URBAN LAND USE CHANGE AND THE FLOODING PATTERNS IN ASHIMOWU WATERSHED, LAGOS, NIGERIA

Transcription

1 URBAN LAND USE CHANGE AND THE FLOODING PATTERNS IN ASHIMOWU WATERSHED, LAGOS, NIGERIA By ODUNUGA, SHAKIRUDEEN SULE (Matric. No ) B.Sc. (Geog. & Planning), M.Sc. (Geography), Lagos THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, UNIVERSITY OF LAGOS, LAGOS, NIGERIA, IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF DOCTOR OF PHILOSOPHY (PH.D) DEGREE IN GEOGRAPHY (HYDROLOGY) MARCH, 2008 i

2 UNIVERSITY OF LAGOS SCHOOL OF POSTGRADUATE STUDIES DEPARTMENT OF GEOGRAPHY CERTIFICATION This is to certify that the Thesis URBAN LANDUSE CHANGE AND THE FLOODING PATTERNS IN ASHIMOWU WATERSHED, LAGOS, NIGERIA Submitted to the School of Postgraduate studies University of Lagos For the Award of the Degree of DOCTOR OF PHILOSOPHY (PH.D) Is a record of original research carried out By ODUNUGA, SHAKIRUDEEN SULE In the Department of Geography AUTHOR S NAME SIGNATURE DATE 1 ST SUPERVISOR S NAME SIGNATURE DATE 2 ND SUPERVISOR S NAME SIGNATURE DATE 1 ST INTERNAL EXAMINER SIGNATURE DATE 2 ND INTERNAL EXAMINER SIGNATURE DATE EXTERNAL EXAMINER SIGNATURE DATE PG. SCHOOL REPRESENTATIVE SIGNATURE DATE ii

3 DEDICATION This project is dedicated to Almighty God, the Absolute, for His mercy, guidance and grace. iii

4 ACKNOWLEDGMENT All praises is due to Almighty God the Omnipotent, Omniscient, the Merciful and Beneficent. To Him are all thanks. I am grateful to Prof. Lekan Oyebande who nurtured my academic and research pursuit from infant to adulthood. The valuable experience, exposure and expertise that I gained from him during the course of my Ph.D programme can not be quantified. Prof., I remain obedient son. Also, my special thanks goes to Dr. Samuel Ademola Omojola, first for introducing me and my peers to the art and sciences of remote sensing and geographical information systems (GIS) at a very early stage of our academic pursuit, second for being a big brother and more importantly for meticulously co-supervising this research work. The Africa small grant fellowship for doctoral student awarded by START is highly instrumental to the successful completion and the high quality of this research. I express my profound appreciation to START for their financial support. Special thanks also go to Dr. Iyiola Oni, Dr. Isaac Balogun, Dr. Tunji Babatola (HOD), Dr. Amos Abu, Dr. Alabi Soneye, Dr. Feyi Oni, Dr. S. Oyegoke (Civil Engineering Department), Dr. Adeboye (Political Science Department), Dr. Chukwu (Marine Biology) and Dr. Badru (Sociology) for their encouragements, support, constructive criticism and critical evaluation of the work. I am also indebted to other academic staff of Geography Department, University of Lagos, for their numerous contributions, suggestions and support. Prof I. A. Adalemo, Prof. Oyediran Ojo, Prof. D. A. Oyeleye, Prof. Olukunle Adegbola, Prof. O. Y. Balogun, Prof. Akintola-Arikawe, Dr. N. O. Uluocha, Dr. Godwin Ekop, Mr. Olatunde Ogunkunle and Dr. Olusegun Adeaga, Thank you all. To the non-academic staff, Mr. Johnson Fasuhan, Miss Olayiwola Titilayo, Mr. Ogundele, Mr. Awolusi, Mrs Ogunkoya Mr. Olomola and Mrs Lukon; I am grateful to you all. iv

