Tiiu han Cdc Khoa hoc vi Trdi ddt ISBN 978 604 913 016 8 DAC DIEM CAU TRUC DAM PHA LIEN QUAN T 6 I THIEN TAI 6 VEN BIEN MIEN TRUNG VIET NAM STRUCTURAL FEATURES OF COASTAL LAGOONS RELATED TO NATURAL HA[.]
Trang 1Tiiu han: Cdc Khoa hoc vi Trdi ddt ISBN: 978-604-913-016-8
DAC DIEM CAU TRUC DAM PHA LIEN QUAN T 6 I
THIEN TAI 6 VEN BIEN MIEN TRUNG VIET NAM STRUCTURAL FEATURES OF COASTAL LAGOONS RELATED TO
NATURAL HAZARDS IN CENTRAL VIETNAM
Nguyen Hfloi Cu
Vien Tii nguyen v i Mdi trudng bien
246 Da Ning, Ngd Quyin, Hii Phdng
Tom tat:
Dam phd, mot trong nhirng logi hinh thiiy vuc ven biin, phd biin a nhiiu nai trin thi gidi, chiim khodng 13% chiiu ddi ba biin Viet Nam cd 12 dam phd tiiu biiu phdn bo a ven biin miin Trung trong khodng tir Uo vi bdc (Ninh Thudn) tai 16o vibdc (Thira Thiin Hui) vai mat do 57 km chiiu ddi ba biin miin Trung cd 1 dam phd vd ba dam phd chiim khodng 21% chiiu ddi ba biin Viet Nam
Hi thong ddm phd ven biin miin Tning Viet Nam la cdc lagun ven biin vi do thdp, nhiet dai ndng dm, khdc nhau vi kiiu logi (gdn kin, kin tirng phdn, ddng kin), vi kich thudc (tir nhd - diin tich mat nuac dual 10 km2, tai lan - diin tich trin 50 km2, thdm chi trin 200 km2 vd thudc logi lan cua thi giai nhu hi dam phd Tam Giang - Cdu Hai), vi ddc trung khdi nuac (tir Ig - nhgt tdi Ig - man, thdm chi siiu man), v.v., ddc biit khdc nhau vi dgc diim cdu tnic hinh thdi liin quan tai tai biin tu nhiin viing ba biin, trong dd cd biin dgng cira ddm phd, lu vd ngap lut ddng bdng ven biin, nhiim man vi miia khd, nggt hod vi miia mua, v v
Ddm phd cd bdn hgp phdn cdu tnic ca bdn: vuc nuac, cira, di cdt chdn vd ba sau Hinh thdi vd tinh dn djnh cua cdc dan vi cdu tnic thay ddi qua cdc giai dogn phdt triin cua ddm phd vd phu thugc vdo ngudn gdc dam phd hinh thdnh trong qud trinh san bdng ba vung vjnh hay ldp ddy cung bdi tich bdng ca chi phdt trien chdu thd.Su thay ddi ciia cira dam phd Id mdt trong nhirng dgng tai biin gdy hdu qud kinh ti-xd hdi vd mdi truang ndng ni cho cdc cdng ddng ddn cu ven biin
Abstract:
Coastal lagoons, one of the kinds of coastal waterbodies, are common in the world, bordering some 13 % of the total world coasline There are 12 typical coastal lagoons in the Centre of Vietnam in a range of 110 N (Ninh Thuan)
-160 N (Thua Thien Hue) They appear on 21 % of the Vietnam coasline with a density of one lagoon in every 57 km of the Central coasline
They are the tropical low-latitude coastal lagoons diverse in typology (nearly enclosed, partly enclosed, and enclosed); in dimension (from small size with an area less than 10 sq.km to large size with an area more than 50 sq km, and even more than 200 sq km ( Tam Giang - Cau Hai lagoon as a large one of the world)); in salinity (from oligohaline, mesohaline, polyhaline, to euhaline, and even hyperhaline); especially in stmctural features in relation to the coastal hazards, among which are instability of lagoonal inlets, flooding and inundation, salt-intnision in dry season, desalination in rainy season, etc
A coastal lagoon is composed of 4 parts of basin, inlet, frontal barriere of sand and sheltered shore, which have changes in morphology and stability dependent
