Where the issuance of bonds has been authorized as provided by Section 59-9-57, and so long as any of such bonds shall be outstanding the board of supervisors of such county, and the governing authorities of the municipality wherein the port of entry is located in such county, are authorized to levy and collect an ad valorem tax not to exceed two mills, for the joint development, construction, maintenance, repair, or operation of harbor and port facilities authorized by this chapter, which levy shall be collected by the tax collector of such county and the tax collector of the municipality, and shall be deposited into a fund to be designated "the county port fund" and into "the municipal port fund", respectively, and which sums shall be disbursed on the requisition of the county port authority, or the port commission of the municipality, as the case may be, and which funds may also be pledged and used for the payment of bonds issued hereunder.
All taxes collected for the payment of principal of and interest on bonds issued hereunder, shall be credited to a special fund in the county and municipal treasuries of such county and municipality and to be known and designated as the "port bonds interest and sinking fund", and all sums credited to said fund shall be used to pay such bonds as they mature and the interest thereon as it accrues and for no other purpose. It shall be the mandatory duty of such board of supervisors and governing authorities of the municipality to transfer funds from said port funds to the port bonds interest and sinking fund in amounts sufficient to pay maturing principal and accruing interest on bonds issued hereunder. To the extent that funds are thus made available for the payment of such bonds and the interest thereon, the special tax levy herein provided for may be correspondingly reduced.