ERDC/EL TR-02-4 

Wetlands Research Program

A Regional Guidebook for Applying the 

Hydrogeomorphic Approach to Assessing 

Wetland Functions of Selected Regional 

Wetland Subclasses, Yazoo Basin, Lower 

Mississippi River Alluvial Valley

R. Daniel Smith and Charles V. Klimas April 2002

Environment

al Laboratory 

Approved for public release; distribution is unlimited. 
The contents of this report are not to be used for advertising,

publication, or promotional purposes. Citation of trade names 

does not constitute an official endorsement or approval of the use

of such commercial products. 

The findings of this report are not to be construed as an official

Department of the Army position, unless so designated by other 

authorized documents. 

PRINTED ON RECYCLED PAPER 
Wetlands Research Program ERDC/EL TR-02-4

April 2002

A Regional Guidebook for Applying the 

Hydrogeomorphic Approach to Assessing 

Wetland Functions of Selected Regional Wetland 

Subclasses, Yazoo Basin, Lower Mississippi 

River Alluvial Valley 

by R. Daniel Smith 

 Environmental Laboratory 

U.S. Army Engineer Research and Development Center 

3909 Halls Ferry Road 

Vicksburg, MS 39180-6199 

Charles V. Klimas 

 CVK & Associates 

12301 Second Avenue NE 

Seattle, WA 98125 

Final report

Approved for public release; distribution is unlimited

Prepared for U.S. Army Corps of Engineers 

Washington, DC 20314-1000 
Corps of Engineers Research Report Summary, September 2001 

Assessing Wetland Functions 

A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland 

Functions of Selected Regional Wetland Subclasses, Yazoo Basin, Lower Mississippi River 

Alluvial Valley (ERDC/EL TR-02-4) 

ISSUE: Section 404 of the Clean Water Act 

directs the U.S. Army Corps of Engineers to

administer a regulatory program for permitting 

the discharge of dredged or fill material in

“waters of the United States.” As part of the 

permit review process, the impact of discharging 

dredged or fill material on wetland functions 

must be assessed. On 16 August 1996, a

National Action Plan to Implement the Hydrogeomorphic Approach (NAP) for developing

Regional Guidebooks to assess wetland functions was published. This report is one of a

series of Regional Guidebooks that will be published in accordance with the National Action 

Plan. 

RESEARCH OBJECTIVE: The objective of

this research was to develop a Regional Guidebook for assessing the functions of selected

regional wetland subclasses in the Yazoo Basin, 

Lower Mississippi River Alluvial Valley, in the

context of the 404 Regulatory Program. 

SUMMARY: The Hydrogeomorphic (HGM) 

Approach is a collection of concepts and 

methods for developing functional indices and

subsequently using them to assess the capacity 

of a wetland to perform functions relative to 

similar wetlands in a region. The Approach was 

initially designed to be used in the context of the 

Clean Water Act Section 404 Regulatory

Program permit review sequence to consider

alternatives, minimize impacts, assess unavoidable project impacts, determine mitigation 

requirements, and monitor the success of the 

mitigation projects. However, a variety of other

potential applications for the Approach have 

been identified, including; determining minimal

effects under the Food Security Act, designing

mitigation projects, and managing wetlands. 

This report uses the HGM Approach to develop 

a Regional Guidebook for assessing the functions of selected regional wetland subclasses in

the Yazoo Basin, Lower Mississippi River 

Alluvial Valley.

AVAILABILITY OF REPORT: The report 

is available at the following Web site: 

http://www.wes.army.mil/el/wetlands/wlpubs.ht

ml. The report is also available on Interlibrary 

Loan Service from the U.S. Army Engineer

Research and Development Center (ERDC)

Research Library, telephone (601) 634-2355, or

the following Web site: http://libweb.wes.army. 

mil/index.htm. Individuals should arrange for 

Interlibrary Loan Service either through the 

library of their business concerns or through the 

interlibrary loan services of their local libraries. 

To purchase a copy, call the National Technical 

Information Service (NTIS) at 1-800-553-6847

or (703) 605-6000, or visit the following Web

site: http://www.ntis.gov/. For help in identifying a title for sale call 1-800-553-6847. NTIS 

report numbers may also be requested from the 

ERDC librarians. 

About the authors: Mr. R. Daniel Smith is a research ecologist at the U.S. Army Engineer Research 

and Development Center Environmental Laboratory, Vicksburg, MS. Dr. Charles V. Klimas is an 

ecologist and principal at CVK & Associates, Seattle, WA. 

Please reproduce this page locally as needed. 
iii

Contents 

Preface.................................................................................................................. ix

1—Introduction ......................................................................................................1

2—Overview of the Hydrogeomorphic Approach .................................................4

Development and Application Phases .............................................................4

Hydrogeomorphic Classification .....................................................................7

Reference Wetlands .......................................................................................10

Assessment Models and Functional Indices ..................................................11

Assessment Protocol ......................................................................................13

3—Characterization of Regional Wetland Subclasses in the Yazoo Basin..........14

Reference Domain .........................................................................................14

Environment and Resources of the Yazoo Basin...........................................14

Physiography and Climate.............................................................................16

Drainage System and Hydrology...................................................................16

Geology and Geomorphology........................................................................18

Development of the Mississippi Alluvial Valley ....................................18

Geomorphic features of the Yazoo Basin................................................20

Soils ...............................................................................................................24

Vegetation......................................................................................................25

Alterations to Environmental Conditions ......................................................31

Land use and management ......................................................................31

Hydrology ...............................................................................................33

MR&T features in the Yazoo Basin ........................................................34

Description of Regional Wetland Subclasses ................................................38

Flats .........................................................................................................40

Riverine Backwater .................................................................................40

Riverine Overbank ..................................................................................40

Isolated Depression .................................................................................41

Connected Depression.............................................................................42

Isolated Fringe.........................................................................................42

Connected Fringe ....................................................................................42

Identifying HGM Wetland Classes and Regional Subclasses .......................42
iv

4—Wetland Functions and Assessment Models ..................................................47

Function 1: Detain Floodwater .....................................................................48

Definition and applicability.....................................................................48

Rationale for selecting the function.........................................................48

Characteristics and processes that influence the function .......................49

General form of the assessment model....................................................50

Function 2: Detain Precipitation ...................................................................51

Definition and applicability.....................................................................51

Rationale for selecting the function.........................................................52

Characteristics and processes that influence the function .......................52

General form of the assessment model....................................................52

Function 3: Cycle Nutrients..........................................................................53

Definition and applicability.....................................................................53

Rationale for selecting the function.........................................................53

Characteristics and processes that influence the function .......................54

General form of the assessment model....................................................55

Function 4: Export Organic Carbon..............................................................56

Definition and applicability.....................................................................56

Rationale for selecting the function.........................................................56

Characteristics and processes that influence the function .......................56

General form of the assessment model....................................................57

Function 5: Remove Elements and Compounds...........................................58

Definition and applicability.....................................................................58

Rationale for selecting the function.........................................................58

Characteristics and processes that influence the function .......................59

General form of the assessment model....................................................60

Function 6: Maintain Plant Communities .....................................................60

Definition and applicability.....................................................................60

Rationale for selecting the function.........................................................61

Characteristics and processes that influence the function .......................61

General form of the assessment model....................................................62

Function 7: Provide Fish and Wildlife Habitat.............................................63

Definition and applicability.....................................................................63

Rationale for selecting the function.........................................................63

Characteristics and processes that influence the function .......................64

General form of the assessment model....................................................67

5—Model Applicability and Reference Data .......................................................68

Subclass: Flats...............................................................................................68

Subclass: Riverine Backwater.......................................................................72

Subclass: Riverine Overbank........................................................................77

Subclass: Isolated Depression.......................................................................81

Subclass: Connected Depression ..................................................................85
v

6—Assessment Protocol.......................................................................................90

Introduction....................................................................................................90

Define Assessment Objectives.......................................................................91

Identify Regional Wetland Subclasses...........................................................91

Characterize the Project Area ........................................................................91

Screen for Red Flags......................................................................................94

Define the Wetland Assessment Areas ..........................................................95

 Collect Field Data ..........................................................................................96 

Procedures for Measuring Assessment Variables........................................101

VAHOR - A horizon biomass....................................................................101

VCEC - Cation exchange capacity............................................................113

VCOMP - Composition of tallest woody vegetation stratum ....................117

VCONNECT - Habitat connections..............................................................118

VCORE - Core area ...................................................................................119

VFREQ - Frequency of flooding...............................................................120

VGVC - Ground vegetation cover ............................................................120

VLOG - Log biomass................................................................................121

VOHOR - O horizon biomass....................................................................121

VPOND - Micro-depressional ponding .....................................................121

VSNAG - Snag density ..............................................................................122

VSOIL - Soil integrity...............................................................................122

VSSD - Shrub-sapling density..................................................................123

VTBA - Tree basal area ............................................................................123

VTCOMP - Tree composition.....................................................................124

VTDEN - Tree density...............................................................................125

VTRACT - Wetland tract............................................................................125

VWD - Woody debris biomass and VLOG - log biomass..........................125

Analyze Field Data ......................................................................................127

Apply Assessment Results...........................................................................128

Special Issues in Applying the Assessment Results ....................................128

References ..........................................................................................................133

Appendix A: Glossary........................................................................................A1 

Appendix B: Spreadsheets..................................................................................B1 

 Tree Basal Area Spreadsheet ........................................................................B1 

 Woody Debris and Log Volume Spreadsheet...............................................B2 

 Functional Capacity Index Spreadsheet........................................................B3 

Appendix C: Reference Wetland Data and Spatial Data....................................C1 

 Reference Wetland Data ...............................................................................C1 

 ArcView Shape Files ....................................................................................C2 

 Digital Geomorphology Maps ......................................................................C3 

SF 298 
vi

List of Figures 

Figure 1. Schematic of development and application phases of the HGM 

approach............................................................................................5

Figure 2. Subindex graph for the Return Interval (VFREQ) assessment 

variable ...........................................................................................13

Figure 3. Mississippi Alluvial Valley ............................................................15 

Figure 4. Principal geomorphic features of the Yazoo Basin.........................21 

Figure 5. Block schematic of geomorphic features of the Yazoo Basin .......22

Figure 6. Major soil associations of the Yazoo Basin....................................28

Figure 7. Major features of the MR&T Project in the Yazoo Basin ..............35

Figure 8. Typical hydrologic conditions, geomorphic settings, and 

 plant communities associated with regional wetland 

 subclasses of the Yazoo Basin ........................................................39 

Figure 9. Areas inundated during a 5-year flood event in the Yazoo Basin ..44

Figure 10. Key to the wetland classes in the Yazoo Basin...............................45

Figure 11. Key to the regional wetland subclasses in the Yazoo Basin...........46

Figure 12. Subindex graphs for Flats ...............................................................69

Figure 13. Subindex graphs for Riverine Backwater .......................................73

Figure 14. Subindex graphs for Riverine Overbank ........................................78

Figure 15. Subindex graphs for Isolated Depression .......................................82

Figure 16. Subindex graphs for Connected Depression...................................87

Figure 17. Example of project area description ...............................................93

Figure 18. A single WAA within a project area...............................................95 

Figure 19. Spatially separated WAAs from the same regional wetland 

 subclass within a project area .........................................................95 

Figure 20. Spatially separated WAAs from different regional wetland 

 subclasses within a project area ......................................................95 
vii

Figure 21. WAA defined based on differences in site-specific 

 characteristics..................................................................................96 

Figure 22. Data Form 1: Variable/Metric Summary .......................................97

Figure 23. Sample plot and subplot dimensions and layouts for field 

 sampling..........................................................................................98

Figure 24. Data Form 2: Cation Exchange Capacity (VCEC )...........................99

Figure 25. Data Form 3: Tree Basal Area, Density, and Snags (VTBA , 

 VTDEN , and VSNAG ).........................................................................100

Figure 26. Data Form 4a: Woody Vegetation Composition (VTCOMP and 

 VCOMP ) for Riverine Backwater....................................................102

Figure 27. Data Form 4b: Woody Vegetation Composition (VTCOMP and 

 VCOMP ) for Riverine Overbank .....................................................104

Figure 28. Data Form 4c: Woody Vegetation Composition (VTCOMP and 

 VCOMP ) for Flats............................................................................106

Figure 29. Data Form 4d: Woody Vegetation Composition (VTCOMP and 

 VCOMP ) for Connected Depressions ..............................................108

Figure 30. Data Form 4e: Woody Vegetation Composition (VTCOMP and 

 VCOMP ) for Isolated Depressions...................................................110

Figure 31. Data Form 5: Woody Debris and Logs (VWD and VLOG ).............112

Figure 32. Data Form 6: Shrub-Sapling, Ground Cover, and Organic 

 Horizons (VSSD , VGVC , VOHOR , and VAHOR ) ..................................114

Figure 33. Estimating soil texture by feel ......................................................116

Figure 34. Connected wetland forest tract boundary .....................................118

Figure 35. Interior core area and buffer zone.................................................119

Figure 36. Wetland tract.................................................................................126 

Figure 37. Example of an FCI calculation spreadsheet..................................130

Figure 38. Recovery trajectories for selected assessment variables...............131

Figure B1. Example of the tree basal area spreadsheet......................................B2 

Figure B2. Example of the woody debris and log volume spreadsheet 

 showing data entry for Size Classes 1 and 2 and calculations.........B4 
viii

Figure B3. Example of an FCI calculation spreadsheet for the Riverine 

 Backwater subclass ..........................................................................B6 

List of Tables 

Table 1. Hydrogeomorphic Wetland Classes..................................................9 

Table 2. Potential Regional Wetland Subclasses in Relation to 

Classification Criteria .....................................................................10 

Table 3. Reference Wetland Terms and Definitions.....................................11 

Table 4. Components of an Assessment Variable.........................................12 

Table 5. Classification of the Principal Soil Associations of the Yazoo 

Basin ...............................................................................................26 

Table 6. Comparisons of Typical Landscape Settings and Soil 

Development for Selected Soil Series in the Yazoo Basin .............27 

Table 7. Composition and Site Affinities of Common Forest 

Communities in the Yazoo Basin ...................................................30 

Table 8. Correspondence Between Putnam's Community Forest Cover 

Types of the Yazoo Basin and Standard Society of 

American Foresters Forest Cover Type Designations. ...................30 

Table 9. Use of Assessment Variables by Regional Wetland Subclass........92 

Table 10. Red Flag Features and Respective Program/Agency Authority .....94 

Table 11. Values of Cation Exchange Capacity for Soil Texture 

Classes ..........................................................................................115 
ix

Preface 

This Regional Guidebook was authorized by Headquarters, U.S. Army Corps 

of Engineers (HQUSACE), as part of the Characterization and Restoration of 

Wetlands Research Program (CRWRP). It is published as an Operational Draft 

for field testing for a 2-year period. Comments should be submitted via the 

Internet at the following address: http://www.wes.army.mil/el/wetlands/hgmhp. 

html. Written comments should be addressed to: Department of the Army, 

Research and Development Center, CEERD-EE-W, 3909 Halls Ferry Road, 

Vicksburg, MS 39180-6199. 

