Section 31.18 - Obligations of owners of bridges and dams(1) The grantee of any permit, the owner of any dam constructed before permits were required by law, and the owner of any bridge at the city of Portage or at any point above that city, over the Wisconsin River, shall maintain and operate all such dams, slides, chutes, piers, booms, guide booms, weirs, tunnels, races, flumes, sluices, pits, fishways, locks, boat hoists, marine railways and all other equipment required by the department for the protection of public rights in such waters, and for the preservation of life, health and property, in good repair and condition, and shall not willfully, or otherwise, injure, remove or destroy the same, or any part thereof, unless the department shall have approved such removal or destruction in writing. In the event of emergency the department shall have power, pending investigation and hearing, to order the repair of any dam without notice and hearing.(2) The owner of any such dam shall open such slide or chute for the passage of any craft or material lawfully navigating the stream, whenever requested so to do by the person in charge of such navigation, without charge or toll therefor. But such owner shall be under no obligation to otherwise aid passage through the slide or chute.(3) Except when emergency shall require the same for the protection of life, health or property, no substantial alteration or addition shall be made to any dam heretofore or hereafter constructed without obtaining an order therefor from the department, which order may be issued only after an investigation and upon a finding that the proposed alterations or additions will not impair the sufficiency of such dam or any existing public rights in such waters.(4) The department shall in the interest of public rights in navigable waters, or to promote safety and protect life, health and property, require the grantee of any permit, under this chapter, or of any permit or authorization heretofore provided for by legislative enactment, prior to flowing any lands by the construction of a dam thereunder, to remove from such lands all or any portion of the standing and fallen timber and all or any portion of the brush. Provided that in cases where the application for permit proposes construction of a dam for water reservoir or water storage purposes, and not for the purpose of operating a hydroelectric generating plant, the nature, extent and time for such removal shall be determined prior to the granting of a permit, except that subsequent to the granting of a permit the department may make such modification in the removal requirements as may be in the public interest and which will not materially alter the economics of the project; and in making such original determination or any modification thereof the economic need for the project shall be considered.