5 To my senior colleagues and friends at the Nigerian Meteorological Agency (NIMET), Dr. Afiesine Mama, Mr. Muyiolu, Mr. Gbuyiro (Now of FUTA) and Mr. Okoloye, I am highly grateful for your support. To Mr. Etu, Alhaji Adeyanju, and Mr Okoye (all of NIMET) I equally express my appreciation. To my wonderful colleagues and friends on the Ph.D programme, Fasona Mayowa, Charles Asenime, Tejuoso Olufemi, Anosike Vide, Okeke Ify, Ege Emmanuel, Okeowo Segun, Okanlawon Kemi, Nma Odim, Odeleye Tunji, Ayeni Amidu, Alex Uriri, Efunshade Kemi, Akinlabi Akintuyi, Adepoju Segun, Vincent Olatunji and Commandant Olagunju of the Federal Road Safety, I thank you all. To Nurayn Alimi, I express my special appreciation first for the moral support and encouragements and second for painstakingly reading through the whole thesis, I quite appreciate your effort. Sister Amina Egberongbe was highly instrumental to the success of the field exercise. I am grateful for your encouragements, moral support and constructive criticism. To Appia Youpele and Adedoyin Belo, I thank both of you for assisting during the field work. To my other friends who in one way or the other have contributed to the success of this work, accept my profound gratitude. I acknowledge the supports, encouragements, patience and endurance of the members of my family. Special thanks and appreciation go to my mother, Mrs. M. Odunuga for her concern and prayers. Mum, thank you. My sisters, Mrs. Omotosho and Alhaja (Mrs) Durojaiye are wonderful personalities; I thank both of you for all the supports. Mama Moria, Ismail, Ibrahim and Tawa (Olori-ebi), thank you all. To my wife, Mrs. Ajibola Jemilat Odunuga, who came in towards the end of this programme, I say thank you for your love and support. v

6 TABLE OF CONTENTS Contents Cover Page Certification Dedication Acknowledgement Table of Contents List of Tables List of Figures List of Plates Abstract Pages i ii iii iv vi xiii xvi xvii xviii CHAPTER ONE 1 INTRODUCTION Background to the study Statement of Problem Research Questions Aim and Objectives Working Hypotheses Study Justification Operational Definition of Terms Study Area Physical Setting Cultural Setting 22 vi

7 1.8 History of Flooding in Lagos Current Initiatives of Flood Abatement in Lagos Thesis Layout 31 CHAPTER TWO 33 CONCEPTUAL FRAME WORK AND THEORETICAL BACKGROUND Introduction Conceptual Framework Climate Change Environmental determinism Functionalism Hydroinformatics Human Response and Adjustments Engineering Approach Ecological / Conservation Approach System Approach Theoretical / Analytical Framework Rational Method Unit Hydrograph Unit Hydrograph Assumption and Limitations 46 CHAPTER THREE 48 LITERATURE REVIEW Introduction Remote Sensing and GIS Techniques as Tools for Urban Land vii

8 Use Mapping Raster Data Structure Vector Data Structure Hydrological Models Mathematical Model Deterministic Model Stochastic Model Multivariate Statistics Hydrological Models for Urban Flood Study Formulae Techniques Catchment Area Formulae The Rational Method Hydrograph Technique Optimization and Stochastic Techniques Linear Least Squares (Programming) Non-Linear Least Squares Computer Modelling and Simulation Techniques Hydrological and GIS Model Integration Digital Elevation Model (DEM) Hydrological Regime and GIS Coupled Urban Flood Simulation Flooding and Climate Change 73 CHAPTER FOUR 76 METHODOLOGY 76 viii

9 4.0 Data Sources Land use / Land cover Definitions of Primary Classes Digital Elevation Model (DEM), Elevation range and Slope Derivation Drainage Blockages Hydro-Climatic Conditions Rainfall Surface Runoff and Flow Data Evapo-transpiration Infiltration Precipitation Water Inundation Model (PWIM) Model Assumption Urban Flood Inundation Hazard Model Verification Climate Change Connection Flood Risk Zone / Vulnerability Mapping Social-Economic Indicators and Peoples Perception on Urban Flooding in Lagos 100 CHAPTER FIVE 102 RESULTS AND DISCUSSION: LANDUSE CHANGE Introduction Drainage Area 102 ix

