A former top aide to then-Interior Secretary Ken Salazar is at the center of a controversy over a suspended federal water-conservation program. Rebecca R. Wodder, a senior advisor to the Interior Secretary on rivers, declined to appear before the House Natural Resources Committee Wednesday afternoon. As the hearing began, a white placard bearing Wodder’s name in black type was placed at the eastern end of a mahogany table and in front of an empty chair. “Unfortunately, the Department will be unable to send a witness to the hearing,” committee spokeswoman Mallory Micetich said an Interior Department official told the committee....