The work was performed under Work Unit 32985, “Technical Development 

of HGM,” for which Dr. Ellis J. Clairain, Jr., Environmental Laboratory (EL), 

Vicksburg, MS, U.S. Army Engineer Research and Development Center 

(ERDC), was the Principal Investigator. 

Mr. Dave Mathis, CERD-C, was the CRWRP Coordinator at the Directorate 

of Research and Development, HQUSACE; Ms. Colleen Charles, CECW-OR, 

served as the CRWRP Technical Monitor’s Representative; Dr. Russell F. 

Theriot, EL, was the CRWRP Program Manager; and Dr. Clairain was the Task 

Area Manager. 

 This report was prepared by Messrs. R. Daniel Smith, Wetlands and Coastal 

Ecology Branch (WCEB), EL, and Charles V. Klimas, CVK & Associates, 

Seattle, WA. The authors wish to acknowledge the efforts of the following 

people for assistance with developing the classification, characterizing the 

regional subclasses, conducting field sampling, and reviewing drafts of the 

Regional Guidebook: Messrs. Russell Pringle, National Resource Conservation 

Service (NRCS); Bill Ainslie, Environmental Protection Agency (EPA), Atlanta, 

GA; John Campbell, EL; Bruce Pruitt, EPA, Athens, GA; Delaney Johnson, 

NRCS, Jackson, MS; and Paul Rodrigue, Mississippi State University, Starkville, 

MS, and Ms. Ramona Warren, Vicksburg District, USACE. Mmes. Carolyn 

Schneider and Monica Craft assisted with the manipulation and analysis of 

reference wetland data and reviewed the draft Regional Guidebook. The 

“Regional Guidebook for Assessing the Functions of Low-Gradient Riverine 

Wetlands in Western Kentucky” served as a template for the development of this 

regional guidebook. The wildlife section authored by Dr. Thomas H. Roberts, 

Tennessee Technological University, Cookville, TN, was particularly helpful, 

and portions of this section of the document are included verbatim. 
x

 This work took place under the general supervision of Dr. Morris Mauney, 

Jr., Chief, WCEB; Dr. David J. Tazik, Chief, Ecosystem Evaluation and 

Engineering Division, EL; and Dr. Edwin A. Theriot, Director, EL. 

 At the time of publication of this report, Dr. James R. Houston was Director 

of ERDC, and COL John W. Morris III, EN, was Commander and Executive 

Director. 

This report should be cited as follows: 

Smith, R. D., and Klimas, C. V. (2002). “A regional guidebook for 

applying the hydrogeomorphic approach to assessing wetland 

functions of selected regional wetland subclasses, Yazoo Basin, 

Lower Mississippi River Alluvial Valley,” ERDC/EL TR-02-4, 

U.S. Army Engineer Research and Development Center, Vicksburg, 

MS. 

The contents of this report are not to be used for advertising, publication 

or promotional purposes. Citation of trade names does not constitute an 

official endorsement or approval of the use of such commercial products. 
Chapter 1 Introduction 1

1 Introduction 

 The Hydrogeomorphic (HGM) Approach is a method for developing functional indices and the protocols used to apply these indices to the assessment of 

wetland functions at a site-specific scale. The HGM Approach was initially 

designed to be used in the context of the Clean Water Act Section 404 

Regulatory Program permit review to analyze project alternatives, minimize 

impacts, assess unavoidable impacts, determine mitigation requirements, and 

monitor the success of compensatory mitigation. However, a variety of other 

potential uses have been identified, including the determination of minimal 

effects under the Food Security Act, design of wetland restoration projects, and 

management of wetlands. 

 In the HGM Approach, the functional indices and assessment protocols used 

to assess a specific type of wetland in a specific geographic region are published 

in a document referred to as a Regional Guidebook. Guidelines for developing 

Regional Guidebooks were published in the National Action Plan (National 

Interagency Implementation Team 1996) developed cooperatively by the 

U.S. Army Corps of Engineers (USACE), U.S. Environmental Protection Agency 

(USEPA), Natural Resources Conservation Service (NRCS), Federal Highways 

Administration (FHWA), and U.S. Fish and Wildlife Service (USFWS). The 

Action Plan, available online at http://www.epa.gov/OWOW/wetlands/science/ 

hgm.html, outlines a strategy for developing Regional Guidebooks throughout 

the United States, provides guidelines and an explicit set of tasks required to 

develop a Regional Guidebook under the HGM Approach, and solicits the 

cooperation and participation of Federal, State, and local agencies, academia, and 

the private sector. 

 This document represents a Regional Guidebook developed for assessing 

several types of wetlands that occur in the Yazoo Basin of the Lower Mississippi 

River Alluvial Valley in the United States. Normally, a Regional Guidebook 

focuses on a single regional wetland subclass (the term for wetland types in 

HGM Approach terminology), however, a different strategy is employed in this 

Regional Guidebook in that multiple regional wetland subclasses are considered. 

 The rationale for this approach is that the lower Mississippi River and its 

tributaries have created a complex landscape that supports a variety of 

interspersed wetland types in the Yazoo Basin specifically and in the Lower 

Mississippi River Alluvial Valley generally. Subtle differences in terrain and 

water movement result in distinctly different functions being performed by 

wetlands that are in close proximity to or are contiguous with one another. 
2 Chapter 1 Introduction 

Further, massive flood control works that have been instituted in this century 

have dramatically affected nearly all of the wetlands in the Lower Mississippi 

River Alluvial Valley. Because the origins of these systems are closely related, 

and they have been universally influenced by flood protection efforts, it is most 

sensible to deal with their classification and assessment in a single integrated 

Regional Guidebook. This does not mean that wetlands of different HGM 

classes and regional wetland subclasses are lumped for assessment purposes, but 

that the factors influencing their functions and the indicators employed in their 

evaluation are best developed and presented in a unified manner. Therefore, this 

Regional Guidebook, as well as others planned for the Lower Mississippi River 

Alluvial Valley, was developed for multiple regional wetlands subclasses that 

commonly occur together in a sub-basin. It is expected that the classification of 

regional wetland subclasses, assessment variables, and assessment models 

developed for the Yazoo Basin will have general applicability in other sub-basins 

of the Lower Mississippi River Alluvial Valley. However, development of 

Regional Guidebooks for other sub-basins will require collection of additional 

reference data that reflect regional variation in wetland characteristics within a 

particular sub-basin. 

 The objectives of this Regional Guidebook are to: 

a. Characterize selected regional wetland subclasses in the Yazoo Basin of 

the Lower Mississippi River Alluvial Valley. 

b. Present the rationale used to select functions to be assessed in these 

regional subclasses. 

c. Present the rationale used to select assessment variables and metrics. 

d. Present the rationale used to develop assessment models. 

e. Provide data from reference wetlands and document their use in 

calibrating assessment variables and assessment models. 

f. Describe the protocols for applying the functional indices to the 

assessment of wetland functions. 

 This document is organized in the following manner. Chapter 1 provides the 

background, objectives, and organization of the document. Chapter 2 provides a 

brief overview of the major components of the HGM, including the procedures 

recommended for development and application of Regional Guidebooks. 

Chapter 3 characterizes the regional wetland subclasses in the Yazoo Basin 

included in this guidebook. Chapter 4 discusses the wetland functions, 

assessment variables, and functional indices used in the guidebook from a 

generic perspective. This discussion includes: 

a. A definition for each function. 

b. A description of a quantitative, independent measure of each function for 

the purposes of validation. 
Chapter 1 Introduction 3

c. Descriptions of ecosystem and landscape characteristics and processes 

that influence assessed functions. 

d. Definitions and descriptions of assessment variables used to represent the 

aforementioned characteristics and processes. 

e. A discussion of the assessment model on which the functional index is 

based. 

f. An explanation of the rationale used to calibrate assessment variables 

and the functional index with reference wetland data. 

 In Chapter 5, the assessment models are applied to specific regional wetland 

subclasses, and the relationships of assessment variables to reference data are 

defined. Chapter 6 outlines the assessment protocol for conducting a functional 

assessment of regional wetland subclasses in the Yazoo Basin. Appendix A is a 

glossary of terms, Appendix B provides spreadsheets for analyzing the data 

collected during the assessment, and Appendix C provides the information 

necessary to access the reference wetland data and spatial information collected 

during the project. 

 While it is possible to assess the functions of selected regional wetland 

subclasses in the Yazoo Basin using only the information contained in Chapter 6 

and the Appendices, it is strongly suggested that, prior to conducting an 

assessment, users familiarize themselves with the information and documentation 

provided in Chapters 2-5. 
4 Chapter 2 Overview of the Hydrogeomorphic Approach 

2 Overview of the 

Hydrogeomorphic 

Approach 

Development and Application Phases 

 The HGM Approach consists of four components including: (a) the HGM 

Classification, (b) reference wetlands, (c) assessment variables and assessment 

models from which functional indices are derived, and (d) assessment protocols. 

The HGM Approach is conducted in two phases. The Development Phase of the 

HGM Approach is completed by an interdisciplinary team of experts known as 

the “Assessment Team” or “A-Team.” The task of the A-Team is to develop and 

integrate the classification, reference wetland, assessment variables, models, and 

protocol components of the HGM Approach into a Regional Guidebook 

(Figure 1). 

 In developing a Regional Guidebook, the team completes the tasks outlined 

in the National Action Plan (National Interagency Implementation Team 1996). 

These tasks include: 

Task 1: Organize the A-Team 

 A. Identify team members 

 B. Train team in the HGM Approach 

Task 2: Select and Characterize Regional Wetland Subclass 

 A. Identify/prioritize regional wetland subclasses 

 B. Select regional wetland subclass and define reference domain 

 C. Initiate literature review 

 D. Develop preliminary characterization of regional wetland subclass 

 E. Identify and define wetland functions 
Chapter 2 Overview of the Hydrogeomorphic Approach 5

 Figure 1. Schematic of development and application phases of the HGM approach 

Task 3: Select Assessment Variables and Metrics and Construct Conceptual 

Assessment Models 

 A. Review existing assessment models 

 B. Identify assessment variables and metrics 

 C. Define initial relationship between assessment variables and functional 

capacity 

 D. Construct conceptual assessment models for deriving functional capacity 

indices (FCI) 

 E. Complete Precalibrated Draft Regional Guidebook (PDRG) 

Task 4: Conduct Peer Review of Precalibrated Draft Regional Guidebook 

 A. Distribute PDRG to peer reviewers 

 B. Conduct interdisciplinary, interagency workshop of PDRG 

 C. Revise PDRG to reflect peer review recommendations 
6 Chapter 2 Overview of the Hydrogeomorphic Approach 

 D. Distribute revised PDRG to peer reviewers for comment 

 E. Incorporate final comments from peer reviewers on revisions into the 

PDRG 

Task 5: Identify and Collect Data From Reference Wetlands 

 A. Identify reference wetland field sites 

 B. Collect data from reference wetland field sites 

 C. Analyze reference wetland data 

Task 6: Calibrate and Field Test Assessment Models 

 A. Calibrate assessment variables using reference wetland data 

 B. Verify and validate (optional) assessment models 

 C. Field test assessment models for repeatability and accuracy 

 D. Revise PDRG based on calibration, verification, validation (optional), 

and 

field testing results into a Calibrated Draft Regional Guidebook (CDRG) 

Task 7: Conduct Peer Review and Field Test of Calibrated Draft Regional 

Guidebook 

 A. Distribute CDRG to peer reviewers 

 B. Field test CDRG 

 C. Revise CDRG to reflect peer review and field test recommendations 

 D. Distribute CDRG to peer reviewers for final comment on revisions 

 E. Incorporate peer reviewers’ final comments on revisions 

 F. Publish Operational Draft Regional Guidebook (ODRG) 

Task 8: Technology Transfer 

 A. Train end users in the use of the ODRG 

 B. Provide continuing technical assistance to end users of the ODRG 

 After organization and training, the first task of the team is to classify the 

wetlands within the region of interest into regional wetland subclasses using the 

principles and criteria of the Hydrogeomorphic Classification (Brinson 1993a; 

Smith et al. 1995). Next, focusing on the specific regional wetland subclass 

selected, the team develops an ecological characterization or functional profile of 
Chapter 2 Overview of the Hydrogeomorphic Approach 7

the subclass. The A-Team then identifies the important wetland functions, 

conceptualizes assessment models, identifies assessment variables to represent 

the characteristics and processes that influence each function, and defines metrics 

for quantifying assessment variables. Next, reference wetlands are identified to 

represent the range of variability exhibited by the regional subclass, and field 

data are collected and used to calibrate assessment variables and indices resulting 

from assessment models. Finally, the team develops the assessment protocols 

necessary for regulators, managers, consultants, and other end users to apply the 

indices to the assessment of wetland functions in the context of 404 Permit 

review. The following list provides the detailed steps involved in the general 

sequence described above. 

