University of Nigeria Research Publications
OBIEFUNA, Gabriel Ikemefuna Author PG/MSc/88/6623 The Hydrogeology of Ogbunike Area and
Title Environs Anambra State, Nigeria
Physical Sciences Faculty
Geology Department
February, 1991
Date
Signature
THE HYDROGEOLOGY OF OGBUNIKE AREA AND ENVTRONS, ANAMBRA STATE, NIGESIA
OBIEFUNA, GABRIEL IKEMEFUNA, B.SC (lions), PG/~~c/88/6623
TkbESIS SUBMITTED TO THE DEPARTMENT GEOLOGY IN THE FACULTY OF PHYSICAL SCIENCES, UNIVERSITY OF NIGERIA, NSUW
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
FEBRUARY, 1 991 MR. GABRIEL IKEMEFUNA OBIEFUNA, a postgraduate student in the Department of Geology and with the
I(cgistra tion ;JcI,. PG/MSc/88/6623 has satisfactorily completed the requirements for course and research work
for the degree of Master of Science in Hydrogeology.
The work embodied in this thesis is original and
has not been submitted in part or full for any other
diploma or degree of this or any other university.
Dr. K.O. Uma Supervisor
Head of Department. DEDICATION
To all those who lost their lives
during the 30 months of Nigerian Civil war
(July 1967 - January, 1970). TABLE OF CONTENTS Page
CERTIFICATION
DEDICATION
ACKNOWLEDGEMENT me LISTOFTABLES .. vii
LIST OF FIGURES ee .. ix AUS'J? RACT .. xii
CHAPTER ONE: INTRODUCTION . . . 1 1.1 Statement of the Problem .. 1 1.2 Objectives and Scope .. .. 2 1.3 Methods of Investigation .. 3 1.4 Location and Extent .. .. 4 1.5 Literature Review/Previous Work .. 6
CHAPTER TWO: PHYSIOGRAPHY AND CLIMATE .. R 2.1 Physiography .. .. 8 2.2 Soil Type and Vegetation .. 9 2.3 Climate ...... 12 CtIAP'l'EH THREE: GENERAL GEOLOGY Z .. ?5
CI-IAPTEII FOUR : HYDROGEOLOGY .. 34 4.1 General Statements . .. 34 4.2 Hydrologic Balance Equation .. 35 4.3 Surface Water Resources .. .. 39 4.4 Groundwater ~esources .. .. - 40 4.4.1 Aquifer systems in the area .. 42 4 -4.2 Aquifer parameters or characteristics 4'7 4.4.3 Statistical and pumping-test methods $3 4.5 Specific Discharge and Average Linear velocity $81
ACKNOWLEDGEMENT
My sincere thanks are due to my supervisor Dr.
H.T. Ezeicjbo for his advice and guidance throughout the
duration of this study. I am equally grateful to Dr.
K.o, Uma for allowing me access to some of his papers.
'i'nc: author is also indebted to a number of colleagues who
kiridly contributed to the success of this study in
different ways: Dr. W. Bauhus of the Department of Geclogy and Paleontology, University of Muenster, Federal Republic
of Germany (F,K,G), for his lectures and fruitful
discussions; Mr. L.O. Mbelede and Mr. A.O. Igeh, bolh
i the Federal Ministry of Water Resources, Enugu, and
Fir. P.C. Nwabuqwu of the Anambra State Water Corporation,
c,~tlica inxb :;t:rvice Engineers, Enuqu, tor making available
zone materials from their libraries; Mr. Ben Anowo of
.hiit ,~,ul\,,.raS ta te I-linis try of Aqricul ture, Enuqu and Mr. J.C.
E~cdnyirnof the Federal Meteorological Station, Enugu, for
providing the meteorological data; Mr. E. Okoh (a chemist)
and MLss 8. Ife (a microbiologist) of the Anambra State
\later Corporation, Enugu, for their help during +,he chemical analysis. My sincere gratitude also goes to my
b '. '. parents, Mr. and Mrs. G.N.O. Obiefuna; my cousin, Mr.
Chris N. Obiefuna of ANAMMCO, Enugu and his wife Mrs. Tina 01-~iefunafor their moral and financial support, The moral support from my brother Mr. Raph Obiefuna (a civil engineer) and sisters Njideka, Chinwe and Ogechukwu are also gratefully acknowledged. My special thanks also go
to my colleagues including Mr. J.U. Agbo, Mr. Iboro
33rnas Udom and others for their contribution towards the
success of this work. I also thank Mr. C.E. Okoji for
t-ypirrg the nranuscript.
Finally, I am absolutely grateful to Almighty God
for sparing me through the difficulties and risks involved
in ttie iit:lci work of this magnitude. LIST OF TABLES T,,,blc Page
Monthly rainfall at Nkwelle-Ezunaka Farm 16 Meteorological data for the 1982/83 Water year ...... 17 Meteorological data for the 1983/84 water year ...... 1'8 Pleteorological data for the 1984/85 water year ...... 19 Meteorological data for the 1985/86 water yedr ...... 2 0 Meteorological data for the 1986/87 water year ...... 21 1 Meteorological data for the 1987/88 water yedr ...... 22 Meteorological data for the 1988/89 water year ...... 23 Potential evapotranspiration at Onitsha area (Nkwelle-Ezunaka) .. 24 Stratigraphic succession in Anambra basin 26 Uorchole and spring locations in the study dred w 49 Trdnsnlissivity values for the Na&gj Sandstone computed from pumping test analysis 53 ~ydrdu1i.cconduativi ty values for the Ib.j~lfkf.) aquifer system computed from pumping test analysis ...... 52 Pumping tcst data from the study area 55
Values of transmissivity (T) and hydraulic conductivity (K) from Logan's Approximation equation ...... 73 Hydraulic conductivity (K) values from statistical analyses of some sandstone samples of the Nanm ~md$fOfle .. 4% LIST OF TABLES CONTD. 'l'dble Page
Hydraulic head values calculated for boreholes around the area .. 86 Spccif ic capacity val ues for some boreholes around the area .. .. 9fl Summary of the various methods of hydro- geochemical analysis used in the study area 99 102
Geochemical analysis of water samples from the upper unconfined aquifer .. 117 Classification of the upper (unconfined) aquifer waters on the basis of their major ion percentages .. .. 132 Geuct~clnicalanalyses of water samples from surface water .. .. 136 Geochemical analyses of water samples irom boreholcs around the study area 738 Cldsslfication of borehole waters on the basis of their major ion percentages 755 Figure Page 1. Map of the study area showing access routes 5 3. Contour map of the study area showing major physiofi;raphic/topographic features Schematic cross-section of east of the study urea 2B Schematic cross-section of West of the study area
c3C Soven yccxs average prbecipitat ion at Nkwelle- Ezunaka farm meteorological station and seasonal variation in precipitation for 198?/83-1988/89 wuter years 3, Geologie map of the study urea
4. Strati(:rilphic section of Nanka studstone along kilometer 20 Onitsha-Enugu express road. 5 IJitholot.;ic lo~sfrom some boreholes mound the study ureu, 6A Correlation of some borehole litholo6;ic logs showing the nature of the clays, sandyclays and shale sequences, GB Diagram showing the &quifer cross-sect ions around the study urea. 7 Mup show in^ the location of boreholes around z the study area, 8 Map showing; locations of hand-dug wells, streams rivers wnd some springs in the study area 9 Map showing hydraulic head distribution and ~roundwuterflow direct ion in the upper hunconfined ) aquifer. 10 Masch and Denny (1966) curves
11 Map showing hydraulic head distribution and groundwater direction in the lower confined , aquifer areund the study area LIST OF FIGURES CONTD. F'i cjure Page
12. Distribution of pH values in the upper (unconfined aquifer .. .. 105 23. Distribution of alkalinity values in the upper ( unconfined ) aquifer .. 107 14. Distribution of chloride concentrations in the upper (unconfined) aquifer .. 1.09 15. Distribution of calcium concentrations in the upper (unconfined) aquifer .. 115 16. Stiff diagram for HW1 Ogbunike .. 1l8 17. Stiff didgram for HW2 Umunya .. 119 I8. Stiff diagram for HW3 Ogidi .. 1 20 . Stiff diagram for HW4 Nkwelle-Ezunaka 1-21 20 Stiff diagram for HW5 Nkwelle-Ezunaka 1.23
21 Stiff diagram for Nkisa-anya-akommiri spring, Oqbunike .. .. It 24 22 Stii-l- di,lqrarn for Ogba cave spring, Ogbunike 129
23 Stil-i- dicrcjrdrn for Nkisi-Osile Spring, Ogbunikc ...... 1 26 t 24.. Stirf diagram for Nwangene spring, Umunya I 27
25. Stiff didcjrim for Obiam spring, Nkwelle- Ezunaka ...... 128 26 Cla~:,ificationdiagram for anion and cation facies in terms of major ion percentages 129
2, Piper's trilinear diagram for the springs , and h~lntl-dug wells in the study area - 131
28, Map of p~ variations in the lower confined aquifer waters .. .. 14-0 LIST OF FIGURES CONTD. l*'i.(]i~rt?
Stiff diagram for Ogbunike Borehole (BH1)
Stiff diagram for Umunya borehole (BH4)
Stiff diagram for Umudioka borehole (BH10)
Stiff tliaqrsrn for Ogidi borehole (BH8
Stiff diagram for Onitsha borehole CBH~~)
Stif 1- didcjrain for Otuocha borehole (BH11)
Stif 1 diagram for Enugwu-Ukwu borehole (BH28 1150
S tii 1- diagram for Onitsha urban borchole (BH10) .. .. 153 Stiff diaqrarn for Umuoji borehole (BH27) 152
Pipc:rt:j trilinear diagram for boreholes around the study area .. 154
(xi AI3SlHACT 2 The study area which is about 175 km in areal extent is underlain by three geologic 'formajcions. These are the Zmo shale to the North, Nanka bandstone (Eocene) to the South und Ogwuuhi-Asubu lormution (~ligocene)to the South-West.
, The Imo Shale consists of thick@ shales, claystones, siltstones and lenses of' sandstone. The Nanka Bandstone is the main aquifer
of the :lr.ea. Its dominant lithology is poorl-y to moderately con~olidr~tedsuIldstone with some afternuting sequence bf clay-
shale und sandy clays. The Ogwashi-Asaba Formation consists of
silty sand, mudstone and lignite. Atmospheric precipitation ranges from &bout 1750mm to 2,000mm with an average of about 1850mm annut.&. About 15.@ of the atmospheric precipitation is lost
;I:; surftlct. runoff into the surface waters, 64.5% as evapotrans-
piration while tho rest (i.e. about 20.5) infiltrates into the
ground to rech;irgc the underlying aquifer. Three aquifer systems
are recognised. These are the upper (unconfined), .the middle (semi-conf incd to confined) and the lower {cohf ilhed) aquifer $ystems.
Y'he depth to water table' in the upper unconfined aquifer is generally less than 15 peters around the Northwest and increa&'cts from l5m to 2b eastwards. This upper aquifer which
is tripped by many hand-dug we1 1s discharges naturally us depression springs or cont~ctsppings where the underlying clays, b Bandy clays or shales cut across ground surgace especially in river vnl.leys. Ilydraulic conductivity (KD values for the upper unconfined I aquifer system det ern.ined from granulometric analysi s range
rrom 1.;'3 x 10-'' 1n/s to 2.40 x lov3 m/s with an average of about I x 0 . Very few boreholes nre tapping the middle sc~ui-confined to confined aquifer systeu. Hydraulic conductivity
(k) values for this quifer system determined fro~nLo;y&anls (1964) ;~gpror.imntionmethod indicate values ranging from 7.72 x low5 nl/c to 1.8 x lo-' m/s with an avnrn~-eof about 6.29 x 10-~m/s. -4 T~';UIrmis:;ivity (T) values range from 6.8 x 19 m2/5 to 5-51
7 x lo-' mL/s with nvrrnpe of about 5.00 x lo-? rn2/s. ;Cell yields in the lower confined aquifer system ranges from 3 :!Lout 5.75 nl /hr 061;bunike to fibout 2,/,3m3 /hr around Ogidi with an nvtlr;l:;e of about 128.38 m 3/hr. The drawdown v;ilues r,n&l;e
J'roln ').Om ;,round Ccbunike to 43.2m around 0~;idi. Values of
hyiir.:~ulic conductivity (k) calculated from pumping test methods
r:in,.;e f'ro~n?.57 x m/s to 1.26 x lom4 m/s with R mean avernp-e - r, of I x I I.Trnnsmissity (T) values r:ince from 1.62 x ' 3 I I.Iiydr:~uli c grndient is ubout 0.0024. This eives
~,~*bunc!wntervelocity of about 1,12.0 rn/ylq and specific discharge
03 :A .om which .i.s rbel:itively hi~h. All these indicate an agquifer 5;y st crr~ of y;encr;illy e,ood perf oruanc e . 't'hc Ilydr.o,,eoc:hewicnl studies indicccte tha?, the unconfined
~;rour:dwster and the lo..er confined roundwa water are slightly
acidic to nt~utr;lland have relatively l ow to moderate concmtration
of' di sgolv<>aonstitutent s. sodium (BE+) and calcium (ce2+) are the dominnnt c:i tyions for both groundwater theras chloride(c15
md' bicilr'lon:lte (HC( -) are the doniinarlt anions. Calcium-sodium 3 f :~cies nnd sodiur:l- calcium fncies are the tieminant cation fncies xiii for the upper unconfined groundwater whereas chloride- sulphate and chl bride- bicarbonate f-gcies and. chlori-de-sulphnte f acies the dominant, cation fuciea and anion facics for the lower conf'incti (~.roundw:!t;t.r, 'L1hese indiccitc thal- there !ace some sirnilathi t;ic:; -in hydro[:eochemistry between the ppper (unconfined) {';roundwater and the lower (confined) groundwater. Graundwater pollution is'not; sippificant for the deep confined groundwater bcctiust? o 1' ft;s relatively great depth of occurrence rind natural pollution attenuatktion mechanisms in operation. Howcver , the upper (unconfined) groundwater is susceptible to pol-lution becnuue of its relatively shallow depth of occursence,
Wu1,er qu:il i.1,~ol' thc s: tudy meu is pnc?rul ~l.ood for most purposes,
xiv CHAPTER ONE INTRODUCTION 1.1 Statement of the Problem
This work covers the hydrogeology of Ogbunike area and environs. The study area includes Ogbunike, Nkwelle-Ezunaka, parts of Umunya, Ogidi and Nkpor all in
Oyi and Idemili Local Government Areas of Anambre State, Nigeria. Thc areal expanse is about 175 km 2 . The population of all the communities within the study
area is at present estimated at around 150,000 and the figure is expected to approach 200,000 by the year 2,000.
The rapidly increasing population of the area and the
increasing rate of industrialization and urbanization will result in much greater pressures on the available
resources including water - and pollution of some kind ' may result if there is uncoordinated management.
A sound appraisal of the water resources of the area is
' therefore most desirable. Accurate determination of the b' b' availdble water resources is necessary for proper planning to ensure sustained and uninterrupted water supplies to the vdrious areas of need whether urban or rural. Where surface water is available, and groundwater exists at not too prohibitive a depth, as-in the study b area, groundwater development often appears more attractive. This is because of its convenient availability near the point of use, its good quality (which typically requires little or rlo tretitrnent,) and its relatively lower cost of development. The conjunctive use of both surface waber and groundwater
s11c:h :is throut1;h induced infiltration is an even more attractive option for maxirrlal non-harmful2 utilization of the water resources of the area as inferred from the hydrolithology.
1.2 OuJective r~nd Scope
The prim:~ryobjeative of this study is to make an
ilcce:;smcnt oC the groundwater resQource potentials . of Ogbunike and environs. .' This is one of the first attempts at making an assessment of p-oundwuter resources potentials of the area. In order to meet the above objectives, aquifer characteristic such :is depth to water table, aquifer thickness and areal extent have been tietcrbmined using hydrogeologic data for some boreholes md htqd-du(; we1l.s around wd within the area. Intientification of possible recharl-e and discharge areas us .well uguifl$* units ad types of aquifers have been carried out Aquifer parameters such as the hydraulic conductivity (K),
transmissivity (TI, specific capacity (SC), groundwater
velocity (V) and yield (Q) have been determined. The groundwater flow direction has also been determined
through water table elevation differences and not through
the use of tracers. I A study of the groundwater chemistry and the effects of 1 pollutants or contaminants on the groundwater quality has
also been made. The influence of groundwater and surface water on soil erosion or gullying processes in the study area has been evaluated. Finally, useful suggestions that will help in the . efficient management of the water resources in the area are highlighted.
1: 3 Methods of Investiqations This investigation was executed in three stages. 1 - The first stage involved Literature review and reconnais- sance trips during which topographic and geologic maps were employed in the identification of rock- formations and their structural as well as stratigraphic relationships.
The second stage involved detailed surface and subsurface
geologic and hydrogeologic studies, This included the L determination of storage potentials and discharge zones, collectict of water Bampl(?s from hand-dug wells, ntr.$calr~S, springs and deep bo~t!holc:; IT^ nwuourc ment of water levels in hand-dug wells.
Borehole lop;^ (lithologic and ~eophysical)pumping test data weye coll.ected from both the Anambra St ate water corporation, Enugu and the Federal Ministry of water Resoarces, Enugu. Piete :orologic& infor~tiationwas collected from both the Anumbra Stato Ministry of Agriculture, Enugu and the Federal Meteorol.o~icu1station, Emene, Enugu. The last stqe involved laboratory studies in which water samples were chemically analysed and granui-8rl~ei?kanalysis were carried out on Samples of aquifer materials,
1.4 T,oc~ltioriil~ld Extent of study area
The urea falls within the Anambra River basin and covers
fibout 1751un2 of territory that includes Ogbunike and environs. Z It is located between longitudes 06' 49'E and 06' 55'E and 1iitit;~rles06' O'f'N and 06' 15'N. It lies about l4Oh North of the gulf of Guinea and about 5km east of the Niger at the nearest points, The main access routes are the old Enugu-Onitsha ro~dand -the Emqy-Onitsha express road (Fig 1). The area is
b underlain by three g;eologic formations nmely the Imo Shale to $he Rorth the Nanka §andstone to the South and Ogtslnshi- Asuba Formation to the southwest.
