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Re: DDe^ o+? Mekong Delta (from Buulong Nguyen)
Again I am forwarding a message from anh Buulong Nguyen:
On Wed, 30 Apr 1997, Vu Nguyen Thanh wrote:
> Ba'c Bu+?u Long la`m o+n gia?i thi'ch ho^. "phe`n" o+?
> dda^y nghi~a la` gi`, ma` la`m sao la.i xanh nu+o+'c
> ddu+o+.c.
Tha^.t ti`nh thi` to^i cu~ng kho^ng bie^'t tha`nh pha^`n ho'a ho.c cu?a
cha^'t ma` ba` con no^ng da^n go.i la` "phe`n". Xin ke^? ra du+o+'i dda^y
va`i contexts, trong ddo' tu+` "phe`n" ddu+o+.c nha('c dde^'n, co' khi
ca'c ba'c la`ng ta se~ chi? gia'o ddu+o+.c cha(ng.
--- PHE`N CHUA dde^? la`m trong nu+o+'c: O+? ddo^`ng ba(`ng so^ng Cu+?u Long
dda.i dda so^' ba` con (i't nha^'t la` cho to+'i nhu+~ng na(m 80) du`ng tru+.c
tie^'p nu+o+'c so^ng trong cuo^.c so^'ng ha`ng nga`y (nu+o+'c mu+a
thu+o+`ng ddu+o+.c du`ng dde^? uo^'ng va` cu~ng kho^ng ddu~ xu+~ du.ng
quanh na(m). Nu+o+'c so^ng chu+'a ra^'t nhie^`u phu` sa ne^n kho^ng du`ng
dde^? na^'u a(n hoa(.c na^'u nu+o+'c uo^'ng ngay ddu+o+.c. Ne^'u ta ca^`m
mo^.t cu.c phe`n chua khoa('ng nhie^`u vo`ng trong lu nu+o+'c thi` phu`
sa se~ la('ng xuo^'ng du+o+'i dda'y lu (cu.c phe`n chua se~ tan trong
nu+o+'c, too). To^i chi.u kho^ng bie^'t tha`nh pha^`n ho'a ho.c cu?a
phe`n chua ra sao.
Caution: Xin ddu+`ng la^`m vo+'i ddu+o+`ng phe`n :-). DDu+o+`ng phe`n
cu~ng o+? da.ng tinh the^? ra('n, ga^`n nhu+ trong suo^'t nhu+ phe`n
chua, nhu+ng co' a'nh va`ng ddu.c va` (ta^'t nhie^n la`) ngo.t nhu+ ...
ddu+o+`ng phe`n.
--- DDa^'t nhie^?m PHE`N, nu+o+'c PHE`N: Context na`y dda~ ddu+o+.c ba'c
Thanh Ca nha('c dde^'n trong recent message ve^` dde^. Dda^'t su?i ma`u
va`ng. Du`ng nu+o+'c dda~ bi. nhie^?m "phe`n" gia(.t qua^`n a'o thi`
mo^.t tho+`i gian sau qua^`n a'o se~ bi. a'm ma`u va`ng. Ho^`i co`n be',
mo^~i la^`n he` ve^` que^ cho+i tro+? le^n Sai`go`n la` ma' to^i than
tho+?: "Qua^`n a'o ma`y ve^` du+o+'i gia(.t nu+o+'c PHE`N va`ng he^'t
tre^n".
--- Context ma` tui nha('c dde^'n xa?y ra khi tui ddi do.c con dde^
o+? vu`ng qua^.n Ca^`u Ke`, ti?ng Tra` Vinh (que^n ma^'t te^n xa~ ro^`i).