Trang 2on lagoonal development in stages and lagoonal formation related either to the
process of equilibrating bay and embayment coasts or to the deltaic progradation
The change of lagoonal inlets is one of the natural hazards with heavy
socio-economic and environmental effects occurring to coastal communities
MO DAU
Dim phi (coastal lagoon) li mdt trong cic loai hinh thuy vyc ven bien tieu bieu cimg vdi cae vimg cira sdng vi viing vjnh, ddng thdi la mdt bd phin eiu triie ria ddng bing ven bien Sau khi hinh thinh, dim phi trii qua eic giai doan phit trien eua minh tir giai doan tre (active), giai doan trudng thinh (grown), tdi giai doan suy tin (ephemeral) vi chet (dead), rdi trd thanh viing triing thip (polder) dudi dang tram, bau nude nggt, dim liy, v.v Trong qui trinh phit trien md rdng ddng bing ven bien mien Trung Viet Nam, ed mat nhieu dim phi ed ldn nhd da tin vi hiu bet eic dim phi hien dai ed ljeh sir hinh thinh tir Holocen giira (Nguyen HQ-u Cir, 1995) Hau bet dim phi li bdn hdi luu cic sdng cd chirc ning dieu tiet lii d mire do nhat djnh, nhung ddng thdi li tie nhin giy ngap lut ddng bing ven bien do de cit chin ngoai va cira hep Trong nhieu trudng hgp khi mire do neap lut ldn, ap lye thuy tTnh giy
hire xung (thixotropy) phi vd de cit tao cira mdi va thim ••• nhieu cira nhu d he dim phi
Tam Giang - Ciu Hai trong trin lu lich sir vio thing 11/1 >'v, 'im phi ed bdn hgp phin eiu tnic CO bin - vyc nude, de cit chin, cira vi bd sau Tiong ML.: .iinh phit trien dim phi, nhieu dang tai bien ty nhien ed lien quan giy hiu qui kinh te-xa hdi ning ne eho edng ddng din eu ven bien Bai viet niy cd mue dich phin tieh die diem eiu tnic dim phi lien quan tdi tai bien
ty nhien lam co sd khoa bge de xuit irng xir tai bien d ven bien mien Trung Viet Nam
1 TONG QUAN VE LAGUN VA DAM PHA VEN BIEN MIEN TRUNG VIET NAM
Tir lagun ndi chung (lagoon, lagune, laguna, v.v.) ed ngudn gdc tir ehii latin - lacuna, dugc sir dung tuong ddi rdng rai de chi eic ddi tugng khie nhau Trong tir dien "Glossary of Geology, 3"^ ed., 1987", lagun dugc hieu li mdt bd phin dugc tich ra khdi mdt vyc nude nhd mdt dang tieh ty chin ngoai Nhu viy djnh nghTa niy rit rdng, bao gdm ci lagun xa bd (offshore lagoon) va ven bd (coastal lagoon), ei vyc nude man vi nude nggt O Viet Nam, ed mat cic lagun xa bd quy md nhd nhu d quan dio Trudng Sa do im tieu san hd tao thinh, ed lagun ven biin d miln Trung Viet Nam, cd lagun ven bien nude Ig, nude man vi thim chi sieu man (Dim Ling Cd, Dim 6 Loan) nhung chua he ndi tdi lagun nude nggt cd ngudn gdc sdng hoac hd nhu djnh nghTa ndi tren
Lagun ven bien, nhu cd mat d ven bd mien Trung Viet Nam, cd khii niem hep hon lagun ndi ehung, dugc xie djnh li: mdt thuy vyc ven bien, duge ngin cich vdi bien nhd mdt dang tieh tu cit chin ngoii, in thdng vdi bien phia ngoii qua mdt hay nhieu cira hoac tham thiu (percolation), chay thim (seepage) qua ehinh the eit chin
Trong sl cic djnh nghTa lagun ven bien hien nay, djnh nghTa eiia Phleger, F P (1981) dugc sir dung phd bien hon - lagun ven bd li mdt loai hinh thuy vyc ven bien nude Ig, nude man hoac sieu man, duge chin bdi mdt de eit va cd cira (inlet) in thdng vdi bien phia ngoai Ten ggi dja phuong ve lagun ven bd tdn tai mang tinh Ijch su va tap quan, cho tdi nay da trd thinh danh tir rieng va viet hoa Vi du nhirng lagun ven bien ndi tieng cd ten ggi ljeh sir li
