Experimental study of scouring downstream of weirs

Studying the scour downstream of spillways allows to project structures that help in the protection of the discharge area. Is important know and predicting the magnitude of the scour. For this, is usual to do physical models that reproduce the movement of particles on the movable bed.

In the last 50 years, various investigations have arisen about the scouring downstream of spillways. In this case, the deflector buckets are structures that launch the jet away from the spillway to avoid damage to the foundation by softening, in addition to ensuring greater dissipation of the jet due to the inclusion of air. As a result of the investigations, empirical equations have been developed to estimate the maximum depth of scour, however, these equations were proposed according to specific cases and their applicability must be verified.

In this research work were analyzed 32 empirical equations using the experimental information obtained from the physical model of the Santa María Dam. This model was built at the Mexican Institute of Water Technology (IMTA) with a 1:96 scale without distortion. The dam has two spillways designed for a Tr = 10,000 years, the Chute 1 has a discharge of 10,078.33 m³/s and the Chute 2 of 6,882.76 m³ /s. The mobile bottom consisted of a gravel of deposit ¾”and ¼” of diameter deposited without compacting in the unloading area. For the test we used three different flows in each spillway, with discharge duration of 1 hour, estimated time in which the equilibrium scour hole is reached; for each flow a different geometry and depth of scour was obtained.

The experimental results showed a defined well geometry with accumulation of material in the periphery. A good estimate of the depth was obtained in those formulas that involve more variables in the calculation, which allowed us to propose an equation that describes the scour behavior in the model.