All sidewalk improvements in public property, whether performed by the owner of the abutting property or by the city, shall be performed under the supervision and inspection of the city engineer and in accordance with the plans and specifications prepared by his office and approved by the city council.  No permanent sidewalk improvements shall be performed until the bed for the same shall have been graded so that when completed such sidewalk will be at the location and grade established by the city engineer.  (Ord. S-30306, 1976).