«> K H O A H Q C C O N G N G H $ •
XAC OINH RANH Gidl M A N - N H A T NLPdC Oydl D A T THEO GIA TRI DIEN TRd S U A T VA 0 0 TdNG KHOANG HOA
VUNG VEN BI^N H A TTNH
pajiM NGQC D>IT, LAI H(fP P H 6 N G
Vi^n Dja chat, Vifn Hdn ldm Khoa hpc vd Cong nghf ViftNam PHAM NGQC K 1 6 N
Tritamg Dai hpc Mo- Dja Chdt, Vi^t Nam TS PHAN VAN TRlfCWG
Vien Khoa hgc Vat lifu, Vi^n Han l&m Khoa hpc vd Cdng nghf Vi^t Nam Tom t i t : Nghien cm thi hien viec dp dung to hap phucmg phdp do sdu dien 2D vd phdn tich ting do khodng hda ciia nudc dual ddt trong cdc trdm tich De tU de khoanh viing man - nhgt khu vuc ven hiin Hd Tinh. Tdi lieu do sdu dien 2D co khd ndng xdc d\nh duoc cdc ddi mgn ~ nhat trong tdng chiia nudc cd theo phuang thdng diing lan phuang ndm ngang, khi ket hap vdi tdi li?u phdn tich Idng da khodng hoa (TDS) dua trin ca sd cong thiic Archie (1942) se xdy dung duac mpt ham sd tuang quan giiia do ddn dien (hoac dien tra sudt) vd TDS cua tdng chUa nuac, tit do xdy dung duac sa do khoanh vitng man nhat cho tdng chtia nudc De tu trong khu vuc nghien ciiu.
Tir khoa: do sau dien; dien trd suat; tdng do khoang hda; ranh gidi man - nhat
Abstract: Determining the salt-fresh boundary of groundwater in the coastal area of Ha Tinh province based on values of electrical resistivity tomography and total dissolved solids
The research represented an application of combining of 2D electrical resistivity tomography and total dissolved solids analysis of the reservoir water to delineate the saline-light water margins of the Quaternary aquifer in the Ha Tinh coastal area. The 2D electrical resistivity tomography data is capable to identify saline intrusion zones both vertically and horizontally, when combined with total dissolved solids analysis resutls (TDS) by the Archie (1942) equation will help to construct a correlation function between the conductivity (or resistivity) and TDS of the aquifer, thereby building a saline-light water map for the Quaternary aquifer in the study area.
Keywords: electrical resistivity tomography; resistivity; total dissolved solids analysis; salt - light boundary.
1. M O DAU giori vd xam nhap m i n da ket hop nghien ciiu Nhihig tac ddng ciia bidn ddi khi hiu, nudc ciu tnic dia chit, dia mao dd lam ro su phan bo bien dang da va dang gay anh hudng Idn tdi ddi cic thd chila nudc man, nhat d cac vimg ven song ciia ngudi dan ciia nhiSu qudc gia tidp giap bidn (J.J. De Vries, 1981); md hinh hda diiu vdi bien trong dd cd Vidt Nam. Hi$n ta(mg xam kien thuy dia hda, dia chit thuy van (H. Kooi vJ nhjp man cac ngudn nudc, die bi?t l i ngudn J. Groen, 2000); d u bao v i dinh gia xam nhap nudc dudi dat trong cac tang dia chit ven bien mjn bing md hinh sd (D. S. Oki etal., 1988, dang ngiy cing hi thu hep thd tich v i nhidm Koch v i Zhang, 1998, Voss va Koch, 2001, m ^ nghiem ttpng. Nhidu vimg da khdng thd Phatcharasak Arlai, 2007, Bithin Datta, 2009, khai thac sir dung nudc nggt cho cac muc dich Wolfgang Gossel, 2010, . . . ) . 6 Viet Nam, cac phat tnen kinh te, xa hoi. Chinh vi vjy, da cd nghien cilu vd v i n dd n i y cua D 5 Trpng Sv va nhieu cong trinh nghien ciiu ve van dd nay tren Nguyin Kim Ngoc (1985) xac dinh ranh gidi khap ca nuac. Cac nghien cuu trudc day tren thi ranh gidi man-nhat tren co sd phan tich dfc
