A. For minor natural washes with a base flood peak discharge of less than two thousand cfs, the following building setbacks shall be required:
1. A distance of fifty feet for watercourses with base flood peak discharges of less than two thousand cfs, but more than five hundred cfs;
2. A distance of twenty-five feet for watercourses with base flood peak discharges of five hundred cfs to one hundred cfs;
3. Alternative safe limits for erosion setbacks approved in writing by the chief engineer based on an acceptable engineering study prepared and sealed by an Arizona registered civil engineer. However, at no time shall a setback of less than twenty-five feet from the top of channel bank be permitted in order to provide for reasonable access and stability of nearby structure foundations, except as allowed pursuant to subsection B of this section.
B. Along minor natural washes where unusual conditions exist, building setbacks shall be established on a case-by-case basis by the chief engineer, using ADWR standards or other applicable engineering methods or an acceptable engineering study is prepared and sealed by an Arizona registered civil engineer and approved by the chief engineer. When determining building setback requirements, the chief engineer shall consider danger to life and property due to existing flood heights or velocities and historical channel meandering. Unusual conditions include but are not limited to historical meandering of the watercourse, large excavation pits, poorly defined or poorly consolidated banks, natural channel armoring, proximity to stabilized structures such as bridges or rock outcrops, and changes in the direction, amount, and velocity of flow of the waters in the watercourse.
C. For constructed channels, channel banks are required to be stabilized to prevent erosion along minor watercourses with base flood peak discharges of less than two thousand cfs, but greater than five hundred cfs. Stabilization is required unless a waiver to the requirement is granted by the chief engineer based on an engineering study prepared and sealed by an Arizona registered civil engineer which demonstrates an appropriate building setback for an earthen channel, based on soil and natural flow conditions. For constructed channels with a base flood peak discharge of less than five hundred cfs, channel stabilization may be required based on engineering analysis and assessment of soil conditions and flow velocities.
(Ord. 2010-FC5 § 1 (part), 2010; Ord. 2005 FC-2 § 2 (part), 2005; Ord. 1999-FC-1 §§ 1 (part) 1999; Ord. 1988-FC2 Art. 12 (B), 1988)