Course Correction on Farmers Branch Creek

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David Rivera

Stormwater Engineer

Note: This article was featured in the June 2020 edition of the APWA Reporter. Read the e-edition here.

Farmers Branch Creek, located in a picturesque North Dallas suburb, offers residents waterside views from their private backyards. But when torrential rains caused two 50-year-old private dams on the 7-mile creek to crumble, the shifting water threatened a third dam, a private home and a public sanitary sewer line. The public emergency forced city leaders to step in and enlist a multidisciplinary team of engineers, scientists and City staff to stabilize the creek and devise long-term repairs.

The project came together during an intense and fast-paced — and often soggy — several months. It succeeded largely because of strong leadership from City staff and officials, plus the team’s consistent focus on cooperation in a high-pressure situation. When unrelenting spring rains undermined an initial set of repairs, the team quickly pivoted. They designed and built a grade-control structure and 500 feet of streambank stabilization that averted a third dam failure and provided much-needed flood and erosion protection for the creek.

This episode demonstrates how a city can manage a complicated weather-induced crisis decisively even under the unusual glare of public scrutiny.

A Confluence of Challenges

Although the City and its consultants had previously dedicated significant effort to planning capital improvements to address erosion along Farmers Branch Creek, unpredictable and uncontrollable weather conditions during fall of 2018 preempted that strategy. More than 30 inches of rain falling in two months caused damage that made quick intervention imperative.

Challenge #1

City leaders initially worked with Freese and Nichols on a plan for temporary repairs to remove pieces of the failed dams from the creek, install grade-control structures to slow headcut migrations and add erosion controls on the banks to protect homes. But heavy spring rains undermined the temporary stabilization measures, with each storm making things worse. An aggressive headcut kept moving upstream, eventually circumnavigating around a sheet pile barrier. That required the team to regroup and find a permanent solution.

The Solution: Design and construction provided a drop structure to arrest the headcut as well as 500LF of bank stabilization improvements, including a combination of modular block retaining wall and a mechanically stabilized earthen slope with a stabilized toe. When the project was completed in late 2019, it provided essential protection for the neighborhood, along with extensive environmental benefits: mitigating erosion, decreasing turbidity in the water and complying with Section 404 of the Clean Water Act.

Challenge #2

Vocal residents and elected officials focused unusually intense public attention on the situation, more than is typical for this type of project. Local media coverage added to the spotlight. The team had to design options that were not only technically sound and affordable for the City but were acceptable to residents.

The Solution: City Council members gathered residents’ feedback at several open meetings and toured the damaged area with directly affected homeowners. The design took public comments into consideration, and Public Works Director Marc Bentley’s oversight of construction included daily site visits.

Challenge #3

Construction faced multiple constraints:

  • The public emergency necessitated a compressed schedule.
  • Because private property fronted the channel, points of access were limited.
  • The contractor, DCi Contracting, Inc., had to minimize disruption to the neighborhood, and construction had to be completed primarily from within the channel.
  • Even in good weather, there is a constant flow of water to manage in the spring-fed creek, but flashy storms during the spring and summer of the repairs interrupted work as construction materials and equipment were moved in and out of the creek.

The Solution: To gain access via a cul-de-sac and private drive, the contractor built a small ramp down to the channel. On dry days, construction workers logged 13+ hours per day, every day it was not raining, including weekends — and finished the project on time.

Challenge #4

Nimble, creative adjustments sometimes were dictated by available materials or changing site conditions. For instance, a sheet pile stabilization design was selected because of the speed of construction, but the contractor couldn’t quickly procure enough 30’ sheet piles or the installation equipment for them.

The Solution: To adapt, 20’ sheet piles were substituted, with additional structural support provided by a grouted rock riprap plunge pool. Flexibilities were built into the design with the understanding that collaboration would be needed during construction.

Enduring Lessons

These takeaways can help guide other cities faced with erosion and flooding emergencies:

  • Be prepared. Farmers Branch did the advanced planning to identify the risk and was moving forward with plans for capital projects when the emergency erupted. Without the prior investments in planning and base information, responding during this crisis would have been much more difficult. Consider investing in that watershed study or erosion assessment now, so you can find those emergencies that are waiting to happen.
  • Keep first things first. Establish clear, prioritized objectives at the outset and keep the focus on those priorities. Address the critical actions needed first. It something comes up that isn’t critical, consider deferring it until all emergency needs are met.
  • Communicate. In emergency situations, circumstances can change rapidly, making good communication more important than ever. Open lines of communication will help everyone stay on the same page and aligned toward a common mission. Stay engaged with elected officials, the public and other stakeholders by providing relevant project updates and incorporating input as appropriate.
  • Organize. Establishing clear roles and responsibilities as well as decision-making processes will help reduce confusion and facilitate making better choices. Reach out to your partners for help and build the right team for the situation — this might include neighboring communities, state and federal partners, or trusted consultants and contractors.
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David Rivera, PhD, PE, CFM, is a Stormwater Engineer in Frisco.