M O T SO KET QUA NGHIEN CUU THUY LljC CONG VUNG TRIEU VA HIEU QUA AP DUNG
GS.TS. T R A N NHl/HOI', TS. T A N G DUC THANG", ThS. NGUYEN THANH H A P
TS. H A N QUOC TRINH^ TS. TRINH CONG VAN^
ThS. TRAN THANH SON'
Torn tdt: Bai bao nay nhdm gidi thieu mdt sd kei qua nghien ciiu ve kei cau tieu nang phdng xdi edng vOng trieu ddng bdng sdng Cuu Long, nhirng kei qua va hieu qua dp dung cua nd.
Mddau
TO sau ngay giai phdng, su nghiep thOy lgi d ddng bdng sdng Cuu Long da cd nhOng bude lien vugt bac ve ky thuat, trong dd ed:
- Ky thuat xay dung cdng ve eac mat: hinh thOc ke't cau cira van tir ddng, tinh todn thuy lire he thdng, gidi phap kei edu va ngudng cdng trinh, ede gidi phdp ket cau tieu nang phdng xdi hgp ly.
- Trong nhieu nam qua. Vien Khoa hge Thuy lgi mien Nam da tie'n hanh nghien euu va co nhieu kei qua ve linh vuc nay. Sau day la mdt sd kei qua nghien cOu tieu bieu ve edng viing trieu. Cac kei qua nay da dugc dp dung rdng rai trong nhieu nam qua, d hdu hei cdc cdng ddng
bdng sdng Cuu Long. ^J^.
1. Ket qua nghien ciru ve tieu nang phdng xdi cdng viing trieu ddng bdng sdng Ciru Long
1.1. Tinh hinh xdi Id cong trinh a mot sd tinh ddng bdng sdng Cdu Long
Cac cdng trinh thuy lgi d ddng bdng sdng Cuu Long dam nhan nhiem vu tieu thodt 10, ung, chua, lay nudc tudi va kiem soat man (trudc day Id ngan man). Ngodi ra cdng cdn gidi quyei giao thdng thuy. cho thuyen be qua cdng vdo nhung 10c thich hgp. Vi vay, su xdi Id edng trinh xay ra d hai phia: phia sdng tieu thoat nude tu ddng ra, phia ddng khi ddn nudc tudi tir sdng vao.
So bd thdng ke nhung cdng trinh bi hu bdng xay dung trong khoang thdi gian tir nam 1978 - 1990 (trudc thdi diem dp dung rdng rai ket qua nghien cuu kei cdu cdng cd bd phan lieu nang phdng xdi cai tien) d mdt sd tinh nhu sau:
1. 2, 3 . \'ien Klioa lioc Thuy ioi mien Nam.
4. V:en Khoa hoc Thii\ loi.
5. 6. Cong ly Co phan Tir \'aii Xav dime Tliuv ioi 2.
Tinh Long An: Ben Tre, Mdng Gd, Tri Yen, Ong Hieu. Rach Chanh. Binh Tam. Ky Son.
Tam Vu, Chg GiOa, Thanh Ha, Bdo Dinh.
Tinh Ddng Thap: Tu Tao, Tan Hda, Be'n Sieu, Ba Cd Khdnh, Chin Cung, Muang Chua. Doi Lira. Ma Trudng, Muong Dap Dinh, Cdng 17. Cdng Cdc, Muong Ldn, Dudng Tdc. Cdng Trdn, Cdt Dai. Tdm Dam, 6 Mdi.
Tinh Cdn Tha: Cai Rdn, Chdng My, Cdng 14, Bdo Rang, Gidng Ke, Cao Hot Be, Nam Khai, Hai Thudng, Hai Yen.
Tinh Bac Lieu: Cdu Mdi, Bd Xang, Cdng Xi Rugi, Tu Lai, Mudi Bd. Dap Ldn. Xdm Ldm.
An Trach, An Hda, Hd Phdng 1, Gia Rai, Long Dien A, Long Dien B. Long Dien C. Hd Phdng 2.
Om Trd Nd, Hd Phdng 14, Gia Binh, Dinh Thanh. Xdm La, Chat Tam. Choi Mdi, Thanh Trudng. Bay Thao, Chang Be.
Tinh Sdc Trang: Gdi Xe, Tie'p Nhat, An Nd, Tu Minh, Tdng Gang, Long Phu. Bd Ken.
