Transcript HYDROGEOLOGICAL SYSTEM ANALYSIS IN ZIWAY –SHALA …

,
CENTRAL ETHIOPIA
Shemelis Fikre
Addis Ababa University,Department of Earth Sciences
POBOX 1176, Addis Ababa, Ethiopia
Are these lakes connected?
 Topography of Ziway-Shala lakes area
Conceptualize the groundwater flow system in
the area
Identify the subsurface hydraulic connections
of the lakes in the area
Investigate the correspondence between
spatial locations and statistical groups.
Assess surface water- groundwater
interactions in the lake watershed system.
Conceptualize the role of geological
structures on the groundwater movement
 Sampling and laboratory analysis
 Hydrochemical techniques
– Physico – chemical analysis
– Statistical cluster analysis (HCA) and distributions of the clusters
 Isotope techniques
• 18O, 2H and 3H are analysed using plots for samples from the
different water bodies
 Both hydrochemical and isotope techniques together
– Scatter plots for the values of 18O versus EC, 18O versus chloride,
tritium versus EC and tritium versus chloride are prepared and
interpreted
– Spatial variation of isotopes in relation with hydrochemistry using
maps
400000
440000
480000
520000
Wo
n
8 40000
Structural map of Ziway- Shala lakes area
Abiyata
Langano
Shala
r
Be
Ziway
r
ul
t
r
8 00000
lt
r
Fa
r
ji
e
e
z
F
t
n
0
840000
30Km
840000
Abiyata
W
on
S
t
il
D
e
br
t
ei
l
au
Zo
880000
880000
920000
920000
N
Langano
Shala
400000
440000
480000
520000
800000
800000
Legend
r
0
400000
440000
480000
30Km
520000
Caldera
Lake
Transverse ridge
Faults
Main fualt
Volcano
r
Recent fissure
Hydrogeology
400000
460000
520000
Legend
Hydraulic Conductivity(m/day)
<1
1
7
2
8
3
9
(Low)
1 to 40 (Moderate)
900000
4
> 40
6
2 00
0
12
13
00
Ziway
300
18
00
160
0
250
Abiyata
0
840000
10
11
5
25
Langano
Shala
780000
(High)
2000
0
10
20
30 Km
0
1= Ignimbrite, tuff, local rhyolite
2= Ignimbrite, tuff, local basalt
3= Ignimbrite covered with lacustrine
soils, recent regression
4= Ignimbrite covered with lacustrine
deposit
5= Rift volcanoes and volcanic ridges
6= Basalt, local ignimbrite
7= Lake
8= Volcano-tectonic structures
9= Drainage
10=Groundwater level contour
11=Cold spring
12=Hot spring
13=Groundwater flow direction,
Circles represent the Hydraulic
conductivity.
N
85 $
%$ %
U
U69
U
%
$ 4
100
Ñ##
$#
8
#
87
$
; ÑÑÑ94 95 42
Ñ
Ñ 86 Ñ
#
Ñ
Ñ
U
%
15 Ñ## 65
Ñ
46
7
#
21 ÑÑ
Ñ # 11
# $ # 25 #
Ñ
13
U
# 30 # 32 Ñ 91
44# #
#
82 %
#
81
104
10
U
%
50
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r
U
;
96
U%
%
113Ñ Ñ
Ñ 63
$
12 6 ## 40
Ñ
#
#
47 # #$ ;
#
103
# 2
# 67
# #
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r Ñ 99
107
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9
