2014-03-03_REPORT - M1988112

• Permit No: M1988112
• IBM Index Class Name: REPORT
• Doc Date: 3/3/2014
• Doc Name: Detailed Inspection Report
• From: DRMS
• To: McClure & Eggleston, LLC / Edwin J. Lobato, Esq.
• Email Name: WHE
• Email Name: GRM
• Media Type: D
• Archive: No

4.2
Initial Assessment of Adequacy of Facility for Flood Events .. .............................26
4.2.1 Flood Events Evaluated ................................................ .............................26
4.2.2 South Diversion Ditch ................................................... .............................26
4.2.3 Drop Structure Inlet Acceleration Chute ...................... .............................27
4.2.4 Flip Bucket and Plunge Basin ....................................... .............................27
4.3
Results of New Evaluations Performed as part of Detailed Dam Safety
Evaluation Process .................................................................... .............................27
4.3.1 Hydrologic Check Analysis .......................................... .............................27
4.3.2 HEC -RAS Modeling of South Diversion Ditch and Drop Structure .........
29
5.0 POTENTIAL FAILURE MODES ........................................................ .............................34
5.1
General Description Dam and Loading Conditions .................. .............................34
5.1.1 Dam Data (elevations in NAVD 88) ............................. .............................34
5.1.2 Hydrology Data ............................................................. .............................35
5.1.3 Seismic Data ................................................................. .............................36
5.2
PFMA Process Summary .......................................................... .............................36
5.3
Potential Failure Modes ............................................................ .............................41
5.3.1 PFM -1 Overtopping of Drop Structure at Left Dam Abutment
during Extreme Flood Event leading to Scour Erosion and Breach
ofDam .......................................................................... .............................41
5.3.2 PFM -2 Internal Erosion or Piping of Embankment Materials
Exiting on Downstream Face of the Dam near the Under -drain
PipeOutlets ................................................................... .............................45
5.4
Potential Failure Modes Ruled Out (Category IV) ................... .............................48
5.5
Summary of Risk Estimates ...................................................... .............................51
6.0 CONCLUSIONS AND RECOMMENDATIONS ............................... .............................53
6.1
Overall Evaluation .................................................................... .............................53
6.2
Recommended Maintenance, Repairs, and Upgrades to Address current
conditions.................................................................................. .............................54
6.2.1 Maintenance and Improvements to South Diversion Ditch .......................54
6.2.2 Drainage Outlet Cleanout ............................................. .............................57
6.2.3 Erosion Protection of Right Groin Area ....................... .............................58
San Luis Project
Miller Geotechnical Consultants
Tailing Dam Data
Report iii February 2014