Operators of Oroville Dam – the nation’s highest – shut down its main spillway Monday so that debris could be cleared and the dam’s hydroelectric turbines could be restarted. It was merely the latest of many operational adjustments state and federal officials have made this year to cope with an unprecedented series of rain and snow storms that swept through the state, putting maximum pressure on its complex system of dams, reservoirs, river channels, canals, bypasses, weirs and other man-made water-control devices. By necessity, they operated on the fly as conditions changed, often suddenly, with Oroville being the centerpiece.