In the San Diego County, an area consisting of approximately 180 acres lying west and south of Palomar Airport as shown on Map 155, which has been placed on file with the Secretary of State on April 22, 1980, shall be excluded from the coastal zone after the City Engineer of the City of Carlsbad approves and the commission certifies a drainage plan for the area, pursuant to the commission’s interim permit authority, which plan the city shall implement and enforce.