1.5 Literature ~eview/~rey.iousWork
The Arneki %rm;ition was first described hy Wilson and Bain (1928), Tattm (1944), Du Preeze (1947), Jones (1948) and
Heyment ~nd13arber (1956) under the name Bende-Ameki Group.
Others such as white (1926), Grove (1951) and sirnpson (1954) described it under the Bende-Ameki series. This description included the Eocene Nanka Sands which was then regarded as a member of the heki Formation. Prom the study, It is found that these Nurku $mds in the study area ure largely consolidated, )a The auk@+ therefore feels that it should be called Nanka &,ndstone. It is underlain by Marine Imo Shale and overillain by li(yits-rich 0t;wnshi- Asaba Formation. Both the Lithology petrogrriphy :~ndenvironment of deposition of the formation have equal-ly becn extensively studied by a numbers of researchers. Heymcnt; (l965), Adegoke (1969) considered the formation to be lithologically heterogeneus and characterized by rapid
J fucies chnnge. R:~sed on the recognition of the following two litholo~ictlly,roups, the lower fine to medium to cearse grained sandstone with intercallations of calcareous shale and thin limestone and the upper with coarse cross-bedded shdstone with bi~ncisof fine k~;rainedsandstone md smdy cloy, as well as fossil
evidence, Heyment (1965) suggested a par* marine, par% 4 nonmarine to estuarine environment for the heki Formntion. Adegoke (1969) suggested that the sediments were deposited
in tl normal mmine environment bqsed on studies of avdailable fossil evidence, by short and stauble (1967) and Kobbe (1976) who described the type section:; of the formation. Orajaka (1975) regared the Nanka $ads as member of the Ameki Formation whereas Nwajide
(l(376) retr,;ircd the Nonka sands as the Later a1 equivalent of the iimeki Formation ;md suggested a formational status to it,
'l'hi:; was supl)or-ted Ogbuka~v(1980). Skoup and Co.Ltd (1978) conducted n pre-feasibility study of whole of Anambra basin in which they determined the runoff coefficient of the basin. Akujieze (1984) studied the hydrogeolo~pof the area south of the uppcr section of Idemili drainage basin. Part of the this area is unrlerluirl by tihe Nunka sands. Based on faunal and lith~bgical studies of Lhc Amcki Formation in its type Locality, Arua and liao (198'?) nut;tl:c?sted that the sediments war ddposited in a burrier rid,;e-1q;oonal complex to marine sediment s of intertidal n I bt%ones of the shel* enviropent s. Ezeicbo (1987) wrot c on t,htt qu:~lit;y of wuter remurccs of Anmbra Stute which ir~cludc:; t.11~study urea and described the vilrious probable mim aourccs and c:iuses of groundwater pollution. Mbanugo (1987) ,' wrote on the water resouces potentials of Cgidi area and environs in wl~ichhe recognised the occurence of Orthogonal block fault in some parts of the area. Fzema (1989) also described t;hc hydroy;eology of the Ok~;bunikearea and environs a.tlcl reco,mir;c?tl I,ht: existence of perched aquifer in the area.
6 CHAPTER TWO
2.1 Physioqraphy The study area is characterized by two types of landforms. It consists of undulating plain to the north (Nkwelle-Ezunaka and Umunya) and ridges sometimes with flat rounded tops to the south (Ogba Hills Ogbunike). The altitudinal range over the study area is from 30 m above mean sea level to the north of the study area to
a maximum of about 153 m to the south of the study area. These landforms are related to the rock types underlying the area and are products of differential erosion. The ridges are underlain by alternating sequence of fine-medium grained sandstone, sandy clays and shales of the NtUlF4 Scrrad~~fl&as shown by borehole lithologic logs. The main trend is to the north-south and have an average elevation of about 61 m above the mean sea level. These ridges which occur mainly around Ogbunike gradually flatten northwards into somewhat undulating plains which end up as a (steep) scarp slope towards Nkwelle-Ezunaka and Umunya. The low lying areas are underlain by poorly consolidated thin clays, sandy clays, shales and sometimes unconsolidated sands. -.
The undulating nature of the area may also be related to the degree of lateritization whereby the more laterite capped units stand out as ridges in the midst of more erodible rion-laterite capped units. In between the ridges and the undUlittin(: plains are vallegs of the Nkisi River and the
Ggi River :mii thcir tributaries (as shown in Fi(;s 2A and 2B).
'l'hese stremr: dissect the are:% from cast to west and while
FSkirji Iiiver uppetlrr; to show a trellis pqt 1 ern of drainafre, the 0 i River arid their tributaries display a dendritic pattern Y VoLLey of in.IVkisi River .r system which originates in
the neii;hbouring Ifite-Ukpo merges with the 0y;ba cave valley
::,y:;tr:rn to klle southwest of tho area. lYbanul:.o (1987) reported the occurrence of nearly OYthogonul block-fault which give rise to t;hc occurrcrlcc of horsts and steepsided hills, trou[:hS and valley
in t;he arcu. This cou1.d have controlled the eastwest flow of the Nkisi River.
,'
2. :hi 1 'l',:,pe :inti Veiy;ctution
'llhe soil type of the area is forrcilitic which are deep
porous brown soils and the red earth md acid sands, The soil profile varies from derived savanna (vegetation)
are3 where the rbed earth and acid sands predominate to
rainforest re:;ion where the deep porous brown soil is ab undant,
t ~NkisiRber 3 z aD V1 0 3 3 V, T 0
Nnakwueze Stream
-0belew1I1 St ream
f'CCL' Oyi River The soils are generally rich in free iron, have a low mineral reserve, low pH values (3.3 to 4.0) are deeply weathered and intensely leached, probably because of high annual rainfall recorded (1850 mrn mean annual preclpi- tation). The hill crests are covered with ferruginuous brass soils.
Usually the top 15 cm of soil is dark brown sandy loam. The fallow period ranges from two or three years in places to as long as seven or eight years in others,
However, the loss of organic matter as the fallow periods shorten and perhaps the washing out of finer particles
both help to cause soil ,deterioration especial1.y at
Nkwelle-Ezunaka farm and Is more marked in the vicinity of Umun ya . The study area is one of the major agricultural
areas of the state. Plajor crops cultivated include yam,
cassava, grown mainly in the plains and lowlands of
4 '~rnunya. Maize is cultivated mainly in sandy soils and new cocoyam (Colocasia antiauorum) thrives very well in the area because of the high rainfall totala (Grove, 19511, The study area falls within the humid tropical Rainforest
region of Nigeri\.<. The annual rainfall is in excess of 1850' mm. The natural vegetation is undoubtedly Rainforest
type but thls has been replaced by Savanna form of vegetation with clumps of trees especially to he south of the study area (Ogbunike and parts of Ogidi) due to agricultural ac.tivities such as bush burning, and shifting
cultivation (Igbozurike, 1975). However, relics of the original tropical Rainforest type are still found to be concentrated in the river valleys (Nkisi and Ori River
valley systems. and their tributaries) and the great
dapression hoirvirig the Ogbunika cave. They are marked by frequenk occurrence of Indian bamboo trees, oil palm (Elaeis quineensis) which are also very common in the area, The oil palms are usually very tell sometimes ' reaching more than 40-50 metres in height.
2.3 Cli.mii te There are two distinct climatic ..msons, both of
which are warm, The wet season generally occurs from
April to October while the dry season generally besins ,in November and ends in March. These seasonal climatic , conditions are caused by the north-south fluctuations
of a zone of discontinuity between the dry continental airmass and the humid maritime Atlantic airmass (Gamier,
1367). At the surface it forms a boundary called a surface of discontinuity whlch lies further south during dry season showing a southward move~nentof winds and
,pressures from the high pressure zones of the Sahara. During the rulny sunnon the front of discontinuity moves northwards. The sahara air causes the dry aeaeon which is accompanied by low humidity 36.4 to 74.38 and intense aridity that makes the atmosphere very dusty, Temperature
goes low during the harrnatten sbbseason and may be aa low as 17.6O~to 25.6'~ but may be as high as 36.2'~.
Tlru rulny crualon f01$owa the advsnoing hklan tic marl Cima air which la accompanied by high humidity 78 to 89 and
intense rains and high vapour pressure (29.79).
Peak rainfalls occur during the months of June to
September. There is character1stl.c "August break1' lasting
dbout 2 weeks in which the rains more or less cease. This
occurs during the rnonthv of August but may extend to early
September. Tables 1 and 2A-2G show the mcteoroloqical
data obtained at Nkwelle-Ezunaka farm and Oni tsha meteoro-
logiddl stations. The rainfall data covering the period
1982-1988 gave an annual average rainfall of 176% mm
(ab6ut 68 inches). Figure 2C shows the seasonal variation in precipitation for the 1982/83 - 1988/89 water years. ,T~Qfigure indicates that the combined average preciplta- tion of 1761 mm could be attributed to excusslire rainfall
in months of July and September. The months of July and
Septemberb are comnlonly also the wettest months iq the at~~dy area. The annual average rainfall of 1761 mm is however sonrcwhdt lower thcln the Incan annudl rainfall value of 1850 rnm for the study urea. The mean annual temperature is about 33'~ whcrcas the mean annual humidity is 77.56. Sun~liinchours rdngc from 1.4 in August to 7.8 in December.
The potmtial evapotranspiration for the study area was cstimdted from data measured at Onitsha (Table 3).
Thc temperd ture was, however, measured at Nkwelle-Ezunaka meteorologiccll station. The mean daily potential evapo- transpiration is about 4.5 mrn/day. The effective or the actual cvdpotranupirdkion is tdkw to he about seventy per cent of the potential cvapotrilnspiratlon giving a value of 3.1 mm/day. Tablc ,I: Mon till y Itsinfall (mm) of Nkwel It?-Ezunaka Fdrm tiainguage Station ( Data f rorn Anambra S td te Mi rd. s try of Agrlcul ture, Enugu )
.I) - - 1382/03 .383/84 1984/85 1985/86 1986/87 .987/88 198R/83 Months Watcr Water Water Water Water Water Water Yk!dl.. Year Yedr Year Year Year Year
_1 Apri'L '1I C3 .E3 14.9 136.1 102.5 52.0 May 302.2 190.8 376-7 298.6 143.7
June 269.1 646.8 268.2 103-6 197.9 July 1 334.2 315.3 244.0 300.8 460.8 109.9 199.6 159.3 209.2 272.0 272.3 335.7 600.2 149.3 135.2 278.4 170.1 November I 1a.s 40.6 40.3 36.8 20.0 December I 0.00 0.0 0.0 0.2 48.8 0.0 90.1 0.0 0.0 0.0 0.0 34 .5 0.0 March 106.5 78-7 27.7 13.7
Total 1752.2 -- Table 2A: Meteorological Data fzr the 1982/83 'dater Year
kpr. June Jan.
34.1
23.2 P8.6!
Relative Huziidity (%I 77.6:
Vapour Prsssure (mb) 29.5'
Piche Evaporation (mm) 3.3
Sunshine Hours (nrs) 6.5
Dew Point Temp. (OC) 23.7i
Kean Wind Ran (km) 0 Piean Temperature ( C)
Relative Hmidity (X) Vapour Pressur (rb)
Table 29: Neteoraloqical Data for the 1985/85 Water Year
Apr. kug. Dec . -Jan. 1Peb. i-kar Ksxixua Ter~erakure('c) 32.9 35.7 33.0 34.0
Kininurn Tenperature (OC) 23.51 s*. 7 20.8 21-4 0 Kean Tenper~ture( C) 28 26.7 25.9
Relative Hunidity (XI 76.6 89.63 61.50 69-39
Vapour Pressure (mb) 29.46 27-89 21.11 25-28
Fiche Evaporation (nv) 3-1 1.5 5-5 3-2
Sunshine Hotrs (hrs) 5.9 3-9 5.3 5.9
Dew Point Teisp. (OC) 23-75 17.68 20.81
Mean Wind Run (kz) 76.43 59.43 56.56
- .-
C\I ~r \-I Ill U', U3 U) CO a', O r*.*.* $1 b cO I,--) q rn Ln ['J N N r.1 cfJ +; Ln o', w rt' 10 ('J M O.\ 03 03 Y) Q3 . . 1 . b OIn~POu, r*) r Cy to N hl Ln U, I-' I-' P IU rw W (3 .b Ch V1 .-4 .W .ci, I.' .U1 01 0 C.) 0 0 T~lblc3: Potential evapotranspiration of Oni tsha ( UIIF t; rr~rn/d;ly ) calculated from meteorologlce\l datd qlven in Table 2 using Tliornthwaitegs formulLi.
.*. PET - lG1OO(-y--'OTi la mm/mon th
0 wilere T i .; rrrc_ian monthly temperature (in C) X - heat index for 12 months of the year
. IJET = Potential evapotranspiration
Jdn. Fc:\). Mar. Apri 1 May June 3.27 !>. 3 0 4.81 4.30 4.59 4.37 July Aug . Sept . Oct. Nov. Dec.
t 3.80 4 59 4.48 4.52 4.72 4.56 G ENE3AL GEOLOGY
The :;t,udy nr8eu lice within the Anrunbru drainage baain whose rock:] r-rinry;efrom upper cretaceous to Hecent in age.
'I'ht? iiictiuccsssion in the bdkn is ahown in Table 4
'L'hree ~~;co.l.o~l;$c'form~tions~outcrop in the area. These are IIIIOSha1.e (&ileoccne ) the Nanka &undstone (Eocene) and the
0i;wushi-Asabu Formation (Oligocene). The Irno Shale underlies the Nanka $andstone and has ty-p locality &rq; Imo River between Umuahia and Okigwe where it h a thickness of about 500 meters. It consists predominatly of thick dark to bluish-grey shales, claystones, calc mudstones,
silt:;t,oncs, ironstonus and lenses of smdstonc. The shales a
Si:;r,ile :md occrtsionr~llyinterbedded with sandstone intercull.
16 tl.~vc:-;rise to ;~quifer-a~uikaredsystems of local significa
'L'he A;~l.e:; occur Lowcircis the Northern portion of the study ar constitutes up to 3576 of the study area. It is dotted with ,' sandstone ridges. The Nanka sandstone was deposited during the regressi-on of the sea in the Eocene (~eyment,1965). It i considered to be the laterlal equivalent of the Ameki Bormati
(Nwrijidc, 19'/9 dk;bukaGu 1980). It underlies about 60% of the study area, !he 0p;washi-Asaba Formation underlies less than b percent of the area. It occurs towards the Southwestern port and consists of a sequence of silty sand, mudstone and lignit 26
Table 4: Stratigraphic Succession in the Anambra Basin (~oiue,1976).
Formations Lithology I Miocene Benin Formation Medi urn-coarse Recent grained, poorly consolidated sands with clay lenses Tortiary strinqess Oligocsna - Ogwashi Asaba UnconsolFdatad sands Miacena t'clrrncs t 1an with liqnite seams Eocene Ameki Formation Grey clayey sandstone Nanka &nds and sandy claystones Paleocene Imo $hale Laminated clayey shales
(Nqukka Formatior Sandstones inter- Upper calating with shales Cre tace- Poorly ~consolldated OUS sandstone, typically crosa bedded with minor clay layers
Lower Shales, sandstones,. Mudstones and coal seams
.C 20 occured alon~;the Enugu- ogbudker* (i~~mcdintelyacross the
a). It is heavily ftiulted and varies bLL,,fi,,,,s front 30 m-50m. The averege dip is about 12' in the southwest ern direction area. b The Nctnka sandstone in the ayea is generally fine-medium
/'- oc c:,ci ~~:illy c or~r fie-grained o r evcn pelbly. Ther are inter- cnl.l.ation of clays, sandy-cla ys and ahales. The clays are 1 very filnstic, 1it:ht grey, and unfoosilifcrous whereas the shales f- are fi ssile hic;hly micaceous, gypsiferous ~ndcarbocncecus.
Outcrops of the Nanlcn S,mdr;tone in the atudy area occur .?lonrr, Nkisi !liver vnlley (location G3) near the h c C,cbun ike-Urn( lnya rand about 4kn from Oye-olise market. - Ii ere a thick sec~uence of cloys, sandy-clay and &illaceous f ine-medium pnined, slightly micaceous, grey sandstone are ovcrlnin by considerable thicknars of red earth overburden. At the base of the foot of the deeply incised valley d beziue:; the hi.11~housins the O~buuikec:~ve popularly known as
Ogbn hills found behind st. Monica's College (location GI), outcrops .of thick moderately consolidated, hi.ghly micnceous,
slic.htly fractur cd, f ine-medium grained sandstone are seen. .- Outcrops of the sandstone which have thin clsiy concretions are seen at 'the root of the c!lve, Thickness of 'this s~ndstone varies froa 5n; to pore than 25m. It is underlain by laterite
whi,ch h-0 D tkimbnnn- nC about 3Om.
niri stream valley (locntion G2). located about 2km west of St. Monica's College (east of Ogbunike town) an outcrop of the same line-medium micaceous, moderately consolidated smdstone unit is sea. It is about 25m thick micaceous und underl~inby well laminated hi~lhlyphale,with intercallations . of micucaas silstone. The shiile is about 5m thick from the
0th~~unb;tu of the for~nritionoutc~~opping in the area ure
to ,?Om of 1:lLcritcs :Ire underlain by :);rcyplastic cl.ay.
At the confluence of Nwangene and Edemdbo streams
(locill, i cln (;>) in Umun~uun illternatinr;; sequence of clriys, hifr;hly me weal;hered and ferru~anishedsandstone md sandy ~lays~overlain by about 40 meters bf laterite overburden. Around km 20 along stratigrapb-ic section ~onsistingof an (alternating) sequence of
mediurm [yaincd c:mdstone (about lorn thick) and 15 meters ~f ' Laterite ;overburden was observed. This section is,illustrated
in P'i,; 4. doni; Onitshu-Nsukka road (i.e. hdani read, near
,Ukwelle-.Lxun;ika oil palm mills) a sequence consistine of c~:o:;s-beddd sandstone, siltstone, clays and laterite overburden
war: rcen. 'i'h~sirndstone is fine-medium grained, weathered and ferrugunized. It {~radesinto siltsize particles in Some l.ocations. The thickness. of this sandstone is about 4Om.
