BY

JOHN A. SHAMONDA DIRECTOR GENERAL

NIGERIA HYDROLOGICAL SERVICES AGENCY (NIHSA)

FEDERAL MINISTRY OF WATER RESOURCES, ABUJA, NIGERIA

AND

CHRIS. M. MADUABUCHI CONSULTANT (ISOTOPE HYDROLOGY), NIHSA

Paper presented at the Kick-Off Meeting on the Project RAF7011: Integrated and Sustainable Management of the Shared Aquifer Systems and Basins of the Sahel Region, IAEA Hqtrs, Vienna, Austria 16 – 20 July 2012 .

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1. Overview of Case Studies on Application of Isotope Hydrology Techniques in the Water Sector in Nigeria

(Hydrological, Hydrochemical & Isotope data): 1. GROUNDWATER RESOURCES IN NIGERIA 1.1 Wurno Project, Sokoto State, NW Nigeria (RAF/8/022) 1.2 Chad Basin Aquifers’ Project, NE Nigeria (NIR/8/006) 1.3 Iullemeden Aquifer System Project (RAF/8/038) 1.4 Artesian Aquifers’ Study in parts of SE Nigeria

(NIR/8/007) 2. IAEA-assisted Regional Project, RAF7011: Sustainable

Management of Shared Aquifer Systems in the Sahel. Aquifer of interest & delineation of area to be covered Locations of Monitoring Wells & Sampling Campaigns Budget (Equipment; Logistics; Geophysical Survey;

Analysis of samples; Capacity Building; etc.)

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The Hydrogeological basins in Nigeria are as defined in the Geological Map. There are groundwater occurrences in both the Sedimentary and Basement complex areas, but in varying degrees of yield. In some of the Sedimentary basins, particularly Chad Basin. Some of the aquifers are already under stress resulting in near mining conditions of the groundwater.

Groundwater occurrence varies from place to place and is dependent on the underlying geological formations and the amount of rainfall that infiltrated into the ground.

Rainfall amount increases from about 2000mm mean annual value in areas close to the coast in the South to about 500mm in the extreme Northern parts of the country.

There are 12Nos. River Basins including the Chad Basin in the NE and the Sokoto Basin (part of the Iullemeden) in the NW

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The Institutional Framework for management of water resources in Nigeria is such that the Honourable Minister, Federal Ministry of Water Resources is vested with the sole authority to coordinate all water resources development and management. Also involved in water resources development are the respective State Water Boards, National Water Resources Institute and Departments of Hydrology in Universities. Water Quality and Sanitation nationwide is monitored nationwide by the Dept of Water Quality & Sanitation in Federal Ministry of Water Resources.

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The Federal Government of Nigeria through the Federal Ministry of Water Resources, commenced integration of isotope hydrology techniques in the water resources development and management programmes of the country, from 1997 to date. Isotope-based projects were implemented under Technical Cooperation (TC) programme of the IAEA, by the former Department of Hydrology & Hydrogeology which in 2010 transformed into Nigeria Hydrological Services Agency (NIHSA).

Isotope hydrologic investigations have been successfully carried out in four (4) critical hydrological basins with a view to addressing the water resources management challenges in the respective areas.

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OBJECTIVES: i. Application of isotope hydrology techniques to determine the

interplay of recharge from rainfall, the Rima River, irrigation return flows and contribution to annual flooding to groundwater.

ii. Quantification of water quality changes in the aquifer systems through complementary use of hydrochemical methods.

The study was informed by the intensive groundwater abstraction from the shallow aquifers of the “fadamas” for accelerated irrigation activities under the World Bank-assisted National Fadama Development Project (NFDP) which commenced in the area in 1993.

Four Sampling Campaigns were undertaken and 53 Nos. sampling points were covered. Three (3) Rainfall Sampling Stations were also established.

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A considerable contrast (range of 60%o for Deuterium) was established in the isotopic composition of the different water bodies which confirmed the efficacy of isotope methods in studying the Rima Hydrological Basin.

Correlation of stable isotopes and tritium data for groundwater from dug wells tapping the shallow alluvial aquifers (depth less than 15m) with those from local precipitation, particularly Tritium, show no significant variation, implying that groundwater in the shallow aquifers are rapidly recharged by direct infiltration.

By similar comparison it was confirmed that the shallow aquifers are also recharged by River Rima and annual flooding. Records on groundwater level monitoring also confirmed sustainability of the shallow aquifers to exploitation for the accelerated irrigation activities under the World Bank assisted National Fadama Development Project (NFDP) -I, 1994-1999.

