INVESTIGATION OF THE SPATIAL AND TEMPORAL VARIATION OF SEDIMENT YIELD AND SURFACE RUNOFF IN OFFA WATERSHED, KWARA STATE

ABSTRACT

In this research, an hydrological modelling tool, soil and water assessment tool (SWAT) used to investigate the spatial and temporal variation of sediment yield in a watershed. The model was run for 31years using spatial data such as Digital Elevation Model, soil map, land use and precipitation, wind and solar radiation. The results showed that the maximum value ofsurface Runoff was estimated as 19100.034mm in the year 2005 while the minimum surface Runoff was 1000.671mm in the year 20017. The maximum value of sediment yield was estimated as 2340.532mm in the 2005 and the minimum value was estimated as 34.769mm in the year 2003

TABLE OF CONTENTS

Title page                                                                                           

Certification                                                                                        ii

Dedication                                                                                           iii

Acknowledgement                                                                                iv

Abstract                                                                                              v

Table of content                                                                                  vi

List of Figures                                                                                      ix

CHAPTER ONE: INTRODUCTION

1.1     Introduction                                                                              1

1.2     Problem Statement                                                                     2

1.3     Aims & Objectives                                                                      2

1.4     Justification                                                                               3

1.5     Scope of Study                                                                           3

1.6     Description of Study Area                                                            3

CHAPTER TWO: LITERATURE REVIEW

2.0     Literature Review                                                                       5

2.1     Sediment Source Analytical Techniques                                         5

2.2     Sediment Yield Measurements                                                      6

2.3     Field Measurements of Sediment Yield                                           7

2.4     Sediment Yield Modeling                                                             7

2.5     Brief Description of Selected Hydrology Models                                       8

2.5.1  RIBASIM                                                                                    8

2.5.2  WEAP                                                                                        9

2.5.3  Realm Resource Allocation Model                                                 9

2.5.4  HSPF Model                                                                               10

2.5.5  AGNPS Model                                                                                       10

2.5.6 SWAT Models                                                                             11

2.6     SWAT Model Description                                                             11

2.7     Water Shed Hydrological Modeling.                                              11

CHAPTER THREE: METHODOLOGY

3.0     Methodology                                                                              13

3.1     Model Selection and Description                                                   13

3.2     Model Input Data                                                                       14

3.3     Digital Elevation Model (DEM)                                                      14

3.4     Soil Map                                                                                    15

3.5     Weather Data                                                                             16     

3.6     SWAT Model Set-up and Run                                                       16

3.7     Water Shed Delineation                                                               16

3.8     Land use map of the watershed                                                    17

CHAPTER FOUR: RESULTS AND DISCUSSION

4.0 RESULTS                                                                                       19

4.1 Temporal Variation of total means for surface runoff                          19

4.2 Temporal variation  of total means for sediment yield                         20

4.3     Temporal variation of annual means for sediment yield                   21

4.4     Temporal variation of annual means for surface runoff                     21

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION

5.0 Conclusion                                                                                     23

5.1 Recommendation                                                                            23

References                                                             

CHAPTER ONE

1. INTRODUCTION

Water is an integral part of life, as human beings derived from the environment several services that are necessary for the survival, Water is one of the basic needs that human beings cannot live without; indeed water is life! Therefore, water-related (hydrological) ecosystem services provided by the environment (e.g provision, regulation and purification of freshwater) are quite valuable and important for human well-being. This underscores the importance of sound watershed management for continued provision of hydrological ecosystem services. From a hydrological point of view, a watershed includes all land contributing water (surface and ground water) to a reference point.     

  It is therefore obvious that land comprising of any watershed would generally be under other uses such as forests, agriculture and urban centers, which might commonly be considered ‘primary’ land uses. This means that watersheds provide other important ecosystem services, beside provision of hydrological ecosystem services. In some cases, enhanced provision of some ecosystem services may also lead to reduced capacity of watersheds to provide other services e.g. intensive cultivation to maximize food production may also lead to increase in soil erosion and consequently degradation of water quality.

Sediment yield is the amount at a point of interest in a particular period of time which occur due to heavy rainfall, are normally as tones per year or kilogram per year.

A large part of failure to achieve reasonable estimates of average annual sediment lies in particles of extrapolating relationship derived from field data with no consideration of appropriateness for future conditions.

Sediment yield is affected by many factors such as climate, soil, relief, vegetation and human influence. Runoff refers to as the part of water cycle that flow over land as surface water.

     Runoff has been used as a variable representing climatic conditions and includes not only the water that travel over the land surface and through channels to reach a stream but also interflow, the water that infiltrates the soil surface and travels by means of gravity toward a stream channel.

      In this study offa water shed is simulated to predict the surface runoff and sediment yield. The spatial and temporal variation obtained can be used as a decision support tool in the management of the water shed.