Gis-Based Assessment Of Water Availability And Water Demand In Asa Catchment, Kwara State

This study arose from the growing water demand within the Asa River Basin due to population upsurge, the absence of existing water demand management strategies, the possibility of scarcity as a result of climate change, and the need for sustainable water resources management.

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Title page                                                                                            i

Certification                                                                                        ii

Dedication                                                                                           iii

Acknowledgement                                                                                iv

Table of contents                                                                                 v

List of figures                                                                                                xiii

List of tables                                                                                        ix

Abstract                                                                                              x

1.0     CHAPTER ONE: INTRODUCTION                                            1-6

1.1     Background to the Study                                                             1

1.2     Problem Statement                                                                     4

1.3     Aim and Objectives of the study                                                   5

1.4     Justificationfor the study                                                   5

1.5     Scope of Work                                                                           6

2.0     CHAPTER TWO: LITERATURE REVIEW                                   7-24

2.1     Introduction                                                                               7

2.2     Water Resources in Nigeria                                                          8

2.3     Water Management Practices and Policy in Nigeria                         10

2.4     Water Allocation Guidelines and Principles                                     10

2.5     Water Resources Management Models for River Basin Simulation     11

2.5.1  MODSIM                                                                          12

2.5.2  MIKE BASIN                                                                     13

2.5.3  RIBASIM                                                                          14

2.5.4  REALM                                                                             15

2.5.5  WEAP21                                                                          16

2.6     Description of the SWAT Modeling and SWAT Components             18

2.7     SWAT Strength and Limitation                                                     20

2.7.1  Limitation of SWAT Model                                                  21

2.8     Previous Water Supply And Demand Studies                                  21

3.0     CHAPTER THREE: METHODOLOGY                                         25-36

3.1     Introduction                                                                              25

3.2     Model Selection and Description                                                   25

3.3     Model Data Requirements and Collection                                                27

3.3.1  Digital Elevation Model (DEM)                                            27

3.3.2  Land Use and Land Cover (LULC)                                       29

3.3.3  Soil Data                                                                          31

3.3.4  Weather Data                                                                   32

3.4     SWAT Model Set-Up and Run                                                       33

3.4.1  Model Setup                                                                     33

3.4.2  Watershed Delineation                                                      34

3.5     Water Yield Potential and Estimation of Available Water Resources  35

3.6     Water demand estimation                                                            36

3.7     Population Forecasting                                                                36

4.0     CHAPTER FOUR: RESULT AND DISCUSSION                          37-42

4.1     Prediction of Water Balance Component                                        37

4.2     Prediction of Water Yield Potentials in the Sub-basin of

Asa watershed                                                                           40

4.3     Estimation of Available Water Resources                                       41

4.4     Estimation of Water Demand of the River Basin                             41

4.5     Comparison of Water Supply and Demand                                     42


5.1     Conclusions                                                                               43

5.2     Recommendations                                                                      44



Figure Description Page No
3.1 Digital Elevation Model of the Study Area 28
3.2 Land Use map of the Watershed 30
3.3 Soil Map of the Study Area 32
3.4 Delineation of Watershed into Sub-Basins 34
4.1 Average annual water balances for Asa watershed 39
4.2 Average monthly water balances for Asa watershed 40
4.3 Total water balances for Asa watershed 41
4.4 Spatial Variation of Water Yield Potential of Asa Watershed 42


Table  Description Page No
3.1 Information on Land Use of the Study Area 30
3.2 Information on Soil of the Study Area 31
4.1 Average annual water balances simulated for a base periods of 1986-2015. 38
4.2 Average monthly water balances simulated for a base periods of 1986-2015 39
4.3 Total water balances simulated for a base periods of 1986-2015 40


