Compensation to the individual Indian owners of the allotted lands within the area described in section 597a of this title shall be made from moneys appropriated for the construction of the Bull Lake Dam and Reservoir at the appraised value of the easements: Provided, That should any individual Indian not agree to accept the appraised value of the easement as it affects his land, the Secretary of the Interior be, and he is, authorized to acquire such easement by condemnation proceedings.