At Alexandria the worst of their troubles awaited them, threatening to make all that had yet been done vain. The river, which ordinarily remains high till June, had not only failed to reach its usual height but had so fallen that they could not pass the rapids. General W.T. Sherman, who had lived at Alexandria before the war, thought twelve feet necessary before going up, a depth usually found from March to June. At the very least seven were needed by the gunboats to go down, and on the 30th of April of this year there were actually only three feet four inches. The danger was the greatest that had yet befallen the fleet, and seemingly hopeless. A year before, in the Yazoo bayous, the position had been most critical, but there the peril came from the hand of man and was met and repelled by other men. Here Nature herself had turned against them, forsaking her usual course to do them harm. Ten gunboats and two tugs were thus imprisoned in a country soon to pass into the enemy's hands by the retreat of the army. Desperate as the case seemed, relief came. Lieutenant-Colonel Joseph Bailey, of the Fourth Wisconsin Volunteers, was at this time acting as Chief Engineer of the Nineteenth Army Corps, General Franklin's. He was a man who had had much experience on the watercourses of the Northwestern country, and had learned to use dams to overcome obstacles arising from shallow water in variable streams. The year before he had applied this knowledge to free two transport steamers, which had been taken when Port Hudson fell, from their confinement in Thompson's Creek, where the falling water had left them sunk in the sand. As the army fell back, and during its stay at Grand Ecore, he had heard rumors about the scant water at the Falls, and the thought had taken hold of his mind that he might now build a dam on a greater scale and to a more vital purpose than ever before.