Programmatic Environmental Assessment draft, Jan 2002

NYC 9/11 Public Portal Document

2.4.3 Floodplain Managetnent/Flood Hazard Reduction

The World Trade Center site was a complex of seven buildings on approximately 16 acres of property. Groundbreaking for construction of the WTC North and South Towers began in 1966 and both buildings were completed by 1973, although tenants leased the lower floors beginning in 1970. In 1972, the City of New York joined the National Flood Insurance Program (NFIP). The effective Flood Insurance Rate Map (FERM) for the WTC area is Community Panel Number 360497 0054B (54 of 131) dated November 16, 1983. According to the FIRM, a portion of the WTC site is situated in a special flood hazard area. Zone A5, having a base flood elevation of 10 feet. The WTC North and South Towers are considered pre-FIRM structures since construction was completed prior to the City’s participation in the NFIP and therefore fully compliant structures within the NFIP. Future development and construction within the delineated flood hazard area would require compliance with Federal, state, and local floodplain management regulations and requirements. HMGP funding may be used to reduce hazards related to flood reduction projects, as prioritized by the State of New York.

No Action Alternative

Under the No Action Alternative, no federal funds would be made available to undertake flood reduction activities. Those areas located in the floodplain would continue to remain at risk from flood disasters.

Proposed Action Alternative

The proposed Stormwater Management actions could include measures that would reduce the potential for flood damage from future flood events. Proposed projects would be implemented to mitigate the potential for flooding by removing critical infrastructure from flood prone areas, decreasing the quantity of runoff and controllmg stormflows, and managing erosion of area soils and the associated sedimentation into area waterways.

Stormwater System Resizing/Replacement/and Maintenance - Stormwater drainage systems may be re-sized, replaced, or maintained to increase or maintain the effectiveness of stormwater distribution. Re-sizing storm drainage to a larger diameter would increase the peak flow of stormwater and more effectively and quickly move stormwater downstream. However, downstream stormwater management would need to be considered.

Floodwall Construction - There is an existing floodwall constructed aroimd the perimeter of the WTC complex. This floodwall may need to be repaired, restored, replaced or new floodwalls may need to be constructed of impervious material. New floodwalls of varying heights (depending on the base flood elevations) may be needed to protect an area from flooding during times of increased flows. Floodwalls typically parallel rivers, but can be constructed around the structures they are to protect, including around entrances to subways and tunnels (including the PATH train tuimel).

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