Any person owning and using a water power for the purpose of propelling machinery shall have the right to acquire, maintain, and utilize the fall below such power for the purpose of improving the same, in like manner and to the same extent as provided in this chapter for the erection or heightening of milldams. After such right has been acquired, the fall shall be considered part and parcel of said water power or privilege, and the deepening or excavating of the stream, tail, or raceway, as herein contemplated, shall in no way affect any rights relating to such water power acquired by the owner thereof prior to such change.