Developing a hydraulic jump length model on horizontal rough beds

INTRODUCTION A hydraulic jump causes kinetic energy dissipation downstream of the hydraulic structures, whenever the flow regime is changed from supercritical to subcritical flow. Stilling basins are considered for energy dissipation to reduce flow energy and create conditions for the occurrence of hydraulic jump in a specific position (Jain 2001). A significant parameter to determine hydraulic jump length is the bed roughness. The results of previous studies have shown that increasing the bed roughness may cause more energy dissipation and, accordingly, may change the hydraulic jump length. Peterka (1984), in the USBR laboratory, presented a graph (Lj/y2 vs Fr1) to determine hydraulic jump length based on numerous experiments in some channels. Ead and Rajarantnam (2002) investigated hydraulic jump over corrugated aluminium beds, and developed an empirical model. They found that hydraulic jump length over corrugated bed surfaces was approximately half the classical jump length. Izadjoo and Shafai-Bejestan (2007) studied hydraulic jump over four corrugated beds. Pagliara et al (2008) determined an equation for hydraulic jump length over both uniform and non-uniform rough beds in horizontal channels. In recent years, Chanson (2009), Alikhani et al (2010), Nasr Esfahani and Shafai Bajestan (2012), Imran and Akib (2013), and Riazi and Jafari (2014) have studied the effect of drop and barrier height, divergence angle of stilling basins and rough and corrugated bed on the characteristics of hydraulic jump and energy dissipation using dimensional analysis. Kumar and Lodhi (2016) investigated the effect of bed roughness heights on the characteristics of a hydraulic jump. They concluded that the bed roughness height has no considerable effect on hydraulic jump characteristics. Due to the impact of roughness on hydraulic jump, the main aim of this study was to develop a new model to estimate hydraulic jump lengths on horizontal rough beds using dimensional analysis and physical model tests.