The avpriql;tt dip of beds of !.he Nanka sandstone in the i.crea range
t'~mci lPO to 1/1° in the southwcot direction. I'hin section study of some of the sandstone simples
(s:m!.lc loci.ct;io~lr;GI, G2, G7,, qnd ~5)indricute presence of qu:lrtz, orI,hoclr~~:e,Biotite und muscovite. The quartz which
make up at)out; 5J076 of the grains :;how preponde~nnceofl , , It
monocryst a11 ine quartz over the pol.ycryst alline ones. The
quurt 7, ~IT'C::; 1;rained and show undul ose extinction. Thc feldspars ctuy -. are currently actively being wetithered to . ' . The study also intl icator-. the presence of' vt~riableambunt of rock f r.niTrncnt.
Cc;l~~c-~ntirl~l;rn;~t,t.~:.i qils consist;:: of cl:iy:; and ironoxide. The rock
'l'h(: :;;~nd::torieunits of t;ho ;trt:u constitute t;hc uquifcr
I r ti w 1 A: ! h sandy clays creut e semi-conf ining condition
(:.iquit u~d:;):loci tihe clays and shales confining condition
(acluicludc*u). At points where the aquitards or aquicludes are exposed at ;!;round surfage springs issue above them that yeild :;ma1 l but, sil;ni ficunt qumt it ies of water.
St I%;(1 :L l of1::; f'rorn some of' tho borehol es mound tho :~reaare
ilI i. 5. Extunintition of tht.:;e 1otl;s rbeveril thiit
,t:hc. :;;lncl:-Lone: :ire m:iinl y fine-medium ained but are occasionally
co::rb::c (l;r*;rilic:tl c:;p(?~i.tillytow~irils th~ web.t rmd south of the
creation of artesian to sub-crrtesim conditions. The fence dia~rans(YiC;. 6) reveal that the thickness of these
artl;il?aceour; runits vary from 8m to 24m. - Lateri te
Cross - bedded Sands tone
Silt sto ne Medium- grnined Sandstone
Fig. 4 'Stratigraphic section of the s along- kilometer 20 Onitsha- Enugu Express Road (Sample Location A G6) .
CHAPTER FOUR I HY DROGEOLOGY I 4.1 General Statemen to
Hydrogeology is the study of groundwater. The study encompasses ita mode of occurrence, migration or how it moves, and ~torege. The quality is alao studisd end ita ralationrhip to the g~ologicenviconmsnt,
1 This chapter diccuaaes the mode of occurrence of 1 I groundwater including springs. Because of hydraulic connection between groundwater and surface water of an 1 area and the importance of surface water resources in 1 the overall water resources management and development in an area, the surface water resources of the study area are also discussed.
Determination of aquifer types and aquifer
parameters such as hydraulic conductivity (K), . 1 transmissivity, (TI and discharge (Q) of the .upper ( ) Z unconfined aquifer were made. The geochemical constitutents of surface and ground- I water samples taken from rivers, springs, hand-dug 1 1 wells and existing boreholes were analysed, Identifi- cation of recharge and discharge areas, the deter-
mination of groundwater velocities and groundwater flow directions were also made. Figures 7 and 8 show the locations of boreholes, hand-dug wells, springs and streams in and around the study area. These are outlined in Table 5.
4.2 The Hydrologic Balance Equation
The ge~ieriilizedhydrf'ologic equilibrium equation which is given below expresses a balance between the total water gains and losses within a basin for a period of time usually a mean water year. It takes into account of all waters whether surface or subsurface applied to and lost from a particular container, basin, area or type of surface. In the study area precipitation is overwhelmingly in thebform of rainfall (dew is insig- nificant) and this rainfall is lost mainly by eyapo- transpiration, surface runoff, and infiltration occurs only after the soil moisture deficit: is met. The generalized hydrologic balance or equi 1ibri urn equation is therefore given as follows: d P=I+R+E 4.1 where,
P = Precipitation I Infiltration
R E Surface runoff
E = Evapotranspiration.
Even though the above equation 4.1 is essential in evaluating the water losses and water gains in a particular basin, area or type of surface, it is an approximate equation. A number of problems bedevil it. Some of these problems include paucity of guaging stations for measuring stream run-off, absence of rating curves for evaluating the-stream discharge and paucity of lysimeters for measuring evapotranspiration. Even where available, lysimeter operations are very costly and painstaking and sometimes disturb the natural soil regime thereby producing results that are not quite accurate. Except for precipitation, all other parameters have been calculated from empirical equations, This is because such parameters as infiltration, runoff and evapotranspira- tion were not measured for the study area by the Meteoro- logical station involved. Meinzer (19421, Ward (19751, Tcdd (1980) and Wilson (1984) discussed some of the methods
,employed in measuring meteorological/hydrological parameters and problems likely to be encountered when measuring the parameters ~~nderfield conditions, Precipitation is defined as all forms of atmospheric . . moisture deposited on the ground (Rodda etz.,1976). It includes drizzles, rain, snow,dew, etc. The meteoro- b logical data from the Nkwelle-Ezunaka farm station in Table 1 show the rainfall 'data for the study area,
The mean annual rainfall is about 1850 mm, For the whole 2 study area of 175 km , the amount of water available from precipitation (rainfall) was thus computed as 3.24 x 108 m 3 a year. Runoff is the component of the precipitation that occurs as overland flow, Surface runoff can be evaluated empirically by mians of the rational formule which rclertw. rainfall rind runoff, Veisman (1972) gave the rational formula sar
Q .I C0RI.A where, 3 Q Peak discharge in m /year or surface runoff
C = Runoff coefficient (this depends on the character~isticsof the drainage basin)
RI a Rainfall intensity in rnm/hr 2 A a Catchment area in km . The basin under consideration is Anambra drainage basin. Skoup (1978) on the basis of baseflow of 15 mm ' per month calculated for the basin, showed that the average runoff coefficient for the basin is 44% (0.44).
The rainfall intensity calculated for the study area which 2 has a catchment area of 175 km is about 0.63 mm/hr.
Applying equation (4.2) the peak discharge (or the 7 3 runoff) for the study area will be 4.85 x 10 m per year or some 15% of the atmospheric precipitatiqn. Values of potential evapotranspiration were caJculated from Thornthwai tels formula from the mean monthly temperature given in Table 2.
Table 3 gives the potential evapotranspiration. The actual evapotranspiration in the study area is taken to be 70% of the potential evapotranspiration ( Hamil and Bell, 1986). The actual evapotranspiration is then given as about 1294.0 mi per year which represents about 64.5% of the atmospheric precipitation. Infiltration, I, which represents the amount of water that infiltrated down the water table to recharge the underlying aquifer is calculated using the water balance approach.
The water balance approgch used in the calculation is given by equation 4.3 below as
where,
The high value of infiltration means that the area has high storage potentials. Precipitation during the
first few months will be lost largely to evapotranspiration
effects whereas the rest will tend to increase the soil
moisture capacity. After the soil moisture capacity ia met infiltration procaeds, Infiltration will continue until infiltration capacity ia attained, then eurface
ponding commences followed by overland flow to the - nearest channel. The runoff is thus increased especially during the later part of the rainy season when the soil moisture capacity is largely met. Also the water table ris~vresulting in increased pore water pressure, and increased effective stress, This will result in increased erosion rate,
4.3 Surface Wa tcr Resources Surface water in the area include the Oyi River
and its major tributaries such as Rivers Kpokili and Nengo and Nkisi river and its major tributary, the Nnakweaestream. These rivers mainly flow over the faCccan~ I~MCSh& z~mwkhm, They are fed by perennial streams and springs and are thus ,' subject to relatively small seasonal water level fluctua- tions and discharge, Contributions from b~sefloware therefore significant. For example, the Nengo river is fed by Nwangene and Edemabo streams which take their
rise from a spring discharging at the contact between
ferrugunized sandstone and clay units within the area ( ulnunya 1 . The Oyl River is a major tributary of the Anarnbrd River. It rises from the neighbourhood of Ukpo-Akpu
in the NJikoka Local Government Area of Anambra State and flows northwards before taking a westerly course
until it joins the Anarribrn River south of Nsugbe. It
itr presently not guaged even though it drains a large area. It followed a dendritic drainage pattern through-
out the study area.
The Nkisi River drains a smaller area than the Oyi RLver. It rises from the neighbourhood of Ogbunike
town and takes a westerly course until it joins the River Niyer at onitsha. It has a trellis drainage pattern. Some springs resulting from groundwater seepage occur at some points along the Nkisi River
vall.ey. These springs usually occur where the permeable
layers are brought into contact with the less permeable lclyer~ ! .
4.4 Croilndwa ter Resources
Evaluation of groundwater resources of any area requires accurate knowledge of hydrogeological para- meters such as hydraulic cmductivi ty (K), trans- b nlissivi ty (T) , hydraulic head (HI and ~pccific capacity (sC). This could be achieved that reliable data on such parameters are kept, Geophysical invustiqatlons to locate'the appropriate site tu locate two more boreholes at Umunya and Nkwelle-Ezunaka have
been carried out at the time of the present investigation.
Efforts made ta get the results of the investigation proved abortive as these data are being jealously guarded by the involved agencies. Borehols lithologic logs for the existing boreholes in the two communities as well as boreholes belonging to private individuals were not collected for tho same reasons.
Hence, only data from the water agencies liated in
the introductory chapter were used. An examination of
some of these borehole 'lithologic logs reveal the following problems and anomalies:
(1) The actual locations and elevations of the boreholes were not given in some records whereas in others only the name of the town was given.
, (2 Dcuct'iption of lithologic units encountered durlng drilllng by the driller was sometimes
rnuddlcd up or inaccurdtely described. Sometimes *lithologic logs were not prepared or kept for all - the existing boreholes. (3) No effort was made to regularly monitor water 6 levels and yield of the boreholes.
'(4) The records showed that water chemistry was
not analysed for all of tho boreholes. (5) The state of the exlsting records and the methods of data storage and analyses were generally poor.
(6) Not much borchole data from the study area were collected, so borehole data from locations few kilometres ot~tsidethe study area were used to
better wderstand the hydrolithology of the study area and groundwater flow directions.
4.4.1 Aquifer Systems in the Area The N(lflk2 94pdSt0~6consists of poorly to moderately conuoliddtcd fine-medium grained sandstone with some alternating sequence of clay-shales, silty clays and
clayey sands. The fine to medium sand units form the
aquifers whereas the silty clays and clayey s-.ids constitute semi-confining media (aquitards) , and the clay-shales confi,ning media (aquicludes1.
h B~~sedon available borehole lithologlc logs three aquifer systems have been identified. These include the upper unconfined, tho middle semi-confined to confined,
and the lower confined aquifer systems.
The upper unconfined zone extends throughout the study
area. Depth to the water table here as obtained from b hand-dug wells range from less than 15 m to the west
around Nkwelle-Ezunaka to from 15 m to 24 m eastwards around Ogbunike and ~munya. Thus groundwater is encountered at shallower levels toward the west. Litholoqlcally, the upper unconfined aquifer consists
of pcrmedblu fine-medium grained sands overlain by laterites and/or red earth. They are underlain by impermeable shale clays.and semi permeable sandy clays. Sometimes these units cut across sloping ground surface created by, for example, deep river valleys, depression of Ogbunike cave, etc., resulting in springs. Some springs
occur in the study area, some of which are listed in
Table 5. Borehole lithologic logs reveal that the depth to the base of the unconfined aquifer varies from 21 m to 24 m
around Onitsha and Ogidi and from 40 m to 45 in at Otuocha and Oybunike. This base is made up of clay-
shales and sandy clays.
J The semi-confined to confined aquifer system consists of thick fine-medium grained sands which some- times grade even into clayey sands. The thickness varies from 15 rn around Ogbunike to more than 45 m around Ogidi.
Depths to the middle semi-confined to confined aquifer
raqge from about 30 m to 32 m around Otuocha and Onitsha to more than 55 m around Ogbunike and Oyidi.
~levath in Meters + Elevation in Meters - B;F%?y-.. .-. \ -Anambsa R.
Elevation in Feet --t
\ lowe aquifer systel s of
f ine-medium t:ruJ.rleu ~~UUUS. AU~: ~ondunits are sometimes intcrlnyered with thin clay bnnds, They are confined (above) - mtiinly by :;hr#le;:, cl:~yu,und sandy @Iriys. This aquifer syetem is confincd uround Ogbunike and west of Ogbunike while
semi-conf inin:< 'COTI~~~~O~Sprobably exists south, and eost of 01:bunike. The perne.t;rated thrEc&ness of this aquifer varies bct;wcn l5m ;ind 75m with an rlvorql:e thickness of nbout 45m. ;h to the lower confined iiquifer varies f'mm less than Wrn around Onitsha to more thun 180m around Ogidi. Neither the Imo shale nor the Ogwashi-Asaba Formation
cant-ribu tcs !.;i~nificantl.yto the hydroeconomy of the area,
'i
kqpf fcr parameters can be determined by e4+"-- r LEGENO. Roods x~r - 0 '5Clllmlrnl & fiiwSr% and Slrmrna Uoreholc ,IIKXI 1 tlJ I 'hhwq tjorcholc locallons around the study urea Scale b L EGEND WMain Road ~wl~and-dug Wells I . - I 0 Settlement ASPspring *stream and ~iver -/&f3ridge 4 - ~i~.8: ~apshowing locatioh of Streams and ~iversHand- dug Wells r and some Springs in the Study area . , - 3V
Tablc 5: Borchole and Spring Locations Around the Study Area
orehole ocal Location umber Ogbunike l0t.63 Ogbuni ke ,Hi574
Ogbuni ke 4/62 Umunya 3 Ogidi 1H30 Ogidi 1H31 Ogidi lH28 Ogidi 3 ewly drilled Ifi ~t yet te-Ukpo lHLOT6 2 ~mmissioned Umudioka ? ewly drillel Otuocha bHLOT61 - Abatetc 1HLOT64 - Onitsha 3H2641 - Onitsha 3H3134 Oni tshd 3H3143 Oni tsha 3H2365 Onitsha 3H2810 Oni tsha 3H2642 Oni tsha 3H3105 Oni tsha BH7 Onitsha BH12 Oni tsha BH20
Nkwellc- 3 Ezunaka Umuo j i BH2197 Umuo j i BH2927 - lewly Enugwu-Ukw~ 3 :omrnissioned Obosi BHll Obosi BH3477 Alor BH2804 Nnobi BH2935 Nando ? Table 6. Hydraulic Conductivity Values (Lower Confined aquifer system of the NctnkQ aquifer system) Computed from Pumping Test Analysis
Borehole Borehole Recovery Cooper- Logan's S/N Location local project Jacobo$ ~(mh-1) Number Number K(mh-i) ~(mh-1) ,;i----BH LOT 63 1 BH LOT 62 9
BH LOT 61 11 4 1 Abatete BHLOT64 12 Table 7: Transmissivity Values (for the Lower Confined Aquifer of the N4nla Aquifer System) Computed from Pumping Test Analysis - I Borehole lorehole Recovery Cooper- Logan s Satu- ~ocation( local ,reject Method Jacob's Yet god rated lumber ~(m~/hr)Method r(m /hr) thick- T( m2/hr: less :in netres Ogbunike ( BHLOT63 Se90 15-81 Ifite- B HLOT6 2 0-36 15 Ot uoc ha I BHLOTG1 18.86 16 30 Abatete I BHLOT64 3-91 15 pumping tests or statistical methods. Statistical methods which provide points values of hydrogeological parameters are based on grain-size properties of the aquifer and is found to be economical and best suited for unconsolidated formations. The statistical grain- size methods include those of Hazen (18931, Harleman --et al. (l963), Masch and Denny (1966) and Uma --et a1 (1989). The methods which will be discussed later in this paper were widely used in the evaluation of aquifer parameters. Sieve analyses and other borehole data employed in the computations are in the appendices. Pumping test method provides situ values rcprescntative of a large aquifer volume and generally gives more reliable result. It is however limited by its high cost and also as a result of the fact that the assumptions under which the pumping test method
are based do not often fit field conditions. It is,
however, better than the existing statistical methods because it is more dependent on the geometry and
hydraulic boundaries of the aquifer. The pumping test methods employed in the determination of aquifer parameters are the Cooper and Jacobs (1946)
Method, Recovery techniques, and the Logan's (1964 )
Approximation Method. Pumping test data obtained for five boreholes tapping the lower confined aquifer of the sandy aquifers of the e\LanKQ Sandstone were used in the evaluation of the aquifer parameters. The data which are shown in Table 8 reveals a good time-drawdown measurement.
