Great Lakes Rip Current Activity

Graduated Circle Map - The first map represents a view of all Great Lakes using a graduated circle mapping technique which depicts concentration clusters of occurrences, with numbers proportionate to circle size (bjelland et al, 2013, pg 23), the more incidents = larger circle. Both Rescues (red) and Fatalities (yellow) are shown for this map, the dispersion of larger circles gravitate to city/town locations favoring higher coastal population densities, suggesting population numbers as the largest contributing factor to Great Lakes incidents.

Isopleth Map - The second map presents an isopleth map, which shows how features or occurrences differ in quantity spatially (bjelland et al, 2013, pg 23). This map illustrates the dispersion of fatality-only incidents around the coasts, showing higher concentration centers (yellow) for areas of highest fatality activity in the last 10 years of recorded accounts. These areas of concentration seem to also gravitate towards towns/cities possibly agreeing with the factors of population.

Dangerous nearshore currents are common in the Great Lakes partly defining the Great Lakes as “inland seas” Each summer there’s and average of 12 fatalities and 23 rescues due to dangerous currents on the Great Lakes. These dangerous currents are known as rip currents, a relatively strong, narrow current flowing outward from the beach through the surf zone and presenting a hazard to swimmers. The Great Lakes areas receive millions of visitors per year at State Parks alone in the summer. Specifically Lake Michigan in the summer attracts the largest amount of incidents due to on shore winds and waves (western MI coast), favorable water and air temperatures, and more free time for activities at beaches/parks, not to mention large population sizes. More than 70% of all rip current fatalities are associated with onshore winds, specifically, a rip current fatality is most likely when a surface high pressure system creates long term onshore winds (Genisi V.A and Ashley, W.S 2010). This can be a contributing factor for incident concentration on the East coast of Lake Michigan, as this coast line attracts more onshore winds during the summer months.

The National Weather Service in Northern Indiana maintains the Great Lakes Current Incident Database (GLCID), a 17 year archive of current-related incidents(the quality of the fatality reporting database available for researchers is also assessed before including into database). Several studies on near shore swimming hazards worked with 591 reliable current-related incidents to learn about where and when dangerous currents form. The focus of research improves National Weather Service beach forecasts and possible beach hazards descriptions. The data was accessed through Arc GIS online search engine and compiled to custom layers to create both graduated circle and isopleth maps. The graphs presented use this data in order to diagnose concentrations of dangerous nearshore current activity and where humans are perceived to be most vulnerable to dangerous nearshore currents. This data can help focus on victim demographics and explain fluctuating frequency of victims annually. Visualizing this data in spatial graphs can help improve beach safety outreach and education efforts in specific areas.

There are several dangerous locations capable of causing swimmers to struggle on the Great Lakes, and any location is capable of creating hazardous currents. Most of these dangerous current incidents have taken place on Lake Michigan due to its eastern shores positioned in main development centers, and it is a popular tourist destination, this can be seen on both maps as the largest graduated circles and concentrations of isopleth measures surround southeastern Lake Michigan. Although Lake Superior has on average larger sea state conditions, fewer people surround the Superior lake shore in comparison to Lake Michigan, thus showing fewer incidents in a more dangerous lake. Something to consider in maps, is that the incidents collected in the GLCID are current related, which means reason for death or near death experience may be only partially caused by rip currents, but definitely involved. (ex. factors of drug influence, swimming ability, conditions of day are not considered in data)

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