Wind wave characteristics at Lake Dunstan, South Island, New Zealand

Information on wave statistics, seasonal characteristics, and their distribution about lacustrine shorelines is virtually non-existent. The absence of such data limits the effective management of lake shores where issues of shoreline erosion are no less significant than on open ocean coasts. Results from instrumentally measured waves during seven storm events in 1995 are presented for the Clutha Arm of Lake Dunstan, South Island, New Zealand. The significant wave height ranged from 0.07 to 0.57 m with a mean of 0.28 m, whereas the maximum wave reached 1.05 m. Peak spectral wave periods ranged from 1.7 to 3.6 s with a mean of 2.46 s. The largest and most destructive waves are observed along the southern shore of the Clutha arm where fetch lengths are at their maximum. These waves exhibit the longest and widest range of periods and are generally the steepest waves, making them highly erosional at the shore. Correlations of waves with those predicted by NARFET, a deepwater wave-hindcasting computer model, revealed reasonable predictions of the wave height (R = 0.77-0.81), particularly for sites exposed to longer fetches, while the correlations with the wave period were lower (R = 0.56-0.69). Wave hindcasting indicates that the wave regime in the Clutha Arm is hi-directional, with most waves arriving from the north or south. Findings from Lake Dunstan have important implications for larger lakes located throughout New Zealand, where considerably larger waves can be expected to occur during severe storm events.