"Floodway area" means that portion of the floodplain which must be preserved in order to maintain the flood carrying capacity of the base flood. Floodway areas regulated by this title include:
A. Federal floodway areas as delineated by FEMA;
B. Administrative floodways for major watercourses with a base flood peak discharge of two thousand cfs or more as determined through engineering analyses using ADWR standards or other applicable engineering method.
1. Administrative floodway areas include the primary channel of the watercourse and any adjacent land areas that are necessary to convey the base flood without cumulatively increasing the water-surface elevation more than one-foot above the base flood elevation under normal flow conditions;
2. In addition, when geologic features confine the flow of a watercourse the following additional areas shall be considered floodway areas:
a. Areas necessary to convey the base flood without increasing the water surface elevation more than one-tenth of a foot above the base flood elevation under normal flow conditions,
b. Areas of frequent inundation as defined by the four percent annual chance (twenty-five-year) flood,
c. Areas with excessive flow depths and velocities (dv 2 ), as defined in Section 16.26.050.G, and
d. Active flow paths and channels based on the presence of unconsolidated alluvium related to fluvial processes and the potential for the flow paths to meander over time.
3. A watercourse can be considered confined when the ratio of the wetted top-widths of the floodplains associated with the base flood and the twenty-five-year flood is one and one-quarter or less and the height of the geologic features are at least one and one-half times the hydraulic depth of the base flood. The watercourse shall be considered confined through all reaches where this criteria is present both upstream and downstream of the subject area.
C. The primary channel of all regulatory minor watercourses with a base flood peak discharge of less than two thousand cfs.
(Ord. 2010-FC5 § 1 (part), 2010; Ord. 2005 FC-2 § 2 (part), 2005; Ord. 1999 FC-1 § 1 (part), 1999; Ord. 1998 FC-1 Section 1, 1998; Ord. 1988 FC-2 Art. 4 (part), 1988)