NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Soil Survey Information for
Floodplain Mapping
USDA-NRCS
National Soil Survey Center
September 2013
David Hoover, National Leader, Soil Business Systems
Sharon Waltman, Soil Scientist, Geospatial Research Unit
NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
2
NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
3
NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Soil Formation
S
= f(s, c,o,r,p,a,n), where
 S = soil classes or attributes (to be modeled)
 s = soil, other or previously measured properties of the soil at a
point
 c = climate, climatic properties of the environment at a point
 o = organisms, including land cover and natural vegetation or
fauna or human activity
 r = topography, landscape attributes
 p = parent material, lithology
 a = age, the time factor
 n = spatial or geographic position
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
NRCS Flooding Definitions

National Soil Survey Handbook Section 618.30
 Definition.—“Flooding” is the temporary covering of the soil
surface by flowing water from any source, such as streams
overflowing their banks, runoff from adjacent or surrounding
slopes, inflow from high tides, or any combination of sources.
 Shallow water standing or flowing that is not concentrated as
local runoff during or shortly after rain or snowmelt is excluded
from the definition of flooding.
 Standing water (ponding) or water that forms a permanent
covering is also excluded from the definition.
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
NRCS Flooding Frequency Class
Flooding
Frequency Class
Definition
None
No reasonable possibility of flooding; one chance out of 500 of flooding in any year or
less than 1 time in 500 years.
Very rare
Flooding is very unlikely but is possible under extremely unusual weather conditions;
less than 1 percent chance of flooding in any year or less than 1 time in 100 years but
more than 1 time in 500 years.
Rare
Flooding is unlikely but is possible under unusual weather conditions; 1 to 5 percent
chance of flooding in any year or nearly 1 to 5 times in 100 years
Occasional
Flooding is expected infrequently under usual weather conditions; 5 to 50 percent
chance of flooding in any year or 5 to 50 times in 100 years.
Frequent
Flooding is likely to occur often under usual weather conditions; more than a 50
percent chance of flooding in any year (i.e., 50 times in 100 years), but less than a 50
percent chance of flooding in all months in any year.
Very frequent
Flooding is likely to occur very often under usual weather conditions; more than a 50
percent chance of flooding in all months of any year.
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
NRCS Flooding Duration Class
Flooding
Duration Class
Duration
Extremely brief
0.1 to 4 hours
Very brief
4 hours to < 2 days
Brief
2 days to < 7 days
Long
7 days to < 30 days
Very long
> 30 days
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
NRCS Flooding Definitions
 Classes
- Estimates of flooding class are
based on the interpretation of soil
properties and other evidence gathered
during soil survey fieldwork.
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Soil Characteristics
NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Field Observed Clues to Flooding