Logan's (1964) Approximation Method The Logan's method is based on the Theim/Dupuit equilibrium equation for steady state condition which is given as:
where Q 3 well discharge
k = hydraulic conductivity
b a aquifer thickness
= steady state drawdown in the pumped well Smw = steady state drawdown in the observation well Sml = distance from observation well to the pumped well
Yw .- radius of pumped well. Logan (1964) transformed the above equation to -.
where yhax a radius of influence of the pumped well. Table 8: Pumping Test Data From ore holes Around the Study Area Pumping Test Data for- Ogbunike Borehole- (BHLOT63I7 ater ra 1ve Dlscharqe Time eve1 zes- Remarks (m) -i ure 6.00 am 0.10 4.8 mins 10.60 Step I .0.2' mins 10.60 .5 mins 10.60 .9.8 mins 10.60 !5.2 mins 10.60 I0 mins 70.80 10.2 mins 70.90 19.2 mins 70.90 7.00 am 70.95 7.30 am 70.95 8.00 am 72-15 8.30 am 72.15 9.00 am 72.15 10.00 am 72.60 11.00 am 72.60 L2.00noor 72.80 1.00 pm 72-80 2.00 pm 72.95 3.00 pm 72.95 4.00 pm 72.95 5.00 pm 73.20 6.00 pm 73.20 7.00 pm 73.20 8.00 pm 73.45 9.00 pm 73.45 10.00 pm 73.45 11.00 pm 73.45 - Water Jalve Discharge Date Time level pres- Remarks (m) -sure
Step I1 - dater Valve Di scharge Date Time Level pres- - Remarks r* m 0 Sure 3 /hr - 8.00 pm 75.23 2 9.00 pm 75.23 10.00 pm 75.23 11.00 pm 75.37 -2.00 am 75.37 1.00 am 75.37 2.00 am 75.60 3 Step I11 3.00 am 75.60 4.00 am 75.60 5.00 am 75.60 6.00 am 75.60 6.06 am 76.11 6.10 am 76.11 6.15 am 76.11 6.19 am 76.11 6.25 am 76.11 6.30 am 76-20 6.40 am 76 20 6.49 am 76.30 7.00 am 76.30 7.30 am 76.30 8.00 am 76.33 8.30 am 76.33 9.00 am 76.33 10.00 am 76.50 11.00 am 76.50 12-00nool 76.68 1.00 pm 76.68 2.00 prn 76.68 3.00 pm 76.68 4.00 prn 76.80 1 - I- Water Draw- Valve Discharge Date Ti me level down pres- Remarks (m) -(m) sure 5.00 pm 6.70 0.009 6.00 pm 6.70 It 7.00 pm 6.81 It 8.00 pm 6.81 It 9.00 pm 6.81 II 10.00 pm 6.81 I1 11.00 pm 6.85 tl 12.00 am 6.85 tt 1.00 am 7.00 II 2.00 am 7.00 tI 3.00 am 7.00 II 4.00 am 7.00 It 5.00 am 7.00 It 6.00 am 7.00 11 PUMPING STOPPED MEASUR RECOV 6.05 am 6.10 am 6.15 am 6.20 am 6.25 am 6.35 am 6.45 am 6.55 am 7.55 am 8.55 am 10.55 am 12.55 pm 2.55 pm 4.55 pm Draw- Valve Discharge Date Time Water level down Pres- Remarks (m) (m) sure m3/sec m3/hr
17/5/83 6.55 pm 70.30 0.20 0 0
II II II Y 8.55 pm 70.25 0.15 II 10.55 pm 70.20 0.10 11 II 11.55 pm 70.10 0.00 " I - I I I I ' I ' I
- - - - dater Draw- Valve Date Time level down pres- Remarks -(m) -(m) -sure 23/8/83 6.05 am t6.45 1.45 8.18 Step I1 .. II 6.10 am t7.00 2 .00 II II 6.15 am 47.02 2.02 tl I1 6.20 47.03 2.03 II II 6.25 .am 47.08 2.08 It I1 6.30 am 47.11 2.11 I1 I1 6.40 am 47.13 2.13 II I1 6.50 am 47.24 2.24 It II 7.00 am 47.25 2.25 I1 It 7.10 am 47.25 2.25 I1 I I 7.20 am 47.40 2.40 11 II 7.30 am 47.45 2.45 I8 I1 8.00 am 47.50 2.50 11 1I 8.30 am 48.00 3.00 I1 II 9.00 am 48.20 3.20 I@ I1 9.30 am 48.30 3.30 I1 II 10.00 am 48.40 3.40 I1 II 11.00 am 48-70 3.70 II I1 12.00 noc 48.90 3.90 It
1I ,' 11 1.00 pm 48.90 3.90 11 3.90 II I1 3.90 I1
II 3.90 II 3.90 11 3.90 tl 3 090 I1 3.90 I1 3.90 I1 3.90 It
3 90 I1 Step I11 - lla ter Valve Disch Date Level - pres- 3 Zemarks (m) -sure -I /sec 6.05 am L8.90 .0046 itep I11 6.10 am 18.90 II 6.15 am $8.90 II 6.20 am 48.90 II 6.30.am $8.90 II 6.40 am 39.35 II 6.50 am 49-44 II 7.00 am 49.75 10 7.30 am 50.00 11 t4.00 am 50.40 11 8.30 am 50.46 II 9.00 am 50.70 11 10.00 am 50.80 I1 11.00 am 51.00 11 12 -00 noor 51.00 11 1.00 pm 51.00 11 2.00 prn 51.00 11 4.00 pm 51.00 I1 6.00 pm 51.00 I1 8.00 pm 51.00 II 10.00 pm 51.00 1I 12.00 am 51.00 1) I 2.00 am 151.00 I1 4.00 am '51.00 ll 6.00 am 51.00 II PUMPING STOPP IEASURI RECOI 30 secs 6.01 am 0.00 se00 1 min 8.90 3-90 30 secs
"64 Pumping Test Data for Otuocha Borehole (BHLOT62) - - Draw- Va 1 ve DischargeL Date Time jown pres- 3 Remarks (m) B ure : m /hr - - .I 6.00 am 5 mins 2.30 i Step I 10 mins 20 30 15 mins 2.40 20 mins 2.50 25 mins 2.50 30 mins 2.60 40 mins 2.60 50 mins 2.70 7.00 am 2.80 7.30 am 2.80 8.00 am 3.00 8.30 am 3.00 9.00 am 3.05
.0.00 am 3.08 4 .1.00 am 3.08 .2.00 noo 3.09 1.00 pm 3.09 2.00 pm 3.09 3.00 pm 3.09 4.00 pm 3 09 5.00 pm 3.09 6.00 prn 3-09 8.00 pm 3.09 10.00 pm 3.10
12.00 am 3 0 10 2.00 am 3.10 4.00 am 3.10 -- - Water maw- Valve Discharge Date Time level down pres- Remarks -(m) -(m) -sure 6.00 am 2.50 3.10 6.05 am 2.61 3.21 Step I1 6.10 am 2.71 3.31 6.15 am 2.80 3.40 6-20.am 2.80 3.40 6.25 am 2.95 3.55 6.30 am 3.02 3.62 6-40 am 3.07 3.67 6-50 am 3.12 3-72 7.00 am 3-15 3.75 7.30 am 3 15 3-75 8.00 am 3.15 3.75 0.30 am 3 19 3.79 9.00 am 3.19 3.79 10-00 am 3.22 3.82 11-00 am 3.22 3.82 12-00noc 3.25 3.85 1-00 pm 3.25 3.85 2.00 pm 3.27 3.87 3-00 pm 3.27 3.87 4.00 pm 3.29 3.89 5-00 pm 3.29 3.89 6.00 pm 3.30 3.90 8-00 pm 3.30 3-90 10.00 pm 3.30 3-90 12.00 am 3.30 3.90 2.00 am 3.30 3.90 4.00 am 3.30 3.90 6-00 am 3.30 3.90 66 rJater Valve Discharge Time Level pres- Remarks (m) sure
6.05 am 3.50 Step I1 6.10 am 3.55 6.15 am 3.55 6.20 am 3.60 6.25 am 3.60 6.30 'am 3.60 Step 111 6.40 am 3.65 6.50 am 3.65 7.00 am 3.70 7.30 am 3-70 8.00 am 3.85 8.30 am 3.85 9.00 am 3.95 10.00 am 4.04 11.00 am 4.04 12.00 noor 4-10 1.00 pm 4.10 2.00 pm 4 10 3.00 pm 4.10 4.00 pm 4-10 5-00 pm 4.10 6.00 pm 4.10 8.00 pm 4-10 10.00 pm 4.10 12-00 am 3.10 2.00 am 4 10 4.00 am 4.10 6.00 am 4-10 PUMPING STOPPE - - .- Water Draw- Valve Discharge Time level down pres- Remarks (m) (m) sure zz"lK
Step I11 - dater Draw- Valve Discharge Date level down pres- Remarks (m) -(m) -sure
9.00 am 9 1 min 3.25 1 min 0.55 30 sec 2 mins, 1.05 3 mins 1.37 4 mins 1.70 5 mins 2 08 0 mins 2.43 5 mins 2.75 mins 3.25 5 rnins 3.48 9.00 am 3.85 9.15 am 4.34 9.30 am 4.80 9.45 am 5.15 0.00 am 5.45 0.15 am 5.84 0.30 am 5.95 0.45 am 6.05 1.00 am 6.10 2.00 nooi 6.10 3-00 pm 6.10 6.00 pm 6.10 9.00 pm 6.10 1200 am 5.10 4.00 am 6.10 8.00 am 6.46 8.01 am 6.96 8.02 am 7.4 2 - draw- Valve Discharge down pres- Remarks 0Sure 8.03 am 7.84 Step XI 8.04 am 8.34 8.05 am 8.90 8.10 am 9.33 8.20.am 9.92 8.30 am LO. 38 8.45 am LO. 94 9.00 am 11.39 9.15 am 11.85 9.30 am 12.37 9.45 am 12.88 0.00 am 13-40 2.00 noo 13.95 4.00 pm 13-95 U.00 pm 13.95 2.00 am 13.95 4.00 am 13.95 8.00 am 14.55 Step I11 8.01 am 15 .22 8.02 am 15.86 8.03 am 16.28 8.15 am 16.82 8.30 am 17.4' 8.45 am 17.92 9.00 am 18.15 12.00 noc 18.20 4.00 pm 18.25 8.00 pm 18.30 12.00 am 18.30 2.00 am 18-30 18.30 Water >raw- Valve Discharge iown level pres- 3 Remarks (rn) sure m /sec m /hr Step I11
PUMPING 5 URE ECOVE, 8.00 am 0 8.01 am It 8.02 am It 8.03 am II 8.05 am It 8.10 am It 8.20 am It 8.30 am It U.45 am It 9.00 am II 10.00 am II 11.00 am It 12.00 noo It 1.00 pm It 3.00 pm I1 6.00 prn tI 8.00 prn It 8.30 prn It
- 7 He reasoned that the ratio of ymax/vw cannot be accurately determined without the use of piezometers.
And thdt, although the variations in %max andhrw may be large, the variation in the logarithm of their ratio is much smaller. Average conditions of radii; that is, Ymax of 250 - 500 m, and V of 0.08 - 0.16 m were therefore assumed.
Based on this, the value (vmaxhw) will range from 3.2 to 3.8 with an average value of 3.5. Substituting this value into equation (4.5) will result in
where b, is the screened length of the borehole,
k is calculated by dividing the value of T by
the screen length, b, such that
The advantage of this method is that, it gives
good estimates of T and K when compared with values got
from other methods (Giusti, 1978). The Usadvantages b are that values got are approximations and could not be used to assess variations in T or K values within a limited area.
If large errors occur in the measurement of discharge (Q) and drawdown (SMw) the equation may yield erroneous results as much as up to 80% or more. Table 9 shows result obtained from the exercise. Test discharges are 3 3 between 16.6 m /hr at Ifite-Ukpo to 181.84 m /hr at 3 Onitsha. A value of 31.8 m /hr was however recorded at Ogbunike.
Cooper and Jacob (1946) Method Thc basis of the above method is the Theis (1935)
non-equilibrium equation which is given as
where,
du u represents the exponential integral or well function (W(U)
Z d drawdown
Q = Constant well discharge
T w Transmissivity
, r = radius of the well t = time of pumping
S 3 Storativity Table 9: Values of Transmissivity (T) and Hydraulic Conductivity (K) Values from Logan's Approximation 'kquations
-- - Borehole Borehole Specific T Values K Values location local yield m/s number m /hr/m
Ogbunike BHLOT 63 4.54 Ogbunike BH 4/62 0.79 Ogbunike BH 1574 - Ogidi BH 28 3.34 Ogidi BH 30 14.71 Ogidi BH 31 5.91 Ifite-Ukpo BHLOT 62 2. 78 Otuocha BHLOT 61 14.51 Abatetc BHLOT 64 3.01 Umuo j i BH 2197 0.92 Umuo j i BH 2927 8.61 Oni tsha BH3143 31.78 Onitsha BH 2365 11.74 Oni tsha BH 2810 3.95 Oni tsha BH 2642 7.60 Oni tsha BH 3105 7.37 Onitsha BH 7 5.78 Onitsha BH 12 2.35 Onitsha BH 20 5.99 Onitsha BH 2641 10.22
Onitsha BH 3134 0 Obosi BH 11 12.5 Obosi BH 3477 16.67
Nnobi ? 0 ~nobi' BH 2935 41.67 Alor BH 2804 1.89 'I?rlu:~t; i on 4.8 thus becomes: Statistical Methods Statistical grain-size method of evaluating the hydraulic conductivity and transmissivity include those of Hazen (18931, Harleman --et al. (1963), and Masch and Denny (19661, Uma --et al, (1989) developed new statistical grainsize method for evaluating the hydraulic conductivity
of sandy aquifers and this was employed in thi8 utudy. Uma --et 51. (1989) 'statistical method which is of the form 2 K - Cd10 i9 similar to the existing method, but in this case, the coefficient, C, varies with the nature of geologic environment, These methods provide an alternative way of calculating or evaluating aquifer parameters in the absence of pumping test data, The basis of these methods
is the interrelationship between the grain size dis-
tribution of the granular porous media and the saturated
hydraulic conductivity (K).
Since the saturated hydraulic conductivity (K) is a +' measure of the ease of transmission of fluid or water through a saturated porous media or aquifer, It is found
to be a property of both the fluid (water) and the porous medium (aquifer). Based on this, Nuthing (1930) expressed (K) as where, K = hydraulic conductivity (LT-') k = permeability p - fluid density (ML-~) -1 -1 g = acceleration due to gravity (ML T ) -1 -1 U P dynamic fluid viscosity (ML T . The intrinsic permeability (k) or simply permeability depends on the grain size properties whereas the ratio
pg/u represents fluid properties. Intrinsic permeability is measured in cm or m, and for water at a temperature of 2 20°c the conversion factor from permeability k(L ) to hydraulic conductivity K(L/T) is given as;
The above equation according to Hazen (1893) is given
where dI0 = effective grain size diameter at which 10% by weight of the sand grains are finer and 90% are
coarser. d10 can be read off from grain size gradation curve (which is a plot of grain size in mm versus per- centage passing). b C - a coefficient equal to 6.54 x loo4 From water at 20'~ and for k (in cm/s) and d10 (in mm) equation (5.8) becomes
2 K(cm/s) - 100d10 (crnls) . . . So+ ". Harleman --et al. (1963) The Harleman &a. (1963) formula is expressed as 2 K(c~/s) - 64.1d10 C~/S . . 5cB
This is similar to the Hazengs equation except that the
value of the coafficient, C, is different.
Masch and Denny (1966) Method
Masch and Denny (1966) developed their method based
on the study of the relationship between grain size , ch~rdcttdstics such as average grain size, skewness,
peakedness, dispersion and modality of sample distribution
and hydraulic conductivity (K). No basic equation was arrived at, rather Masch and Denny recommended the plotting of gradation curve using phi (B) scale units (Folk and
ward, 1957). The procedure is as follows:
The median diameter in phi scale (Uso ) was used to obkain the average grain diameter. Then the inclusive standard deviation (a1) which measures the spread or the dispersion about the median diameter is calculated using the formula given below:
where, the particle diameter in Phi (g) units %4 of which 84% of the material is coarser. Having got the inclusive standard deviation using the formula above, the k value is read off from the Masch and Denny curves shown in Fig/&.
Urna --ct al. (1989) Method Uma --et al. (1989) developed another statistical method of evaluating aquifer parameters such as hydrauli
conductivity (K), and transmissivity. The equation is , of the form:
&' where, A is the empirical coefficient which combines
the effect of the solid matrix and fluid properties. K - hydraulic conductivity, whereas d10 is the effective grain diameter at 10% by weight of the sand grains are finer and 90% are coarser. b Uma --et al. (1989) method is similar to other statistical methods, except that the empirical coefficient, A, varies with the degree of conlqolidation of the porous medium.
A, varies from 6.0 for poorly consolidated sediments, 3.8 for moderately consolidated sediments (example is the sandy aquifers of the Nanka ~and~ton~1 to 2.0 for well consolidated sediments.
Transmissivity and Hydraulic Conductivity Values
The values of hydraulic conductivity, K, for the upper (unconfined) aquifer were determined from granulo- metric analyses. They range between 1.23 x log4 m/s to 2.40 x log3 m/s with an average of 6.93 x loo4 m/s. Values of hydraulic conductivity got from statistical analyses are displayed on Table 10. Harleman --et ale (1963) method gave K values ranging from 1.44 x low4 tn/s to 3.14 x log3 m/s with a mean value of 8.04 x low4 m/s. The Masch and Denny method gkm K values
, ranging from 1-13 x lom4 m/. to 1.36 x log4 m/s with s ,' mean of 2.46 x log4 m/a. Hazen's (1893) method gave the highest range of values of 2.25 x log4 m/s to 4.9 x log3 m/s, with a mean value of 1.38 x log3 m/s. Uma & 2. (1989) mcthod grve K velucs ranging from 8.55 x log6 m/s to 1.86 x log4 m/s with a mean value of 5.24 x log5 m/s. TG~K values generally fall within the range (loD1 cm/s to
loo3 cm/s ) which indicate good aquifers. Values of hydraulic condwtivity, K, got from the Logan's Approximation Method for boreholes around the study area are shown in Table 9. The values for the middle semi-confined to confined aquifer are 7.72 x loo3
m/s at Alor and 1.18 x loo3 m/s at Onitsha with an - average of about 6.29 x low4 m/s. Those of the lower confined aquifer ranges between 6.66 x loob n/s at Ifite-Ukpo tb 2.22 x loo2 m/s et Ogidi with a value of 1.04 x log4 m/s at Ogbunike. The mean, K, value around the study area is 3.53 x loo1 m/s. The values are essentially uniform and compare favourdbly with values got from various pumping test me,thods such as the Cooper-Jacob (1946) method and the recovery method. The values of hydraulic conductivity,
K, got from the various pumping test methods as shown in Table 6 ranges from 7.73 x loo6 m/s at Tfite-Ukpo
to 1.73 x m/s at Otuocha with a mean value of 7.1 x loo5 rn/s . A value of 5.73 x lo-' m/s was however recorded at Ogbunike borehole. Transmissivity is defined as the ease with which
d s~tur-dtcdaquifer transmits water through its entire
thickness. It is represented mathematically as
b where K = hydraulic conductivity (m/s)
b = saturated thickness of confined aquifer . Table 1C: Hydraulic ~ropet'ties of sorw SafX~leSof the IVanka Sandstone (Upper L'nconfined Aquifer) from the Study AI
1 Hvdraulic Conductivity Value (m/s) Transnissivity Value (m2 /s) Harleman Kasch anc! Uma et Harleman Easch and Uma et Average Average Location et al. Denny a1 etal.' ~enny a1 . -- - <. -- - Nkisi-Osile Spring Sandstone 1 2. 25~10-~11.44~10-~11.13~10-~ Thickness: 8 m I I I Ogba cave I spring Sandstone Thickness: 10 m Nkisa-anya- akommiri Sprinq Sandstone i TO^- layer) 14.0~16~1 2.56~10-~ 11. 77~10-~ ~hickness:15 mf Nkisa-an ya- akommiri S~rinq
Thickness: 15 m Km 20 Onitsha- Enugu Express Road Sandstone Sample Thickness: 20 m Krn 8 hitsha- Nsukka Express i Road ( Adani Road) Sandstone 2.03x10-~ 1.30x10-~ 7. 55x10-~ Sample Thickness: 25 m or the height of the water table above the top of the
underlying aquitard that bounds the aquifer for the
unconfined aquifer (Freeze and Cherry, 1979). The
saturated thickness of the upper unconfined aquifer was estimated from the surface exposures of the aquifer whereas
those of the lower confined aquifer were calculated using
the screened length to represent the saturated thickness
of the aquifer.
