Introduction to the Hydrogeomorphic (HGM) Classification System

Objectives – The Student Will be Able to:

• Define the 7 HGM Classes • List the 3 Parameters That Define HGM

Classes • List the Major Water Budget Components for

Each Class • Select Appropriate Local Reference Domains • Determine Useful Local HGM Sub-classes • Relate HGM Sub-Classes to Soils • Ready to Learn how to Select the Appropriate

Analysis Technique for Sub-Classes

HGM

•Originally for Development of “Functional Assessment Models” (Brinson, et. al.) •Starts with 7 Wetland Classes •Requires the Determination of a “Reference Domain” where a certain “subclass” exists •Must make a decision between “lumping” and “splitting”

Three Factors that Define Wetland Classes •Landscape Position •Dominant Water Source •Hydrodynamics

The Seven HGM Classes

•RIVERINE •SLOPE •MINERAL SOIL FLAT •ORGANIC SOIL FLAT •ESTUARINE FRINGE •LACUSTRINE FRINGE •DEPRESSION

Mineral Flats Indiana Flatwoods

Slope Puerto Rico

Depressional Carolina Bay

Estuarine Fringe Oregon

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Reference Domains - Major Land Resource Areas

Site Concept Valid Within MLRA Extent (or subdivision of MLRA)

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HUC-12 in MLRA 103 Northeast Kansas

• “Headwater” HUC • Similar to other Headwater

HUC in MLRA 103 “Reference Domain”

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Same Map Units Correlate to Similar Sub-Classes in Adjacent HUCS (Same MLRA)

Floodplain Landscape

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Landscape Boundaries - RIVERINE

Wabash Occasionally Flooded Poorly Drained Backswamp?

Kennebec Moderately Well Drained Occasionally Flooded Natural Levee?

RIVERINE Wetlands

Landscape Position Floodplains Dominant Water Source Surface Flooding AND/OR Groundwater Inputs Hydrodynamics Horizontal, Bi-Directional

Floodplain Oxbow -Wyoming

Landscape Position:

RIVERINE Wetlands

Soils Geomorphic Description - “Floodplain”

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RIVERINE – Dominant Water Source – Stream Hydrograph Soil “Water Features” •Flooding •Ponding •Groundwater Hydroperiod

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RIVERINE – Surface Flooding (Lotic)

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RIVERINE – Ponding (Lentic)

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RIVERINE – Floodplain Groundwater

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How Many Sub-Classes?

Upland: Non-wetland

Natural Levee: Non-wetland

Backswamp: Groundwater

Active Channel: Flooding

RIVERINE Landscapes Can have Multiple HGM Sub-Classes

Unique: • Landform • Plant Community • Groundwater Table • Flood Frequency • Flood Duration • Ponding Potential • Soil

USDA | NRCS | Module Name 18

Introducing - Endosaturated Riverine

Ninnescah River, Kansas

Tongue River, Wyoming

“Saturated from Below”

USDA | NRCS | Module Name 19

Groundwater Rises and Falls with the Stream Water Surface

Endosaturated Riverine Features • High Ksat Floodplains (Sands

Gravels) • Wet from high groundwater • Attenuated hydrographs • Strong Baseflow in channel • Surface Flooding not needed to

create wetland hydrology

• High groundwater • No ponding • Flooding need not

be long duration or high frequency for ecological function

USDA | NRCS | Module Name 20

Introducing - Episaturated Riverine

Iowa photo: NRCS Photo Gallery

USDA | NRCS | Module Name 21

Episaturated Riverine Features • Low Ksat Floodplains (Silts and

Clays) • Weak Connection between

stream water surface and floodplain Groundwater level

• Wet when inundated or ponded only

• Perched groundwater

• Ponding in backswamps

• Frequency and Duration of Flooding critical for ecological functions

RIVERINE, Backswamp, episaturated herbaceous

USDA | NRCS | Module Name 22

RIVERINE – Ponded Backswamp

Hydric (Floodplain Oxbow)

Partiallly Hydric (Floodplain Flat)

