In contrast to the innumerable local flood measures that would be required to protect vulnerable infrastructure, it seems possible to protect the core of the city and northern New Jersey docks and transportation facilities with three storm surge barriers and associated embankments constructed at strategic locations. These structures would be placed at: (1) the Verrazano Narrows; (2) the mouth ofArthur Kill near Perth Amboy; and (3) across the upper East River near the Whitestone Bridge (see Figure 9.1). Protecting southern Brooklyn, Queens, Jamaica Bay and JFK airport would require a fourth barrier across Rockaway Inlet and extensive seawall extensions.
Based on current NASA GISS projections of sea level rise to the year 2100 (see Figure 9.6) and SLOSH modeling (see Figure 9.4), each barrier would need to be about 15 m in height with associated seawalls stretching to higher ground. But this is a first estimate. Given the high uncertainty in projected rates of sea level rise and changes in weather patterns, more careful calculations based on the improved surge models that are under development and the best climate models are needed. Planning must take into account the worst case that could ever be contemplated over the life of the barriers (say 200 years); anything less would be inviting disaster.
The barriers would normally be kept in the fully opened position. During unusually powerful tropical storms and hurricanes, the barriers would be closed for periods of hours to block the associated surge. For nor'easters, the barriers might be closed only during high tides, and opened intermittently over a few days as opportunities arose near low tide to release impounded water.
The surprise is that the feasibility of this concept to protect the NY-NJ metropolitan area has not yet been established. While there would be many engineering challenges to be overcome, there can be little doubt that such structures could be built, the questions are:
• How physically and cost effective would barriers be in protecting the city core?
• Would such barriers amplify surges on the weather (ocean) side to an unacceptable degree?
• Would the rivers swollen with rainfall lead to flooding within the barriers anyway?
• Would there be sufficient protection and greater cost-effectiveness with partial blockage at some of the barrier locations?
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