State water resources officials and federal regulators caused the failure of the Oroville Dam spillway in February by ignoring long-established guidelines and neglecting their duty to manage risks and detect flaws, a scathing report by a Berkeley engineering expert concluded Thursday. Robert Bea, a professor emeritus of engineering at UC Berkeley, said in his analysis of the causes of the spillway failure at the nation’s tallest dam that the “progressive deterioration” of the chute could have been prevented if proper procedures had been followed.