Numerical investigation on flow and transport characteristics to improve long-term simulation of reservoir sedimentation [Elektronische Ressource] / von Tesfaye Kebede Gurmessa

Numerical investigation on flow and transport characteristics to improve long-term simulation of reservoir sedimentation [Elektronische Ressource] / von Tesfaye Kebede Gurmessa

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Heft 162 Tesfaye Kebede Gurmessa Numerical Investigation on Flow and Transport Characteristics to Improve Long-Term Simulation of Reservoir Sedimentation Numerical Investigation on Flow and Transport Characteristicsto Improve Long-Term Simulation of Reservoir SedimentationVon der Fakult˜at Bau- und Umweltingenieurwissenschaften der Universit˜at Stuttgart zurErlangung der Wurde˜ eines Doktor-Ingenieurs (Dr.-Ing.) genehmigte AbhandlungVorgelegt vonTesfaye Kebede Gurmessa˜aus Ambo, Shoa, AthiopienHauptberichter: Prof. Dr.-Ing. habil. Bernhard WestrichMitberichter: Prof. Dr. rer.nat. Dr.-Ing. habil. Andr¶as B¶ardossyMitberichter: Prof. Gerhard H. Jirka, Ph.D.Tag der mundlic˜ hen Prufung:˜ 21. Juni 2007Institut fur˜ Wasserbau der Universit˜at Stuttgart2007Heft 162 Numerical Investigation on Flowand Transport Characteristics toImprove Long-Term Simulation ofReservoir SedimentationvonDr.-Ing.Tesfaye Kebede GurmessaEigenverlag des Instituts fur˜ Wasserbau der Universit˜at StuttgartD93 NumericalInvestigationonFlowandTransportCharacteristicsto Improve Long-Term Simulation of Reservoir SedimentationTitelaufnahme der Deutschen BibliothekKebede Gurmessa, Tesfaye:NumericalInvestigationonFlowandTransportCharacteristicstoImproveLong-TermSimulationof Reservoir Sedimentation / von Tesfaye Kebede Gurmessa. Institut fur˜ Wasserbau, Universit˜atStuttgart. Stuttgart: Inst.

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Heft 162 Tesfaye Kebede Gurmessa

Numerical Investigation on Flow and
Transport Characteristics to Improve
Long-Term Simulation of Reservoir
Sedimentation Numerical Investigation on Flow and Transport Characteristics
to Improve Long-Term Simulation of Reservoir Sedimentation
Von der Fakult˜at Bau- und Umweltingenieurwissenschaften der Universit˜at Stuttgart zur
Erlangung der Wurde˜ eines Doktor-Ingenieurs (Dr.-Ing.) genehmigte Abhandlung
Vorgelegt von
Tesfaye Kebede Gurmessa
˜aus Ambo, Shoa, Athiopien
Hauptberichter: Prof. Dr.-Ing. habil. Bernhard Westrich
Mitberichter: Prof. Dr. rer.nat. Dr.-Ing. habil. Andr¶as B¶ardossy
Mitberichter: Prof. Gerhard H. Jirka, Ph.D.
Tag der mundlic˜ hen Prufung:˜ 21. Juni 2007
Institut fur˜ Wasserbau der Universit˜at Stuttgart
2007Heft 162 Numerical Investigation on Flow
and Transport Characteristics to
Improve Long-Term Simulation of
Reservoir Sedimentation
von
Dr.-Ing.
Tesfaye Kebede Gurmessa
Eigenverlag des Instituts fur˜ Wasserbau der Universit˜at StuttgartD93 NumericalInvestigationonFlowandTransportCharacteristics
to Improve Long-Term Simulation of Reservoir Sedimentation
Titelaufnahme der Deutschen Bibliothek
Kebede Gurmessa, Tesfaye:
NumericalInvestigationonFlowandTransportCharacteristicstoImproveLong-TermSimulation
of Reservoir Sedimentation / von Tesfaye Kebede Gurmessa. Institut fur˜ Wasserbau, Universit˜at
Stuttgart. Stuttgart: Inst. fur˜ Wasserbau, 2007
(Mitteilungen / Institut fur˜ Wasserbau, Universit˜at Stuttgart: H. 162)
Zugel.: Stuttgart, Univ., Diss., 2007
ISBN 3-933761-66-2
NE: Institut fur˜ Wasserbau < Stuttgart >: Mitteilungen
˜Gegen Vervielf˜altigung und Ubersetzung bestehen keine Einw˜ande, es wird lediglich um
Quellenangabe gebeten.