 During the Application Phase of the HGM Approach, the assessment 

variables, models, and protocols are used to assess wetland functions. This 

involves two steps. The first is to apply the assessment protocols outlined in the 

Regional Guidebook to complete the following tasks. 

a. Define assessment objectives. 

b. Characterize the project site. 

c. Screen for red flags. 

d. Define the Wetland Assessment Area. 

e. Collect field data. 

f. Analyze field data. 

 The second step involves applying the results of the assessment at various 

decision-making points in the permit review sequence, such as alternatives 

analysis, minimization, assessment of unavoidable impacts, determination of 

compensatory mitigation, design and monitoring of mitigation, comparison of 

wetland management alternatives or results, determination of restoration 

potential, or identification of acquisition or mitigation sites. 

 Each of the components of the HGM Approach that are developed and 

integrated into the Regional Guidebook is discussed briefly in the following 

paragraphs. More extensive treatment of these components can be found in 

Brinson (1993a,b; 1995a,b), Brinson et al. (1995, 1996, 1998), Smith et al. 

(1995), Hauer and Smith (1998), Smith (2001), Smith and Wakeley (2001), and 

Wakeley and Smith (2001). 

Hydrogeomorphic Classification 

 Wetland ecosystems share a number of common attributes including 

relatively long periods of inundation or saturation by water, hydrophytic 

vegetation, and hydric soils. In spite of these common attributes, wetlands occur 

under a wide range of climatic, geologic, and physiographic situations and 
8 Chapter 2 Overview of the Hydrogeomorphic Approach 

exhibit a wide range of physical, chemical, and biological characteristics and 

processes (Ferren, Fiedler, and Leidy (1996); Ferren et al. 1996a,b; Mitch and 

Gosselink 1993; Semeniuk 1987; Cowardin et al. 1979). The variability of 

wetlands makes it challenging to develop assessment methods that are both 

accurate (i.e., sensitive to significant changes in function) and practical (i.e., can 

be completed in the relatively short time frame normally available for conducting 

assessments). “Generic” wetland assessment methods have been developed to 

assess multiple wetland types throughout the United States. In general, these 

methods can be applied relatively rapidly, but lack the resolution necessary to 

detect significant changes in function. One way to achieve an appropriate level 

of resolution within a rapid time frame (i.e., one day or less) is to employ an 

approach that focuses on a subset of the wetland universe, thereby reducing the 

level of variability that must be considered (Smith et al. 1995). 

 The HGM Classification was developed specifically to accomplish this task 

(Brinson 1993a). It identifies groups of wetlands that function similarly using 

three criteria that fundamentally influence how wetlands function. These criteria 

are geomorphic setting, water source, and hydrodynamics. Geomorphic setting 

refers to the landform and position of the wetland in the landscape. Water source 

refers to the primary source of water in the wetland, such as precipitation, 

overbank floodwater, or groundwater. Hydrodynamics refers to the level of 

energy and the direction that water moves in the wetland. 

 Based on these three criteria, any number of “functional” wetland groups can 

be identified at different spatial or temporal scales. For example, at a continental 

scale, Brinson (1993a,b) identified five HGM wetland classes. These were later 

expanded to the seven classes described in Table 1 (Smith et al. 1995). In some 

cases, the level of variability encompassed by wetlands at the continental scale of 

HGM class is still too great to allow for developing assessment indices that can 

be applied rapidly while retaining the level of sensitivity necessary to detect 

changes in function at a level of resolution appropriate to the 404 Permit review. 

For example, at a continental geographic scale, the depression class includes 

wetlands as diverse as California vernal pools (Zedler 1987), prairie potholes in 

North and South Dakota (Kantrud, Krapu, and Swanson 1989; Hubbard 1988), 

playa lakes in the high plains of Texas (Bolen, Smith, and Schramm 1989), 

kettles in New England, and cypress domes in Florida (Kurz and Wagner 1953, 

Ewel and Odum 1984). 

 In order to reduce both inter- and intraregional variability, the three classifycation criteria must be applied at a smaller, regional geographic scale to identify 

regional wetland subclasses. In many parts of the country, existing wetland 

classifications can serve as a starting point for identifying these regional subclasses (Stewart and Kantrud 1971; Golet and Larson 1974; Wharton et al. 1982; 

Ferren, Fiedler, and Leidy 1996; Ferren et al. 1996a,b). Regional subclasses, like 

the continental scale wetland classes, are distinguished on the basis of geomorphic setting, water source, and hydrodynamics. Examples of potential 

regional subclasses are shown in Table 2 (Smith et al. 1995; Rheinhardt, Brinson, 

and Farley 1997). In addition, certain ecosystem or landscape characteristics 

may also be useful for distinguishing regional subclasses in certain regions. 

For example, depression subclasses might be based on water source (i.e., 
Chapter 2 Overview of the Hydrogeomorphic Approach 9

Table 1 

Hydrogeomorphic Wetland Classes

HGM Wetland Class Definition 

Depression Depression wetlands occur in topographic depressions (i.e., closed elevation contours) that allow the 

accumulation of surface water. Depression wetlands may have any combination of inlets and outlets or lack 

them completely. Potential water sources are precipitation, overland flow, streams, or groundwater/ interflow 

from adjacent uplands. The predominant direction of flow is from the higher elevations toward the center of the 

depression. The predominant hydrodynamics are vertical fluctuations that range from diurnal to seasonal. 

Depression wetlands may lose water through evapotranspiration, intermittent or perennial outlets, or recharge to 

groundwater. Prairie potholes, playa lakes, and cypress domes are common examples of depression wetlands.

Tidal Fringe Tidal fringe wetlands occur along coasts and estuaries and are under the influence of sea level. They intergrade 

landward with riverine wetlands where tidal current diminishes and river flow becomes the dominant water 

source. Additional water sources may be groundwater discharge and precipitation. The interface between the 

tidal fringe and riverine classes is where bidirectional flows from tides dominate over unidirectional ones 

controlled by floodplain slope of riverine wetlands. Because tidal fringe wetlands are frequently flooded and 

water table elevations are controlled mainly by sea surface elevation, tidal fringe wetlands seldom dry for 

significant periods. Tidal fringe wetlands lose water by tidal exchange, by overland flow to tidal creek channels, 

and by evapotranspiration. Organic matter normally accumulates in higher elevation marsh areas where 

flooding is less frequent and the wetlands are isolated from shoreline wave erosion by intervening areas of low 

marsh. Spartina alterniflora salt marshes are a common example of tidal fringe wetlands. 

Lacustrine Fringe Lacustrine fringe wetlands are adjacent to lakes where the water elevation of the lake maintains the water table 

in the wetland. In some cases, these wetlands consist of a floating mat attached to land. Additional sources of 

water are precipitation and groundwater discharge, the latter dominating where lacustrine fringe wetlands 

intergrade with uplands or slope wetlands. Surface water flow is bidirectional, usually controlled by water level 

fluctuations resulting from wind or seiche. Lacustrine wetlands lose water by flow returning to the lake after 

flooding and evapotranspiration. Organic matter may accumulate in areas sufficiently protected from shoreline 

wave erosion. Unimpounded marshes bordering the Great Lakes are an example of lacustrine fringe wetlands. 

Slope Slope wetlands are found in association with the discharge of groundwater to the land surface or sites with 

saturated overland flow with no channel formation. They normally occur on sloping land ranging from slight to 

steep. The predominant source of water is groundwater or interflow discharging at the land surface. 

Precipitation is often a secondary contributing source of water. Hydrodynamics are dominated by downslope 

unidirectional water flow. Slope wetlands can occur in nearly flat landscapes if groundwater discharge is a 

dominant source to the wetland surface. Slope wetlands lose water primarily by saturated subsurface flows, 

surface flows, and evapotranspiration. Slope wetlands may develop channels, but the channels serve only to 

convey water away from the slope wetland. Slope wetlands are distinguished from depression wetlands by the 

lack of a closed topographic depression and the predominance of the groundwater/interflow water source. Fens 

are a common example of slope wetlands 

Mineral Soil Flats Mineral soil flats are most common on interfluves, extensive relic lake bottoms, or large alluvial terraces where 

the main source of water is precipitation. They receive virtually no groundwater discharge, which distinguishes 

them from depressions and slopes. Dominant hydrodynamics are vertical fluctuations. Mineral soil flats lose 

water by evapotranspiration, overland flow, and seepage to underlying groundwater. They are distinguished 

from flat non-wetland areas by their poor vertical drainage due to impermeable layers (e.g., hardpans), slow 

lateral drainage, and low hydraulic gradients. Mineral soil flats that accumulate peat can eventually become 

organic soil flats. They typically occur in relatively humid climates. Pine flatwoods with hydric soils are an 

example of mineral soil flat wetlands. 

Organic Soil Flats Organic soil flats, or extensive peatlands, differ from mineral soil flats in part because their elevation and 

topography are controlled by vertical accretion of organic matter. They occur commonly on flat interfluves, but 

may also be located where depressions have become filled with peat to form a relatively large flat surface. 

Water source is dominated by precipitation, while water loss is by overland flow and seepage to underlying 

groundwater. They occur in relatively humid climates. Raised bogs share many of these characteristics but 

may be considered a separate class because of their convex upward form and distinct edaphic conditions for 

plants. Portions of the Everglades and northern Minnesota peatlands are examples of organic soil flat wetlands.

Riverine Riverine wetlands occur in floodplains and riparian corridors in association with stream channels. Dominant 

water sources are overbank flow or backwater from the channel or subsurface hydraulic connections between 

the stream channel and wetlands. Additional sources may be interflow, overland flow from adjacent uplands, 

tributary inflow, and precipitation. When overbank flow occurs, surface flows down the floodplain may dominate 

hydrodynamics. In headwaters, riverine wetlands often intergrade with slope, depressional, poorly drained flat 

wetlands, or uplands as the channel (bed) and bank disappear. Perennial flow is not required. Riverine 

wetlands lose surface water via the return of floodwater to the channel after flooding and through surface flow to 

the channel during rainfall events. They lose subsurface water by discharge to the channel, movement to 

deeper groundwater (for losing streams), and evapotranspiration. Peat may accumulate in off-channel 

depressions (oxbows) that have become isolated from riverine processes and subjected to long periods of 

saturation from groundwater sources. Bottomland hardwoods on floodplains are an example of riverine 

wetlands. 
10 Chapter 2 Overview of the Hydrogeomorphic Approach 

Table 2 

Potential Regional Wetland Subclasses in Relation to Classification Criteria

Classification Criteria Potential Regional Wetland Subclasses 

Geomorphic Setting Dominant Water Source Dominant 

Hydrodynamics 

Eastern United States Western United 

States/Alaska 

Depression Groundwater or interflow Vertical Prairie pothole marshes, Carolina 

bays 

California vernal 

pools 

Fringe 

(tidal) 

Ocean Bidirectional, 

horizontal 

Chesapeake Bay and Gulf of 

Mexico tidal marshes 

San Francisco 

Bay marshes 

Fringe (lacustrine) Lake Bidirectional, 

horizontal 

Great Lakes marshes Flathead Lake 

marshes 

Slope Groundwater Unidirectional, 

horizontal 

Fens Avalanche chutes

Flat 

(mineral soil) 

Precipitation Vertical Wet pine flatwoods Large playas 

Flat 

(organic soil) 

Precipitation Vertical Peat bogs; portions of Everglades Peatlands over 

permafrost 

Riverine Overbank flow from channels Unidirectional, 

horizontal 

Bottomland hardwood forests Riparian wetlands

groundwater versus surface water) or the degree of connection between the 

wetland and other surface waters (i.e., the flow of surface water into or out of the 

depression through defined channels). Tidal fringe subclasses might be based on 

salinity gradients (Shafer and Yozzo 1998). Slope subclasses might be based on 

the degree of slope, landscape position, source of water (i.e., throughflow versus 

groundwater), or other factors. Riverine subclasses may be based on water 

source, position in the watershed, stream order, watershed size, channel gradient, 

or floodplain width. Regional Guidebooks include a thorough characterization of 

the regional wetland subclass in terms of its geomorphic setting, water sources, 

hydrodynamics, vegetation, soil, and other features that were taken into 

consideration during the classification process. 

Reference Wetlands 

 Reference wetlands are the wetland sites selected to represent the range of 

variability that occurs in a regional wetland subclass as a result of natural 

processes and disturbance (e.g., succession, channel migration, fire, erosion, and 

sedimentation) as well as cultural alteration. The reference domain is the 

geographic area occupied by the reference wetlands (Smith et al. 1995). Ideally, 

the geographic extent of the reference domain will mirror the geographic area 

encompassed by the regional wetland subclass; however, this is not always 

possible due to time and resource constraints. 