This study arose from the growing water demand within the Asa River Basin due to population upsurge, the absence of existing water demand management strategies, the possibility of scarcity as a result of climate change, and the need for sustainable water resources management. The aim of the study was to assess water availability and water demand of Asa catchment using GIS-based hydrological model. The methodology involved the input of spatial and temporal data into Soil and Water Assessment Tool (SWAT) using Geographic Information System (GIS) as interface. After the model was configured, set up and run, the water balance components and water yield potential were predicted. The modelling results showed that evapotranspiration is the highest water balance component while the lowest is lateral soil flow. The spatial distribution of water yield potentials in the sub-basins of the study area showed that sub-basin 9 has the lowest water yield potential while sub-basin 84 has the highest. The total water yield potential of the study area is 1,296,676.5mm while the total area of the river catchment is 5,618.28km2. The available water resources in the catchment were estimated to be 7.2 billion m3. The projected total population of the domiciled local governments in the catchment for 2015 is 1,203,743 persons and the water demand for this population was estimatedas 1.3 billion m3. Comparing the water demand with the available water resources shows that the available water resources outweigh the water demand, which implies that there was no scarcity. However, there may be future scarcity due to the increasing population and climate change.



  • Background to the study

Water is a vital resource for every human activity. Water makes life possible. Without it, life and civilization cannot develop or survive (Ojekunle, 2011). Water forms the largest part of most living matter and is vital  to  man  just  as  air  and  food  are  (Ayoade,  2003).  The management and maintenance of water is thus very important (Fiorilloa, 2007). The  accelerating  growth  of  human  population,  the  rapid  advances  made  in  industry  and agriculture  have  resulted  in  a  rapidly  increasing  use  of  water  by  man,  to  the  extent  that  the availability of water as well as the control of excessive water has become a critical factor in the development  of  every  regions  of  the  world  (Williams,  2010).

Over  the  decades,  water  supply management  has  proved  to  be  insufficient  to  deal  with  strong  competition  for  water  with growing  per  capita  water  use,  increasing  population,  urbanization  pollution  and  storages (Wang  Xiao  –  Jun  et  al, 2009).  In addition, the need for domestic, industrial and agricultural water supply is growing, but the absence of demand management strategies means that the increase in demand will likely outstrip the available supply, hence water scarcity (UNESCO, 2006). One-third of the world’s total population of 5.7 billion lives under conditions of relative water scarcity and 450 million people are under severe water stress (UN, 1997). The issue of water scarcity in the world and its implication on development of new political and economic  relations  among  countries  may  result  to  crisis  in  the  future.  Thus, there is need for the implementation of effective water resources management which becomes particularly important towards determining how much  water  is  available  for  human  use  and  economic  activities  that  water  should  be shared between  users.

Population growth is a major contributor to water scarcity.  The global population is expanding by 80 million people annually, increasing the demand for freshwater by about 64 billion m3a year (Population Institute, 2010). Rapid population growth and urbanization could expose more people to water shortages, with negative implications for livelihoods, health, and security. These demographic trends, coupled with increasing per-capita water consumption, will be a huge development challenge (Bates, Kundzewicz, Wu and Palutikof, 2008).  Growthin population implies mounting demand and competition  of  water  for domestic, industrial, and municipal uses (Population Action International, 2011). Population  growth  leads  directly  to  increases  in  overall  water  demand,  while  other demographic factors such as population distribution and age structure modifies the pattern in demand and determines  increases  in  household  water  demand.  Overall, the amount of water each person uses is expected to increase as incomes grow and consumption increases (UN-Water and FAO. 2007).

Evidences are ample that there is an explosion in the population of cities in Nigeria (Eja, Inah, YaroandInyang, 2011; Nwosu, 2013). The effect of the rapid urban population growth is noticeable through the provision of municipal services such as pipe-borne water. Expectations of the populace on the activities of policy makers for the supply of water are quite high. (Sule, 2008). Water can be said to be adequate when an individual is availed a quantity of at least 50 litres per day (World Health Organization, 2003).

The unavailability of water in required proportion for man’s use has assume global crises dimension. According  to  the  Population  Institute  (2010),  only  20  percent  of  the  global  population  has  access  to running water and over 1 billion people do  not have access to clean water. The Population Institute noted further that with a projected population of the world to expand to 9 billion people by 2050, it is estimated that 90 percent of the additional 3 billion people will be living in developing countriess, many of which are already experiencing water stress or scarcity therefore, it is pertinent to manage water resources sustainably.