The significant variations in Tritium values between waters of the two main aquifers – Wurno and Taloka, suggest different episodes of recharge and support the hydrogeological evidence that both aquifers are not interconnected in the Wurno area.

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WURNO PROJECT: SUMMARY OF RESULTS (Contd) The interpreted radiocarbon age of groundwater of the deeper

Taloka Formation (Maestrichtian in age) about 15ka BP at Hamma Ali in the control area, SW of project area, suggest limited recharge from rainfall implying that recharge in Taloka aquifer took place during a much wetter and colder climate, in that area.

Results of Chemical Analysis show that waters from different sources in the project area are generally of Calcium, Sodium Bicarbonate type. The Bicarbonates can be attributed to dissolution of calcite in the sand dunes in the area.

Though variations in the chemical compositions of the different water bodies in the project area are significant for Na2+, K+ and Cl-, yet the waters are generally within tolerable limits for their respective use for domestic and irrigation purposes.

However, apparent contamination of groundwater by fertilizer/sewage, was observed at Wurno and Lugu villages as Nitrate concentration approached highest permissible levels set by WHO .

Results of the study have been published in the November 1999 edition of the Journal of Nigerian Association of Hydrogeologists (NAH), a copy of which is attached.

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OBJECTIVES: i. Evaluation of the target depths, thicknesses and area

extent of the three most exploited aquifers (Upper, Middle and Lower ) and the regional flow system (hydrodynamics) of the aquifers,

ii. Recharge areas and recharge patterns of the aquifers including their age correlation and interconnectivity,

iii. Lake Chad waters – Groundwater interaction and

iv. Hydro-chemical scenarios, contaminant transport and possible numerical modeling of the aquifer systems.

There were 5 Nos. Sampling Campaigns covering 127 locations. 92 Nos. water samples were collected from various aquifers and surface sources including Lake Chad in addition to 28 Nos. rainfall samples.

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y = 0.48x - 2.59

R2 = 0.998

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MAJOR CHEMICAL CONSTITUENTS

ION

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me

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CONTROL UPPER MIDDLE LOWER

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d D = 5.2 d18

O - 2.3

d D = 8 d18

O + 10

-80.0

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-10.00 -8.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 6.00

d18O [‰]

d2H

[‰

]

MWL

Evaporation line

Surface

Mean Precipitation

Precipitation

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d D = 5.2 d18

O - 2.3

d D = 8 d18

O + 10

-80.0

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d2H

[‰

]

Middle

Lower

MWL

Evaporation line

Mean Precipitation

M+L Aquifers

d D= 8d18

O + 3

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SW NE

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meters

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Bedrock

-700

Chad Lake

Chad

Maiduguri

Pays Bas

P

Pliocene (P)

Quaternary (Q)

→ Water flow direction

The Hydrochemical results indicate no concern for

water quality except the excessive concentration of iron and fluoride in some localities leading to browning of teeth and dental florisis, respectively as observed in some inhabitants.

The stable isotope data on precipitation and surface water, plot along the GMWL . The deuterium excess parameters also correlate with the global average of 10%o which confirms the continental nature of the precipitation.

The enrichment of Lake Chad waters in stable isotopes composition (d18O = 4.84%o and d2H = 23.5%o) as a consequence of evaporation is

evident.

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Stables isotopes of the Middle and Lower Aquifers plot along a line of slope 8 comparable to the GMWL but with a lower Deuterium excess of 3%o.

Isotopic results show that at low depths in the Phreatic Aquifer and the control areas in Kano and Jigawa States, there is evidence of modern recharge while the deeper formations, Middle and Lower Aquifers have depleted isotopic signatures of the stable isotopes, indicating recharge from a wetter and cooler phase that current climatic conditions.

Furthermore, the two aquifers show no significant contrast in their stable isotope compositions thus inferring a considerable degree of mixing (interconnectivity) of the two aquifers as amplified by Tritium Vs Oxygen-18 graph.

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The age of groundwater in both the Middle and Lower Aquifers (about 400m, 600m target depths, respectively) were determined by Carbon-14 dating to be about 37 ka BP, inferring minimal recharge to the aquifers. However, it could be possible that they may be receiving meteoric inputs but are old due to low velocities and long flow paths as it had been suggested that the Lower Aquifer receives recharge from its outcrop areas outside Nigeria while the Middle is recharged from far away control area SW of the basin.

This needs to be further investigated by collaborative studies by countries sharing the Chad Basin Aquifers.

The results of the project have been published in the September 2006 Edition of Science of the Total Environment (STOTEN).