O^ng cha'u ho. cu?a tui (go.i la` "o^ng cha'u" vi` o^?ng na(m ddo' dda~ tre^n
50 tuo^?i ro^`i, nhu+ng la.i vai cha'u cu?a tui) ke^u: "Chu' U't coi dda`o
ba con dde^ la`m dda^'t no^?i phe`n he^'t ra'o". Tui nhi`n theo tay o^?ng chi?
thi` tha^'y nu+o+'c ma^'y cho^? ddo' co' a'nh xanh va` trong va('t chu+'
kho^ng va^~n ddu.c phu` sa nhu+ nhu+~ng cho^? kha'c. Ma^'y ho^m sau lo^.i
bo^. doc. theo ma^'y con dde^ tu+` xa~ Hie^'u Phu.ng, qua^.n Vu~ng Lie^m,
ti?nh Cu+?u Long, dde^? y' cu~ng tha^'y va`i cho^? nu+o+'c co' anh' xanh
va` cu~ng trong va('t. Ho^`i ddo' tui ho.c lo+'p 9 (he^. 12 na(m) ro^`i,
hoa' ho.c cu~ng kho^ng "dduo^.i" la('m ne^n cu~ng nghi~ la` du+o+'i
sulphat ddo^`ng.
> Theo to^i hie^?u ma`u xanh thu+o+`ng ddi lie^`n
> vo+'i Cu2+.
To^i cu~ng hie^?u nhu+ ba'c Tha`nh la` ma`u xanh thu+o+`ng ddi lie^`n vo+'i
ddo^`ng.
> Ion na`y trong dda^'t nghe chu+`ng hie^'m.
Kho^ng bie^'t ddie^`u kie^.n ddo^`ng ba(`ng so^ng Cu+?u Long ra sao
nhu+ng theo cho^? to^i bie^'t thi` Cu2+ va^~n xua^'t hie^.n trong dda^'t
dda^'y ba'c a. (sorry for "mu'a ri`u qua ma('t tho+.")
Ho^m qua to^i co' ho?i hai vi. soil scientists ve^` vu. na`y. Mo^.t vi.
la` Prof. Dr. S.M. Kroonenberg, tru+o+'c 9/96 la` chu? nhie^.m bo^. mo^n
DDi.a Cha^'t va` Tho^? Nhu+o+?ng, DDa.i Ho.c No^ng Nghie^.p Wageningen,
nay la` chu? nhie^.m bo^. mo^n Sedimentology, khoa Applied Earth
Sciences, Delft U. of Technology (DUT).
Vi. nu+?a la` Mrs. Drs. M.J. Moens-Gigengack, senior lecturer in Soil Sciences
o+? khoa Kie^'n Tru'c, cu~ng o+? DUT.
Theo hai vi. a^'y thi` trong Cu2+ occurs trong dda^'t du+o+'i da.ng sa?n
pha^?m phong hoa' cua? hai copperore minerals: Malachite va` Azurite.
Nhu+ ba'c cu~ng bie^'t malachite, Cu2(OH)2CO3 co' ma`u xanh la' ca^y va`
azurite Cu3(CO3)2(OH)2 (also called chessy copper or chessylite) thi` co'
ma`u xanh du+o+ng.
Ngoa`i ra ba` Moens-Gigengack co`n cho bie^'t la` sa('c nu+o+'c xanh
trong ruo^.ng lu'a co`n co' the^? do su+. hie^.n die^.n cu?a orgacnic
materials, hoac do su+. hi`nh tha`nh khi' metan.
DDe^? bie^'t xem dda^'t vu`ng Mekong delta co' chu+'a ddo^`ng hay kho^ng
thi` pha?i pha^n ti'ch ma^?u dda^'t. Ngoa`i ra, kho^ng bie^'t nhu+~ng vu`ng
nu'i ma` so^ng Mekong cha?y qua co' intrusive rocks kho^ng? va` rocks o+?
dda^'y co' chu+'a nhie^`u copperores kho^ng? If positive, thi` ra^'t co'
the^? sa?n pha^?m phong ho'a chu+'a ddo^`ng cu?a ca'c lo.ai rocks a^'y
cu~ng co' ma(.t trong tra^`m tic'h o+? Mekong basin.