Rach sau, Trd Teo, Sau Que'.
Tinh Ben Tre: Vam Ddn, Tdng Cang, Cdng 30/4, Nha Thd, Binh Thanh, Cdng 2B, Cdng K20, Lang Sen, Ba Tri, Hai Cua, Nd Sau, An Hda.
Tinh Tra Vinh: Cha Va, Thau Rau, La Ban (cO)...
NhOng cdng trinh bi xdi Id nghiem trgng ed ve chieu sau va chieu ngang. tam hd xdi thay ddi theo thdi gian va khdng gian, vdi chieu sau hd xdi ldn ban 4,5 - 5.0m va chieu dai hd xdi 30-
120m la: Vam Ddn, Rach Chiee, Cai Xe, Tiep Nhat, An Nd. Tu Minh. Tdng Gang. Long Phu, Bd Ken, Rach Sau, Trd Teo, Tdng Can, Be'n Tre, Mdng Ga, Tri Yen, (Dng Hieu, Rach Chanh, Tam Vu, Lang Sen, Nd Sau, Cdng 13, Ma Trudng, Chg GiOa, Ky Son, Binh Tam, v.v.. Su xdi Id da lam hu hdng nang san sau cua tudng canh va san tieu nang.
1.2. Mot trudng hgp xdi Id cu the
Cac cdng bi xdi Id neu tren, deu ed tai lieu ehi tiei ve dien bien xdi lei, d day ehi trinh bay dien bien xdi Id cua cdng Vam Ddn.
Cdng dugc xay dung nam 1985, tai xa Huong My, huyen Md Cay, tinh Ben Tre, nam canh rach Vam Thom dd ra sdng Cd Chien (sdng Tien). Cdng ed nhiem vu ngan 10 xam nhap tu sdng Tien vao va tieu Ong cho 7.000 ha cua 5 xa phia nam huyen Md Cay; ngan man tao didu kien nggt hda, keo dai thdi gian nggt hda trong nam. Kei hgp ldy nudc nggt dua phO sa vao rudng trong dieu kien do man eho phep tai Vam Ddn, ma khdng anh hudng den sinh trudng cay trdng va sinh hoat cua dan vOng budng lgi, phuc vu giao thdng thuy trong vung. Nhu vay, edng lam viec 2 chieu: mua mua tieu Ong. nude chay tu ddng ra sdng; mua khd lay nudc tudi, nude chay tir song vao ddng.
Cdng cd 5 khoang cua, ban day dai 24m, cao trinh day -3.5m) gdm 4 khoang ngdm. mdi khoang rdng 2,5m, cao 3m va 1 khoang hd cho thuyen be qua lai rdng 5m. cao 6m. Hai ben cdng: phia .sdnj va phia ddng deu cd be tieu nang day (-5.0). dai 15m. ndi tiep vdi be tieu nang la san sau dai 28-30 m. cao trinh -3,5m, day rdng 34m duge gia ed bdng be tdng tdm lat.
Nam 1986, ehi qua 1 nam khai thac, sir dung, cdng trinh da bi xdi Id nghiem trgng.
Nam 1986 - 1987 tien hdnh dgt sua chOa ldn thu nhdt, theo nguyen tac xdi chd nao thi gia CO bdng rg da va cue be tdng d dd. Nhung xdi Id vdn khdng hei, cdn tiep tuc md rdng. kht)ct sau va vj tri di chuyc n phuc tap.
95,8
>80,0 -10,1 0.0
86,0
>90,0 -10,1 0,0
Nam 1989. tien hanh xir ly dgt 2. Vien Khao sdt Thiei ke Thuy Igi Nam Bd thiei ke sira chua va cdng trinh xay dung thuy lgi 10 td chuc thi edng vdi lugng vat lieu la 10.000 m'' cue be tdng da hoc d dang rg da. Nhung trai vdi mong mudn, xdi Id da khdng ngan ehan dugc, ma miic do xdi Id lai cu tiep tuc phdt trien trdm trgng ban.
