Some Observations on the Undular Jump

For the surge in an open channel in which the outflow is suddenly cut off, the water under the surge profile is brought to rest relative to the bed. The hydraulic jump resulting from applying simple relative motion therefore corresponds to a situation in which channel friction is minimized effectively. For the undular type of phenomenon, it should therefore be possible to overcome inherent measurement difficulties and obtain a good correlation of test data with analysis. By reference to the properties of the solitary wave, the maximum (first-crest) depth and the final (parallel-flow) depth of the undular jump are related easily. A simple hydraulic explanation is provided for the characteristic undulations and for the development of the breaking crest roller. Experimental data are presented that give confirmation both for undular conditions and for circumstances where the roller begins to develop.