The district, hereinafter designated as combining FW (floodway) district, is established to be combined with other districts in certain areas which are uniquely susceptible to fast-moving waters associated with periodic inundation and which are necessary to carry and discharge such waters, as determined by engineering analysis of hydrological, meteorological, topographical, and other data. The regulations are intended to restrict or prohibit uses which are dangerous to health, safety, or property in times of flood or which cause increase in flood heights or velocities. The regulations are also intended to help preserve natural riparian areas and to prevent uses encroaching within the floodway, which usually require costly public improvements for their protection. The regulations of any district with which a FW district is combined shall remain the same, except as to matters specified in Sections 17.30.020 through this section, which shall apply in addition to those contained in the basic underlying zoning district. (Prior gen. code § 8-44.3)