hi - H I Mat Trdi (Solar Pond) d Israel, Hi Togo (Lac Togo) d Guinea, Ho Mellah (Lac Mellah) d ven bd ddng Dja Trung Hii, li vjnh - Vinh Roekport (Rockport Bay) d Texas hay Vinh Florida (Florida Bay) - li lagun ven bien dien hinh tao bdi eic ran san hd chin ngoii
Trang 3Tiiu ban: Cdc Khoa hgc vi Trdi ddt ISBN: 978-604-913-016-8
(2> Viet Nam, cic lagun ven bien duge ggi li "dim" hoac "phi" Vi du, d Thira Thien Hue
cd ten ggi phi Tam Giang, dim Sam, dim Thanh Lam, dim Hi Trung, dim Thuy Tu vi dim
c i u Hai, ma tit ci ehung li nhirng thiiy phin khdng ed ranh gidi ty nhien hgp thinh mdt lagun ven biin thong nhat Ngay tir xa xua, trong thu tjch cd eiing nhu trong din gian, tdn tai nhilu ten ggi theo ranh gidi hinh ehinh, ed ten phi Hii Hac, phi Tam Giang, dim Nieu, dim
Da Di, vjnh Ddng, vjnh Minh Luong vjnh Hung Binh, vjnh Giang Tan, vjnh Ha Bac, v.v Cho tdi nim 1831 (thdi Minh Mang), mot sd dugc ddi ten trong thu tjch thinh Dim Thanh Lam, Dim Hi Trung, v.v nhung trong din gian vin giir eich ggi rieng vi ngiy nay vin ggi tit la phi Tam Giang - Cau Hai va thim ehi ggi phi Tam Giang Cimg ddi tugng dd d Quing Ngai cd ten ggi dim An Khe hay Dim Nude Man (Sa Huynh), d Binh Djnh ed ten ggi dim Tri 6, dim Nude Nggt hay dim Thj Nai, d Phii Yen - Khinh Hda ed ten ggi dim O Loan va thim ehi dim Nha Phu mi dim Nha Phu li mdt vjnh ven bd (bay) dien hinh Trong khi dd, d nhieu noi khie sir dung ten ggi "dim" theo truyen thdng de ehi mdt loai hinh thuy vyc ty nhien, tao ra do mdt doan sdng chet, mdt viing trung cdn sdt lai trong qua trinh phit trien ddng bing ven bien cd lien quan tdi qui trinh liy hda hien nay Loai hinh nay tuong irng vdi
"trim" vi "biu" theo cich ggi ten d mien Trung Hon nira, ehinh ngudi din ven bien ty tao ra mdt loai hinh thiiy vyc viing trieu (quiy dap mdt phin bii trieu) de nudi thiiy sin nude Ig roi Cling ggi nd li "dim"
Do dd, de tien lgi va nhim phin anh diing ban chat ciia mdt he ty nhien, chiing tdi de nghj sir dung ei tir dja phuong ed viet hoa - Dim Ciu Hai, Phi Tam Giang, vi tir khoa bge da phien im tieng Viet mi khdng viet hoa - lagun Khi de cap tdi mdt van de khoa hgc thi diing tir phien im vi khi de cap tdi ddi tugng eu the thi diing tir dja phuong Ching ban, he Dam phi Tam Giang - Cau Hai li mdt lagun ven bien, hay qui luat phin bd trim tich day Dim 6 Loan bieu hien mdt lagun ven bien dang phat trien d giai doan trudng thinh, v.v
Vin de phin loai lagun rit phire tap va ngay ei phin biet giiia lagun, vjnh vi viing cira sdng ciing khdng de bdi tinh chuyen tiep giiia ehiing Tuy nhien, cd thi phin loai theo vj tri tuong ddi tren them lue dja thinh lagun xa bd vi lagun ven bien Lagun xa bd duge hiiu la mdt phan cua bien hoac dai duong dugc tich ra nhd im tieu vdng (atoll) Sy phit triln ciia ehiing khdng bj inh hudng bdi eic qui trinh luc dja Lagun ven biin duge bilu la mdt phin eua bien ven bd, duge tieh ra nhd mdt dang tich Ui thudng li cat, hiim khi li im tieu viin bd
Sy phit trien eua lagun ven bien phuc tap bdi tuong tic giGa cic qui trinh biin (sdng, thuy trieu vi ddng chiy) va lyc dja (sdng, van ddng kiln tao khu vuc, v.v.)
