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Kathryn Cox, Emily Jennings, Daniel Schwartz, Sylvia ZakiProfessor BirdSeminar 3 Final ReportDecember 21, 2012Combatting Storm Surge Flooding and its Effects on the NYC SubwayIntroduction:According to the National Weather Service’s “Introduction to Storm Surge” report, storm surge is “an abnormal rise of water generated by a storm, over and above the predicted astronomical tide” (NWS 2008).? In other words, this is an increase in the usual water level that is caused specifically by a storm.? There is no specific benchmark for what height of water constitutes storm surge, as each body of water has its own usual water level.? Additionally, storm surge is the difference between the height of the storm-influenced tide and the level the tide usually reaches; combining the two numbers would produce the storm tide level.? Storm surge has become an increasingly dire problem in New York City, particularly in light of the Massachusetts Institute of Technology study “Physically based assessment of hurricane surge threat under climate change”, in which the researchers predict that due to increasing sea levels, by the end of the century, the current 100-year surge floods will occur every 3-20 years and 500-year surges will occur every 25-240 years (Lin et al 2012).Just a few months after the publishing of that study, it has been estimated that on October 29, 2012 the water level surged to 14 feet over the average low tide mark and 9 feet over the average high because of Hurricane Sandy.? As one might assume, surge heights of that magnitude caused flooding throughout the lower part of Manhattan, and with that came the flooding of the subway lines with East River tunnels.? According to Klaus Jacob of Columbia University, the minimum surge height that would have caused subway flooding was 5.9 feet, and the surges caused by Sandy greatly surpassed that mark (Jacob et al 2011).? Moreover, this severe flooding was not without warning—Jacob calculated that if the storm surge caused by Tropical Storm Irene in August 2011 swelled just another foot, the East River subway tunnels would have flooded then as well.Although the majority of subway lines flooded by Sandy have been restored, city dwellers had to make do for several days riding on compromised lines that maneuvered around the flooded areas of lower Manhattan.? Even though a week or so seems like a lifetime to many residents of New York City, the damage to the subway system could have potentially been much more severe.? Jacob originally estimated that top-to-bottom flooding of the East River tunnels would take at least 29 days to fully recover from.? What saved the city from damage to that extent was the fact that the city’s mass transit system was completely shut down at 7 p.m. on October 28, the day before the storm was due to hit.In addition to causing the inconvenience of the subways being out of commission for weeks, storm surge damage also costs a significant amount of money to repair.? In the Metropolitan Transportation Authority’s November 2011 budget report, it was announced that $49 million would be needed to repair the damage caused by Tropical Storm Irene in August 2011 (MTA 2011).? No numbers have been released yet as to what the total amount of repairs after Sandy will cost, but considering the East River tunnels did not experience significant flooding during Irene, the cost will most probably be more than $49 million.? This is why it is unacceptable for the East River subway tunnels to flood as a result of storm surge, and therefore why the goal is to keep storm surge waters out of the tunnels and prevent any flooding of these tunnels by the year 2082.Strategy: Elevated Subway Station EntrancesCurrently, most of New York City’s subway stations that lie along the East River and south of Canal Street have lowest critical elevations (LCE) greater than or equal to 5.9 feet above NGVD29 (Jacob et al., 2001). A station’s LCE is determined by the lowest station opening that provides access to its tunnel, and can be derived from the elevation of a station entrance, emergency exit, ventilation shaft or street level grate (Jacob et al., 2011). These elevations are measured in reference to NGVD29, the National Geodetic Vertical Datum of 1929, a set of control data used to measure position above or below mean sea level (FEMA, 2007).More specifically, the A and C lines have a lowest critical elevation of 7.0 feet, the R line of 7.5 feet, the 2 and 3 lines of 9.1 feet, the 4 and 5 lines of 9.9 feet and the F line of 10.0 feet (Jacob et al., 2001). According to a 2011 report titled “Transportation,” without accounting for sea-level rise and without prior preparations, 100-year flooding will cause complete flooding of the tunnels leading into Brooklyn of the aforementioned subway lines (Figure 1). Low lying subway entrances, especially those situated in proximity to the shore, are at high