(a)   Where natural drainage channels intersect any street right-of-way, it shall be the responsibility of the subdivider to have satisfactory bridges and/or culverts constructed. Where culverts are required, minimum requirements shall be observed as follows:
      (1)   All culverts shall extend through the right-of-way. The cover over the culvert and its capacity shall be determined by the developer’s professional engineer and approved by the City Engineer. The minimum diameter of the culvert pipe shall be twelve (12) inches. Depending on the existing drainage conditions, head walls may be required. Where driveway culverts are wholly or partially in the street right-of-way, they shall have a minimum length of twenty (20) feet and minimum diameter of twelve (12) inches. The driveway culverts shall be laid so as to maintain the flow lines of the ditch or gutter.