The department shall construct the project when, in its judgment, appropriations, contributions, and revenues from all sources which are available or which will be made or become available upon, during, after, or before construction of the project, including contracts which the department may negotiate and enter into with responsible persons, public or private agencies, the United States, and state agencies for the sale or disposal of water, water flow, the use of water, water storage, electric power, or other resources and facilities to be made available by the project, are or will be available from such sources in such amounts and at such times as will afford funds sufficient to pay and discharge as and when the same become due and payable all cost and expense incurred prior to construction, and all cost and expense of construction, operation, and maintenance of the project, together with necessary repairs and replacements thereto, including funds sufficient to meet and pay, as and when they become due and payable, all bonds, with interest accruing thereon, within a period of not to exceed 70 years after the beginning of the construction of the project.