Nam 1990 - 1992, Cdng ty Tu van Xay dung Thuy Lgi 2 va Sd Thiiy lgi Ben Tre lai phai khao sat, xdc dinh vi tri, hinh dang bd xdi phdn an sau vdo cdc bd phan ddn ddng va tieu nang cdng trinh. lap binh dd hd xdi phia sdng va phia ddng vdi vi tri, kich thude ea ban eiia cdc hdxoi nhu sau:
Dac trirng hd xdi Phia ddng Phia sdng - Chieu rdng (m)
- Chieu dai (m) - Do sau (m)
- Khoang each gdn nhdt tu mieng hd xdi den mep be' tieu nang (m)
- Ban dav ngudng be tieu nang va tudng ednh, hd xdi
' -2,0 -3,0 dang ham e'eh an sau vao (m)
So vdi hd xdi sau chdng xdi ldn 1 thi hd xdi sau chd'ng xdi ldn 2 cd quy md, kich thude, hinh dang, vi tri cua hd xdi do nam 1992 deu ldn ban, nguy hiem ban, vi khdng nhung sau, rdng, dai han ma nd da phdt trien md rdng an sau vdo ede bd phan chinh yeu cua cdng trinh la be tieu nang va tudng ednh hudng ddng. Nhu vay nhung Idn sira chua trong cdc nam 1986, 1989 tdn kem khdng nhd nhung khdng dat hieu qua mong mudn Id ngan ehan sir xdi Id. Cdn neu nhin d khia canh dien bien phdt trien xdi, thi hinh dang hd xdi duge tao ra d mdi ldn sira chua lai la tien de gdp phdn lam cho phdt trien xdi nguy hiem ban.
Theo thdng ke, bdo edo cua cdc ban quan ly khai thde edng trinh thuy lgi d ede tinh dong bdng sdng Ciru Long thi trong tdng sd cdng trinh duge xay dung trong khodng thdi gian tu nam 1978 de'n nam 1990 ed de'n 70% edng trinh bi hu hdng do xdi Id gdy ra. Chat lugng edng trinh nhu vay da dnh hudng den hieu qua cdng trinh. Dieu nay cung phu hgp vdi danh gia cua Cue Quan ly nude va Cdng trinh Thuy lgi la "He thdng edng trinh thuy lgi chi phdt huy dugc 60% so vdi nang luc tieu tudi thiei ke...". • •!
1.3. Nguyen nhdn xdi Id
Qua nhieu nghien cOu. nguyen nhan xdi Id sau edng vung trieu da dugc xdc dinh la:
- Nen dai yeu, kha nang chdng xdi cua ddt nen thap: ddi vdi Idng ddn tre, vung chau th6 tre nhu long dan sdng Ciru Long va ddng bdng sdng Cim Long thi qua trinh sdp xep tu nhien chua du de cac hat chen chat vao nhau. Trong ddt dinh, d cde khe rdng vdn cdn cd nudc tir do la can trd ma cde hat ed kei vdi nhau. Chinh vi vay, ma viec chd'ng lai cdc tac dung phan khai hat do ddng ehdy gay ra ddi vdi long ddn d ddng bdng sdng Cim Long la yeu kem. rdt nhay cam vcfi bien dang xdi. Sir nhay edm xdi Id cdn phdi dac biet chu y khi biei rdng, lugng ede mudi de hoa tan nhu NaCl, MgCK, MgSO,, NaHCO,, Ca(CH03)2, Mg(CHO,), Na^SO^ chiia trong dat nen Idng ddn cua ddng bdng sdng Cuu Long len den 0,7 - 1% trgng lugng ddt khd.
- Kei cdu cdng cdn ehua thieh hgp vdi viec phdng ehdng xdi Id.
1.4. Phuang phdp vd ket qud nghien cdu cdc gidi phdp tieu ndng phdng xdi
1.4.1. Phuang phdp nghien citu
Nghien euu phdng ehdng xdi eho cdc cdng duge tien hdnh bdng ca ly thuyet va thue nghiem. Viec nghien cOu ly thuyet ehu yeu neu ra dinh hudng cac gidi phdp phdng chd'ng xdi, con nghien cuu thuc nghiem (thi nghiem trong phdng vd kiem nghiem hien trudng) se xdc dinh cac thdng sd ky thuat cua kei ca'u phdng chd'ng xdi.
