Achieving Resiliency Goals through Comprehensive Vulnerability Assessment & Flexible Adaptation Plan


  • Anni Luck - Hazen and Sawyer

Among the many manifestations of climate change, it is virtually certain that sea levels will continue to rise for many centuries. Coupled with the effects of storm surge from more frequent and intense extreme events, resulting impacts are expected across a range of sectors, predominantly in densely populated coastal regions. Within the water resources sector, wastewater treatment plants are particularly vulnerable due to their placement at low-lying elevations for collection by gravity and proximity to water bodies for discharge purposes. Protection of these facilities is of vital importance to avoid disruption of public service, damage to equipment, and spillage of wastewater into nearby waterways.

Adaptation design and implementation can be complicated by evolving or conflicting stakeholder needs. Balancing capital budgets and the level of desired protection is intrinsic to most designs. Use of different funding sources (for example FEMA and state revolving funds) on the same resiliency project may result in varying scheduling requirements and protection requirements as reflected in different design flood elevation determinations. Differing stakeholder preferences for project bundling could also impact final resiliency design and implementation. As such, successful resiliency projects must not only address specific infrastructure risks, but also allow for flexible resiliency planning which can evolve to balance stakeholder requirements. The purpose of this talk is to walk through a proven resiliency framework that facilitates an efficient and comprehensive vulnerability assessment while also allowing for flexible adaptation planning that accommodates varying stakeholder, budgeting, and scheduling constraints.

This comprehensive and versatile risk management framework was recently used to assist the Westchester County Department of Environmental Facilities (DEF) in developing three alternative strategic and cost-effective plans to secure infrastructure at the Port Chester Wastewater Treatment Plant. This 5 MGD plant, located close to the mouth of the Byram River at the Long Island Sound, is particularly low-lying, flat, and vulnerable to sea level rise and surges. The vulnerability assessment, which included comprehensive analysis of flooding mechanisms and asset characterization, found nearly all structures on site and over 700 assets to be at risk of flooding in the 100-year FEMA flood event with 30 inches of projected sea level rise. All process tanks would be flooded, and total damage in a single 100-year event could exceed $23 million.

The study found that DEF could mitigate on the order of $100 million in risk over the next 50 years through implementation of one of three strategic mitigation plans which meet different levels of protection and address different tradeoffs between varying stakeholder needs. The alternative plans include: 1) an option with a plant-wide barrier; 2) an option which isolates individual buildings and locations on site with smaller scale adaptation measures; and 3) an option with localized curb barriers to isolate processes and tanks. This talk will demonstrate the advantages and challenges of each, and more specifically describe the key steps, including extensive characterization of vulnerabilities on site, strong stakeholder communication, and a systematic method for deriving costs for resiliency implementation, required to allow for the expedited and flexible development of the three resiliency plans.

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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