risk for incurring floodwater during an intense storm. The potential for subway tunnel flooding can be met by flood heights associated with 1-in-100 year flood events, storm surge flooding associated with hurricanes of all intensities, and even 1-in-10 year flood events by the end of the century (Horton et al. 2010).Figure 1: Figure 1: 100-year flooding without sea level rise of lower Manhattan subways and adjacent East River tunnels crossing into Brooklyn; the heavy blue lines indicate fully flooded tunnels, and broken lines show overflow into tunnels located in areas that are not flooded above-ground; background colors show topographic surface elevations (yellow≥30ft). Sea level rise is expected to only worsen subway-flooding events (Jacob et al., 2011).Category 2 hurricanes are generally associated with storm surge-induced flooding of up to 16.6 feet and SLOSH maps indicated that lower Manhattan would experience 12.0 feet of flooding under such hurricanes (Figure 2). In order to reduce the risk of subway tunnel flooding, subway tunnel entrances that precede East River tunnels should be reconstructed so as to increase their respective LCE to 20 feet. A similar suggestion was proposed during a recent conference titled “What is the State of the Art in Preparing for Extreme Weather Events?” by research scientist Klaus Jacob. Dubbed the “Taipei Solution,” Jacob’s proposition suggested that the New York City government look to the organization and construction of Taipei’s Mass Rapid Transit (MRT) system to improve infrastructure resilience. Suggested improvements include elevating subway station entrances, installing gates and installing higher capacity water pumps (Chiang & Huang, 2012). Similarly, Bangkok’s MRT stations, through a combination of elevation and floodgate protection, are able to withstand up to 9 feet of water (Fernquest, 2011).Figure 2: Figure 2: SLOSH Map flood levels associated with category 2 hurricanes. As indicated above, lower Manhattan would experience 12 ft. of flooding during such a hurricane (The City of New York, 2009).Commuters in Taipei and Bangkok must first go up a flight of stairs or ascend via escalator into the station before descending towards the train platform. Furthermore, some subway stations in these cities are outfitted with computer-controlled floodgates that are activated when floodwater levels reach a critical point; they also further increase the station’s LCE. Construction of similar elevated structures throughout lower Manhattan will ensure the impermeability of subway station entrances to floodwaters resulting from a Category 2 hurricane or lower.Discussion: Elevated Subway Station EntrancesElevating the LCE of lower Manhattan subway station entrances might prove to be an intuitive, efficient strategy for combatting East River tunnel flooding, however, there are major holes in the information available about the feasibility and cost of this project. In a metropolis such as New York City, the concept of a major overhaul of downtown topography created by constructing elevated station will be met with opposition. However, should this strategy prove effective, it will provide an impenetrable barrier to floodwaters entering through subway entrances and into tunnels. By protecting the tunnels and the stations, this strategy will aid in preventing the $23 million lost everyday due to transportation shutdown (Jacob et al., 2011). Therefore, it is necessary that, through evaluation, land and station surveys and research, the efficacy and cost of such a project be determined. The following, however, is an evaluation of the feasibility of implementing this strategy based on available research. One of the most obvious obstacles implementation of this strategy faces is the shortage of available space for subway entrance construction. Lower Manhattan, especially, is incredibly dense in terms of pedestrian thoroughfare and infrastructure (buildings, roads, traffic control equipment, etc.).? Many of the subway stations that precede stretches of under-river tunnel track are located in areas that do not have the space required for the construction of above-grade structures.Possible alternatives exist, however. Subway station entrances can be integrated into buildings that lie above or around the below-grade portion of the station (Teo & Woo, 2011). However, close coordination between architects, engineers and the owners of the buildings in question must be achieved in order to seamlessly integrate commuter thoroughfare into the lobby or basement of such buildings. Furthermore, safety regulations must be followed to ensure evacuation routes and proper ventilation is available for the station.Subway station entrances can be consolidated into one central, elevated entrance if a sizable area of space is allocated for a certain subway station. Subway entrances of this sort might encounter problems with congestion—long lines and large crowds—if metro card