Hydraulic Verification of the Existing Spillway of Gatun Lake System

The project of the expansion of the Panama Canal through the construction of a third set of locks for larger ships demand the increase of the reservoir water levels of Gatun Lake. As a consequence of that, the discharge capacity of the existing spillway (in service since 1914) under these new boundary conditions must be analyzed, determining in this way the necessary discharge capacity for an auxiliary spillway. In fact, the original spillway was designed for a flow rate close to 4,500 m³/s, while the hydrological and operational conditions of the system analyzed in the context of the expansion project of the Panama Canal, indicate the need to ensure a discharge of 13,000 m³/s for the flood of 10,000 years of recurrence. For this reason, the National Institute of Water from Argentina carried out the construction and exploitation of a 1:40 length scale physical model of the existing Gatun Lake spillway, in which the discharge capacity and the energy dissipation conditions were evaluated for the increased levels of the lake. The hydraulic study of the existing spillway showed that it is capable of discharging up to 6,070 m³/s, without implying risks to the control structure or to the dissipation structure. In fact, with the maximum levels required in the context of the expansion of the Panama Canal, the discharge capacity exceeds practically 40% the design condition originally established, without cavitation risks in chute blocks arranged downstream of the spillway, or other conditions that could be critical from the point of view of the safety of the structures. In this article, the most important aspects of the hydraulic evaluation of the existing spillway are highlighted, which is particularly important in relation to the safety of the works and the operating conditions of the complex, which are of fundamental importance in the integral framework of the system management as well as in the design of complementary works to be executed for the control of extraordinary floods.