It shall be the duty of the said councils (of Philadelphia) after the requisite surveys and soundings shall have been made, to fix the lines, beyond which no wharf or pier shall be constructed, and to keep the navigable waters within said city forever open and free from obstructions. The city councils shall authorize the construction of wharves upon a plan and scale to meet the demands of commerce, keep the same, and the avenues leading thereto open and free from obstructions.
53 P.S. § 16851