Any such person, firm or corporation may exercise the power of eminent domain, for the purpose of acquiring such lands as it may be necessary or convenient to flood or otherwise utilize in order to improve navigation as provided in this article, such lands to include as well as all the area submerged a strip of land 50 feet in width bordering upon the margins of the slack water pool or pools as the same may be defined at the highest stage of the river at any time after the completion of the improvements herein provided for; and the right hereby conferred to exercise such power of eminent domain is cumulative. No person, firm or corporation shall acquire the rights granted by this article, unless the dam or system of dams, and lock or system of locks, to be constructed by such person, firm or corporation are so planned as, when constructed, will by the operation thereof improve the navigation of the river in which the dam or system of dams, lock or system of locks, are to be built, and will develop the full power of such river over the length of same upon which navigation is to be improved, as provided in this article. Such person, firm or corporation shall commence work upon said dam or system of dams, lock or system of locks, within five years from the date of securing the consent of the federal government to do so, and shall complete the same within the time prescribed by the United States government. No foreign corporation shall acquire the rights granted under this article until it has complied with the laws of Alabama with reference to foreign corporations.