NGHIEN CLTU CAC GIAI PHAP KHOA HOC CONG NGHE BAO VE BC> KHU Virc CLTA SONG, VEN BIEN NAM BO
PGS.TS. HOANG VAN HUAN'
Tdm tdt: Tren co sd phan tieh dac diem sat Id bdi ty bd, eua sdng. ven bien khu vye Nam Bg, bai vidt trinh bdy cdc tiep can phuong phap nghien cOu va ede giai phdp bdo ve bd. Cde gidi phdp bdo ve bd duge dd cap dya tren khoa hgc cdng nghe trong nghien eOu, thiei ke', thi cdng vdi viec Ong dung edng nghe mdi, vat lieu mdi. Ben canh dd ede nghien cOu quy hoach ehinh tri bdo ve bd eho mdt sd khu vye dai dien cho cde vung eua sdng ven bidn Nam Bd dugc dd cap nhu Id mot Ong dung thyc td trong sdn xudt.
I. Dac diem tinh hinh sat id, bdi tii bd khu virc cita sdng, ven bien Nam Bd
Trong tdng sd chidu dai dudng bd bidn ed 400km bd phia ddng, phia tay ddi 350km, theo tai lieu hon 100 nam quan trde (1885-2000) didn bidn bd bien Nam Bd cd the chia ra cde kidu dudng bd:
• Kieu hd tuang ddi dn dinh: Ben bd phia ddng kieu nay ehidm 20%, doan dudng dai nhdt la 45km tO Vinh Chau (Sdc Trang) de'n Vinh Thuan (Bac Lieu), cde doan khde dai khdng qud 10m.
Phia bd tay kieu dang bd dn dinh ehidm 60%. Doan dai nhdt tu sdng Ong Dde ddn gdn vinh Rach Gid tren 70 km, doan tu Ha Tien ddn vinh Cay Duong ddi tren 30km.
• Kieu bd hdi tu: Bd phia ddng ehi ed tdng edng 115km tap trung d mdt sd eua sdng Cuu Long: cua Tieu, eua Ba Tri, Thanh PhO. Bd bien phia tay kieu dang bd bdi ed ehieu dai 118km mdi nam ldn ra 25-30 m, ed chd den 80m/nam, vi dy nhu bd bien phia tay Cd Mau cd tde dd ldn bien 50-80m/nam, mdi nam tao ra bai bdi tren 120ba.
• Kieu hd .xdi Id: Ben bd phia ddng dai gdn 100 km, phia tay ddi 100 km. Doan bd xdi Id dai nhai la eua Ganh Hdo ddn cira rach Dudng Keo, trong doan nay d khu vye Bd Di ed tde do xoi Id 30-50m/nam.
• Kieu bd .xdi Id hdn hgp: Tap trung phia ddng vdi tdng ehidu dai 65km va thudng xdy ra d viing gdn mdt .sd cua sdng Cuu Long nhu Binh Dai (Be'n Tre), tO nam 1885 de'n nam 1940 doan nay la'n ra bien 2,2km. TO nam 1940 den nam 1965 bi Id vao sau 0,8km sau dd tuong ddi on dinh ed thd bdi nhe khu vye nay phdt tridn ehu ydu cdc lach trieu cd ldn, eac eua sdng hinh pheu.
1. Vien Khoa hoc Tliiiy loi mien Nam.
• Khu vife Cdn Gid, thdnh phd Hd Chi Minh: Day la khu vye bai tridu rdng 5-7km, do dd'c bai nhd. Vat lieu ehu ydu la set bOn. Theo eae tdi lieu khdo sdt eiia Vien Hdi duang hge - Nha Trang tu nam 1989-1992: Khu vye nay bi xdi Id manh do dnh hudng eua sdng va gid chudng va trieu eudng xay ra tu thang 11 nam trudc tdi thang 1 nam sau. Tdc do xdi trung binh 5- 7km/nam. do sau xdi 0,8-Im, do ddi xdi 8km. Hien nay he thdng ke vd md ban ket hgp xay dyng tO nam 1994 da bao ve bd tuang ddi tdt.
