using soil attributes for hgm wetland classification · 2017-09-21 · epipedon horizon •...
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Slide 1
Using Soil Attributes for HGM Wetland Classification
Richard Weber Wetland Hydraulic Engineer Wetland Team (Ret.) CNTSC, Fort Worth, TX
Data Sources:
Slide 2
• Web Soil Survey • County Scale • Smaller than Reference Domain • Pre-built Interpretations
• Geospatial Data Gateway • Statewide Data • Raster and Vector • Larger than Reference Domain • User Selected Interpretations • MLRA Attribute Selection
“crunches” an entire State’s data
Slide 3
Major Land Resource Areas
GIS Layer – Geospatial Data Gateway
Slide 4
The Reference Domain
The area within which a defined Subclass Exists
Major Land Resource Area is a Good Default
MLRA Subdivisions may Exist for Further Refinement
Slide 5
Map Unit Polygons – Also Occupy Landscape Positons in the Watershed
SSURGO Geomorphic Descriptions are Useful, i.e.: • Upland Drainageway • Terrace • Floodplain • Depression • Many, many others used
Hydrologic Soil Group - HSG
Slide 6
Developed ONLY for use to determine Runoff Curve Number (RCN) – NRCS RCN Method • HSG – A, B, C, or D • A – Low runoff (think sponge) • Low Runoff infers high recharge • D – High Runoff (think Duck’s back) • High Runoff infers low recharge
• Important in assessing wetland watershed
• Q: Is a watershed of HSG A or B soils likely
to support Discharge Wetlands? • HSG is in both WSS and SSURGO data
Slope Class
Slide 7
• Soil Map Units have Slope Class Data • Only Available in SSURGO • Directly Applicable to Mineral Flats (0-2%)
Willamette Valley, Oregon Wet Prairie (Tufted Hairgrass Provides Microtopography)
Slide 8
Water Features •WSS Provides Flooding, Ponding, and Groundwater Frequency and Duration by Month – Quickly •SSURGO requires user to access multiple tables, BUT more detail is available •Flooding – Lotic – RIVERINE AND SLOPE Classes •Ponding – Lentic – DEPRESSION, and Depressions in RIVERINE
Slide 9
Taxonomy: Use With Care: • Orders:
• Histosols – ORGANIC FLATS and discharge sites like SLOPE and Discharge DEPRESSION
• Require near continuous saturation to form and maintain
• Entisols – Young Soils like floodplains • Suborders:
• Aquic (wet), Fluvic (water formed) • Great Groups
• Includes Minerology – Calcic indicates discharge • Sub-Groups • Available in both WSS and SSURGO • Lack of evidence in the taxononomy does NOT mean
absence of the attribute • Presence of evidence in the name is more useful
Slide 10
“Endo”saturated and “Epi”saturated Great Groups: Use With Care: • Endosaturated soils indicate Discharge • Episaturated soils indicate Recharge • Definition is depth of saturation down to 200
cm – Not meant to be a hydrodynamic interp.
• Typical Episaturated wetlands: Episaturated RIVERINE, Recharge DEPRESSION, MINERAL FLAT
• Typical Endosaturated wetlands: SLOPE, Discharge DEPRESSION, Endosaturated RIVERINE
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Minerals and Great Groups
• Groundwater Dissolved Minerals • At point of Discharge, ET leaves mineral
concentrations behind • Best Example is Calcium (calcic), ex:
“calciaquolls” • Horizonation - Bk
Slide 12
Saturated Hydraulic Conductivity (Ksat) Function of: • Texture • Structure • Bulk Density • Others Increase in Ksat with Depth Indicates Vertical Downward Movement (Recharge) • Recharge Wetlands – MINERAL FLATS,
Recharge DEPRESSIONS • Episaturated RIVERINE • Ex. – Bt horizons
Slide 13
Other Useful Soil Attributes from SSURGO:
• Geomorphic Description • Drainage Class • Slope Class • Taxonomy • Horizons • Water Features
• Flooding Freq. and Dur. • Ponding Freq. and Dur. • Groundwater Depths
Useful Database Tables: • Component • Map Unit • Map Unit Aggregated
Attributes (muaggat)
Digital Elevation Data Can be used also to Aggregate and Dis-Aggregate Map Units Beyond our Scope Today…
Slide 14
Selection by Attributes •SSURGO Vector Polygons •Site or HUC-12 Scale •“Heads-up” Mapping
Red • Calcareous Wet Prairie • MINERAL FLAT Green • Calcareous Marsh • DEPRESSION
Slide 15
HUC -12 Scale •Large Enough to Display all HGM subclasses •Small Enough to Visualize
Floodplain Landscape
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RIVERINE ATTRIBUTES
• Geomorphic Descrition – “floodplain” term • Water Features – “Flooding” means Lotic
inundation • Flood Frequency – higher than “Rarely” • RIVERINE Water Features can include Flooding,
Ponding, and Groundwater – all 3
Slide 17