• KHOA HQC CONG NGHE •
diem dia chdt thuy vdn, d^c didm dia hinh va cd dia ly; Dang Hiiu On (1996, 2002) da tinh todn, du bdo kha nang nhiem man doi vdi cdng trinh khai thac nudc dudi ddt ven biln Bd Ria ~ Vung Tdu bdng bom hiit nudc; Ngd Ngpc Cdt (1999) da ddnh gid so bd hien trang xdm nhdp mdn ddi ven bien tii Hdi Phdng ddn Ninh Binh; Nguyen Vdn Hodng (2000) da dp dung mdi tuong quan giiia luu luang nudc dudi ddt thodt ra bidn vd chieu sdu xam nhdp man ciia nudc bidn vao tdng chiia nudc dS xdc dinh trit lu(?ng ddng t\r nhien ciia tdng chiia nudc Pleistocen vung ddng bdng Bdc Bd; Pham Quy Nhdn (1996) dd nghien ciiu xdm nhdp man khu vuc Ha Ndi bdng md hinh dich chuydn MT3D ; Nguyen Viet Ky (2003) dd nghien ciiu ca chd hinh thanh cdc ddi nhiem mdn nudc dudi ddt khu vuc Bdc sdng TiSn;
Nguyen Van Lam (2006) da xdc dinh ranh gidi mdn - nhat vung Hdi Trieu, Tien Lii, Hung Yen ph\ic vu cdng tdc cap nudc cho cdc thi trdn nhd.
Ngoai ra, cdn cd mdt sd cdng trinh nghien cuu khdc nhu cua Hd Vuang Binh (1997), Nguyen Dinh Tidn vd nnk (2005),...
Cdc nghien ciiu trudc day ve dp man tren tai li^u thdm dd dien cd the ke den nhu: sd dyng phuong phdp dia vdt ly nhu do sau dien, dia v|it ly gidng khoan kdt hop vdi s6 li?u phan tich thdnh phan hda hgc nudc dudi ddt de nghien ciiu su phdn bd man nhat tdng chua nudc (E.
Edet, 2001, Sung Ho Song, 2007, Evgeny A.
Kontar, 2006, Eloisa Di Sipio, 2011,...);
Nguyin Nhu Trung vd nnk (2007, 2008), Trinh Hoai Thu (2012) da du bdo khd ndng xam nh$p man nudc dudi dat d cac khu vyc ciia ddng bdng sdng Hdng bdng kdt hap tdi lieu do sdu dien trd vd phuong phap md hinh hda dia chat thiiy vdn;
Hoang Van Hoan (2013) dd sii dung phuang phdp dia vdt ly (trudng chuyen), ket hgp phdn tdng dia chat thiiy vdn va ket qud phan tich thanh phan hda hoc nudc dudi dat da ldm sdng td ranh gidi mdn - nhat trong cac tang chiia nudc trdm tich De tii vung ciia sdng ven biln vung Nam Dinh... Tuy nhien, trong cdc nghien ciiu ndy, phuong phdp dien dugc sur dung la 1D
(mpt chilu), vdi md hinh dia di$n thu dugc gdm cac ldp cd di?n trd suat chi thay doi theo chieu sdu tai mpt dilm do dja v^t ly, do vgy kit qud thi hien tren Idt cdt dja dien cua tuyln do cat qua ranh gidi man nhat dua vdo viec ngi suy sy biln dli gid tri di?n trd suat giiia cdc diem do sdu dia vdt ly trSn cung tuyln do. Trong khi dd, qud trinh xdm nhdp mdn trong cdc tang chiia nudc viia thay ddi cd theo chieu sau lan phucmg tuyen do. Vi v$y, viec dp dung phuang phdp dia vdt ly cd khd ndng nghien ciiu dien trd suat theo hai chieu (2D) se cho ket qua md hinh dia di?n phu hgp vdi dilu ki?n dia chat hon. Trong nghien ciiu nay, chiing tdi dp dung phuang phdp do sau di^n trd 2D, mdt phuong phdp dugc dp dung ph6 biln trdn thd gidi va Vi|t Nam, ket hgp vdi tai lifu phdn tich tdng dd khodng hda (TDS) trong nudc de thilt lap ranh gidi m ^ - nhat theo cd chieu ngang (dien tich) va chieu sdu cho tdng chiia nuac De tii vung ven bien tinh Hd TTnh.
