Community Impact

July 1, 2021 | Kim Krieger - UConn Communications

For Future Flood Control, Cities Need Strategy

What we consider a 100-year event is a conservative version of a 10-year event plus 20 inches—what will be a normal flood in 2050

Climate models predict that Long Island Sound will rise 20 inches in the next 30 years. On the left, the image shows a typical flood plus 20 inches; on the right, a 100 year flood similar to Hurricane Sandy, plus 20 inches. The color scale shows the flood water level: green < 0.5 feet (0.5’), yellow is between 0.5’ and 1’, orange between 1’ and 2’, and red is flooding over 2’. Flooding at the 2’ level washes away cars and SUVs and undermines many structures.

Climate models predict that Long Island Sound will rise 20 inches in the next 30 years. On the left, the image shows a typical flood plus 20 inches; on the right, a 100 year flood similar to Hurricane Sandy, plus 20 inches. The color scale shows the flood water level: green < 0.5 feet (0.5’), yellow is between 0.5’ and 1’, orange between 1’ and 2’, and red is flooding over 2’. Flooding at the 2’ level washes away cars and SUVs and undermines many structures (contributed image).

Carefully placed flood control structures could protect Connecticut’s vulnerable infrastructure from severe flooding even if sea level rises significantly, UConn researchers reported during a webinar last Friday as part of the Resilient Connecticut research webinar series.

Caterina Massidda analyzed the area around New Haven’s Tweed Airport to see how 20 inches of sea level rise—which is likely to happen in Long Island Sound by 2050—would affect the damage done both by typical storms and by a 100 year flooding event. The results showed that while 20 inches of sea level rise would significantly increase the number of streets and buildings flooded, strategically placed flood barriers could protect critical infrastructure.

A 100 year flood is a high water event that has a 1% chance of occurring in any particular year; in other words, such events are rare but not vanishingly so. Hurricane Sandy, for example, created a 100 year flood in New York City and parts of Long Island, according to the US Geological Survey. It also caused severe flooding in Connecticut’s Fairfield and New Haven counties.

Massidda is a data analyst at the Connecticut Institute for Research and Climate Adaptation (CIRCA) at UConn. She and her CIRCA colleague Chang Liu, a storm surge modeler, chose to use Sandy as an example case because it is a well known event that in Connecticut is estimated to be somewhere between a 40 year and a 100 year flood. The findings of her study show that what we currently consider a 100-year event is a conservative version of a 10-year event plus 20 inches—that is, of what will be a normal flood in 2050.

Tweed Airport doesn’t suffer much damage from normal flood events at present. But just 20 inches of sea level rise could change that, flooding portions of the airport’s grounds as well as 30 miles of roadways surrounding it and more than 500 nearby buildings, according to Massidda’s analysis. And a 100 year flooding event plus 20 inches would flood more than 115 miles of street and 2,177 buildings, as well as all the airport’s runways, nearby electric substations, water treatment plants, a ferry, and other critical businesses.

Tweed Airport is surrounded by waterways, including Morris Creek, Morris Cove and the Farm River. Building flood reduction structures along all of them would be expensive and perhaps unworkable. But according to Massidda’s analysis, the majority of the floodwaters enter the area through Morris Cove, and a flood control structure such as a tide gate or seawalls on just that waterway would prevent most of the damage, even from a 100 year flood plus 20 inches of sea level rise.

This type of analysis could be done for any area, and Massidda suspects many municipalities in Connecticut could benefit from it.

“You can simulate different scenarios of the same flood event. You can try different areas to test where the major flooding source is coming and see if a flood control structure is effective,” Massidda says. “We did our test cases only on the Tweed Airport for now, but it can be done for other areas as well.”