machines malfunctioned, for example. Therefore, station designs of this sort would have to allow for seamless access to station platforms.Elevated station designs also face accessibility issues. Commuters with disabilities would only be able to access elevated station platforms via elevator. However, the elevator shaft provides another entrance for floodwater during an intense storm. If the integrity of the station were to be kept intact, two sets of elevators would have to be installed—one to provide access to the peak of the station, and one to descend toward the platform. Further alternatives would have to be conceived and tested to ensure an effective method of entrance for commuters with disabilities while providing no further entry to floodwaters.In light of the issues implementation faces, close cooperation and coordination between the MTA, New York City and New York State government must maintained in order to assess the feasibility of construction at the sites of many station proximal to Manhattan’s east bank. A massive survey of the topography of lower Manhattan will be conducted between 2014 and 2017 to address integration and accessibility issues and the changes that will have to be made in order to accommodate elevated entrances. In regards to an order of implementation, Subway stations with the highest risk of incurring floodwaters (closest to the shore, lowest critical elevation) would be elevated first. This method of implementation would allow officials to evaluate the effectiveness of this strategy by testing the impermeability of the first elevated station before moving construction forward onto further stations. However, an in-depth survey of every subway station lying below Canal Street and east of Broadway must be conducted to document their respective LCEs, proximity to the East River, and overall susceptibility to flooding to determine the order of implementation. As proposed by this report, starting June 2014, a survey of this sort would commence. Similarly, the cost of construction per subway line would have to be determined within the three-year period (2014-2017) set aside for information gathering. This way, funds can be allocated per subway line and would ensure that under river tunnels are protected one and at a time. A possible source of funding could be the federal government (The Department of Transportation). The daily $23 million lost due to transportation shutdown reflects the economic lag resulting from the loss of transportation options, especially in lower Manhattan where Wall Street, one of the nation’s, if not the world’s, largest economic hub resides (Jacob et al., 2011). Funds allotted from the federal government could take time to process; therefore, roughly 15 years will be given per subway line for construction so that by 2080, the R, 2, 3, 4, 5, and F line stations will be elevated. Strategy: Elevated Subway GratesBecause the New York City’s public transit system in lower Manhattan is an underground infrastructure, it is extremely vulnerable to flooding, especially flooding caused by storm surge. In August 2007, 3.5 inches fell within two hours during the morning rush. More than 30 sections of the subway network were flooded, practically crippling the system (Metropolitan Transportation Authority 2007). In 2012, damages from Tropical Storm Sandy shut down subway service beneath 34th Street for one week, and even longer for select lines. One cause for this vulnerability is the floodwater that flows from the street into subway ventilation grates, and inevitably onto the subway tracks, which lay 30 feet below (Metropolitan Transportation Authority 2007). The MTA’s drainage system can only handle 1.5 inches of rain per hour, meaning that any rainfall exceeding this amount could potentially paralyze the system (Chan 2007). Unfortunately for their poor water capacity, subway grates often prove to be necessary components to our underground transportation system. According to Tunnels and Tunneling International, underground trains’ auxiliary systems and breaks cause a great deal of heat, which would be contained within subway tunnels if it were not for subway grates (SOURCE?). Additionally, subway grates serve to combat the “piston effect,” which is an increase in pressure caused “when air is trapped in a shaft and forced through by a moving object.” (SOURCE?) Lastly, subway grates help to regulate temperature and humidity within subway tunnels by allowing fresh air to enter the tunnels and smoke to exit through the grate in the event of a fire. Because subway grates prove to be critical components of the mass transit system, the MTA searched for methods to make necessary subway grates more resistant to flood water. In 2008, under then-CEO and Executive Director Elliot Sander, a new proposal was made to modify subway ventilation grates by increasing their elevation 6 to 18 inches above the sidewalk. Rogers Marvel Architects and di