He thdng phan loai lagun ven biin eua Nichols, M and Allen, G (1981) khii quit hon va duge su dung rdng rai hien nay He thing phan loai nay dya theo nguyen tie ddng lye, phin anh ddng lye hinh thinh va phit trien lagun trong the tuong quan giiia eic qua trinh biin (sdng, ddng chiy, thuy trilu) vi cie qui trinh lue dja (sdng) thdng qua hinh thii va qui trinh
uu the trong lagun He thdng phin loai niy chia cie lagun ven biin dai duong thi gidi thinh bdn kieu: lagun cira sdng (esUiarine lagoon), lagun hd ("open" lagoon), lagun kin timg phin (partly closed lagoon), lagun ddng kin (closed lagoon)
O Viet Nam, eac lagun hien dai tieu bilu phin bo d ven biin miln Trung dugc chia thinh 3
kieu (Nguyen Hiru Cir, 1995) nhu sau: kilu gin kin (nearly-enclosed), kilu kin tirng phin (partly-enclosed), kilu ddng kin (enclosed)
Vj tri tuong ddi cae kieu cua hai each phin loai nay khdng hoan toin triing khdp nhau mac dii ciing nguyen tic phan loai ddng lue - hinh thii Kilu gan kin d day mang ei hai ylu tl
"hd" vi "kin timg phan" do cic nguyen nhan dja phuong tao ra
Trang 42 CAU TRUC HINH THAI D A M PHA LIEN QUAN T 6 I THIEN TAI
2.1 Kich thirac cabdn cdc ddm phd
O ven bien mien Trung Viet Nam trong khoing vT do 11° - 16° bie, cd mat 12 dim phi tieu bieu vdi tdng dien tieh mat nude 436,9 kml Cie dim phi niy da dang ve kich thudc (bing 1), trong dd, nhd nhit li Dim Nude Man (Sa Huynh) cd dien tich 2,8 km^ ldn nhit la he Dim Phi Tam Giang - Ciu Hai (Thira Thien Hul) vdi dien tieh 216 km^ ldn nhit Ddng Nam A vi thude loai ldn cua the gidi Theo thir ty vl phia nam, he thdng dim phi bao gdm: he Dim Phi Tam Giang - Ciu Hai, Dim Ling Cd (tinh Thira Thien Hue), Dim Trudng Giang (tinh Quing Nam), Dim An Khe, Dim Nude Man (tinh Quing Ngai), Dam Tri 6, Dim Nude Nggt (Degi), Dim Thj Nai (tinh Binh Djnh), Dim Cii Mdng, Dim 6 Loan (tinh Phii Yen), Dim Thuy Trilu (tinh Khinh Hda), Dim Nai (tinh Ninh Thuin)
Bdng 1 Diin tich vd kich thuac cdc dam phd ven biin miin Trung Viet Nam
(N H Cir, 1996, 1999) (cd bd sung theo tdi lieu khdo sdt vdo thdng 6 ndm 2005)
TT
1
2
3
4
5
6
7
8
9
10
11
12
Dam pha
Tam Giang
-Cau Hai
Lang Co
Tmdng
Giang
An Khe
Nude Man
T r a O
Nude Ngot
Thi Nai
Cii Mong
0 Loan
Thuy Trieu
Nai
Dien tich (km^)
216
16 36,9
3,5 2,8
14,4 15,6
50 30,2
18
25,5
8
Kich thudc (km) Dai
68
6,0 10,0
3,0
3,0
6,0
8,5
15,6 17,6
9,3
17,5
6
Rong
2 - 10
3,5 5,0
1,1 1,0 2,5 2,5 3,9 2,2 1,9 0,3-3,0 3,5
Do sau (m) Trung
binh
1,6
1,2 1,1
1,3 1,0 1,6
0,9
1,2 1,6 1,2 1,5
2,8
LOTI
nhat
4,2
2,0 2,0
2
1,6 2,2
1,4 2,5
3,5 2,0
4,0
3,2
Kich thuoc ciia (m) Dai
Thuan An :6000
Tu Hien:
100
1000
An Hoa
500 Tam Hai 400
3000
300
5000
2000
1200
500
6300
1000
2500
Rong
350-50
150
4 0 0
-200
150
120
150
125
900
350
50
1000
500
Sau
2
-111
1 - 8
4 1
1 1,5
1 - 4 1,6
7
5 1,5 4,0
4 - 6
2.2 Dgc diem cdu tnic ddm phd
