International Research Journa Vol. 4(12), 19-27, December (2 International Science Community Associa Origin and Recharge Es Environmental Isotopes i Betiok L.P. Fareze 1 *, J 1 Institut National des Sc 2 Aix Marseille Université Ava Received 21 st Octobe Abstract Hydrochemical and environmental isotope the sedimentary aquifer of Mahafaly, sou according to the geological formation and represents freshwater with Na-Ca-HCO 3 -C the flow paths, where in the border of the O deep groundwater mixed with local rainw Onilahy River, which represents a mixing the aquifer is partially recharged by loc dominant which control the groundwater 0.83TU, which confirms that the majority from different areas. Hot springs have a zone. We propose a mean groundwater r recharge rate of 60mm/year giving a total Keywords: Hydrochemistry, Isotopes, Rec Introduction Water is the source of life. Since 200 government attempts to increase the access to the rural zones of the country, by installing water sources. Despite these installations, t drinking water remains very limited both in Only limited areas had been supplied wit sources, yet, in most of the regions, which h water source infrastructures, a long term a drinking water is still difficult to meet. Techn hydrogeological issues are often the causes o which are linked to both the groundwater qu In the southwestern region of Madagascar, the drinking water is less than 38%, one of the country, making the region one of the least Island 1 . The water resources problem in the re water quality due to agricultural or mining p quantity resulting from well water exhaustion water table during the dry winter season². aims at helping the NGOs working in the Dis supply safe drinking water while determin groundwater recharge and their rate in sedimentary aquifer of Mahafaly plateau us al of Earth Sciences_______________________________ 2016) ation stimation of Groundwater using C in the Mahafaly Sedimentary Aqu ky Southwestern Madagascar J. Rajaobelison 1 , V. Ramaroson 1 , C. Vallet-Coulomb 2 ciences et Techniques, P.O Box 4279, 101 Antananarivo-Madag é, CNRS, IRD, CDF, CEREGE UM 34, 13545 Aix en Provence, [email protected]ailable online at: www.isca.in, www.isca.me er 2016, revised 9 th December 2016, accepted 16 th December 20 es studies are used to determine the groundwater origin uthwest of Madagascar. The groundwater chemical typ d the altitude of the sampling site. Groundwater at high alt Cl type and it changes to more saline downwards while fo Onilahy River the water type becomes Na-Ca-Mg-SO 4 -Cl water occurs in the Sakamena basin except for the grou with the river. Groundwater isotopic composition results cal rainfall during the summer season. Mixing and eva r mechanism recharge. Besides, the tritium results hav of the samples, around 60%, are produced by mixing of r tritium value less than 0.2TU indicating a paleo-rechar residence time in the study zone of around 75 years, wh recharge of 2.7*10 8 m 3 /year over the total study area. charge, Groundwater, Residence time, Madagascar. 07, the Malagasy o drinking water in improved drinking the access to safe n space and time. th drinking water had benefited from availability of safe nical and/or mainly of those limitations, uality and quantity. e access rate to safe lowest rates in the t developed of the egion is of twofold: pollution and water n due to decreasing The present study strict of Betioky to ning the source of nfiltration in the sing environmental isotopes and chemical investigation indicators often serve as effect multiple problems in hydrology and semi-arid and arid regions 3 . Hydroc powerful used to identify the sour systems and to trace the groundw 18 O, 14 C, 3 H, 3 H/ 3 He and dissolved which help to give better estimatio scales 5 . Study zone: The study zone is situ district, between the 23°15’S and 44°10’E and 45°00’ E longitudes surrounded in the north by the dist Benenitra in the eastern part and th south. The district consists of wid