Author(s): Ryoichi Matsumoto; Isao Nihei; Kousuke Tabata
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Keywords: Local scouring; Mini-Model; Froude’s similarity law; Roughness coefficient; Spur dyke
Abstract: Ordinary micro-models are very small models of rivers, and the use should be limited to verification, education and communication since rivers are modeled into water channels not wider than 4 cm, the distortion of vertical scale sometimes reaches 20, Froude number is exaggerated up to 3. 7 times, and the water level of the actual river is not reproduced on the model. The differences between an actual field and its micro-model should be attributable to the uncertainty of monitored data of the site and large relaxation of the law of similarity. Micro-models are calibrated so as to reproduce the flow regime and riverbed forms of actual rivers by adjusting the longitudinal slope of the channel so that the Froude number of the model agrees with that of the river. Thus, micro-models prepared in this method are difficult to reproduce hydraulic phenomena since the longitudinal slopes of the channels are different from those of actual rivers, disabling Froude’s similarity law to be applied. To solve the problem, a model was prepared in which channel widths and water depths were at least 5 cm and the Froude number of the model was matched with that of the site by adjusting roughness and not longitudinal slope. The model almost fully reproduced the water level profiles and the locations of sand bars in the Tone River. Knowledge of using micro-models is reported. Since CTI Engineering Company has prepared flow-reproducing models of rivers for display and education, which are called Mini-Models, before the development of micro-models, the term is also used in this paper to denote the models.
Year: 2007