Domenico + Partners proposed that these ventilation grates be elevated in an effort to divert some of the water and rubbish from entering the subway system. This same year, the MTA began examining the 1,212 grates located in Hillside, Queens to determine which of these were necessary. Over 200 were planned to be elevated, and another 300 were deemed un-necessary and were to be permanently sealed (Metropolitan Transportation Authority 2007). These grates have also been introduced in Astoria, Queens and along West Broadway in Manhattan. To combat flooding in low elevation areas surrounding East River subway tunnels, these elevation grates can be implemented in the areas surrounding subway stations in these areas. (Duap, David W. 2008).To make the structures more aesthetically pleasing, they would be modeled to have a dual purpose as either bike racks or seats for weary pedestrians. A year later, the MTA enacted a $31 Million budget to combat flooding in underground subway tunnels. Rogers Marvel Architects would later receive an award for their efforts in assisting the MTA with combatting flood impacts. Although these elevated subway grates would not be effective in high intensity storm surge events (such as those expected to face a 500% increase in frequency), the grates can help to divert at least some of the water that would have otherwise infiltrated the subway tunnels below. It would be most effective to implement these structures in areas of lower Manhattan that are most susceptible to storm surge flooding, and then use sandbags to block a percentage of the additional flood water. These subway grates would also be an effective means of keeping rubbish from falling through the ventilation grates and onto the subway tracks. This has the potential to decrease the amount of time that task forces are required to clean up the tracks in preparation for a high intensity storm.Discussion: Elevated Subway GratesThe established criteria that have been decided upon for the purpose of evaluating the strategies are as follows: feasibility, cost, and efficiency. Taking these factors into consideration, elevated subway grates are clearly feasible for the lower Manhattan region along the East River. These grates have been implemented in various areas throughout Queens and there are even some on West Broadway in the TriBeCa area of lower Manhattan. Although the MTA has made the cost of these structures available to the public, in comparison with the other strategies suggested to prevent the flooding of East River Subway tunnels, it is clear that elevated subway grates are one of the cheaper options. Finally, these elevated grates are also quite effective in stopping flooding. For example, in August 2007, flash flooding led to temporary delays in the running of the mass transit system. A year later, after the installation of subway grates in Hillside Queens, when the city was faced with Hurricane Hanna, the MTA was only shut down for a total of 15 minutes along the F line. This decrease in recovery time proves the efficiency of the elevated subway grates in this region. The main possible exception to their effectiveness would be flooding that is caused by a 1-in-100 year storm, but this should not be a deterrent, as these storm events are quite rare.In 2008, the MTA allotted a $31 million budget to protect the subways from flooding (SOURCE?). Because of the feasibility and efficacy of elevated subway grates, it would be sensible for the MTA to increase funding for this project to be extended to grates surrounding the East River subway tunnels and stations. If the MTA were to increase the cost of the unlimited monthly MetroCard, even by a mere $10 a month, and dedicate this increased revenue solely to flood prevention, it could be a potential source for funding. Additionally, because of the large influence that the MTA has on commuters living in New York City, the MTA can request that the federal government step in (as they did when the MTA first emerged) and ask that the government contribute to its budget for flood prevention.Strategy: Subway Tunnel PlugsA simple yet effective way of tackling the flooding in the subway tunnels is by blocking it as one would block a drain or a whine bottle: with a plug. The Department of Homeland Security, or DHS, is currently developing an inflatable tunnel plug whose purpose would to block any source of water from filling the tunnels (Ahlers 2012). Originally designed as protection from potential terrorist attacks, these plugs are 32 feet long and 16 feet in diameter (Department of Homeland Security 2012), designed to mold to the shape of the tunnel and block out whatever may come at them (Figure 3). Made from Vectran, a flexible yet durable fiber that is moisture and impact resistant, they can withstand up to 500,000 pounds of force (Department of Homeland Security 2012). Vectran is the same material used by NASA to engineer astronaut suits and to make space-bound