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Combined 3D Hydrodynamic and Watershed Modelling of Lake Tana, Ethiopia
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
2011 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 398, no 1-2, 44-64 p.Article in journal (Refereed) Published
Abstract [en]

 The growing high demand for lake Tana water portends a disturbing future. The main objective of this paper is to make a contribution to the development of a sustainable use of the water of Lake Tana. A fully three-dimensional hydrodynamic model was combined with a watershed model and together, these models were successfully validated for the year 2006. The flow structure is characterized by large recirculation and secondary flow regions. Secondary flows are induced by hydrodynamic instabilities occurring at the interfaces of layers with a velocity gradient and the interaction with the irregularities of the bed. The weak stratification process in Lake Tana is characterized by a classic summer profile, which is more pronounced during January-February. Mixing processes in the lake are controlled by wind, the mixing energy induced by both river inflows and the lake outlet, and convective mixing due to the negative buoyancy. An alarming fall of the water levels in Lake Tana was found in response to the planned water withdrawal. The long flushing time (19 months) will not allow a fast decay of contaminated materials released into the lake. The flow structure will not be significantly modified by the planned water withdrawal but the flushing time will decrease. The hydrodynamics of Lake Tana resemble a closed system similar to a shallow reservoir with an overflow type outlet. The implication is that the lake is vulnerable to changes in external conditions and sustainable use of the water resource of the lake will require awareness of this vulnerability. The combined watershed and hydrodynamic models would be effective tools to achieve this awareness. It is also necessary to address the impact of climate change on the fate of the lake. These are all difficult challenges that need to be addressed to safeguard the sensitive eco-system of the area.

Place, publisher, year, edition, pages
2011. Vol. 398, no 1-2, 44-64 p.
National Category
Geophysical Engineering Water Engineering
URN: urn:nbn:se:kth:diva-12023DOI: 10.1016/j.jhydrol.2010.12.009ISI: 000287267600005ScopusID: 2-s2.0-78951473738OAI: diva2:294424
QC 20110307 Ändrad från submitted till published 20110307Available from: 2010-02-17 Created: 2010-02-17 Last updated: 2011-03-07Bibliographically approved
In thesis
1. Modelling Hydrological and Hydrodynamic Processes in Lake Tana Basin, Ethiopia
Open this publication in new window or tab >>Modelling Hydrological and Hydrodynamic Processes in Lake Tana Basin, Ethiopia
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area. The growing high demands in utilizing the high potentials of water resource of the Lake to its maximal limit, pictures a disturbing future for the Lake. The objective of this study was to assess the influence of topography, soil, land use and climatic varia-bility on the hydrological and hydrodynamic processes of the Lake Tana Basin. The physically based SWAT model was successfully calibrated and validated for flow and sediment yield. Se-quential uncertainty fitting (SUFI-2), parameter solution (ParaSol) and generalized likelihood un-certainty estimation (GLUE) calibration and uncertainty analysis methods were compared and used for the set-up of the SWAT model. There is a good agreement between the measured and simulated flows and sediment yields. SWAT and GIS based decision support system that uses multi-criteria evaluation (MCE) was used to identify the most vulnerable areas to soil erosion in the basin. The results indicated that 12 to 30.5% of the watershed is high erosion potential. Pro-jected changes in precipitation and temperature in the basin for two seasons were analyzed using outputs from fifteen global climate models (GCMs). A historical-modification procedure was used to downscale large scale outputs from GCM models to watershed-scale climate data. The results showed significant changes in streamflow and other hydrological parameters in the period between 2045-2100. SWAT was combined with a three dimensional hydrodynamic model, GEMSS to investigate the flow structure, stratification, the flushing time, lake water balance and finally the Lake‘s water level response to planned water removal. We have found an alarming and dramatic fall of the water levels in Lake Tana as response to the planned water withdrawal. The combination of the two models can be used as a decision support tools to better understand and manage land and water resources in watersheds and waterbodies. The study showed that the Lake Tana Basin may experience a negative change in water balance in the forthcoming decades due to climate change as well as over abstraction of water resources.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. viii, 66 p.
Trita-LWR. PHD, ISSN 1650-8602 ; 1057
Lake Tana, Climate Change, SWAT, Hydrological Modeling, Hydrodynamic, GEMSS, MCE, Streamflow, Sediment yield
National Category
Oceanography, Hydrology, Water Resources Water Engineering
urn:nbn:se:kth:diva-12024 (URN)978-91-7415-558-7 (ISBN)
Public defence
2010-03-05, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
QC 20100720Available from: 2010-02-17 Created: 2010-02-17 Last updated: 2011-05-24Bibliographically approved

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