The main spillway at Oroville Dam is riddled with design flaws and so badly damaged that an independent panel of experts hired by the state has concluded it’s probably impossible to repair the structure completely before the next rainy season begins in November. The panel of four engineering consultants, in a recent memo to the state Department of Water Resources, said it believes the concrete spillway can be made functional enough to release water from Lake Oroville during the next rainy season.