> Vo+'i la.i dda('p dde^ thi` se~ la`m ha. mu+.c nu+o+'c
> nga^`m sao la.i no^?i phe`n le^n ddu+o+.c.
To^i xin thu+? tra? lo+`i ca^u ho?i na`y cu?a ba'c in two parts:
1). DDe^ dddu+o+.c dda('p ho^`i a^'y la` dde^? pho`ng khi nu+o+'c lu~
tra`n ve^`. DDa('p no^?i tru+.c tie^'p tre^n be^` ma(.t, kho^ng dda`o
mo'ng sa^u dde^? ta.o impermeable wall ne^n kho^ng la`m ha. mu+.c nu+o+'c
nga^`m. Ne^'u lu~ ve^`, mu+.c nu+o+'c giu+?a hai con dde^ se~ cao ho+n
trong ruo^.ng. Khi ddo' nu+o+'c se~ ti`m ca'ch cha?y nga^`m du+o+'i dde^
dde^? va`o ruo^.ng (under dyke seepage). Nhu+ng permeability cu?a dda^'t
bao gio+` cu~ng tha^'p ho+n ra^'t nhie^`u so vo+'i khoa?ng tro^'ng giu?a
hai dde^ ne^n nu+o+'c thoa't ddi chu? ye^'u do.c theo con "ke^nh no^?i"
ddo'. ("Ke^nh no^?i" la` tu+` ba` con no^ng da^n o+? Cu+?u Long nga`y
a^'y go.i the structure formed between the dykes).
2). Gia? su+? la` mu+.c nu+o+'c nga^`m se~ bi. ha. tha^'p do dde^
(gio^'ng nhu+ tru+o+`ng ho+.p polder o+? Hoa`lan) hay do ba^'t ky` mo^.t
nguye^n nha^n na`o kha'c, thi` phe`n lai. ca`ng co' ddie^`u kie^.n dde^? no^?i
le^n chu+'. Let's consider the hydrogeological profile below:
PROFILE I
____________________________________ ground surface
------------------------------------ phreatic groundwater level
- - - - - - - - piezometric level of
confined water
____________________________________
low permeable layer ||
____________________________________ \/
confined aquifer flow direction
In this case the piezometric level is lower than the phreactic water
level, hence a vertical downward flow exists. In the second profile
below, the phreatic level is lower than the piezometric level and a
upward vertical flow can be expected. If the confined aquifer contains
brine water or water with high mineralization (high concentration of
different ions), this water will flow accross the low permeable layer. We
can than expect changes in mineralization of the phreatic water.
PROFILE II
____________________________________ ground surface
- - - - - - - - piezometric level of confined water
----------------------------------- phreatic water level
___________________________________
low permeable layer /\
___________________________________ ||
confined aquifer flow direction
Tuy va^.y trong message tru+o+'c to^i co' vie^'t la` dde^ ddu+o+.c dda('p
ba(`ng dda^'t dda`o ngay ta.i cho^?, va` vi` pha?i dda`o sa^u ne^n dda`o
qua ca? lo+'p dda^'t se't la`m no^?i phe`n. Va^~n cu+' la^'y profile I
la`m reference, ta se~ tha^'y la` dda`o dda^'t qua' sa^u se~ ta.o ra
hydraulic window giu+?a hai aquifer (the upper phreatic aquifer and the
underlying confined aquifer). Because of pressure difference, water will
flow from the underlying aquifer through the hydraulic window to the
overlying aquifer. If the confined water posseses high mineralization or
contains specific minerals, the upward seepage will lead to significant changes
in mineralization of the phreatic water.
