Flooding occurs when the channel capacity is exceeded and flows overtop onto the floodplain. When the channel capacity of the rivers downstream of the Snowy Scheme is exceeded, our releases are limited to what the flows would have been had the Scheme not existed. This is known as the calculated ‘Pre-SMA’ flow.
This means that during a flood we do not release any more water than what would have naturally flowed down the river. As such, we do not in any way exacerbate flooding downstream of the Scheme.
The Scheme can provide limited storage capacity for high inflows, which in turn can provide some short term assistance. However, water cannot be diverted back to Eucumbene from lower catchments such as Khancoban, Geehi or Talbingo. These are small storages and once they are full, the water must flow downhill.
To pass the water safely and effectively through the Scheme, Snowy Hydro aims to utilise our series of power stations where possible, rather than operating other spillways at a dam. This means we must generate and will often have to bid that power into the NEM at very low prices (even possibly at $0) to ensure that our plant is dispatched to pass flood flows.
During flood operations, we liaise closely with the BoM, local SES and councils to ensure that the most up to date information is available for landholders and flood response activities.