Predicting the flow velocity at the toe of a labyrinth stepped spillway

Abstract EN

The velocity at the toe of a spillway is a major variable when designing a stilling basin.

Reducing this velocity leads to reduce the size of the basin as well as the required appurtenances needed for dissipating the surplus kinetic energy of the flow.

If the spillway chute is able to dissipate more kinetic energy, then the resulting flow velocity at the toe of the spillway will be reduced.

Typically, a stepped spillway is able to dissipate more kinetic energy than that of a smooth surface.

In the present study, the typical uniform shape of the steps has been modified to a labyrinth shape.

It is logical to expect that the labyrinth shape will lead to dissipate more kinetic energy.

This impression comes through creating more regions of circulation and turbulence along the lateral sides of each step in addition to those that occur towards the streamwise.

This action can also reduce the jet velocities near the surfaces, thus minimizing cavitation.

At the same time, the increase in circulation regions will maximize the opportunity for air entrainment, which also helps to dissipate more kinetic energy.

The undertaken physical models consisted of three labyrinths of stepped spillways with magnification ratios (width of the labyrinth to width of conventional step) WL/W are 1.1, 1.2, and 1.3 as well as testing a conventional stepped spillway (WL/W=1).

Two empirical forms of the coefficient are proposed, one for labyrinth shape stepped spillway denoted KL and another for conventional stepped spillway denoted KS.

Once the value of the coefficient is known, the actual flow velocity at the toe of a stepped spillway can easily be computed without having to resort to measurements on-site.

It is concluded that the spillway chute coefficient is directly proportional to the labyrinth ratio and its value decreases as this ratio increases.