Effects of continuous triangular roughnesses on the hydraulic jump characteristics in horizontal Stilling basin

Ahydraulic jump is a surprising phenomenon in the science of hydraulics which dissipates hydrokinetic energy. Hydraulic structures like stilling basin frequently use this important characteristic of the hydraulic jump in order to dissipate energy in downstream of spillways, gates and torrents. Since dimensions of these structures are directly dependent on characteristics of the hydraulic jump therefore to make them economical many wide surveys have been conducted on characteristics of hydraulic jump and how to control them or minimize their dimensions. For example in the recent years it has been suggested that continuous roughness of the Stilling basin could be effective in reducing jump dimensions. The present study has been performed by considering this assumption and it is tried to determine level and type of this effect using laboratory experiments. To achieve this aim various experiments were performed for input numbers ranging 5-12.5 in flume that is 35 cm wide. In these experiments triangular roughnesses and their combination were installed and tested in the floor of flume in such a way that upper surface of roughnesses and spillway crest are on the same level and some parameters like flow rate, roller length, first depth, secondary depth, jump length, water surface profile were measured. Analysis of data showed that roughnesses decrease jump length to moderate size of 57% and provide about 20% decrease in secondary depth of jump than classic type. This decrease can be caused by increase in flow turbulency level between roughnesses that causes approximately 13-fold increase in shear stress.