The transmissivity values for the upper unconfined -2 2 aquifer range from 9.81 x log4 m2/s to 4.79 x 10 m /o with a mean value of 1.38 x log2 n2/s. Those of the middle confined to semi-confined aquifer range from 6.8 x log4 m2/s to 5.31 x log3 m2/s with an average of about -3 2 3.00 x 10 m /s. The transmissivity values for the . lower confined aquifer range from 1.16 x log4 rn2/s at Ifite-Ukpo to 2.82 x log3 m2/s at Otuocha with a mean -3 2 . value of 1.13 x 10 m /s. A transmissivity value of ,' -4 2 9.13 x 10 m /s was recorded at Ogbunike.
4.5 Specific Discharqe and Average Linear Velocity
Specific discharge or the Darcy Velocity (Vd)
equals the product of the constant (K), known as the
b hydraulic conductivity and the hydraulic gradient, 1. This is based on Darcy's law and expressed mathematically Vd = Ki .a* s19 where,
Vd = specific discharge or Darcy velocity K hydraulic conductivity
i I hydraulic gradient.
The average hydraulic conductivity for the lower confined aquifer was taken as 7.25 x log4 m/s. This value when multiplied by the average hydraulic gradient which was computed as 0.0024 gave a specific discharge value of
55.0 m/yr. The average hydraulic conductivity value determined for the upper unconfined was 1.38 x loo3 m/s whereas the hydraulic gradient was 0.0022, This gave a specific discharge of 96-0 m/yr.
The averago linear groundwater velocity Va as given by Todd (1380) is:
where n P porosity of the porous material (or aquifer) Thc porosity of the lower confined aquifer (which consists of fine to coarse grained sand) was estimated based on Pettijohn (1975) at about 0.45. From this, tbe average linear groundwater velocity was calculated as 122.0 m/yr which is relatively high- 4.6 Groundwater Flow Directions, Recharqe and Discharqe Areas The hydraulic head distribution in the study area is displayed in Figure 11 and Table 11. Figure 11 shows that the genera1:direction of groundwater flow in the lower confined aquifer is generally towards the west and northwest. Two flow systems are recognised in the area. These are the local flow system (occurring in the upper unconfined aquifer) and the regional flow systems (occurring in the lower confined aquifer).
The upper (unconfined) groundwater flow system receives direct recharge from rainfall over its permeable soil cover. Flow is from areas of higher elevation such as undulating ridges and hills to areas of lower elevation such as river or stream valleys.
It is therefore mainly topographically controlled. They are discharged naturally as contact or depression
#' springs in areas where the water bearing units or aquifers such as laterites, fine-medium grained sand- stone or weathered red earth with its underlying units such ds clay-shale, mudstone, etc. intersect ground surface (in river valleys or stream valleys). .The hydraulic head distribution of the upper unconfined
aquifer in the study area is displayed in Figure 9.
Figure 9 indicates that a localised recharge area of Fig. 9: Map showing Hydraul'rc head distribution direction in the Upper (Unqonfined ) Aquif Curves 18.6 Table 11: Hydraulic Head Values Calculated for the oreh holes Around the Study Area
Borehole Elevation Depth to {ydraulic Location local above sea static water read number level (m) level (m) ,m)
Ogbunike DHLOT 63 Ogbunike BH 1574 Ogbuni ke BH 4/62 Ogidi BH 30 Ogidi BH 31 Ogidi BH 28 Ifite-Ukpo BHLOT 62 Otuocha BHLOT 61 Umuo j i BH 2197 Umuo j i BH 2937 Abatcte BHLOT 64 Alor BH 2804 Nnobi BH 2935. Nnobi 3 Obosi BH 3477 Obosi BH 11 Oni tsha BH 2641 Oni tshd BH 2642 Onitsha BH 7.. Oni tsha E3H 12 Onitsha BH 20 Onitsha DH 2365 Onitsha BH 2810 Onitshd DH 3105 Oni tsha BH 3134 Onitsha BH 3143 'm the upper unconfined aquifer occurred southeast of the study area around Ogbunike and Umunya. The regional groundwater flow system in the area occurs at a depth of about 70 m below the ground surface - and flow is mainly toward the west, north and northeast of Ogbunike with a hydraulic gradient of gradient of 0.0024. The recharge ares of this flow system occurs southedst of the study area around Abatete and Oraukwu. It discharges naturally towards the west and northwest of the area around River Niger and River Anambra. According to Meyboom (19661, Toth (1966) and
Brassington (19881, recharge and discharge areas can be delineated on the basis of topography, Piezometric patterns, hydrogeochemical trends, the use of environ- mental isotopes and soil and land surface features. The dominant soil type in the study area which is typically sandy and ranges from deep porous brown soils to b wedthered red earth and acid sands. The highly porous and permeable sandstone of the Non~qJand.~joqe underlying the study area indicates high infiltration. Infiltration
in the study area accounts for about 20.5% of the mean annual precipitation. The study area is most probably 'transitional between a recharge area and discharge area. The topography is moderate, the unsaturated zone over
the upper unconfined aquifer is not quite deep. F'ICJ11 ' Map shaving ~~draulichead distrht ion and grwndwater flow directions In the lower (conf incd) aquifer of the study area licr.11(11-11.(3 OCCUT~Z;over i t;s pq.rmc:ubl e soil cover while dinchnrpe
occ:ur l,llrout;h :iprinl:s itnd hor;efl.own.
The ucu is therefore probubly an intermedit1 te zone.
unit tlrnwdown. It is the ratio of di:;charj~;eto well drawdown. Specific capacity (sC) of an aquifer is related to the discharf:e
(SW) by the ralation:
... her where,
SC = Specific capacity m 3 /hr/m
!i= rl i ::c ha qr;e m 3/hr
'I'sbl~s~9 [lnd 12 show the specific capacity values for boreholes around the :Area. The values ran(l;es from 2.76 m 3/hr/m around Ifite-Ugpo to 31.78 m 3/hr/ni around OniSsha. Values of
0. '79 m 3/hr/m :\rzcl 4.5 m 3/hr/m were record cd uround O~bunike wherca:; wu1uc;s ol' 14-51 m 3 /hr/m to 14.71 m 3 /hr/m were recorded arou~dOtucha and Ogidi. A look at Tuble:; 9 md 12 roveul:~u ~~;cnrtriilly 1 ow vtlluon of specific cupricit-,i.c:;. It is probnb1.y
Where
b' b' b :. ilvclb,iy,e :;i~turutc?dtlli ckness of Lhe qquif ere
sy = specific yield estimated at 25% after qohnson (1967)
.. (in Todd, 1980).
2 'l'ho areal c:xt,cr~t, o I' t;he aquifers is estimated to be [*bout 10Okm b which reprlc:;crzt,:; about sixty percent of thc study area
For Ll~r: up;)c:r unconf int:d uqyyifor: 1 12: Specific Capacity Values for Some Boreholes Around the Study. Area
! Borehole Discharge Drawdown Speci f ic 1 Location local 3 capacity rn /hr (rn) number ~~/hr/rnt
Ogbunike BHLOT 63 31.8 Ogbunike UH 4/62 17.64 Ogbuni ke I311 1574 3.75 Ogidi UH 28 144.13 Oyidi r311 30 75 Oyidi BII 31 233.86 Ifite-Ukpo BliLOT 62 16.56 Otuocha BIILOT 61 68.20 Abatete UIILOT 64 55 Umuoji Dl1 2197 21.5 Umuo j i nIc 2927 62.00
Nnobi Btt 2935 50 Alor L3I1 21301 25.25 Oni tsha UtI 3143 410 Oni tsha UH 23G5 77.5 Onitsha nci 2810 22.5 Oni tsha DH 2642 18.25 Onitsha Uki 3105 250 Onitsha ti7 181.84 Oni tsha BII 12 127.29 Onitsha Uli 20 131.84 Onitsha BH 2641 4.6 Oni tsha Dl I 3134 7 Obosi 1311 11 75
Obosi I UtI 3477 7 5 3 . . C?,a = 33 x 0.25 x 100,000,000 m of water €3 = 8.25 x 10 m3 of water
For Lhr-, middle semi-confined to confined aquifer:
'i'he penetru1;cd Lhicltness of this aquifer is equrll to 45m. CHAPTER FIVE
HYDROGEOCHEMISTRY AND WATER QUALITY
5.1 General Statements ; Hydrogeochemistry describes the geochemical properties and principles that control the behaviour of dissolved constituents in the groundwater environment. Therefore it helps in the understanding of chemical evolution that accompanies flow. We thus, have the geochemical cycle of surface and groundwater. The geochemical cycle of surface and groundwater shows the principal chemical changes involved in water as it travels through the hydrologic .cycle from precipitation
8 to groundwa term
The chemical and biochemical constituents of groundwater determines its usefulness for industry, agricul ture or household use. The study of groundwater may yield important indications of the geologic history of the
b enclosing rock, the velocity and direction of groundwater movements and even the presence of hidden ore deposits. The mode 05 origin of a particular water within the hydroloqlc cycle can also be determined. Many large resorts have been located at springs having water of unusual chemical composition and sometimes temperature.
This is because such springs are reputed to be curative
springs. These are called spas. Finally chemical processes in the groundwater zone can influence the strength of geologic material. In situation where they are not recognised may cause failure 8 * of artificial slopes, mining excavation and other features of importance to man. In this chapter, the groundwater quality problems in the study area as well as chemical evolution of both the upper unconfined groundwater (obtained from springs and
hand-dug wells), and the deep groundwater have been
discussed. Sources and causes of pollution and probable
pollution attenuation mechanisms in the area were also
discussed. 8 The hydrogeochemical data were obtained from the analyses
of water samples from boreholes, hand-dug wells, springs and some rivers. More samples could have been analysed and more ionic constituents tested for, if not for the
following reasonst
,' 1 Lack of and/or scarcity of the required chemical reagents and the prohibitive cost of such chemicals and instruments, even where available in the market.
I 2. Lack of culture media for bacteriological analysis
3. Lack of and/or scarcity of required instrumentation such as pH meter, conductivity meter, etc., which a are necessary to measure such hydrogeological
parameters as pH, Eh, temperature, electrical corrductivi ty, acidity, alkalinity. These parameters are better measure.d in the field because changes are inevitable by the time samples reach a . laboratory.
Tables 15, 17 and 18 show the chemical analysis of water samples from some of the hand-dug wells, springs,
boreholes and some rivers in the study area. Table 14
givesthe standard limits for drinking water,
irrigat.ion and industrial water supplies. R The findings indicate that the water from the, study area is generally good or suitable for domestic
use, irrigation and industrial purposes. It also indicates that the chemistry of the upper unconfined
groundwater obtained from springs and hand-dug wells is different from the chemistry of deep groundwater.
5.2 Method of Sampling In order to obtain water meeting specific quality
8' 8' criteria the following factors influencing the design of
any water sampling program for chemical analyses are nated: I 1. Geology (that is, both surficial and subsurface geology) and soil characteristics
2. Purpose of the sampling (study).
3. Method and time of collection of samples and
its subsequent time of transfer to a laboratory 96
for analysis. >.
Number and depth range of the aquifers involved , ;< Cost of analyses. Geographical distribution of wells, springs, etc.
Method and place ~f storage of samples prior to analyses.
Operating conditions of the wells immediately
prior to the sampling and a record should be made
of the well location, depth of sample, size of
casing, date, water temperature, odour, colour
and turbidity. C
The above factors were taken into account while
sampling water from both the hand-dug wells and deep boreholes in the study area. In sampling water from hand-dug wells the following
Factors or conditions affecting or endangering water quality arc noted: 3 1 Effects of human activities such as sanitary conditions in and around the wells, for example, I some of the wells are not properly covered with the result that insects such as cockroaches and rodents sometimes fell inside them; furthermore 6 abstraction is often affected by means of dirty
ropes tied to buckets that may not be clean themselves. >. 2. Effects of environmental constituents such as * ;* surface scums and leachate con tamination on water quality.
'l'hc fol.lowing factors are taken cognition of in sampling water from springs and streams:
(1) The geology (especially lithology) and soil types at the spring location, for example, the passage of water over and through the soil and rock types will affect the properties
of a given source of water.
(ii) Human activities at the springs and streams
such as the use of the waters for fermentation of cassava, bathing or general laundry. 8 (iii) The presence of decayed organic plant remains. In sampling groundwater for quality analysis water-proof plastic cans were used for the study. After rinsing ,' the cans with the water being sampled, the sample was
then collected and sealed. This is done, in order to get fresh Sample that is devoid of contamination. The samples were stored in a refrigerator before the actual
5.3 Method of Analysis Standard methods .for the examination of groundwater and waste water have been prepared, approved and published .. jointly by the following bodies such as American Water
Works Association (A.W.W.A) , at& Pollution Control r Federation (W.P.C.F) and the American Public Health
Association (A.P.H.A). Those methods are used in support of water quality standards at all levels of responsible
government AIKIdetails of the procedure used in this
study yere borrowed from their manuals. Water quality s tandards normally identify the concentration of component properties shown by experience or scientific judgement
to be safe, desirable and acceptable, and to be attainable
from available water sources. A summary of the various
methods of anal.yses used is given in Table 13.
Water AnalysLs Diagrams Used in the Study: For easy comprehension and visual inspection, the result of chemical analysis are presented graphically.
,L They range from simple diagrams such as bar, circular, radial, and stiff diagrams to complex diagrams such as Pipers trilinear diagram, Schoeller semi-logari thmic diagrams, etc. Both the Piper's and the stiff diagrams D are used in the present study. Stiff or pattern diagrams
coufd either be constructed from individual analyses or from a group of analyses. Table 13: Summary of Some of the Various Methods of Hydrogeochemical Analysis Used in the Study
Test for Method
Indometric method
Phenan throline method (calorimeter)
Hardness EDTA ti trimetric method
Chloride Argentometric method
Calcium EDTA titrimetric method Magnesi um EDTA ti trimetric method Colour Platinum cobalt method Silica Molybdosilicate method
Sulphate Turbidometric method Stiff diagrams for the study area was constructed from
individual analysis in order to appreciate easily waters
, , ', .' of similar quality which is us'ually defined by dis- tinctive graphical shape. Stiff diagram of displaying - chemical analyses is represented in the study by three
parallel axes separated by a vertical zero axes, 2+ concentration of major cations such as Ca , FIg2' and + ~a+(usually added to K+, as Na + K+) are plotted to the left of vertical zero axis whereas major anions 2- such as bicarbonate (usually with carbonate C03 1, 2- sulphate (SO4 and chloride (~1-1are plotted to the right of the vertical zero axis.
The diagrams are constructed on the basis of the existence
of electroneutrality in electrolyte solutions. Theore-
tically, there is supposed to be a balance between total ionic concentration of the cations and total Sonic
concentration of the anions. Practically, this is never d achieved becau:;e of either the presence of undetermined
ionic specics at significant concentration levels that were not. intzlucled in the analysis or duo to analytical error in concentration determinations, For the purpose
of these computations, the units are in milliequival&nt per litre. The milliequivalent per litre for a
constituent is evaluated by dividing the constituent concentration in milligrams per litre by a factor. This factor is obtained by dividing the molecular weight of the constituent by its oxidation state (valency). Stiff - diagrams drawn for the study area are discussed later. Piper's trilinear diagrams were used in the classificatisn of the groundwater in the study area. This is becquse the diagrams permit the cation and the anion composi tions of many samples to be represent&d in a single graph in which major groupings or trends in the
data can be discerned visually. Unlike the stiff diagrams, the Piper's trilinear diagram is based on cations, expressed as percentages
of total cations (~a', Plg2+, ~a++ K+) in milliequivalent per litre, and on anions, expressed as percentages of 2- total anions (cln, SOq and ~0:- + HCO;) in milli- equivalents per litre. In spite of its complexity, the
trilinear diagram has greater potential to accommodate a larger number of analyses without becoming confusing
and is convenient for showing the effects of mixing of (two) waters from different sources.
5.4 Hydroqeochemistry of the Upper (Unconfined) Aquifer Artificial discharge of this aquifer is effected by means of hand-dug wells whereas natural discharge
occurs through springs. Many hand-dug wells and springs (collin and sheffer, 1985)
C udmium Chromium
Sodium
dissolved solids occur in the area of study. Only five of the springs and five of the hand-dug wells were sampled and analysed.
