Stormwater and Wastewater Resilience

Water, wastewater, and stormwater utilities in the United States - and throughout the world - recognize that a changing climate means changing precipitation, storm, and flooding patterns. Utilities also recognize that they must account for these changes in current and future projects.

While water utilities must consider the impact of climate change on long-term water supply and demand, wastewater and stormwater utilities (herein after referred to as utilities) must consider how to adapt to changing performance standards, regulatory drivers, and flooding impacts as extreme storms become more intense and back-to-back or compound events become more frequent under a warming climate.

Many of the WUCA member utilities are actively planning for future climate regimes and related impacts to their systems. Yet, there is no consistent federal guidance or regulatory mandates that require utilities to use forward-looking climate modeling and information in their planning. As a result, each agency typically uses their own methods to prepare for future risk, based on their own analyses and available climate science, and their own leadership directives.

WUCA members solicited this study with the goals of:

Identifying best available methods and tools for utilizing historic data and future precipitation projections
Summarizing best approaches in use or under development related to future extreme precipitation events
Characterizing the major challenges related to using future condition precipitation projections
Highlighting successful approaches and lessons learned related to using future precipitation projections
Documenting the outcomes in an easy-to-read report that summarizes the elements above
Recommending next steps to close data gaps

Case studies

The project team developed four practitioner case studies of utilities across the U.S., at various scales of planning and implementation, to demonstrate the breadth of different methodologies, successes, and lessons learned.

Given the paucity of literature or resources that clearly document data and methodologies to allow other practitioners to easily replicate successful efforts, these case studies provide a valuable tool for encouraging peer-to-peer learning. Sharing field-tested practices, which describe successful solutions as well as unsuccessful attempts, helps the entire field advance.

Moreover, climate models are theoretical projections of the future; it is only when practitioners attempt to use this information, highlighting what types of outputs are useful, and which are not, that a bridge can be built between climate scientists and engineers. Practical applications of climate modeling can, in turn, inform climate modelers to encourage development of future outputs that can continue to inform future planning.

These case studies were developed following a structured interview with each utility, supplemented by a review of documents related to the utilities’ efforts. The full case studies provide a detailed narrative overview of how the utility addresses climate change in their planning and design, as well as detailed descriptions of the model projections used, barriers and challenges overcome, the final application and outcomes, and the lessons learned.

Transforming Global Climate Model Precipitation Output for Use in Infrastructure Planning and Design Applications

Philadelphia Water Department (PWD) led an initiative to develop guidance based on in-depth analysis of climate projections. The guidance is informing a department-wide revamp of standards and criteria for resilience planning.

Developing Future Precipitation Projections and Design Standards

The City of Virginia Beach commissioned a study to assess changes in historical and future extreme precipitation in response to heavy flooding events. The study, which received a third-party review, resulted in updates to the Department of Public Works Design Standards Manual (2020), including new requirements and design parameters for stormwater management. The effort also included an assessment of sea level rise and the potential for combined flooding impacts from extreme precipitation and storm surge events.

team in construction gear posing in front of sign that says, "Mudhoney"

Ship Canal Water Quality Project – Combined Sewer Overflow Program – Preparing for Extreme Rainfall with Climate Ready Design

Seattle Public Utilities' (SPU's) Ship Canal Water Quality Project used both observations of increased precipitation and overflows with modeled future extreme precipitation projections to inform the design of a 2.7-mile-long storage tunnel to manage combined sewage and stormwater overflows into the future.