It shall be the duty of said commission to mature and adopt such plan or plans, from examinations and surveys made prior to March 1, 1893, and from such additional examinations and surveys as it may deem necessary, as will improve the navigability of all the rivers comprising said systems, deepen their channels, and protect their banks. Such plan or plans shall be matured with a view of making the same effective as against the encroachment of and damage from debris resulting from mining operations, natural erosion, or other causes, with a view of restoring, as near as practicable and the necessities of commerce and navigation demand, the navigability of said rivers to the condition existing in 1860, and permitting mining by the hydraulic process, as the term is understood in said State, to be carried on, provided the same can be accomplished, without injury to the navigability of said rivers or the lands adjacent thereto.
[Mar. 1, 1893, ch. 183, § 4], [27 Stat. 507].)