Hydraulic Engineering

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Browsing Hydraulic Engineering by Author "Abereham, Ashenafi"

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    Watershed modeling and uncertainty analysis on Gumara watershed
    (Addis Ababa University, 2013-02) Abereham, Ashenafi; Hailu, Habtamu(PhD)
    The objective of this thesis work is to model stream flow at the outlet of the gauged Gumara watershed and analyze the associated uncertainty that can affects the accuracy in estimation of the stream flow. Having good certainty on simulated flow helps planners and policy makers to implement appropriate water resource management as Gumara catchment is getting threatened as a result of increasing number of farmers using the river for different purpose, especially for irrigation. The Soil and Water Assessment Tool (SWAT) model was applied to estimate stream flow of the Gumara catchment and associated uncertainty with the simulated outputs. The SWAT model was calibrated for the period of 1995 to 2003 and validated for the period of 2004-2009 based on ten parameters identified during sensitivity analysis. The uncertainty analysis was done by using first SUFI-2 and to check parameter uncertainty using SWAT-CUP, which are both packages of SWAT CUP, were used to establish the uncertainty bounds of the model. The calibration and validation of the model was found satisfactory as performance rating criteria value of coefficient of correlation (R2) and Nash-Sutcliffe simulation efficiency (ENS) is found to be 0.63 and 0.56 for calibration and 0.71and 0.71 for validation ,respectively. In the same order from the model uncertainties analysis the percentage of the simulated data within the uncertainty bound is only 31% for calibration and 27% for validation, which shows that there is uncertainty in the process. Then using SWAT CUP parameter uncertainty was tested and found with ENS value of 0.68 for calibration and 0.82 for validation. And this shows that the overall associated uncertainty come from either conceptual or input or a combination of them but not from parameter identification. Even though the predicted amount of flow of 1317.33MCM is almost equivalent to the latest study, the uncertainty might come due to either neglected abstractions or poor quality of input data. Therefore, this simulated amount should not be used for any water resource development works unless the correction of these cause of uncertainties are reduced as uncertainty in estimation of simulated flow will lead to wrong water resource management decision.