 | 03/25/1999 | Landslide | | Penstock buried in a mudslide | Mudslide | |
 | 01/01/1942 | Deterioration | Wood | Leak in woodstave pipe due to deterioration | Deterioration/Seepage/Piping (Periodic Inspection) | |
 | 04/01/1995 | Penstock Discharge | Steel | Penstock buckling due to vacuum in the pipe | Penstock Buckled | |
 | 11/08/1996 | Inflow Flood - Hydrologic Event | | Erosion at the penstock | Flood | |
 | 04/17/1998 | | Riveted Steel | Riveted steel penstock ruptured | A section of the original riveted steel of penstock No. 3 ruptured. | Penstock rupture caused erosion of fill and flooding of the powerhouse. This, in turn, caused a powerhouse shutdown, release of oil into the river and knocking out a local distribution line. |
 | 07/01/1997 | Lightning | Steel | Penstock buckling and penstock rupture | Penstock Failure | |
 | 06/14/1996 | Broken Turbine Needle Tip | | Penstock rupture | Penstock failure; faulty needle valve caused water hammer which caused metal fatigue and failure | Unit 3 offline for four weeks; some erosion and minor damage to powerhouse |
 | 03/12/2009 | | Concrete | Loss of support due to a void under the penstock | Void under penstock | |
 | 01/21/2010 | | | Roof of the box conduit collapsed | Failure along conduit | Conduit roof collapsed and filled with mud. |