Faculty of Engineering, Civil Engineering

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Browsing Faculty of Engineering, Civil Engineering by Subject "ABCD HYDROLOGICAL MODEL"

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    Assessment and regionalization of hydrological model parameters in neighboring Pho Chhu and Mo Chhu basins in Bhutan :
    (2019) Choden, P; Rajapakse, RLHL
    In the cold regions because of harsh climates, there exists no or an inadequate number of monitoring stations. It is indeed a challenge to generate the hydrographs of ungauged basins with scanty information from limited gauged basins. As a result, it has important implications for existing water resources systems as well as for future water resources planning and management since high elevation mountains are all important sources of water to the billions in the lowlands in these climatic regions. The Mo Chhu and Po Chhu catchments in Bhutan are used in this study to assess the regionalization of hydrological model parameters from one catchment to the other neighbouring catchment having similar characteristics using ABCD hydrological model incorporating snowmelt parameter. The Mo Chhu catchment was considered as the gauged catchment and its hydrological parameters were simulated through model calibration and validation, and then transferred to the neighbouring Pho Chhu catchment. For the corresponding watersheds, precipitation, streamflow and temperature daily data were collected for the 11 years from 2006~2017 from the National Centre for Hydrology and Meteorology in Bhutan and checked by visual comparison, single and double mass curve analysis and annual water balance to ensure data reliability, consistency and to identify suitable data periods for model calibration and validation. For the model performance evaluation, Root Mean Square Error (RMSE), Pearson correlation coefficient (r) and Coefficient of determination (R2) were used as the objective functions. The Pearson correlation values for calibration and validation of Mo Chhu basin are 0.84 and 0.88, respectively. When the same model parameters were transferred to Pho Chhu basin, Pearson value for validation was found to be 0.82, indicating good inter-basin parameter transferability and effective model regionalization. Comparing and analyzing the results of ABCD model with and without snow parameter "m", it can be concluded that the model with snow parameter performs better due to proper simulation of the major contribution to basin flow from snowmelt. Approximately, over 52% of the basin flows can be attributed to snowmelt during summer and spring and the incorporation of snow processes in the monthly ABCD model has thus significantly improved model performance in snow-covered areas in Bhutan
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    Precipitation trends over the three climatic zones of Mahaweli basin and evaluation of climate change impacts on streamflow variability
    (2019) Yadav DK; Rajapakse RLHL
    Climate change is expected to inflict severe consequences on the hydrological cycle and water resources of a catchment. With this backdrop, it is crucial to have better insight into the functioning of current water resources systems along with future water resources planning and management due to the fact that amidst growing populations and ever-increasing resource use, competition among users, and more recently, widespread ecosystem degradation and climate change impacts have exacerbated the already grave situation. In order to assess this impact, a semi-distributed monthly water balance model was adopted and developed to simulate and predict the hydrological processes incorporating several predicted future climatic scenarios. This study focuses on analyzing the long-term precipitation trends in the three distinct climatic zones and climate change impacts on streamflow variability in Mahaweli basin which extends over wet, dry and intermediate climatological zones. Monthly precipitation data for a span of 30 years from 1988-2018 have been used for trend analysis using Mann-Kendall and 15-year monthly rainfall and streamflow data set is used for calibration and validation of “abcd” hydrological model to evaluate the climate change impacts on streamflow for future water resources management at three selected sub-watersheds in each zone of the basin. The changes in precipitation and temperature during the study period were correlated differently with observed changes in streamflow. The rainfall trends in the intermediate and dry zone parts of the basin were identified to be positive while the trend in the wet zone part was found to be decreasing, however, not statistically significant in both cases. Streamflow precipitation elasticity was evaluated for sensitivity check. The “abcd” hydrologic model can be recommended to use for streamflow simulations and water resources investigations in monthly temporal resolution for the watersheds which are having similar characteristics with parameter values in the ranges of a (0.961-0.998), b (0-250), c (0.001-0.999) and d (0.01-0.999). The abcd model has proven to be a valuable tool not only for assessing the hydrologic characteristics of diverse watersheds but also for evaluating the hydrologic consequences of climate change in selected basins which may also be helpful in both pre-disaster risk management and post-disaster rehabilitation.