Hydraulics of Flow in Stilling Basins with Vertical Drops Using Grating and Netting Dissipators

Abrupt change in the channel bed elevation in the hydraulic systems tends to create a severe flow
kinematic energy. This excess energy results in different unfavorable phenomena including
tremendous forces on hydraulic structures, scouring and degrading the channel bed which results in
the destruction of the downstream structures. These phenomena would intensify while a number of
vertical drops constructed consecutively along the channel. The main goal of the present study is to
explore methods for increasing the energy dissipation efficiency of vertical drops by installing new
types of dissipators, namely Grating and Netting drop-type dissipators based on the
analytical/experimental modeling. These types of dissipators could be established over the drop crest
looking like a bottom racks. In addition, the features of pressure distribution along the pool and
reaction force over the pool floor were investigated. By assembling the above mentioned structures
over the stilling basins of vertical drops, the jet flow direction is changed and the degree of turbulence
increases and as a result there is an increase in the head loss. The enhanced efficiency of the proposed
structures was quantified based on the experimental data obtained in this study. Both analytical and
experimental investigations were performed in the present study. Based on the model experimentation
data, empirical equations were presented to estimate the force acting on the basin floor. The proposed
semi-analytical model compared well with the experimental results. However, there are small
discrepancies between the analytical and experimental results of netting dissipators. This is partly due
to the flow high turbulence and complicated phenomena existed in the stilling basins of netting
dissipators. Also, the air bubble entrainment is another source of the difference between the two sets of
results.