Table 15 shows the physiochemical properties as well as .. the concentration of the constituents in water samples
taken from the aquifer. The concentrations are given
in milligrams per litre except where otherwise stated. Physical quality study indicates that water samples
from some hand-dug wells in the study area hew colbur
values ranging from 5 Hazen units at Ogbunike (HW1) to more than 70 Hazcn units at Nkwelle-Ezunaka (HW4). The turbidity values range from 22 F.T.U at Ogbunike
(HW1) to 82 F.T.U. at Nkwelle-Ezunaka (HW4). However, two hand-dug wells at Nkwelle-Ezunaka (HW5 and HW4)
indicate colour valuao of 64 to more than 70 HaZen units and turbidity values of 70 F.T.U and 82 F.T.U. .The
high colour value recorded may indicate groundwater
exposed to peats or other organic deposits. Most of this colour is probably caused by humic and fluvic type acids and protein lignin compounds that comprise the stableorganic matter (humus) in the soil. Brownish discolouration can also occur when groundwater with
dissolved ferrous iron is exposed to the atmosphere b and insoluble ferric hydroxide are formed (Bouwer, 1978).
The high turbidity of the groundwater may be due to the presence of clay, silt and other fines that enter the well from the aquifer. This is due to poor development of the well. It could also arise frpm the oxidation of
b . dissolved ferrous iron to insoluble forms. This is
buttressed by the high values of suspended solids (71.3 to 181 mg/l) recorded for the two wells at Nkwelle-Ezunaka. Colour imparted from soluble ferrous compounds according to Ezeigbo (1987) may be removed through oxidation to
ferric compound:; Except for a hand-dug well HW1 at Ogbunike which recorded a pH value of 8.17 (slightly alkaline), the pH recorded for the study area generally ranged from 4.68 to 6.75 (acidic), Figure 31displays the spatial dis- tribution of pH values in the upper unconfined aquifer of the study area. The entire area of study could not be c contoured duo to the uneven distribution of' hand-dug wells that were sampled. Figure 1% however, reveals that to the southeastern portion of the study area, i.e. around Ogbunike, the pH decreases towards the east. To the western portion of the study area around Nkwelle-Ezunaka, isolated values of pH ranging from 6.12 to 6.75 were b recorded. Thc acidic waters are probably due to the leaching out of organic acids from decaying vegetation or due to the presence of peat (pyrite) or gypsum in the 2 3 I(~TI i , ., .". i.-- . .. - ., LEGEND fi pa------. m-...-.--- ...--.-*.-.. - #: i Settlement i Acl2:Map showing pH vur iatbns in the upper (unconfined) aqui fc ;I' I06 underlying clays of the upper unconfined aquifer. It -u could also be due to hydrolysis of iron in laterite, <. red earth or ferrugunised sandstone overburden that is - abundant in the area (Ezetgbo, 1988). The alkaline condition may be due to calcareous shale within the aquifer zone or due to the presence of limcstonc nodules in the formation. Water from hand-dug wellsin the study area show~d alkalinity values ranging from 9 mg/l to 57 mg/l with HW1 Ogbunikc and HW2 Umunya giving the highest values of 42.2 mg/l and 57 mg/l, respectively. Figure 13 shows the spatial distribution of alkalinity values in the upper (unconfined) aquifer in the study area. It revealed that to the southeastern portion of the study area around Ogbunike, the alkalinity value increases towards the west. The increasing alkalinity towards L the west is probably due to the presence of calcareous unit of the ' that also increases in magnitude towards that direction. This alkalinity is 2- probably due to presence of carbonates (C03 ) and bicarbonates ( HCO; which arise from these calcareous unlts. To the western portion of the study area around Nkwelle-Ezunaka, isolated values of alkalinity ranging from 9 mg/l to 23.1 mg/l were recorded. Alkalinity ~i~ - 13 . Areal dktribut ion of Alkalinity values for the Upper unconfined aquifer could also be attributed to the bicarbonate ion derived from dtmospheric carbondioxide and/or carbondioxide released from decaying organic matter in the biologically active soil zone. The study area indicates generally low contents of sulphate ranging from 9.0 mg/l to 25.6 mg/l. Water samples from two hand-dug wells HW4 and HW5 at Nkwelle- Ezunakil gave higher sulphate concentration values of 17.3 mq/l and 25.6 mg/l, respectively. This may suggest thc presence of sulphate bearing minerals such as pyrite (or msrcasite), anhydrite and/or gypsum in the silty cldys that form intercalations in the aquifer. Chloride concentrations generally range from 6.3 mg/l at HW2 Umunya to 30 mg/l at HW3 Ogidi. Figure 14 shows the spdtial distribution of chloride values in the upper unconfined aquifer of the study area. It revealed that to the southeastern portion of the study area around .' Ogbunika, the chloride value (concentration) decreases towdrds the west. This is probably due to the presence of sornc evaporitcs within the soil zone (or aquifer zone) which decrease in magnitude towards the west. To the western portion of the study area around Nkwelle-Ezunaka, * isolated values of chloride ranging from 17.3 mg/l to 29.3 mg/l occurrcd. Significant chloride values may also bc due to contribution from human activities or relatively long residence time of the upper unconfined COKK d 98 aquif er water. Silica concentrations range from 10 mg/l to 16 mg/l whereas sulphate concentrations range from 3.0 mg/l to 25.6 mg/l. Silica and sulphate in significant concentrations may be due to the presence of clay minerals, pyrites (or marcacite), gypsum, and/or anhydrite in the clays that form intercalations in the aquifer. fi. Total hardncss studies of the unconfined groundwater reveal the prcscnce of soft water with total hardn~ss (17s CaC03) of 5 mg/l at Ogidi (HW3) to moderately hard water with total hardness (as CaC03) of 126 mg/l at Ogbunike, The hardness (as CaC03) of 126 mg/l recorded for HW1 Ogbunikc may be due to the presence of limcstonn nodules or other calcareous units in the Ncnl/4 ~u,nd~f-/~n~,. alongside the thick top soils that overlie them. The generally low content of dissolvd oxyqen ' ranging from 0.8 mg/l to 1.2 mg/l reco~dedmay be due to the presence of organic matter in the: :;oil. These organic matter consumed much of the dissolved oxygen in the infiltrating rain water. It may also be due to depletion of dissolved oxygen in the infiltrating rain water by bacterial activity. The total dissolvcd solids concentration range from 23 mg/l to 100 mg/l, Lowest value of 23 mg/l was recorded at Ogbunike (HW1) whereas highest values of 92.0 mg/l and 100 mg/l were recorded at Ogidi (HW3) and Nkwclle-Ezunaka (HWS 1. This indicates younger water at Ogburlike giving way br rise to relatively older waters at Ogidi and Nkwelle-Ezunaka. The chemistry of the waters of springs is largely controlled by the mineral and chemical composition of the rocks and soils in contact with it. It could also be cuntrol1t:d by the presence and magnitude of vegetation dnd orgmic matter in contact with springs or human activi ti I?:; around the springs. Physical analysis of the spring waters show colour valucs r'inging up to 12 Hazen units, and turbidity values ranging up to 28 F.T.U. This indicates moderately c1ea.r to cleur water. The pH value ranged from 5.6 to 7.2 which implies slightly acidic to neutral waters. pH value of below 6 was recorded at Ogba cave spring Sp2, ,' Ogbunike whereas pH values of 6.2, 6.2, 6.9 and 7.2 were recorded at Nkisi-Osili spring Sp3, Obiam spring Sp5, Nkisa-anya-akommiri spring Spl, and Nwangene spring Sp4, respectively. Figure 14 shows the spatial distribution of pH values for both the springs and hand-dug wells that constitute the upper (unconfined) aquifer. This has earlier been explained. The acidity of the spring waters is probably due to the leaching out of org,~nicdcid3 from the underlying cerbonaceous shale and clays in the aquifer furnishing water to the spring. Alkalinity values measured for springs within the study area ranged from 6 mg/l to 30 mg/l which is relatively low. Spatial distribution of alkalinity values of both the springs and hand-dug wells is shown in Figure 13. Alkalinity is due to bicarbonate ion which i:; probL~l)lyderived from the dction of (atmospheric) carbondioxide dissolved in infiltrating water. Chlorldc concentration in the springs ranged from 2.5 my/l to 42.7 mg/l. Ogba cave spring, Ogbunike, gdvcn tl~c!highest value of 42.7 mg/l, Figure 16 shoes the spatial distribution of chloride for both the hand-dug wells and springs in the study area, High chloride value rccorded at Ogba cave springs may be due to the presence of evaporites in soils and rocks in contact with the z sprinq water and/or human activities around the spring. Silica concentrations for the springs ranged from 6 mg/l to 12 mg/l while sulphate concentration ranged .from 3.0 mg/l to 25.6 mcj/l. Silica and sulphate ions m'iy I)(.. tlcrivcd from clay minerals, pyrites (or marcasites 1, gypsum md/or anhydrite that may be present in the * undt:rlyilng cl.~yswithin the rlrcta the springs issue out. The spring water is soft water. The hardness 1.43 (as Ca~0~)ranged from 10 mg/l to 42 mg/l and is therefore good for laundry purposes. The dissolved oxygen is generally low and ranged from 0.08 mg/l to 1.7 mg/l. This may also be due to depletion of dissolved oxygen in the infiltrating water as A study of the cation concentrations for both the hand-dug wells and springs in the study area reveal following: The total iron concentrations are somewhat high. Tile hand-dug well HW4 Nkwelle-Ezunaka gave the highest value of 1.14 mq/l. This is probably due to any of the following; the presence of iron-rich lilteritc:~in contact with the water or the 1,re:jenCe of iron-clay mineral and/or the presence of ferromagnesium micas in the (micaceous) sandstone with which it came in contact. All but one of ttw smp11:s s howud wa tar whom iron content exceeded the U.S.E.P.A (1975) limit of 0.3 mg/l. Calcium concentrations are relatively high with rcspec t to the magnesium ion concentration. 2+ 2+ This yielded high Ca /Mq ratlo ranging from 1.23 mg/l to 7.56 mg/l for the upper unconfined groundwater. The fact that calcium predominates ovtbr ma~gncsiumin moat of the uppor unconfined groundwater implies that calcium is the greater contributor to water hardness than magnesium. Figure 15 shows the spatial distribution of calcium v~iluksfor the upper unconfined aquifer in the study area. It revealed that to the southeastern portion of the study area around Ogbunike, the cdlcium values decrease towards the west. This is probdbly due to the presence of calcium-bearing clay minerals such as kaolinite, illite, etc., within the aquifer zone which increases in magnitude towards the east. To the western portion of the study area around Nkwelle-Ezunaka isolated vdlues ranging from 9.4 mg/l to 14.1 mg/l were recorded. I . :,id LUIN ccx~ccntration runqt9d f ran 2 .H mg/l to 27.8 mg/l. These values are generally high, especially the values of Ogba cave spring, Nkisa-anya-akommiri spring all in Ogbunike. The I hiqh values encountered are probably due to the @ presence of clay minerals in the underlying (or intercalated) clays and/or due to soil reactions * ~iversand Streams -- F;~.IS : Mup showing areal distribution of Calcium Concentrut in thc upper aquifer . 146 such as deposition of salts (or evaporites), ion exchange, oxidation and reduction. It can also result from leachate contamination or contamination from surface . water bodies. Ttm sodium ad:mt-ptAon rcaklo (S.A.H. whlch rangc-d Prom 0.83 to 18-70 is generally low. It thus indicates low alkali hazards and the water therefore could be cmployed for irrigation purposes. A study of the stiff diagrams (Figs 16 to 25) and thc Piperls trilinear diagram (Fig. 27) for the upper unconfined groundwater revealed the following: (a) The major cation for the spring watcr in the study arm is sodium whereas the major cation type for hand-dug wells is of sodium and calcium-type. HW3 Oqidi indicates sodium (~a+)as the dominant cation type whereas Nwangene spring Sp4 reveals ,' calcium (ca2+) as the dominant cation type. However, both the HW4 and HW5 Nkwelle-Ezunaka and Sp5, also at Nkwelle-Ezunaka, reveal no dominant cation type. (b) Chloridc (~1")in the major anion typ. lor the spring waters whereas bicarbonate (HCO;) is the ,major anion type for waters from hand-dug wells, The two hand-dug wells at Nkwclle-Ezunaka, i.e. HW4 and HW5 however, show no dominant anion type. ,~le15: 2ocheriiical Analyses Data for h'ater Sanc?ss From Hand-dug wells and Springs in the study Area A A 4 Fig.26 :Clasif icathn, diagram for the anions and Cations Fac~es'in terms of Major - \on percentages . (Freeze and C her ry ,1979 ) (c) able 16 shows the geochemical classification of the upper aquifer groundwater system. It reveals the following hydrochemical facies: calcium-sodium facies, calcium-magnesium facies, chloride-bicarbonate facies and bicarbonate- chloride facies as being dominant, Hydrogeochemical facies as defined by Back and Hanshaw (1965) are distinct zones that have cation and anion concentrations describable within composition categories, As already noted, both the stiff method of representing chemical analysis and the Piper's method of classification of hydrochemical facies were used in the study. Figure 27 and Table 16 are based on Figure 24 which is the Piper's classification diagram, The study shows that the predominant hydrogeochemical 2+ + 2+ cation facies are the Ca -Na facies and the ~a+-ca facies, The predominant hydrogeochemical anion facies 2- are the c1--so4 facies and the ~1--HCO;facies. At present the quality of the upper unconfined ground- water appears to be good for most purposes, Except for iron which is high for both the springs. and hand-dug wells, all other analysed constituents fall within the recommended concentration limits set by W, H.O. (1982) ca2+ Cat iors CL' - Anions - F J =HW1 ~gbunike P = ~kisa-anya - akommiri spring K=HW2 Umunya Sp 1 Ogbwni ke L =HW3 Ogid~ Q =Ogba Cave spring Sp2 Ogbunike M =HW4 Nkwelle- E zunaka R =Nkisi-Clsile spring Sp 3 Ogbunike N =W5 N kwelle- Ezunaka S= Nwangene spring Sp 4 hhya T=Obiarn spring Sp5 Nkdk-Ezunclka Fi9-23;Pipers trilinear diagram for the springs hand- dug Mls in the study area, Table 16: classiiication of the Upper Unconfined Water in the Study Area on the Basis of Their Major ion percentages )ring/ Yajor md-dug anion Facies Location ~11No. type HCoi-Type Jmunya (K) HCoi-Type ja2+-~a+facies ' 2- cl--Type C1 -SO4 facies Vkwelle- No domi- 3zunaka (M) nant. . ~1--HCO;facies Nkwelle- No domi- Szunaka (N) No dominant nan t ~1--HCO;facies + Ogbuni ke ( P: Na -Type ~1~-Typec~--so:- facies + Ogbunike (Q: Na -Type Cl--~ype cL--so~- facies + 2- Ogbuni ke ( R Na -Type ~l--~y~ec~--so~ facies 2+ Umunya (S) Ca -Type No domi- ~a+-ca~+facies Nkwelle- HCO-41-f acies Ezunaka (TI 3 and U.S.E.P.A. (1975). However, since groundwater quality is fluctuating daily, it is most likely that the situation would change in future. Both surface and subsurface contamination mainly due to human activities such as laundry activities as well as leachate contamination may probably lead to the deterio- ration of groundwater quality in the future. In order to prevent these analysed constituents such as chloride, sulphate, total alkalinity, etc., from increasing beyond the limits set by W.H.O. (1982) and U.S.E.P.A. (1375) in future, the following conditions must be met: (a) Correct refuse disposal method such as through the use of properly constructed and maintained sanitary landfills over impermeable strata. This will minimise or even eliminate leachate contamination as well as the effects of environ- mental constituents such as surface scums on water quality. (.b) Improvement in the sanitary condition in and around the wells and springs, laundry activities should be at proper sites and careless defaecation stopped. .'a 95 5.5 Hydrogeochemistry of Surface Water Bodies, The chemical quality of streams or rivers depends on the origin of the water, the rate of evapotranspiration, the nature of soils and rocks that are encountered along the course of the stream or river. It also depends on the nature of the rock underlying the stream bed, the length of the contact time with the soil and rocks, and the minerals in the soils and rocks (Linskov and Kimball, 1984). Physical quality of water depends on2 the nature of the soils and rocks along the flow path. Two surface water bodies were analysed in the study area. These are the Nkisi River (sample collected under the bridge across Nkisi River along Ogbunike-Umunya road) and the Oyi River (sample collected under the bridge) across Oyi River along Onitsha-Nsukka road (Adani road). Physical analysis of these water samples reveal that .. the colour value was 20 Hazen units at Nkisi River and 25 Hazen units at Oyi River. The turbidity values are 4 F.T,U, at Nkisi River and 28.2 F.T.U. at the Oyi River. Thea.waters are turbid. The colour is probably due to the presence of suspended matter such as ferric hydroxide formed as a result of exposure of groundwater with L dissolved ferrous iron to the atmosphere. Turbidity of the water may be due to the presence of clay, silt and other finzs in the soil through which the water flows. Alkalinity value was 16.3 mg/l in the Nkisi River and 20 mg/l in the Oyi River. The most important source of alkalinity is the bicarbonate ion which is probably derived from decaying organic matter in the soil. Silica concentration is uniformly 16 mQ/l whereas sulphate concentration was 6.1 mg/l at Nkisi River and 26.1 mg/l at Oyi River. Chloride concentration was 5.5 mg/l at Nkisi River and 30.3 mg/l at Oyi River. The chloride concentration is low. The dissolved oxygen value was 0.95 mg/l in the Nkisi River sample and 1.02 mg/l in the Oyi River sample. The generally low dissolved oxygen content is probably due to bacterial activities and/or oxidation reactions . in the soil zone. Total hardness (as CaCO value was 6 mg/l in the 3 Nkisi River and 81.3 mg/l in the Oyi River. This indi- cates that the water from Nkisi River is generally soft whereas the water from the Oyi River is moderately hard. The- sodium adsorption ratio (S.A.R.) for the surface waters is low and the values were 3.6 and 4.39. There is thus, low alkali hazard. The water could therefore be employed for irrigation purposes. A look at the cation concentration (in Table 17) suggests that apart from iron content which is somewhat Table 17: Geochemical Analyses of Water Samples for Surface Water Samples Values indicated as mg/l (except otherwise indicated ) Colour (Hazen units 'rurbidi ty (F. T.U. 1 PH Temperature (OC 1 Electrical conductivity (U ohms/cm) Total hardness (la2+ Hardness as CaC03 2+ Mg Na + Silica as Si02 (mg/l) Chlorides as C1 (mg/l) Chlorides as NaCl (mg/l) Total iron as Fe (mg/l) 2- ~ul~hatesas SOq (mg/l) Dissolved oxygen Total alkalinity Total. solids dried at 103~~ Total dissolved solids (T.D.S) Suspended solids 2+ 2+ Ca /mg S.A.R. I3? high with values 0.45 mg/l in the Nkisi River and 0.82 mg/l in the Oyi River, all other analysed cation concentrations fall within the recommended WHO (1982) and U.S.E,P.A. (1975) limits. The calcium concentration value was 0.8 mg/l in Nkisi River and 22.41 mg/l in Oyi River whereas magnesium concentration values were 1.2 mg/l and 5.47 mg/l, respectively. Unlike the Nkisi River, the calcium con- centration in Oyi River is by far higher than magnesium concentrations (22.41 mg/l calcium to 5.47 mg/l magnesium), Calcium is thus a much greater contributor to water hardness than magnesium in the Oyi River. 