In order to effectuate the policy declared in sections 701a and 701b of this title, and to correlate the program for the improvement of rivers and other waterways by the Department of the Army with the program for the improvement of watersheds by the Department of Agriculture, works of improvement for measures of run-off and water-flow retardation and soil-erosion prevention on the watersheds of waterways, for which works of improvement for the benefit of navigation and the control of destructive floodwaters and other provisions have been adopted and authorized to be prosecuted under the direction of the Secretary of the Army and supervision of the Chief of Engineers, are authorized to be prosecuted by the Department of Agriculture under the direction of the Secretary of Agriculture and in accordance with plans approved by him. The Secretary of Agriculture is authorized in his discretion to undertake such emergency measures for run-off retardation and soil-eros