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New Navigate the Flood guide offers tools to manage urban stormwater and climate-induced flooding


Erica DePalma, Water Center at the University of Pennsylvania

Erica DePalma, Water Center at the University of Pennsylvania

Since the time of the Industrial Revolution, communities across the U.S. have developed and expanded, increasing both in population and impervious surfaces. Artificial structures such as roads, sidewalks or pavement, yielded some incredible efficiencies for an ever-expanding city life. However, these rapid large-scale infrastructure changes came with unintended consequences. Today, particularly in communities with combined sewer systems, impenetrable surfaces give rise to localized flooding and a flood of human waste.  

For utility, municipal or authority leaders tasked with managing these challenges, this is nothing new. However, for lower-capacity communities, addressing these issues has become more daunting.  

For decision makers in need of guidance or funding support, check out the new Navigate the Flood guide, a joint initiative of the Water Center at the University of Pennsylvania and the WaterNow Alliance. Navigate the Flood offers a step-by-step, curated list of technical and financial resources to support city and utility staff as they tackle local flood and stormwater challenges – including those resulting from separate and combined sewer systems or climate-induced flooding.

This new guide features:

  • Five process-oriented steps to Navigate the Flood, each with user-friendly explanations and customized resources.
  • Over 85 external technical and financial resources in the filterable, curated library, including the type of information each resource provides, as well as the original source.
  • Navigator’s Checklist: Looking for something to print and take into the field? Download the checklist and have questions to ask your team as they begin to define the condition of your community’s system on-hand, anywhere, anytime. 
  • Stakeholder Engagement Plan, detailing the role of stakeholder engagement at every step of the way.
  • A list of national, state and regional Technical Assistance Providers and information on how to access them.

The Navigate the Flood guide received funding support from The Kresge Foundation’s Environment Program through its Climate Resilient and Equitable Water Systems (CREWS) initiative, which was launched in 2016 to transform urban stormwater and wastewater systems to provide reliable, equitable and innovative services to all community residents. 

The CREWS initiative supports more than 30 organizations working to advance solutions to climate-related storm and flood impacts on low-income communities and communities of color, both of which are disproportionately vulnerable to urban flooding and extreme rainfall. 

How flooding impacts urban communities  

There are two types of sewer systems: combined sewer systems (CSS) and separate sewer systems (SSS). 

In a separate sewer system, there are two separate pipes – one that carries stormwater (rain water) from storm drains to local streams, and one that carries sanitary sewage to a wastewater treatment plant. In this system, the stormwater that is conveyed to local streams receives little to no treatment. 

In a combined sewer system, there is one pipe that carries stormwater and wastewater to the wastewater treatment plant. At its inception, this combined system was considered to be a modern marvel and extremely efficient (less infrastructure to accomplish two tasks). 

However, as cities continue to expand both in population and impervious surfaces, less rain infiltrates into the ground and instead runs off directly into the combined sewer system. This also means more sewage fills up the same system. 

It doesn’t take much rainfall for the combined system to reach capacity before the wastewater (combined stormwater and sewage water) can reach a treatment facility. 

So, where does it go? It outfalls directly into small streams adjacent to neighborhoods throughout the city via combined sewer outfalls.

As the Water Center’s Executive Director and former commissioner of the Philadelphia Water Department, Howard Neukrug, often says, “What happens when you combine one gallon of rainwater and one gallon of sewage? You get two gallons of sewage.” 

The compounding challenges that arise from increased rainwater, increased impervious surfaces, and less infiltration are localized flooding and sewage back-ups as the stormwater overwhelms the capacity of drainage systems.  

For those of you who are surprised by this, we encourage you to research how your own city manages stormwater and flooding. 

We recognize there is a lot of information out there, so we developed a comprehensive, vetted guide to support community leaders who are navigating stormwater and flood management challenges. We did the work. We dug through the federal, state, local and non-profit websites and financial and technical resources to curate what we hope will be  a helpful tool to support decision makers at every step of the process.  

For experts in the field, we hope you find this guide useful and encourage you to provide feedback online or by email at [email protected]

For the general reader, we encourage you to do some digging of your own into how your local leaders and decision makers manage stormwater and flooding challenges. Find out what it takes to keep the excrement out of public streets. It may give you new insight about the stormwater fee on your monthly bill. 

Erica DePalma is a research program coordinator at the Water Center at the University of Pennsylvania. Follow the organization on Twitter at @WaterCenterPenn. Learn how to tackle your local flood and stormwater challenges by visiting