Almost a dozen New England towns were rendered virtual islands Monday as floodwaters from the remnants of Hurricane Irene reshaped parts of Vermont and upstate New York, turning placid rivers into raging torrents and some streets into treacherous mud bogs. Hundreds of roads remained closed, dozens of bridges were gone and entire towns were cut off from assistance in the worst flooding some areas have seen in a century. A day earlier, Irene dumped up to 11 inches on parts of Vermont and more than 13 inches on some areas of New York — a deluge that quickly overwhelmed waterways,...