Procedure: Dam Safety Surveillance

Purpose. This procedure describes the routine surveillance inspections, instrument readings and reporting required for the Mitta Ranges dam under the dam safety program.

1.Scope

This procedure applies to the weekly walkover inspection, the monthly instrument readings and the post-event inspections after heavy rain, earthquake or unusual readings at the Mitta Ranges concrete gravity dam and its spillway, outlet works and downstream area.

2.Step 1: Prepare

The operator must review the previous inspection report and readings, check the storage level and recent rainfall, and take the inspection checklist, camera, torch, probe and the piezometer reading equipment. Two people must attend any inspection of the gallery or the downstream toe.

3.Step 2: Walkover inspection

The operator must walk the crest, both abutments, the downstream face, the toe and the spillway, looking for new seepage, wet areas, cracking, movement, displaced blocks, vegetation growth and blocked drains. Each observation must be photographed and located against the survey markers.

• Crest and parapet: cracking, settlement, displacement
• Downstream face and toe: seepage, wet areas, staining
• Abutments: seepage, erosion, movement
• Spillway and outlet works: obstruction, damage, gate operation
• Gallery drains: flow rate, clarity, blockage

4.Step 3: Instrument readings

The operator must read every piezometer, seepage weir and survey point on the schedule, must compare each reading to the last reading and the alert level, and must report any reading above the alert level to the Renewables Manager before leaving site.

5.Step 4: Record and report

Observations and readings must be entered in the Operations Log on the day. The monthly surveillance report must be prepared using the technical report template and sent to the dam safety engineer. Any condition above the alert level must be recorded as a hazard in the HSE Incident Register.

6.Step 5: Post-event inspection

After rainfall above the trigger, an earthquake felt at site or any unusual reading, a full walkover and instrument reading must be completed within 24 hours and reported the same day.