1.4.2. Nguyen tac cua ket edu tieu ndng phdng xdi
Nghien cuu ly thuyei ehi ra mdt sd yeu eau ky thuat ddi vdi kei cdu tieu nang phdng xdi la:
- Tao dugc ddng chay thdng tuyen true edng trinh trong mgi trudng hgp chenh lech muc nude;
- Ddng ehdy lan can phdn tiep xue vdi kenh ddt (kei thue phdn gia ed) ed van tdc be ndm trong kha nang ehdng xdi cua ddt nen.
1.4.3. Kei edu tieu ndng phdng xdi
Nhieu nam qua, bdng ede nghien euu tren md hinh phuc vu san xuat va nghien cOu khoa hge, Vien Khoa hge Thuy lgi mien Nam, Vien Khoa hge Thuy lgi, Cdng ty Tu vdn Xay dung Thiiy lgi 2 da ed nhung tdng kei, chudn hda ddn nhOng bd phan trong kei cdu tieu nang phdng xoi. Ve hinh thue kei edu, dang co ban dang duge su dung hien nay la dang "3 ngudng", ldn ddu tien duge de xuat tu cudi nhung nam 1980, sir dung ddu tien trong cdng Cai Luc, Ben Tre, va de'n nay da sir dung trong hdu hei cac edng d ddng bdng sdng Cuu Long va duge Bd Ndng nghiep va Phdt trien ndng thdn ddnh gia cao. Kei cdu nay cd mdt sd dac diem sau (Hinh 1):
- Su dung ludi gd (ngifdng thu nhdt) de tgo ra do md eifa van Idn nhdt (md sat thanh tru pin/tru bien), tao dieu kien thuan lgi cho ddng chay thang tuye'n true cdng.
- Dimg 2 ngudng (tren he tieu ndng vd sdn sau thu 2) de tgo phdn hd ddng ehdy tren mat bdng thieh hgp eho phdng .xdi, trong dd ngudng thu 3 dat cudi san sau thu 2: tao hudng ddng chay thang theo tuyen true cdng, phan tan ddng ehdy rdng tren mat bdng, giam thieu cac khu xoay true dung hai ben mang cdng, tao ddng chay dn dinh (loai bd dugc ddng udn lugn), tao nen phan bd ddng chay ed lgi cho phdng xdi (nhd d day, ldn d mat).
TO kei qua nghien cOu tren md hinh thuy lire tuong tu cua ban 50 cdng trinh va tai cd da ap dung thue te', da dua ra so dd kei cdu tieu nang phdng xdi la he thdng lien hoan gdm: ludi, gd, ngudng, san sau, hd phdng xdi.
san sau ehi can chieu dai L = (2 - 3)h|,. Thuc te cua ban 50 edng trinh thi L = 8 -13m.
Cao trinh hieu qua cua day hd phdng xdi la tu V - 5,0 den V - 6,0. Mdi dde hd phdng xdi theo hudng ddng chay m = 5,0 - 6,0.
- Su dung hd phdng xdi tao nen sir ndi tie'p vdi kenh ddn ha luu tdt, tdt nhanh nhieu ddng bai Igi d phdn kenh ddn ndi tiep. Chung tdi xin nhdc lai rdng day la hd phdng xdi, ngan ngOa xdi tien nhanh vao edng trinh de cd the dua ra eac bien phdp sua chOa kip thdi; khdng nen hieu day
Id hd xdi, vi hd xdi cd quy md ldn han (vua sau ban, vira rdng ban). Tuy nhien, hien nay ta thudng hay ggi ngdn la hd xdi nhung cdn hieu dung thuc chat cua nd la hd phdng xdi. Ddi vdi eac cdng hien nay, cao do hd phdng xdi khoang -5,5 den -6,0m, mdi dd'c hd xdi m = 5-6.
Vdi diem chd y ve hd phdng xdi:
Quan diem tinh todn hd phdng xdi la tai mgi die'm tren pham vi hd xdi lan can gidi han ldp bdo ve phdi dam bdo thdi gian xudt hien van tde ddy tife thdi ldn han van tdc ddy eho phep phdi nhd han nwt gidi hgn ndo dd: •• nvj
T „ < U _ < k . T (2)
Trong dd: u,„^„ [v] la van tdc tuc thdi ldn nhdt va van tde xdi cho phep ciia ddt nSn (deu tinh ngay tai day hd xdi); T la thdi gian lam viec ciia cdng trinh (hoae thdi gian tinh toan nao dd).
