Flood Map Updates Underway – Sept 2020

New flood studies are underway in many watersheds of Vermont.  If consistently funded, the timeline from the initial Discovery meetings to the effective date of new Flood Insurance Rate Maps, is typically about five years.  The table below summarizes updates from Kerry Bogdan, FEMA Region 1 Senior Engineer and FEMA Regional Risk MAP Geospatial Lead as of 9/3/2020

Watershed

Discovery Meetings

Contractor

Missisquoi with
Franklin and Orleans Counties
Discovery Report Spring 2019
Surveying is completed.
Enhanced hydrology and hydraulics will begin soon.
USGS
Lamoille Discovery Meetings 2019.
Field Survey for priority reaches will be initiated in
spring 2021. This study has been funded through
Hydrologic and Hydraulic analysis.
Compass
Winooski Reviewing previously completed
2D Rain on Grid Large Scale Automated Engineering
(LSAE)
Compass
Otter Creek DM October 29, 30, 2019
Selection of priority reaches is complete.
Surveying is underway.
USGS
Lake Champlain DM October 29, 2019 
Floodplain mapping as redelineation
will proceed with neighboring watersheds.
USGS
Mettowee and Hudson-Hoosic Initiating 2D LSAE

Compass

Passumpsic Watershed DM October 28, 2019 
Selection of priority reaches is complete.
Surveying is underway.
USGS
Waits River, Ompompanoosuc, Stevens 
(As Mascoma Study)
Virtual Discovery Meetings 5/26/20,
5/27/2020 and 6/2/2020
USGS
White River Virtual Discovery Meetings 5/26/20,
5/27/2020 and 6/2/2020
USGS
Black-Ottauquechee and West Contracted summer 2020

Compass

Middle Connecticut
(South of Brattleboro)
Preliminary FIRMs and FIS are projected
to be issued to communities in summer 2022.
This study has been funded through the
Community Consultation Officer (CCO) meeting.
Compass
Deerfield Discovery Meeting 2019. 
Discovery report is undergoing final review
and will be issued to communities in fall 2020.
Hydrology for the watershed study is ongoing.
This study has been funded through
Preliminary FIRMs and FIS, which are projected
to be issued to communities in spring 2023.
Compass

Regarding the Mapping Process

2D Rain on Grid Large Scale Automated Engineering (LSAE) and Base-Level Engineering (BLE) methods generate computer model-based Zone A flood maps.  Zone As are high risk Special Flood Hazard Areas that do not have published Base Flood Elevations.  This process requires high quality topographic data, such as the equivalent of two-foot contours, or better, from lidar.   Vermont now has acquired lidar across the state through a multi-agency partnership led by the Vermont Center for Geographic Information.  Much of this contour information, in one foot or two foot intervals, is available now in tile form, or in small custom clips.

Model-based Zone A maps provide a significant improvement in the quality of flood risk identification in places that otherwise have no maps, or hand-drawn Zone A maps.   In low density areas, model-based Zone A maps, may be incorporated directly into future updated Flood Insurance Rate Maps (FIRM).   Model-based Zone As were incorporated into the most recent Digital FIRM of 2015 in Bennington County and these can be viewed on the Flood Ready Atlas bit.ly/floodatlas   

Detailed studies require additional work to integrate field survey and construction details about bridge constrictions and other data.  This level of study is typically focused on areas with more people living in or near floodplains, and is prioritized during the Discovery processes with input from municipal officials. 

The Flood Ready Atlas bit.ly/floodatlas displays only officially-digitized Flood Insurance Rate Maps (DFIRMs).  A special layer on the Flood Ready Atlas indicates the current extent of Digital FIRMs and paper FIRMs.   All effective FIRMs can be viewed from the FEMA Map Service Center at www.msc.fema.gov

Ultimately, the updated Flood Insurance Rate Maps (FIRM) will inform the flood hazard management of communities that participate in the National Flood Insurance Program.  Broadly, this update process will provide a substantial improvement in the level of map accuracy and precision.

Municipal Deadline 

At least six months before the effective date of the new FIRMs communities need to have had their bylaws reviewed and approved by FEMA Region 1 as meeting or exceeding the requirements for participation in the NFIP.   Please be in contact with your Regional Floodplain Manager regarding your current bylaw standards.

www.FloodReady.vt.gov has more information on Flood ResilienceFlood Hazard Areas and Hazard Area Maps and Flood Hazard Bylaw Updates