1 D 6 I TlTC^fNG VA P H ^ VI NGHIEN CCtJ Trong khu vuc nghien ciiu thudc dong bang ven bien Hd TTrih cd dif n tich ty nhien khoang 1000km2, phia bdc gidp vdi sdng La, phia tay la viing ddi mil trung du cd cdt cao dia hinh den +25m, phfa nam gidp vdi huy?n Cdm Xuyen (Hd TTnh) vd phia ddng la Vinh Bdc bd cd dudng bd bien ddi 37km (hinh 1).
-
\ ^ ^ C A A I J : . • • ' * . , , / ACHLCIAI ' • y ' ( S '? "^TP^ATlSfll \
^—-- Viing nghi4n Clhl ^ O v f ^ ' v - ** "• ' '' > "
^ - - •• Ranh gi6i ihSnh ph6. huyf n \ r ^ \ * ff \ " T »
—TjY Tuytfn do dia vaUJ 0 l o t h O v " " ' - , , '
« M Td T< 7! H W M « M '01 « 1D''"
Hinh I. Vf tri nghien cicu va cdc diim khdo sdt nuac dual ddt
TAPCHfTAl NGUYEN Nl/(5CS(5 1-2019 29
• KHOA HQC C 6 N G N G H | _ ;
Nudc dudi ddt tdn tai chii ylu trong hai tang chiia nudc Holocen (qh) vd Pleistocen (qp).
Ddt da chiia nudc tdng qh la cdc tram tich hien dai (Q2^), ngudn goc sdng (aQi''^), biln ddm Idy (mbQi'"^), sdng biln (amQi'"^), bien (mQi'"
^). Thdnh phdn thach hgc gdm cd cdt, cat pha, cdt hat min, bdt set d tren vd cugi, sdi, san, cat pha d dudi. Tdng chiia nudc qp ndm ngay tren cdc da gdc, ddt da chiia nudc gdm cd: cac tram tich sdng biln (amQi''): phan bd rdng d ven ria ddng bdng, trdm tich lg ra ldp bOt set lan it cdt.
Trdm tich sdng (aQi^'^) thudc he tang Yen My va sdng bien, sdng lii (amQi'"^, apQi'"^) h?
tdng Nghi Xuan. Chung bi phii bdi cdc tram tich tre hon vdi di?n phdn bo khd rpng rai trong vung nhung khdng lien tue ma tao thdnh nhung khu, nhiing ddi rieng trong cdc Idng chao, nhftng thung liing rpng d viing ddng bang vd dpc theo cdc sdng, sudi. Thanh phdn thiich hpc cd cugi, san, cdt, bdt set, phdn tren la cudi, san lan it tdng vd bdt set, nhidu noi chii yeu Id cdt hoac chi gap cudi, sdi. Vdi tram tich D? tii cda khu vuc ndy, gia trj dien trd suat ciia tang chiia nudc thay ddi phu thudc chu yeu vao TDS ciia nudc dudi ddt.
