Hurricane Sandy badly flooded Red Hook, Brooklyn in October, 2013. One of the many terrific responses from inside the community was the map made by cartographer Jim McMahon.
Jim McMahon works for Scholastic and lives in Red Hook. McMahon went around Red Hook and measured the elevation above sea level at many points and recorded where there was flooding. PortSide NewYork would like to thank him for allowing us to share this map. It is a very useful guide for calculating the risk of Red Hook flooding in the future.
He suggests that elevation markers be placed flood zones for future preparedness. See the DNAInfo story about why he created the map here
To calculate the risk of flooding at a location:
You need to take the height of the expected storm surge, the time it is expected, and compare that time to the tide cycle in the harbor. Places are most vulnerable at the point of high tide. To calculate projected surge risk at that point, you have to add the height of the incoming water to the height of the tide at that time.
There is about a 5 foot difference between high and low tide in NYC; so a 5' surge, if it comes at low tide, will not run into Red Hook. That's why we were were spared by 2011's hurricane Irene, the surge did not hit at high tide.
There are two high tides and two low tides each day. There is roughly six hours between high tide one and low tide, and then another six hours until the second high tide. In other words, the high tides are 12 hours apart and the low tides are 12 hours apart.
Wind can compound the effects of rising waters in that winds from the south will push the Atlantic Ocean onto land and push the water in the Upper Bay towards Red Hook. Winds from the northeast would push the waters away from Red Hook.
Wind also has an effect on the water within the harbor in terms of creating local waves. The big Upper Bay (between Red Hook and the Statue of Liberty and Staten Island) is a big water space which can create fetch issues if the wind is coming from west or southwest. Tide + surge + wind over water or fetch = more water hitting the shore at peak of crashing waves. If we don't have big waves, we are at the lowest range of risk for the tide level. Here is a definition of fetch.
An area of the water surface over which waves are generated by a wind having a constant direction and speed. Also, it is the name given to the length of the fetch area, measured in the direction of the wind from which the seas are generated. One of the ingredients for lake effect snow is the fetch of the water over which cold air can gain moisture. from http://www.weather.com/glossary/f.html
In Red Hook, there were also many underground springs, so sometimes flooding here comes from groundwater welling up and not just seawater coming in. Add to that, the water coming from overflowing sewers, and Red Hook can have water coming in from many sides.
Due to climate change, we all need to be more aware of flooding risks, engage in emergency preparedness and resiliency planning.
Red Hook is developing a community support network to deal with disasters and emergencies. after Sandy.
Fun historical fact: There is one spot close to the harbor which did not flood during Sandy, that is the square defined by the blocks of Dikeman, Coffey, Van Dyke Street between Conover & Ferris Street. That is where there was once a high hill near the Revolutionary War era Fort Defiance (the fort for which the local restaurant is named), a hill which was leveled to make fill. The site of that hill remains higher than the filled area near it.
You can see the hill on old maps, such as the one below. This also shows how much of Red Hook has been filled to make the peninsula as it is today.
PortSide NewYork creates programs that capture and explain such history; we call them WaterStories since they tell Red Hook's history along a waterfront theme. This historical information clearly has applicability to emergency planning in addition to general education.
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This is from a "Ratzer map" or a map drawn by Bernard Ratzer in the 1770s. There is a story of the Ratzer map at the Brooklyn Historical Society here