ONAWAY, Mich. — Tom and Diane Peterman tried to buy flood insurance when they moved to their retirement home on the shores of Black Lake 14 years ago but were told it wasn’t available. John Solum was told he wasn’t in a flood zone when his family bought a 1940s-era cabin there. Then came this spring’s historic and devastating floods across northern Michigan — in some areas, for the first time anyone can remember — swamping homes, pushing dams to the brink of failure and washing out roadways.