle Size Analyzer) Kdt qua phdn tich cho thdy kich thudc thanh phdn hat d day sfing Id giao dgng tir 5|am-150|im.
Dudng kinh trung binh cd hgt khoang 5pm-7pm.
Ta cd thi nhan thdy rdng tai ddy sdng, vat lipu hau nhu la gdm cac hgt bim set. Vi vgy khi tmh toan
gja tri tdc do xdi ta phdi sd dung cdng thiic cd xet din ddc tinh dinh ciia vat lieu.
3. TINH TOAN VAN TOC XOI M 6 N CUA V^T LIEU L 6 N G S 6 N G
Trong nghidn ciiu ndy phdn bd van tic dugc tinh toan gid sir theo theo h ^ logarithm vd tdc dg xdi mdn cua vdt lipu set dinh dugc dien ta trong eac phuang trinh sau:
; i : = A A , - - + - i n - (1) ES=OC.RJ,5,.U^ (2) oc (T) = 3 3 X 1 0 1 0 ' ^ T + 5.8 X 10"* (3)
Trong dd T Id nhipt dp; Es la tdc dp xdi mdn;
Rwc Id ham lugng ngam nudc (dO dm); k Id he sd nhdm; K Id hang so Kalman; U la van tdc trung binh cua ddng chay; u* la van toe ma sdt; R la bdn kinh thuy lye.
Hirkll. vgn tdc ma sdt vd^ nhdm
.^ aooce J . aooo4
^„„„„.
^ aooo2
2 . 5
Hwc-0.8 ^^^,'
-'"' ^^ "^
:
3 3.S 4 V|ntScm«.it(on/.)
Hirth 12. Tuang quan giiea van tdc ma sdt vd tdc do xoi mon cho cdc truong hap dQ dm khdc nhau Truong hgip tinh toan ducjc xem xet K=0.4;
T=250. Tir do, oc=l ,4x10-5. Theo nghiSn cuu ciia Nishimori va Sekine 2009 thi xoi mon long song se khong xay ra khi gioi ban chay cua vat li^u dinh (dit set) nho hon gia tri toi ban. Vi
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vay, chiing tdi cho rdng gidi han chdy ciia vat lipu thu dugc tir Idng song cung cd the Idn hon gid tri ham lugng ngam nudc (dp dm) cua vat lipu day sfing noi md cd gia tri R^vc = 0.6,0.7,0.8. Vi vgy, kich ban nay dugc dua vdo tinh toan tgi cac thdi diem md van toe ddng chay dat gid tri Idn nhdt vdi gia tri do dugc Id U=0.92 m/s. Dya vao kit qud do dgc tir ADCP, ban kinh thiiy lye dugc tinh nhu sau:
R = ^ = n . 3 ( m )
Su dyng phuong trinh (1), sy biln dfii ciia gid tri van tfic ma sdt la mOt hdm sd ciia dp nham k=0.1mm-10mm nhu Hinh 11.
Vi vay, khi gid tri van toe ma sdt u, = 2.62 - 3.9 cm/s (tuong ling vdi dp nhdm k=0.1mm - 10mm), vat lipu day sdng tgi nhiet dp nudc T=25° cd ham lugng ngam nudc la 0.6, 0.7, 0.8 thi gid tri vdt tdc xdi dugc tinh toan la 0.00007 - 0.00048 cm/s. Kit qud the hipn tren Hinh 12.
Dieu ndy ed the nhgn dinh rdng, vdo thdi dogn khodng 5 gid ddng hd khi ma gia tri van tic dgt dinh thi Idng sfing se hi xdi mdn khodng tir 1.3cm den 8.6cm. Tuy nhien khi ham lugng ngam nudc ciia vgt lipu set tgi long sdng nhd han gidi han chdy thi hipn tugng xdi mdn se hdu nhu khdng xdy ra. Vi v$y, didu quan trpng nhdt Id phdi nghien ciiu ro su phan bd gid tri ham lugng ngam nudc cua vdt lieu Idng sdng theo chidu sau dia chdt cua v$t lipu long sdng.
4. KET LUAN
Trong nghien ciiu nay, sy khdo sat, thu thdp, do dac mpt si gia tri ca bdn cua vat lipu long sdng dd dugc tiinh bdy. Tir dd gia tri tdc do xdi mdn Idng sfing dugc tinh toan dya trdn mgt sd gid thidt. Kit qud cho thdy ring, vgt lieu long song Sdi Gdn doan qua bdn dao Thanh Da hdu hit Id set. Vao thdi doan 5 gid dfing hfi khi md van tdc dgt dinh, thi Idng sdng dg hi bdo mdn khoang 1.3CITI den 8.6cm.
Ldi cam on:
Nghidn ciiu nay dugc thyc hipn trong khudn khi dl tai d&t hang cua Trung tam CARE-RESCIF, HCMUT-VNUHCM. Md so Tc-KTXD-2018-05.
Cdc thidt hi phyc vy khdo sdt vd phan tich kit qud dugc ho trg tir trudng Ritsumeikan, Kyoto vd Tohoku Nhgt Ban.
TAI LI|:U THAM KHAO
1. Nishimori, K & Sekme. M (2009) "
Erosion rate fomula of cohesive sediment"
Joumal of Hydraulics, Coastal, and Enviromental Engineering, Vol. 65,127-140.
2. N.V. Giang, L.N. Thanh, LZietek, J.Moscicki, 2008: Characteristics of sedimentary structure of Mekong and Saigon river banks by geophysical and geological data. Poster presentation at the Near-surface 2008 EAGE
3. Ld Manh Himg. Dinh Cdng San, 2002;
Xdi Id bd sdng Ciiu Long vd gidi phap ph6ng trdnh cho cdc khu v\rc trgng dilm. NXB Nfing Nghidp, Tp. Hd Chi Minh, 196tr
4. Le Mgnh Hung, Nguyen Tudn Long, 2001:
Thuc trgng sat Id bd sdng Cdu Long. Tc. Ho?!
dpng Khoa hpc, thdng 10/2001. BO KHCNMT.
5. Huynh Ngpc Sang, Nguyen van Thibh, Thilm QuIc Tudn, 2003: Bdn vl nguyen nhan sgt Id khu vuc Thanh Da Tp. Ho Chi Minh. Tc Phdt triln KHCN, tgp 6, sd 3+4/2003, ti-.43-50.
6. L.N. Thanh, N.V. Gidng, N.S. NMn, 2008: D^c didm cdu tnic bd sdng Tiln (khu v\ic Sa Dec) theo tai lipu dia vdt ly-dja chdt. Tc. Cdc Khoa hpc vl Trai Ddt, T.30,1, ti-.84-90
7. https://news.zing.vn/37-diem-sat-lo-bo- song-kenh-rach-sai-gon-nam-o-dau- post872408.html
Ngu&iphdn bi^n: TS. Nguyen Quang Truoug Ngdy phdn bi^n xong: 10/11/2018
54 TAP CHf T A I NGUVeN Nl/(3C S6 1-2019
