GROUNDWATER RESOURCE IN WATER SUPPLY: General Context

1. GROUNDWATER RESOURCE IN WATER SUPPLY: LAGOS STATE CASE STUDYByPROFESSOR E.O. LONGE, PhDFACULTY OF ENGINEERINGDEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERINGUNIVERSITY OF LAGOSAKOKA, YABALAGOS, NIGERIA

2. GROUNDWATER RESOURCE IN WATER SUPPLY: General Context • High rate of urbanization contributed to increased water demand (Oteri and Atolagbe, 2003) • Continuous influx of people, increasing commercial & industrial activities, and management affects potable water supply • Lagos is the most urbanized and densely populated state in Nigeria (estimated population of 18m from only 3.6m in the early 80s) • Above leads to inability of the state Water Corporation to cope with demand • This situation has also led to unplanned/uncontrolled groundwater exploitation with siting of boreholes by both skilled and unskilled technicians with varying degree of success (Longe, 2010) Professor E.O. Longe

3. GROWING DEPENDENCE ON GROUNDWATER • Directly related to: economic development, social prosperity and environmental conservation, • Increasing dependence on groundwater resource is could also be • linked to climate change scenarios with increased frequency of surface water drought, with consequences on the reliability of urban water supply sources • Groundwater resources have better short-term security being less directly and rapidly affected by climatic variability • Groundwater development for water supply purposes either in the rural or urban centres in the state has not fully succeed due to widespread failure to implement adequate wellhead protection zones, identification and conservation of recharge areas Professor E.O. Longe

4. Water Resources Availability and Usage in Lagos State (Longe et al., 2008) Professor E.O. Longe

5. Capacity and Capacity Utilization of Water Supply Sources in Lagos State (Longe et al,. 2008) Professor E.O. Longe

6. GROUNDWATER QUANTITY ASSESSEMENT AND USEHydrogeology and Groundwater Resource Availability of groundwater resources in the state is constrained by hydrogeological setting with wide spatial variations: • The sub-surface geology and hydrogeology of Lagos metropolis and environs is well detailed (Longe et al., 1987, Longe, 2010). • The sub-surface geology indicates a complex lithology of alternating sequence of sand and clay deposits. • The most significant identified aquifer formation for water supply purposes in the state is the extensive Coastal Plain Sands Formation. • Three major aquifer horizons are known in Lagos, Ikeja, Agege, Badagry and Apapa(Longe et al., 1987). Professor E.O. Longe

7. Delineated of Aquifer Horizons in Lagos Metropolis (Longe et al., 1987) Aquifer Horizons 1st 2nd 3rd 1st is water table aquifer 2nd is confined aquifer 3rd is confined aquifer Professor E.O. Longe

8. Characteristics of Aquifers in Lagos (Longe et al., 1987, Longe & Kehinde, 2000, Longe, 2011) Professor E.O. Longe

9. Groundwater Resources Potentials and Development in Lagos State • Estimated groundwater yield: about 650, 000 m3/day (CoodBlizard, 1997). • Wells sited in the coastal aquifers especially in the Coastal Plain Sands are generally of high yields (Longe et al. 1987, Oteri and Atolagbe, 2003, Longe, 2011). • Noticeable contrasts in the transmissivity values of the multi-layered aquifer systems exist which depicts the heterogeneity of the water bearing zones • Existence of clay lenses and pockets of water bodies affect lateral continuity of the aquifer system • Pumping tests have revealed that well losses within the aquifers systems constitute significant portion of the total drawdown despite high well yields obtainable from the aquiferous zones (Longe, 2011) Professor E.O. Longe

10. Examples of Well Losses from Coastal Plain Sands (after Longe, 2011) T=Transmissivity, B=Formation loss coefficient, C= Well loss coefficient, Q=Discharge rate Causes of Well losses: Poor well completion & development Professor E.O. Longe

11. Groundwater Recharge and Discharge of Lagos Aquifer No record of recharge characteristics and recharge rate of aquifer systems in Lagos State. Knowledge of recharge volumes & the rate water is transmitted are needed to avoid over-exploitation &management of the resource Professor E.O. Longe

12. Managing processes of aquifer recharge Professor E.O. Longe

13. Groundwater-Related Environmental Concerns(Groundwater and the city) Professor E.O. Longe

14. Groundwater-Related Environmental Concerns(Highlights From Figure) • Inadequate Knowledge base of the resource • Increasing demand of the resource • Over-allocation and overuse • Threats to groundwater quality • Inter-aquifer contamination • Contamination • Saltwater Intrusion Professor E.O. Longe

15. Groundwater-Related Environmental Concerns(Some Highlights of Actions) • improve the skills of groundwater managers and users • Improve our knowledge of the resource • quantify how groundwater systems function and are affected by extraction • Determine sustainable extraction regimes for surface and groundwater systems. • Monitoring aquifers to detect problems early • Use of appropriate (e.g. strong, non-corrosive) materials in the construction of bores. • Ensure operations that avoid mixing aquifers of varying water quality • Maintaining bores while they are active • Decommissioning bores in the appropriate manner; and • Use only professionally licensed drillers who employ proper standards. Professor E.O. Longe

16. Groundwater Management(Highlights of Actions- Inventory) INVENTORY Professor E.O. Longe

17. Groundwater Management(Highlights of Actions: Allocation & Licensing) • The right to divert and use groundwater should be ascertained • The terms and conditions of the licence should be well stated with sole intention to protect the source • Category of users:- • Household user (has priority over others) • Traditional agriculture user • Licensee • Formal licensing be required from wells that supply: More than two households; Larger agriculture operations; Municipal users; Industrial users & Other major water users. Professor E.O. Longe

18. Groundwater Management(Highlights of Actions: Obtaining a License) Only by application for diversion and use of groundwater for purposes other than household or subsistence agriculture use Information required: • Location of well(s), existing or newly drilled • Anticipated depth interval that water will be taken from (depth to the aquifer) • Total quantity of water needed • Time frame for water use (year round or seasonal) • A yield test • A survey of nearby groundwater users Professor E.O. Longe

19. Groundwater Management(Highlights of Actions: Protection & Conservation) Protecting groundwater resources against overuse, mining and pollution should be an integral part of a holistic water management strategy • All licensed water well contractors must obtain an approval that authorizes them to drill water wells in the province. • Drilling standards and manual as well as for, constructing and reclaiming wells must be produced and should apply to all water wells, whether they are installed for temporary water supply or for long term use. Professor E.O. Longe

20. IN CONCLUSION While regulations and legislation go a long to way to protect our common groundwater resource, it is the users who have the greatest impact on the safety of its supply. We can no longer take for granted an unending supply of good quality groundwater. Groundwater must be managed, protected and conserved for future use I THANK YOU FOR YOUR ATTENTION Professor E.O. Longe