Anna Fu, Vice President of Construction, SIMCO Engineering
The year 2021 broke many records with the number of natural disasters occurring in the United States. In New York City, Tropical Storm Henri deluged the city on August 21st with a record-breaking rainfall rate of 1.94 inches in an hour, with total rainfall amounts of over 8 inches in 36 hours. Then, only 11 days later on September 1st, that record was also broken by Hurricane Ida submerging the city in 3.15 inches of rainfall in an hour, totaling 8.13 inches of rainfall in one night – and also tragically ending the lives of 45 people in New York and New Jersey. Clearly, new solutions are urgently needed to combat these flooding events that are becoming more frequent, intense, and dangerous.
“One of the simplest ways to effectuate a needed paradigm shift is to go back to basics”
Episodes of flash flooding occur when large amounts of rain suddenly fall on mostly impervious areas in a short period of time. With minimal places for the water to go for absorption into the soil and back into recharging the local ground water tables, the stormwater is instead pouring into subway stairwells and platforms, infiltrating into the basements of homes and businesses, and causing polluted overflows of combined stormwater and raw sewage being directly dumped out into the surrounding waterways (CSOs).
While city agencies have adopted integrated water resource management approaches for some years now by incorporating green roofs and green infrastructure into overall strategy and area development, the pace and results and have been far too little too late in the face of these intensified storms currently inundating the city. A lot more, and better, has got to be done -- if cities like New York are to adapt to and overcome some of the disastrous effects of climate change.
Perhaps one of the simplest ways to effectuate a needed paradigm shift is to go back to basics. If this is a problem of simply too much water at one place at a time, what can be done to reduce the amount of water? One solution can be from realizing that it doesn’t make complete sense to bring in fresh potable water from over a hundred miles away and using most of it in households just to literally flush down the toilet. Instead, rainwater (and grey water) can be captured, stored, and treated to tertiary standards onsite to be used for this very purpose, rather thandiverting it miles away into an energy intensive treatment plant to then drain and discard out to surrounding waterways. There are about 1 million buildings in the city, representing an average of 40,000 acres of rooftop space. With an average rain fall of 46 inches per year, about 49.9 billion gallons of water per year can potentially be captured on just rooftops, treated, and used onsite – amounting to close to 10 percent of the city’s total water demand (not yet taking into account interferences, runoff coefficients etc.). Further, this “water budget” likewise reduces the corresponding stormwater amount, and can help drastically reduce the average 20 billion gallons of untreated raw sewage and polluted runoff from being dumped out at the shorelines throughout the five boroughs.
Further, politicians, planners, engineers and other stakeholders could also continually re-examine how resources and processes are designed and managed,
rather than automatically reaching for the status quo of viewing rainwater as a “waste” to get rid of instead of as a “resource” to hold on to. Greater recognition of the value and use of vegetation can also play a major role in catchment and evaporation processes, immensely benefitting developments, especially in flood prone areas.
By reducing impervious areas and introducing vegetation, immediate results of reducing flooding can be brought by allowing stormwater to infiltrate into the soil as well as up taken by plants. Vegetation also allows for water to go through a pre-treatment process by sedimentation of suspended matter as well as more directed and intentional bioremediation processes, thereby reducing pollution into our water bodies. Also, encouraging smaller scale, localized, grass root efforts will have a major impact and bode well for the neighborhood as well. One great local approach is by having rain gardens instead of lawns, and reintroducing native prairie grasses back into the area, such as what the Texas-based landscape firm Ecosystem Regeneration Artisans (ERA) practices. As Shannon Brown, founder of ERA, recently told me, native prairie grasses can have root systems that grow to 15 feet in depth, as compared to lawn grasses that generally grow only 4-8 inches. When these native prairie grasses grow, their root systems open up “root channels” that further help the water sink deeper into the soil, which in turn helps reduce flooding, reduce soil erosion, and recharge the groundwater. With additional synergies and multitudes of other benefits, such as reducing the heat island effect, providing recreational opportunities in biophilic spaces, and reduction of pollution and CSOs to name a few, a community’s quality of life can further be enhanced.
As we’re witnessing the increasing and intensifying effects of climate change to the hydrological cycle, and the devastating effects it’s having on life and property, it’s clear that innovative approaches are urgently needed. It’s time to think outside of the catch basin box.