Control of Hydraulic Jump in Trapezoidal Stilling Basin by Basin Blocks

Over the decades, extensive data have been gathered for the design of stilling basins but most of these
data are restricted to jumps in rectangular channels. However, geometries different from the
rectangular such as trapezoidal cross sections are also considered for stilling basins. On the other
hand, unsteadiness of jump and increase in jump length are unwanted changes in the characteristics of
such basins. In this study, the effect of basin blocks on the jump characteristics in a stilling basin of
trapezoidal cross section is investigated. Five different block sizes corresponding to Froude numbers
of 4, 5.5, 7, 8 and 9 for three different block locations of 0.8d2, d2 and 1.2 d2 from the jump toe were
studied (d2 is the sequent depth). The results show that the installation of a set of basin blocks may
improve the jump condition and decrease the unsafe transverse waves and vortices. It was also found
that the basin blocks cause a significant reduction in the sequent depth ratio and jump length, and an
increase of the energy loss in the jump relative to those observed in the jumps occurring in a
trapezoidal stilling basin without blocks.