Design and Assessment of a Dentate Ski-jump

Condor Cliff Project is located on the Santa Cruz River, in Argentina. Its spillway is designed for a maximum flood of 4163 m³/s. Geological and geomorphological constraints led to the selection of a ski-jump structure for the dissipation of the energy in spite of the local weak rock formation. One of the evaluated alternatives includes a ski-jump with curved trapezoidal deflectors to reduce the impact energy over the rocky bed. The design of deflectors was tailor made based on some examples found in the literature and compared with published guidelines based on the analysis of several structures. Then a pre-excavated plunge pool was designed. A physical model 1:50 scale was built and a program of test was made with fixed and mixed (partially fixed and partially mobile) bed. During the fixed bed stage throw depth, velocities, mean and fluctuating pressures in the pool were measured. Maximum throw distance was consistent with the estimates made with empirical formulae but minimum distance was quite shorter. Considering the difficulties of the selection of an adequate granular material that could represent both the bed rock and the alluvial upper sediments, tests were conducted with two different grain size materials: a fine sand and a coarser one. Extension and depth of the scour holes were measured for several discharges. Bed material size did not show important influence in the scour depth, but it did in the extension of the scour hole. Also there was a small difference between the scour depths for the different discharges.