2014: 96% of dam Piezometers inoperative - only 3 left & "thought" to be functional - FERC directing DWR to develop plan to monitor internal water levels in dam (Phreatic surface)
I found one of the FERC references where FERC Part 12/DSRB Report states "…a plan for long-term monitoring of the phreatic surface within the dam embankment needs to be developed and implemented."
Essentially, DWR doesn't have working piezometers to give "health" status on this indicator of the internal water pressure levels from piezometers. Based on a piezometer reading, it indicates the water pressure & thus the inferred water level above the sensor. Only 3 sensors are "thought" ?!? to be working. Two are in the core and one is in the upstream zone 2 transition layer. No indication as to the centering of these sensors with respect to the abutments.
Grout Galleries have seepage measurement weirs at sectioned elevations - allows seepage measurement in left abutment - "porting" around dam should be detected by these weirs
Seems there are built in detection systems for abutment seepage at sectioned elevations. Measurement weirs are emplaced in drain channels in the Grout Gallery tunnels. These weirs provide a seepage "flow rate" measurement capability. Upthread I had surmised that seepage could be detected in the CtJ's of the Gallery concrete enclosure, however, they already designed in a "seepage" detection system. This weir detection system should have given DWR indicators if there was "porting" of water around the core of the dam through the hillside. Seepage would increase in these collection channels & weirs (fractured "weathered" rock would leak downslope to these weirs even if the porting was at/near high a crest elevation). This may lessen Scott Cahill's theory on the hillside "porting" around the dam.
What is interesting is that there was an "action item" given to DWR to analyze an unusual sediment collected in one of the weirs. The concern was that this sediment could have been from the core. The soil test results came back as having a high organic content. DWR's engineers "believed" that this sediment was from particulates accumulating in the tunnel and then in the drain weirs from the airflow from the Grout Gallery entrance Ventilation fans.
Note: the DWR's Board concerns over the 50 year old anchor tendons to the Radial Trunnion Gates of the main spillway (i.e. concerns of failure and/or loss of tensioning).
The Green Area, at the June and August combined dates of this inspection report noted that it was dry. The reservoir level was low at that time and precipitation was very low to zero during that time.
