What is a large dam?

The Act defines a large dam as a dam that retains three or more metres depth and holds 20,000 cubic metres or more of water or other fluid. 

For the purposes of defining whether a dam meets the large dam threshold, the volume and depth shall be based on a reservoir level based on one of the follow:

• Where there is current hydrological information available for a particular dam and the spillway capacity meets the NZSOLD Dam Safety Guidelines based on the potential impact classification of the dam – the reservoir level is calculated using the corresponding reservoir levels of the dams design flood level.
• Where there is a free overflow flood spillway (minimum 3.0metres width) and the design hydrology for the dam is not known or current (typical of rural dams) - the reservoir level is measured at the spillway crest level plus 300mmm of spillway operation.

Where there is only an outlet pipe (and no overflow flood spillway, or the overflow flood spillway is less that 3.0meters wide) – the reservoir level is taken at the dam crest.