, central ethiopia are these lakes connected? shemelis fikre addis ababa university,department of...
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,CENTRAL ETHIOPIA
Are these lakes connected?
Shemelis Fikre
Addis Ababa University,Department of Earth Sciences
POBOX 1176, Addis Ababa, Ethiopia
Topography of Ziway-Shala lakes area
400000 420000 440000 460000 480000 500000 520000 540000
780000
800000
820000
840000
860000
880000
900000
920000
0 10 20 30 K m
1 6 3 5
1 5 8 51 5 8 0
1 5 5 0
C h ila lo (4 0 0 5 )
A lu to
K a k a (4 2 4 5 )
C o rb etti
< 1 7 5 0 m (R ift f lo o r)
1 7 5 0 -2 0 0 0 m (E sca rp m en t)
> 2 0 0 0 m (H ig h lan d s)
L ak es
C atch m en t
L egen d
b o u n d a ry
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
Structural map of Ziway- Shala lakes area
N
r
r
rr
r
Shala
Langano
Ziway
Abiyata
S i lte
Debr e
ze i t F
aul t Z
on
Wo
nj i
Fa
ul t
Be
l t
400000
400000
440000
440000
480000
480000
520000
520000
8000
00
800000
8400
00
840000
8800
00
880000
9200
00
920000
0 30Km
Caldera
Faults
Lake
Main fualt
Transverse ridge
Volcano
Recent fissurer
Legend
N
Sha a
Langano
Ziway
Abiya a
400000
400000
440000
440000
480000
480000
520000
520000
8000
00
800000
8400
00
840000
8800
00
880000
9200
00
920000
0 30Km
Caldera
Faults
Lake
Main fualt
Transverse ridge
Volcano
Recent fissurer
Legend
HydrogeologyHydrogeology400000 460000 520000
7800
0084
0000
9000
00
0 1 0 2 0 3 0 K m
Z iw a y
A b iy a taL an g a n o
S h a la
1= Ignimbrite, tuff, local rhyolite2= Ignimbrite, tuff, local basalt3= Ignimbrite covered with lacustrine
soils, recent regression 4= Ignimbrite covered with lacustrine
deposit5= 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 spring13=Groundwater flow direction, Circles
represent the Hydraulic conductivity.
H y d rau lic C o n d u c tiv ity (m /d ay )L eg en d
< 1
1 to 4 0
> 4 0
(L o w )
(M o d era te )
(H ig h )
8
9
1 02 0 0 0
11
1 2
1 3
1
2
3
4
5
6
7
ÊÚÊÚ
ÊÚÊÚÊÚÊÚÊÚÊÚ
$
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r
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1
126-127 5
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1519
21
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3839
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7578
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8687
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98 99103
104
113
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117118
85
82
76 119-122
115
45101
46
37
1072
944100 8
0 30Km
BoundaryRift floorEscarpmentHighlandlakesDrainage
ÊÚ Geothermal well$ River%U Cold springr Hot springÑ Hand dug well; Lake# Boreholes
N
The locations of sampling The locations of sampling sitessites
Na Ca Mg Cl HCO3 SO4Major Ions
0.1
1.0
10.0
100.0
1000.0
10000.0
C onc
ent ra
tions
(mg/l
)
Na Ca Mg Cl HCO3 SO4Major Ions
0.1
1.0
10.0
100.0
1000.0
10000.0
100000.0
C onc
ent ra
tions
(mg/l
)
Legend
Max.
75 percentile
Median
25 percentile
Min.
Groundwater Lake waters
1. Physico – chemical analysis
a) Major ion variability
390000.00 430000.00 470000.00 510000.00
X(m )
775000
815000
855000
895000
935000
Hydrochemical Map
Legend
100 0 100 m eq/l
N a C l
C a H C O 3
M g SO 4
0 1 0 2 0 3 0 K m
Groundwater flow direction
Major ion chemistry ………..
