GROUNDWATER RESOURCE IN WATER SUPPLY: LAGOS STATE CASE STUDY By PROFESSOR E.O. LONGE, PhD FACULTY OF ENGINEERING DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING

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


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


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


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).


Delineated of Aquifer Horizons in Lagos Metropolis (Longe et al., 1987)Aquifer Horizons


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


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)


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


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


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


Groundwater-Related Environmental Concerns(Groundwater and the city)


Groundwater-Related Environmental Concerns(Highlights From Figure)


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)


• 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)


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)


• 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)


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)


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


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

Documents

GROUNDWATER RESOURCE IN WATER SUPPLY: LAGOS STATE CASE STUDY By PROFESSOR E.O. LONGE, PhD FACULTY OF ENGINEERING DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING