National Wetlands
Inventory Mapping In
Vermont
Ralph Tiner, Regional Wetland Coordinator
U.S. Fish and Wildlife Service
Northeast Region
Hadley, MA
Background
 National Program
 90% of coterminous
US mapped
 50% digitized
 Regional Status
 12 of 13 states
mapped
 Updating in progress
on a FWS priority
basis and where
outside funding is
received
Purpose of Mapping
 To inventory wetlands across the nation for natural
resource conservation purposes
 To identify and classify larger wetlands based on
photointerpretation (recognizing limitations inherent in
this approach)
 To report on the status and trends of US wetlands
and for states as mapping is completed
 The NWI is not designed to map all the wetlands in
any locality – that would require on-the-ground
surveys applying wetland delineation techniques
Limitations of Photointerpretation for
Mapping Wetlands
 Photo Scale
 Seasonality (environmental conditions at time
of photo capture)
 Photo Quality
 Wetlands that are difficult to photointerpret
Photo Scale vs. Area
Scale
1:80K
1:58K
1:40K
1:24K
1:12K
Area In One Square Inch
1020 acres
540 acres
~250 acres
92 acres
~25 acres
Photo Scale vs. Mapping Unit
Photo Scale vs. Target Mapping Unit
 1:80,000 = 3-5 acres
 1:58,000 = 1-3 acres
 1:40,000 = 1 acre
 1:24,000 = 0.25-0.50 acre
 1:12,000 = 0.10 acre
1:80K vs. 1:58K
1:40K vs. 1:24K
1:24K vs. 1:12K
1:80K vs. 1:40K
1:80K vs. 1:12K
Photo Scale vs. # of Photos
Scale
1:80,000
1:58,000
1:40,000
1:24,000
1:12,000
# of Photos/Quad
1
1.5
4
20
42
#Photos/VT*
160
240
640
3200
6720
*Estimates based on 58 sq. mi/quad and Vermont land
surface area.
May be approx. 220 quads (1:24K) covering the state
Pen Width vs. Ground Distance
Earlier maps were hand-drawn, so pen-width
was a factor.
Scale
000 (0.25mm) 0000 (0.18mm)
1:80K
~67ft
~50ft
1:58K
48ft
34ft
1:40K
33ft
23ft
1:24K
20ft
14ft
1:12K
10ft
7ft
Scale Limits on Wetlands
 Not simply acreage dependent
 Relates to shape

one-acre block vs. one-acre linear
 Relates to easy or difficulty of
photointerpretation of type
Wetland Type
 Easy to identify types

Marshes, bogs, seasonally flooded swamps,
ponds
 Harder to identify types




Drier-end wetlands
Evergreen forested wetlands
Temporarily flooded wetlands
Wetlands on slopes (seepage)
Seasonality
 Environmental Conditions






Leaf on vs. Leaf off
Spring vs. Fall (leaf off)
Ambient weather
Water tables and flooding
Extreme flooding vs. droughts
Snow and ice
Photo Quality
 Emulsion



Black and White (panchromatic)
True Color
Color Infrared
 Resolution
 Processing (over vs. under exposed)
 Date (best available at 1:40K or smaller; now
use DOQ/DOQQ)
Original NWI Maps for Vermont





1:80,000 CIR
October 1977
Target Mapping Unit = 3-5 acres
Inventory done in late 1970s/1980.
Mapping Procedures





Photointerpretation
Limited Field Work
Consultation with Soil Surveys? (No hydric soils
lists/indicators)
Regional QC (spot checking)
National QC (spot checking)
NWI Results vs. Hydric Soils
NWI
Soil Data
220,000 acres
3.7% of the state
341,000 acres
5.5%
Updated NWI Mapping




1:40,000 CIR
1992-1994
Target Mapping Unit = 1 acre
Mapping Procedures






Edit original NWI data
Photointerpretation
Limited field checking
Consult with soil surveys (interpretation)
Regional QC (entire photo)
National QC (automated verification)
Status of Updates in Vermont
New Mapping Procedures (2006)
 Edit existing NWI data
 Photointerpretation on-screen

DOQ or DOQQ base
 Limited field checking
 FWS QC, automated verification
 Add undeveloped hydric soil map units
 FWS QC, automated verification
Enhanced NWI
 Current NWI database
 Add other descriptors:




Landscape Position
Landform
Water Flow Path
Waterbody Type
 Use data to predict wetland functions
LLWW Descriptors
 Landscape Position
 Lotic, Lentic, Terrene
 Landform
 Floodplain, Basin, Flat, Fringe, Slope
 Water Flow Path
 Inflow, Outflow, Throughflow, Bidirectional
Flow, Isolated
 Waterbody Type
 Pond and lake types, impounded rivers, etc.
Functional Assessment
9 Functions for Inland Wetlands
 Surface Water Detention
 Streamflow Maintenance
 Nutrient Transformation
 Sediment Retention
 Shoreline Stabilization
 Fish and Shellfish Habitat
 Waterfowl/Waterbird Habitat
 Other Wildlife Habitat
 Conservation of Biodiversity
Updated NWI - Highlights





Smaller wetlands
Refined boundaries
Incorporates more hydric soil map units
Can be enhanced to be more descriptive
After enhancement, can use for preliminary
functional assessments
 Still will not map all wetlands – need ground
surveys applying delineation procedures to
do this; potential vernal pool mapping through
remote sensing