3. PHlTONG FRAP NGHIEN CtTU 3.1. Moi quan h^ giura dien trd suat va TDS Ddt dd d cac tdng chiia nudc gdm 2 phan:
cac khodng vat t^o da khdng cd tinh dan di?n, va lo hdng trong da. Trong Id hdng ciia ddt da cd thi nudc (ddi tugng dan dien tdt) va khi (ddi tugng khdng dan dien). Nudc tu nhien Id cdc chat dien phdn chiia cac loai ion. Khi xudt hi?n di?n trudng thi cdc ion dd se chuyin dich va tao nen ddng difn. Cudng do ddng dien phy thupc vdo mat dd, loai ion vd tdc dp di chuyen cua chiing. Dipn trd sudt ciia nudc pw dugc xdc dinh theo cdng thiic sau (Nguyen Nhu Trung va nnk, 2007):
^ 10
Trong dd: Ca vd Cc la ham lugng ciia anion va cation, Va va Vc la tdc do di chuyin ciia anion vd cation, ^ vaf la dp linh ddng ciia anion vd
cation phu thudc vdo hdm lugng mudi hod tan va thanh phdn hda hgc cua chiing. Thong thudng Ca=Cc = C, nen cdng thiic (1) cd dang:
10 _A
^"'cY^ivj.^vjyc ^2*
6 day, A = v^—-^ r - •
Ve bdn chdt dan dien ciia ddt dd cd the gdm dan dien dien tur, ddn didn bdn ddn vd dan dien ion, tuy nhien, cdc tdng chiia nudc lo hdng thudng xudt hipn dang ddn didn cua cdc ion co trong nudc. Theo dinh ludt Archie (1942), di^n trd sudt cua mdt tdng chiia nudc ty le thudn vol dipn trd sudt cua nudc ldp ddy trong cdc lo hong vd ty i$ nghich vdi do lo hdng dat da. Mdi quan hp ndy dugc bieu dien nhu sau:
P,.„=F.p.=-^p,=^ = M.C-' (3) k k .c
VmM=—, a~l.
k"
Trong dd: pb^ik la di?n trd suit cua ting chiia nudc, F = — la h? sd cau thinh ting chua
k
nudc; pw - didn trd suat cua nudc lap diy cic lo hdng ciia dat da; a - he sd ph\i thupc vao lo^i d^l di (thdng thudng a: 0,4 - 1,4); i - dp lo hdng cua dit da; « - hd sd ciu tnic (n; 1,3- 2,2).
Ddi vdi ting chda nudc ddng nhit thi h? s6 ciu thinh ting chda nudc (F) khdng thay dSi, do dd di^n trd suat cua cac ting chira nudc chi bidn ddi phii thu^c vao tinh chit cua nudc chiia trong dd, cd nghia la gia tri TDS li mot trong nhtmg yeu td inh hudng chinh.
TDS bao gdm khoang chit, mudi va cic kim loai ton tai trong mot khdi lu<;mg nudc nhSt dinh, don vi bidu thj thudng la mgA hoic ppm (phan nghin). TDS tdn tai dudi d?ng cac cation va anion, do nudc ludn cd tinh hoi tan rit cao nen nd thudng cd xu hudng liy cac ion tir cic vat mi nd tidp xiic. Gii tri TDS < lOOOmg/l tuong duang vdi vung nhzit vi TDS > lOOOmg/1 tuong duong vdi vimg man. TDS cd lien quan mjt thiet vdi cac dai lu(;mg trong mau sd ciia
• KHOA HOC CONG NGHE •
cdng thurc (1), mit khac, dien trd suit cua ting chiia nudc Ijii ty Id thuan vdi didn trd suit ciia nudc trong ting chura.Vi vay, tu mdi tuang quan gilra gia tri TDS cua nudc dudi dit vi kit qui do didn trd suit ting chda nuac cd thi xic dinh dupc ranh gidi ddi man - nhat ciia nudc dudi dit (Trinh Hoii Thu vi Nguydn Nhu Trung, 2012).
3.2. Phirong phap do sau di^n 2D Do siu dien 2D (do sau didn da cue) li phuang phap do sau didn khio sat dien trd suit bieu kien pk theo ci chidu ngang x vi chidu siu z theo mdi quan he pk (x, z), vdi mang ludi each ddu theo tuydn (Hinh 1), bing each md rpng kich thudc hd cue vdi bdi sd li cip sd cpng cua
1 ' \
H? cvc the k M N
i "^ i ^ i
MN = a, de khio sat lat cat dia dien hai chieu pt
(X, z).
\'\ \ \ i i 1 1
H\nh 1: Bd tri dien cue trong do sdu di^n 2D (Theo Lake. 2001)
Trong dilu kien cd cap chuyen dyng cd thd do sau ddng thdi theo cdc hp eye: 2 cue (pole- pole), 3 cue (pole-dipole), luang eye (dipole- dipole), 4 cue ddi xdng Wenner-Schlumberger (W-S) khi tdng kich thudc hp cue theo cdp so cdng Id bdi s6 cua a (hinh 2).
