N.D. Cent. Code § 40-24-18
All special assessments and taxes levied and other revenues pledged under the provisions of this title to pay the cost of an improvement shall constitute a fund for the payment of such cost, including all principal of and interest on warrants and other obligations issued by the municipality to finance the improvement, and shall be diverted to no other purpose. The city auditor shall hold all moneys received for any such fund as a special fund to be applied to payment for the improvement. Each such fund shall be designated by the name and number of the improvement district in or for which said special assessments, taxes, and revenues are collected. When all principal and interest on warrants and other obligations of the fund have been fully paid, all moneys remaining in a fund may be transferred into the general fund of the municipality.
N.D.C.C. § 40-24-18