Since the tallest dam in the United States threatened California with catastrophe last winter, state officials have responded with policies to stanch the flow not just of water but of information. The latest example is the Legislature’s vote to exempt a whole class of crucial information about dams from the state’s public-records law. A provision in the recesses of a lengthy budget-related bill requested by the governor and passed by both houses last week could prevent public and press access to plans for responding to dam emergencies.