A M N B j na I a I na i
He 4 eye doi xu-ng (W-5)
A B M N
i ' i 1 I ' \
Hinh 2. Cdc he cue trong do sdu di$n 2D (Theo Lake, 2001)
Vdi bdi n < 8, khi do vdi chieu sau Idn, cd thd do vdi h$ eye gdi tiep nhau bdng cdch tang a'den miic 2a, 3a,... Trudng hgp vdi may chuyen dung do sdu da cue cd thd dieu khien thi cdng theo trinh ty do, neu khdng cd the do timg loai hp cue, thudng chi do 4 cue, luang cue vi cdc phuang phap ndy cd dp phdn gidi cao.
Theo Loke (2001), dipn trd suat bilu kien do dugc tinh theo cdng thiic:
p,=K^(^am) (4)
Trong do K la hp sd thiet bi phy thu^c vao loai hp dipn cue, AU la hipu didn thi do dugc giua 2 dipn cue thu M, N; I Id cudng dg ddng dipn phdt vao mdi trudng qua 2 dipn eye phdt A, B.
Ket qud do dien trd sudt bieu kien pk tai cdc dilm do vdi timg kich thudc thilt bi cd thi bilu didn dudi d^g cdc Idt cdt dia di^n theo tuyln do bdng viec gidi ngugc do sau dien 2D bdi phdn
mem RES2DINV (Loke, 2001). Lat cdt ffia dipn 2D tir so lipu do sdu dien phdn anh cau tnic dia dipn dudi sdu theo cd phuong ngang (phucmg tuyln do) va phuong thdng diing (theo chilu sdu).
3.3. Quy trinh nghiSn cihi
Ngodi thuc dia, tiln hanh do sdu dipn 2D vd lya chpn tren 9 tuyen do d khu vuc ven biln Hd TTnh. Sau dd, thii nghipm tren md hinh ly thuylt bdng phdn mim RES2DM0D (Loke, 2001) 6k xdy dyng bieu dd vd ham sd tuong quan giiia gid tri dipn trd suat vd gid tri TDS cua tdng chua nudc. Tir hdm tuong quan nay, xdc dinh dugc sy phdn bd gia tri TDS ciia nudc trong tang chiia, sau dd khoanh viing man - nhat nudc dudi ddt.
4. KET QUA VA THAO LU^N 4.1. Tren mo hinh ly thuylt
Md hinh dugc xdy dyng gdm 4 ddi tugng cd dien trd suat khdc nhau tuang ling vdi md hinh xam nhap m|in tai khu vyc ven biln Hd TTnh
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. KHOA HOC CONG NGHE •
(Hmh 3). Ddi tupng thii nhit cd gia tn di$n trd suit 8 (Cim) gii dinh li khu vuc hi nhiem man cd gii tri dien trd suit thip, ddi tupng thir hai li ldp thd nhuong tren bi m?t nhutig chua hi nhidm mSn cd gii tri dien trd suit 30 (Qm), chidu siu phan bd td tit mat dit din 25m, ranh gidi mit nhat nim d vi tri tit 215m dSn 255m tren tuydn. Ddi tupng 3 vi 4 dupc md phdng la cac ldp ttim tich khdng bi nhidm m ^ , nam dudi ddi tupng 1 va 2, cd gii tri di$n trd suit lin luat li 80 flm va 150 flm. Trong dd, ddi tuang 3 nim d chidu sau tir 25m din 60m, ddi tupng 4 nim d chidu sau 60m din hem 70m. Md hinh dupc thidt lap tren tuyen cd dp dii 420m vi chidu sau khoang 70m. Do didu ki$n tang chila . nudc nhiem min va ranh gidi mjt nhat li doi tucmg cd kich thudc Idn, dd de thi cdng mi van dam bio phat hi?n dupc ddi tupng ndn hf 4 eye ddi xiing Wenner-Schlumberger dupc lua chpn de giii bai toin thuan.
Schlumberger va kich thudc a = 20m nhu da chimg minh d tren di giai quyet nhi$m vy xac djnh ranh gidi min - nhat d ngoai thuc ti.
