Coconino County presents new local floodplain maps for Tuscon, says adoption would reflect public-safety risk

Coconino County Flood Control District staff on Nov. 8 presented new hydrology and floodplain mapping for the Tuscon watershed and said they plan to ask the district board to adopt a regulatory floodplain that would include the new local mapping at a Dec. 9 board session.

Lucinda, a representative of the Coconino County Flood Control District, said the district paid “a couple $100,000” for updated science and that the goal is to "reflect the risk accurately" rather than to "prevent or enhance development." She said the district would issue public notice in advance of the Dec. 9 board meeting.

The new mapping, prepared by JE Fuller Hydrology, layers the existing FEMA Zone A (an approximate federal special flood hazard area) with a larger locally defined floodplain. Ian Sharp, a civil engineer with JE Fuller Hydrology, said the firm modeled discharges across the 59-square-mile watershed, calibrated the model to the August 2023 storm and produced depth and inundation results used to derive the local flood limits. "The gauge by the treatment plant" recorded about "1,400 cubic feet per second," Sharp said, "enough water to fill an Olympic swimming pool in a minute." He contrasted that observed value with the modeled 100-year…