Long Term Trends in Lake Michigan Wave Climate

2019-06-10T18:02:50Z (GMT) by Nicholas R Olsen
Waves are a primary factor in beach health, sediment transport, safety, internal nutrient loading, and coastal erosion, the latter of which has increased along Lake Michigan's western coastline since 2014. While high water levels are undoubtedly the primary cause of this erosion, the recent losses may also be indicative of changes in the lake's wind-driven waves. This study seeks to examine long-term trends in the magnitude and direction of Lake Michigan waves, including extreme waves and storm events using buoy measurements (National Data Buoy Center Buoys 45002 and 45007) and the United States Army Corps of Engineers Wave Information Study (USACE WIS) wave hindcast.

Tests show significant long-term decreases in annual mean wave height in the lake's southern basin (up to -1.5mm/yr). When wave-approach direction was removed by testing directional bins for trends independently, an increase in the extent of the affected coast and rate of the shrinking waves was found (up to -4mm/yr). A previously unseen increasing trend in wave size in the northern basin (up to 2mm/yr) was also revealed.

Data from the WIS model indicated that storm duration and peak wave height in the southern basin has decreased at an averaged rate of -0.085hr/yr and -5mm/yr, respectively, from 1979 to 2017. An analysis of the extreme value distribution's shape in the southern basin found a similar pattern in the WIS hindcast model, with the probability of observing a wave larger than 5 meters decreasing by about -0.0125yr-1. In the northern basin, the probability of observing a wave of the same size increased at a rate of 0.0075yr-1.

The results for trends in the annual means revealed the importance of removing temporal- and spatial-within-series dependencies, in wave-height data. The strong dependence of lake waves on approach direction, as compared to ocean waves, may result from the relatively large differences in fetch length in the enclosed body of water. Without removal or isolation of these dependencies trends may be lost. Additionally, removal of the seasonal component in lake water level and mean wave-height series revealed that there was no significant correlation between these series.