 Reference wetlands serve several purposes. First, they establish a basis for 

defining what constitutes a characteristic and sustainable level of function across 

the suite of functions selected for a regional wetland subclass. Second, reference 

wetlands establish the range and variability of conditions exhibited by assessment 

variables and provide the data necessary for calibrating assessment variables and 

models. Finally, they provide a concrete physical representation of wetland 

ecosystems that can be observed and measured repeatedly. 
Chapter 2 Overview of the Hydrogeomorphic Approach 11

 Reference standard wetlands are the subset of reference wetlands that 

perform the suite of functions selected for the regional subclass at a level that is 

characteristic of the least altered wetland sites in the least altered landscapes. 

Table 3 outlines the terms used by the HGM Approach in the context of reference 

wetlands. 

Table 3 

Reference Wetland Terms and Definitions

Term Definition 

Reference Domain The geographic area from which reference wetlands 

representing the regional wetland subclass are selected 

(Smith et al. 1995). 

Reference Wetlands A group of wetlands that encompass the known range of 

variability in the regional wetland subclass resulting from 

natural processes and human alteration. 

Reference Standard Wetlands The subset of reference wetlands that perform a 

representative suite of functions at a level that is both 

sustainable and characteristic of the least human altered 

wetland sites in the least human altered landscapes. By 

definition, the functional capacity index for all functions in a 

reference standard wetland is 1.0. 

Reference Standard Wetland 

Variable Condition 

The range of conditions exhibited by assessment variables in 

reference standard wetlands. By definition, reference 

standard conditions receive a variable subindex score of 1.0. 

Site Potential 

(mitigation project context) 

The highest level of function possible given local constraints 

of disturbance history, land use, or other factors. Site 

potential may be less than or equal to the levels of function in 

reference standard wetlands of the regional wetland 

subclass. 

Project Target 

(mitigation project context) 

The level of function identified or negotiated for a restoration 

or creation project. 

Project Standards 

(mitigation project context) 

Performance criteria and/or specifications used to guide the 

restoration or creation activities toward the project target. 

Project standards should specify reasonable contingency 

measures if the project target is not being achieved. 

Assessment Models and Functional Indices 

 In the HGM Approach, an assessment model is a simple representation of a 

function performed by a wetland ecosystem. The assessment model defines the 

relationship between the characteristics and processes of the wetland ecosystem 

and the surrounding landscape that influences the functional capacity of a 

wetland ecosystem. Characteristics and processes are represented in the 

assessment model by assessment variables. Functional capacity is the ability of a 

wetland to perform a specific function relative to the ability of reference standard 

wetlands to perform the same function. Assessment models result in a Functional 

Capacity Index (FCI) ranging from 0.0 - 1.0. The FCI is a measure of the 

functional capacity of a wetland relative to reference standard wetlands in the 

reference domain. Wetlands with an FCI of 1.0 perform the assessed function at 

a level that is characteristic of reference standard wetlands. A lower FCI 

indicates that the wetland is performing a function at a level below the level that 

is characteristic of reference standard wetlands. 

 For example, Equation 1 shows an assessment model that could be used to 

assess the capacity of a wetland to detain floodwater. 
12 Chapter 2 Overview of the Hydrogeomorphic Approach 

( )



 



 + + + = ×

4

LOG GVC SSD TDEN

FREQ

V V V V FCI V (1) 

The assessment model has five assessment variables including: frequency of 

flooding (VFREQ), which represents the frequency at which a wetland is inundated 

by overbank flooding, and the assessment variables of log density (VLOG), ground 

vegetation cover (VGVC), shrub and sapling density (VSSD), and tree stem density 

(VTDENS), which together represent resistance (i.e., roughness) to overbank 

floodwater within the wetland. 

 Assessment variables are ecological quantities that consist of five 

components (Schneider 1994). These include: (a) a name, (b) a symbol, (c) a 

metric and a procedure for measurement, (d) metric value (i.e., the numbers, 

categories, or numerical estimates that are generated by applying the procedural 

statement (Leibowitz and Hyman 1997)), and (e) units on the appropriate 

measurement scale. Table 4 provides several examples. 

Table 4 

Components of an Assessment Variable

Name Symbol Metric and Procedure Metric Value Units (Scale) 

Redoxomorphic 

features 

VREDO Metric: Status of redoxomorphic features 

Procedure: Visual inspection of soil profile 

for redoxomorphic features 

Present 

Absent 

Unitless (nominal scale) 

Floodplain 

roughness 

VROUGH Metric: Manning’s Roughness Coefficient 

(n) Procedure: Observe wetland 

characteristics to determine adjustment 

values for roughness component to add to 

base value 

0.01 

0.1 

0.21 

Unitless (interval scale) 

Tree biomass VTBA Metric: Tree basal area 

Procedure: Measure diameter of trees in 

sample plots (cm), convert to area (m2), 

and extrapolate to per hectare basis 

5 

12.8 

36 

m2/ha 

(ratio scale) 

 Assessment variables occur in a variety of states or conditions. The state or 

condition of an assessment variable is denoted by the value of the metric used to 

assess a variable. For example, tree basal area, the metric used to assess tree 

biomass in a wetland, can be large or small, or recurrence interval, the metric 

used to assess frequency of overbank flooding, can be frequent or infrequent. 

 Based on the metric value, an assessment variable is assigned a variable 

subindex. When the metric value of an assessment variable is within the range of 

conditions exhibited by reference standard wetlands, a variable subindex of 1.0 is 

assigned. As the metric value deflects in either direction from the reference 

standard condition, the variable subindex decreases based on a defined 

relationship between metric values and functional capacity. Thus, as the metric 

value deviates from the conditions exhibited in reference standard wetlands, it 

receives a progressively lower subindex reflecting the decreased functional 

capacity of the wetland. Figure 2 illustrates the relationship between metric 

values of return interval (VFREQ) and the variable subindex. As shown in the 

graph, when return interval is 2 years or less, a variable subindex of 1.0 is 
Chapter 2 Overview of the Hydrogeomorphic Approach 13

Return Interval (VFREQ)

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Return Interval (years)

Subindex

 Figure 2. Subindex graph for the Return Interval (VFREQ) 

 assessment variable 

assigned. This relationship is based on samples of reference standard wetlands 

where the condition of return interval was found to be 2 years or less. 

 In some cases, the variable subindex drops to 0. For example, when no trees 

are present, the subindex for tree basal area is 0. In other cases, the subindex for 

a variable does not drop to 0 because the metric value does not drop to 0. For 

example, regardless of the condition of a site, Manning’s Roughness Coefficient 

(n), by definition, will always be greater than 0. 

Assessment Protocol 

 The final component of the HGM Approach is the assessment protocol. The 

assessment protocol is a defined set of tasks, along with specific instructions, that 

allows the end user to assess the functions of a particular wetland area using the 

assessment variables, assessment models, and functional indices in the Regional 

Guidebook. The first task is characterization of the wetland ecosystem and the 

surrounding landscape, describing the proposed project and its potential impacts, 

and identifying the wetland areas to be assessed. The second task is collecting 

the field data for assessment variables. The final task is an analysis that involves 

calculation of functional indices. 
14 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

3 Characterization of 

Regional Wetland 

Subclasses in the Yazoo 

Basin 

 This chapter begins with a description of the Yazoo Basin reference domain, 

and then provides an overview of physical and biological characteristics of the 

reference domain. It concludes with descriptions of the HGM wetland classes 

and regional wetland subclasses that occur in the reference domain and 

guidelines for recognizing them in the field. 

Reference Domain 

 The reference domain for this guidebook is the portion of the Yazoo River 

Basin that occurs between Memphis, TN, and Vicksburg, MS, bounded on the 

east by the valley wall and on the west by the Mississippi River mainline levee 

system that controls Mississippi River flooding. (Figure 3). The reference 

domain does not include the non-alluvial portions of the Yazoo River Basin that 

lie east of the valley wall of the alluvial plain of the Lower Mississippi River 

Valley. In addition, the reference domain does not include the batture, the 

relatively narrow strip of land that occurs between the Mississippi River channel 

and the mainline levee system. The batture is subject to significantly different 

hydrologic regimes than the areas protected by the mainline levee system and is 

therefore excluded from the reference domain. 

Environment and Resources of the Yazoo Basin 

 All of the wetlands within the Yazoo Basin are on landforms created by the 

action of the Mississippi River or its tributaries. Cultural alteration within the 

Yazoo Basin has drastically affected both the hydrology of the basin and certain 

physical features that influence wetland conditions. Therefore, it is important to 

understand the geology and geomorphology of both the Lower Mississippi 

Valley as a whole and the Yazoo Basin, as well as the history and effects of 

human alterations to that landscape. Only in that context can the characteristics 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 15

Figure 3. Mississippi Alluvial Valley (from Saucier 1994) 
16 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

and functions of the wetlands within the basin be described in a manner consistent with the HGM Approach. The following subsections review major 

concepts that have bearing on the classification and functions of wetlands in the 

modern landscape of the Yazoo Basin. 

Physiography and Climate 

 The Yazoo Basin occurs within the Mississippi River Alluvial Plain Section 

of the Coastal Plain Physiographic Province. The Yazoo Basin is the largest of 

six major sub-basins within the Mississippi Alluvial Valley, occupying an area of 

approximately 20,000 km2

. The basin is approximately 800 km long and 80 to 

160 km wide, with an average southward slope of about 11.3 cm/km (0.6 ft/mile) 

(Hunt 1967, Saucier 1994). Surface topography within the alluvial valley is 

defined by the characteristics of a deep alluvial fill that overlies Coastal Plain 

geologic formations and deeper Paleozoic and older rocks. The Mississippi 

Alluvial Valley is bounded on the east and west primarily by exposures of the 

Coastal Plain sediments. 

 Climate within the Yazoo Basin is humid subtropical, with temperate winters 

and long hot summers. Prevailing southerly winds carry moisture from the Gulf 

Coast, creating high humidity levels and a high incidence of thunderstorms. 

Tornadoes and ice storms occur commonly in the area (National Weather Service 

1998). Monthly mean temperatures in the northern part of the basin range from a 

low in January of 5.5 EC (42 EF) to highs of 27.2 EC (81 EF) in July and August, 

with an overall annual average of 16.7 EC (62 EF). In the southern part of the 

area, average summer temperatures are one or two degrees warmer than the 

overall basin average, but January temperatures are about -13.8 EC (7 EF). Daily 

average maximum temperatures are 32.2 EC (90 EF) during June, July, and 

August throughout most of the area, and freezing temperatures reach the entire 

area for short periods in most years (Brown et al. 1971, Southern Regional 

Climate Center 1998). 

 Long-term average total precipitation does not vary greatly within the Yazoo 

Basin, ranging from about 127 to 132 cm (50-52 in.) per year, depending on 

location. Precipitation is highest from December to April with an average of 

more than 12 cm (4.7 in.) per month. August, September, and October are the 

lowest precipitation months, averaging less than 8 cm (3.1 in.) per month 

(National Weather Service 1998). Snow or sleet falls in the area in most years, 

but does not persist. The distribution of precipitation is such that excess moisture 

is present in the winter and spring months, and frequent soil moisture deficits 

occur through the months of May to October (Brown et al. 1971). 

Drainage System and Hydrology 

 The dominant drainage feature of the Mississippi Alluvial Valley is the 

Mississippi River, which formed the topography of the basin and thereby largely 

determined the configuration and locations of most of the existing wetlands and 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 17

stream systems (see the following section, Geology and Geomorphology). Prior 

to construction of modern flood protection works, the Mississippi River also 

dominated the hydrology of the valley during major floods, and it continues to 

exert a major influence during high river stages by causing backwater flooding. 

 The drainage area of the Mississippi River basin is approximately 

3,227,000 km2

, which is about 41 percent of the land area of the continental 

United States (USACE 1973). Major floods on the lower Mississippi River 

usually originate in the Ohio basin and can crest in any month from January to 

May. High flows that originate in the upper Mississippi River system generally 

occur in late spring and early summer (Tuttle and Pinner 1982). 

 Average flow of the Mississippi River at Vicksburg is 16,225 m3

/sec 

(573,000 ft3

/sec) , and 250 million tons of sediment are transported past that 

point annually (Bolton and Metzger 1998). Discharges during floods often have 

been 3 to 4 times the average flow; the 1927 flood peak discharge at Vicksburg 

was approximately 64,506 m3

/s (2,278,000 ft3/s) (Tuttle and Pinner 1982). 

Seventeen major floods have occurred on the Lower Mississippi River since 

1879. This is an average of one major flood every 7 years, but the actual interval 

between major events has ranged from 1 to 23 years (USACE-MVD 1998). 

 Prior to construction of modern levees, major Mississippi River floods would 

have inundated most or all of the Yazoo Basin (Moore 1972). However, modern 

mainstem levees that prevent Mississippi River overbank flooding do not 

completely eliminate the influence of the river on hydrology of the Yazoo Basin. 

 High stages on the Mississippi River cause impeded drainage of tributary 

streams, which results in backwater flooding. An analysis of the major flood of 

1973 (USACE 1973) indicated that the event would have inundated the entire 

Yazoo Basin had flood protection works not been in place; however, even though 

no Federal levees failed in the Lower Mississippi Valley, approximately 40 

percent of the Yazoo Basin was flooded anyway, mostly due to backwater 

effects. 

 Except during major floods, surface water entering the Yazoo Basin arrives 

as precipitation or as runoff from the hills along the eastern flank of the basin. 