Onilahy River flows westwards th plateau. The total geographical are km². The altitude of the plains vari Globally, the district is complete bounded in its eastern border by the by the Mahafaly plateau. Thus, th into three categories, the Betioky h east valley in Sakamena and Sa _______ E-ISSN 2321–2527 Int. Res. J. Earth Sci. 19 Chemistry and uifer, District of gascar , France 016 and recharge estimation in pe in the study zone varies titude of the Isalo formation ollowing the direction along l-HCO 3 . Highly mineralized undwater samples near the s in the study area show that aporation are the processes ve a mean value of around recent and old groundwater rge from a distant recharge hich corresponds to a mean n. Isotopic and hydrochemical tive methods for resolving d hydrogeology, especially in chemical and isotopic data are rces of groundwater recharge water flow 4 . Temperature, ²H, gas are environmental tracers on of recharge and flow time uated in the middle of Betioky d 24°10’S latitudes and the s. The district of Betioky is trict of Toliara, the district of he district of Ampanihy in the de plains through which the hrough the Mahafaly kartsic ea of the study zone is 4,500 ies between 100 m to 400 m. ed of large peneplains. It is e Sakoa basin and in the west he whole area can be divided hill, the alluvial plains and the akoa basins. The district is
9
Embed
Origin and Recharge Estimation of Groundwater using ... · , Groundwater, Residence time, Madagascar. isotopes and chemical investigation. Isotopic and hydrochemical indicators often
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
International Research Journal
Vol. 4(12), 19-27, December (201
International Science Community Association
Origin and Recharge Estimation
Environmental Isotopes in the Mahafaly
Betioky Southwestern MadagascarL.P. Fareze
1*, J.
1Institut National des Sciences et Techniques, P.O Box 4279, 101 Antananarivo2Aix Marseille Université
AvailableReceived 21st October
Abstract
Hydrochemical and environmental isotopes studies are used to determine the
the sedimentary aquifer of Mahafaly, southwest of Madagascar. The groundwater chemical type in the study zone varies
according to the geological formation and the altitude of the sampling site. Groundwater at high altitude of the Isalo formation
represents freshwater with Na-Ca-HCO3-Cl type and it changes to more saline downwards while following the direction along
the flow paths, where in the border of the Onilahy River the water type becomes Na
deep groundwater mixed with local rainwater occurs in the Sakamena basin except for the groundwater samples near the
Onilahy River, which represents a mixing with the rive
the aquifer is partially recharged by local rainfall during the summer season. Mixing and evaporation are the processes
dominant which control the groundwater mechanism recharge. Besid
0.83TU, which confirms that the majority of the samples, around 60%, are produced by mixing of recent and old groundwater
from different areas. Hot springs have a tritium value less than 0.2TU indicating
zone. We propose a mean groundwater residence time in the study zone of around 75 years, which corresponds to a mean
recharge rate of 60mm/year giving a total recharge of 2.7*10
Keywords: Hydrochemistry, Isotopes, Recharge
Introduction
Water is the source of life. Since 2007, the Malagasy
government attempts to increase the access to drinking water in
the rural zones of the country, by installing improved drinking water sources. Despite these installations, the access to safe
drinking water remains very limited both in space and time.
Only limited areas had been supplied with drinking water
sources, yet, in most of the regions, which had benefited from
water source infrastructures, a long term availability of safe drinking water is still difficult to meet. Technical and/or mainly
hydrogeological issues are often the causes of those limitations,
which are linked to both the groundwater quality and quantity.