5.6 Ilydrogeochemistry of Lower Confined Groundwater The deep confined aquifer extend throughout the' study area. No natural discharge of this aquifer occurs within the study area but probably occurs towards the west and northwest of the study area. Artificial discharge is however effected by means ofborehole: .About 9 or 10 borehole samples around this study area were analysed. Table 18 shows the hydrogeochemical composition of the lower confined aquifer, The colour o$ the water generally ranged from 5 to 15 Hazen units and turbidity value was from 5 F.T.U. to 12.4 F.T.U. LC 0 'ti The water is thus generally clear. Only in the Onitsha (~~18)borehole was an exceptionallyhigh colour value of more than forty ( 40) Hazen units and turbidity value af 74.15 F.T.U. recorded. This is probably due to poor well completion and development. The pH values ranged from 5.16 at Otuocha borehole to 6.55 at Umudioka with a value of 5.35 at Ogbunike. This indicates slightly acidic waters. The pH values trend which is illustrated in Figure 2% reveal a decreasing pH toward the discharge zones. This implies decreasing alkalinity and increasing acidity of groundwater along flow path. All waters entering the groundwater flow system usually pass through the recharge zone which occurs within the biologically active soil zone. Carbon- dioxide and organic acids produced by plants and other living organisms in the soil will lower the pH of the . water. In this way the soil zone influences the chemistry of water that infiltrates through it by production of high amounts of acids and consumption of all oxygen in 'the water (Bouwer, 1978). Carbonic acid is the most important acid in this zone. Freeze and Cherry (1979) C attributed low pH along flow path to anaerobic condition b produced as a result of the fact that groundwater tends to contain less oxygen and is non-fluxing along the flow LEGEND R~versand Streams F ;g. 23: Map of pH variations in the deep lower confined aquifer mters . 7 4-a path, Acidity could also resul k from contamination from surface water bodies and possibly from chemical reactions associated with groundwater mixing. Hydrolysis of iron in laterite deposits is abundant in the study area. Alkalinity values range from 801 mg/l at Os~dito 122 mg/l at Umunya. A value of 13 mg/l was recorded at Oybunike. The main cause of alkalinity is the bicar- bonate ion. The high alkalinity values may also be attributed to sulphate reduction. Typically, waters experiencing sulpha te reduction tend to have high bicarbonate and carbondioxide contents and also contain hydrogen sulphide. This is because sulphate reducing bacteria utilize the oxygen from sulphate ions to biochemically oxidize hydrocarbons such as propane and methane derived from decaying organic matter within the son1 zone. Tht: total dissolved solids concentration ranged from 9.8 mg/l to 109.84 mg/l which is quite low. Values of 33,30 mg/l, 38.12 mg/l and 90.81 mg/l were recorded at Ogbunike, Umunya and Otuocha borehole water samples, r~spectivelyo The water thus has low residence timeo Sulphate and silica concentrations are generally low with sulphate values ranging from 3 mg/l at Jgidi borehole to 2; mg/l at Ottcjlcha borehole and silica vs'ues ranging from 6 mg/l at Ogbunike borehole and Onitsha borehole (BH16) to 20 mg/l at Umunya borehole. Chloride concentrations range from 3.48 mg/l at Ogidi borehole (BH8) to 36.19 mg/l at Onitsha borehole (BH18). A chloride value of 6.1 mg/l was however recorded at Ogbunike borehole (BH1). Chloride as sodium chloride values ranged from 5.09 mg/l around Ogidi to 55.11 mg/l around Onitsha. Salts are added to groundwater passing through soils by soluble products of soil weathering and of erosion by moving water. Salt is also added to groundwater through the dissolution of soil material, and selective adsorption of salts by plants as well as.from the evap3transpiration process which tends to concentrate salts in drainage waters. The dissolved oxygen is generally low ranging from 0.08 mg/l to 1.02 mg/l. The low value may be attributed to consumption of oxygen in oxidation reactions and bacterial activities during infiltration through the soil zone. The waters are generally soft except at Urnunya borehole where a total hardness (as CaCO3 ) value of 207 mg/l was recorded. This may also be attributed to the b presence of calcareous units within the underlying Nnnka 5@nJ~lt011e. A study of the cation concentrations in the deep +$j confined waters show that calcium Is higher than magnesium. Total iron is somewhat high whereas sodium relatively high. Stiff diagrams of the waters appear in Figs +q to 37 whereas Fig 38 shor:s the Piper's trilinear diagram for the ssme system. A study of the diagrams led to the following conclusions: 1. Sodium (~a') and calcium (ca2*)are of equal importance as the major cation type for the study area. However, Ogbunike borehole (BHl), Ogidi borehole (BH81, Otuocha borehole (EH11) and Onitsha borehole (BH23) show no dominant cation type. Nkisi River had sodium as the dominant cation type whereas Oyi River showed no domdnant cation type. 2. Chloride (~l-)and bicarbonate (HCO;) anions are of equal importance as the dominant anion species. Howc-~er, other boreholes such as Ogbunike borehole (Btil), Ogidi borehole (BH8) and Otuocha borehole (BH1) showed no dominant anion type. Chloride is the dominant anion for the NkPsi River whereas Oyi River showed no dominant anion type b species. 3. The predominant hydrogeochern!.cal cation facies + + consists of Na - ca2' facies, ca2+ - Na facies 2 c and Ca -MCJ~+ facies whereas ~1-- HCO;, and c.1- - SO:- facies are the predominant hydro- geochemical anion facies. The water of this aquifer is probably a product of mixing of two or more water types. Also the water chemistry may reflect partly marine sedimentary conditions whose organic components cause sulphate reduction (L,eohnert, 1986). Further hydrogeochemical and possibly isotopic studies are necessary in order to indisputably establish this. k comparison of the water quality criteria especially those given by WHO (1982) and U.S.E.P.A. (1975) and chemical composition of the lower csnfined groundwater indicate that apart from iron, the water is gen~cally of good quality, soft and good for various purposes, However, the borehole at Umunya (BH4) revealed water that is moderately hard, The iron content of all the boreholes (with the exception of cgbunike borehole (BHI)) is high. The water from Onitsha borehole (DHIO), Otuocha borehole (BH11) and Ogidi borehole (BM1S) with values between 1.0 mg/l and 4.0 mg/l should be treated before use. ~='OgbwrikeBoreholr @HI) G Enugwu-ukwu -hole (EM28 €3 Umunyu Borehole (BH4) H = Onitsha Urban Borehde (BH13 : C = Umudioka Borehole (BH10) U ~muoji Borehole (8142'7 D= Ogidi Borehole (BH 8) V = Nkki ~iver. E On itsha Urban Borehole (BH16) Z = Oyi Riwr , F =Otuocha Borehole (BH11) Fh 3%:R'prs trilinear diagram for the borehahles arid smi Riwrs in the study am . 934 4: Table 19: Classification of the Lower Confined Aauifer Waters Around the Study Area on the ~aiisof their Major ion Percentages Major Yajor Location cation anion Facies type type Ogbunike No domi- No domi- :1--HCO;facie (BH1) A nan t ?ant Umunya ( BH4 2+ (Bl-lrl) B Ca -type HCO;-T~~~ Urnudioka (BH10) C ~a+-T~~e~1ZType Ogidi No domi- No domi- (BH8) D han t nan :~--Hco- facie. t 3 Onitsha + 2- Urban (~H16)E Na -Type c 1-- ~ypeEl - -SO4 facie No domi- No domi- Otuocha ~1--HCO;facie (BH11) F nant nant Enugwu-Ukwu + (BH28) G Na -Type C1--Type Oni tsha No domi- Urban (BH18) l nan t c 1-- Type Na+-Ca2+ facie Urnuo j i 2+ (DH27) U Ca -Tjrpe HCO;-TY~ ca2*-Na' facie + Nkisi River \ Na -Type C1--~ype CI--SO;- facie Oyi River Z No domi- No domi- nant nant Na+-Ca2+ facie Compari son of the Hydroqeochemistry of the Upper Unconfined Groundwater and the Lower Confined Groundwater Besides the differencesin depth of occurrence and aquifer parameters, there are significant differences in hydrogeochemistry of these twogroundwaterflow systems. The water from the upper unconfined aquifers with the ' exception of spring waters have poorer colour, and are more turbid than the deep lower confined groundwater. The spring water however, are generally clearer and less turbid than water from the hand-dug wells. The pH range from the upper unconfined groundwater was 4.68 - 8.17 whereas that of the deep confined groundwater was from 5.16 - 6.55. Thus the waters from the upper unconfined groundwater are acidic to slightly alkaline. The deep confined groundwater, however, reveal pH values that are not more than 6.55. The water is thus (slightly) acidic to neutral. Calcium and magnesium concentrations are generally higher in the upper unconfined aquifer than in the 2+ lower confined aquifer. Ca /Mg2+ ratios and S.A.R. are generally higher in the upper unconfined groundwater than in the deep lower confined groundwater. The unconfined water is therefore higher in alkali hazards than the lower confined water. Iron content is generally higher in the lower confined groundwater than the upper unconfined groundwater. 41 Average alkalinity value for the upper unconfined groundwater is 22.44 mg/l whereas the average for the lower confined groundwater is 27.53 mg/l. Alkalinity is therefore relatively low, nearly uniform and in both cases are due to the bicarbonate ion. The bicarbonate anion may be derived mainly from the action of carbondioxide dissolved in infiltrating water and/or to effects of decaying organic matter including sulphate reduction which react with carbonates in the sail ta form the bicarbonate ion. One of the most significant differences between the two flow systems is the dominant ion types and their hydrogeochemical facies. Tables 1s and 18 show that 2+ sodium (~a+)ion and calcium (Ca ) ion are the dominant cations in the upper unconfined groundwater , whereas sodium (~a+)is the dominant cation in the lower confined groundwater. This indicates that sodium ions predominates over calcium ion at deeper levels. Bicarbonate (HCO;) and chloride (~1-1ions are the dominant anions for both flow systems. The predominant cation geochemical facies for the upper unconfined groundwater are the ca2' - *a+ facies 2* and Ca - M~*+facies whereas that of lower confined 158 groundwater is the ca2* - ~a+facies. The principal 4; anion. facies for both flow systems is the ~1-- HC03 f acies. The above data provide useful information necessary in understanding the groundwater evolution of the study area. 'Groundwater evolution of an area or basin can be described in terms of three main zones which correlated in a general way with depth (Dornenico, 11972). These are The upper zone - characterized by active ground- water f 1ushing through relatively we1 1-leached rocks. Water in this zone has bicarbonate (KO;) as the dominant anion and is low in total dissolved solids. The intermediate zone - characterized by less active groundwater circulation and higher total dissolved solids. Sulphate is normally the dominant anion in this zone. The lower zone - characterized by very sluggish groundwater flow. Highly soluble minerals are commonly present in this zone because very little groundwater flushing has occurred. High chloride concentration and high total dissolved solids are characteristic of this zone. IS9 These three zones cannot be correlated specifically with 4i distance of travel or time, other than to say that travel distance and time tend to increase from the upper zone to the lower zone. Freeze and Cherry (19791, however, pointed out that any given groundwater flow system must not necessarily follow the systematic geochemical trend described above. Thus, the depth of occurrence of groundwater ih the srea, groundwater chemistry and velocity (flux), as well as the distance of travel from the ultimate recharge area . were used in explaining the geochemical evolution of groundwater in the study area. As earlier noted the study area is a transition zone with recharge occurring few kilometres southeast of Ogbunike and discharge occurring into Rivers Niger and Anambra to the west and northwest of the area. This conclusion has been made taking . cognisance of generally low values of total dissolved solids (T.D.S) recorded around Ogbunike as opposed to higher values recorded at Onitsha and Otuocha areas. The generally high values of hydraulic head recorded southeast of Ogbunike as opposed to much lower values recorded west and northwest of the study area around Rivers Niger and Anambra. Groundwater from the study area is soft and slightly , , - ., I 60 acidic to acidic which is typical of groundwater that 4; has not travelled far from the recharge area. The depth of occurrence of gr'oundwater for the upper unconfined, middle semi-confined to confined and lower unconfined aquifer systems are generally less than 100 metres which is relatively shallow. The average linear groundwater velocity of the study area is 1.22 x lo2 m/yr which is high, This suggests active groundwater " flushing. Collation of the above data lead to the following conclusions with regards to the geochemical evolution of groundwater in the study area. (i There is active flushing within the groundwater zone considered. (ii) Chloride (~1-1bicarbonate (HCO;) are the principal anions in this zone. (iii) The groundwater appears not to have travelled far from recharge area. It appears that the study area is transitional, i,e, has both the features of recharge and discharqe areas but has mare of the features of a recharge area from hydro- geochemical point of view. ' 161 5.8 Sources of Pollution 4i .Groundwater pollution may be defined as the arti- ficially induced degradation of natural groundwater quality. Pollution can impair the use of water and can create hazards to public health through toxicity and spread of disease. Sources and cause of groundwater pollution in the study area include both distributed and point sources. Most pollution in the area originate from human activities such as the use of surface waters (especially Rivers Niger and Anambra) in and around the area for waste disposal including indiscriminate defaecation in places washed into surface waters. Also leachates from refuse in landfills and dumps (found at Ogbunike, Nkwelle-Ezunaka and Umunyaj have Contributed in surface water and groundwater pollution. These have probably contributed to the relatively high chloride (~1-), low dissolved oxygen, hardness, alkalinity as well as high iron recorded in some of the 1 ind-dug wells in the study area. ,. A look at Table 15 shows that alkalinity, hardness, total iron and total dissolved solids values are generally higher in hand-dug wells than in springs in b the study area. This is probably due to the pollution attenuation mechanisms of which filtration, chemical reaction, such as oxidation/reduction reactions and probably sorption are the most important. These attenua- 4; tion .mechanisms act on the waters from the time it enters the upper unconfined flow system to the time it is discharged as springs. Pit latrines in the study area which sometimes penetrate the upper unconfined water'table are significant sources of bacteriological pollution. This is particularly important at Nkwelle- Ezunaka where the depth to water table may be as low as 8 metres in the inhabited area. Pollution from industrial activities of, for example, the Alpha Mills at Ogbunike, the Tempo Vita at Umunya and Nkwelle-Ezunaka Oil mills, etc., need a more detailed study. A monitoring programme for the study area is needed for an accurate study and evaluation of the extent of harm done from these sources. Also needed to be studied are the effects of fertilizer application to groundwater quality. A nitrate anion monitoring is more relevant here. Poor casing and/or sealing of some boreholes in the study area result in- direct ingress of contaminated surface water into groundwater. In order to prevent this, efforts should he made to ensure that borehole construction meets b acceptable (health) standards. Finally, people should be educated on proper waste disposal methods such as through the use of sanitary landfills over impermeable strata to minimize or even 3; eliminate groundwater pollution (Ezeigbo, 1987). CHAPTER SIX 6.1 GEOTECHNICAL PROBLEMS Geotechnical problems associated with groundwater which already constitute or may constitute a future threat to the people of the study area is soil erosion. Soil crosibn is the process by which surficial soil particles are removed directly by various erosive agents such as rainsplash and concentrated runoff, wind, man anq/or soil wash through sheet erosion. It ranges from small dendrically shaped rills to deep gullies. Field studies (ecg. by Grove, 1951; Ofomata, 1965; Ogbukagu, 1976; Egboka and Nwankwa, 1982; Uma and Onuoha, 1987) have been carried out to investigate the influence of geomorphological and geologic processes as well as hydrogeological parameters such as hydraulic conductivity, K, transrnissivi ty, T, and specific discharge, Vd, on gully development. They summarized the following factors on which soil erosion depends as: 1. Erodibility of the soil (susceptibility of the soil to erosion). 