Every person who shall throw or put any ballast, earth, ashes, stones, or other thing into the harbour or dock shall for every such offence be liable to a penalty not exceeding F1level 1 on the standard scale: Provided always, that nothing in this Act contained shall prejudice or prevent any person from adopting any measures which but for the passing of this Act he would be lawfully entitled to adopt for recovering any land which shall at any time have been lost to him, or severed from land belonging to him, by reason of the overflowing or washing of any navigable river, or for protecting his land from future loss or damage by the overflowing or washing of such navigable river.