ABSTRACT 
This study was carried out on River Atuwara in Ota, Ogun State, Nigeria with the aim of developing a coefficient of re-aeration model applicable to River Atuwara and other rivers in the Nigerian environment. This was achieved by sourcing for data once every month from 22 sampling locations of interest within a pre-selected segment of the river over a period covering the dry and wet seasons. The data collected include hydraulic data (depth, width, velocity and time of travel) and water quality data such as Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD). Excel Spreadsheet and MATLAB were used for data processing. Regression analysis was carried out where stream velocity and depth were the regressors and the re-aeration constant k2 (as a function of BOD, DO and Temperature) was the dependent variable.  A coefficient of re-aeration, k2, (Atuwara re-aeration model) was developed and validated statistically. Its performance was also verified by comparing the model with 10 other internationally recognized models. It was  found that even though Atuwara model performed better than Agunwamba model and most of the other well cited models, both Atuwara model and Agunwamba model could be safely adopted for future water quality modelling researches in the Nigerian environment.  Results of detailed water analysis of samples from River Atuwara shows high level of pollution hence it is unfit for human consumption without adequate treatment. It is recommended that River Atuwara and similar rivers in the country should be regularly monitored for quality control.

TABLE OF CONTENTS      PAGE 
Title Page          i
Declaration         ii
Certification         iii
Dedication          iv
Acknowledgement        v
Table of Contents         vii
List of Figures         x
List of Tables         xi
List of Plates         xiv
Abbreviations and Symbols       xv
Abstract          xvi

CHAPTER ONE: INTRODUCTION 
1.1  Background Information       1
1.2   Water Quality modelling       3
1.3   Description of Study Location     5
1.4   Statement of The Problem      6
1.5   Aim         6
1.6   Objectives        6
1.7   Significance of Study       6
1.8   Scope of Study       7

CHAPTER TWO: LITERATURE REVIEW
2.1  Water Quality Modelling as a Field of Study    8
2.2   Coefficient of Re-aeration, k2      9
2.2.3  The Indian k2 Model       13
2.2.4  The Chilean k2 Model       14
2.2.5  The Nigerian k2 Model     15
2.3    Water Laws and Standards       15
2.4    Statistical Analysis       17
2.4.1  Some Relevant Statistical Operations   17
2.4.2  Statistical Software     19
2.4.3  Model Calibration and Validation in Water Quality
Data       20
2.4.3.1      Sum of Squares Due to Error  21
2.4.3.2      R-Square        21
2.4.3.3      Degrees of Freedom Adjusted R-Square 22
2.4.3.4      Root Mean Squared Error   22

CHAPTER THREE: METHODOLOGY  
3.1   Selection of the Study Area       24
3.2   Determination of Sampling Stations      27
3.3   Field Activities        49
3.3.1  Field Observations      31
3.3.2  Field Sampling Visits      31
3.3.2.1     Rationale for Gathering Data Once Every Month  32
3.3.2.2     Activities During the Field Exercises  33
3.4     Materials        34
3.5     Laboratory Analysis       36
3.6     Data Analysis        37
3.6.1    Time of Travel       38
3.6.2    Re-aeration Coefficient Model     39

CHAPTER FOUR: DATA PRESENTATION AND INTERPRETATION 
4.1 Data Gathering       40
4.1.1   Hydraulic Data      41
4.1.2   Physico-Chemical Data     50
4.1.3  Monthly Variations in DO, Temperature, Stream Depth       57
4.2  Computation of Measured k2                                                              63
4.3  Re-arrangement of Sampling Stations    67
4.3.1  Time of Travel      68
4.3.2  Hydraulic Radius                 80
4.3.3  Ultimate BOD and De-oxygenation Rate              80
4.3.4  Saturation DO and the Upstream and Downstream DO deficits  80
4.3.5  Determination of k2                 80
4.3.6  Model Parameters                 80
4.3.7  The Model                  83
4.3.8  Comparison with other Selected Models              83
4.4  Water Use Practices                             103
4.5       Pollutants and Public Health Implications              106