• Khu vife Gd Cdng Ddng (Tien Giang): Do rdng eua bai khd ldn, cd chd tu 5-7km. Vat lieu phu bai ehu ydu la set bOn, ldp phu thyc vat tucmg ddi phong phO, ehu ydu la rung dugc trdng theo quy hoach. Toan dai ven bd 4-5km phia bde thi tran Tan Thanh da duge ke be tdng, ben trong la de ngan man.
Khu vye bi sat Id manh la khu tap trung dan eu. Tuy da cd bien phap chd'ng xdi xong hien tugng xdi Id vdn xay ra, tdc do xdi trung binh tai day tu I0-I5m/nam, do xdi sau Im. Dac diem gdn day la ede vOng xdi manh kha tap trung. Thdi gian bi xdi Id manh tu' thang 10 nam trudc tdi thdng 3 nam sau, manh nhdt la vao giai doan tu thdng 1 den thdng 3. Thdi ky gid va sdng ed hudng Ddng (E).
• Khu vife Ganh Hdo (Bgc Lieu): Khu vye nay ed bai tridu rdng tu 2-5km, do dde bai nhd tO 0,001- 0.002. Vat lieu phu bai chu yeu la set bun, ldp phu thyc vat chu ydu la loai cay hoang dai mgc thua thdt. Xdi Id thudng xay ra d khu vye nay vao giai doan tu' thdng 10 nam trudc tdi thang 3 nam sau (vao thdi ky gid chudng manh). Giai doan xdi manh nhat la vdo khoang thdi gian sau Tdt Nguyen Ddn (tO thdng 1 ddn thdng 3). Tu sau nam 1975 tdi nay dudng bd tai khu vye da dich chuyen sau vdo lye dia khoang 300-500m, tde do xdi binh quan hang nam tu 20-30m theo ehidu ngang va 0,5-Im theo phuang thdng dOng, tren khoang ehidu dai dudng bd 3-4km. Khu vye bi xdi Id manh nhdt bien nay ndm d phia Bde cOa sdng Ganh Hdo.
• Khu vife Tdy Nam Bd (tdCd Mau tdi Hd Tien): Khu vye nay phd bidn la ddng bdng ngap man. it eae gidng eat, do ldn thuy tridu d vung ndy nhd xdp xi Im. Tridu mang tinh chat nhat trieu. Tram tich de tu ed be day tu vai ehye tdi gdn 200m, mdng da gd'c tai do sau nay hien nay chi quan sat cd 5 khu vye bi sat Id vdi ehieu dai eiia khu vuc sat Id khdng ldn. Cdc doan bd cdn lai tai khu vye nay ehu ydu la bd hdi ty, tai khu vye Dat Mui tdc do Ian bidn tu 100-120m, tdc do bdi tu giam dan ve hai phia cua Dat MOi (khu vye U Minh tde do la'n bidn trung binh 5- 6m/nam, tai Ca Mau tde do nay 2-3m/nam).
Trong giai doan hien nay cdng tde phdng ehdng sat Id ba cira sdng, ven bidn khu vuc Nam Bd lay viec dy bao di ddi phdng tranh thien tai la ehinh ed kdt hgp bdo ve bd nhung vung trgng didm: Cd y nghia vung kinh td, xa bdi; ed y nghia quan trgng vd hinh thai cua sdng va qua trinh bidn ddi long ddn (nOt han chd v.v.).
2. De xuat cac loai vat lieu mdi, cdng nghe mdi iimg dung cho cdng trinh bao ve bd khu viic ciia sdng d Nam Bd
Bao ve bd bang tham be tdng FS
Ifu diem:
• Thieh hgp vdi ndn mem ydu do phan bd lye ddu, vua be tdng dan trdi che kin ndn, trai lien tue tu dudi len tren.
