Stormwater Control Lessons in the Age of More Extreme Weather Debris Removal, Repair and Mitigation of Drainage System Damages, and FEMA Funding By Matthew Burnette
Water is a cornerstone of life and commerce as well as something we need to manage, specifically through drainage infrastructure. Thus, water presents both opportunities and challenges for localities that are required to control its flow in a great many forms. Managing water, wastewater, and stormwater are foundational services that local gov- ernments provide to their citizens and as such should be a top priority for elected officials and municipal staff. The issue of properly managing stormwater has become more complex in recent years due in part to the confluence of aging infrastructure and more extreme rain events. Like all levels of government, locali- ties across the country face deteriorating infrastructure in their com- munities. Our infrastructure is in desperate need of investment. In a 2017 report from the American Society of Civil Engineers, the group estimated that the United States needs to spend trillions of dollars to address all the needs. Capital investment for the nation’s wastewater and stormwater systems will require an estimated $300 billion over the next two decades to fix. Although this level of funding is highly unlikely, especially given budgetary constraints at all levels of govern- ment, these numbers illustrate the degree to which aging infrastructure presents a challenge. Combine that reality with the increased frequency of bigger and more damaging weather events. The National Oceanic and Atmospheric Administration (NOAA) has reported that tropic storm intensities and rainfall rates are expected to rise across the globe in coming years. These extreme rain events tax aging drainage systems to the max and beyond. Significant rainfall in a short period of time, whether from a hurricane or another storm, will tax already strained systems and could lead to disastrous consequences. Exploring the impacts of Hurricane Florence (2018) on the drainage system in the City of New Bern, North Carolina offers instructive in- sights. The City of New Bern’s drainage system includes over 80 miles of open ditch network for conveying stormwater runoff. Like many municipalities across the country, New Bern’s infrastructure was aging and even included terra cotta piping. Hurricane Florence left a lasting impact on the City by overrunning the stormwater system, flooding the City, and wreaking havoc on the drainage network. Among the storm’s last impacts was the significant amount of debris, such as sediment
and vegetative debris, it deposited in the City’s drainage system. This debris greatly reduced the capacity of the City’s drainage system and significantly increased the likelihood of future flooding. After an ex- treme weather event, it is common for municipalities like New Bern to face complex challenges on multiple levels. Recognizing the need to repair and improve its drainage system, the City of New Bern is focused on a multitude of solutions to address all damaged elements. After evaluating the damaged pipe systems constructed of historic materials, such as terra cotta, engineers have recommended replacing those systems with more modern materials, such as concrete, metal, or HDPE. Additionally, the City of New Bern is exploring mitigation options including upsizing existing pipes to account for current and projected future development in hopes of preventing future damage and flooding during extreme weather events. Thus, undertaking mitigation efforts can yield additional benefits to support further development in a community. Furthermore, the City of New Bern conducted an exhaustive review of its drainage system and identified areas with erosion concerns. Areas of erosion will be stabilized using a variety of methods. One mitigation option for severely eroded embankments includes the construction of new retaining walls. Finally, the City of New Bern is exploring debris removal strategies to restore the capacity of the drainage system to the pre-disaster con- dition. These strategies include the removal of sediment and debris, primarily vegetative including hazardous limbs, trees, and brush, from the City’s drainage ditches. High stormwater flows have resulted in bank erosion that has led to undercutting, and ultimately failure, of a stormwater pipe. The eroded bank material has been deposited in the drainage channel, consequently reducing the capacity of the channel to convey future stormwater runoff.
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may 2020
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