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The accuracy of flood routing is an important subject for research in hydrology and hydraulics. Accurate information of the flood peak attenuation and the duration of the high water levels obtained by channel routing are of most importance in flood forecasting operations and flood protection works (Subramanya, 2008). This study implements two hydrological methods for channel routing, the basic Muskingum and the constant coefficient Muskingum-Cunge methods on the River Brosna, Co. Offaly in Ireland. Previous researches have reported the simplicity and applicability of these methods on most natural streams within certain limits. These limitations are encountered in the River Brosna where the available outflow data included a significant degree of error which makes it difficult to use for comparison and modelling purposes. Moreover, other factors influenced the implementation and the accuracy of these methods, in particular the backwater effects due to a weir located nearly four kilometres upstream the selected reach and the gradient of the channel which was very small (0.00047) to dampen the error in the routing procedure. This error is found to be greater when using a minimum time increment in the routing calculation. The results of this study showed that the hydrological methods failed to simulate the outflow hydrograph in the selected reach. Determining the models parameters was not possible by using the basic Muskingum method, whereas, the constant coefficient Muskingum-Cunge method calibrated some negative values for the attenuation, which contradicted the diffusivity of the flood wave and confirmed the significant effect of the weir located downstream the river. The conclusion is that an alternative method is needed to account for the factors that these methods neglect.
Elbashir, S.: Flood Routing in Natural Channels Using Muskingum Methods. Dissertation submitted in partial fulfilment of the requirements for the DIT’s Master of Engineering Computation. 2011.