$
98
29
101 #
73
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126-127
%
U
#
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119-122
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$
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%
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#
U rrr%
U75
r%
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78 26
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23 r r%
;
$ #
U%
%
U#
74
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58
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68 27
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115
90
80
37#
1
Ñ
U
%
#
51
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;r
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r
11731 #
54
118
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# # 34 #
66 #
#
53# ## 49 70
U
%
48 ## 52
83
19
Ê
Ú
Ú
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56
5960
##Ñ 71
U
97 %
a) Major ion variability
100000.0
Legend
Max.
75 percentile
10000.0
Median
Ê
Ú
ÚÊ
Ê
Ú
Ê
ÚÚ
Ê
Ú
Ê
0
1. Physico – chemical analysis
1000.0
Concentrations (mg/l)
84
Boreholes
Lake
Hand dug well
Hot spring
Cold spring
River
Geothermal well
Drainage
lakes
Highland
10000.0
Escarpment
Rift floor
Boundary
30Km
Concentrations (mg/l)
#
;
Ñ
r
U
%
$
Ú
Ê
100.0
10.0
1.0
25 percentile
1000.0
Min.
100.0
10.0
1.0
89
Ñ
0.1
0.1
Na
The locations of sampling sites
Ca
Mg
Cl
Major Ions
HCO3 SO4
Groundwater
Na
Ca
Mg
Cl
Major Ions
Lake
waters
HCO3 SO4
Major ion chemistry ………..
Hydrochemical Map
935000
Legend
Na
Ca
Mg
Cl
HCO3
SO4
895000
100
100 meq/l
Groundwater flow
direction
855000
815000
0 10 20 30Km
775000
390000.00
0
430000.00
470000.00
X(m)
510000.00
b)Water types and physiography
Rift floor
Legend
Legend
Legend
Legend
40
J
Mg
40
20
20
Mg
M
M
M
M
H
O
80
O
20
SO4
L
80
60
8400
20
60
40
60
Ca
20
Cl Cl
40
Ca HCO3+CO3
Na+K HCO3+CO3
Na+K
60
20
H
L
60
40
40
G
Hot
spring
O
20
I Langanoo 20
M River Mg
SO4
E Shala
M
M
O
MM
80
K Ziway 80
O S
J
KHKJMM
S
60
60
K LLML HO
HHM O OS
HH
HS
SO
I
E
A
40
40
H
E
I
J
H
JL MJ JAO
LHJJJ AEJ
MH J
20
20
M KKKMHML HHJHHHHJH
M MH JHHMHLO J HMJMJ S S
M J LLH J OLMJHJOHJHMHJJHHJHJH HHHMJHJHMJJJLLAJELIHEIISOHOSOH O S
IAOES JHLJMKHJJKM AOAEO O
80
80
A
80
dug well
J Hand
River
SO4
20
40
60
Cl
80
20
40
60
80
20
40
60
Ca
Na+K HCO3+CO3
60
H
40
H
80
Ca
L
JH
LLJHLLHH
Coldspring
Hand dug well
well
SO Geothermal
Hot spring
GJ L
80
80
80
L
80
S
J
J
H H
M
HK M
K
JL H
S
J
60
60
60
60
K LLML
J HH
60
O
H
H
S
HHM
LH H
L HJ
OO
O
HJLHJ
HH
L H 40
HS
S
I
E
HJ H H
40
40
A
40
H
E
I
J
JL MJ JA
H
O
40
J
H
J
H
J
J
JH
E
LHJ A
HOHHH H
J
M
J
H
HH
H
H
J
20
20
H
HH
20
20
H
M KKKM
JLL LJ HHJLJ OH
JH
L
H