The only surface outlet is through the Yazoo River, which enters the Mississippi 

River at the southern end of the basin near Vicksburg (Figure 3). Most surface 

water discharge in the Yazoo River originates in the uplands along the eastern 

flank of the basin and is carried to the Yazoo via the Coldwater, Yocona, 

Tallahatchie, and Yalobusha Rivers as well as several smaller streams. Interior 

drainage is provided by numerous small streams that discharge to Deer Creek, the 

Big Sunflower River, Steele Bayou, or Bogue Phalia, which flow to the lower 

Yazoo River. The pattern of drainage within the basin is generally southward, 

but can be quite convoluted, reflecting the influence of a complex topography 

dominated by abandoned meander belts of the Mississippi River (Saucier 1994). 

 Groundwater also is a significant component of the hydrology of the Yazoo 

Basin. The geologic units that flank and underlie the alluvial valley include 

significant non-alluvial aquifers. In places, these are contiguous with the alluvial 

aquifer within the Mississippi Alluvial Valley, which occupies coarse-grained 
18 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

deposits that originated as glacial outwash and from more recent alluvial activity. 

Generally, the surface of the alluvial aquifer is within 10 m of the land surface 

and is approximately 38 m thick. It is essentially continuous throughout the 

Mississippi Alluvial Valley and constitutes one of the largest and most heavily 

used freshwater sources in the United States. Where the topstratum is made up of 

coarse sediments, the alluvial aquifer is recharged by surface waters and the 

aquifer subsequently contributes to stream baseflow during low-flow periods 

(Saucier 1994, O’Hara 1996). 

 All of the major elements of the drainage system and hydrology of the Yazoo 

Basin have been modified to varying degrees in historic times. At the time of 

European settlement, much of the Yazoo Basin was subject to: prolonged, 

extensive ponding following the winter wet season in virtually all years; 

localized short-term ponding following rains at any time of year; and extensive 

inundation within tributary flood basins due to rainfall in headwater areas in most 

years. During major flood events, large-scale backwater flooding influenced 

numerous tributary systems, and complete inundation of most, or all, of the basin 

occurred when Mississippi River stages were high enough to cause overbank 

flows. The engineering projects and agricultural activities which have 

incrementally altered, and continue to alter, these various sources of wetland 

hydrology are described in the Alterations to Environmental Conditions section 

of this chapter. 

Geology and Geomorphology 

Development of the Mississippi Alluvial Valley 

The first comprehensive discussion of the geology and geomorphology of the 

Mississippi Alluvial Valley was presented by Fisk (1944). The only major 

reassessments since that work have been an overview by Autin et al. (1991) and a 

major synthesis by Saucier (1994). Unless otherwise attributed, the discussion 

below is derived primarily from the latter source. 

 The Mississippi Alluvial Valley had its origins in the continental rifting, 

warping, and uplifting that shaped the Mississippi Embayment, a massive 

syncline where Paleozoic rocks downwarp as much as 3,000 m. Areas of 

narrowing and changes in the orientation of the Lower Mississippi Valley reflect 

areas of uplift in west-central and southern Mississippi and in northeastern 

Louisiana and southeastern Arkansas. Faulting has occurred at various locations, 

but the effects are not particularly evident in most instances. However, faulting 

and uplift have occurred in recent times (Holocene) in the northern portion of the 

Lower Mississippi Valley in the area known as the New Madrid Earthquake 

Zone. Some of the more dramatic effects of this activity have occurred in 

historic times in the Reelfoot Lake area of western Tennessee, but there are no 

significant surface expressions of tectonic activity within the Yazoo Basin 

(Saucier 1994). 

 The modern valley is, for the most part, bounded by Tertiary and Mesozoic 

sediments of the Gulf Coastal Plain (Autin et al. 1991), although older rocks are 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 19

present at the surface on Crowley’s Ridge in Arkansas and parts of the western 

valley margin (Saucier 1994). Formations exposed in the bluffs flanking the 

eastern edge of the Yazoo Basin reflect environments of deposition ranging from 

marine (lowest) through estuarine, fluvial, and eolian (highest). As a result, 

streams draining the uplands and entering the Yazoo Basin are eroding a wide 

variety of materials, including limestone, marl, and thick clays deposited in 

marine and estuarine settings, as well as gravels and sands transported by flowing 

water from the Appalachians or the continental interior in the late Tertiary. They 

also carry wind-blown fine silts (loess) that originated in the glacial outwash 

carried down the Mississippi Valley during waning Wisconsin glacial cycles. In 

historic times, erosion rates have increased by orders of magnitude due to forest 

clearing and agriculture, particularly in the highly erodible loess deposits 

(Barnhardt 1988, Saucier 1994). 

 The modern Yazoo Basin is one of six major sub-basins within the Lower 

Mississippi Valley, and it must be understood in that context. Although the 

Lower Mississippi Valley developed as a result of the downwarping of Paleozoic 

rocks and confinement by uplifted surfaces, the characteristics of the existing 

landscape were shaped largely by erosion and deposition processes. By the end 

of the Tertiary, the downwarped surface had been largely filled by sediments 

transported from the north and upland flanks to the east and west. The ancestral 

Mississippi River was established in a valley smaller than the present, the source 

area (drainage area) was smaller than it is now, and the river had lower discharge. 

 Pleistocene glaciation enlarged the river’s drainage area by diverting formerly 

north-flowing rivers into the Mississippi system. Over an estimated 2.8 million 

years, periods of waxing and waning glaciation and associated changes in flows, 

sediment loads, and base level gradually produced a wider valley filled with thick 

alluvium, with the Mississippi and Ohio Rivers flowing on opposite sides of 

Crowley’s Ridge and converging somewhere south of present-day Helena, 

Arkansas. This general configuration was maintained until late in the Wisconsin 

stage, when the Mississippi shifted east of the Ridge and the Ohio became 

confluent farther north. The alluvial landforms within the valley that resulted 

from glacial outwash during the Pleistocene epoch usually exhibit surface 

features characteristics of braided-stream deposition, such as relict braid bars and 

gathering channels. They dominate the alluvial valley north of the latitude of 

Memphis. 

 Glacial outwash deposition ceased within the Lower Mississippi Alluvial 

Valley at the beginning of the Holocene epoch, about 10,000 years ago. Sea 

level variation continued to influence depositional processes in the southernmost 

parts of the valley, but, in the central and northern portions of the Valley, all 

Holocene alluvial surfaces have been primarily the result of meandering stream 

processes, which have reworked much of the earlier braided-stream deposits and 

produced distinctly different landscape features. During Holocene times, the 

Mississippi and Arkansas Rivers, and various smaller streams, have reworked 

portions of the glacially deposited material within broad meander belts, and the 

larger streams have relocated and established new meander belts at various times. 

 Within its meander belts, the Mississippi River has removed the pre-Holocene 

glacial outwash to an average depth of about 30 m (the average depth of the river 

channel) and replaced it with a complex of depositional features that include 
20 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

abandoned stream channels, abandoned stream courses, point bar deposits, and 

natural levees. Within the Yazoo Basin, the existence of six distinct Mississippi 

River meander belts is indicated. Each meander belt is 5 or more kilometers 

wide, but their characteristics vary, evidently reflecting differing levels of 

discharge in response to climatic variation or because they carried only part of 

the total discharge of the river, the remainder being carried by a separate channel. 

 The current meander belt has been occupied and carrying the full flow of the 

Mississippi River for about 2,000 years. Because sedimentation rates are highest 

along the active stream channel, meander belts tend to develop into an alluvial 

ridge, where elevations are higher than the adjacent floodplain. The result is that 

local drainage is directed away from the major stream channel, and the areas 

between meander belts become basins that collect runoff, pool floodwaters, and 

accumulate fine sediments. 

Geomorphic features of the Yazoo Basin 

 The combination of Pleistocene alluvial terraces and modern (Holocene) 

floodplain features and depositional patterns has resulted in distinctive landforms 

that have been mapped in considerable detail throughout the valley (Figure 4). 

Within the Yazoo Basin, these landforms are categorized as valley trains, 

backswamps, point bars, abandoned channels, abandoned courses, and natural 

levees (Kolb et al. 1968, Saucier 1994). Each of these landforms is discussed 

and illustrated in the following paragraphs (Figure 5). 

a. Valley trains. Valley trains are Pleistocene glacial outwash deposits 

from the Mississippi and Ohio Rivers, with surface features that reflect 

braided-stream depositional regimes. Although they make up about 54 

percent of the Mississippi Alluvial Valley as a whole, they are of limited 

extent in the Yazoo Basin, where they have been largely eroded away by 

lateral channel migration or buried by deep sediments during recent 

(Holocene) times. The remnant valley train landscapes that occur in the 

northeastern and west-central part of the basin are evidently late 

Wisconsin in age, meaning they are at least 11,000 years old, but their 

precise age is not known. The topstratum of valley train deposits is a 

1.5- to 3-m-thick layer of predominantly fine-grained material that forms 

a continuous blanket across the relict braided channels and interfluves 

but does not obscure their presence. 

The topstratum may include materials laid down during waning stages of 

glacial outwash deposition, loess, and slackwater overbank deposits from 

later Mississippi River meander belts. The buried channel systems on 

valley trains differ from abandoned channels within the Mississippi 

River meander belts in that the valley train channels tend to be filled with 

coarse sediments (massive sands) below the surface veneer of finegrained material, whereas more recent channels are typically filled with 

fine-grained material throughout. 

b. Backswamps. Backswamps are flat, poorly drained areas bounded by 

uplands and/or other features such as natural levees. In the Yazoo Basin, 

they are commonly found between the various past and present meander
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 21 Figure 4. Principal geomorphic features of the Yazoo Basin (from Saucier 1994) 
22 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

 Figure 5. Block schematic of geomorphic features of the Yazoo Basin (from Saucier 1994) 

belts of the Mississippi River or adjacent to the valley wall. Backswamp 

environments are underlain by coarse glacial outwash, but surface 

deposits are fine-grained sediments that were slowly deposited in slackwater conditions. Thus, under unmodified conditions, backswamps 

characteristically have substrates of massive clays and are incompletely 

drained by small, sometimes anastomosing, streams. They may include 

large areas that do not fully drain through channel systems but remain 

ponded well into the growing season. In much of the Mississippi 

Alluvial Valley, backswamp deposits are 12 m thick or more, although 

they tend to be somewhat thinner in the south-central portion of the 

Yazoo Basin. 

Note that sites mapped as valley train and backswamp have essentially 

the same sequence of deep, coarse glacial outwash overlain by finegrained slackwater deposits. The basis for separating them as map units 

is the thickness of the fine-grained deposits; they are mapped as 

backswamp where the surface deposits are sufficiently thick to obscure 

the braided channel pattern on the valley train surface. On valley trains, 

surface deposits (other than those from historic erosion) are typically 

older and thinner and occupy better-drained landscape positions than 

similar fine-grained deposits of backswamps. 

c. Point bars. Point bar deposits predominate within the Yazoo Basin. 

They generally consist of relatively coarse-grained materials (silts and 

sands) laid down on the inside (convex) bend of a migrating stream 

channel. The rate at which point bar deposition occurs and the height 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 23

and width of individual deposits vary with sediment supply, flood stage, 

and other factors. The result is a characteristic topography of low 

arcuate ridges separated by swales. Point bar swales range from narrow 

and shallow to broad and deep and usually are closed at each end to form 

depressions. The scale and depth of point bar swales depend on the 

depositional environment that formed the adjacent ridges and the degree 

of sedimentation within the swale since it formed. 

d. Abandoned channels. These features are the result of cutoffs, where a 

stream abandons a channel segment either because flood flows have 

scoured out a point bar swale and created a new main channel (chute 

cutoff) or because migrating bendways intersect and channel flow moves 

through the neck (neck cutoff). Chute cutoffs tend to be relatively small 

and to fill rapidly with sediment. They do not typically form lakes, but 

may persist as large depressions. The typical sequence of events 

following a neck cutoff (which is much more common than a chute 

cutoff) is that the upper and lower ends of the abandoned channel 

segment quickly fill with coarse sediments, creating an open oxbow lake. 

Usually, small connecting channels (batture channels) maintain a 

connection between the river and the lake, at least at high river stages; so 

river-borne fine-grained sediments gradually fill the abandoned channel 

segment. If this process is not interrupted, the lake eventually fills 

completely, the result being an arcuate swath of cohesive, impermeable 

clays within a better-drained point bar deposit. Often, however, the river 

migrates away from the channel segment and the hydraulic connection is 

lost, or the connection is interrupted by later deposition of point bar or 

natural levee deposits. In either case, the filling process is dramatically 

slowed, and abandoned channel segments may persist as open lakes or 

depressions of various depths and dimensions. 

e. Abandoned courses. An abandoned course is a stream channel segment 

left behind when a stream diverts flow to a new meander belt. 