/--\ /--\
PROFILE III / \ / \
(not to scale) / dyke \ / dyke \
___________ _ / _______\ /________\_ ____ground surface
piezom. level | | | | |
- - - - - |- - | | old | | |
-----------|-------|------------|-canal---|---------|--------|- phreatic level
| | \_________/ | |
| <--|---- excavations in ground -----|--> |
___________| |________________________________| |______________
| | low permeable layer | |
___________\_______/________________________________\________/______________
^^^^^^ ^^^^^^^
seepage (initially) confined aquifer seepage
> Theo to^i thi` dda^'t chua vi` ly' do kha'c. Trong ddie^`u kie^.n
> anaerobic thi` lu+u huy`nh na(`m o+? reduced form. Khi
> nu+o+'c nga^`m ru't no' bi oxidised tha`nh H2SO4 do ddo'
> pH co' the^? xuo^'ng to+'i 2-3 gi` ddo'.
> Dda^'t na`y thi` kho^ng tro^`ng lu'a ddu+o+.c ro^`i nhu+ng tro^`ng du+'a
> thi` tuye^.t. Lu'a thi` re? tie^`n ma` ta cu~ng co' nhie^`u
> ro^`i chu+' du+'a thi`...nhem nhem...ngon la('m.
To^i cu~ng co' ddo.c tha^'y ve^` nguye^n nha^n na`y cu?a su+. chua ho'a
cu?a dda^'t.
No'i dde^'n du+'a va` lu'a la`m nho+' dde^'n no^ng tru+o+`ng Le^ Minh
Xua^n (hi`nh nhu+ ga^`n Cu? Chi thi` pha?i). Sau 75 thanh nie^n xung
phong xua^'t qua^n ra^`m ro^. le^n "ca?i ta.o vu`ng dda^'t mo+'i". DDa`o
ke^nh dda('p dda^.p, khi' the^' la('m. Mu.c tie^u la` mo+? ro^ng "va`nh
ddai xanh cua? Tp HCM". Ke^nh dda`o loa'ng ca'i la` xong. Lu'a tro^`ng
xuo^'ng, cha(m ca'ch ma^'y cu~ng kho^ng chi.u to^'t. Sau anh em thanh
nie^n xung phong "pha't huy tri' tue^. ta^.p the^?" ke^'t ho+.p vo+'i
"ho.c ta^.p kinh nghie^.m qua^`n chu'ng" (ma^'y ba` con chung quanh
tro^`ng du+'a le^n to^'t qua') be`n chuye^?n sang tro^`ng du+'a. Tu+`
ddo' no^ng tru=o+`ng a(n ne^n la`m ra, du+'a thu hoa.ch xua^'t kha^?u
a^`m i? sang Lienxo (cu~) va` DDo^ngA^u. DDa^u la` no^ng tru+o+`ng co`n
ddu+o+.c hua^n, huy chu+o=ng lao ddo^.ng ha.ng gi` ddo' nu+?a.
Nhu+ng cha('c ba'c kho^ng ddi.nh "chua ho'a" ca? Mekong delta dde^?
tro^`ng du+'a chu+' :-)
> Dda('p dde^ se~ chu? ddo^.ng ho+n, nghe no'i bo.n
> ta`u no' la`m dda^.p o+? thu+o+.ng nguo^`n muo^'n cho
> ta lu.t lu'c na`o tu`y thi'ch.
Ca'i a^m mu+u "pha' hoa.i nhie^`u ma(.t" na`y thi` ta pha?i dde^` pho`ng
to^'i dda.
Ba'c Huy o+? UK trong recent message titled "Mekong Dykes & Canals" co'
dde^` xua^'t nhie^`u gia?i pha'p ky~ thua^.t dde^? co' the^? qua?n ly'
thu?y che^'. Ho`a lan cu~ng ddang nghie^n cu+'u mo^.t
gia?i pha'p dde^? khi nu+o+'c lu~ ve^` thi` ddo'ng dde^ la.i, nu+o+'c
tha^'p thi` dde^ mo+? toang ra cho trong ruo^.ng ngoa`i so^ng dde^` hue^`.
Ne^'u ca'c ba'c interested tui se~ post ve^` va^'n dde^` na`y la^`n kha'c.
Ba^y gio+` pha?i cha.y ra Fast Food che'n ca'i dda~. 19h00 ro^`i, ddo'i
kho^ng chi.u no^?i.
Regards, Buu-Long