Analytical models of confluences: A survey and models' assessment | Pregled i ocena analitičkih modela ušća
2011
Đorđević, D., Građevinski fakultet, Beograd (Serbia)
Assumptions upon which development of 1D models of free-surface flow rest are not valid at open-channel junctions. Thus, the 1D flow equations cannot be used for calculation of upstream flow depths, or water levels in a dendritic channel network. To facilitate design of river confluences and/or networks of drainage canals, about ten analytical models have been proposed since 1940- ties. Development of these models was either based on the theoretical considerations, or on the combination of the theoretical considerations and laboratory experiments. The models are valid only for the confluences with equal channel-bed elevations (concordant beds confluences), the majority being derived for the subcritical flow. In this paper three models are examined in detail, two of which are based on the assumption of equal upstream flow depths (the models of Gurram et al. and Hsu et al.), whereas the third one allows different upstream flow depths and diffrerent channel widths of the combining channels (the model of Shabayek et al.). The paper indicates some inconsistency in derivation of the equaldepths models and assesses the influence of the inconsistent terms through comparison with the existing experimental data. It is found that, in the steady flow conditions, taking into account the junction angle instead of the flow angle at the tributary entrance to the confluence results in negligible difference in the prediction of upstream flow depth. The future research should reveal how the flow angle delta varies with the junction angle a and the discharge ratio of the tributary and main river flows – d=f (a, q).
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