Nhuac diem:
• Gid thdnh cao, cdng nghe thi edng phOe tap, thidt bi thi edng chuyen dung ldn.
2.2. Thdm be tdng tu chen ludi thep - thdm P.D.TAC-M 2.2.1. Vien thdm:
Vien thdm P.D.TAC-M 2.2.2. Ludi thdm:
Ludi thdm duge dan theo dang ludi B40 bdng thep 6-8mm, rdng tu 2,6-4m, ddi 20-100m.
Cde vien thdm duge dinh vi 3 ehan vao 3 d eua ludi thdm.
2.3. Mdng mem be tdng tu chen P.D.TAC-178 vd thdm dd reno mattress
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ca'u kien P.D.TAC - 178
2.4. Vdi dia ky thuat
Vdi dia ky thuat dOng trong dia ky thuat vdi ede ehue nang Igc, phan cdch, tieu, gia cd hoae bdo ve.
Ddi vdi ede edng trinh hdo ve hd vdi dia ky thuat phdi ddp img ddng thdi cde yeu edu sau:
Chdn ddt tdt, thdm mfde tdt, ehdng tde, do hen thi edng, tudi thg cao.
2.5. Cd bdn be tdng cdt thep ung sudt trudc
CO ban be tdng edt thep ung sudt trudc ed kich thude nhu sau:
-I- Chieu rdng ban eO: 996 mm; ehidu dai: 3-21 m -t- Chidu day: 60-120cm: chieu cao: 120-600mm
2.6. Cu bdn nhua vinyl
CO ban nhya doge chd tao to PVC (Poly Vinyl Chloride) va eac phy gia dac biet, dam bdo chat lugng khdng thay ddi vd kich thude sdn phdm dn dinh. CO ban nhya duge chd tao thudng ed ehieu ddy 5 - 12mm, ehieu rdng ban cO nhya 0,3 - 0,6m, cir ban nhya ed the duge cdt ngdn de dang tuy theo chidu ddi edn thiei.
2.7. Khdi Tetrapod
O Viet Nam, khdi Tetrapod da duge sir dung d nhidu noi nhung ehii yeu la trong cdc cdng trinh ngan eat, gidm sdng eiia eac be cang edn trong cdc cdng trinh bdo ve bd thi chua dugc ung dung nhieu. Thyc td khdi Tetrapod ed the su dyng tdt trong cdc cdng trinh bao ve bd cira sdng, ven bidn.
2.8. Cd chdng xdi mdn Vetiver
Cd Vetiver la loai ed luu nien thude hg Andropogoneae, khdng ed ldng ciing, deo chdc, nhdn. Cay mgc thdnh khdm ldn tu gde rd, ed than thdng dung cao 0,5 - 1,5m, rd cd the an sau vao ddt de'n 3m.
2.9. Cong nghe thi cdng trdi vdi dia ky thuat dudi nudc
Vdi thiei bi trdi vdi chuyen dOng, vdi duge trdi ra dp vdo mdi long sdng theo nhu mdi thidt kd.
2.10. Cong nghe thi cdng thd thdm dd dudi nudc
Cdng nghe dOng eho ede edng trinh bdo ve bd ma ldng sdng doge bdo ve tdi dd sau 10m ddn 40m.
2.11. Cong nghe thi cdng ddng cgc chieu ddi ldn
Cong nghe ddng ege ddi > 45m da duge mdt sd cdng ty trong nudc thi edng d eae edng trinh nhu: edng Tan Thuan (thanh phd Hd Chi Minh), cdng Hiep Phudc, cang Hdi Phdng... Vi vay, ddi vdi nhOng edng trinh bdo ve bd cua sdng, ven bien Nam Bd ed dia chat ydu su dung kdt cdu ege be tdng cdt thep chieu ddi ldn thi hodn todn cd the Ong dung edng nghe ddng ege ndy trong thidt kd va thi edng.