L
J
20
M
J
H
H
H
H
M
S
M H JHHMHLO
J M
MJ H HSO
M
JJGLM
HHH O HLS
HHHHJJHJOHO
H
HM
LM
H
M
LHLLHHHH
HJ O
JHH
M
H
M
H
L
J
H
HO
I
J
J
L
J
E
J
J
SHHHO
L
J
J
S
E
K
H
O
H
J
A
J
HO
J
H
OHH HGLHJOHJLHJHJJLHHHL
H
L
H
JO
M
H
IA
IE
K
JH
H JH
H
JS
J LL A
LJJH
JHM
O
IJHA
O
E
HL HLLHLH H LJ
LJHHHHH H
20
60
20
Mg
SO4
L
H
JLL
HLLH H
H
80
40
40
20
20
LJ
60
Hand dug well
40
40
20
40
J
80
Na+K HCO3+CO3
80
60
Legen
60
60
80
40
Highland
80 H Borehole 80
Escarpment
80
Coldspring
60 L
60
60
80
20
80
Rift floor
A H Abijata
Borehole
HL Borehole
Coldspring
Cl
S
J
O
I
M
E
K
c) Electrical conductivity
900000
• There are clear zonations in EC of natural
waters following the rift ward directions
Legend
<150
Lake
Ziway
860000
150-500
500-1500
1500-10000
Lake
Abiyata
Lake
Langano
>10000
820000
Lake
Shala
Structures
Groundwater
flow direction
780000
Km
0
400000
440000
480000
10
20
30
520000
2)
Statistical analysis
Statistical analysis…
• Spatial distribution and chemical differences of the HCA
derived subgroups for groundwaters
Collins Bar Diagram
100%
N
85#
#
#
87
19 ###20
#
86
21 # 11
46
100# ##33694
##
17# 93
42
#
95
# 43
##
65
64
7
#
#
#
#
Lake
44
Lake
25
#
91
#
#
106
#
30
112 Ziw
#
#32
Ziwa y
50
10
81
104
#
#
#
79
#
#
130
#
35
96
12
113 #
#
#
63
#
98
6 #41
#
108 45
#
40
2
47 #61# 111
#
#
#
#
#
110
67
103 # #99
101 122
#
#
9
#
107
29
#
#
73
#
5
#
129
#
126
# #119
#
##
88 92
## # #
39
#
22
121
120
#
#
#
28
76 #
#
##
#
75
23
#124
38
#
# 77
#
78 26
Lake
# #
Ab iyata109 Lake
#
74 58
102 74
#
#
#
Lang
#
Lang ano
ano
68 27
90
37 115
80
105
#
#
1
#
#
#
51
#
Lake
Lake
116
##
Sh ala
ala
#
62
117 31 #
# 34
54
118 125
# ##
#
53 33 #
66
#
70
#
# 57
#
#
48
49 #52
#
56
60
59 #
# #
97
#
71
0
30 Km
89
#
0%
8%
0%
20%
1%
4%
5%
4%
16%
15%
80%
#
#
#
#
70%
46%
45%
37%
38%
24%
31%
25%
0%
2%
1%
5%
HCO3
50%
40%
30%
2%
3%
1%
3%
2%
4%
4%
1%
0%
2%
#
Na
21%
Mg
38%
48%
52%
0%
0%
Subgroup 4
49%
49%
50%
0%
Subgroup 5
0%
Subgroup 6
0%
Subgroup 7
20%
10%
Sampling sites
Subgroup & Watertype
4 (Na-HCO3-Cl)
Structures
1 (Na-Ca-HCO3)
5 (Na-HCO3-Cl)
Lake
2 (Na-HCO3)
6 (Na-HCO3-Cl)
3 (Na-HCO3)
7 (Na-HCO3)
CO3
K
6%
Legend
SO4
Cl
60%
% meq/l
82
1%
5%
90%
69
84
83 #
1%
6%
14%
3%
4%
Subgroup 1
Subgroup 2
0%
Group-A
Subgroup 3
Group -B
Ca
Hydrochemical evolutions and
groundwater flow
Starting from highland and
escarpment waters and ending
with rift floor waters; 1234.
Total dissolved solids (TDS)
concentration increases with
increasing subgroup number
E E
E EEEE
60
40
40
20
20
Mg
SO4
80
Subgroup-3
Subgroup-4
30
NB
L
40
30
B
NL
HJ
HBI
HHHIIIBB
20
20
Subgroup-5
Subgroup-7
10
10
A
20
80
20
40
60
80
Na+K HCO3+CO3
40
60
A
2D G
C
3
G
D CNGLJ DAC JNL
Cl
Chemical
Evolution
Path-From
the recharge
