The Secretary of the Army may cause proceedings to be instituted, in the name of the United States, in any court having jurisdiction of such proceedings, for the acquirement by condemnation of any land, right-of-way, or material needed to enable him to maintain, operate, or prosecute works for the improvement of rivers and harbors for which provision has been made by law; such proceedings to be prosecuted in accordance with the laws relating to suits for the condemnation of property of the States wherein the proceedings may be instituted: Provided, however, That when the owner of such land, right-of-way, or material shall fix a price for the same, which in the opinion of the Secretary of the Army, shall be reasonable, he may purchase the same at such price without further delay: And provided further, That the Secretary of the Army is authorized to accept donations of lands or materials required for the maintenance or prosecution of such works.