Reduced level (aka relative level) in surveying means the height above or below a common assumed datum. A common assumed datum can be any nominated point.

Therefore, the reduced level is a way to compare heights.

In Australia, this point is called the "Australian Height Datum" (AHD) and is the relative height of a point in relation to the Australian mean sea level. You may see RL and AHD used interchangeably.

Typically, the RL is calculated and provided when a dam is surveyed.

The reduced level will only be shown if you upload your dam's survey. See how to upload your dam survey here