The legislature shall never authorize the permanent obstruction of any of the navigable waters of this State; but may provide for the removal of such obstructions as now exist, whenever the public welfare demands; this section shall not prevent the construction, under proper authority, of draw-bridges for railroads, or other roads, nor the construction of “booms and chutes” for logs in such manner as not to prevent the safe passage of vessels, or logs, under regulations to be provided by law.