Flooding that has hit parts of the Midwest hard has nearly paralyzed an American Indian reservation in southern South Dakota, swamping roads, trapping people in homes and cutting off water supplies to thousands. The situation on the sprawling Pine Ridge Reservation was improving Tuesday, but two weeks of severe flooding could put the Oglala Sioux tribe in recovery mode for months, if not longer, and deal a serious blow to its economy, President Julian Bear Runner said. “This is going to have a devastating effect on us, I feel,” he said.