Rain fell on San Diego Monday. It wasn’t a lot of rain – an Accuweather forecast called for “a brief morning shower or two” with an anticipated rainfall of 0.01 inches. But it was enough to prompt a beach closure at the Tijuana Slough, just south of Imperial Beach. That section of the beach is closed whenever the Tijuana River is flowing. Cross-border sewage spills have been an issue in South County for decades.