Herausgegeben 2007 vom Eigenverlag des Instituts fur˜ Wasserbau
Druck: Sprint-Druck, StuttgartPreface
Planning,constructionandmaintenanceofwaterreservoirsbecomeincreasinglyimportant,
in particular in countries and regions which are vulnerable to climate change. Therefore
reservoir sedimentation and sustainable sediment management is an important issue in
water resources engineering and management. Reservoir sedimentation has great technical,
economic and social implications. It is a challenging task for hydraulic and environmental
engineers to develop appropriate methods and tools to perform a long term prediction of
reservoir sedimentation, in order to develop mitigation measures, extend the reservoir life
time and enhance the beneflt of the storage capacity.
The presented work is an in depth investigation on sedimentation processes of medium size
reservoirs by using a 2-dimensional physically based numerical model. Reservoirs of typical
size and shape have been analyzed focussing on their response to temporal variation of
in owing discharge and suspended sediments as well as reservoir operation. The numerical
investigation provides basic information and a deep insight into the overall sediment trap-
ping characteristics of reservoirs under unsteady discharge and suspended sediment input
conditions.Theresultsshowthekeyroleoftheshapeandmeanresidencetimeofthereser-
voir on the damping of the amplitude and the modiflcation of the frequency of in owing
discharge and suspended sediment concentration, in particular for highly unsteady ood
events. Some important criteria for long term numerical simulation are developed resulting
in an aggregation of input data and a combined quasi-steady and unsteady numerical mod-
eling. The modeling strategy was successfully applied to a daily storage reservoir in South
of Germany to predict the sedimentation for some future decades.
Furthermore, the candidate Mr. Kebede Gurmessa has shown that if a good database is
available the application of a multiple regression based on the principle component analysis
allows a reliable medium-term prediction of the development of the deposited sediment
volume including the spatial distribution of the deposits.
The thesis is an important scientiflc contribution to the engineering modeling of non-
stratifled reservoirs that undergo long-term sedimentation processes. The combined ap-
proach of both mathematical-numerical modeling of the unsteady reservoir ow and sedi-
ment behavior and of multivariate statistical techniques has yielded useful insights on how
these systems can be predicted e–ciently in order to manage their long-term behavior. The
guidelines developed therein have important implications for engineering practice.
Bernhard Westrich
IAcknowledgment
Above all, I am very grateful to Prof. Bernhard Westrich, the head of Versuchsanstalt fur˜
WasserbauattheUniversit˜atStuttgartfortakingthepositionofanadvisorinthisresearch.
He followed the work closely and gave me invaluable suggestions and critiques without any
hesitation.Healsoprovidedmewithnecessaryresearchfacilitiesandencouragementsduring
the period of this work.
I would like also to extend my thank to Prof. Andr¶as B¶ardossy, chair of Lehrstuhl fur˜
HydrologieundGeohydrologie,anddirectoroftheInstitutfur˜ WasserbauattheUniversit˜at
Stuttgart, for taking the position of internal co-advisor. His guidance was very crucial
particularly in the second part of this work.
IwouldalsoverymuchthankProf.GerhardH.Jirka,directorofInstitutfur˜ Hydromechanik
at the Universit˜at Karlsruhe for overtaking the position of external co-advisor. He gave me
both critical oversight and words of encouragement.