areas to
discharge
areas
H Lake Langanoo
I Lake Shala
E Lake Ziway
H
IGB Lake Abiyata
C B
Subgroup-6
E EEEEE
E
60
40
40
4
NL
J
20
60
Ca
Subgroup-1
Subgroup-2
A Subgroup-1
D Subgroup-2
C Subgroup-3
L Subgroup-4
J Subgroup-5
N Subgroup-6
G Subgroup-7
80
A 1
20
C BGI
HHHHBBIII
HBBI
JH
HCO3
60
A
D
C
L
J
N
G
80
Legend
D
A
40
Legend
Legend
80
50
50
Cl+SO4
•
Groundwater-lake water
interactions
D
0
0
0
10
20
30
NA
Note:-
40
50
0
10
20
30
40
50
NA+K
Represents direction of anion
and cation dominance in
groundwaters and lake
waters along flow path from
recharge to discharge area
100
80
D = 5.4818O + 8.5
60
f19
40
f1
f5
f12
Cold well
Cold spring
Geothermal well
Hot spring
Lake
Rain
River
GMWL
LMWL
LEL (Lake)
b7
20
Oitu
d4
f22
e3
a4
0
a2
d1
2
H (%0)
Lake Ziway and
Langano
e2
e5
b2
Lake Abiyata
and Shala
b6
-20
f18
-40
-10
-8
-6
-4
-2
0
18
2
4
6
8
10
O (%0)
-60
sampling sites for
isotope analysis:-
Deuterium (2H) and oxygen(18O )
isotope
Deuterium (2H) and oxygen(18O ) isotopes
– The LMWL is plotted above the GMWL this is due to the isotopic
concentrations of precipitation in the study area has more
deuterium excess (that is D excess=2.35) than the global
averaged precipitations.
– The majority of groundwaters, river waters and rain waters are
plotted near the LMWL .This indicate the importance of
present day precipitation for groundwater recharge.
– The lake Waters are plotted far to the right and shifted right
down of the LMWL .This shows that the lakes are more
enriched with 18O and 2H resulted from substantial
evaporative loss of the lake waters as compared to the
present day precipitation .
– Groundwaters (waters from hot spring, cold springs, cold wells,
and geothermal wells) are scattered at different positions on the
plot and have differences in 18O and 2H concentrations.
11900
9900
•
The relations between 18O with Cl
2200.0
The relations between 18O with EC
1700.0
Oitu
Cold spring
Cold spring
Geothermal well
Hot spring
5900
1200.0
River
Cold Well
3900
1900
f18
f17
-100
-5.00
-3.00
Lake Langano
and Horakelo river
Lake
b6
b2
f16
a2
a1 a4
-1.00
Lake Ziway
and Bulbula river
f1 f12
1.00
3.00
18
O (%0)
5.00
Hot spring
Cl(mg/l)
EC(us/cm)
7900
7.00
9.00
Lake
River
700.0
f21
b6
f22
f2
Cold well
b4
b7
200.0
f18
f17
-5.00
-300.0
f1
a1
-3.00
-1.00
1.00
3.00
18
O (%0)
f19
c12 c9
f12 f20 c10
c13
5.00
7.00
9.00
11.00
The relations between 18O with EC …
The cold spring waters have negative 18O constituents and low EC similar
to the rivers( except Bulbula and Horakelo) indicates that they are
rechrged by shallow circulating groundwaters which have undergone
little rock- water interactions.Groundwater flows from lake Ziway to lake
Langano