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3+CO3 Cl
Mg SO4
H
H
H
HH
H
H H
H
H H
H
HH
H
H H
H
HH
H
H H
HH H
H
H
H
H
H H
H
HH
H
HH
H
HH
H
HH
H
H
H
H
H H
H
H H
H
H H
H
H H
H
HH
H
H H
H
LL
L
L
L
L
LL
L
LL
L
L
L
L
J
J
J
J
J
J
J
J
J
JJ
J
J J
J
JJ
J
J
J
J
J
J
J
JJ
J
J
J
J
O O
O
O O
OG
G
G
LegendLegend
H Borehole
L Coldspring
J Hand dug well
O Hot spring
G River
Escarpment
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3+CO3 Cl
Mg SO4
H
H
H
H
H
H
HH
H
H
H
H
H
H
H
H
H
H
HH
H
HH
H
HH
H
HH
H
H H
H
HH
H
H
H
H
L L
L
LL
L
L L
LL
L
L
LL
L
L
L
L
L
L
L
L
L
L
L
L
L
J
J
J
J
J
J
LegendLegend
H Borehole
L Coldspring
J Hand dug well
Highland
b)b)Water types and physiographyWater types and physiography
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3+CO3 Cl
Mg SO4
Rift floor
A A
A
A A
A
A A
A
I I
I
I I
I
I I
I
E E
E
E E
E
E E
E
K
K
K
K
K
K
K
K
K
HH
H
HH
H
H H
H
H
H
H
H H
H
HH
H
H H
H
H H
H
H H
H
H H
HH H
H
H H
H
HH
H
H H
H
H
H
H
H H
HH
H
H
H H
H
H H
H
H H
H
H H
H
H H
H
L L
L
L L
L
L
L
L
LL
L
L L
L
SS
S
S S
S
S S
S
SS
S
S
S
S
J J
J
J J
J
J J
J
J JJ
J J
J
J J
J
JJ
J
JJ
J
J J
J
J J
J
J J
J
J J
J
J J
J
J J
J
J J
J
J J
J
O O
O
O O
O
O O
O
O O
O
O O
O
OO
O
O O
O
O O
O
M M
M
MM
M
MM
M
M M
M
M M
MM M
M
MM
M
M M
M
MM
M
MM
M
LegendLegend
A Abijata
H Borehole
L Coldspring
S Geothermal well
J Hand dug well
O Hot spring
I Langanoo
M River
E Shala
K Ziway
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3+CO3 Cl
Mg SO4
Rift floor
A A
A
A A
A
A A
A
I I
I
I I
I
I I
I
E E
E
E E
E
E E
E
K
K
K
K
K
K
K
K
K
HH
H
HH
H
H H
H
H
H
H
H H
H
HH
H
H H
H
H H
H
H H
H
H H
HH H
H
H H
H
HH
H
H H
H
H
H
H
H H
HH
H
H
H H
H
H H
H
H H
H
H H
H
H H
H
L L
L
L L
L
L
L
L
LL
L
L L
L
SS
S
S S
S
S S
S
SS
S
S
S
S
J J
J
J J
J
J J
J
J JJ
J J
J
J J
J
JJ
J
JJ
J
J J
J
J J
J
J J
J
J J
J
J J
J
J J
J
J J
J
J J
J
O O
O
O O
O
O O
O
O O
O
O O
O
OO
O
O O
O
O O
O
M M
M
MM
M
MM
M
M M
M
M M
MM M
M
MM
M
M M
M
MM
M
MM
M
LegendLegend
A Abijata
H Borehole
L Coldspring
S Geothermal well
J Hand dug well
O Hot spring
I Langanoo
M River
E Shala
K Ziway
c) Electrical conductivity• There are clear zonations in EC of natural waters
following the rift ward directions
400000 440000 480000 520000
7800
0082
0000
8600
0090
0000
0 10 20 30
K m
L a k eZ iw a y
L a k eA b iy a ta L a k e
L a n g an o
L a k eS h a la
< 1 5 0
1 5 0 -5 0 0
5 0 0 -1 5 0 0
1 5 0 0 -1 0 0 0 0
> 1 0 0 0 0
L eg en d
S tru c tu re s
G ro u n d w ate r
f lo w d irec tio n
2) Statistical analysis
• Spatial distribution and chemical differences of the HCA derived subgroups for groundwaters
14%
4%0% 0% 0% 0% 0%
6%
3%
0% 0% 0% 0% 0%
21%38% 48% 52% 49% 49% 50%
3%
3%
4% 1% 2% 5% 2%
2%1%
2% 4%0%
1%0%
46%45%
37%
24% 31% 25%38%
6% 5% 8%
20%16%
15%4%
1% 1% 0% 0% 1% 4% 5%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Subgroup 1 Subgroup 2 Subgroup 3 Subgroup 4 Subgroup 5 Subgroup 6 Subgroup 7
% m
eq/l
SO4
Cl
HCO3
CO3
K
Na
Mg
Ca
Group-AGroup -B
Statistical analysis…
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74
1
3
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2
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171921
