Investigating the effect of porous permeable bed in the stilling basin on the hydraulic jump characteristics

An important application of the hydraulic jump has been to control channel scour downstream from high-velocity conveyance systems such as chutes and spillways by dissipating a large portion of the kinetic energy in a hydraulic jump stilling basin. Hydraulic jump stilling basin generally is made of smooth and impermeable Concrete which has environmental, cost and construction problems. It is becoming more common to use hydraulic jump stilling basins in natural rip-rap lined or bound rock channels. These basins are inherently rougher and permeable compared to traditional basins. At present the influence of channel permeability on the hydraulic jump characteristics such as sequent depth and jump length is uncertain. In this research hydraulic jump characteristics in a stilling basin with porous permeable bed as an alternative to concrete basins is studied. To conduct the experiments a laboratory flume of 6 meters long and 80 centimeters wide with glass walls, equipped with a head tank up to 3 meters high was designed and built at Ferdowsi University’s hydraulic laboratory. The flow rate required for the experiments was supplied by a centrifuge pump with a capacity of 100 liters per second. Two slice gates were used at the beginning and at the end of the flume to develop super-critical flow, adjust the downstream depth and fix the jump position. Three different types of well-granulated gravel in the range of 9.8 to 38 millimeters with different lengths and thicknesses were used to create the permeable bed. The experiments were carried out for five different Froude numbers within the range of 5.3 to 7.4. For each experiment initial depth, sequent depth and jump length were measured and compared with the results of smooth impermeable bed. In general the various purpose of this study have been achieved. Primarily, these were to evaluate the potential effects of stilling basin bottom permeability on the hydraulic jump characteristics of sequent depth ratio and jump length. The experiments showed that parameters such as mean grain size of porous bed, length and thickness of the bed and Froude number of upstream flow affect the hydraulic jump dimensions and the energy dissipation caused by the jump. Permeability of the bed reduces the hydraulic jump dimensions so that the sequent depth ratio is reduced by an average of 19 percent compared to smooth bed and also the jump length is reduced by about 31 percent.