Each year, the shorelines of the Great Lakes slip away, taking beaches, stairways and other infrastructure with them. Faced with difficult decisions about how to respond, local officials aren’t sure what to do, in part because the erosion has multiple causes. Extreme changes in water levels, fierce storms, decreasing ice coverage and infrastructure that interferes with the natural coastal cycles are all playing their parts in sculpting drastic and unwelcome changes to the shoreline — an...