He sd k thudng chgn tOy theo tiem luc kinh te vd tdm quan trgng cua edng trinh. Nhieu nude de nghi khdng che trong mgi trudng hgp khdng cho luu tdc tuc thdi vugt qud luu tdc cho phep (tuong ung vdi k=0). O Viet Nam, tiem lire kinh te cdn cd ban, mat khdc rai kho cho thi cdng, khdng the dam bao dugc dieu kien k=0, phdi chgn miic dam bdo tha'p ban. Sau mdt qua trinh khai thac se dai tu, sira ehua. Hien nay, theo nghien euu cua Vien Khoa hgc Thuy lgi mien Nam, he sd k trong ede cdng trinh dang dugc chgn trong khoang 0,2 -^ 0,5.
Tuy nhien ne'u cdng ldn, dia hinh tuye'n phue tap, dat qua yeu (vi du nen la cdt min) thi can giam bdt he sd nay.
Luai ga
y^
Nguoiig cong
•^;;n
Nguang 1: Go tang do nxr va 6n dinh cira van
Nguang 3
Hinh 1. So dd ket cau tang do md va tieu nang phdng xdi cai tien ciia Vien Khoa hgc Thuy loi mien Nam
2. Cac nghien ciiru ve tang do md ciira van tir ddng
2.1. Cdc tdn tgi trudc ddy cua cua van tuddng
Ciia van tu ddng dang canh cua ldn ddu tien dp dung d cdng Be'n ThOy (Nghe An), sau dd da duge cai tien de dp dung cho eac edng vOng trieu ddng bdng sdng Cuu Long, vdi cac uu diem la cau tao dan gidn, van hdnh thich hgp vdi sir thay ddi nhanh cua trieu.
Cifa van tif ddng logi ndy khdng md dugc het khi edng ldm viec a che do ehdy ngap, thudng chi md duge d gde a = 70 - 80", gay ra nhung hau qua xau, nhu xudt hien ddng xien va CO hep chu luu, dan de'n su tap trung luu lugng va xuat bien luu tdc ldn d mdt phdn cOa be ngang ha luu, gay ra xdi sau va xdi ngang. Van de ndy ludn xdy ra trong cac cdng vOng trieu ddng bdng sdng Cuu Long, kbi ma do chenh lech AZ cua miie nude thugng ha luu bien thien trong mot dai rdng.
Nhu vay, nhiem vu quan trgng la nghien cuu gidi phap kei cdu edi thien do md cua van.
lam cho ednh cua tu ddng md hei (a « 90") trong mgi trudng hgp nhdm cai thien phan bd ddng chay ha du thieh hgp eho phdng chd'ng xdi.
2.2. Gidi phdp ket cdu edi thien do md cua van
Ve mat ly thuyet, cua van chiu tdc dung cua cac lire thOy ddng, ma sat va lech true.
Phuang trinh can bdng cua canh cua duge viei dudi dang tdng quat:
j j „ ( P „ - P , ) y d F - M , M„,.. =0
Trong dd:
P„, P,: ap sudt thOy ddng cua ddng chay tac dung len mat ngoai va mat trong cua ban cua.
dp, y, D: dien tich vi phan dF cua ban mat cua; canh tay ddn cua md men lire vi phan tren dien tieh dP; va dien tieh bdn mat cua.
M|„ M„„: md men lech true, md men ma sdt cua canh cua ldy ddi vdi true quay.
True quay cOa cua van
^ - ^
dF
Bien phap kei eau duge dua ra la nhdm cai thien phan bd ap luc thuy ddng mat trong (P,.
phia tru pin hoae tru bien) va mat ngodi tiep xOc vdi ddng chay qua edng (P„).
Bdng nghien euu thirc nghiem tren cdc md hinh, mdt ket cau thich hgp da dugc tim thdy.
Dd Id kei cdu ludi ga vd gd. Gd dugc xay dung d tren ban day hoae san tieu nang, vudng gde vdi ddng ehdy vd dat d vi tri ngang vdi dudi cira khi md het. Ludi gd rdng 0,9 -1,2m, ngay dudi vi tn"
cua khi md hei.
Giai phdp nay da duge dp diing cho hdu hei cdc cdng ke tir khi nd dugc de nghi, va cho thdy rdng cd hieu qud rdt tdt, md cira van md hoan todn trong mgi trudng hgp khi chenh lech mue nude > 3 ^ 4 cm, dOng nhu da dugc nghien cuu trong phdng.
