Whenever in the construction or maintenance of such intracoastal waterway from Winyah Bay, South Carolina, to the State boundary line in the Savannah River, and its tributaries, or the Ashley River or Shipyard River projects, lands theretofore submerged shall be raised above the water by the deposit of excavated material, the United States of America shall have a perpetual right and easement to enter upon, excavate, cut away and remove any and all of such land, including submerged land, composing a part of the prism required for the channels, anchorage areas and turning basin, and their slopes and berms, as may be required at any time for construction and maintenance of such intracoastal waterway and any changes, modifications or extensions thereto and any tributaries thereof and of said Ashley River or Shipyard River projects and to maintain the portion so excavated and the channels, anchorage areas and turning basin thereby created, as a part of the navigable waters of the United States, and a further perpetual right and easement to enter upon, occupy and use any portion of such land, including submerged lands, composing a part of the spoil disposal area not so cut away and converted into public navigable waters, as aforesaid, for the deposit of dredged material and for such other purposes as may be useful in the construction, maintenance and improvement of said intracoastal waterway and any changes, modifications or extensions thereto and any tributaries thereof and of the Ashley River and Shipyard River projects, if within the limits of such rights of way or spoil disposal areas.