objects more durable. Not only is it is designed to block out water, but also debris and grime from subway tunnels as well as any creatures that may decide to try feasting upon the plug. According to the DHS, one plug takes a total of thirty minutes to be inflated and pressurized to its maximum by an electronic pump. Our proposed plan of action is to place two plugs in each of the East River subway tunnels, those essentially connecting Manhattan and Brooklyn. The plugs would be attached to the side of the subway tunnel, in protective casing, and released and inflated when there is risk of flooding due to storm surge. The plugs would be installed in the 4/5, A/C, 2/3, N, and B/D subway tunnels, all of which are in the lower east side of Manhattan and all of which were flooded after Tropical Storm Sandy. More than two plugs may be installed based on risk of flooding of each tunnel. By 2080, all of the subway tunnels should be protected from any flooding in a storm event of a category two or less.Figure 3: Figure 3: A fully inflated and pressurized tunnel plug taken next to a human. Plugs are 16 ft in diameter and 32 ft wide. (Solon, 2012)Discussion: Subway Tunnel PlugsThese plugs, although fairly simple in design, are quite effective in blocking water, keeping the tunnels from flooding. This plan is also not expensive; The DHS has estimated that each plug would cost around $400,000. The MTA, with aid from the federal and state government, will find that it is an easier and more cost-effective alternative to strategies such as sea walls. Although the plugs do not completely block out all of the water, depending on the amount and the force, they do block a significant amount, enough for the already installed water pumps to be able to handle. The water may filter in from other areas, but the plugs should block out most of it, minimizing the damage to the subway tunnels. The larger issue is that the plugs are not fully developed and may need to be altered somewhat to fit in each tunnel. The development process may take another two to five years before the plugs can be properly installed. On top of that, the MTA will need aid from the government, so a great deal of convincing and petitioning of will need to take place. Much patience will be needed, but this strategy will, in the long run, protect much of lower Manhattan as well as save the city millions of dollars.Strategies: Interim Flood ReliefAlthough our goal is to prevent any flooding in the East River subway tunnels, this will not be accomplished in all tunnels by the year 2082.? Therefore, it is necessary to have certain “backup” strategies to use in the meantime in preparation for the storm surge flooding that may happen during a hurricane.One possible option for use between now and 2082 would be to assign a task force, hired by the MTA, to clear any rubbish out of the storm drainage system below Canal Street the day before a hurricane or tropical storm is due to hit.? This way, the drains would be at optimal water-holding capacity during the storm and they would not fill up as quickly.? Since the MTA’s drainage system can only handle 1.5 inches of rain per hour (Metropolitan Transportation Authority 2007), it is imperative that they begin a storm at optimal capacity to prevent the water from overflowing and backing up.? This would cost the MTA whatever fee would be necessary to hire a cleaning crew to remove the rubbish from the drains. If certain subway tunnels below Canal Street were to flood during a hurricane between now and 2050, having each station equipped with high-capacity sump pumps could be quite useful in removing water after the storm.? Currently, the MTA’s sump pumps can remove water in a tunnel at a rate of 17 gallons per minute (Metropolitan Transportation Authority 2007).? Installing pumps that remove water at a rate of 5,000 gallons per minute would increase efficiency by 300 percent.? If four pumps were installed in each station, this would reduce the amount of time needed to clear top-to-bottom flooding out of a tunnel to at most five days.? Discussion: Interim Flood ReliefAlthough it could possibly be beneficial to hire a clean up crew to clear out the storm drains prior to a hurricane, more research would need to be done on the possible benefits of a cleaning crew. Before implementing this as a necessary course of action before each Category 2 hurricane or lower, the MTA would need to conduct research on whether or not clearing the rubbish out of the drains before a hurricane would make enough of an impact on keeping water out of the tunnels to warrant hiring a clean up crew to take care of this. Additionally, if the studies did show that cleaning out the drains would in fact make a significant difference in the amount of water entering the tunnels, even more research would need to be conducted to see if paying an outside business to do this work would be cost effective in regard to the amount of