10 5.2 Land Use/Land Cover Change Analysis Land use / Land cover Change: Trend and Rate Nature and Location of Changes in Land use / Land cover Specific Land use and Land cover Distribution of Ashimowu Watershed (2003) : Spatial Pattern of Land use and Land cover Distribution (2003) 114 CHAPTER SIX 120 RESULT AND DISCUSSION: DEM, DRAINAGE CONDITIONS AND HYDRO-CLIMATIC CONDIIONS Introduction Digital Elevation and Slope Drainage Condition Point of Blockages Hydro-Climatic Condition Storm Rainfall Analysis Infiltration Peak Flow from Storm Rainfall 133 CHAPTER SEVEN 135 RESULT AND DISCUSSION: WATERSHED SYSTEM RESPONSE SIMULATION AND CLIMATE CHANGE CONNECTIONS Introduction Precipitation Water Inundation Model (PWIM) Peak Flow Simulation 135 x

11 7.1.1 Precipitation Water Inundation Model (PWIM) Peak Flow on 1965 Land use Scenario Precipitation Water Inundation Model (PWIM) Peak Flow on 1975 Land use Scenario Precipitation Water Inundation Model (PWIM) Peak Flow on 1987 Land use Scenario Precipitation Water Inundation Model (PWIM) Peak Flow on 2003 Land use Scenario Inundation Area from Peak Flow Using PWIM Model Verification Impact of Land use / Land cover Change on Hydrological Fluxes Impact on Runoff and Peak Flow Test of impact of urban land development on peak flow Impact on Infiltration Test of association between urban land development and infiltration Climate Change Connection Flood Risk/ Vulnerability Zone 150 CHAPTER EIGHT 152 RESULT AND DISCUSSION: SOCIO-ECONOMIC IMPLICATION AND PERCEPTION Introduction Social-Economic Characteristics of Respondents 154 xi

12 8.2 Economic Implications of Urban Flood in Lagos Perception of People to Urban Flooding Statistical test of perceived consequence of urban land development on flooding. 164 CHAPTER NINE 167 SUMMARY OF FINDINGS AND POLICY IMPLICATIONS Summary of Results and Findings Policy Implication of the Findings Contribution to Knowledge Conclusion Recommendations Suggestion for further Studies 176 REFERENCES 177 APPENDIX 1 Lagos State Government on Drainage Setback of Water Bodies and Gorges 186 APENDIX II Sample of readings from hydro-meteorological station 189 APPENDIX III Storm characteristics 190 APPENDIX 1V Flow data for selected storm 194 APPENDIX V Questionnaire 200 LIST OF TABLES Pages Table 1.1 The Population distribution of study area 22 Table 1.2 Extent and causes of flooding in Greater Lagos 28 Table 3.1 High Resolution Optical System 51 Table 4.1 Data Sources and their Characteristics for Land use / Land cover 76 xii

