Loud cracks of thunder and driving rain woke up RJ Harber and his wife, Annie, early on July 4 as they vacationed in a cabin along the Guadalupe River. But it should have been a warning siren that alerted them to the catastrophic Hill Country flood. A public siren should have roused the Dallas couple long before water began pouring into their cabin. Long before the flood claimed the lives of their two daughters and Harber’s parents, who were in a nearby cabin. A new state law passed in the wake of the disaster requires flood warning sirens to be installed in counties prone to flooding and with histories of related deaths or with dense residential or recreational use. Senate Bill 3, authored by Sen. Paul Bettencourt, R-Houston, also creates a grant program to help cities and counties defray the costs of installation and maintenance. The sirens must be installed by next summer.For Harber, that is too late. By the time the loud storm awakened him and his wife at about 3:30 a.m., water already covered the floor of their cabin and was rising fast. They barely escaped through a window and s