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OBJECTIVES:

i. To determine hydrogeological parameters; define water quality problems which help to define the groundwater dynamics and response to climate change and human impact.

ii. To establish a capacity to identify, reduce and mitigate trans-boundary risks from changing land and water use and from climate change in the shared Iullemeden Aquifer System IAS), through establishment of a Consultation Mechanism for the Management of the IAS by Nigeria, Niger and Mali.

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The Iullemeden basin is located in the semi arid environments of the three contiguous countries – Nigeria, Niger and Mali. It covers an area of about 525,000km2 and consists of Sedimentary deposits.

In Nigeria where about 63,000km2 of it occurs, it is known as the SOKOTO BASIN and covers the States of Kebbi, Sokoto, Zamfara and parts of Katsina and lies between longitudes 3o40’E and 8oE and latitudes 10o30’N and 14oN.

The Iullemeden basin is a multi aquifer system referred to as the Iullemeden Aquifer System (IAS) with total exploitable groundwater reserves estimated at about 2000km2. The IAS represents one of the major freshwater reservoirs of West Africa.

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The principal aquifers of the Sokoto basin can be categorized into four distinct sedimentary sequence consisting, from west to east:

Tertiary Gwandu formation(Continental Terminal)

Tertiary Sokoto Group (Kalambaina and Dange formations);

Cretaceous Rima Group (Wurno, Dukamaje and Taloka formations) and

Gundumi-Ilo (Continental Intercalaire) formations (Upper Cretaceous/Jurrasic)

Aquifers of the Sokoto Basin are exploited at various locations within the basin, for domestic, irrigation, horticulture and animal husbandry.

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Observations: It is pertinent to note that though Nigeria participated in

Project RAF/8/038 alongside Niger and Mali, no isotope data were acquired in respect of the project. This was due mainly to communication problems with the IAEA at the time, with regards to where the water samples collected under the project would be forwarded for isotopic analysis.

However, isotope data obtained under the Wurno project in the Rima Hydrological basin, though less than 20% of the Iullemeden Basin in Nigeria (Sokoto Basin), have been discussed in Section 1.1 and are annexed to this report.

Hydrochemical data from boreholes, acquired under the project including baseline information on hydrology and hydrogeology in project area have also been collated and are attached.

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Activities under the project were undertaken by respective national teams with OSS serving as a facilitator for the project implementation.

The database and Geographic information system created have made it possible to represent the IAS in a mathematical model which shows that in 1995, the aquifer began to experience over exploitation with the year’s withdrawal estimated at 152million m3/year, exceeding the estimated annual recharge of 150million m3/year.

From the model, Nigeria accounts for over 60% of the abstraction. However, there is need to revisit this conclusion, in view of the fact that out of the 17,200 inventorized water points used for the modelling, only 2% (300 Nos.) were obtained from Nigeria while 94% (16,174 Nos.) were from Niger and 4% (740 Nos.) from Mali.

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The project was designed to investigate groundwater in parts of the South Eastern States of Nigeria where artesian flows had been recorded in boreholes drilled in the area.

In 2001, the Federal Government commenced a gigantic water supply augmentation scheme aimed at exploiting the artesian aquifers at the Oji River area and conveying the water to Enugu city, about 32km away, for municipal water supply.

The above was against the backdrop of inadequate information on the recharge, regional flow system, origin, age and hydrochemistry of the groundwater of the artesian aquifers.

The project was therefore initiated to evaluate the entire artesian belt in the region by applying isotope methods complemented by hydrochemistry with a view to proffering informed advice to water resources managers in the region on the viability of replicating the above scheme elsewhere within the region.

Establishment of Isotope Hydrology Laboratory was also part of the goals of the project.

1 No. sampling campaign was carried out and 33 water samples were collected.

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Isotope graph

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-5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0

TR

ITIU

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OXYGEN-18

TRITIUM VERSUS OXYGEN-18 FOR THE PROJECT AREA

AJALI FORMATION

NSUKKA FORMATION

SURFACE STREAMS

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Interpretation of isotope data confirmed that the groundwater was young and well recharged from precipitation, a situation supported by available hydrological information. The artesian aquifers were determined to be viable and therefore amenable to large scale exploitation.

Interconnectivity of the two main aquifers, the Ajali and Mamu geological formations were inferred from the interpretation of isotope data.

Though chemical results did not indicate any degradation in water quality, routine monitoring of the areas established to have high iron content in parts of Enugu and Anambra States including a holist water quality surveillance in the region, was recommended.

Indiscriminate sinking of boreholes was decried and the need for synergy among stakeholders in the exploitation of groundwater resources in the region was advocated.

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