All lands in the State of Minnesota described in and withdrawn from sale by the proclamations of the President of the United States for the reason that said lands would be required for or subject to flowage in the construction of dams, reservoirs, and other works proposed to be erected for the improvement of the navigation of the Mississippi River and certain of its tributaries, are declared to be, and to have been at all times prior to February 27, 1901, subject to the provisions of sections 934 to 939 of this title as fully, effectually, and to the same extent as though said lands had not been described in said proclamations, or withdrawn from sale thereby, but had remained with the body of public lands subject to private entry and sale: Provided, however, That any and all parts of said lands acquired by any railroad company under said sections shall at all times be subject to the right of flowage which at any time may become necessary in the construction or maintenance of dams, reservoirs, or other works which may be constructed or erected by or under the authority of the United States for the improvement of the navigation of the Mississippi River and its tributaries: Provided further, That the railroad companies availing themselves of this section shall, in addition to filing the maps required by law on February 27, 1901, to be filed, also file maps of definite location with elevation of rail of their lines of railroad over said water-reserve lands in the office of the Secretary of the Army; and no location shall be permitted which takes for right of way or stations or interferes with submergence of lands needed for the use of the reservoir system, existing on February 27, 1901, or in the construction of dams or other works, or any proposed or probable extension of the same, or which will obstruct or increase the cost of the present or prospective reservoir system: Provided further, That the plan for the location and construction of any such railway, or any part thereof, shall be first submitted to the Secretary of the Army and approved by him and by the Chief of Engineers of the United States Army.