water that would be kept out of the tunnels. This is why the idea of hiring a clean up crew prior to storms cannot be fully endorsed at the moment, as more research into the topic is clearly needed.As for the sump pumps, there are issues with these as well. However, there are several drawbacks to sump pumps.? Firstly, their pumping efficiency would be greatly reduced in the event of combined sewer overflow.? Additionally, if the power were to go out the pumps would be rendered useless.? This could, however, be remedied by purchasing backup generators at approximately $1,500 apiece (Jacob et al 2011), provided that the generators could reach pumps deep in a tunnel, but this cost would be on top of the few thousand dollars needed to purchase each high capacity sump pump.? In order to maximize efficiency and decrease expense, portable pumps and generators should be purchased first and be readily available for a Category 2 hurricane or lower, while sump pumps upgrades would need to take place gradually, perhaps upgrading one East River tunnel every two years. Sump pumps are therefore a possible option for use between now and 2082 to help the East River subway tunnels clear out any water that enters them as a result of storm surge, but because they are not directly related to keeping water out of the subway tunnels they would not be included as part of the main implementation plan.Conclusion:After much careful research and analysis, several strategies were found that can be implemented to help eradicate the problem of East River subway tunnels flooding during a Category 2 hurricane or lower. Subway tunnel plugs and elevated subway grates would be two of the most efficient and cost-effective ways of keeping water out of the tunnels, and due to their relative ease of implementation should not pose a great deal of problems in their actual institution. Although elevated subway entrances would not be nearly as easy to implement as the two aforementioned strategies, the fact that they would be greatly effective in keeping water out of the tunnels means that it would be worth conducting further research on how to more easily integrate them into city streets that are so busy each day. Implementing these three strategies to all East River subway lines below Canal Street by the year 2082 should provide a good chance of completely protecting the East River tunnels from flooding during a Category 2 hurricane or lower. Reaching this goal would then prevent New York City from losing $23 million each day the subway system is shut down due to storm surge-related flooding.Works CitedAhlers, Mike M. “Huge Plugs Could Have Spared Subways from Flooding, Developers Say – .”?CNN. Cable News Network, 01 Nov. 2012. Web. 30 Nov. 2012.Badger, Emily. “5 Ideas That Could Have Prevented Flooding in New York.”?The Atlantic Cities. N.p., 31 Oct. 2012. Web. 30 Nov. 2012.Chan, Sewell. “Flooding Cripples Subway System.”?The New York Times. N.p., 8 Aug. 2007. Web. 30 Nov. 2012.Chan, Sewell. “Why the Subways Flood.”?The New York Times. N.p., 8 Aug. 2007. Web. 30 Nov. 2012.Duap, David W. “New Subway Grates Add Aesthetics to Flood Protection.”?The New York Times. N.p., 19 Sept. 2008. Web. 14 Nov. 2012.Dzieza, Josh. “Hurricane Sandy’s Lesson for Flood-Proofing a Subway.”?The Daily Beast. N.p., 4 Nov. 2012. Web. 30 Nov. 2012.Fernquest, John. “Can It Flood in the Subway?”?Bangkok Post: Learning. Bangkok Post, 28 Oct. 2011. Web. 30 Nov. 2012.Gornitz, Vivien.?Sea Level Rise and Storm Hazards, New York City. Publication. NASA/Goddard Institute for Space Studies and Columbia University, 2007. Web. 14 Nov. 2012.Jacob, Klaus, George Deodatis, John Atlas, Morgan Whitcomb, Madeleine Lopeman, Olga Markogiannaki, Kennett Zackary, Morla Aurelie, Robin Leichenko, and Peter Vancura. “Transportation.”?Responding To Climate Change In New York State: The CLIMAID Integrated Assessment For Effective Climate Change Adaptation In New York State: Final Report. Vol. 1244. Oxford: Blackwell Science Publ, 2011. 299-362. Annals of the New York Academy of Sciences.?Web of Science. Web. 14 Nov. 2012.Jacob, Klaus H., Noah Edelblum, and Jonathan Arnold.?Risk Increase to Infrastructure Due to Sea Level Rise. Rep. N.p.: n.p., n.d.?Metropolitan East Coast Regional Assessment. CIESIN Columbia University, 2001. Web. 20 Nov. 2012.Lin, Ning, Kerry Emanuel, Michael Oppenheimer, and Erik Vanmarcke. “Physically Based Assessment of Hurricane Surge Threat Under Climate Change.”?Nature Climate Change?2.6 (2012): 462-67.?Web of Science. Web. 14 Nov. 2012.Metropolitan Transportation Authority.?August 8th, 2007: Storm Report. Rep. 20 Sept. 2007. Web. 14 Nov. 2012.“MTA Flood Mitigation Street Furniture & Urban Plan.”?Rogers Marvel Architects. Web. 30 Nov. 2012.Teo, Audrey, and Jenny Woo.?Integration of MRT Entrance with Private Development. Rep. Land Transport Authority, 2011. Web. 30 Nov. 2012. ................
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