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION 
5.1  Conclusion                  110
5.2 Contribution to Knowledge                111
5.3  Recommendations                 111

REFERENCES                   113

APPENDICES  
Appendix 1: Matlab Code for Beta               121
Appendix 2: Matlab Model Output                          128
Appendix 3: Matlab Code and Output for Plot of all Models           132
Appendix 4: Mix Calculations               140
Appendix 5: Laboratory Reports               147
Appendix 6: Procedure for data Analysis              160

LIST OF FIGURES                                           PAGE 
Figure 1.1 – Nigerian Household distribution by source of water supply  2
Figure 1.2 – Nigerian Household distribution by Toilet Facilities   3
Figure 1.3 ” General Layout of the Study area     5
Figure 3.1″ Field Sampling Stations       28
Figure 3.2 ” Linear representation of Sampling Points    29
Figure 3.3 – Sampling Cross-section       33
Figure 4.1 ” An 8-month mean stream velocity record    59
Figure 4.2 ” An 8-month mean ambient temperature record    60
Figure 4.3 ” An 8-month mean water temperature record    61
Figure 4.4 ” An 8-month mean stream depth record      61
Figure 4.5 ” DO Fluctuations over an 8-month period    62
Figure 4.6 – Flowchart showing the progression of the statistical analysis            86
Figure 4.7 ” Plot of 11 models using January data                93
Figure 4.8 ” Plot of measured k2 against computed k2 using January data            94
Figure 4.9 ” Plot of 11 models using March data                96
Figure 4.10 – Plot of measured k2 against computed k2 using March data            97
Figure 4.11 ” Plot of 11 models using July data                99
Figure 4.12 – Plot of measured k2 against computed k2 using July data            100