Hinh 3. Md hinh bdi todn thudn ranh gidi man/nhgt.
Kdt qua giii bii toin thu$n theo md hinh ly thuyet bing phin mem RES2DM0D li dau vao di giii bai toin ngupc (RES2D1NV). Tir dd, xay dyng dupe lat cit giii ngupc vdi nhieu kich thudc tdi thieu giiia cac di?n cue (tham sd a) cd gia t4 khac nhau. Vdi a = 30m cho thay ranh gidi b} keo dii ra so vdi md hinh ly thuydt, cic kdt qui vdi a = 20m vi 10m ddu thi hien ro dupc vj tri vi di?n trd suat ciia cic ddi tupng khdp vdi md hinh ly thuyit. Lit cit di^n trd suit giii ngupc (hinh 4), vdi h^ dien c\rc a = 20m, cho thay cac tham sd di?n trd suit giai ngupc deu the hifn kha trimg khdp so vdi md hinh ly thuyet ca ve vi tri tren tuyen do vi chidu sau. Do viy, lua chpn he dien cue Wenner-
Hinh 4. Mat cdt dien tra sudt md hinh ranh gidi man - nhat.
4.2. Tren tii li^u thuc te
Kdt qui do dia vat ly tai dong bing ven bien Hi Tinh tren 9 tuydn vdi tdng sd 103 diim do va 3230 m tuyen do (hinh 5), ciing vdi dd lata!
li$u phan tich TDS trong cie mau nudc tai cic gidng khoan trong khu vuc thupc cic ting chia nudc qh vi qp da xiy d\mg dupc so di ding trj TDS cho viing nhien ciiu xic l$p cic mit cat didn trd suit thdng qua him tuong quan cd the tmh dupc gii tri TDS, tir ^° ^^'^ djnh dupc ranh gidi m ^ - nhat nudc dudi dat.
Theo su phan bo ting chda nudc theo chieu sau vi tii lifu giii ngupc do sau di?n de tien hanh xiy dvmg mdi lien h? giiia dp dan di?n ciia ting chiia nudc vdi gii tri (ting ham lupng chat rin hda tan (TDS). Ham tuong quan giOa TDS vi dp dan dien cua tang chiia nudc cho thay, giiia chung cd mii quan hd rit ch^t chg vdi R = 0.9497 (hmh 7), dupc the hi$n qua biiu thirc:
TDS = 17343a-28.617 (5) Trong dd TDS li tdng dp khoing hda (mg/1);
a = — la dd din didn ciia ting chia nudc P
(Simen/m).
D4 din d1«n cAa ting chi>a nuitc (S/m)
Hinh 7. Mdi tuang quan giiia TDS va dp c dien cua tdng chiia nudc.
• KHOA HQC CONG NGH$ •
TII bieu thiic (5), ranh gidi m ^ - nhat cd thi dugc phdn chia bdi gid tri dien trd sudt xap xi 17 Qm, tuang img vdi gid tri TDS la 1000 mg/l.
Hinh 8 bilu dien cac gid tri tham sd dipn trd sudt thu dugc trdn 9 tuyln do diln hinh cua viing nghidn ciiu. Tuyln sd 6 cd chilu dai 300m dugc bd tri 11 diem do cd gid tri dien trd suat thay ddi tu vai Qm cho den vdi nghin Qm, dg man phdn bd dchilu sau tir 55 din dOm.Ddi sanh vdi tdi lieu dia chat, day Id dd gdc rdn chdc cd dien trd suat tuong ddi cao. Tir vi tri tir ddu tuyen den 180m, gid tri dien trd sudt cao ban so vdi vi tri cudi tuyen, tuong duong vdi vimg nudc nhat vd tit vi tri 180m den cudi tuyen d dp
sdu tu 0 din 20m la phdn cd gid tri di$n trd suit 7 din 8 Qm thi hien la viing hi xam nh$p m§n.
Tir lat cdt dien trd sudt tuyln s6 1 cho thay dp man tdng dfin tir ddu den cudi tuyln vd ranh gidi mdn - nhat thi hi|n rd tai vj tri 180m trdn tuyln.
