Watershed hydrological responses to changes in land use and land cover, and management practices at Hare watershed, Ethiopia [Elektronische Ressource] / Kassa Tadele Mengistu

Kassa Tadele Mengistu

Informations

• Publié par: universitat_siegen
• Publié le: 01 janvier 2009
• Nombre de lectures: 84
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Universität Siegen




Watershed Hydrological Responses to Changes
in Land Use and Land Cover, and Management
Practices at Hare Watershed, Ethiopia


















Kassa Tadele Mengistu


November, 2009

Universität Siegen
Fakultät Bauingenieurwesen
Research Institute for water and Environment




Watershed Hydrological Responses to Changes
in Land Use and Land Cover, and Management
Practices at Hare Watershed, Ethiopia




Zur Erlangung des akademischen Grades eines
Doktors der Ingenieurwissenschaften
(Dr.-Ing.)



dem Fachbereich
Bauingenieurwesen
der Universität Siegen

vorgelegte
Dissertation





Von

Kassa Tadele Mengistu, M.sc



Referent: Prof. Dr.-Ing. G. Förch, Universität Siegen
Koreferent: Prof. Dr.-Ing. habil. Hans -B Horlacher, TU Dresden



ABSTRACT

This study investigates hydrological responses to changes in land use, land cover and
management practices at Hare River watershed, Southern Rift Valley Lakes Basin, Ethiopia.
It addresses methods that are required to better characterize impacts of land use and cover
and climate change scenarios and understand the upstream-downstream linkages with respect
to irrigation water allocation. Understanding how the changes in land use and cover influence
streamflow and subsequently optimization of available water resources utilization can
enhance the ability of planners, practitioners, researchers and farmers to formulate and
implement sound policies to minimize undesirable future impacts and devise management
alternatives.

Three land use and cover maps were developed using aerial photographs and satellite image
through visual interpretation of the aerial photographs and supervised classification of the
satellite image. The rates of land use and land cover changes were identified for two periods
at watershed and sub-watershed levels. Two physical-based, semi-distributed hydrological
models, SWAT2005/ArcSWAT and HSPF, were utilized to simulate hydrological responses
to land use and climatic changes. Streamflow data at the outlet of the watershed was utilized
to analyze seasonal stream flow variability due to land use and land cover changes. The
performances of the models have been evaluated through sensitivity analysis, calibration,
validation and uncertainty analysis. Consequently, impacts of hypothetical land use and
climate change scenarios were developed to analyze their impacts on downstream water
users. Eventually, based on the results these scenario analyses a new optimal irrigation water
allocation tool was developed to allocate available water resources among competing
irrigation sites.

The results of the land use and land cover change analysis identified that farmlands and
settlements class has expanded during the past four decades. Detailed impacts of these
changes were analyzed employing the SWAT2005. Sensitivity analysis using the SWAT2005
model has pointed out some crucial parameters that control the surface and subsurface
hydrological processes of the studied watershed. Consequently, results of the models
performances assessment illustrated that both SWAT2005 and HSPF have resulted acceptable
outputs with some efforts of acquiring data in areas where there is limited available data.
However, the SWAT2005 model performs slightly better than HSPF for monthly and
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seasonal streamflow analysis. As a result, streamflow variability during the dry and wet
seasons was further analysed using this model based on pre-identified scenarios.
Furthermore, uncertainty analyses were performed and discussed using ParaSol,
SUNGLASSES, SUFI-2 and GLUE methods. On the other hand, results from the climate
change scenario analysis using GCM for the period of 2010-2099 showed that an increase in
future average annual precipitation and average temperature when compared to the baseline
period. Similarly, analysis made on intervention of small scale irrigation in the upper and
middle reach of the watershed resulted in substantial decrease in mean monthly discharge
during the dry season, while increased discharge during the wet season.

Consequently, an optimal tool was developed to allocate scarce water resources among three
upstream and downstream demand sites with a prime objective of achieving equitable
resources utilization while maintaining acceptable economic efficiency and environmental
sustainability. The analysis revealed that a substantial volume of water can be saved through
deficit irrigation principles. It is also noted that, in the face of intense competition among
irrigation water users where there is a significant water shortage throughout a watershed,
equitable and efficient utilization of water resources has always remained a social goal.

The developed tool can be used in other watersheds too by decision makers and planners
where there exist irrigation water allocation problems between competing upstream and
downstream irrigation sites. However, it needs simulation outputs from SWAT2005 and
needs to specify the exact sub-watersheds where the irrigation sites are located. In order to
utilize outputs from other models, the tool needs some modification in the algorithm (visual
basic) specifically on the declaration of the input files. Generally, the results highlighted that
use of an integrated simulation-optimization approach has a paramount importance to
investigate impacts of land use and cover and climate change on hydrological regime and
consequently allocate limited available water resource in an equitable manner among
competing sites.


II


ACKNOWLEDGEMENT

First and above all, I praise God, the almighty for providing me this opportunity and granting me
the capability to proceed successfully. Next, I would like to forward heartfelt thanks for those
who deserve it, for their assistance, guidance and realization of this work.

My utmost words of thanks go to my major supervisor Prof. Dr.-Ing. Gerd Förch for his
constructive supports, advice and guidance throughout my study period. I very much appreciate
his encouragement and understanding. I also owe a sincere gratitude to Prof. Dr.-Ing. habil. Hans
–B. Horlacher for his willingness to co-supervise my research and for his invaluable comments
and suggestions during the research work. I also would like to thank chairman of the examining
committee Prof. Dr.-Ing. Jürgen Jensen and member of the committee Prof. Dr.-Ing. Monika
Jarosch for their valuable comments and inputs to my research.

I am thankful for German Development Cooperation (GTZ) and European Union (EU) that made
this research possible through financing my stay in Germany and during my field work in
Ethiopia. Thanks to the Germany Academic Exchange Service (DAAD) through which I obtain
the sponsorship and support during my study. The kind collaborations of Ethiopian National
Meteorological Service, Department of Hydrology of Ministry of Water Resources, Ethiopian
Mapping Agency and Chencha Woreda Agricultural Office and the community during my field
work and data collection process are very much appreciated.

My special gratitude is extended to my colleague Adane Abebe with whom we passed all the
good and bad times together during the research journey. I would like also to give special thanks
to the staffs at Arba Minch University, particularly Dr. Mekonen Ayana, Dr. Semu Moges and
Dr. Tarekegn Tadesse (President of Arba Minch university) for their invaluable support,
assistance and taking care of my family in Ethiopia during my absence. I am also grateful to the
Water Resources Management Group at Universität Siegen namely Dr. Stefan Thiemann, Mrs.
Ingrid Althoff, Mrs. Beate Boehme, Mr. Ruger Winnegge, Mrs. Frauke Koch and other technical
staffs for their full support and exciting environment during my stay in Germany. Thanks are also
due to the water quality and soil mechanics laboratory technicians at Arba Minch University who
assisted me in facilitating the laboratory works.

Last but most importantly, I would like to extend my most profound gratitude to my wife
Tadelech Millo and our children Tsion, Nahom, Bethlehem, Kassech and Aynalem for their
patience, understanding and all the inconvenience that they have encountered during my absence.
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CONTENTS Page

ABSTRACT ..................................................................................................................................... I
ACKNOWLEDGEMENT ................. III
LIST OF ABBREVIATIONS ............................................................................................................. VII
LIST OF FIGURES .......................... XI
LIST OF TABLES ......................................................................................................................... XIII
CHAPTER 1: INTRODU