ASSESSMENT OF THE IMPACT OF ROAD CONSTRUCTION ON PHYSICAL LAND DEGRADATION IN CENTRAL HIGHLANDS OF ETHIOPIA: THE CASE OF TWO …

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ASSESSMENT OF THE IMPACT OF ROAD CONSTRUCTION ON PHYSICAL LAND DEGRADATION IN CENTRAL HIGHLANDS OF ETHIOPIA: THE CASE OF TWO …
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     ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES ASSESSMENT OF THE IMPACT OF ROAD CONSTRUCTION ON PHYSICAL LAND DEGRADATION IN CENTRAL HIGHLANDS OF ETHIOPIA: THE CASEOF TWO SELECTED PROJECTSTHESIS SUBMITTED TO   THE SCHOOL OF GRADUATE STUDIES OFADDISABABA UNIVERSITY  IN PARTIAL FULFILLMENT OF THEREQUIREMENTS FORTHE DEGREE OF MASTER OF SCIENCE IN ENVIRONMENTALSCIENCE PROGRAMME BY SOLOMON ADDISU  AUGEST 2009 ADDIS ABAB  ii ACKNOWLEDGEMENTS  Above all, always and forever my blessing and praise goes to the almighty God, who gaveme all the stamina and everything I ever asked, to keep myself on track.This study would never be completed without the contribution of many people to whom Iwould like to express my gratitude. First of all I would like to thank my advisor, Dr.Mekuria Argaw for guiding and educating me during the different stages of this thesis:ignition of the research idea, writing my proposal, conducting fieldwork and writing thisthesis. The discussions and suggestions were helpful to get me back on track andstructuring my thoughts. Thanks also for always reminding me that there is time for a bikeride.The two translators and field assistants Habtamu Assefa and Negusu Tefera wereindispensable for the field work in translating and gathering data .To all the villagers of the study area Peasant Association, who were so kind to share their way of live.I extend my recognition to Ato Negasi who strongly assist me by GIS work, andEnvironmental science students, who have been in great help all the way up to thecompletion of this study. Finally, the unfailing encouragement, tolerance and support rendfrom my friends Solomon Habtewold and, all staff members of Addis college and all myfamilies deserves particular thanks. The prayers of my mother and Father have contributedto the success of my work.  iii Table of Contents LIST OF TABLES .............................................................................................................. VI   LIST OF FIGURES .......................................................................................................... VIII   LIST OF ACRONYMS ........................................................................................................ IX   LIST OF APPENDICES ....................................................................................................... X   ABSTRACT ...................................................................................................................... XI   1. INTRODUCTION ............................................................................................................ 1   1.1.   B ACKGROUND ...................................................................................................................... 1 1.2.   S TATEMENT OF THE PROBLEM ................................................................................................. 3 1.3.   O BJECTIVES ......................................................................................................................... 5 1.3.1 General Objective .......................................................................................................... 5   1.3.2. Specific Objectives ......................................................................................................... 5   2. LITERATURE REVIEW ................................................................................................... 6   2.1.   L AND D EGRADATION ............................................................................................................ 6 2.1.1. Definitions ................................................................................................................... 6   2.1.2 Physical Degradation ...................................................................................................... 7    2.2.   L AND DEGRADATION IN E THIOPIA ........................................................................................... 8 2.3.   R OAD C ONSTRUCTION AND L AND D EGRADATION ........................................................................ 9 2.3.1 .Level of road construction In Ethiopia ............................................................................... 9   2.3.2 Land Degradation Related to Road  .................................................................................. 10   2.4.   S OIL D EGRADATION AND E ROSION P ROCESS ............................................................................ 11 2.5.   S OIL EROSION AND MANAGEMENT PROBLEMS ........................................................................... 12 2.6.   W ATER EROSION ................................................................................................................. 13 2.6.1. Forms of water erosion ................................................................................................. 13   2.6.1.1 Raindrop splash erosion ............................................................................................... 14 2.6.1.2. Surface flow erosion (sheet or laminar erosion) .................................................................. 14 2.6.1.3. Channelized flow erosion ............................................................................................ 14  iv 2.6.2- Factors affecting water erosion ...................................................................................... 14   2.6.2.1. Rainfall Intensity and Runoff  ........................................................................................ 15 2.6.2.2. Soil Erodibility ........................................................................................................ 15 2.6.2.3. Slope Gradient and Length .......................................................................................... 15 2.6.2.4. Vegetation / Crop Cover ............................................................................................. 16 2.7.   