He thdng eac de cit chin tao nen dim phi ven bien mien Trung Viet Nam deu li cic dang tich tu cit ndi dio trong qui trinh san bing bd viing vjnh hoac lip diy eung bd theo co che phit trien ddng bing chiu thd trong ljeh sir Holocen, dien hinh li de eit chin Dam Phi Tam Giang - Ciu Hai (Dai Tnrdng Sa) keo dii tir cira Viet lien quan tdi qui trinh phit trien ddng bing Quing Trj - Thira Thien Hue, de eit chin Dim Trudng Giang keo dii tir cira Dai tdi ciia Tam Hii lien quan tdi qui trinh phit trien ddng bing Hdi An - Tam Ky, v.v De eit chin gdm hai the he gdi tiep nhau The he thu nhit li cic edn cit miu tring mudi tudi Holocen sdm-giira, eao trung binh 6-8m d phia trong, hien li noi quin eu ehinh eua eic cdng ddng din eu ven bien The he thu hai li eic cdn eit miu xam ving cao dd so, Uidi Holocen mugn, eao trung binh 20m, eao nhit tren 40m Dgc theo dim phi phia trong de cit chin, d nhilu noi xuit hien bii bii dang them duge sir dung lim dit d, eanh tie ndng nghiep hoac nudi thuy san De cit li hgp phin ciu tnic ehinh tao nen dim phi, nhung ddng thdi la vit cin lu vi giy ngap lut
Trang 5Tiiu ban: Cdc Khoa hgc vi Trdi ddt ISBN: 978-604-913-016-8
ding bing ven bien He thdng de cit chin eao dd so chay dgc bd bien hang ehue kilomet di lam thay dii co ban hudng chiy cua sdng rdi qua cira dim phi trudc khi ra bien, lim cho thoat lii cham ding ke Trong dieu kien ngap lut ldn vi dii ngay, ddng lii cd the phi vo de cat
chin d noi xung ylu dk tao cira mdi, giy thiet hai kinh te-xa hdi ning ne eho cdng ddng din
eu ven bien
Vdi ting dien tich mat nude 436,9 km^ he thdrig dim phi ven bien mien Tning Viet Narn rit da dang vl quy md (trong khoing 2,8 - 216 km') vi cd the duge phin biet thinh 4 cip - rat nhd (dudi 10 km^), nhd (10-20 km^), trung binh (20-50 km^) vi ldn (tren 50km'), trong dd Idn nhit li Dim Phi Tam Giang - Ciu Hai vi thudc loai ldn cua the gidi
Thudc tinh chung nhit cua lagun ven biin tren toin thi gidi li thudng cd hinh ding keo dai (elongate) dgc theo de cit chin, bilm khi ding thudc (equilateral) Neu liy ehi sd hinh bge 1
la ty sl ^iira chilu dii vi chilu rgng dl dinh gii, thi trudng hgp I = I (thyc thy ding thudc)
se rit hiem, khdng dinh gii duge die dilm ty nhien ciia thuy vyc ven bien kieu lagun Nhieu lagun ven biin eiia thi gidi eiing dugc md ti li ding thudc nhung chi sd I trong khoing 1 - 2
Do vay, cd thi coi lagun ding thudc khi I trong khoing 1 - 1,5, bin ding thudc (semi-equilateral) vdi 1 trong khoing 1,6-2, va keo dii vdi I >2 Theo dd, nhiing lagun ven bien nhu Dim Ling Cd vi Dim Nai duge eoi li ding thude, cic Dim Trudng Gian^, An Khe, Nude Man, Tri 6 vi Nude Nggt - bin ding thudc, cac Dim Phi Tam Giang - Ciu Hai, Cii Mdng, Thuy Trilu, Thj Nai vi 6 Loan - keo dii Nhd sire chira thuy vyc mi dim phi ed vai trd dilu lii d mirc do nhit djnh nhung edn tiiy thudc vio hinh ding va khi ning thoit lii qua cira Cie Dim Lin^ Cd, Dim Thj Nai hay Dim Nai ed hinh ding ding thude vi cira thoat lii tit, ngap lut ddng bing ven bien khdng ldn vi it khi xiy ra