Abandoned course segments can be hundreds of miles long, or only short 

segments may remain where the original course has been largely 

obliterated by subsequent stream activity. There are a variety of possible 

fates for abandoned courses. In some cases, they are captured by smaller 

streams, which meander within the former channel and develop their own 

point bars and other features. Within the Yazoo Basin, much of the 

Tallahatchie and Yazoo Rivers, and portions of many smaller streams, 

flow within abandoned courses of the Mississippi River. Where the 

stream course is abandoned gradually, the remnant stream may fill the 

former channel with point bar deposits even as its flow declines. Thus, 

while abandoned channels often become depressions with heavy soils, 

abandoned courses are more likely to be fairly continuous with the point 

bar deposits of the original stream or to become part of the meander belt 

of a smaller stream. 

f. Natural levees. A natural levee forms where overbank flows result in 

deposition of relatively coarse sediments (sand and silt) adjacent to the 

stream channel. The material is deposited as a continuous sheet that 
24 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

thins with distance from the stream, resulting in a relatively high ridge 

along the bankline and a gradual backslope that becomes progressively 

more fine-grained with distance from the channel. Along the modern 

Mississippi River, natural levees rise about 4.5 m above the elevation of 

the adjacent floodplain and may extend for several kilometers or more 

from the channel. Natural levees formed by smaller streams or over 

short periods of time tend to be proportionately smaller, but the 

dimensions and composition of natural levee deposits are the product of 

various factors, including sediment sources and the specific mode of 

deposition. Natural levees may be deposited in association with 

sheetflow or as a series of crevasse splays, which are deltaic deposits 

formed by small channels that breach the existing natural levee during 

high flows. 

A different type of crevasse splay occurs where man-made levees have 

been breached during major floods. These splays have an irregular, 

hummocky surface, and are composed of very coarse sediments, may be 

very extensive. They are the result of very high-velocity flows, because 

the initial levee break releases water that has a surface much higher than 

the adjacent land surface. Often, the point at which the levee failed is 

marked by a deep scour pool, commonly called a “blue hole.” 

Soils 

 Parent materials of soils in the Yazoo Basin are fluvial sediments. The 

periodic influx of glacial outwash and subsequent development of multiple 

Mississippi River meander belts produced complex but characteristic landforms 

where sediments are sorted to varying degrees based on their mode and 

environment of deposition. The sorting process has produced textural and 

topographic gradients that are fairly consistent on a gross level and result in 

distinctive soils. Generally, within a meander belt, surface substrates grade from 

relatively coarse-textured, well-drained, higher elevation soils on natural levees 

directly adjacent to river channels through progressively finer-textured and less 

well-drained materials on levee backslopes and point bar deposits to very heavy 

clays in closed basins within large swales and abandoned channels. Backswamp 

deposits between meander belts are also heavy clays. Valley train deposits 

typically have a topstratum (upper 1.5-3 m) of fine-grained material (clays and 

silts) that blankets the underlying network of braided channels and bars (Brown 

et al. 1971, Saucier 1994). 

 The gradient of increasingly fine soil textures from high-energy to lowenergy environments of deposition (natural levees and point bars to abandoned 

channels and backswamps) implies increasing soil organic matter content, 

increasing cation exchange capacity, and decreasing permeability. However, all 

of these patterns are generalizations, and quite different conditions occur 

regularly. The nature of alluvial deposition varies between and within flood 

events, and laminated or localized deposits of varying textures are common 

within a single general landform. Thus, natural levees dominated by coarsetextured sediments may contain strata with high clay content, and valley train 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 25

surfaces that are usually fine-grained may have some soil units with high sand 

content. Point bar deposits, which typically have less organic matter 

incorporated into the surface soils than backswamps or abandoned channels, may 

actually contain more total organic matter on a volume basis due to the presence 

of large numbers of buried logs and other stream-transported organic material 

(Saucier 1994). 

 Climate also has had significant influence on soil development, particularly 

with respect to organic matter accumulation and weathering processes. In 

general, the A horizons of soils in the Yazoo Basin are lighter than those in more 

northerly portions of the Mississippi Alluvial Valley where colder temperatures 

and lower rainfall inhibit the oxidation of organic material. Similarly, soils to the 

south of the Yazoo Basin also have dark A horizons due to a longer growing 

season and more evenly distributed precipitation, which promote high plant 

productivity and maintain equilibrium between organic matter gains and losses 

(Brown et al. 1971). 

 Soils of older meander belts are likely to show greater A soil horizon 

development than soils in equivalent positions within younger meander belts 

(Autin et al. 1991). Similarly, older soils are likely to be more acid and deeper, 

show less depositional stratification and more horizonation, and have other 

characteristics of more advanced soil development than soils of younger meander 

belts. The classification of soils in the region reflects the importance of soil age 

and related development at the highest classification level (Soil Order). Alfisols 

are the oldest and most developed soils; Entisols are the most recent deposits 

with the least development; and Inceptisols are of intermediate age and 

development. At the suborder level, degree of wetness is a major classification 

factor, and, at lower levels of classification, the characteristics of specific soil 

horizons are among the principal discriminating factors. A brief overview of the 

principal soil associations within the Yazoo Basin is presented in Table 5. 

 Table 6 contrasts selected characteristics of soils on surfaces of increasing 

age (meander belt 1 is youngest, 5 is oldest) for relatively coarse-textured 

(Commerce-Mhoon-Dundee) and clayey (Sharkey-Alligator) deposits. Note that 

“pedogenic succession” is more pronounced in the coarser materials (Autin et al. 

1991). The distribution of the major associations in the Yazoo Basin is 

illustrated in Figure 6. It should be noted that the classification of soils within the 

Yazoo Basin has been undergoing considerable modification recently. However, 

the existing soil surveys and maps do not reflect these changes; therefore, the 

classification and terminology used in this discussion remain consistent with the 

existing published resources. 

Vegetation 

 The Yazoo Basin is in the east-central portion of the Mississippi Alluvial 

Plain Ecoregion (Omernik 1987, USEPA 1998). It is included in the Mississippi 

Alluvial Plain Section of the Southeastern Evergreen Forest Region of Braun 

(1950) and is classified as the Southern Floodplain Forest Type of Kuchler 
26 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

Table 5 

Classification of the Principal Soil Associations of the Yazoo Basin (after U.S. Department of Agriculture-SCS-MAFES 1974 and U.S. Department of Agriculture-NRCS 1998b)

Order Alfisols: Soils that are medium to high in bases and have gray to brown A horizons and B horizons of clay 

accumulation. 

Suborder Aqualfs: Seasonally wet Alfisols that have mottles, iron-manganese concretions, or gray colors. 

Great Group Ochraqualf (now called Endoaqualfs): Dominantly wet soils with a gradual change in texture from the A 

horizon to the B horizon of clay accumulation. 

A-2 Dundee-Dubbs association 

Nearly level or gently sloping and somewhat poorly drained; and well-drained silty soils on natural 

levees. 

A-3 Dundee-Forestdale-Dubbs association 

Nearly level or gently sloping and somewhat poorly drained silty soils; poorly drained soils with silty A 

horizons and clayey B-horizons; and well-drained silty soils on natural levees. 

A-4 Forestdale-Alligator association 

Nearly level, poorly drained soils with silty A horizons and clayey B-horizons on natural levees; and 

poorly drained, clayey soils on floodplains. 

Suborder Udalfs: Alfisols that are usually moist but, during the warm season of the year, may be intermittently dry in 

some horizons for short periods. 

Great Group Hapludalfs: Dominantly soils with light colored A horizons and brownish or reddish moderately thick B 

horizons of clay accumulation. 

A-10 Dubbs-Dundee association 

Nearly level and gently sloping, well-drained and somewhat poorly drained silty soils on natural 

levees. 

Order Entisols: Soils that have no little or evidence of development of pedogenic horizons. 

Suborder Aquents: Entisols that are wet for long periods and have gray colors. 

Great Group Fluvaquents: Dominantly wet soils of floodplains with a content of organic matter that decreases irregularly 

with depth. 

E-3 Commerce-Robinsonville-Crevasse association 

Nearly level, somewhat poorly drained, silty soils; well-drained, loamy soils; and excessively drained, 

sandy soils. 

E-5 Commerce-Tunica-Bowdre association 

Nearly level, somewhat poorly drained, silty soils; and poorly drained and somewhat poorly drained, 

clayey over loamy soils. 

E-6 Falaya-Collins-Waverly association 

Nearly level, somewhat poorly drained, moderately well-drained, and poorly drained, acid, silty soils. 

Suborder Fluvents: Dominantly soils that are brownish colored, are rarely wet, and have a content of organic matter 

that decreases irregularly with depth. 

Great Group Udifluvents: Dominantly soils of floodplains that are usually moist. 

E-11 Morganfield-Adler association 

Nearly level, well-drained and moderately well-drained, nonacid, silty soils. 

Order Inceptisols: Soils that have weakly differentiated horizons; materials in the soil have been altered or removed but 

have not accumulated. 

Suborder Aquepts: Inceptisols that are seasonally wet and have gray colors 

Great Group Haplaquepts: Dominantly wet soils with a light colored or a thin dark A horizon. 

I-1 Alligator association 

Nearly level, poorly drained, acid, clayey soils in backswamp areas of the floodplain. 

I-2 Alligator-Forestdale association 

Nearly level, poorly drained, clayey soils on floodplains; and poorly drained soils with thin silty A 

horizons and clayey B horizons on natural levees. 

I-4 Sharkey association 

Nearly level, poorly drained, nonacid, clayey soils on floodplains. 

I-5 Sharkey-Alligator association 

Nearly level, poorly drained, nonacid and acid, clayey soils on floodplains. 

I-6 Sharkey-Commerce association, frequently flooded 

Nearly level, poorly drained, nonacid, clayey soils; and somewhat poorly drained, nonacid, silty soils. 

I-7 Sharkey-Tunica association 

Nearly level, poorly drained, nonacid, clayey soils; and somewhat poorly drained, nonacid, clayey 

over loamy soils on floodplains. 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 27

Table 6 

Comparisons of Typical Landscape Settings and Soil Development for Selected Soil 

Series in the Yazoo Basin. (Adapted from Autin et al. 1991, with supplemental 

information from Brown et al. 1971 and U.S. Department of Agriculture-NRCS 1998a)

Mississippi River Meander Belts1

Characteristics 1,2 1,2 3,4,5 1,2,3 3,4,5 

Soil Series Commerce Mhoon Dundee Sharkey Alligator 

Classification Aeric 

Fluvaquent Typic Fluvaquent Aeric Ochraqualf Vertic 

Haplaquept 

Vertic 

Haplaquept 

Geomorphic setting levee crest and 

backslope levee backslope levee, low 

terraces 

levee backslope. 

backswamp 

backswamp, low 

terraces, (valley 

train) 

Solum thickness, cm 50-100 50-125 60-150 90-150 100-150 

Typical horizon 

sequence A-B-C A-Bg-Cg A-Btg-Bg-Cg A-Bg-Cg A-Bg-Cg 

1

 Of the meander belts included here, meander belt 1 is the active meander belt of the Mississippi River and meander belt 5 is 

the oldest. 

(1969). Forests of the basin are referred to as bottomland hardwoods, a term 

which incorporates a wide range of species and community types, all of which 

can tolerate inundation or soil saturation for at least some portion of the growing 

season (Wharton et al. 1982). Bottomland hardwood forests are among the most 

productive and diverse ecosystems in North America. Under presettlement 

conditions, they were essentially continuous throughout the Lower Mississippi 

Valley, and they interacted with the entire watershed, via floodwaters, to import, 

store, cycle, and export nutrients (Brinson et al. 1980, Wharton et al. 1982). 

Although these conditions have changed dramatically in modern times (see the 

following section, Alterations to Environmental Conditions), the remaining 

forests still exist as a complex mosaic of community types that reflect variations 

in alluvial and hydrologic environments. Within-stand diversity varies from 

dominance by one or a few species to forests with a dozen or more overstory 

species and diverse assemblages of understory, ground cover, and vine species 

(Putnam 1951, Wharton et al. 1982, Wiseman 1982, Klimas 1988). These forests 

support a detritus-based trophic network that includes numerous resident and 

migratory wildlife species that are adapted to the highly dynamic and diverse 

environment (Fredrickson 1978, Wharton et al. 1982). 

 Most major overviews of bottomland hardwood forest ecology emphasize the 

relationship between plant community distribution and inundation, usually 

assuming that floodplain surfaces that occupy different elevations in relation to a 

river channel reflect different flood frequency, depth, and duration (e.g., Wharton 

and Brinson 1978, Brinson et al. 1981, Larson et al. 1981, Wharton et al. 1982). 

This leads to classification of forests in terms of hydrologic “zones,” each zone 

having characteristic plant communities. In most cases, the authors employing 

zonal classification systems acknowledge that parallel bands of vegetation rarely 

exist and that most floodplains are geomorphically complex and support mosaics 

of communities. Nevertheless, zonal characterization systems generally reference 

most sites to a presumed stream entrenchment process that leaves a sequence of 

terraces, and they often regard features such as natural levees as relatively minor 

components of the landscape (e.g., Larson et al. 1981). A certain degree of such 

sequential zonation occurs in some major stream drainages within the Mississippi 
28 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

Figure 6. Major soil associations of the Yazoo Basin 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 29

Alluvial Valley, such as the Cache River in Arkansas (Smith 1996). However, 

zonal concepts have limited utility in the Yazoo Basin, where multiple meander 

belts of the Mississippi River dominate the landscape. All major stream systems 

that internally drain the basin are either captured by these meander belts or are 

constrained between them and have not formed a series of abandoned floodplain 

“terraces.” In the Yazoo Basin, the term “terrace” generally refers to glacial 

outwash valley train deposits rather than abandoned floodplains of extant 

tributary streams. Features such as natural levees and abandoned channels, 

which may be rather minor components of some southeastern floodplains, are 

major deposits that occupy thousands of square kilometers in the Yazoo Basin. 

In much the same way, the general zonal models imply that the principal 

hydrologic controls on community composition are flood frequency, depth, and 

duration, as indicated by elevation relative to a stream channel. As described 

previously, overbank flooding is just one of many important sources of water in 

the wetlands of the Yazoo Basin, and factors such as ponding of precipitation 

may be more important than flooding effects in many landscape settings. 