Water resources management has a significant impact on the socio-economic development of a catchment. The water demands and availability depends on the economic, ecological, land use, and climatic changes of a region (Droogers,2012).Water resource management is a multifaceted issue that becomes  more  complex  when  considering  multiple  nations’  interdependence  upon  a single shared trans boundary river basin (Teasley and McKenney, 2011). The  management  of  water  resources  as  a  common  resource  would  require  trade-off  among  countries  and  water users (Yang and Zehnder, 2007). The need therefore to devise means by which available water can be consumed and allocated among the various uses is pertinent.

The planning of human activities involving rivers and their floodplains must consider hydrological facts; (…) the flows and storage volumes vary over space and time (Loucks et al, 2005).  The  necessity  of  predicting  the  hydrological  patterns  is  essential  to  the  reservoir management.  The  reservoirs  have  to  insure  not  only  the  water  quality,  but  also  the  human,  the industrial  and  the  agricultural  consumption. Nowadays the environmental concerns such as the aquatic biodiversity and the environmental pressure have an increased influence in the decision-making.

Asa River is one of the major sources of water supply in Kwara state. This study simulates the hydrological process of Asawatershed that allows for the estimation of available water resources, so that sustainable and rational utilization, conservation and management of available water resources will be adopted using Soil and Water Asessment Tool (SWAT) model. The study also proffers alternative strategies for water conservation that will meet water demand within the basin.

1.2     Problem Statement

In the study area, there has been an increase of population over the last three decades which leads to strong competition for water with growing per capital water use. Also, there is possibility of scarcity due to the potential effects of global climate change on water resources. Asa river basin faces freshwater management challenges, some of which includes allocation of limited water resources, inadequate environmental quality monitoring, and policies for sustainable water use.

1.3.    Aim and Objectivesof the study

The aim of the study was to assess water availability and water demand of Asacatchment using GIS-based hydrological model.The specific objectives achieved in this research are:

  1. topredict water balance components of Asa river basin during the modelling period.
  2. to predict total water yield potential of the basin.
  3. toevaluate water demand of Asa river basin using projected population of the inhabitant of the basin.
  4. toevaluate available water resources of Asa river basin from 1986-2015.
  5. tocompare the volume of available water resources with the actual water demand of the catchmentarea within the modelling period.
  • Justificationfor the study

Water is vital resource for every human activity. Water is scarce and there is need for efforts to improve its availability and explore itsustainability. To achieve reliable  prediction  of  the  various  hydrologic  parameters  including  rainfall,  runoff  etc.  for river catchment, it is very tough and time consuming by conventional methods. So it is very important to  search  suitable  methods  and  techniques  for  quantifying  the  hydrological  parameters. The fundamental objective of hydrology modeling is to gain an understanding of hydrological system in  order  to  provide  reliable  information  for  managing  water  resources  in  a  sustained  manner.

1.5     Scopeof Work

In this study, thirty years meteorological data such as rainfall, temperature, humidity, solar radiation etc. were used. Validation and calibration of model were not included due to non-availability of observed data. Population projection using geometric method was adopted.



2.1     Introduction

Water is a natural resource of fundamental importance and supports all forms of life. Water demand already exceeds water supply in many parts of the world, and as world population continues to rise at an unprecedented rate, many more areas  are expected to experience this imbalance in the near  future (Wikipedia, 2008). It was revealed  in the 4thWorld  Water Forum  march (2000) that a person  living  in  an  urban  area  uses  an  average  of  250  liters/per  day;  but  individual  consumptions varies around the globe. Nigeria  is endowed with abundant natural water resources evident in  her substantial  yearly rainfall, large surface bodies of water-rivers, streams and lakes, as well as in abundant reservoirs of underground  water  whose  extent  and  distribution  have  not  been  fully  assessed


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