Sy biin ddng cira dudi cic dang khie nhau (lip cira, thu hep, chuyen ddi vj tri, v.v.) deu co the sinh tai bien mdi trudng dja chit, lim thay ddi eo bin tinh chit cua vyc nude (tinh chat thuy hda, mdi trudng nude vi sinh thii thuy vyc, v.v.), thim chi bin ehat kieu loai vi thue day nhanh qui trinh phit trien d giai doan trudng thinh din tdi suy tin (ephemeral) va chet
He thdng dim phi ven bien mien Trung Viet Nam di phit trien qua giai doan tre vi dang phat trien d giai doan trudng thinh Trong giai doan tre, hinh thii eic hgp phin ciu tnic din phit trien tdi can bang, nhung trong giai doan trudng thinh, chiing phit trien phin dj manh, lam gia tan^ tinh khdng dn djnh eiu tnic he, trong dd cd tinh khdng dn djnh cira Cira di trd thinh hgp phan ciu tnic quan trgng die biet quyet djnh sy tdn tai vi kieu loai lagun Dim An Khe (Quang Ngii) vi Dim Tri 0 (Binh Djnh) li vi du dien hinh ve lagun dang phit trien d giai doan suy tan Do ddng bdi tich cit dgc bd hudng ddng nam-tiy bic phit trien manh ve miia
he, cira bj djch chuyen tren doan bd dai 3-4 km, lire diu cira cdn ddng, md djnh ky theo miia, rdi sau gin nhu bj lip hin, lim eho vyc nude phia trong din trd thinh biu nude nggt vi lagun
da suy tin Cira ddng, md tire thdi nhu cira Tu Hien, cira Hoi Duin d Dim Phi Tam Giang -Ciu Hai sinh tai bien cip dien nhieu lin trong ljeh sir va giy hau qui ning ne Cira tan dan nhu cira Dim An Khe vi cira Dim Tra 6 sinh tai bien trudng dien, tuy cham nhung hiu qui
vd eiing to ldn - lam thay ddi ban chit dja he, he sinh thii lagun ven bien, giim gia trj tai nguyen, thay ddi sinh ke, thim chi mit cic dieu kien sinh cu cira cdng ddng din cu ven bien
Cd the dinh gia tinh chit dn djnh cira theo die diem eiu tnic cira (bing 2)
Nam giira de cat chin (kieu 1), cira khdng dn djnh li tat yeu dudi dang lip, md, djch vi ehuyen ddi vj tri do ddng bdi tieh eit dgc bd cd hudng vi cudng do thay ddi theo miia
Bdng 2 Tinh dn dinh cira theo ddc diim cdu tnic
Kieu cau true
I.Nam giiia de cit chin
2 Nam giira de cit vi
Tinh on dinh Khdng dn djnh dudi dang lap,
md, dich va chuyen ddi vj tri Khdng In dinh do doi cat phit
Dam pha lien quan Tam Giang - Cau Hai, Tnrdng Giang, An Khe Lang Cd, Nude Man Tri
Trang 6bd di gdc
3 Nim giiia bd di gdc
4 Nim giira bd vjnh vi
de eit chin
trien tir mdt phia theo miia gay bdi lip vi thu hep trie dien
On dinh
On dinh
O, Nude Nggt, Thj Nai,
O Loan, Nai Cii Mdng Thiiy Trieu