LIST OF TABLES                                                                                  PAGE 

Table 2.1 ” The self-purification factor, f, of different water bodies at 20oC  9
Table 2.2 ” Solubility of Oxygen in water      10
Table 3.1 – Details of Sampling Stations      30
Table 3.2 ” Parameters Measured with Relevance to study    32
Table 3.3 ” Parameters, equipment and Processes of  parameter determination
Schedule for field work        34
Table 4.1 – Sampling dates and conditions      40
Table 4.2a ” Hydraulic Data for January      42
Table 4.2b ” Hydraulic Data for February      43
Table 4.2c ” Hydraulic Data for March      44
Table 4.2d ” Hydraulic Data for April      45
Table 4.2e ” Hydraulic Data for May       46
Table 4.2f ” Hydraulic Data for July       47
Table 4.2g ” Hydraulic Data for August      48
Table 4.2h ” Hydraulic Data for September      49
Table 4.3a ” Physico-Chemical Parameters for January    50
Table 4.3b ” Physico-Chemical Parameters for February    51
Table 4.3c ” Physico-Chemical Parameters for March     52
Table 4.3d ” Physico-Chemical Parameters for April     53
Table 4.3e ” Physico-Chemical Parameters for May      54
Table 4.3f ” Physico-Chemical Parameters for July      55
Table 4.3g ” Physico-Chemical Parameters for August    56
Table 4.3h” Physico-Chemical Parameters for September    57
Table 4.4 ” Mean Monthly Ambient and Water Temperatures   60
Table 4.5 ” Determination of Reaches for the River      64
Table 4.6 – Dilution Effects for January      65
Table 4.7 – Dilution Effects for February      65
Table 4.8 – Dilution Effects for March      65
Table 4.9 – Dilution Effects for July       66
Table 4.10 – Dilution Effects for August      66
Table 4.11 – Dilution Effects for September      66
Table 4.12 ” Re-arrangement of station numbers      67
Table 4.13 ” Computation of time of travel on Programmed Excel Spreadsheet for January          68
Table 4.14 ” Computation of time of travel on Programmed Excel Spreadsheet for
February          69
Table 4.15 ” Computation of time of travel on Programmed Excel Spreadsheet for
March           70
Table 4.16 ” Computation of time of travel on Programmed Excel Spreadsheet for
July           71
Table 4.17 ” Computation of time of travel on Programmed Excel Spreadsheet for
August                      72
Table 4.18 ” Computation of time of travel on Programmed Excel Spreadsheet for
September                     73
Table 4.19 ” Computation of k1 and k2 on Programmed Excel Spreadsheet for JanuaryTable 4.20 ” Computation of k1 and k2 on Programmed Excel Spreadsheet for
February                     75
Table 4.21 ” Computation of k1 and k2 on Programmed Excel Spreadsheet for March
76
Table 4.22″ Computation of k1 and k2 on Programmed Excel Spreadsheet for July
77
Table 4.23 ” Computation of k1 and k2 on Programmed Excel Spreadsheet for August
78
Table 4.24 ” Computation of k1 and k2 on Programmed Excel Spreadsheet for
September                     79
Table 4.25″ Model fit and goodness of fit Summary for Dry Season              81
Table 4.26″ Model fit and goodness of fit Summary for Rainy Season           82
Table 4.27 ” Selected Models for Model Validation (Test of performance)    84
Table 4.28″ Goodness of fit using January Data                 91
Table 4.29- Goodness of fit using March Data                 91
Table 4.30- Goodness of fit using July Data                            92
Table 4.31: Graphical Goodness of fit using January, March and July Data  102
Table 4.32 ” Order of Composite Goodness of Fit               103
Table 4.33 ” Comprehensive River water and Industrial Effluent Analysis   107
LIST OF PLATES                                            PAGE
Plate 3.1 ” The industrial effluent flowing along the road down towards the river 25
Plate 3.2 ” the effluent accumulates (left) from where it seeps into the river body 25
Plate 3.3 ” Effluent accumulation beside the river body    26
Plate 3.4 ” Villagers of Iju tapping the river water for domestic use   26
Plate 3.5 ” Sewage being taken near the river for disposal    27
Plate 3.6 ” Field pH meter        35
Plate 3.7 ” Eurolab digital thermometer with sensitive probe   35
Plate 3.8 – Geopacks Stream flow sensor with its pole and fan-like impeller  36
Plate 3.9 – Measuring the river width with a tape      36
Plate 3.10 ” the Speedtech Portable Depth Sounder (yellow torchlight shaped
instrument)          57
Plate 4.1 ” Sampling Station 10 in Rainy season (August)    58
Plate 4.2 ” Sampling Location 10 in Dry season (March)    58
Plate 4.3 ” Human skeleton found in the River               104
Plate 4.4 ” Pollution along the river channel                          104
Plate 4.5 ” The research team could not proceed because of blockage of the river  105
Plate 4.6 ” Water intake station for Ogun State Water Corporation                        105
Plate 4.7 ” Man swimming after the day’s work               106

ABBREVIATIONS AND SYMBOLS 
1.  DO ” Dissolved Oxygen
2.  BOD –  Biochemical Oxygen Demand
3.  QUAL ” Stream Water Quality models
4.  CORMIX ” Cornell Mixing Zone Expert
5.  WASP ” Watershed Quality Analysis Simulation Programme
6.  FEPA ” Federal Environmental Protection Agency
7.  USEPA ” United States Environmental Protection Agency
8.  USGS ” United States Geological Society
9.  UNESCO ” United Nations Education, Scientific and Cultural Organization
10. DV ” Dependent Variable
11. IV ” Independent Variable
12. ANOVA ” Analysis of Variance
13. SSE ” Error Sum of Squares
14. SSR ” Residual sum of squares
15. SST ” Total sum of squares
16. R2 ” correlation coefficient
17. Adj. R2″ Adjusted Correlation coefficient
18. RMSE ” Root mean square error
19. APHA – American Public Health Association
20. SPSS ” Statistical Package for Social Sciences
21. MATLAB ” Matrix Laboratory software
22. GPS ” Global Positioning System
23. k2 ” re-aeration coefficient
24. k1 ” de-oxygenation coefficient
25. f ” self purification factor
26. 2 ^σ  – estimated variance
27. mg/l ” milligram per litre