Use of the Swat Model to Evaluate the Impact of Land-Use Change on Ebonyi River Watershed

ABSTRACT

SWAT was applied a large watershed (3,765km2 ) in south-eastern Nigeria, to predict streamflow and sediment discharge from the Ebonyi River Watershed using globally available data downloaded from the internet. Digital elevation, land-use and soil maps of the study area from global databases and historical weather data measured locally were used. SWAT model was setup to use the MapWindow GIS interface. The model predicted an average daily streamflow and sediment discharge of 24.32m3 /s and 341.31 metric tonnes, respectively, at the watershed outlet for the case of no land-use change. The major land-use of the study area (savanna) was then altered to grassland and row-crop agriculture to simulate six land-use change scenarios, representing combinations of decreasing grassland (93.76% - 0.09%) and increasing agricultural land (0.09% - 93.76%). Other model inputs were kept constant and experimental runs were performed to obtain streamflow and sediment discharges for a one-year period in daily time steps. Results show that expansion of agricultural land to about 19% of the watershed area increased average daily streamflow and sediment discharge to about 29% and 44%, respectively. A further respective increase of streamflow and sediment discharge to about 52% and 79% was simulated for expansion of agricultural land to 56%. Also, about 72% and 99% increase were obtained for streamflow and sediment discharge, respectively, when agricultural land was expanded to 94% of the watershed area. Generally, as more of the watershed is allocated to row-crop agriculture, streamflow and sediment discharge increased and the measure of increase reflected watershed characteristics and conditions. 

TABLE OF CONTENTS

APPROVAL - - - - - - - - - i

DEDICATION - - - - - - - - ii

ACKNOWLEDGMENT - - - - - - - iii

ABSTRACT - - - - - - - - - iv

TABLE OF CONTENTS - - - - - - - v

LIST OF TABLES - - - - - - - - vi

LIST OF FIGURES - - - - - - - - vii

CHAPTER ONE: INTRODUCTION

1.1 Background - - - - - - - - 1

1.2 Objectives of the Study - - - - - - 2

1.3 Justification of the Study - - - - - - 3

1.4 Scope of the Study - - - - - - - 3

CHAPTER TWO: LITERATURE REVIEW

2.1 Land-Use/Cover Change - - - - - - 4

2.2 Water Yield - - - - - - - - 5

2.3 Sediment Yield - - - - - - - 12

2.4 Water Quality - - - - - - - - 15

2.5 Watershed Modelling - - - - - - - 20

2.6 The Soil and Water Assessment Tool (SWAT) - - - 22

2.7 SWAT2005 Model Description - - - - - 25

2.8 Theory of the SWAT Model - - - - - - 26

2.9 Geographic Information System (GIS) Interface - - - 44

2.10 Performance of SWAT on Hydrologic Studies - - - 46

2.11 Performance of SWAT on Sediment Studies - - - - 48

2.12 SWAT Model: Advantages and Disadvantages - - - 49

CHAPTER THREE: METHODOLOGY

3.1 The Study Area - - - - - - - 51

3.2 Model Inputs - - - - - - - - 52

3.3 MapWindow-SWAT(MWSWAT) Model Setup - - - 56

3.4 Calculation Methods - - - - - - - 58

3.5 Land-use Scenarios - - - - - - - 58

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1 Simulated Streamflow and Sediment Discharge - - - 60

4.2 Land-Use Scenarios - - - - - - - 62

4.3 Discussion - - - - - - - - 65

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION

5.1 Conclusion - - - - - - - - 68

5.2 Recommendation - - - - - - - 69

REFERENCES - - - - - - - - 70

APPENDICES - - - - - - - - 81