13 Table 4.2 Coordinates used for Georectification of the Scanned Mosaic Aerial Photographs 78 Table 4.3 Urban Hydrological Land use Classification Scheme for Flood Simulation 79 Table 4.4 Infiltration Rates and Capacity adapted from Stephenson et al 91 Table 4.5 The Multiplying Factor / Percentage of Increments for Precipitation Drivers 98 Table 4.6 The multiplying Factor for Urbanization Drivers 98 Table 4.7 No of Questionnaire Administered and Returned by Location 100 Table 5.1 Static LU/LC distribution for 1965, 1975, 1987 and 2003 in Ashimowu watershed 104 Table 5.2 Land use Land cover Change Statistics for the Three Periods 108 Table 5.3 Land use / Land cover Change Statistics for Three Periods 109 Table 5.4 Annual rate of Change (Hectare) 109 Table 5.5 Land use and Land cover Change Matrix in Ashimowu Watershed for 1965 and Table 5.6 Land use and Land cover change matrix in Ashimowu Watershed for 1975 and Table 5.7 Land use and Land cover change matrix in Ashimowu Watershed for 1987 and Table 5.8 Specific landuse/landcover Distribution of Odo-Ashimowu Watershed (2003) 114 Table 5.9 General Land use of Itire Segment 115 Table 5.10 Specific Land use of Itire Segment 115 Table 5.11 General Land use of Lawanson Segment 115 Table 5.12 Specific Land use of Lawanson Segment 115 Table 5.13 General Land use of LUTH-Idi Araba Segment 116 Table 5.14 Specific Land use of LUTH-Idi Araba Segment 116 Table 6.1 Elevation Range of Ashimowu Watershed 120 Table 6.2 Characteristics of Channels within the Study Watershed 122 Table 6.3 The Design and Actual Capacity of Primary and Secondary xiii

14 Drainage Systems 123 Table 6.4 Point of blockage on the Primary and Secondary Drainage Systems (UTM) 124 Table 6.5 Characteristics of measured rainfall 127 Table 6.6 Landuse, Particle Size, soil types, antecedent soil moisture/soil Group, Infiltration rate and Capacity 130 Table 6.7 Spatio-Temporal infiltration rate and capacity of Drainages within Ashimowu watershed 131 Table 6.8 Spatio-temporal change in Infiltration rate of Ashimowu Watershed 131 Table 6.9 Spatio-temporal change in Infiltration capacity of Ashimowu Watershed 133 Table 6.10 Peak flow along Odo-Ashimowu for the measured rainfall 133 Table 7.1 Simulated Runoff and peak Flow for observed storms on 1965 Land use Scenario 136 Table 7.2 Simulated Runoff and peak Flow for observed storms on 1975 Land use Scenario 137 Table 7.3 Simulated Runoff and peak Flow of observed storms on 1987 Land use Scenario 138 xiv

15 Table 7.4 Simulated Runoff and peak Flow of observed storms on 2003 Land use Scenario 140 Table 7.5 Statistical parameters from weighted least square regression 141 Table 7.6 PWIM area inundation 141 Table 7.7 Summary of Regression Model 143 Table 7.8 Standardized Estimate of Beta Coefficients 144 Table 7.9 Analysis of Variance ANOVA 144 Table 7.10 PWIM simulated flood parameters for 25 years Medium High Climate Change 148 Table 7.11 PWIM simulated flood parameters for 25 years High Climate Change 148 Table 7.12 PWIM simulated flood parameters for 50 years High Climate Change 149 Table 7.13 PWIM simulated flood parameters for 100 years High Climate Change 149 Table 8.1 Respondents Sex by Location 154 Table 8.2 Respondents Occupations 155 Table 8.3 Purpose of individual respondents 155 Table 8.4 Respondents benefit from Flooding 156 Table 8.5 Monetary value of loss 159 Table 8.6 Flood Experience of the respondents by locations 161 xv

16 LIST OF FIGURES Pages Fig. 1.1 Ashimowu Watershed in Lagos Metropolis 18 Fig. 1.2 Mean Monthly Rainfall 21 Fig 2.1 Conceptualisation of the Water Cycle (Schematic view) 34 Fig 2.2 Subsystem of Urban storm water disposal 35 Fig 2.3 Hydro-informatics for urban flood study 43 Fig. 4.1 Flow Chart of the Research Methodology 77 Fig 5.1 Segments of Ashimowu Watershed 102 Fig. 5.2 Measurement Location, Drainage Channels and the Segments of Ashimowu Watershed 103 Fig 5.3 Static LULC distribution for the four Periods in Ashimowu Watershed 105 Fig. 5.4 Land use and Land cover of Ashimowu in Fig. 5.5 Land use and Land cover of Ashimowu in Fig. 6.1 Elevation Range and Contour of Ashimowu Watershed 121 Fig. 6.2 Rainfall Distribution (22 nd August 2005) 128 Fig. 6.3 Rainfall Distribution (11 th October 2005) 128 Fig. 6.4 Spatio-Temporal Infiltration Rate for Ashimowu Watershed 132 Fig. 6.5 Spatio-Temporal Infiltration Capacity of Ashimowu Watershed 132 Fig 6.6 Itire rainfall / discharge hydrograph for 28 th August 2005 storm 134 Fig 7.1 PWIM Simulated Area Inundated for Three Observed Storms 142 Fig. 7.2 Level of Flood Risk/Vulnerability in Ashimowu Watershed 152 xvi

