Neb. Rev. Stat. § 14-105

The city council of a city of the metropolitan class may require any and all lots or pieces of ground within the city to be drained, filled, or graded, and upon the failure of the owners of such lots or pieces of ground to comply with such requirements, after thirty days' notice in writing, the city council may cause the lots or pieces of ground to be drained, filled, or graded, and the cost and expense of such work shall be levied upon the property so filled, drained, or graded and shall be equalized, assessed, and collected as a special assessment.