Neb. Rev. Stat. § 16-672.10

All the special assessments provided for in section 16-672.08 , shall, when levied and collected be placed in a sinking fund for the purpose of paying the cost of the improvements as provided in sections 16-672.01 to 16-672.11 with allowable interest thereon, and shall be solely and strictly applied to such purpose to the extent required; but any excess thereof may be by the mayor and city council, after fully discharging the purposes for which levied, transferred to such other fund or funds as the mayor and city council may deem advisable.