There are a number of people to mention in the IWS who were helpful in the process of
the research: Prof. Helmut Kobus gave critical remarks during the doctoral seminars of the
ENWATprogram.Dipl.-Ing.JoachimKarnahl,Dr.-Ing.GeorgeJacoub,andDipl.-Ing.Sven
Wurms˜ with whom I made discussions relevant to the TELEMAC modeling system. Dipl.-
Phys. Gerhard Schmid supported the research in providing all necessary computational
facilities. He also helped in organizing fleld sample collection and laboratory analysis on
sediment samples, on which two other colleagues, Dipl.-Geo˜okol. Thomas Jancke and Herr
Werner Bareth took part. Dr.-Ing. Yeshewatesfa Hundecha Hirpa deserves my thanks for
valuable discussions relevant to the work. I would also like to thank Mr. Jefirey Tuhtan
for proofreading the work. I also thank Dr.-Ing. Sabine Manthey for her suggestions on
editorial aspects. The lecturers of the Fakult˜at Bau- und Umweltingenieurwissenschaft at
the Universit˜at Stuttgart from whom I learned valuable ideas also deserve my thank.
There are also people to mention from various organizations which deserve my thanks: Mr.
Pierre Lang from SOGREAH/LHF gave me advices on the TELEMAC modeling system.
Dr.-Ing. Roberto Kohane from Lahmeyer International, Herr Ralf Klocke from Lech Elek-
trizit˜atswerk, and Herr Thomas K˜ohler from Bayerisches Landesamt fur˜ Umwelt provided
me with the data used in this research. Dipl.-Ing. Thomas S. Hille, from the university of
technology of Delft, made proofreading of some part of the work as well as translation to
the Deutsche Zusammenfassung in which Dipl.-Ing. Sven Wurms˜ had a share.
My thank extends to the IPSWaT program initiated by the German Federal Ministry of
EducationandResearchforsupportingmeflnanciallyintheperiodoftheresearch.Iwould
also like to thank all my friends and my family. Finally, I would like to give thank to the
almighty God for giving me health and strength to accomplish this work successfully.
Stuttgart, April 2007 Tesfaye Kebede Gurmessa
IIContents
Preface I
Acknowledgement II
List of Figures VII
List of Tables XII
List of Abbreviations XIII
Abstract XVII
Zusammenfassung XIX
1 Introduction 1
1.1 Modeling of reservoir sedimentation . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1 Numerical modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2 Data driven modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.3 Empirical models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.4 Physical scale models . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2 Objectives of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 Structure of the work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Part I. Physically-Based Modeling Approach 11
2 Modeling of Flow and Sediment Transport 13
2.1 Mathematical models of ow . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
IIIIV Contents
2.1.1 Continuity and Navier-Stokes equations . . . . . . . . . . . . . . . . . 13
2.1.2 Turbulence closure assumptions . . . . . . . . . . . . . . . . . . . . . 14
2.1.3 Shallow water equations . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 Mathematical model for sediment transport . . . . . . . . . . . . . . . . . . 18
2.2.1 Basics of model conceptualization . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Governing equations of suspended sediment transport . . . . . . . . . 22
2.3 Coupling ow and suspended sediment transport . . . . . . . . . . . . . . . . 24
2.4 Finite element method in ow and suspended sediment transport . . . . . . 25
2.4.1 Time discretization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.2 Spatial . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5 Aspects in application of numerical models . . . . . . . . . . . . . . . . . . . 28
2.5.1 Selection of appropriate model . . . . . . . . . . . . . . . . . . . . . . 29
2.5.2 TELEMAC modeling system. . . . . . . . . . . . . . . . . . . . . . . 30
2.5.3 Steps in morphological simulation . . . . . . . . . . . . . . . . . . . . 32
3 Reservoir Response and Unsteadiness Simpliflcations 35
3.1 Ideal reactors and their application . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Periodic system inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3 Aggregate response of reservoirs to inputs . . . . . . . . . . . . . . . . . . . 41
3.4 Quasisteady approximations . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4 Data Evaluation in Morphological Modeling 57
4.1 Data acquisition and management . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 Database of the Lautrach reservoir . . . . . . . . . . . . . . . . . . . . . . . 59
4.2.1 Description of the Lautrach reservoir . . . . . . . . . . . . . . . . . . 60
4.2.2 Topographical data analysis of the reservoir . . . . . . . . . . . . . . 61