Any corporation of the character described in this chapter, in order to secure additional water for the irrigation of the lands of its stockholders to supplement their natural flow rights, by the construction of dams or other works and the storing or impounding of winter flow, or flood, or other waters, may contract with the United States bureau of reclamation, public works administration, reconstruction finance corporation, resettlement administration or any other federal agency or instrumentality, or with any person, agency or corporation, for the construction of necessary works, or the loan of moneys for such construction, and may provide in such contract that said corporation will annually levy an assessment against its stockholders sufficient in amount to pay all obligations created by such contract, as the same mature, and will collect the same as tolls, and may provide that no part of such supplementary water shall be delivered to any stockholder until his annual toll and assessment levied with respect to such supplemental water has been paid. Any corporation so contracting shall not deliver such supplemental water to any stockholder or user except upon payment in full of such annual toll and assessment; provided, however, that no such contract may be entered into by any corporation unless and until its board of directors shall have been authorized so to do by resolution of its stockholders adopted at a regular or special meeting thereof. Nothing herein contained shall be construed to in any way affect or impair any rights such corporation now has under the law to levy and collect assessments for corporate purposes.