Extent of flooded areas, flood debris in trees, damage to fences and bridges, and other signs
of maximum water height are recorded
Aerial photographs showing former river channels, oxbows, point bars, alluvial fans,
meander scrolls, sloughs, natural levees, backswamps, sand splays, and terraces
Vegetation that grows in flood areas may furnish clues to past flooding
Thin strata of material of contrasting color, texture, or both
An irregular decrease in organic matter content, not due to human-alteration by mixing or
transportation of material, which is an indication of a buried genetic surface horizon
Soil layers that have abrupt boundaries to contrasting kinds of material, which indicate that
the materials were laid down suddenly at different times and were from different sources or
were deposited from stream flows of different velocities
Laboratory analyses of properly sampled layers are often helpful in verifying these
observations. Organic carbon and particle-size analyses are particularly useful in verifying
flood deposits.
Microscopic observations may detect preferential horizontal orientation of plate-like
particles; microlayering, which indicates water-laid deposits; or mineralogical differences
between layers.
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
g Strong gleying
This symbol indicates either that iron
has been reduced and removed
during soil formation or that
saturation with stagnant water has
preserved it in a reduced state.
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Flooding and Water Table Reports
Flooding frequency is an annual
value. That annual value is shown in
the months in which it exists.
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Attribute Tables
Mapunit
Component
Comonth
 Using
SSURGO &
gSSURGO for Flood
Frequency Mapping
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1:500,000
Map Scale
FEMA Flood Hazard
Source: HSIP GOLD 2012
Flood Hazard Areas 1
Flooding Frequency and Duration relative to Soil Climate
Rainfall occurs mostly in the winter months for
Xeric or Mediterranean Soil Moisture Regime
January
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
February
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
March
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
April
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
May
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
June
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
July
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
August
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
September
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
October
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
November
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
December
Annual Flooding
Frequency Class
Very frequent
Frequent
Occasional
Rare
Very rare
• Annual Flooding Duration
January
Annual Flooding
Duration Class
Very long
Long
Brief
Very brief
Extremely brief
April
Annual Flooding
Duration Class
Very long
Long
Brief
Very brief
Extremely brief
August
Annual Flooding
Duration Class
Very long
Long
Brief
Very brief
Extremely brief
November
Annual Flooding
Duration Class
Very long
Long
Brief
Very brief
Extremely brief
FEMA Flood Hazard
Source: HSIP GOLD 2012
Flood Hazard Areas 1
NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Useful References
gSSURGO web site
 gSSURGO
Data Availability & Content
http://soils.usda.gov/survey/geography/ssurgo/description_gssurgo.html
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Useful References
 gSSURGO
Data Availability & Content
gSSURGO web site
gSSURGO User Guide & Fact Sheet
Geospatial Data Gateway FAQ
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Useful References
gSSURGO web site
gSSURGO User Guide & Fact Sheet
Geospatial Data Gateway & FAQ
 gSSURGO
Data Availability & Content
Scroll
Down to
“Soils”
section
http://datagateway.nrcs.usda.gov/GDGHome.aspx
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Useful References
 gSSURGO
gSSURGO web site
gSSURGO User Guide & Fact Sheet
Geospatial Data Gateway - Status Maps & FAQ
Data Availability & Content
http://datagateway.nrcs.usda.gov/GDGHome.aspx
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Content
Download from Gateway
Zip Archive Contains:
 gSSURGO
Data Availability & Content
http://soils.usda.gov/survey/geography/ssurgo/description_gssurgo.html
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Content
gSSURGO in ArcCatalog
SDM_State_XX file geodatabase
Valu_fy2013 file geodatabase
Metadata files
 gSSURGO
Data Availability & Content
http://soils.usda.gov/survey/geography/ssurgo/description_gssurgo.html
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Content
 gSSURGO
VALU Table Database
http://soils.usda.gov/survey/geography/ssurgo/description_gssurgo.html
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NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Example map using 10m gSSURGO Value Added Look Up (VALU) Table Database
“Ready to Map” theme
(http://soils.usda.gov/survey/geography/ssurgo/description_gssurgo.html)
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NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Historical Soil Survey Data
1913
1986
http://soils.usda.gov/survey/printed_surveys/
2012
45
NRCS
Natural Resources Conservation Service
NCSS
National Cooperative Soil Survey
Soils Web Sites

NRCS Soils Website - http://soils.usda.gov/
Latest information and links to technical and training documents

NRCS Soils YouTube Site – http://www.youtube.com/user/nrcsnssc
100s of videos on soil topics

Web Soil Survey - http://websoilsurvey.nrcs.usda.gov/app/
Site for viewing, downloading, and report preparation

SoilWeb - http://casoilresource.lawr.ucdavis.edu/gmap/
Soils data that is GPS enabled (if your device is)

National Soil Survey Handbook - http://soils.usda.gov/technical/handbook/
Guidelines and definitions

Geospatial Data Gateway - http://datagateway.nrcs.usda.gov/
Selection and download of SSURGO, gSSURGO and other data
46
NCSS
NRCS
National Cooperative Soil Survey
Natural Resources Conservation Service
Soil Survey Information
USDA-NRCS
National Soil Survey Center
September 2013
David Hoover
National Leader
Soil Business Systems
[email protected]
402-437-4013
Sharon Waltman
Soil Scientist
Geospatial Research Unit
[email protected]
304-293-9835
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