17 LIST OF PLATES Pages Plate 1.1 Wetland encroachment (Mushin High School, Idi-Araba, July, Plate 1.2 A flood area at LUTH, Idi-Araba, Lagos, July 2005) 11 Plate 1.3 Defective & inadequate Drainage System (Daniyan St., Idi-Araba, 2005) 11 Plate 1.4 Refuse blocking free flow of water (Moshalashi St., near LUTH, November, 2004) 12 Plate 1.5 Sediment blocking flow of drainage in Cele bus stop (Apapa Oshodi express, August, 2005) 12 Plate 4. 1 The meteorological Station established at Lagos University Teaching Hospital, September, Plate 4.2 Inside view of the event recorder housing. The event recorder is on the Top of the table, September, Plate 4.3: The weekly replacement of the chart of the recorder, September, Plate 4.4 A meteorologist field assistant reading the instruments inside the Stevenson screen 86 Plate 4.5 A meteorologist field assistant inspecting the tipping bucket, September, Plate 4.6 A field assistant replacing the water level gauge chart, September, Plate 5.1 Continuous built up area in Lawanson and Itire sub-segment of Ashimowu watershed 118 Plate 6.1 Weeds and Refuse blocking free flow of water on system c6 Near LUTH, September, xvii

18 ABSTRACT Ashimowu watershed, located in the central part of Lagos within the mainland section of the metropolis has attracted the attention of many individuals, corporate organizations and NGOs for two reasons. The changing land use into a dense urbanised environments and the annual perennial flooding that disrupts socio-economic activities, threaten live and destroy properties. The land use driver and its associated anthropogenic activities such as indiscriminate use of wetland, encroachments into floodplain and streams right of ways, inadequacy of the hydraulic capacity and refuse dumping into the drainage systems are further exacerbated by the tropical location of the city of Lagos and indeed Ashimowu watershed. Also, high intensity short duration rainfalls which are typical of tropical environments combine with the human activities to create perennial flood situation on the watershed. This study therefore investigate the Urban Land use Change and the Flooding Patterns in Ashimowu Watershed and proffers strategies for alleviating the urban flood hazard not only within the studied watershed but also elsewhere with similar characteristics. Both spatial and non spatial data were used to accomplish the objectives of this study. The spatial data are sub-divided into two; (I) Land use / land cover (1965,1975,1987 and 2003) and relief data. (II) Hydro-climatic data, which includes rainfall, infiltration and runoff. The non-spatial data includes Administrative Data, Literature Search and Field Survey using questionnaire to generate information on the socio-economic aspect of urban flooding. Using a pragmatic hierarchical classification scheme that takes into cognizance, the urban nature and the inherent hydrological processes, the land use situation of the studied watershed for 1965, 1975 and 1987 were generated from mosaics of sheets of aerial photograph of the three years mentioned while IKONOS 2 image was used to map 2003 land use scenario. Two major analyses within GIS environment were carried out on the land use to detect the changes that has taken place. These are: (i) Area calculation of the land use / land covers for the four scenarios (1965, 1975, 1987 and 2003) to generate trend and rate of change ( ). xviii