The source of some hot springs is surface waters and shallow groundwaters.
The relations between 18O with Cl ...
•The lake water labeled c12 (lake Ziway) has similar chloride concentration with c9
(lake Langano) but the 18O enrichment in c9 is higher than c12.This is due to the high
evaporation water loss from lake Langano. From this it is evidence to conclude that
there is southward migration of lake Ziway waters towards lake Langano
• The geothermal water labeled f19 has similar 18O enrichment but higher Cl
concentration than lake Ziway waters (labeled c12).Lake waters labeled c13 has also
similar 18O enrichment and Cl concentrations with the geothermal water labeled f20.
This shows that there is dilution of the geothermal water by the lake Ziway water.
From this it is evidence to conclude that there is mixing of the lake waters with the
geothermal waters.
3000
Tritium versus Chloride
Tritium versus EC
2500
700.0
b3
0.30
Hot spring
River
500.0
Cold well
1500
1000
f13
Bulbula
f9
500
Cl (mg/l)
EC us/cm)
2000
Lake
f7
400.0
1.00
f10
f15
f11
2.00
Cold well
300.0
Lake
200.0
c14
100.0
c12
0.0
0
0.00
Hot spring
b4
Ziway (1992)
f14
f8
Geothermal well
600.0
3.00
4.00
5.00
6.00
7.00
8.00
9.00
-100.00.00
10.00
f9
f8
1.00
b5
2.00
Ziway (2006) f10
Ziway (1995)
f11
3.00
4.00
3
3
•
•
H (TU)
The borehole waters near the lakes
have similar EC and tritium values to •
the lake waters indicating the
interaction of the lake waters with the
surrounding groundwaters.
Boreholes near the geothermal system
has higher EC and lower tritium values
may indicate mixing
5.00
6.00
7.00
8.00
9.00
H(TU)
The lake Ziway water shows a decrease in
tritium content and chloride concentration w
time indicates the decrease in the amount
of surface inflow in to the lake
Spatial variation of isotopes in relation with
hydrochemistry
Oxygen-18 Distribution
a5
-4.5 to -3.5
a2
d3
f11
f16
e3
f14 f7
f4
-3.5 to -2.75
f15
f10
f9
c14
a1
f17
f12
c13
c12
d4
f8
c4 f5 c16
f1
f18
e7
-1.75 to -1
d2
f3
0 to 7
7 to 10.5
c3
c5
-1 to 0
a3
f21
f2f22
f19
e2
b2
e4c11 b2-b6
c18
c9
c1
d1
c2
c8
c20
c10
c21
e8
b7
e1
e5
f20
-2.75 to -1.75
f6
Tritium Distribution
e6
0 to 0.5
a4
0.5 to 10
10 to 100
0
10
20
30Km
Faults
EC (µs/cm)
symbol label
begins with
“a” are cold
spring, with
“d” are rain
and “e” are
river
samples
•
The high spatial ionic variations follows systematic trend. This
reflects the different groundwater flow systems and the existence of
hydrochemical evolution of waters along the flow path

On the highlands and escarpments there is shallow circulation of
groundwaters from direct recharge of precipitation and these waters
have undergone no marked rock-water interactions.

The low EC & TDS and isotope depleted waters in highly faulted rift
waters which have similarity in EC, TDS and depletion with the
highland and escarpment waters indicates the southward migration
of highland and escarpment waters through faults and finally to lake
Langano. The tectonic structures play a great role on the
groundwater flow and chemical evolution

There is deeper groundwater circulation of old age on the highly
faulted areas
CONCLUSIONS……

The lake waters, the majority of the groundwaters and surface
waters have similar tritium contents. This shows that these
waters have similar recharge source.

Tritium contents of water from deep wells and hot springs are
different from lake waters indicates they have different
sources

Groundwaters north of lake Langano have similar 18O content
with the lake Ziway waters may show that there is subsurface
hydraulic connection between lake Ziway and lake Langano

The chemical composition of borehole waters between lake
Abiyata and Langano is similar for the nearby lake waters.
This shows that there is flow of waters from lake Langano to
lake Abiyata along the NE-SW trending fault
Thank You