Tropical Storm Isaac threatens dam

Authorities in two states along the US Gulf Coast urged residents to seek shelter Thursday amid fears a dam could fail as Tropical Storm Isaac doused an already drenched region. Local officials in Mississippi called for precautionary evacuations of the area near Lake Tangipahoa after the Percy Quin Dam showed signs of heavy damage due to the storm, a statement said. In Louisiana, Tangipahoa Parish President Gordon Burgess called for a mandatory evacuation along the Tangipahoa River. Word of a possible breach came as forecasters warned of life-threatening floods, tornadoes and storm surges due to the slow-moving and ferocious mix of wind and rain, downgraded from a hurricane to a tropical storm Wednesday. At 1500 GMT, forecasters said Isaac was 165 miles (270 kilometers) northwest of New Orleans, where officials on Wednesday ordered the evacuation of some 3,000 people in coastal Plaquemines Parish, the area hardest hit by the storm. The storm has revived memories of Hurricane Katrina, which devastated the region exactly seven years ago, flooding New Orleans and killing at least 1,800 people in the broader Gulf Coast area.But this time around, new multi-billion-dollar post-Katrina flood defenses appeared to be holding but authorities still urged residents to stay indoors and three regional airports remained closed. In Slidell, a town to the north of Lake Pontchartrain where hundreds of homes and businesses are submerged, about 100 people were rescued with high-water trucks and boats after rain swelled the surrounding bayou. Dozens more remained trapped in their homes as waist-high flood waters made roads impassable. \"We weren\'t expecting it,\" police chief Randy Smith said. Latoya Sanders, 26, was ready to move back to California after riding out her first hurricane in Slidell. \"I\'m scared,\" she said after police carried her five children aged one to seven into a truck. Packing maximum sustained winds of 40 miles (65 kilometers per hour), the storm could dump up to 14 inches (35 centimeters) of rain over much of Louisiana, Mississippi, southwest Alabama and Arkansas through Friday. And some areas could see levels of up to 25 inches (64 centimeters), the National Hurricane Center said. \"Even though Isaac is no longer a hurricane, life-threatening hazards from storm surge, inland flooding and tornadoes are still occurring,\" they said. Isaac may wind up causing as much as $2.5 billion in damage in and around Louisiana and in the offshore oil sector in the Gulf of Mexico, according to early estimates from natural disaster modeler Eqecat. Meanwhile, the Mississippi River flowed backwards for nearly 24 hours due to pressure from Isaac, the US Geological Survey said. The waterway similarly went into reverse gear during Katrina, cresting at 13 feet (nearly four meters) about its previous level. More than 760,000 people made do without electricity in Louisiana, Mississippi, Arkansas and Texas, local power company Entergy said as the weather system snapped utility poles and downed transmission lines. Across Louisiana, more than 4,000 people were crammed into shelters. Dozens of nursing home residents, many in wheelchairs, were among those taken to higher ground by the National Guard in high-water trucks. US President Barack Obama, who has been regularly briefed on the storm, late Wednesday declared a \"major disaster\" exists in Louisiana and Mississippi, paving the way for more federal aid to local authorities. \"We\'ve got to make sure everybody\'s safe, then we\'ll start looking at what it\'ll take to recover,\" FEMA Administrator Craig Fugate said after surveying some of the damage on Wednesday.