3. Cac nghien ciiru ve khau do cdng vung trieu thich hgp
Hien nay, md hinh sdn xudt d ddng bdng sdng Cim Long dang cd nhieu thay ddi. Cac he thdng ven bien dang duge khai thde theo hudng da dang hda sdn pham, ca ndng nghiep vd nuoi trdng thiiy sdn. Mdt sd yeu cdu ddi vdi ede he thdng ven bien Id:
- Cdng ed khd nang kiem soat man (cd nhiem vu ldy man) de' nudi trdng thiiy san.
- Phdi cd khd nang trao ddi nudc ldn.
- Phdi ldy dugc ddu nude cao trong ddng.
De ddp ung yeu cdu nay, viec nghien eifu khdu do cdng, kenh vd bdtri hap ly chung trong he thdng Id mdt trong nhOng yeu cdu bOrc xue. Dac biet, ty le giua khau dien cdng va kenh (sdng) tu nhien tai vi tri xay cdng phai ddm bdo ldn hon mdt gidi ban nao dd, Iy tudng Id bdng 1.
Kei qua nghien euu bude ddu cua Vien da chi ra rdng, ndi chung ty le nay ndm trong khodng 0,3 -0,5 la cd the giai quyet ve co bdn nhiem vu lay nudc nggt vd man. Tuy nhien, day mdi ehi la nghien cuu edn rdt so luge, phai duge nghien euu sau ban ve nhieu mat, chang ban nhu de ldy man, thau rira he thdng, ban che lan truyen benh thuy san trong he thdng, giam thieu d nhiem mdi trudng trong he thdng.
4. Hieu qua ap dung
Theo ddnh gid so bd, ddi vdi mdt cdng vira cd khau do 5-7m, viec dp dung kei cau tieu nang phdng xdi edi tien ed the tiei kiem dugc tu 2-3 ty ddng kinh phi xay dung; cdn vdi cac cdng ldn ban thi cd the tiei kiem dugc 3-5 ty ddng hoae ldn ban.
Hien nay, tien bd ky thuat nay da dugc dp dung cho hau het cdc edng vira va Idn d ddng bdng sdng Cuu Long (tren 60 edng) vd kinh phi tiei kiem dugc ed the den hang tram ty ddng.
5. Ket luan
Gidi phap ludi, gd, ngudng, sdn sau, hd phdng xdi la mdt ket qua nghien curu da dugc kiem chung cho phdn ldn cde edng vira va ldn d ddng bdng sdng Cim Long, ma tde dung cua nd la lam cho cua van md hodn todn, phan tdn ddng chay ha luu tren dien rdng, han che tap trung dong ehdy, tao ra trudng phan bd van tde ldn d be mat va nhd d ddy long ddn ldm cho viec gia cd long ddn ha luu dugc gidm nhe.
Day la kei qud nghien cuu ung dung da dugc ddnh gid cao, duge chgn la mdt trong sd cac nghien cuu dien hinh cd ndi dung khoa hgc phong phu, hieu qua kinh te cao, dang dugc dp dung rdng rai vao san xudt.
TAI LIEU THAM KHAO
[1] Kixeiep: Sd tay tinh toan thuy lire, 1984.
[2] Ts.E. Mirtskhoulava.- Scouring by flowing water of cohesive and noncohesive beds. Journal of Hydraulic Research; Vol. 29, 1991.
[3] G.J.CM. Hoffmans, K.W. Pilarezyk: Local Scour Downstream of Hydraulic Structures, Journal of Hydraulic Engineering; Vol. 121, No4, 1995.
[4] Vien Khoa hgc Thuy lgi mien Nam: Cdc bdo edo ket qud thi nghiem md hinh thiiy life cdng ddng bdng sdng Citu Long.
[5] Trdn Nhu Hdi vd nnk: Phuang phdp kiem dinh vd ddnh gid ehdt litgng edng trinh tieu ndng phdng xdi cdng viing trieu ddng hdng sdng Cuu Long vd hudng khdc phuc, Bdo cao de tai capBd, 1998.
Summary
This paper will present some issues about erosion prevention structures of tidal sluices in the Mekong delta, about some research results on erosion prevention structures and its applied effectivenese.