 Despite the complexity of the landscape and the limited applicability of zonal 

models of plant community distribution, plant communities do occur on 

recognizable combinations of site hydrology and geomorphology within the 

Yazoo Basin. The synthesis documents of Putnam (1951) and Putnam, Furnival, 

and McKnight (1960) adopt a perspective that recognizes the unique terrain of 

the Mississippi Alluvial Valley and summarize the principal combinations of 

landscape setting, drainage characteristics, and flood environment as they 

influence plant community composition. Table 7 is based on that approach. 

Table 8 equates Putnam’s (1951) community types with corresponding 

community designations in the most commonly referenced forest classification 

system, the Society of American Forester’s (SAF) cover types (Eyre 1980). 

 Under natural conditions, forest stands within the Yazoo Basin undergo 

change at various temporal and spatial scales. Primary succession occurs on 

recently deposited substrates, which include abandoned stream channels, point 

bars, crevasse splays, and abandoned beaver ponds. One familiar example is the 

colonization of new bars adjacent to river channels by black willow (Salix nigra), 

which is replaced over time by other species such as sugarberry (Celtis laevigata) 

and green ash (Fraxinus pennsylvanica) and eventually by long-lived, heavyseeded species such as oaks (Quercus sp.) and hickories (Carya sp.) (Putnam, 

Furnival, and McKnight 1960, Meadows and Nowacki 1996). Although this 

sequential replacement does occur, it is actually a complex process that includes 

changes in the elevation and composition of the substrate as colonizing plants 

and flood flows interact to induce sedimentation and, on a longer-term scale, as 

soils mature and river channels migrate away from the site and cease delivering 

large volumes of new sediments. In the Yazoo Basin, creation and colonization 

of new point bars is limited, because many of the internal streams are deeply 

entrenched within old Mississippi River channels or have been channelized and 

do not migrate significantly. Creation of other new substrates due to Mississippi 

River channel migration and overbank flows has been curtailed in the Yazoo 

Basin by levee construction and bank stabilization projects (Klimas 1991). 
30 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

Table 7 

Composition and Site Affinities of Common Forest Communities in the Yazoo Basin 

(after Putnam 1951)

Forest Cover Type Characteristic Species Site Characteristics 

Sweetgum - 

water oaks 

Liquidambar styraciflua 

Quercus nigra 

Quercus nuttallii 

Quercus phellos 

Ulmus americana 

Celtis laevigata 

Fraxinus pennsylvanica

In first bottoms except for deep sloughs, 

swamps, fronts, and poorest flats. Also 

on terrace flats. 

White oaks - 

red oaks - 

other hardwoods 

Quercus michauxii 

Quercus stellata var. paludosa 

Quercus falcata var. pagodifolia 

Quercus shumardii 

Quercus falcata var. falcata 

Fraxinus americana 

Carya spp. 

Nyssa sylvatica 

Ulmus alata

Fine, sandy loam and other well-drained 

soils on first bottom and terrace ridges. 

Hackberry - 

elm - 

ash 

Celtis laevigata 

Ulmus americana 

Fraxinus pennsylvanica 

Carya aquatica 

Quercus phellos 

Low ridges, flats, and sloughs in first 

bottoms, terrace flats, and sloughs. 

Occasionally on new lands or fronts. 

Overcup oak - 

water hickory 

Quercus lyrata 

Carya aquatica 

Poorly drained flats, low ridges, 

sloughs, and backwater basins with 

tight soils. 

Cottonwood 

Populus deltoides 

Carya illinoensis 

Platanus occidentalis 

Celtis laevigata 

Front land ridges and well-drained flats. 

 

Willow Salix nigra Front land sloughs and low flats. 

Riverfront 

hardwoods 

Platanus occidentalis 

Carya illinoensis 

Fraxinus pennsylvanica 

Ulmus americana 

Celtis laevigata 

Acer saccharinum 

All front lands except deep sloughs and 

swamps. 

Cypress - 

tupelo 

Taxodium distichum 

Nyssa aquatica 

Nyssa sylvatica var. biflora 

Low, poorly drained flats, deep sloughs, 

and swamps in first bottoms and 

terraces. 

Table 8 

Correspondence Between Putnam’s Community Forest Cover Types in the Yazoo Basin 

and Standard Society of American Foresters (SAF) Forest Cover Type Designations

SAF Forest Cover Types 1 Type # Putnam’s Cover Type2

Cottonwood 63 Cottonwood 

Willow Oak - water oak - diamondleaf (Laurel) oak 88 Sweetgum - water oaks 

Swamp chestnut oak- cherrybark oak 91 White oaks - red oaks - other hardwoods 

Sweetgum - willow oak 92 Sweetgum - water oaks 

Sugarberry - American elm - green ash 93 Hackberry - elm - ash 

Sycamore - sweetgum - American elm 94 Riverfront hardwoods 

Black willow 95 Willow 

Overcup oak - water hickory 96 Overcup oak - bitter pecan 

Baldcypress 101 Cypress - tupelo 

Baldcypress - tupelo 102 Cypress - tupelo 

Water tupelo - swamp tupelo 103 Cypress - tupelo 

1

 SAF forest cover type naming conventions. 

2

 Putnam (1951). 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 31

 Typically, natural regeneration processes in established forest stands are 

initiated within small forest openings that occur due to windthrow, disease, 

lightning strikes, and similar influences that kill individual trees or small groups 

of trees (Dickson 1991) or in larger openings caused by fire, prolonged flooding 

(especially due to beaver), tornados, hurricanes, or ice storms. The resulting 

openings are rapidly colonized, but the composition of the colonizing trees may 

vary widely depending on factors such as existing advanced reproduction, seed 

rain from adjacent mature trees, and importation of seed by animals or 

floodwaters. Often, this pattern results in small, even-aged groves of trees, 

sometimes of a single species (Putnam, Furnival, and McKnight 1960). 

 Under presettlement conditions, fire may have been a significant factor in 

stand structure, but the evidence regarding the extent of this influence is unclear. 

 Putnam (1951) stated that southern bottomland forests experience a “serious fire 

season” every 5-8 years and that fires typically destroy much of the understory 

and cause damage to some larger trees that eventually provides points of entry 

for insects and disease. Similarly, it is difficult to estimate the influence of 

beaver in the presettlement landscape, because they were largely removed very 

early in the settlement process. However, it is likely that widespread beaver 

activity resulted in extensive areas of dead timber, open water, marsh, moist soil, 

and shrub swamp at any given time. 

Alterations to Environmental Conditions 

 The physical and biological environment of the Yazoo Basin has been 

extensively altered by human activity. Isolation and stabilization of the 

Mississippi River have effectively halted the large-scale channel migration and 

overbank sediment deposition processes that have continually modified the 

Yazoo Basin over the past 10,000 years (Smith and Winkley 1996). At the same 

time, sediment input to depressions and sub-basins within the area has increased 

manyfold in historic times due to erosion of uplands and agricultural fields 

(Barnhardt 1988, Smith and Patrick 1991, Saucier 1994). The Mississippi River 

no longer overwhelms the landscape with floods that course through the basin, 

but it continues to influence large areas through backwater effects. Patterns of 

land use and resource exploitation have had differential effects on the distribution 

and quality of remaining forest communities. Assessment of wetland functions in 

this highly modified landscape requires an understanding of the scope of some of 

the more ubiquitous changes that have taken place. 

Land use and management 

Natural levees, which commonly are the highest elevations in the landscape 

of the Yazoo Basin and often are in direct proximity to water, have been the 

focus of human settlement during both prehistoric and historic times (Saucier 

1994). At the time of European settlement, natural levees were extensively used 

for maize agriculture by Native Americans. By the time detailed surveys of the 

Mississippi River were made in the 1880s, there were extensive agricultural 

fields on the natural levees adjacent to the Mississippi River through the entire 
32 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

reach bordering the Yazoo Basin (Mississippi River Commission 1881-1897). 

Lower terrain had not been similarly developed, however, and in 1879 less than 

10 percent of the Yazoo Basin had been cleared. With improved flood control 

and farming equipment, conversion of forested land to agriculture progressed to 

other sites. From an estimated original area of 9 to 10 million hectares, 

Mississippi Alluvial Valley forests were reduced by about 50 percent by 1937, 

and, currently, less than 25 percent of the original area remains forested (Smith, 

Hamel, and Ford 1993). Much of the remaining forest is highly fragmented, 

with the greatest degree of fragmentation occurring on drier sites (such as natural 

levees) and the largest remaining tracts being in the wettest areas (Rudis 1995). 

The differential conversion of higher, drier sites to agriculture may be a major 

contributing factor in the near disappearance of the extensive stands of cane 

(Arundinaria gigantea), which many early travelers remarked upon as common 

features of the natural levees (Remsen 1986, Dickson 1991). Within the Yazoo 

Basin, approximately 10 percent of the original forest area remains. 

 Nearly all of the remaining forests within the basin have been harvested at 

least once, and many are in a degraded condition due to past high-grading 

practices (Putnam 1951, Rudis and Birdsey 1986). However, large intact tracts 

remained in the interior lowlands until at least the mid 1930s. Conarro (undated) 

described his efforts to purchase forested land in the Yazoo Basin on behalf of 

the U.S. Forest Service in 1935 (the origins of the Delta National Forest). He 

mentioned the purchase of “14,000 acres of virgin timber” (for $55 per acre), 

much of which he immediately marked for a timber sale. He also mentioned 

another “large block of virgin hardwood” that was currently being cut by a 

lumber company, and he noted his interest in purchasing another tract of “about 

46,000 acres of land from which the redgum and other high-grade species had 

been removed.” 

 Limited old-growth areas are protected within the Research Natural Area 

system on Delta National Forest, but most of the remaining forests are in various 

stages of recovery from past harvests, and many of the current stands of mature 

forest date from a period of intensive harvest activity in the 1930s and 1940s. 

Clearly, many of these stands originated from high-graded stands, and many have 

been subjected to additional selective harvests, some with the objective of timber 

stand improvement. Not all of the current forests are in a “managed” condition 

by any means, and very few are in any condition that reflects the “natural” 

development of forested stands over many generations. 

 Forest management has shifted to an emphasis on wildlife habitat in recent 

decades on many of the remaining large tracts. Much of this has come about as 

an attempt to mitigate some of the impacts of flood control and navigation 

projects within the Yazoo Basin and elsewhere in the region. Parts of the Delta 

National Forest were converted to green-tree reservoirs in the 1980s in an attempt 

to provide habitat for wintering waterfowl. Management of these areas requires 

pumping water into shallow, forested impoundments during late fall (Bolton and 

Metzger 1998). Water management systems have also been constructed within 

existing national wildlife refuge lands (Young 1998), and large forest tracts have 

been converted to wildlife management areas. Approximately 5,600 ha of former 

bottomland forest and wetlands that had been converted to agriculture have been 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 33

replanted, and more than 7,000 ha are scheduled for acquisition and reforestation 

in the future (Young 1998). In addition to these Federal mitigation efforts, 

considerable reforestation is underway on private lands, primarily under the 

auspices of the Wetland Reserve Program (WRP) administered by the Natural 

Resources Conservation Service of the U.S. Department of Agriculture. 

Hydrology 

The hydrology of the Yazoo Basin has been modified extensively and 

purposefully. Federal projects have largely protected the basin from the effects 

of major floods, allowing extensive land clearing and agricultural development. 

The water that enters or underlies the modern basin is rerouted, stored, and 

exported from the system in complex patterns that can result in more or less 

water available to remaining wetlands. For example, the uneven annual 

distribution of rainfall makes both supplemental irrigation and drainage common 

agricultural practices (Brown et al. 1971). Drainage may involve land leveling as 

well as ditching and can have various effects on wetlands, which may serve as 

sumps to which adjacent fields drain, and/or they may themselves be drained to 

streams or larger ditches. During periods of backwater flooding, these same 

artificial drainage networks may function in reverse and deliver water to low 

areas far from the source stream channels. Groundwater withdrawals, particularly 

for agricultural purposes, have caused depletion of the aquifer in some areas. In 

1994, more than 2,000 Mgal/day was withdrawn from wells in this aquifer 

(O’Hara 1996). However, the overwhelming influence on hydrology in the basin 

has been the Mississippi River and Tributaries Project (MR&T), which is the 

largest flood control project in the world (USACE, MVD 1998). In order to 

understand the extent to which hydrology has been modified in the Yazoo Basin 

and the way the remaining wetlands receive and move water, it is essential to 

understand the development and current status of the MR&T. 

 Efforts to control flooding on the lower Mississippi River began with the 

construction of small private levees in the early 19th century (Mississippi River 

Commission 1970). Levee construction in the Yazoo Basin portion of the Delta 

advanced quickly, and more than 500 km of levee were in place by 1858. Corps 

of Engineers activities through most of the 1800s focused principally on survey 

and engineering efforts relating to navigation improvement. In 1879, Congress 

authorized the creation of the Mississippi River Commission to oversee a 

coordinated Federal effort, carried out by the Corps of Engineers, to provide 

reliable navigation throughout the entire Mississippi River (Moore 1972). Over 

the next 5 decades, the authority of the Commission was expanded to include 

flood control, and its jurisdiction gradually enveloped various tributary stream 

systems. Funding was appropriated to support basic studies and projects, 

including channel dredging and the construction of an extensive levee system 

(Moore 1972). During the first decades of this century, local drainage districts 

were formed throughout the region to improve interior drainage (Barham 1964, 

Sartain undated). By 1927, levee construction and related works were believed 

to be providing effective protection from Mississippi River floods, as well as 

effective drainage for communities and farmlands throughout the entire lower 

valley. 
34 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

 A devastating flood in 1927 showed that the flood protection works were 

inadequate, and the Flood Control Act of 1928 authorized the Corps of Engineers 

to implement a new and comprehensive plan for preventing flooding in the 

Lower Mississippi Valley. The approach included construction of larger and 

stronger levees as well as various channel improvements, bank protection works, 

and other features. The multiple elements of this plan and its subsequent 

modifications are collectively referred to as the Mississippi River and Tributaries 

Project (MR&T) (Moore 1972). 

