Study of Hydraulic Jump Lengths on Inclined Channel Beds

A hydraulic jump is generally used to dissipate kinetic energy of flow to protect man-made structures such as spillways, drop structures, and outlet works. It serves as a perfect location for chemical mixing right before the jump. Therefore, to determine the location of a hydraulic jump is essential in designing related hydraulic structures. For instance, a chemical purification point should be constructed at the toe of hydraulic jump to have the best effects. This study investigated lengths of hydraulic jump on inclined channel beds based on model tests, where channel bed slopes varied from 1° to 5°. Based on experiment results, the following conclusions are made: (1) The ratio between the hydraulic jump length, L j , and its corresponding water depth before the jump, Y 1 , has a linear relation with the Froude number of the flow before the jump, F 1 . On the other hand, the relations of L j /Y 2 versus F 1 is not linear, where Y 2 is the water depth after the jump. (2) A general linear relation exists between the ratio of water depths, Y 2 /Y 1 , and Froude number, F 1 . (3) Graphs of jump height verses corresponding Froude number F 1 , which can be used for designing the height of a stilling basin, were develped, where the jump height was defined as the difference of water depths before and after the jump.