2.72. Xu ly ehdng xdi Id bd bien bdng cdng nghe STABIPLAGE
STABII'I.A(;E Chim - Sons i*"nK dtfrtnR hd
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ESPikCEPUH
tfinh 5: So dA ldp d^t cdt lo<^i cfing trinh Slahiplaae
STABIPLAGE la 1 cdng trinh dugc thidt ketheo phuong sach sau:
Cde kich thude eung nhu lya chgn vat lieu va phuang phdp bam cat vao cdng trinh dugc thieh ung hod ddi vdi tirng khu vuc. Cdc cdng trinh ty thich ung vdi nhidu kieu tang ndn, trong nhidu loai mdi trudng. Sy Idp dat STABIPLAGE khdng can cd nhidu thiet bi, may mdc nhung cdng viec thi cdng nhanh chdng vd khdng gay rdi loan mdi trudng. STABIPLAGE la I ket cau dia-vat lieu tdng hgp (gdocompositte) dugc phun cat vira thiiy luc. Tinh chat eua nd la nguyen khdi vd dang mdi cita nd tao thdnh dang cdng trinh, chiem it dien tich be mat dong thdi tao ra 1 edng trinh mdi la cho mdi trudng. Nguyen ly chit yeu cua cdng nghe nay Id thu giu, tich tu va duy tri tai chd ede trdm tieh.
3. Ket luan va kien nghj
Cira sdng, ven bien Nam Bd bao gdm eae cira sdng tir Binh Thuan den Ha Tien vdi hang chuc cua sdng dd ra bien Ddng vd bien Tay, la nai tuang tdc giira sdng va bien va cung la noi nhay cam sy tac ddng qua lai giOa ede ye'u to sdng va bien. O day cd che do thiiy van sdng bien, noi ed sy dao ddng theo mOa. Vung cira sdng bi md rdng, day dugc nang cao. Qua trinh xdi Id, bdi ty dan xen nhau theo mOa vd nam la ket qua tuang tde giu'a ddng nudc va long ddn. Giira mdt ben la pham tru co hge chat ldng (ddng nude) vd mdt ben Id pham tru ca hgc chat rdi (long ddn), cdc pham trO nay vd'n di dOng rieng da rat phO:e tap.
Dinh hodng eac gidi phdp chd'ng sat Id, dn dinh cira sdng la can thiet khdng dugc cham trd.
Tren CO sd khoa hgc each tidp can nghien cOii didn bien long ddn va gidi phap bao ve bd, bai viet da de xudt so dd gidi phdp bao ve bd cung nhu cdc van de cd lien quan ve thiet ke, thi cdng, u'ng dyng cdng nghe mdi, vat lieu mdi phye vu bao ve bd khu vuc ciia sdng. Vdi cdc khu vye dai bieu nghien cOu quy hoach ehinh tri vd bd tri cdng trinh bao ve bd: cira Lagi sdng Dinh - Binh Thuan, cira Ganh Hao - Bac Lieu da minh chOng vd khang dinh chung ta cd the lam dugc cdng trinh, de xudt nhung gidi phdp hgp ly bdo ve bd khu vuc cira sdng mdt each an toan, ben vung.
TAI LIEU THAM KHAO
[1] Hoang van Huan vd nnk: "Bdo cao tdng ket dd tai khoa hgc cap Bd", Vien Khoa hgc Thuy lgi midn Nam, nam 2003.
[2] Luang Phuang Hau vd nnk: "Cdng trinh bdo ve bd bien va hai dao", nam 2001
[3] Hoang Van Huan vd nnk: "Bdo cao didu ehinh nghien cuu kha thi du an phdng chd'ng sat Id khu vye eua sdng Ganh Hdo - Bac Lieu", Vien Khoa hgc Thuy Igi mien Nam, nam 2003.
Summary
On the basic analysis of the characteristics for river banks, estuaries and coastal areas erosion, siltation of the southern part, the paper has presented research methodology and methods for bank protection. These methods have suggested based on the technology in research, design and installation by applying new technology and modern materials. Besides, some studies on river training planning for bank protection in some typical areas have
