Maximizing green infrastructure and associated co-benefits in resilience programs

Major flood events resulting in significant impacts to human health and the environment have been significantly increasing over the last 20 years. Nearly all counties in the United States have experienced some level of flooding over the past 20 years — 99% according to Floodsmart.gov. With changing weather patterns, we can expect an increase in intensity and frequency of storms, higher rainfall quantities, sea level rise and larger storm surge which all contribute to flooding. The U.S. cross-agency report from 2022 of Global and Regional Sea Level Rise Scenarios for United States anticipates by 2050 a ten-fold increase in minor flooding events and a five-fold increase in major flooding events averaged across the United States. The west and southwest of the U.S. are experiencing changing climate patterns primarily as drought and wildfires. It is important to note that these conditions facilitate flash floods and mudslides during heavy precipitation events since dry and burned soil becomes hydrophobic and leads to greater overland flow.

Resilience strategies help plan for the future and mitigate risk for these increasingly strong weather events. Municipalities are creating resilience focused plans that include a comprehensive look at stormwater management and flood control. These plans include traditional “grey infrastructure” like stormwater piping, culverts and concrete canals and pump stations. Increasingly, they also contain plans for Nature Based Solutions like bioretention areas, rainwater harvesting, wetlands and other natural and nature-inspired systems. These solutions offer not only stormwater management but also numerous co-benefits like green spaces for the community, habitat for native species, air quality improvement, heat island reduction and more.

Recent disasters in Texas have shown a spotlight on the need for flood control and resilient infrastructure. Hurricane Harvey in 2017 resulted in more than 100 deaths in Texas and Louisiana and $125 billion in damage primarily in Houston and Southeast Texas where rain stalled over the metropolitan area and dumped 40 inches of rain as well as storm surge, high winds and tornados. Earlier this year, well inland of the coast, Kerr County received 10-12 inches of rain overnight resulting in the Guadalupe River overflowing its banks as it rose 36 ft in three hours, taking the lives of more than 120 people.

To help address disasters like these, the state has been actively developing solutions for communities. For example, Texas was able to leverage sizable Community Development Block Grant Mitigation funds (CDBG-MIT) to mitigate flood risks and other associated impacts from Hurricane Harvey and other smaller flood events that year. The resulting mitigation plan created in 2020 outlines a variety of mitigation projects including traditional stormwater management solutions like culverts, flooding alert systems and backup power, and elevating critical systems above base flood elevations. It also includes guidance for implementing permeable pavement, constructed wetlands and other natural barriers and collection points, and native plantings. In Dallas, Texas, the Nature Conservancy and Texas A&M Agrilife Extension published a study titled “Green Stormwater Infrastructure for Urban Flood Resilience.” The report uses modeling to identify hotspots which are areas of undersized drainage networks likely to contribute to flooding. Dallas will see an increase of 26% in hotspots by 2045 for 2-, 10- and 100-year, 24-hour storms as rainfall totals increase. The report also found that using Green Infrastructure in conjunction with grey infrastructure is “77% less costly than upgrading gray infrastructure alone.”

In places like Florida, counties and cities are planning for increasing frequency and intensity of storms and hurricanes, tidal flooding and rising sea levels. Numerous counties and cities are creating resiliency plans funded by the Resilient Florida Program that target solutions for different areas and needs like urban spaces, coastal communities and suburbs. Green infrastructure options target these areas of concern to increase storage, slow water and redirect water from population centers and infrastructure.

Rivers have in the past been straightened, covered, and confined to make room for development. By making room for rivers and creeks by restoring natural floodways and stream paths, rivers can provide additional storage and allow natural flooding to occur without damage to structures or people. Similarly, natural shoreline restoration is becoming more popular. The National Oceanic and Atmospheric Administration (NOAA) provides guidance encouraging the use of the softest shoreline approach possible for a given area. Bulkheads, seawalls and revetments may be required where space is limited and the shoreline experiences high energy waves. Wherever possible, buildings and especially critical infrastructure should be relocated away from areas vulnerable to flooding to make room for shores to be naturalized to increase aquatic habitat to yield co-benefits of green infrastructure like creating natural spaces for recreation along the shoreline. These areas can then safely flood during high-water events.

Water can also be stored upstream by improving existing green spaces or repurposing vacant buildings as pocket parks to house stormwater management devices. Localized flooding can also be managed through small scale green infrastructure like bioretention areas, permeable pavement or bioswales within neighborhoods and urban areas.

Other coastal areas in the northeast have also analyzed future flood risks and are designing and building projects to protect their shoreline. Dense and urban areas exist in spots that were previously wetland — experiencing both coastal flooding from storm surges and inland flooding from rivers and large rainfall events. Designs to mitigate severe flooding utilize traditional infrastructure to address undersized utilities and updating pump stations. However, it also relies on enhancing existing public green spaces as well as creating new green infrastructure to treat and temporarily store stormwater. These plans call out the benefits of tree planting to store and release water back to the atmosphere.

The extreme weather events across the United States should encourage us to look at our own strategies and make resilience a priority. Even with Federal and State grants and loans, money for these long-term concerns is always limited, so it is important that every dollar spent returns maximum benefits. Pairing green infrastructure with grey infrastructure can go a long way to maximize not just stormwater benefits but provide additional co-benefits to communities.