Building Churchill Downs - The City of Ann Arbor Gets a Solution for Recurring Flooding

WASHTENAW COUNTY - The devastating storm that struck the Lansdowne/Churchill Downs area in Ann Arbor on March 15th, 2012, left a permanent mark on the community. Between I-94 and Scio Church Road, residents found themselves grappling with extreme flooding and overland flow, prompting urgent action from local authorities to address the pressing need for effective stormwater management measures.

In the aftermath of this catastrophic event, the City of Ann Arbor turned to the Washtenaw County Water Resources Commissioner (WCWRC) for assistance. Recognizing the significance of the situation, the Water Resources Commissioner’s office embarked on a collaborative effort to identify and implement a solution to mitigate the impacts of future storms.

In 2013, the WCWRC hired Spicer Group to conduct a comprehensive study of the affected area, with a particular focus on the Upper Mallets Creek watershed.

“This study aimed to evaluate potential opportunities for improvements and identify viable solutions to address the recurring flooding issues that many residents had experienced, resulting in damage to their homes and properties,” Project Engineer Megan Kluczynski, P.E., said.

The findings of Spicer Group’s study laid the groundwork for several key recommendations and options for the WCWRC and the City of Ann Arbor to consider. Over 15 potential solutions were identified and publicly vetted as part of an extensive evaluation process.

**Downstream end of outlet control structure**

Community input was valued as a key component in identifying the best solution. Efforts were made to involve the community through various channels, including the development of a mobile app and dedicated website. These digital platforms served as crucial sources for updates, project details, and essential resources, providing residents with convenient access to information and a means to contribute to the project.

Additionally, landowners were encouraged to actively participate by submitting photographs and other pertinent information regarding flooding in their area. This data played a crucial role in ensuring the accuracy of the floodplain model developed by Spicer Group’s engineers and helped build trust within the community through evidence-based decision-making.

Public meetings were held regularly throughout the project’s development to facilitate community input and enhance public understanding of the flooding issues and proposed solutions. While not mandatory, these meetings played a vital role in keeping the public informed and engaged.

Additionally, a site walk-through was conducted with the public before the start of construction, allowing residents to gain a better understanding of the project’s construction impact.

Ultimately, a phased approach was selected to address the stormwater management challenges, with the creation of flood storage in three key locations identified as a priority. Among these locations, Churchill Downs Park on the east side of I-94 emerged as the initial focus due to its suitability for accommodating the proposed flood storage area.

A cost-benefit analysis was conducted on the three proposed stormwater storage areas, with the flood storage in Churchill Downs Park identified as the most cost-effective option. As the park was owned by the City of Ann Arbor, land acquisition would not be a factor impacting the project’s design and implementation process.

**Downstream end of project, outlet control structure**

In 2017, Spicer Group officially began the project design, laying the groundwork for construction of a new 11-foot-deep floodplain area boasting 10.8 acre-feet of storage volume.

A remarkable feature of the Churchill Downs Natural Floodplain Area Project was the unconventional design of the outlet control structure.

“Typically, detention basins or floodplain areas are designed to detain the initial flows and then gradually release water after the peak of the storm has passed,” Kluczynski said.

In this project, a control structure was designed to allow for the selective passage of water, prioritizing low-flow drainage and temporarily detaining high-flows from large storm events in the natural floodplain, rather than detaining all the initial flows.

This alternative method allows typical storm events to pass through the system and provides protection downstream during large storm events. Extensive modeling was completed to evaluate and design the control structure and ensure it would reduce downstream flooding without having negative impacts for upstream landowners.

The design team also had to reroute the Malletts Creek Drain for this project. This was a meticulous process that required understanding of hydrology, urban planning, and ecological conservation. The design incorporated planting vegetation along the drain which will help improve water quality and enhance the ecosystem. Additionally, sediment management measures were implemented to prevent sediment from reaching downstream water bodies, further safeguarding water quality and environmental integrity.

**Floodplain excavation continues, preparing for outlet control structure installation**

Along with the Malletts Creek Drain, the project area was also traversed by a 20-inch watermain serving southwest Ann Arbor. Any impact on this watermain would have resulted in widespread service disruption. Therefore, the project team had to design the project to ensure their operations did not damage the watermain. Due to the size of the watermain and number of residents it served, it could not be taken offline for more than 24 hours. Line stops were installed and construction of the enclosure under the watermain was completed quickly to ensure water service to residents was not impacted.

**Downstream end of floodplain and walking path**

Over the course of construction, 60,000 cubic yards of spoils had to be hauled away to two separate disposal locations. The logistics of this massive operation involving excavation, transportation, and disposal stretched over a period of 29 days. Furthermore, it is worth noting that this is the first of three regional detention basins that were proposed as part of the broader flood control solution. The scale and complexity of the project was just a first step in the larger initiative, showing the depth of what is required to mitigate the flooding issues. The project was substantially completed toward the end of fall 2023.

Despite the challenges and complexities inherent in a project of this magnitude, the Churchill Downs Natural Floodplain Area project emerged as a comprehensive and cost-effective solution to the pressing need for effective stormwater management in the Lansdowne/Churchill Downs area. Through collaboration, innovation, and a commitment to environmental stewardship, the project set a precedent for sustainable urban planning and engineering excellence, safeguarding the community for generations to come.

The project was awarded the 2024 MACDC Innovation and Excellence Award at the MACDC Winter Drain Conference held in Kalamazoo, Michigan.