mapping groundwater potential zones in enugu state...

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Mapping Groundwater Potential Zones in Enugu State

using Remote Sensing and GIS Techniques

1F. U. Okoli,

2Johnson, N.G.,

3Ejikeme, J. O

1

Geoinformatics & Surveying Department, University of Nigeria, Enugu Campus, Nigeria 2Department of Surveying and Geoinformatics, Kogi State Polytechnic, Lokoja, Nigeria

3Department of Surveying and Geoiformatics, Nnamdi Azikiwe University, Awka, Nigeria

ABSTRACT

Groundwater forms part of the natural water cycle and is present within underground strata.

Groundwater constitutes an important source of water for various purposes, such as domestic,

industrial and agricultural needs. In the Hydrological cycle, groundwater occurs when surface water

from rainfall seeps into the earth and fills the soil pores and rock fragments. Groundwater flows in the

aquifer layer toward points of discharge, which include wells, rivers, lakes and ocean. The geology of

Enugu consists of mainly alluvium soil, granite, limestone, and sandstone, hard rock formation. In this

study, the application of Remote Sensing apred techniques was used to produce Groundwater

potential Map in Enugu. Various maps were prepared (Landuse, slope and Drainage, Lithology,

Lineament, Elevation, Soil types, and Rainfall gauges) from LandSat7 satellite imagery, and other

ancillary data. These maps were integrated to produce the groundwater potential zones map of the

study area based on the modified DRASTIC model. The Groundwater Potential map produced

comprised five categories of groundwater yield –Very High, High, Moderate, Poor or Very Poor. It

was found that all the alluvial plains and sandstones have high and low drainage densities

respectively.

Keywords: Groundwater, Remote Sensing, DEM, Enugu State, GIS, ArcGIS, Mapping

1.0 INTRODUCTION

In the world today, groundwater is of major importance to civilization, because it is the largest reserve

of drinkable water and major sources of supply in regions where humans inhabit. Groundwater may

appear at the surface in the form of springs, or it may be tapped by wells. Groundwater forms part of

the natural water cycle and constitutes a major portion of the cycle. Groundwater is present in various

types of geological formation and occurs in permeable geologic formation called Aquifers which can

store and transmit water. Groundwater inevitably occurs in geological formations. To understand the

occurrence of groundwater the distribution of geological materials of varying hydraulic conductivity

and porosity is important. Fracture is a general term but it has a second meaning - breaking along

irregular, often curved, surfaces. Breaks that tend to create planar failure surfaces are called faults or

joints. Fractures create secondary porosity in the rock Fracture traces are surface expression of joints,

zones of joints concentration, or faults.

Muheeb M. Awawdeh& Mohammed Al- Mohammed (2009) in their work „Integrated GIS and

Remote Sensing for Mapping Groundwater Potential Zones in Tulul al Ashaqif Highlands, NE

Jordan‟ prepared 8 thematic layers and they are selected: Geomorphology, soil texture, lithology,

elevation, slope, annual rainfall, drainage density, and lineament density. The thematic layers were

combined using weight index overlay method. The weights assigned to the data layers to reflect their

relative importance were determined using analytical hierarchy principle (AHP) and the classes in

each theme arranged in decreasing order of rating (0-100) based on previous work and experts.

Krishnamurthy et. al. (1996) in his project titled „Approach to demarcate ground water potential

zones through remote sensing and a geographical information system‟ prepared different thematic

maps such as, lithology, landforms, lineaments and surface water bodies at a 1:50000 scale using

remotely-sensed data as well as drainage density and slope classes from Survey of India topographical

International Journal of Innovative Environmental Studies Research 5(1):33-46, Jan.-Mar., 2017

© SEAHI PUBLICATIONS, 2017 www.seahipaj.org ISSN: 2354-2918

http://www.seahipaj.org/

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sheets in order to demarcate the ground water potential zones of Marudaiyar basin. All the thematic

layers were integrated and analyzed using modified DRASTIC model developed with logical

conditions in the geographical information system (GIS).

