Wave efficacy is a measure of the effectiveness of waves at mobilising sediment.
Low efficacy means there will be no sediment transport; high efficacy means sediment transport is likely.
Details on how it is calculated are available here.
The data come from the MetOcean wave model at node ltvwr (Lyttelton virtual waverider buoy), at 172.86°E 43.5685°S, as shown on the map.
This webpage is updated weekly.