Dirn phi Tam Giang - Cau Hai cd hai cira, Thuin An vi Tu Hien Ke tir khi md cira Hda Duin lin diu vao nim 1404, cira Tu Hien khdng nhirng mit vai trd duy nhit mi cdn trd thinh cira phu, vi ei hai cira Tu Hien vi Hda Duan deu khdng dn djnh, bien ddng mang tinh chu ky vdi tin suit eao din Cua Tu Hien bien ddng ehu ky ngin vdi tin suit ting dan (Nguyen Hiru Cir, 1996)
Tuong ty Dim Phi Tam Giang - Ciu Hai, Dim Truong Giang eiing ed hai cua Tam Hii vi
An Hda cich nhau qua mdt dang tich tu kieu tombolo dien hinh ndi vdi mii Bin Than (Miii
An Hda) Cira Tam Hii nim giiia thdn 4 va 5 bj de dga bdi lip manh ve miia gid ddng bic trong khi cira An Hda d thdn 2 xa Tam Hii dn djnh hon do ddng bdi tich dgc bd ve miia gid ddng bie yeu va triing vao miia lii, ddng bdi tich dgc bd ve miia he phit trien manh vdi gid ddng nam nhung d ngoii cira vung An Hda
Dim An Khe cd mdt cira, tuy nim giira de eit chin nhung phit trien uu the tir mdt phia trii qua hai giai doan Vio giai doan Holocen giira, cira nim bd di gdc d phia nam vi doi eit Holocen giira d phia tiy bie, cira khi rdng vi siu Vio giai doan Holocen mudn vi hien dai, doi cit dgc bd tir phia ddng nam phit trien manh, djch cira ve phia tiy bie tdi 3 km , ludng cira (entrance) nhd vi hep nhu ddng sdng, rdi nhanh chdng bj bdi lip Ket qui li dim An Khe dan nggt hoi vi ndng, din tdi suy tin
Nim giira de cit vi bd di gdc (kieu 2), cua kieu nay phd bien d cie dim phi hinh thinh trong qui trinh san bing bd viing vjnh trong Holocen Tinh chit dn djnh cira tiiy thudc vio cudng do ddng bdi tieh cit dgc bd phit trien theo miia vi lugng nude sdng dd vio dim phi duy tri trao ddi nude vdi bien Bien dgng cira phd bien dudi dang thu hep trie dien ve miia khd, md rdng trd lai ve miia mua, dien hinh li cira An Cu Ddng eua Dim Ling Cd, ed the de doa lap eiia ve miia khd vi phii xiy ke md hin (groin) ngin ddng bdi tich dgc bd, dien hinh li cira Dim Nude Man, Nude Nggt, Dam Nai Dam Tri 0 vi O Loan eiing trii qua hai giai doan phit trien tuong ty Dam An Khe Trong Holocen sdm-giira, cira rdng vi dn djnh hon bdi
sy phit trien ban ehe eiia doi eit ndi dio Trong giai doan Holocen mudn vi hien dai, doi eit phat trien manh ve phia tiy bic nhd ddng bdi tieh ddi dio ve miia he, din tdi djch chuyen cira
ve phia tiy bic tdi 3-4 km vi lip ciia Hi Ra ciia Dim Tri O Dim Tri O dang d giai doan suy tin do lugng nude sdng ve miia mua qui nhd khdng du giy hire xung md cira mdi nhu Dam
O Loan (cira Tin Quy li cira ed tdn tai tir Holocen sdm-giira, Cira Phii Luong va cira An Hii tdn tai luin phien trong Holocen mudn vi hien dai
Cira nim giira hai bd da gdc (kieu 3) nhu cira Dim Cii Mdng hay giira de cit chin vi bd vjnh (kieu 4) nhu eii'a Dim Thuy Trieu li cira cd trang thii dn djnh liu dai bdi ddng bdi tich dgc bd hiu nhu khdng ding ke
Tie ddng eiia eon ngudi lim thay ddi din ciu tnic hinh thii dam phi ehu yeu li xay dyng