In Enugu State, which is known for its natural coal deposit, the means of groundwater assessment has

been a trial and error exercise in the estimation/identification of potential groundwater area(s) for the

inhabitants. The conventional methods used to prepare groundwater potential zones are mainly based

on ground surveys which takes time, money and lots of workforce. The groundwater conditions vary

significantly depending upon the slope, depth of weathering, presence of fractures, surface water

bodies, canals, irrigated fields etcetera. These factors can be interpreted or analyzed in GIS using

remote sensing data.

2.0 Study Area

The study area is the whole of Enugu State. The study area lies approximately within Latitude 6o

20”N and 6o 30”N and Longitude7

o 20”E and 7

o 30”E and is bounded by several other states; in the

North by both Benue and Kogi States, in the South by Abia and Imo States while in the west and east

Anambra and Ebonyi State. The Official population Figure of Enugu urban area from the 2006

population census stands at 722,664 (NPC, 2007). Settlement in towns is usually laid out in distinct

camps and residential quarters. In Enugu urban centre, for example, residences are delineated into the

Government Residential Area (GRA), the Ogui, Asata, Uwani, New Haven, Awkunanaw, Garki,

Abakpa Nike and OguiNike Areas, the Independence Layout, the Colliery Camps, China Town and

the Railway Artisan Quarters. The climate is tropical hinterland in nature and is comparatively

congenial. These are characterized by high temperature, high humidity and substantial rainfall. The

mean monthly temperature in the hottest period of February to April is about 33°C. The rain is

entirely seasonal, most of it falling between May and October. Humidity is highest between the

months of May and October and low between the months of December and February.

The relief of the study area is dominated by a prominent landform unit in the West of the town in the

Enugu escarpment. This is part of the Udi-hills, which carries the false-bedded sandstones of the Asali

formation and contains some isolated gravels domes. This gradually merges into shale undulating

flood plains of the Manu-Adada River complex. The high land region extends from Outkpo junction

through NsukkaUdi, Afikpo and Okigwe areas. The western escarpment is heavily dissected by run-

off and streams producing fully erosion-prone surfaces in the study area. This yield the isolated steep

sided topped hills, which form part of the Nsukka – Okigwe Plateau. These relief features gave rise to

the dendrite characteristic drainage pattern governed by two main river system – the Nyaba and Ekulu

river system. These two rivers and their tributaries flow in the general direction of South East to the

Cross- River plain.

Figure 1.0 Enugu State Map

Okoli et al …. Int. J. Innovative Environ. Studies Res. 5(1):33-46, 2017

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3.0 Data Products

The following data sets were used for this project in the Table 1 below.

Table 1. Data Products

S/no D a t a S c a l e D a t a S o u r c e

1 . S R T M / D E M - G e o - i n f o r m a t i c s & S u r v e y i n g D e p a r t m e n t

2 . Rainfall data New_LocClim software - G e o - i n f o r m a t i c s & S u r v e y i n g D e p a r t m e n t

3 . Satellite imagery 2001 (Landsat-7ETM) - G e o - i n f o r m a t i c s & S u r v e y i n g D e p a r t m e n t

4 . Geology map of Nigeria 1:250,000 G e o - i n f o r m a t i c s & S u r v e y i n g D e p a r t m e n t

5 . Digital Soil Map of Nigeria - N k w u n o n w o U . C ( 2 0 0 9 )

“Digital Soil Map and Soil Database of Nigeria”

Geo-informatics & Surveying Department

4.0 METHODOLOGY

4.0.0 Groundwater Model (DRASTIC)

DRASTIC Model is an empirical model developed by U.S. Environmental Protection Agency (EPA)

which is widely used for evaluating relative groundwater pollution susceptibility by the use of hydro-

geological factors (Aller et al, 1985). It evaluates the Intrinsic Vulnerability (IV) of groundwater by

considering factors including Depth to water table, natural Recharge rates, Aquifer media, Soil media,

Topographic aspect, Impact of vadose zone media and hydraulic Conductivity. It is an acronym for

the seven (7) most important hydro-geological features affecting groundwater pollution, which are:

Groundwater Pollution Potential = D+ R+ A+ S+ T+ I+ C. . . (1)

Where D= depth to water table, R= net recharge, A= Aquifer media, S= Soil media

T= Topography, I= Impact of vadose zone media, C= hydraulic conductivity of aquifer

In this project, the modified DRASTIC model of Khairul Anam et al, 2000 was adopted to estimate

the groundwater potential.