23
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30
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3235
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5354
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59 60
62
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8687
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3334
41
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57
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64
75
79
92
93
106
110111
112
119121
122
124
126129
130
LakeLake
ZiwayZiway
LakeLake
LakeLakeLakeLakeAbiyataAbiyata
LanganoLangano
ShalaShala
0 30Km
N
Sampling sites#
Structures
Lake
Subgroup & Watertype
1 (Na-Ca-HCO3)
2 (Na-HCO3)
3 (Na-HCO3)
4 (Na-HCO3-Cl)
5 (Na-HCO3-Cl)
6 (Na-HCO3-Cl)
7 (Na-HCO3)
Legend
Hydrochemical evolutions and groundwater flow
• Starting from highland and escarpment waters and ending with rift floor waters; 1234. Total dissolved solids (TDS) concentration increases with increasing subgroup number
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na+K HCO3+CO3 Cl
Mg SO4
AA
A
D D
D
C C
C
L L
L
J J
J
NN
N
GG
G
LegendLegend
A Subgroup-1
D Subgroup-2
C Subgroup-3
L Subgroup-4
J Subgroup-5
N Subgroup-6
G Subgroup-7
1
2
3
4 Chemical Evolution Path-From the recharge areas to discharge areas
0 10 20 30 40 50
NA+K
0
10
20
30
40
50
C l+S O
4
BBBBB
B
B
B
BBHH
H
HHH
HHHIIIIIIIII
A DC
L
J
N
G
EE EEE
EE
LegendLegend
A Subgroup-1
D Subgroup-2
C Subgroup-3
L Subgroup-4
J Subgroup-5
N Subgroup-6
G Subgroup-7
H Lake Langanoo
I Lake Shala
E Lake Ziway
B Lake Abiyata
0 10 20 30 40 50
NA
0
10
20
30
40
50
H CO 3
BBBBB
B
B
B
BBHH
H
HHH
H HHIIIII
IIII
AD
C
L
J
N
G
EE EEE
EE
Note:- Represents direction of anion and cation dominance in groundwaters and lake waters along flow path from recharge to discharge area
Groundwater-lake water interactions
N
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&\
&\ &\
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&\
&\
&\
&\&\
&\
&\
&\
&\
&\
&\
$$
$
$
$
$
$
$
Ñ
Ñ
Ñ
Ñ
%
%
%
%
%
ð
ð
ððð
r rrr
r
r b7
b2-b5
b6f2
f19f20 f21
f22
a1
a2
a3
a4
a5
a1
a2
a3
a4
a5
d1
d2
d3
d4
e1e2
e3
e4
e5
e6
e7
e8
c1
c6
c8
c9c2
c3
c4
c10
c11
c13
c16
c17
c18
c20
c12
c14
c21
c22
f1 f3
f4
f5
f6
f7
f8
f9f10
f11
f12
f13
f14
f15f17
f18
f16
c19
0 20 30Km10
Cold springs%
Geothermalð
Hot springsr
Lake&\
RainÑ
River$
Well#
Legend
N
b7
b2-b5
b6f2
f19f20 f21
f22
a1
a2
a3
a4
a5
a1
a2
a3
a4
a5
d1
d2
d3
d4
e1e2
e3
e4
e5
e6
e7
e8
c1
c6
c8
c9c2
c3
c4
c10
c11
c13
c16
c17
c18
c20
c12
c14
c21
c22
f1 f3
f4
f5
f6
f7
f8
f9f10
f11
f12
f13
f14
f15f17
f18
f16
c19
0 20 30Km10
Cold springs%
Geothermalð
Hot springsr
Lake&\
RainÑ
River$
Well#
Legendsampling sites for sampling sites for isotope analysis:-isotope analysis:-
D = 5.4818O + 8.5
-60
-40
-20
0
20
40
60
80
100
-10 -8 -6 -4 -2 0 2 4 6 8 1018O (%0)
2H
(%0)
Cold well
Cold spring
Geothermal well
Hot spring
Lake
Rain
River
GMWL
LMWL
LEL (Lake)
Lake Abiyata and ShalaLake Ziway and
Langanof12f5
f1e2
f19
f22
b7
f18
a4
a2d1
d4
b2
b6
e3
e5
Oitu
Deuterium (2H) and oxygen(18O ) isotope