Active Channel

RIVERINE, Backswamp, episaturated herbaceous In MLRA 73

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RIVERINE Morphology - •Natural Levees •Backswamps

Osage Series •Hydric •Backswamp

Verdigris Series •Partially Hydric •Natural Levee

SLOPE

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Dominant Water Source – Groundwater Discharge

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SLOPE

Landscape Position – Concave Topographic positions, usually stream headwaters –

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Topographic SLOPE Wetland Plan View Concave Landscape Positions Typical of Stream Headwaters

Topographic SLOPE Cross-Section • “Deep”

Discharge Shown Here

• Often is Shallow Subsurface Flow in Soil

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Potential Bog Turtle Habitat “Typic Endoaquults” Groundwater Dominated Soils In Low Stream Order Landscapes

SLOPE, Headwater

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SLOPE Wetlands

Kansas Headwater

Idaho Headwater Fen

New York Headwater Fen

Fens • SLOPE Class • Near continuous discharge • Organic Soil

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Slope HGM Class Wetland Wyoming (Sage Grouse Country)

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SLOPE Wetland Before “Restoration”

• Surface Saturated • Groundwater Fed • Large Scale • Not “Flooded” • Not “Ponded”

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SLOPE Wetland After “Restoration”

• Lowered Groundwater • Aerated Organic Soil • Lateral Effect of Constructed “Stream Restoration” • Loss of Wetland Hydrology

USDA | NRCS | Module Name 33

To Drain a SLOPE Wetland -

Groundwater From Uplands

Intercept Groundwater at Point of Discharge

Finger Lakes Region, NY

Simply Plug the Ditch – Restores Groundwater Discharge

USDA | NRCS | Module Name 34

OR – Install a Drainage Ditch Through It

Des Moines Lobe, Iowa

Groundwater Discharge

USDA | NRCS | Module Name 35

OR – Allow a Gully to Form Through It

Current Groundwater Discharge Level

Aerated Organic Soil

Formerly Saturated Surface Upstream Dam has Captured Sediment

Nebraska Sand Hills

MINERAL SOIL FLAT Dominant Water Source- Direct Precipitation

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• Landscape Position – Interfluves • Low Flow Accumulation • Depressions may be embedded within Mineral Flats

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MINERAL FLAT Wetland Hydrodynamics – Vertical, Downward

• Dominant Water Source - Precipitation

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• 0-2% Slopes • Poorly Drained to

Very Poorly Drained • Decrease in Ksat

with Depth • Perched Water

Table

Mineral Flat Extent Map

ORGANIC SOIL FLAT Dominant Water Source – Direct Precipitation

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Pocosin – North Carolina

•Ombotrophic •“Bogs” •“Pocosins”

ESTUARINE FRINGE Dominant Water Source - Tides

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Estuarine Fringe •Organic Soils are Common

•Tidally Influenced Salt, Brackish, or Freshwater

•Adjoins Riverine HGM landscapes

ESTUARINE FRINGE – Tidal Inlet Channels

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Yellowstone Lake, Wyoming

Horizontal, bi-directional

LACUSTRINE FRINGE Dominant Water Source- Lake Fluctuations

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Nebraska Rainwater Basin – Recharge Depression

Wyoming – Recharge Depression, Gillette

South Dakota Prairie Pothole

South Carolina – Carolina Bay

DEPRESSIONAL Closed Topographic Depressions

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DEPRESSIONAL Dominant Water Source – Surface Runoff and/or Groundwater

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Depressional – Recharge

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Depressional – Discharge or Flow Through

Recharge Go > Gi Discharge Gi > Go Flow Through Gi = Go

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Texas Playas – Recharge Randall Clay

South Dakota Prairie Potholes – Recharge, Discharge, and Flowthrough

DEPRESSIONS Web Soil Survey Map Units

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Generalized Landscape Map

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HGM Parameters

The Hydrogeomorphic (HGM) Classification System is based on 3 factors – •Landscape Position

•WHERE it is •Dominant Water Source

•Not the ONLY Source •Hydrodynamics

•The direction(s) of water movement in and out

Questions?

Kansas Flint Hills photo: Jon Fripp