PLT31 - Poster-Lightning Talks: When Hydraulics Meet Habitats: A Unique Emergency Action Plan for the Phoenix Zoo Dams

Abstract Description: Home to more than 3,000 animals and four “Monkey Islands,” the Phoenix Zoo relies on five dams that create unique habitats and visitor-friendly exhibits for over one million annual guests. These five dams are hydraulically connected to three additional dams located upstream in the City of Phoenix’s Papago Park. Originally constructed in the 1930s as fish hatcheries, this system of eight dams provides a combined reservoir capacity of nearly 75 acre-feet. Although once registered with the Arizona Department of Water Resources, regulatory jurisdiction was rescinded in 1974 for each dam individually due to updated minimum size requirements for dams. However, structural aspects of dams have changed and ability to operate each dam as an individual facility was lost due to damaged outlet works. For the past 50+ years, the eight dams have functioned as a single interconnected system, with minimal freeboard and constant water movement over modified spillways. Historically, the dams operated without a formal Emergency Action Plan, leaving significant gaps in response capability during storm events.

To address these vulnerabilities, the City of Phoenix partnered with Black & Veatch to conduct comprehensive formal inspections, perform hydrologic and hydraulic modeling, and a facilitate risk assessment workshop. Using 2D HEC-RAS simulations, the team evaluated inundation scenarios for the 100-year, ½ PMF, and PMF events which revealed overtopping risks with several pedestrian areas and zoo habitats identified as high-danger zones. To evaluate the increased risk from a potential cascading failure of the interconnected system, progressive dam breach modeling was performed.

This effort helped establish a unique Emergency Action Plan that considers the multiple stakeholders for the interconnected system, the high-use public setting, the current (lack of) outlet works functionality, and the zoo animals living within and downstream of the reservoirs. Lessons learned offer guidance for floodplain managers and dam owners seeking to strengthen emergency preparedness for aging infrastructure in public spaces, while balancing safety and regulatory compliance with unique recreational goals.