Tuyln s6 9 dugc bd tri 14 dilm do cho thdy gia tri dipn trd sudt cd gid tri tir 3Qm din hon 200 Qm. Ci phdn ddu tuyln chilu sau hon 10m cd Ic^ dien trd sudt cao hem, theo tai lipu doi sdnh dia chdt, ddy Id ldp set chiia nudc kem. Phdn cd dien trd thdp khodng tir 8 din 9 Qm cd chilu sdu tir 20m xudng dudi la khu vyc cd dp khodng hda cao, ranh gidi thi hipn dp mdn tai vi tri 240 m tren tuyen.
LJ1 c i i Slta ttir ault tuyln »- i t Cim Y i n - C i m Xuyln - Ha TTnh
Hinh 8. Cdc lat cdt dien trd sudt khu vuc ven bien tinh Hd Tinh
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• KHOA HOC CONG NGHE •
Tuang ty vdi cdc tuyln do cdn lai, cho thdy:
(i) tir cac m^t cdt di^n trd suit cd the xac dinh dugc cdc ranh gidi giiia mdi trudng m§n va khdng mdn; (ii) xu hudng phan bd cdc gid tri dien hd suat hen cdc mat cdt tucmg ddng vdi chilu hudng dien biln dp m|n; (iii) tdn tai 2 hhih thdi xam nhdp mdn chinh: xam nhap man tir be mat xudng sau va xdm nhap mdn do anh hudng
cua hoat ddng ddng ngdm; (iv) Chilu sdu phan bd m ^ thudng dien ra d dg sdu tir 25 din 40 m.
Tir kit qud do sdu dien va tdi lipu quan trie chat lugng nudc theo TDS doi vdi cdc ham tich Dp tii ddng bdng ven bien Ha TTnh, cdc viing mdn - nhat da dugc khoanh dinh (hinh 9), trong dd thi hipn dien phdn bd m ^ tdng qh Id 308km^
vd tang qp Id 532km .
Hinh 9. Sa dd khoanh viing man - nhgt theo kit qud do sdu di$n 2D va TDS trong tdng chua nudc qh (a) vd qp (b) vung ven bien Hd Tinh
Viec ket hgp giiia tdi lipu do sdu dipn 2D va phdn tich tdng do khodng hda de chinh xdc hda ranh gidi vd hinh thai man - nhat trong cdc tang chiia nudc. Mdi quan he mdt thiet gifia TDS vd dp dan dipn ciia tang chiia nudc theo cdng thiic Archie (1942) la co sd khoa hpc de tdng dp chinh xdc trong phdn viing man - nhat nudc dudi dat.
Vipc dp dung do sau dipn 2D lam gidm di tinh da tri cua bdi todn ngugc thdm dd dien so vdi cdc phuong phdp thdm dd di^n ID, ddng thdi cd khd ndng phdt hipn nhimg thay ddi vl dipn trd sudt theo cd phuong tuyln do vd chieu sdu. Do dd, cdc ket qua thu dugc tir tdi lieu do sdu di$n 2D trong nghien ciiu nay cd khd ndng ddnh gid chinh xac hon vi tri vd su phdt triln theo chieu sau cua cdc ddi tugng xdm nhdp mdn so vdi cdc tai lipu'do sdu dipn ID va tdi lieu do
sau trudng chuyin ID trong cdc nghien c ^ c6 trudc tai Vipt Nam. Gid tri dipn trd suat thap lien quan den tdng chira nudc nhiem m§n co the bj nhdm Ian vdi cac ddi khoang hda cd trong khu vi^c nghien ciiu, vi d\i nhu cdc ddi khoang hda lien quan din md sdt Thgch Khe (Hd Tuih).
Chinh vi vay, ta cdn them mdt sd thdng tin tir cac phuong phap khdc dl khdng djnh ddi nhiem mdn trong khu vuc nghien ciiu.
5. KET L U ^
Phuong phdp do sau dipn 2D cd the dupc ip dyng hipu qud trong vipc xac dinh ranh gidi m$n - nhgt nudc dudi ddt theo ca chilu sdu vd chieu ngang ciia viing bi man. D\ra tren tai lipu nay, tgi khu vuc ven biln Ha TTnh dd xac dinh dugc 2 hinh thai phdn bd mdn chinh la: (i) mdn theo chieu sau cd trong tdng qh vd qp va (ii) mSo theo dipn rgng.