Groundwater Potential = Rf + Lt + Ld + Lu + Te + Ss + Dd + St ...(2)

Where

Rf= annual rainfall

Lt= Lithology

Ld= lineament density

Lu= land use

Te= topography elevation (Contour)

Ss= slope steepness

Dd= drainage density

St= soil type

In order to demarcate the groundwater potential zones of Enugu State eight (8) different thematic

maps were prepared from Remote Sensing data, SRTM, geology Map, and in conjunction with the

existing maps like Soil maps. The Figure 2 below gives the methodology flowchart for this project.


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Figure 2 Methodology Flowchart for Groundwater Potential Zoning

4.1.0 Analysis, Approaches and Results

The raster flow directionshown in (Fig. 3) shows the flow across a surface which will alwaysbe in the

steepest down-slope direction and it was used to determinethe stream network. Flow direction map

created from a rastershows the direction of flow of the river runs North East and North West

directions joining both the rivers connecting Ugwuoba Rivers in Anambra state and Rivers in

Abakaliki.

The raster flow accumulation created isshown in (Fig. 4), indicated that the low accumulation values

representridge tops whereas higher accumulation values representvalleys and stream channels.

Figure 3 Flow Direction Map Figure 4 Flow Accumulation Map


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4.1.1 Preparation of Lithology Map

Figure 5 Lithology Map

Lithology map as shown in Figure 5 above was prepared by digitizing each Lithologic unit/ rock type

in ArcGIS software package from geology/Soil maps obtained from Geo-informatics & Surveying

Department. Moreover each lithologic unit or rock type is classified based on the legend available on

the geology map.

4.1.2 Preparation of Lineament Map

The operation consists of the delineation of lineaments. The sequence of operation is the application

of filters for image enhancement, geo-referencing using map coordinates. The edge enhancement of

the satellite image, 3*3 Laplacian filter, high pass filter and gradient filter in X direction were applied

with visual interpretation. The processed image was imported into ArcGIS to digitize the lineament

features in the image. The lineament density map was then prepared using the Spatial Analyst

Tool|Density|line option.


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Figure 6. Lineament Density Map Figure 7.Lineament Map

4.1.2 Preparation of Slope Map

The slope map of the Study area was extracted from the prepared SRTM /DEM of the Study area

using ArcGIS. The SRTM was imported into the ArcGIS using the Add button and the slope

wascalculated using the Spatial Analyst Tool.


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Figure 8. Slope Map

4.1.3 Preparation of LandUse/Cover Map

The LandUse/Cover Map was prepared using the LandSat7-ETM image coverage of Enugu. The

image was enhanced using various filtering algorithms edge enhancement, PCA, Band Rationing etc.

Supervised classification was used with some GCPs for proper Sample Set preparation. The

Maximum Likelihood Method was adopted to generate the landuse-cover information.

Figure 9 Landuse/cover Map


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4.1.4 Preparation of Rainfall Coverage Map

Figure 10.Rainfall precipitations Map

Figure 11. Rainfall Krig Map


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The Annual Rainfall data precipitation was generated using the New_LocClim software. The rainfall

coverage was prepared by importing the annual rainfall data into ArcGIS. The rainfall coverage was

then interpolated using the Spatial Analyst Tool|interpolation|Kriggingmethod was used to produce

Rainfall Coverage Map.

4.1.5 Preparation of Drainage Density Map

The Geology Map of Nigeria was scanned which was imported into ArcGIS. The geology map was

georeferenced. The Rivers within the study Area was digitized which was used to prepare the

drainage Map. The Drainage Density Map was then performed using the Spatial Analyst

Tool|Density|Linein ArcGIS.