19 (ii) Overlay of the generated landuse of different years ( ), ( ) and ( ) that provides information in matrix format on specific point by point change detection procedure that generate the nature, location and magnitude of the changes. Mini meteorological and hydrological stations were put in place within the study area to capture the second maximum rainfall (August November) events for year Events recorded were rainfall and channels flow. Infiltration component of the hydro-climatic data was derived from infiltration coefficient of U.S. Soil Conservation Service (SCS). Precipitation Water Inundation Model (PWIM) was developed. PWIM is a model that synthesis hydrological processes on urban surface characteristics generated in a GIS environment and simulate runoff and peak flow from precipitated water. Stochastic approach was adopted in determining the hydrological implication of the baseline components (Land use, rainfall, runoff, infiltration and relief) derived by the study. Adopting the PWIM to analyse future scenario, analysis of climate change connection in intra-urban watershed flooding was based on the change in two of the most important drivers of urban flooding; Precipitation and Urbanization (Land use change). Predictions were made for 25 years, 50 years and 100 years. Questionnaire survey instrument was used to obtain data / information on social economic connection and perception analysis of urban flooding in Lagos. Multivariate and descriptive statistics were adopted for the analysis of social economic and perception study. However, the activities described above reveals that the total catchment area of Odo- Ashimowu watershed is km 2. Of this total area, LUTH-Idiaraba sub-section constitute 50.17% (6.75 km 2 ) while Itire and Lawanson constitutes 21.02% (2.83 km 2 ) and 28.82% (3.88 km 2 ) respectively. The built up area progressively increased on the watershed from about hectares (12.40%) in 1965 to hectares (91.46%) in 2003 at an average rate of hectares per annum. This increase indicates that extensive anthropogenic activities for residential and institutional developments have resulted and by extension, led to the massive wetland reclamation on the watershed. The elevation of the watershed ranges between 1meter and 10 meters above mean sea level. There is a strong positive linear relationship between land use change and infiltration xix

20 process. Rainfall / runoff relationship within the watershed shows continuous increase in peak flow and area inundated as land use increases. The design capacities of most primary drains have been reduced to less than 50%. The correlation coefficient (r) of land use of the four scenarios with PWIM simulated peak flow shows an average of 0.96 while the coefficient of determination (r 2 ) reveals an average of 0.92 (92%). This indicates a high linear and positive relationship between urban developments and flood generation. The area inundated by a particular storm event was found to be largely determined by the rainfall intensity. Four levels of vulnerability were determined; these are very high, high, medium and moderate risk zones. The very high and the high are limited to the LUTH-Idi Araba sub-watershed. The study also reveals that the impact of climate change on urban flooding will be more severe in the first 20 to 30 years, using year 2003 urbanization driver as the base year, and that peak flow and other related velocity for the 25years high climate change will increase by an average of 16.1% while inundation area will increase by an average of 2.46%. There is a highly weak positive relationship between flood experience and economic benefits derived during flooding. On the socio-economic implication of urban flooding, it was found that, there is a weak positive relationship between flood experience and benefits during flooding. 39.2% of the respondents have their economic activities affected by flood. The monetary value of loss in economic activitie due to flooding from single storm events are; N 10,000:00 - N 20,000:00 (19.1%), N 20,001:00 N 50,000:00 (10%), N 50,001 N 100,000:00 (4.1%), N 100,001 N500,000:00 (4.1%), N 500,001 N 1,000,000:00 (1.6%) and more than N 1,000,000:00 (0.3%). The low income and female gender are more vulnerable while small and medium scale industries are highly affected. Also, the inhabitants of flood prone areas in Lagos do perceive urban flash flood to be harmful, but other issues, such as safety of their wards as well as the acquisition of landed property are perceived to be more significant than the seasonal inconveniences and losses they experience from urban floods hazard. Policy implementations that embrace the use xx

21 of the PWIM with public campaign / awareness as well as improving the socio-economic status of the vulnerable individual were recommended. Also, there is need for continuous monitoring of the geomorphology, hydrology and ecological dynamism of the urban environment at watershed level while provisions should be made for the anticipated future climate scenario in any intervention. xxi