34 TAP CHl T A I NGUYEN Nl/OC S6 1 -2019
• KHOA HOC CONG NGHE •
Vide kit hpp tii lieu do sau dien 2D vi gii tri TDS trong cac gidng khoan giiip chinh xic hda cic ranh gidi min - nhjit trong cic ting chila nudc theo ca chidu sau vi tren binh dien phan bd. Ket qua thu dupc la ngudn thdng tin dang tin c^y phuc v\i cdng tic quin ly, khai thic, su dung hpp 1^ tii nguyen nudc dudi dit cho vung ddng bing ven bidn Hi TTnh, cung nhu ap dung ddi vdi cac vimg khic cd dieu kien tu nhien tuong t\r.
Ldi cam on: Tap tM tdc gid xin trdn trpng cdm an sir cho phep sit dung tdi li^u trong khuon kho Du dn Diiu tra ca bdn ndm 2018- 2019 (Md sd UQDTCB.02/18-19) do Vien Han ldm Khoa hpc vd Cong ngh$ Vi$t Nam qudn ly.
TAI LIfU THAM KHAO
1. Archie, G.E., 1942. The electrical resistivity log as an aid in determining some reservoir characteristics. Transactions of the AIMS, 146(a\), pp.54-62.
2. De Vries. J.J (1981), "Fresh and salt water in the Dutch coastal area in relation to geomorphological evolution". Quaternary Geology: a farewell to A.J. Wiggers,Geologic en Mifnboitw 60, p. 363 - 368.
3. Dhar, Anirban, and Bithin Datta.
"Saltwater intrusion management of coastal aquifers. I: Linked simulation- optimization." Journal of Hydrologic Engineering 14, no. 12 (2009): 1263-1272.
4. Edet. A. E, Okereke C.S (2001),
"Aregional study of saltwater intrusion in southeastern Nigeria based on the analysis of geoelectrical an hydrochemiscal data".
Environmental Geology, 40, p. 1278 -1289.
5. Koch, M. and G. Zhang (1998),
"Numerical modelling and management of saltwater seepage from coastal brackish canals in southeast Florida", In:Environmental Coastal
Regions, CA. Brebbia, (ed), pp. 395-404, WIT Press, Southampton.
6. Nguyen Nhu Trung, Trinh Hoai Thu, Nguyen Van Nghia (2008), "Application of the electrical resistivity and hydrogeology modeling methods to map and forecast the saltwater intrusion in Thai Binh province". Tap chi Bia cAai 31-32, tt.241-248.
7. Nguyen Trpng Nga (2005), Tham dd dipn trd va dien hda, Giio trinh, NXB Giao thong van tii.
8. Trinh Hoii Thu, Nguyen Nhu Trung (2012), "Xac dinh ranh gidi xam nhap .man ting chiia nudc Pleistocen khu vyc ven bidn Ddng bing sdng Hdng theo kit qui phan tich hda va do sau dien", Tap chi Khoa hpc vd Cong nghe BiinTl2(4A), tr.163-170, ISSN:
1859-3097.
9. Nguydn Nhu Trung, Nguyen Vin Nghia, Nguyin Bi Minh (2007), "Du bdo xdm nhpp man nu&c ngdm vung Hdi Phdng bdng phuang phdp mo hinh hod dien tra vd dia chdt thuy vdn". Tap chi Cac khoa hpc vd Trii dat, T. 29, sd3,tr227-283.
10. Phan Van Trudng (2015), fl^cAe'm//>«)' dia hda vd thuc trang nhiem man nudc dudi ddt trong cdc trdm tich De tU vitng ven bien Hd TTnh. Tap chi Cac Khoa hpc ve Trii dat, T^p"
37(1), tr 70 - 78 .v.v.
Ngudi phdn bien: PGS.TS Do Van Binh Phdn bifn xong: 12/2018
TAP CHf TAl NGUYtN MOC SO 1 -2019 35