eo sd ha ting (eiu, dudng, eing, hd chira trong luu vyc, v.v.), chiem eir khdng gian lim noi sinh eu, eanh tie, boat ddng du ljeh, thim ehi li do thj hda Bii bdi thip dugc sir dung rdng rai vao nudi thuy sin, dien hinh li Dim phi Tam Giang - Ciu Hai, Trudng Giang, Thj Nai, 6 Loan, v.v Bai bdi eao dugc sir dung phd bien lim dit canh tie, dit d, ngoai ra edn duge sir dung vao lim mudi nhu d Dim Nude Man, Nude Nggt, Thuy Trilu vi Dim Nai
Trang 7Tiiu ban: Cdc Khoa hgc vi Trdi ddt ISBN: 978-604-913-016-8
KET LUAN
(1) Dim phi ven bien mien Trung Viet Nam da dang vl hinh ding, ciu tnic yi quy md tir nhd tdi ldn, thim chi vio loai ldn ciia the gidi Hiu bet dim phi ven bien li bdn hdi luu eua nhilu sdng ldn nhd, cd vai trd dieu tiet lii nhit djnh, nhung ding thdi eiing li tic nhin gay ngap lut ding bing ven bien, giy nggt hoi vyc nude ve miia mua va xim nhip man siu theo sdng ve miia khd
(2) Trong qui trinh phit trien dim phi qua cie giai doan, eic hgp phin cau tnic din thay dii kem theo tai biin ty nhien giy biu qui kinh te-xi hdi ning ne eho cie egng ddng din eu ven biin, trong dd cd biln ddng cira Tinh chit dn djnh cira biy thude vio kieu eiu tnic Nim giira de eit chin, cira tit ylu khdng In djnh; nim giira de eit va bd di gdc, tinh dn djnh cira tiiy thudc vio sy phit triln cua de eit; nim giiia bd di gdc hay bd vjnh kin, eua tit yeu on djnh
TAI LIEU THAM KHAO
1 Nguyen Huu Cir, 1995 He thdng dim phi ven bd mien Trung Viet Nam Cic cdng trinh nghien cim Dja chit vi Dja vit ly biln, trang 113 - 120 Nxb KH & KT, Hi Ndi
2 Nguyen Hum Cir, 1996 Die diem dja chit he dim phi Tam Giang - Ciu Hai (Thira Thien Hue) trong Holocene va phire he triing Id chira trong chung Luin in PTS, Ha Ndi
3 Nguyen Huu Cu, 1999 Tdng quan tinh hinh nghien cuu tii nguyen vi mdi trudng dim phi ven bd mien Trung Viet Nam Tii nguyen vi Mdi trudng bien, tip VI, trang
126 - 142 Nxb KH & KT, Hi Ndi
4 Nguyen Hiiu Cir, 2000 Djnh hudng chien luge kien soit lii mien Trung Viet Nam Tai nguyen vi Mdi trudng bien, tip VII, trang 289 - 302 Nxb KH & KT, Hi Ndi
5 Nguyen Hiru Cu vi nnk, 2002 Tic ddng eua eon ngudi tdi mdi trudng dja chit he dim phi Tam Giang Ciu Hai Tii nguyen va Mdi trudng bien, tip IX, trang 103
-120 Nxb KH&KT, Hi Ndi
6 Nguyen Hiru Cu vi nnk, 2006 Nghien cim ddng thii mdi trudng dim phi ven bd mien Trung Viet Nam lam co sd lya chgn phuong in quin ly.Bio cio tdng ket Nhiem
vy hgp tic Viet Nam-Italia theo Nghj djnh thu
7 Nichols, M And Allen, G, 1981 Sedimentary processes in coastal lagoons Coastal lagoon research Unesco teehn pap mar sci N° 33, p 27-80
8 Phleger, F B., 1881 A review of some general features of coastal lagoons Coastal lagoon research Unesco teehn pap mar sci N° 33, p 7-14
9 Frignani, M., Nguyen Huu Cu et al 2003 Research on coastal lagoons of Central Vietnam as a guide to management Present knowledge and perspectives Teehn Rep N°86, CNNR, Italia