2. Theenergyof the erosive agents 3. The protective influence of the vegetation. 4. Human activities. The increasing soil erosion menace in the study 1. I65 area depends larqely on human activities, the energy li of the erosive agents, protective influence of the vegetation and the erodibility of the soil. The under- lying hank4 Sandstone units in the study area consists of fine-medium grained, poorly to moderately sorted sandstone witti high K, T, and Vd values. The hydraulic conductivity (K) value fall within the range (10-I to whereas the specific discharge Vd is about 55 m/year which is high, This implies high seepage force. The sandstone which is sometimes weathered and li teri te- capped is relatively permeable and allows. infiltration, This causes a rise in water table, which increases pore water pressure, reduces the effective stress and thereby weakens the soil. Rainfall of mostly hiqh intensity occurs over a . duration of seven months (April to October) thereby causing hiqh velocity run-offs with high erosive energy, thus leading to increased erosion, Human activities such as road construction, indiscriminate and unplanned building of houses without proper drainage system, removal of the vegetative cover through bush burning and carel~ssfarming, favour increased erosion in the study area. Road construction helps in creating artificial slopes on which numerous 4i gully spots are generated ma and Onuoha, 1987). Removal of vegetative cover, and Improper drainage system increases the volume of overland flow especially when the soil moisture is at its full capacity. Hence, before any major remedial measure that will have arly meaningful effect is taken, a proper study of I the factors responsible for the erosion process should be undertaken. Such factors as the effects of rainfall, soil and rock properties and especially groundwater (seepage force) and its chemistry on soil erosion have to be well understood. Also human activit.ies that are inimical to soil erosion must be curtailed. 6.2 Water Supply Prospects and Problems Communities within the study area such as Qgbunike, Ogidi, Nkwele-Ezunaka and Umunya have semi-urban status, They need water for many purposes which include: 1 Drinking (culinary) and other household uses such as for washing, bathing, cooking and laundry, (2) Industrial processes protecting life and properties against fire and for irrigating farms especially during the dry season, etc. The population of the communities is about 150,000 and capita per day to maintain basic hygiene, they wfil 5 require about 750,000 litres (750 rn ) of water per clay, out the study area and is currently ta?$ea tnr~w~i, hand-dug wells and exist naturally as sprinqs. 1,. cc .... ., account for as much as half (or more) of the presp?!'it demand if properly managed through the spacing out ot a nurnbcr of shallow wells. The upper unconfineu ar,~;h: :r neither complex nor Lime consuming. Some oi the G,3,iiCi4:.~~ wells arc installed with pumps (either hand oh- motor~.::~:s pumps) making abstraction easier whereas some are abstracted physically by means of bucket tied to ropc s, Local inhabitants who could not af faid hdnd-dug wk*. '.r, makc tic with springs which are cjenerah 1 y of sa?.i.:ji'cia: l:c;i&-,k~ yuali ty and occur within toierrainie distances fro$, t:i;e inhabi tcd ark. Some of the springs are installed ~~iith coll ec tor-reservoir which helps in conservl..;.iq wntcr: for later. use. Major rivers in the study area such as OyX and Nkisi and their tributaries are generally good for most purposes. They are increasing used for washing, tstk,incj, fermentation of cassava, etc. The Nkisi ,?Aver is soft and has low alkali hazard (low ca2+/Mg2' ratio) and good for laundry and irrigation purposes, The rivers also contribute substantially to the water needs of the communities and is also within the easy reach of the local inhabitants, Given the increasing rate of popula t,os, ~hr51~0 the lower aquifer systems should also be explorced CG augment upper aquifer supplies. This wiiP help prevt?ri t the land subsidence. Already the state and the federal governments have drilled some boreholes around the area. Some ~jrefunctioning whereas some are non-functional because of any or a combination of the following reasons: (li Non-inst-Plation of submersible pmps or the use of lower capacity pungs. , (2) Lack of proper well rehabilitation and mair?ccnarice (3) Lack of proper well completion and development Eoc optimum yield. b However, taking into consideration that the date: qdallty oi f- ;. study area is ge.~erallygood and that the gr~undw~~t~brreserves for the three aquifer syst?ms in 9 the study area is quite high reaching up to 4.72 x I0 cubic metres of water. Tilere are very bright pnospects for groundwater resources deueloym~atin the area, The transieLonal character of the ;oweL- aquifer ~rodncwhk~:: is most probably bde to m;xins in tne h'lcpr kib'ei wukZ:r. Induced infiltration thus could be a management option in the future. . . in expanse, Tho topopaphy consists of unda2a";i.ry: n.cii::n: t:~!t t.5: south but con.sists mainly of plains to -the North. 1% is underlain by thme geo1oy;ic formation. The Imo 5hnl.e to t'b? nbrth, Nanka Sandstone to the south and the 0gwash-i-baaha Forms tion Lo L3.e southwest. The Nanka Snndst,on.e whi:oh is !;hi:? main qukfer cofisists 0:' poorly to rnodera.te1.y consol.ic:at!>d, .i't:lt:?-- These a.re .the upper Tinconfined, t;;i.1e n~i:l\l:I.z semi.-con.fined -to confined nn.d the bwer confined a.quifer systems. The upper unconfined aquifer which occxrs t;hroughout the area is exnio.,.l;:r:::i Determination of the hydraulic conductivity vaiues :'r,:,r:. ,the -4 % Transmissivity values rani7;ecl from 9-81 x 10 n /s with :In -2 2 average of ribcut 2.4 x 10 m 1s. Aq?uj.fer pa:r%aa:!.,ic.:.:; cnlcu.l.atetl froni .the logan (1964) and coc;;,e.r. arie. Zzcob (';fj46 method gave the averog~.hydrsullc ccnc,~uctfivit;g(A) o;' l;-~.c - 5 lower confimd aqciif er system as app;-oximately ?,? x 'I(:: - IL/:; A and the transmissivity value as about 1.1 3 x 10-~ml/s. Two poundwater flow systems have been reco~nis~c~.'!'hc~se are the local flow system exhibited in the upper ~inconfineclaipifc~, and the retl;ional i;rounwate;- fbw system exhi-~:i.te2. 5.r.:. the :crinier cor,fi.r;ed aq-ilil'er. The regional .flow dl.rect:ion is towa.rcl. t;he .we:-:i; ..~.. . an6 northwest di !~.recti.on,i.. e, , tobiari! s Rivers j';lircr. arid Anitn~b:rc:;, Annual precigitation is about 1850 mm. About 'l5.076 of .the atmr\sy)hc.;:.. ic preci~it;ation escapes a.s runoff whc~easevavotranspi.rat.IL 011 accounts for about 64.5%- The rest inf i1.tre.te.s as rech:'~?e!kt0 , -.. . the underlying aquifer. Hydro,.:eoche~ic.ai sttdle:; i.nalc,C~ -rrJ .I.. ""~.;.Lc z, domimmt cations for the upper unconfined aqujfer. whe~en.:: sodium '(Na + ) ion is the dominant cation in the lower r:c~a:ficeii Suc?pest or;s for Fu-tu,y.-e';$:.;oyt;: -..--. -.-.-.,".. . -- j '7 l2 rrl-"l,. .,,. -,. s 6n.e attemp'i; to.wa~6 s ev:i.!.~la.?;in[< .;:!ni.': co!?.r,o?.ii: rif :i.:: -; ' ','& the hydrogeo1ci;;l.c datz ?or t,he :;i;tld;;r area, ..4.LLcV~OT~K caul-5 be improved upon in futmre as more da-La are col.?..ict;c?, col.l;!-t;ed ,ii;lj ahalysed, Suggesticns that wit1 not only hel;p in fu1,ur.e improvement of th~:work but also in efficient 6evclopen.t arid ~,~nagernentof the f;roun.dweter resourcer: of -!he::t;ldy area i~lcl~cii::.. area with a view of even supplying 0niC:;na ora ;any ot't,e.- less endowed area which is near by with :-i;r~oicniilrr::t,r-r.:-'' REFERENCES 173 Adegake, OxS. 1969 Eocene stratigraphy of southern Nigeria. Collucpe Sur L'EOCENE PARIS 1968 Extrait de Memoires du R.R.G.M. No 69, pp 23-48. 4. Akujieze, C.N. 1984 Hydrogeology of the Area (Nanka sands) South of the Upper Sector of Idemili drainage basin. Unpublished M.Sc. thesis University of Nigeria, Nsukka. American Water Works Association, 1970 Standard Methods for the Examination of Water and Waste Water. ,13th edition ALPHA, AWWA and WPCF, Publi. by ALPHA, New York. Arua, I.. and, V.R. Rao 1987 ~ewstratkgraphic data on the Eocene Arrleki Format ion. Jour of Africm Earth Sciences, Vo1.6, (4) PP 391-397. 1 Back, W and B.B. Hanshaw, 1965 Chenlical Geochronology in Chow, V.T. (ed), Advance in Hydroscience. V.Z. Academic Press London. Bouwer, H. 1978 Groundwater Hydrology. Mc Graw Hill Inc. Tokyo. Brassington, R. 1988. Fiedl Hydrogeolo~g. J. Wiley and Sons, New York. Cooper, 1I.H. Jr. , and C.E. Jacob, 1964. Generalised ~raphicalmethod for evaluating format i on const ants and summarising well- field history, Trans her. Geophysical Union V.27 PP 526-5340 Domenico, P.A. 1972. Concepts and models in ~roundwaterhydrology. McGraw - Hill New York. Du F'reeze, J. W. 1947 Further observations on the lignites of Onitsha Province. Ann. rpt. Geol.. Surv. Nig, (194-6) pp 25-26. Egboka, B.C.E. and G.I. Rwankwo 1985. The hydrogeological and geot echnical parameters as arl:ents for the expansion of A~ulu-Nanka gull@ Anambra State, Nir-eria Journal of African Earth Sciences. Vo1.3, No 4, pp 417-425. Ezeama, J.C.O. 1989. The Hydrogeology, of Ogbunike and Environs Unpublished FGD thesis Dept. of Geological Sciences Anambra State University of Technology Enup Nig. 6 Ezeigbo, H.1. 1987. Quality of Water i7esources in Anambra State, Nif;eria. Wigeria Jour. Nin. Geol. Vol. 23 (l4,2) pp 97-103. Ezeigbo, H.I. 1988. Geological and hydrogeological 4; influences on the Nigerian environment Water Resources (NAH) vol.l(l) pp.37-44 Fetter, C.W. (Jr) 1980. Applied hydrogeology. Charles E. Mer r ill Pub. Co. London. Folk, H.L. and W.C. Ward, 1957. Brazos. River; a study in the significance of grainsize parameters. . J. Sed. 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Groundwater Vol. 2 Nr. 1: PP 35-37 Masch, F.D. and K.J. Dew, 1966. Grainsize distribution and its effect on the permeability of unconsolidated sands. Water Resources Research Vol. 2: -pp. 665-677. Mbanu~l;~,R.E. 1387. The Water Resources of Ogidi Area. Unpublished Msc, thesis Dept of Geological Sciences, Anambra State University of Technology Enup Nie. Meinzer, LO; 1942 Hydrology MeGraw-Hill pp 280-359. Meyboom, P. 1966. Groundwater studies in Assiniboine drainage basin: I The evaluation of a flow system in the South central saskatchewan. Geol. Surv. Can. Bull. 139. Nuthing, P.G. 1930. Physical analysis of oil sands. Bull. Amer. Assoc. Petr. Geol. Vol, 14: 1337-1349. Nwajide, C. S. 1977 Sedimentology and stratigraphy of Nanka Sand. Unpublished M,Phil, Thesis Dept. of Geol. Univ. of Nigeria, Nsukka. b Ofomata, G.E.K.? 1964 Soil, erosion in the Enugu region of Ni{i;erla. African Soils Vol. ix(2): pp 287-319. Ogbukagu, I.N. 1976. Soil erosion in the Northern parts of the Awka-Orlu Uplands, Nigeria. J. Min. Geol. Vo1.13(2 4; p? 6-19. 1980 The roperties and Drovenance of the Nanka sand (Eocene7 in the Anambra State of Nigeria. Cashier Geologiques Numero 94 Tour 16. 1988 Summary appraisals of the Anambra State 7Nizeria): Surf ace Water and Groundwater Hydrolo~y..,- . &d'-'Ghemistry. Submitted for publication.- ~rajnka,S.O. 1975, Geology in Ofomata, G.E.K.(~~)Nigeria in Maps. Ethiope Fubl-. Benin-City Nigeria, pp 5-7. 1 Pettigolm, F. J. 1975, Sedimentayy rocks 3rd ed.) Rarper and How, New York. Reyment, H.A. and Barber, V.M. 1956. Nigeria and Camerouns. Lexique Stratigraphique International Afrique V.4, No. 24-pp 35-59, Reyment, R.A. 1965, Aspects of the geology of Nigeria. University of Ibadan Press, Nigeria. Rodda, J.C., Downing, R.A. and Law, F.M. 1976 sys-tematic hydrology, Butterworth and Go. Pub. Ltd. London, Short, K.C. and Stauble, A.I. 1967. Outline of Geology of Niger Detta. Bull. A.A.P.G., V. 54, pp 761-779. . Simpson, A. 1954, The Niceria Coal fields, the geology of parts of Onitsha, Owerri and Benue Provinces. Geol, Surv. Nig. Bull. 24. Skoup and Co. 1978 Pre-feasibility report on the Anambra River Basin. Tattam, C.W. 1944, A review of Nigerian Biostratigraphy. Rep. Geol. Sum. Nig. pp 26-27. Todd, D.K. 1980. Groundwater Hydrology (2nd ed). J. Wiley and Sons New York. b REFERENCES 177 To th, J. 1966 Mapping and international of field phenomena 4 for groundwater reconnaissance in a prairie environment, Alberta Canada, Bull. Intern. Assoc. Sci. Hydrol. V.Il(2) p 1-49. Uma, K.O. and K.M. Onuoha, 1987 Groundwater fluzes and qully - development in Southeastern Nigeria (Ofoegbu, C.O. ed. Groundwater and mineral resources of Niceria. Friedviewey & Sohn, Rraunschweig/Weisbaden. p. 39-59. Uma, K.O., Egboka, B.C.E. and 1C.M. Onuoha, 1989. New Statistical Grain-size method of evaluating the hydraulic conductivity of sandy aquifers. Jour. of Hyarology, 108: pp 343-366. 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Report of Sieve Analysis of Water Producing Horizon (Sandstone) of Ogba Cave Spring Date: 5/2/90 li Sample No: Location G1 - Method of Analysis: (a) Screen type: Half Phi interval ASTM (b) Shaker type: Automatic (c) Sieving time: 15 minutes - U C 0) Class interval E E 0 -U Modal class - ' Sievc Loss: 0.23 Total weight: 49.77 lieport of Sieve Analysis of Water Producing Horizon (Sandstone) of Bottom Layer of c* .Nkl.sa-anya-akommiri Spring Date: 5/2/90 Sample No: Location G2 ~cthodof Analysis: (a) Screen type: Half .Phi interval ASTM (b) . Shaker type: ~utomatic (c) Sieving tirgle: 15 minutes Weight of Sample: 54.05 r, Class interval C i Phi 0 -U -2.00 -2.00- -1.50 -1.50- -1.00 -2.00- -0 -50 -0.50- -0.00 3.00-0.50 0.50-1.00 1.00-1.50 1.50-2.00 2.00-2.50 Modal zlas: 2.50-3.00 3.00-3.50 3.50-4.00 4.00-4.50 4.50 Sieve Loss: 0.15 Total weight: 53.90 grams 380 Report of Sieve Analysis of Water Producing Horizon (Sandstone) of the Upper Layer of + . Nkisa-anya-akommiri Spring Date: 5/2/90 Sample No: Location G2 I.1et;hod of Analysis: (a) Screen type: Half. Phi interval ASTM (b) shaker type: Automatic (c) Sieving tlme: 15 minutes llcight of Sample: 45.72 g - JJ C Class interval E 0 . mm Phi -U 4.00 4.00-2.80 2.80-2.00 2.00-1.40 1.40-1.00 . 1.00-0.710 0 ..710-0. SOC 0.500-0.355 0.355-0.25( 0 250-0.18( Modal elas: o.iso-0.12: 00125-0.09( 0.090-0.06: - 0 .063-0-04' 0.045 Scive Loss: 0.21 Total weight: 45.51 181 1~ - Report of Sieve Analysis of Water Producing 4; . Horizon (Sandstone) of Nkisa-Osile Spring Date: 5/2/90 Sample No: Location G3 Method of Analysis: (a) Screen type: Half Phi interval ASTM (b) Shaker type: Automat.ic (c) 'sieving time: 15 minutes Sample: grams II - - - - Re- :or- ummu- tained rec ted ative zum, :om- Class interval on vt. grn t st. nen t sieve Phi -wt gm - - - -2.00 p2.00- -1.50 ~1.50- -1.00 81.00- -0.50 ~0, 50-0.00 1.00-0.50 0.23 0.49 1.50-1.00 0.88 1.86 .moo-1.50 1-77 3-75 1.50-2.00 4.61 9.77 e.00-2.50 '1.05 44.61 Mod;: 2.50-3.00 40.07 84.91 clas 3.00-3.50 43.78 92.77 3.50-4.00 44.50 94.3c 4.00-4.50 45.46 96.3: 47.19 LOO. OC Sicve Loss: 0.05 Total weight: 47.15 Report of Sieve Analysis for Ameki Sandstone r i ( Oni tshe-Nsukka road, i .e. ~daniRoad) Outcrop Date: 15/2/30 Sample No: Location \ Method of Analysis: (a) Screen length: Half Phi interval ASTM (bl Shaker type: Automatic (c) Sieving time: 15 minutes 54.02 LJeigHt of Sample: - a C Class intc val QI E E mm Phi 0 -U 4.00 -2 .00 4.00-2.80 -2.00- -1.50 2.80-2.00 11.50- -1.00 2.00-1.40 .1.00- -0.50 1.40-1.00 .0.50-0.00 1.00-0.710 1.00-0.50 0.710-0.500 0.50-1.00 0.200-0,355 1000-1.50 Modal 0. 355-0025C 1.50-2.00 clas: 0.250-0.18C 2.00-2.50 0.180-0.125 2.50-3.00 0 125-0 009~3.00-3.50 0.090-0.06: 3.50-4.00 0.063-0.04: 4.00-4.50 *I. 0.045 4. EiO Sieve loss: 0.04 Total weight: 53.98 Report of Sieve Analysis for Ameki Sandstone + (km 20 Onitsha-Enugu Express Road,) Outcrop Date: 5/2/90 Sample No: Location G6 Method of ~nalysis: (a) Screen length: Half Phi interval ASTM (b) Shaker type: Automatic (c) Sieving time: 15 minutes Weight of Sample: 54.60 - I C, C aJ E Class interval E -u0 Moda elas Sieve Loss: 0.02 Total weight: 54.58 roba ability curve for the water bearing Sandstone 389 horizon of Ogba cave spring -~r& size (mm) , > 1m Probability cur= for the water bearing sandstone horizon ( bottom byer ) of Nkisi-anya-&ommi spring -Grain size (mm ) , Rababilit curve for the water bearing Sandstone horizon (Top Layer) af N kisi - anya - akommi ri spring 1 Gmln size (mrn) -Grain size in phi (PI) Units - 71388 ~robabil'ttyc we for hki%Mrtmc horizon of ~kisaOsile sprhg. I. Grain size (mm )- !I 'I Probability curve , for Ameki Sandstone [0ni tsha-~sukka(Adan;) rood J Out crop C -Grain -size in Phi ($%)units ---k - - ' . I .*I I90 fkbnbility curve for Ameki ~hdstone(krn 20 Onitsha- ~nugu Express road ) Out crop . 4 +-Grain size (mm) -