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                                                             
LIST OF FIGURES

CHAPTER ONE

• 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.

1.2   PROBLEM STATEMENT

Recent flooding issues in Nigeria as a result of excessive rainfall has resulted into runoff and sediment yield in the area. Therefore in order to manage the water shed sustainability, it is necessary to predict the variation of sediment yield and runoff in the area which can serve as a data base in managing the watershed.

1.3     AIM AND OBJECTIVES

The aim of the research was to investigate the spatial and temporal variation of sediment yield and runoff in Offa watershed.Specific objectives achieved are:

1. Predict the surface runoff and sediment into watershed
2. Develop temporal variation map of sediment yield and runoff

• Develop spatial variation map of sediment yield and runoff

1.4     JUSTIFICATION

The Spatial and temporal variation of sediment yield and runoff in the catchment area can serve as a decision support tools to water managers in the area to plan a sustainable management of the water shed.

1.5     SCOPE OF STUDY

The scope of the work was limited to the study of temporal variation of sediment using temporal data of 31years from 1986 to 2016. the analysis was based on preliminary modeling results obtained from digital elevation model (DEM) land use and soil map to predict the optimum variation of sediment yield and runoff generation in Offa water shed.

1.6     DESCRIPTION OF STUDY AREA

Offa water shed is located in offa local government area of kwara state Nigeria. It is one of the main water supply in its locality, it is about 43km from Ilorin the capital of kwara state it fall within the latitude 8.1393^o N and 4.7174⁰ E. The map  is shown in figure 1.1-1.3

CHAPTER FIVE

5.0     CONCLUSION AND RECOMMENDATION 

5.1     Conclusion

In this research, SWAT model was successfully applied to stimulate surface runoff and sediment yield at Offa water shed, Kwara State.

The investigation of spatial distribution for sediment yield and surface runoff show that the maximum surface runoff was obtained as 19100.034mm in the year 2005 and also the minimum value of total means was obtained as 1000.673 in the year 2007. The maximum sediment yield was obtained as 2340.532mm in the year 2005. Also the minimum value was obtained as 34.769mm in the year 2003.

5.2     Recommendation

Further research to be carried out on the validation and calibration of the model to improve the model performance.