GROUNDWATER RESOURCE IN WATER SUPPLY: LAGOS STATE CASE STUDY
By
PROFESSOR E.O. LONGE, PhDFACULTY OF ENGINEERING
DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERINGUNIVERSITY OF LAGOS
AKOKA, YABALAGOS, NIGERIA
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
GROWING DEPENDENCE ON GROUNDWATER
i. Directly related to: economic development, social prosperity and environmental conservation,
ii. Increasing dependence on groundwater resource is could also be
iii.linked to climate change scenarios with increased frequency of surface water drought, with consequences on the reliability of urban water supply sources
iv. Groundwater resources have better short-term security being less directly and rapidly affected by climatic variability
v. 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
Water Resources Availability and Usage in Lagos State (Longe et al., 2008)
SURFACE WATER RESOURCE (Ml/day) GROUNDWATER RESOURCE (Ml/d)
SAFE YIELD
LSWC CAPACITY
LSWC USAGE
INSTALLED CAPACITY USAGE
DEVELOPED LSWC 140 21
OGUN RIVER 1,636 520 289 Others 60 60
OWO RIVER 54 18 7 Total 200 81
SUB-TOTAL 1,690 538 298 (3 x reserve)
UNDEVELOPED Existing Capacity = (5x reserve )
OSHUN RIVER 260 Potentials 450
YELWA RIVER 250 Total 650
OWORU SOLORO RIVER
180
AYE RIVER 110
SUB-TOTAL 800
TOTAL RESERVE 2,500
Professor E.O. Longe
Capacity and Capacity Utilization of Water Supply Sources in Lagos State (Longe et al,. 2008)
Professor E.O. Longe
TYPE OF WORK LOCATION CAPACITY(ML/D)
PRODUCTION CAPACITY(ML/D)
CAPACITY UTILIZATION %
Main Water Works with intake from Surface water
ADIYAN 315 170.1 54IJU 205 118.9 58ISHASI 18 7.4 41
SUB-TOTAL 538 296.4 55Mini-Water Works with intake from groundwater
IKOYI 10.8 2.5 23SAKA TINUBU 10.8 3.7 34APAPA 10.8 2.3 21SURULERE 10.8 0.6 6SHASHA 10.8 0.4 4SHOMOLU 10.8 1.8 17ISOLO-MUSHIN 13.5 2.0 15OTA-ONA/IKORODU
13.5 2.4 18
EPE 13.5 2.8 21BADAGRY 10.8 1.8 17VICTORIA ISLAND 4.5 0.5 11AJEGUNLE 4.5 0.0 0LEKKI 4.5 0.7 15ALAUSA 4.5 1.1 25IDIMU 4.5 0.0 0EREDO 4.5 0.9 21SUB-TOTAL 143.1 21.8 15TOTAL 681.1 318.3 47
GROUNDWATER QUANTITY ASSESSEMENT AND USEHydrogeology and Groundwater Resource
Availability of groundwater resources in the state is constrained by hydrogeological setting with wide spatial variations:
i.The sub-surface geology and hydrogeology of Lagos metropolis and environs is well detailed (Longe et al., 1987, Longe, 2010).
ii.The sub-surface geology indicates a complex lithology of alternating sequence of sand and clay deposits.
iii.The most significant identified aquifer formation for water supply purposes in the state is the extensive Coastal Plain Sands Formation.
iv.Three major aquifer horizons are known in Lagos, Ikeja, Agege, Badagry and Apapa (Longe et al., 1987).
