Integrated Community and Ecosystem Flood Control Solution

Weekes Wash drains a portion of the Superstition Mountains east of metropolitan Phoenix. The usually dry watercourse cuts through desert foliage and is often defined by flash floods. When heavy storms hit, it all quickly comes out in the wash – floodwater, sediment, debris – with destructive force. In harm’s way is Apache Junction, a growing suburb of approximately 40,000 residents.

To protect lives and property from storms, the city is implementing a new multi-use detention facility along Weekes Wash. Designed by the team of Black & Veatch and Dibble with strong community engagement, the facility will reduce the number of structures flooded in Apache Junction during 100-year storm events by more than 99%. The project’s nature-based features additionally serve to preserve the wash’s environmental functionality and promote recharge of the area’s groundwater resources.

Black & Veatch further helped Apache Junction realize the project by proactively securing approximately half the funding for the $90 million legacy project via $44 million in competitive grants from the Federal Emergency Management Agency (FEMA) – the most it has ever awarded in Arizona.

Delivering on a Dream

With flood mitigation as its top public works priority, especially with climate change impacts increasing the intensity and frequency of area storms, Apache Junction along with Pinal County turned to Black & Veatch and Dibble for a feasible long-term solution. Beginning with the question “What if,” the team conducted a comprehensive alternatives analysis and community outreach program. The consensus solution: build a facility able to detain 100-year floods while allowing flows from smaller storms to pass through. Specifically, the Weekes Wash Regional Detention Facility is designed to:

• Extend more than 12,000 feet in line with Weekes Wash as it enters Apache Junction

• Pass stormwater exceeding the 100-year event threshold through a piano-key weir whose labyrinth-like style provides high discharge capacity and overflow efficiency

• Impound flood waters behind a 34-foot-high earthen embankment, providing storage for a 100-year storm event (1,015-acre-feet of storage)

• Preserve the wash’s hydrological and ecological functions via the low-flow outlet

• Augment the community’s groundwater resources via permitted rainwater harvesting and groundwater recharge

• Provide recreational and educational amenities

• The project will enhance Apache Junction’s safety and livability by reducing the risk to lives and mitigating damage to properties and city services while enhancing the community’s water resilience. That includes reducing the city’s reliance on water from the Colorado River.

Its integrated approach qualified the project for funding from FEMA’s Flood Mitigation Assistance Program. The grant program supports community-scale flood mitigation projects as part of the federal government’s investment in efforts to enhance resilience to climate change and extreme weather events. To win the funding, Black & Veatch developed applications for three nationally competitive grants. Backed by strong support from the community and elected officials plus a favorable cost-to-benefit ratio, the applications secured critical funding that will allow Apache Junction to make the project a reality.