Observing Irma

September 11, 2017

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On September 11, 2017, Hurricane Irma pushed a surge of water into the Charleston area, which resulted in the third highest tide on recorded. This is an account of the that day written immediately after the waters receeded. 

Surge guidance for Irma indicated that Charleston could see significant tidal flooding, but I think it still surprised many people - myself included. Most people have never seen water that high. While Hurricane Matthew, which made landfall in 2016 just north of Charleston in McClellanville, technically produced a higher surge, it came at a lower tide and did not stage as high (9.28' MLLW). The region was also under a mandatory evacuation during Matthew, so there were not as many people in town to experience its effects. Irma's tide peaked at 9.919' (preliminary) becoming the 3rd highest tide on record behind Hurricane Hugo (12.52' MLLW) and an unnamed hurricane in 1940. If you didn't live here in 1989 - and the population has grown significantly since then - you had not experienced tide levels like we saw from Irma.

Many areas of the peninsula were inundated with water, and a significant portion of the areas were old tidal creeks that were filled-in and paved over as Charleston developed. The two maps below show an elevation analysis depicting Irma's peak tide elevation over the Charleston peninsula and and the location of historic tidal creeks. Rainfall associated with Irma, ranging from 5 to 9 inches, on top of the tides resulted in significant portions of the City being flooded.

Just before 1 PM, we sheltered in the City of Charleston Gaillard Center Parking Deck due to tornado warnings in the area. While in the parking deck, the tide continued to rise and rains continued to fall, inundating the surrounding streets and making them impassable. We were temporarily stuck. Luckily, there were no impacts from tornadoes in the vicinity. As the photos below show, even after the peak tide elevation was observed in the harbor, flood levels continued to rise for at least an hour.

By 3 PM the water levels had receded enough so we could leave the parking deck and head out to inspect the flooding and impacts. Much of the City was still underwater and impassable, and we had to navigate our way around higher streets. We made our way up to the upper peninsula area of town, and then worked our way back down to the battery along the original 'high ridge' of the peninsula.

As the afternoon continued, it became apparent that, although the tide was lowering, there was nowhere for the flooded water to go. Low tide observed late in the evening was over 3.5' above predicted levels (at approximately the same level of some high tides). Flood waters were trapped in low lying areas until tide cycles returned to normal levels or until the water could be pump out. For the third year in a row, many residents of Lowcountry were significantly impacted by flood waters.

I think it's important to note that, all things considered, Irma's impacts on Charleston could have been much worse. Had her track shifted to the east, we could have seen higher tides, more rainfall, and higher winds. Having witnessed the rise and fall of Irma's surge, it's scary to imagine the devastation of a direct hit on Charleston.

Charleston is vulnerable - and becoming more vulnerable - to the impacts of tidal flooding. We experienced, according to NOAA, 50 days of tidal flooding in 2016, which broke 2015's record of 38 days. Historically, we've seen the third (Irma), fourth (Matthew), and sixth (10/27/15) highest tide observations on record over the past three years. It's time we have difficult conversations about how we move forward and address these issues. We need to learn how to live with water rather than fight it. We need to think about where we build - and where we rebuild. Most importantly, we need to engage and keep the conversation going. As Seth Godin states in They're raising the weather tax, "action now is a bargain compared to what it's going to cost everyone later."