scope:

Purpose and Scope of Model Investieation

One of the major project concerns was the potential retention of floating debris at the upstream face of the tunnels. Blockage at the portal face resulting from the accumulation of debris would raise the headwater in the approach area and thereby decrease the available freeboard on the diversion structure. The study was initiated to evaluate the adequacy of the proposed tunnel entrance to pass debris and to maintain the design freeboard, and/or to develop modifications that would not only improve the hydrodynamic conditions, but also mitigate potential debris problems at the upstream portal.

Both a physical and a mathematical model were used to evaluate the The mathematical model was used proposed entrance approach. in conjunction with the physical model to screen alternatives, while the physical model investigated these alternatives in detail for their ability to pass debris by simultaneously reproducing the SPF hydrograph while an expected volume of scaled debris was introduced. The main objectives of the study were to evaluate and improve the hydrodynamic design of the entrance approach, and to select a design configuration, especially regarding the tunnel piers and portal face, that minimizes head losses associated with debris.