I MPACTS OF R OAD AND PHYSICAL L AND D EGRADATION ............................................................. 16 2.7.1. Gullying and Rilling ..................................................................................................... 16   2.7.2. Mass failures /Landslid/  ................................................................................................ 16   2.7.3. Sloughing ................................................................................................................... 17    2.8.   R OAD CONSTRUCTION AND EROSION PROBLEMS ........................................................................ 17 2.8.1. Parts of Road which are sensitive for erosion Problem ....................................................... 18   2.8.1.1. Road Culverts .......................................................................................................... 18 2.8.1.2. Road Ditches ........................................................................................................... 18 2.8.2. Gully Erosion Risk of Road Building ............................................................................... 19   2.8.3. Parameters of gully erosion ........................................................................................... 22   2.9.   M ODELING A PPROACH ......................................................................................................... 23 2.10.   B EST MANAGEMENT PRACTICES FOR CONTROL OF EROSION ORIGINATING FROM ROAD CULVERTS ANDDITCHES ................................................................................................................................. 23 3. MATERIALS AND METHODS ........................................................................................ 25   3.1.   D ESCRIPTION OF THE STUDY AREA .......................................................................................... 25 3.1.1 Addis Ababa to Fiche Road  ............................................................................................ 25   3.1.2. Addis Ababa to Ambo Road  ........................................................................................... 25   3.1.3. Climate ...................................................................................................................... 26   3.1.4. Economic Activities along the road  ................................................................................. 28   3.2.   M ETHODS ......................................................................................................................... 28 3.2.1. Reconnaissance Survey ................................................................................................. 28   3.2.2. Study Design ............................................................................................................... 29   3.2.3. Data collection ............................................................................................................ 30   3.2.3.1. Gully measurements and Computation of gully parameters .................................................... 30  v 3.2.3.2. Data used for the Formulation of Model ........................................................................... 32 3.2.3.3. Determination of gully head area from DEM ..................................................................... 33 3.2.3.4. Socio-economic data acquisition and sampling techniques ..................................................... 35 3.4.   D ATA ANALYSIS ................................................................................................................. 35 4 .RESULTS AND DISCUSSION ......................................................................................... 37   4.1.   E XTENT OF PHYSICAL L AND DEGRADATION .............................................................................. 37 4.2.   S OIL L OSS FROM G ULLY EROSION AND ITS CHARACTERISTICS ................................................ 40 4.2.1. Impact of Road on GullyCharacteristics ........................................................................... 43   4.2.1.1. Gully Length ........................................................................................................... 44 4.2.1.2. Gully width and Depth ............................................................................................... 44 4.2.1.3. Gully Texture and its ratio to the total catechement area of the road segments .............................. 45 4.2.1.4. Gully Density .......................................................................................................... 46 4.2.1.5. Gully Volume .......................................................................................................... 47 4.2.1.6. Gully Category ........................................................................................................ 48 4.3.   T HE R ELATIONSHIP BETWEEN GULLY CHARACTERISTICS AND SEDIMENT L OADING ............................ 49 4.3.1. Relationship between morphometric parameters of the studied gullies ................................... 49   4.3.2. Relationship between the volume of gully and its morphometric characteristics ....................... 50   4.4.IMPACT   OF   ROAD   ON   G ULLY D RAINAGE AREA . .................................................................... 51 4.4.1. Gully Head Drainage area for Road Segments on Fiche Site. ............................................... 53   4.4.2. Gully Head Drainage area for Road Segments on Ambo Site. ............................................... 55   4.5.   F ARMERS ’ PERCEPTION OF PHYSICAL L AND D EGRADATION A FTER THE ROAD REHABILITATION . .......... 56 5- CONCLUSION AND RECOMMENDATIONS .................................................................... 62   5.1-   C ONCLUSION ..................................................................................................................... 62 5.2   R ECOMMENDATIONS ............................................................................................................ 63 6. REFERENCES .............................................................................................................. 65   7. APPENDICES ............................................................................................................... 70  
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