In the southwestern region of Madagascar, the access rate to safe
drinking water is less than 38%, one of the lowest rates in the
country, making the region one of the least developed of the Island1. The water resources problem in the region is of twofold:
water quality due to agricultural or mining pollution and water
quantity resulting from well water exhaustion due to decreasing
water table during the dry winter season². The present study
aims at helping the NGOs working in the District of Betioky to
supply safe drinking water while determining the source of groundwater recharge and their rate infiltration in the
sedimentary aquifer of Mahafaly plateau using environmental
Journal of Earth Sciences_____________________________________
(2016)
Association
Recharge Estimation of Groundwater using Chemistry
in the Mahafaly Sedimentary Aquifer
Betioky Southwestern Madagascar *, J. Rajaobelison
1, V. Ramaroson
1, C. Vallet-Coulomb
2 Institut National des Sciences et Techniques, P.O Box 4279, 101 Antananarivo-Madagascar
Aix Marseille Université, CNRS, IRD, CDF, CEREGE UM 34, 13545 Aix en Provence, [email protected]
Available online at: www.isca.in, www.isca.me October 2016, revised 9th December 2016, accepted 16th December 201
and environmental isotopes studies are used to determine the groundwater origin and recharge estimation in
the sedimentary aquifer of Mahafaly, southwest of Madagascar. The groundwater chemical type in the study zone varies
mation and the altitude of the sampling site. Groundwater at high altitude of the Isalo formation
Cl type and it changes to more saline downwards while following the direction along
of the Onilahy River the water type becomes Na-Ca-Mg-SO4-Cl
deep groundwater mixed with local rainwater occurs in the Sakamena basin except for the groundwater samples near the
Onilahy River, which represents a mixing with the river. Groundwater isotopic composition results in the study area show that
the aquifer is partially recharged by local rainfall during the summer season. Mixing and evaporation are the processes
dominant which control the groundwater mechanism recharge. Besides, the tritium results have a mean value of around
0.83TU, which confirms that the majority of the samples, around 60%, are produced by mixing of recent and old groundwater
from different areas. Hot springs have a tritium value less than 0.2TU indicating a paleo-recharge from a distant recharge
zone. We propose a mean groundwater residence time in the study zone of around 75 years, which corresponds to a mean
recharge rate of 60mm/year giving a total recharge of 2.7*108m
3/year over the total study area.
Recharge, Groundwater, Residence time, Madagascar.
Water is the source of life. Since 2007, the Malagasy
government attempts to increase the access to drinking water in
the rural zones of the country, by installing improved drinking water sources. Despite these installations, the access to safe
ter remains very limited both in space and time.
Only limited areas had been supplied with drinking water
sources, yet, in most of the regions, which had benefited from
water source infrastructures, a long term availability of safe difficult to meet. Technical and/or mainly
hydrogeological issues are often the causes of those limitations,
which are linked to both the groundwater quality and quantity.
In the southwestern region of Madagascar, the access rate to safe
less than 38%, one of the lowest rates in the
country, making the region one of the least developed of the . The water resources problem in the region is of twofold:
water quality due to agricultural or mining pollution and water
from well water exhaustion due to decreasing
water table during the dry winter season². The present study
aims at helping the NGOs working in the District of Betioky to
supply safe drinking water while determining the source of ir rate infiltration in the
sedimentary aquifer of Mahafaly plateau using environmental
isotopes and chemical investigation. Isotopic and hydrochemical
indicators often serve as effective methods for resolving
multiple problems in hydrology and hydrogeolog
semi-arid and arid regions3. Hydrochemical and isotopic data are
powerful used to identify the sources of groundwater recharge
systems and to trace the groundwater flow18O, 14C, 3H, 3H/3He and dissolved gas are
which help to give better estimation of recharge and flow time
scales5.
Study zone: The study zone is situated in the middle of Betioky district, between the 23°15’S and 24°10’S latitudes and the
44°10’E and 45°00’ E longitudes. The
surrounded in the north by the district of Toliara, the district of
Benenitra in the eastern part and the district of Ampanihy in the
south. The district consists of wide plains through which the
Onilahy River flows westwards througplateau. The total geographical area of the study zone is 4,500
km². The altitude of the plains varies between 100 m to 400 m.
Globally, the district is completed of large peneplains. It is
bounded in its eastern border by the Sakoa
by the Mahafaly plateau. Thus, the whole area can be divided
into three categories, the Betioky hill, the alluvial plains and the east valley in Sakamena and Sakoa basins. The district is