Deuterium (Deuterium (22H) and oxygen(H) and oxygen(1818O ) O ) isotopesisotopes
– The LMWL is plotted above the GMWL this is due to the isotopic The LMWL is plotted above the GMWL this is due to the isotopic concentrations of concentrations of precipitation in the study area has more precipitation in the study area has more deuterium excessdeuterium excess (that is D excess=2.35) than the global (that is D excess=2.35) than the global averaged precipitations.averaged precipitations.
– The majority of groundwaters, river waters and rain waters are The majority of groundwaters, river waters and rain waters are plotted near the LMWL .This indicate the plotted near the LMWL .This indicate the importance of present importance of present day precipitation for groundwater rechargeday precipitation for groundwater recharge..
– The lake Waters are plotted far to the right and shifted right down The lake Waters are plotted far to the right and shifted right down of the LMWL .This shows that of the LMWL .This shows that the lakes are more enriched with the lakes are more enriched with 1818O and O and 22HH resulted from substantial evaporative loss of the resulted from substantial evaporative loss of the lake waters as compared to the present day precipitation . lake waters as compared to the present day precipitation .
– Groundwaters (waters from hot spring, cold springs, cold wells, and Groundwaters (waters from hot spring, cold springs, cold wells, and geothermal wells) are scattered at different positions on the plot geothermal wells) are scattered at different positions on the plot and have differences in and have differences in 1818O and O and 22H concentrations. H concentrations.
• The relations between 18O with EC
a1a2
a4
b2b6
f17
f18f16 f12f1
-100
1900
3900
5900
7900
9900
11900
-5.00 -3.00 -1.00 1.00 3.00 5.00 7.00 9.0018O (%0)
EC(u
s/cm)
Cold spring
Hot spring
River
Cold Well
Lake Lake Langano and Horakelo river
Lake Ziway and Bulbula river f20
a1
f19
f21
f22f2
b4b6
b7
Oitu
c12 c9
c10c13f17
f18f1 f12
-300.0
200.0
700.0
1200.0
1700.0
2200.0
-5.00 -3.00 -1.00 1.00 3.00 5.00 7.00 9.00 11.00
18O (%0)
Cl(m
g/l)
Cold spring
Geothermal well
Hot spring
Lake
River
Cold well
c19
The relations between The relations between 1818O with ClO with Cl
The relations between The relations between 1818O with ECO with EC … … The The cold spring waterscold spring waters have negative have negative 1818O constituents and low EC similar to O constituents and low EC similar to the rivers( except Bulbula and Horakelo) the rivers( except Bulbula and Horakelo) indicates that they are rechrged indicates that they are rechrged by shallow circulating groundwatersby shallow circulating groundwaters which have undergone little rock- which have undergone little rock- water interactions.Groundwater flows from lake Ziway to lake Langanowater interactions.Groundwater flows from lake Ziway to lake Langano
The source of some hot springs is surface waters and shallow groundwaters.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.
