After this charter takes effect local improvements commenced prior thereto shall be completed and assessments may be levied and securities issued for the financing thereof as prescribed by the law (or charter provision) applicable thereto. The council may prepare and adopt a comprehensive ordinance prescribing the procedure which shall be followed thereafter in making all local improvements and levying assessments therefor. Such ordinance shall supercede all other provisions of the law on the same subject and may be amended only by unanimous vote of the council. In the absence of such ordinance all local improvements may be made and assessments levied therefor as prescribed by an applicable law.