Final Environmental Impact Report - Whittier Bridge/I-95 ...

Whittier Bridge/I-95 Improvement Project FEIR
Chapter 1.0: Changes Since the Draft Environmental Impact Report and Resolution of Additional Issues
In the event the preparation of a contingency plan is required, this document will be submitted to the
Amesbury Conservation Commission and other regulatory agencies for review and approval prior to
implementation.
1.4.6 Hydraulic Analysis and Floodplain Issues
The DEIR Certificate requested that the FEIR include an analysis of the project‘s compliance with
the Federal Emergency Management Agency (FEMA) requirements for work within the floodplain.
A technical evaluation of the project‘s probable impact on the Merrimack River base (100-Year) flood
elevation profile and regulatory floodway delineation as determined within the 2012 Essex County
Flood Insurance Study (FIS) 1 was performed. An Executive Summary and brief narrative sections
discussing general project base floodplain regulatory compliance requirements, engineering
methods employed in this evaluation, and pertinent analytical results of the same follow directly.
Introduction
The purpose of this evaluation is to quantitatively determine the probable impact of project
implementation on the Merrimack River‘s existing National Flood Insurance Program (NFIP) base
flood elevation (BFE) profile and regulatory floodway delineation in proximity to the Whittier Bridge
crossing location. This evaluation was performed in a manner consistent with current Federal
Highway Administration (FHWA) and FEMA base floodplain coordination guidelines 2,3 . The results of
this evaluation are critical to establishing whether or not project implementation will necessitate
revision of existing Merrimack River NFIP base floodplain mapping products, and the degree to
which this project complies with Executive Order 11988 (EO 11988), Floodplain Management 4 .
Project Base (100-year) Floodplain Regulatory Compliance Requirements
The existing Whittier Bridge (Bridge No. A-07-016=N-11-007) crosses a reach of the Merrimack
River with a NFIP Zone AE Special Flood Hazard Area (SFHA) coding and a regulatory floodway
delineated within the mapped base (100-Year) floodplain limits. This NFIP SFHA designation means
that the river‘s BFE profile, and the horizontal limits of the regulatory floodway, have been
determined by application of detailed hydrologic/hydraulic engineering methods and are presented
within the affected communities Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM)
mapping. The Merrimack River‘s NFIP BFE profile at the Whittier Bridge crossing is shown on Flood
Profile Sheet 81P (Attachment 1) of the 2012 Essex County FIS. The limits of the river‘s local
regulatory floodway delineation are listed in Table 12, Floodway Data of that FIS, and illustrated on
Essex County Digital Flood Insurance Rate Map (DFIRM) Number 25009C0108F.
The proposed Whittier Bridge/I-95 Improvement Project is a federally funded action, with the FHWA
acting as the lead federal agency. As such, the project must comply with the terms of the National
Environmental Policy Act (NEPA). Because of the existing bridge‘s location relative to the Merrimack
River‘s NFIP base floodplain, FHWA regulations require that MassDOT demonstrate the project‘s
compliance with EO 11988 as part of the NEPA review process.
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2
3
4
Essex County Flood Insurance Study (FIS), July 2012.
Federal Emergency Management Agency, The National Flood Insurance Program and Related Regulations,
Code of Federal Regulations (CFR) Title 44, Parts 59, 60, 65, and 70 (44 CFR Parts 59, 60, 65, and 70).
Federal Highway Administration (FHWA), Procedures for Coordinating Highway Encroachments on Floodplains
with the Federal Emergency Management Agency, 23 CFR, Section 650.115, September 1992.
Executive Order 11988 - Floodplain Management, May 24, 1977.
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