RIVERINE Soil System – Multiple HGM Sub-Classes • Look for more geomorphic description detail –
Ex. – “Backswamps, Natural Levees, Oxbows on Floodplains”
• Look for more Water Features. Ex. – “Ponding” means it’s a backswamp
Slide 18
Problem! – Stream Functions Vary with Scale
2nd Order Kennebec
5th Order Kennebec
Map Unit Dis-Aggregation
SLOPE – Headwater Reaches
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• Look for: • High Water Table • Histosols or Histic
Epipedon Horizon • Non-Floodplain
geomorph (i.e. Upland Drainageways)
• No decrease in Ksat with Depth
Slide 20
Landscape Functional Break: SLOPE to RIVERINE HGM Class
Blue – Ackmore Colo Complex, Endoaqolls, Upland Drainageways, WTD < 12” – SLOPE Class
Green – Floodplains
Slide 21
SLOPE Wetlands – Watershed Reaches Above Floodplains
Attributes: • Taxonomy – “endosaturated” Great Group • Taxonony – Histosol or Histic • Geomorphic Description – Ex. “upland
drainageways” • Water Features – WTD < 12”, most months
Kansas Headwater
Idaho Headwater Fen
New York Headwater Fen
Slide 22
Nebraska Rainwater Basin – Recharge DEPRESSION
Wyoming – Recharge DEPRESSION, Gillette
South Dakota Prairie Pothole – Recharge DEPRESSION South Carolina – Carolina Bay
Discharge DEPRESSION
DEPRESSION CLASS
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DEPRESSION - Recharge
• Horizonation – Perching Layer. Look for Bt horizon
• Drastic decrease in Ksat with depth
Slide 24
DEPRESSION - Discharge
No perching layer
Taxonomy Ex. – Calcic subgroup
Taxonomy – Histosols or Histic
Recharge Go > GI Discharge Gi > Go Flow Through Gi = Go
High Infiltration Uplands Support Strong Discharge Wetlands
Slide 25
MINERAL FLAT and DEPRESSION Brown – MINERAL FLATS • Interfluves (geomorphic desc.) • 0-2% Slope Class • Poorly Drained • Also – Decrease in Ksat with
Depth • Water Features – no ponding, no
flooding, only WTD < 12”
Yellow – DEPRESSION • Depressions (geomorphic desc.) • Ponding Frequency and
Duration • No Flooding
Slide 26
Defining Landscape Ecological Function with the use of Hydrodynamic Vectors
Slide 27
Wetland sub-classes: • Have a System Boundary • Same Water Budget within the boundary • Same Ecological Functions within the
boundary • Same Plant Community • Same Maintenance Processes • Same Response to Disturbance • Same Management Prescriptions • Same Soil Attributes
Hydrology Informed Wetland Classification
Slide 28
Ecological Site Descriptions • Starts with Plant Community • States in Transition Driven by Disturbance Hydrogeomorphic (HGM) Landscape Classification • Landscape and Hydrology Based • Originally Developed for Wetland Functional
Assessment Cooperative Soil Survey • Mapping Driven by Landscape and Hydrologic
Factors
Existing Landscape Classification Concepts
Slide 29
Tool for Wetland Definition Using Soils and Hydrology - Needs
• Simple • Qualitative to Quantitative • Translates to Spatial Mapping and
Modeling • Provides Visual Representation • Uses Existing Soils Database • Applies to all landscapes • One-dimensional to three-dimensional
Slide 30
Nebraska Sandhills
Indiana Flatwoods
High Plains Colorado
Prairie Pothole Region
Uplands (Interfluves)
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Wet Interfluves- Mineral Flats
• < 1 acre Drainage Area • WT < 12” • Feeds Discharge Sites
Delmarva Peninsula
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Moist Upland Sites
Headwaters
Utah
Idaho Panhandle
Iowa Des Moines Lobe
Nebraska Sandhills
Slide 37
Losing Watershed Reaches NOT A WETLAND
Slide 38
Wet Headwaters
Boundary County, ID
Slide 39
Groundwater Supply is increased with HSG A, B Soils
Slide 40
Closed Recharge Depressions
Prairie Potholes
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Slide 42
Closed Recharge Depressions and Wet Headwaters
Slide 43
Slide 44
Landscape Definitions Vector Parameters – Magnitude and Direction • Runoff • Runon • Recharge • Discharge Apply to Landforms: • Watershed Elements
– Interfluves – Headwaters – Stream Corridors
Slide 45
Jasper County, IA • Brown –
Recharge/Discharge Mineral Flat
• Green – Runon/Discharge Depression
• Blue – Runon/Recharge/Discharge Headwater
• Yellow – Runon/Runoff/Discharge Floodplain
Questions?
Wet Headwater – Kansas Flint Hills photo: Jon Fripp
Slide 47
Thanks!
NRCS is an Equal Opportunity Employer and Provider
Questions?
Wetland HydrologyTechnical Note: “Technical Note No. 3 - Soil Hydrodynamic Interpretations for Wetlands” http://www.nrcs.usda.gov/wps/portal/ nrcs/main/national/water/wetlands/restore/
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