Reservoir drawdown lowers the water level to allow inspection, maintenance, or construction work on the dam structure, spillway, or outlet works. The process exposes workers to unstable sediments, confined spaces in valve chambers, and the risk of uncontrolled water release. Drawdown must be carefully controlled and monitored throughout. This talk covers the hazards and the safe working procedures during reservoir drawdown operations.
Key Hazards
Uncontrolled water release through valve or sluice gate failure during drawdown
Unstable sediments and soft ground exposed as the water level falls
Confined space hazards in valve chambers, culverts, and outlet tunnels
Slope instability on the reservoir embankment caused by rapid drawdown
Control Measures
Follow the drawdown plan prepared by the reservoir engineer specifying the rate and sequence.
Monitor embankment stability throughout drawdown using survey points and visual inspection.
Restrict access to exposed reservoir bed areas until ground conditions have been assessed as safe.
Treat all valve chambers, culverts, and outlet tunnels as confined spaces requiring entry permits.
Maintain communication with the dam control room throughout all drawdown and work activities.
Position rescue equipment at the work location including lifebuoys if residual water remains.
Brief all operatives on the emergency procedure for uncontrolled water release during drawdown.
Monitor for gas accumulation in enclosed structures exposed as the water level drops.
Record all drawdown levels, monitoring readings, and observations in the project log daily.
Emergency / Rescue
If uncontrolled water release occurs, evacuate all personnel from the downstream area immediately. Raise the alarm and contact the reservoir engineer and emergency services. Do not attempt to close valves without authorisation.
Remember
Follow the drawdown plan exactly as specified by the reservoir engineer at all times
Monitor embankment stability throughout the drawdown using survey points and visual checks
Treat all valve chambers, culverts, and outlet tunnels as confined spaces requiring permits
Restrict access to exposed reservoir bed areas until ground conditions are assessed as safe
Know the emergency procedure for uncontrolled water release before work begins
Applicable Legislation: Reservoirs Act 1975 · CDM Regulations 2015 · Confined Spaces Regulations 1997 · Health and Safety at Work etc. Act 1974