Figure 12. Drainage Map Figure 13. Drainage Density Map

4.1.6 Preparation of Elevation Map

The Elevation of the study area was extracted from the SRTM using ArcGIS. The SRTM was

imported into ArcGIS and the SRTM was cleaned from arbitrary sinks (fill) due to random errors in

the data. These sinks prevent flow algorithms to follow a complete flow path to the watershed‟s

outlet. Then the Fill function was done and ready to use. The Elevation Map was then prepared using

the Spatial Analyst|Surface|Contour with 50m interval for the generation of the contours.


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Figure 14. Elevation Map

4.1.7 Preparation of Soil Map

The Soil map of Enugu was extracted from thework of Nkwunonwo U.C (2009), “Digital Soil Map

and Soil database of Nigeria” by clipping the study area Enugu using ArcGIS Data management

Tool|clip.

Figure 15.Soil Map


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Table 2. Weighting of the Eight (8) thematic Maps

S/No

Theme

Description

S c a l e

(1 To 9 )

Weight

%

1

Lineament

Density

(km/km2)

0 -3 4 . 1 6 5

34.165-68.330

68.330-102.494

102.494-136.658

136.658-170.823

3

3

4

6

8

2.25

2

Drainage Density(km/km2)

0 - 3 9 . 1 1 5

39.115-78.223

78.223-117.344

117.344-156.460

156.460-195.574

8

7

3

2

1

19.17

3

Soil Type

S a n d y c l a y

Sandy Loam

Silt Clay

Concrete clay

Loamy fine clay

5

2

7

6

4

4.55

4

Lithology

i.) S h a l e s

ii.) Sandy materials

iii.) Nupe and

Other cretaceous

iv.) Sandstone /shales

v) Recent Alluvium

vi) Old recent Alluvium

vii) Colluvialdeposites

viii) Sandstone,shales /Mudstones and shales

5

2

5

6

7

5

7

3

34.87

5

Slope

0 - 1

1-2

2-3

3-4

4-5

5

4

3

2

1

9.05

6

Elevation

0 - 5 0

50-150

150-250

250-350

350-450

450-550

6

5

4

3

2

1

1.56

7

Rainfall

1 - 2

2-5

5-7

7-9

2

3

5

8

9.05

8

Landuse/cover

B u i l t u p A r e a

Bare surfaces

Wetlands/water bodies

Heavy Forest

Light forest

1

1

7

3

4

19.17


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4.1.8 Preparation of groundwater Potential Map

Preparing the groundwater prospects (potential) map the following procedure was followed. First a

groundwater prospects map was prepared by integrating the information from

lithological,Landuse/cover and hydrological maps in ArcGIS as indicated in the stepsbelow.

Step 1: A fresh layer in ArcGIS software was created, and each theme layer transferred in the new

layer

Step 2: Each of the layers was overlaid using ArcGIS extension tools |Spatial Analyst|overlay|overlay

weighted. Step 3. Then the weights and their scores inputted in the overlay weighted operations accordingly.

Step 4. The overlay operation is run to produce the groundwater map.

Figure 16. Groundwater Potential Map


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Figure 17. Groundwater Bar chart

5.0 CONCLUSION

The integrated thematic maps with its weight assigned accordingly to their degree of influence, the

groundwater potential (GWP) map ofEnugu State was generated as shown in Figure 16above. Five

classes of groundwater Potential were adopted. The Zone of very High GWP is found in favourable

biophysical environment-water bodies, vegetation, and wetlands located in flat to rolling with

elevation of <50m having underlying alluvium and very low annual rainfall. Zone of very low GWP is

however characterized by unfavourable conditions-very low annual rainfall; urban and cultivated area;

low lineament density; sandy loamy; elevation exceeding 150m above mean sea level; low lineament

density and slope exceeding 5 from the slope table.

In general in hard rock areas, the groundwater potential is high in areas with high lineament density

and low drainage density. It was found that the clay materials, sandstone with granite have high to

very GWP while steep mountains with recent alluvium areas of low lineament density have very low

GWP.

In this project, a sincere attempt was made to estimate the groundwater potential zones map of Enugu

State with the available data. It was concluded that combination of remote sensing and GIS is a useful

technique for the groundwater exploration and has aided the successful locations of groundwater

potentials. It also can be considered as a time and cost-effective tool for delineations and

identification of high ground water potential target area.

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mapping groundwater potential zones in enugu state...

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