Tritium versus EC
b3
f9
f8 f11
f10f15f14
f7
f13
c12c14
0
500
1000
1500
2000
2500
3000
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.003H (TU)
EC u
s/cm
)
Hot spring
River
Cold well
Lake
Bulbula
Tritium versus Chloride
0.30
b5
b4
f10f11f8f9
Ziway (2006)Ziway (1995)
Ziway (1992)
-100.0
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00
3H(TU)
Cl (m
g/l)
Geothermal well
Hot spring
Cold well
Lake
• The lake Ziway water shows a decrease in tritium content and chloride concentration with time indicates the decrease in the amount of surface inflow in to the lake
• 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
Spatial variation of isotopes in relation with hydrochemistry
a1
a2
a3
a4
a5
b 2
c5
c8
c9
c1 0
c1 1
c1 2c1 3
c1 6
c1 8
c2 0
d 2
d 3
d 4
e3
e4
e5
e6
e7
e8
f2
f4
f5
f6f1 7
f2 1e1
f1 0
f1 4
f1 5
f7
f8
f9
0 1 0 2 0 3 0 K m
0 to 0.5
0.5 to 10
10 to 100
O xygen-18 D istribution
Tritium D istribution
-4.5 to -3.5
-3.5 to -2.75
-2.75 to -1 .75
-1.75 to -1
-1 to 0
0 to 7
7 to 10.5
E C (µ s /c m )
F au lts
f1 2
c1 4
f1 6
d 1
b 7f1 8
c1
f1f2 0
f3
f1 9 f2 2e2
c4
f1 1
c3
c2
b 2 -b 6
c2 1
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 The high spatial ionic variations follows systematic trend. This reflects the different groundwater flow systems and the existence of reflects the different groundwater flow systems and the existence of hydrochemical evolution of waters along the flow pathhydrochemical evolution of waters along the flow path
On the highlands and escarpments there is shallow circulation of On the highlands and escarpments there is shallow circulation of groundwaters from direct recharge of precipitation and these waters groundwaters from direct recharge of precipitation and these waters have undergone no marked rock-water interactions.have undergone no marked rock-water interactions.
The low EC & TDS and isotope depleted waters in highly faulted rift The low EC & TDS and isotope depleted waters in highly faulted rift waters which have similarity in EC, TDS and depletion with the waters which have similarity in EC, TDS and depletion with the highland and escarpment waters indicates the southward migration highland and escarpment waters indicates the southward migration of highland and escarpment waters through faults and finally to lake of highland and escarpment waters through faults and finally to lake Langano. The tectonic structures play a great role on the Langano. The tectonic structures play a great role on the groundwater flow and chemical evolutiongroundwater flow and chemical evolution
There is deeper groundwater circulation of old age on the highly There is deeper groundwater circulation of old age on the highly faulted areasfaulted areas
CONCLUSIONS……CONCLUSIONS……
The lake waters, the majority of the groundwaters and surface The lake waters, the majority of the groundwaters and surface waters have similar tritium contents. This shows that these waters have similar tritium contents. This shows that these waters have similar recharge source.waters have similar recharge source.
Tritium contents of water from deep wells and hot springs are Tritium contents of water from deep wells and hot springs are different from lake waters indicates they have different different from lake waters indicates they have different sourcessources
Groundwaters north of lake Langano have similar Groundwaters north of lake Langano have similar 1818O content O content with the lake Ziway waters may show that there is subsurface with the lake Ziway waters may show that there is subsurface hydraulic connection between lake Ziway and lake Langanohydraulic connection between lake Ziway and lake Langano
The chemical composition of borehole waters between lake The chemical composition of borehole waters between lake Abiyata and Langano is similar for the nearby lake waters. Abiyata and Langano is similar for the nearby lake waters. This shows that there is flow of waters from lake Langano to This shows that there is flow of waters from lake Langano to lake Abiyata along the NE-SW trending faultlake Abiyata along the NE-SW trending fault
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