Professor E.O. Longe
Delineated of Aquifer Horizons in Lagos Metropolis (Longe et al., 1987)Aquifer Horizons
Professor E.O. Longe
1st is water table aquifer 2nd is confined aquifer3rd is confined aquifer
1st
2nd
3rd
Characteristics of Aquifers in Lagos (Longe et al., 1987, Longe & Kehinde, 2000, Longe, 2011)
LOCATION AQUIFER HORIZON
AVERAGE DEPTH (M)
AVERAGE THICKNESS(M)
YIELD (M3/H)
SPECIFIC CAPACITY (M3/H/M)
TRANSMISSIVITY (M2/S X 10-3)
AGEGE 1 27 9 unknown unknown unknown 2 55 12 unproductive NA NA
3 72 26 54 52 1.5SHASHA 1 20 12 unknown NA NA 2 Non-existent - unproductive NA NA
3 100 38 71 3.71 2.8SHOMOLU 1 12 Variable (12) unknown unknown unknown 2 35 32 100 7.96 5.1 3 135 25 83 12.20 26AGUDA 1 27 16 unknown unknown unknown 2 20 20 unproductive NA NA
3 Variable (35) 27 97 28.6 59.3APAPA 1 2 20 unknown unknown unknown 2 40 30 Not tested Not tested Not tested 3 125 Variable (12m) 99 17 35BADAGRY 1 9 11 unknown unknown unknown 2 15 24 58 6.8 27 3 113 Variable (90-
180m)101 3.48 44
Professor E.O. Longe
Groundwater Resources Potentials and Development in Lagos State
Estimated groundwater yield: about 650, 000 m3/day (Cood Blizard, 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
Examples of Well Losses from Coastal Plain Sands (after Longe, 2011)
WELL NO
YIELD (M3/H)
SPECIFIC CAPACITY(M3/H/M)
T (M2/D)
B (H/M2)
C (H5/M5)
BQ(M)
CQ2
(M)% WELL
LOSS
1 100.4 9.9 414.74 0.0918 0.00009 9.1970 0.9073 8.98
2 63.3 6.3 224.64 0.1482 0.0002 9.3793 0.8011 7.86
3 62.1 32.3 2073.6 0.1373 0.0015 9.2032 0.7713 7.73
4 100 5.49 2332.8 0.1528 0.0004 15.2812 4.0001 20.75
5 78.3 6.93 2332.8 0.0689 0.0011 5.3949 6.7440 55.56
6 95.4 17.8 1555.2 0.055 0.00001 5.2470 0.0910 1.7
Professor E.O. Longe
T=Transmissivity, B=Formation loss coefficient, C= Well loss coefficient, Q=Discharge rate
Causes of Well losses: Poor well completion & development
Groundwater Recharge and Discharge of Lagos Aquifer
Professor E.O. Longe
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
Managing processes of aquifer recharge
Professor E.O. Longe
Groundwater-Related Environmental Concerns(Groundwater and the city)
Professor E.O. Longe
Groundwater-Related Environmental Concerns(Highlights From Figure)
Professor E.O. Longe
i. Inadequate Knowledge base of the resource
ii. Increasing demand of the resource
iii. Over-allocation and overuse
iv. Threats to groundwater quality
v. Inter-aquifer contamination
vi. Contamination
vii.Saltwater Intrusion
Groundwater-Related Environmental Concerns(Some Highlights of Actions)
Professor E.O. Longe
• 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.
Groundwater Management(Highlights of Actions- Inventory)
Professor E.O. Longe
INVENTORYHYDROGEOLOGICAL INFORMATION OTHER PERTINENT INFORMATION
Water well drillers’ reports Well owner’s name
Baseline water well testing reports Legal land location
Geophysical logs Driller’s name
Lithology Drilling date
Water quality data Well construction details
Intended water use
Water requirement
Groundwater Management(Highlights of Actions: Allocation & Licensing)
Professor E.O. Longe
• 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:- o Household user (has priority over others)o Traditional agriculture usero Licensee• Formal licensing be required from wells that supply:
More than two households; Larger agriculture operations;
Municipal users; Industrial users & Other major water users.
Groundwater Management(Highlights of Actions: Obtaining a License)
Professor E.O. Longe
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
Groundwater Management(Highlights of Actions: Protection & Conservation)
Professor E.O. Longe
Protecting groundwater resources against overuse, mining and pollution should be an integral part of a holistic water management strategy
i.All licensed water well contractors must obtain an approval that authorizes them to drill water wells in the province.
ii.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.
IN CONCLUSION
I THANK YOU FOR YOUR ATTENTION
Professor E.O. Longe
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