 Congress directed changes to the MR&T plan in the 1930s and 1940s that 

included the addition of cutoffs, tributary reservoirs, and an emphasis on 

maintenance of a stable, deep Mississippi River channel as a levee-protection 

measure and to provide navigation benefits. In the 1950s, 60s, and 70s, the 

project was expanded to include numerous tributary improvements, pump 

stations, harbor improvement projects, and lock and dam projects, as well as 

channel and levee projects, throughout the system. During this latter period, fish 

and wildlife considerations also became authorized project purposes. Meeting 

fish and wildlife objectives generally involved constructing water control 

structures within floodways and sump areas to allow habitat management for 

waterfowl (Moore 1972). 

 With the advent of the National Environmental Policy Act (NEPA) in 1969 

and other environmental legislation, proposed modifications to the MR&T have 

been subject to more complex planning and coordination requirements than 

previously existed. Actions likely to adversely affect fish, wildlife, wetland 

ecosystems, and other natural resources have been re-evaluated to identify ways 

to avoid or minimize environmental impacts (Moore 1972, Bolton and Metzger 

1998). Compensation for impacts deemed unavoidable has included acquisition 

and restoration of many thousands of acres of forest within the project area, as 

well as construction of additional water management facilities to benefit wildlife, 

particularly waterfowl (Young 1998). Maintenance of existing project features 

continues, and additional authorized features are under construction or in 

planning stages. The Yazoo Basin portion of the MR&T Project area has been 

the focus of a large proportion of the work to date, and additional flood control 

work is in the planning stages (Bolton and Metzger 1998). 

MR&T features in the Yazoo Basin 

 The original 1928 Flood Control Act required that flood control plans for 

certain tributary streams be developed in addition to the general plan for flood 

abatement along the mainstem Mississippi River. A 1931 report on the Yazoo 

Basin portion of the project area identified three major sources of flooding: 

overflow from the Mississippi River, backwater due to high stages on the Mississippi River, and direct overflow of the Yazoo River and its tributaries. The 

mainstem levee solved the first of these problems, but the remaining flooding 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 35

Figure 7. Major features of the MR&T Project in the Yazoo Basin 

sources have been addressed by a complex series of projects that were 

incrementally developed, authorized, and constructed over the past six decades. 
36 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

The planned work has not been completed to date, and in recent years the Corps 

has undertaken reformulation studies of the uncompleted work to develop 

alternatives that address changing objectives and concerns. Most of the major 

elements of the existing Yazoo Basin Project were carried out as three distinct 

components under separate authorizations. These are described in the following 

paragraphs and illustrated in Figure 7. 

a. Yazoo Headwater Area. The Yazoo Headwater Area includes about 

6,000 km2

 of the Mississippi Alluvial Valley and 17,000 km2 of hilly 

uplands upstream of Yazoo City. The principal project features are four 

detention reservoirs on headwater streams and a system of levees and 

channel works throughout the project area. Sardis Reservoir, on the 

Little Tallahatchie River, was completed in 1940; Arkabutla, on the 

Coldwater River, was completed in 1943; Enid, on the Yocona River, 

was completed in 1952; and Grenada, on the Yalobusha River, was 

completed in 1954. Together, these reservoirs reduced peak flows 

immediately downstream by more than two-thirds (Bolton and Metzger 

1998). Channel enlargements, clearing, and cutoff construction began in 

1939 and within 5 years work was underway on the Yalobusha, Yazoo, 

Tallahatchie, Little Tallahatchie, and Coldwater Rivers, as well as the 

Panola-Quitman Floodway and the Cassidy and Bobo Bayous. In the 

late 1940s and 1950s, channel excavation and clearing proceeded on the 

Arkabutla Canal, the Yocona River, the David and Burrell Bayous, and 

the Hillside Floodway. In the 1960s, the Lower Auxiliary Channel (Will 

M. Whittington Auxiliary Channel) was completed, which greatly 

reduced flooding on the lower Yazoo River (Bolton and Metzger 1998). 

Channel improvements and pumping facilities on McKinney Bayou were 

also built in that decade. Levee construction was an integral component 

of many of these actions, and by 1972 about 400 km of levees were in 

place within the headwater project area. 

b. Big Sunflower Area. The Big Sunflower Area includes approximately 

10,600 km2

 in northwest Mississippi. Work began in 1946 and 

consisted of channel clearing, enlargement, realignment, cutoffs, and 

other projects on the Big Sunflower, Little Sunflower, Huspuckena, and 

Quiver Rivers and their tributaries and on Hull Brake-Mill Creek Canal, 

Bogue Phalia, Ditchlow Bayou, Deer Creek, and Steele Bayou. In the 

1960s, additional work was authorized on Steele Bayou as well as Gin 

and Muddy Bayous. By 1972, 1,000 km of channel improvements had 

been completed under these authorizations. 

c. Yazoo Backwater Area. The Yazoo Backwater Area occupies the 

southern portion of the Yazoo Basin between the Mississippi River levee 

on the west and the valley wall to the south and east. It extends 

approximately 100 km to the north, to about the latitude of Belzoni. 

Flooding within the Yazoo Backwater Area can occur from various 

sources. Under the original flood control plan for the entire Lower 

Mississippi Valley, backwater areas (including the Yazoo Backwater) are 

protected by levees designed to be overtopped to relieve pressure on 

mainstem levees during extreme floods on the Mississippi River. 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 37

Further, such areas are designed to carry floodwater entering through 

gaps in the backwater (tributary) levee during high stages on the 

Mississippi River. Therefore, the Yazoo Backwater Area is a floodstorage component of the overall MR&T Project. However, because the 

backwater levee system also impounds internal drainage and extends 

flood durations and depths within parts of the backwater area, the project 

authorizations have included provisions to protect certain areas from 

backwater flooding and to evacuate impounded floodwaters as quickly as 

possible. 

The Yazoo Backwater Area project is subdivided into five parts. The 

first part, know as the Yazoo Area, comprises about 82 percent of the 

backwater area west of the Will M. Whittington Auxiliary Channel. The 

Big Sunflower River, Little Sunflower River, Deer Creek, and Steele 

Bayou flow through the area, and the Deer Creek natural levee forms a 

divide between the Steele Bayou and Sunflower River drainage basins. 

A levee along the west bank of the Yazoo River connects the Mississippi 

River mainstem levee with the Will Whittington Auxiliary Channel 

levee, and it incorporates drainage structures at the mouth of the Little 

Sunflower and at the mouth of Steele Bayou. The other major project 

components are channels, from the Big Sunflower to the Little Sunflower 

Rivers and then to Steel Bayou, which connect the sumps and leveeimpounded areas interior to the levee system. These features were all 

completed between 1969 and 1978. The final planned element of the 

project was a pumping plant at Steele Bayou to allow evacuation of 

water ponded within the levee system during periods when high water on 

the Mississippi and Yazoo Rivers preclude opening of the drainage 

structures at the Little Sunflower and Steele Bayou. The pump station 

has not been completed (see the following section, Yazoo Basin 

Reformulation Study) 

In the 1970s, the Yazoo Backwater Project was modified to include 

installation of a water control structure to improve water quality and 

facilitate fish management. Another modification to the Project was the 

construction of green-tree reservoirs and slough impoundments within 

Delta National Forest as mitigation for fish and wildlife impacts resulting 

from constructed flood control works in the backwater area. 

The second part of the Yazoo Backwater Area, known as the Carter 

Area, occupies about 400 km2 that lie east of the Auxiliary Channel and 

west of the Yazoo River. It is not protected from Yazoo River flooding 

in the reach from Yazoo City to the Auxiliary Channel east levee. The 

authorized project calls for completion of a levee on the west bank of the 

river and construction of an interior channel and drainage structure to 

evacuate interior flooding. No work has been initiated on these project 

features, and, in recent years, large sections of the Carter Area have been 

converted to environmental purposes. For example, the majority of the 

Panther Swamp National Wildlife Refuge and part of the Lake George 

Wildlife Wetland Restoration Project are within the Carter Area. 
38 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

The third part, known as the Rocky Bayou Area, is located east of the 

Yazoo River and west of the hills, between Yazoo City and Satartia. A 

locally constructed levee system provides partial protection to an area of 

about 57 km2

. Interior drainage is provided through a floodgate near the 

southern junction of the levee and the hills. The authorized project 

would bring the levee system up to project standards and replace the 

floodgate, but no work has been completed other than a short levee 

segment upgraded in conjunction with a highway construction project. 

The fourth part of the project area, known as the Satartia Area consists of 

about 115 km2

 that includes the town of Satartia and lands to the south of 

town, between the Yazoo River and the hills. In 1976, a loop levee was 

completed around this area, tying into the hills, and with internal 

drainage provided by a floodgate. 

The fifth part, known as the Satartia Extension Area, is a 13-km2

 area 

south of the Satartia Area. Flood protection measures similar to those 

employed in the Satartia Area have been authorized, but no construction 

has been initiated. 

d. Yazoo Basin Reformulation Study. In 1989, the Yazoo Basin Reformulation Study was initiated to consider the remaining unconstructed features 

of the Yazoo Basin Project. Alternatives under consideration fall into 

three general categories: (a) no further action, (b) implementation of 

nonstructural solutions to flooding problems (such as purchasing flood 

easements), and (c) implementation of structural solutions. Structural 

alternatives are likely to be of significantly reduced scope relative to the 

authorized projects and to incorporate various measures to minimize or 

offset environmental impacts. However, structural alternatives under 

consideration include extensive channel enlargement in the YazooTallahatchie-Coldwater Rivers, installation of the Steele Bayou pumping 

plant, and similar actions that would effect considerable changes in the 

hydrology of portions of the Yazoo Basin. Similarly, mitigation 

measures that would accompany implementation of such structural 

solutions would involve extensive reforestation, other habitat restoration, 

and water management specifically to benefit fish and wildlife (USACE 

1997). 

Description of Regional Wetland Subclasses 

 Reconnaissance studies during 1997 and 1998 indicated that four of the 

seven HGM wetland classes identified by Smith et al. (1995) were relatively 

common within the Yazoo Basin. These included the Flats, Riverine, Depression, and Fringe classes. These four wetland classes were subdivided into seven 

regional wetland subclasses including Flats, Riverine Overbank, Riverine 

Backwater, Isolated Depression, Connected Depression, Isolated Fringe, and 

Connected Fringe. A general description of each of these regional wetland subclasses is provided in the following paragraphs. Figure 8 illustrates typical 
Characterization of Regional Wetland Subclasses in the Yazoo Basin 39 Figure 8. Typical hydrologic conditions, geomorphic settings, and plant communities associated with regional wetland subclasses of the Yazoo Basin 
40 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

hydrologic conditions, geomorphic settings, and plant communities associated 

with each of the regional wetland classes and subclasses. 

Flats 

 The Flats Subclass may occur on a variety of depositional surfaces, but is 

most characteristic of point bar deposits. It includes the driest communities in 

the study area, with species such as shagbark hickory (Carya ovata) and water 

oak (Quercus nigra) being characteristic. There is also a wet phase of the flats 

community, found in large, shallow depressions that do not meet the criteria for 

the Depression Subclass. These vernal pool sites typically support species such 

as overcup oak (Quercus lyrata) and water hickory (Carya aquatica). 

Riverine Backwater 

 The Riverine Backwater Subclass includes those wetlands subject to 

backwater flooding from streams at frequencies of 5 years or less. Backwater 

flooding is defined here as inundation resulting from impeded drainage, usually 

due to high water in downstream systems. A typical backwater flooding scenario 

is that a large stream in flood stage will prevent the tributary network from 

draining efficiently, and the low-lying areas associated with those tributaries will 

fill with relatively still water. In the Yazoo Basin, there is an additional type of 

backwater flooding that is related to the operation of structures within the floodcontrol project. However, in both cases, the principal criteria that establish areas 

as Riverine Backwater are: 

a. There is a direct connection to a channel system during flood stages (at 

least 5-year frequency). 

b. The channel connection is principally through backwater rather than 

overbank flows (at least 5-year frequency). 

c. Floodwaters largely drain from the site back to the channel as flood 

stages fall (rather than being retained on-site in large depressions). 

 The Riverine Backwater Subclass is similar to the Flats Subclass in that it 

occurs on various substrates and supports a broad range of community types. 

However, in its most common form it occupies backswamp deposits, and 

characteristic species include green ash (Fraxinus pennsylvanica) and Nuttall oak 

(Quercus nuttallii). Like the Flats Subclass, Riverine Backwater sites may have 

included vernal pools supporting species such as overcup oak (Quercus lyrata) 

and water hickory (Carya aquatica). 

Riverine Overbank 

 The Riverine Overbank Subclass includes those wetlands subject to direct 

overbank flooding at return intervals of 5 years or less. Overbank flooding 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 41

differs from backwater flooding in that flows move parallel to the stream channel 

and maintain moderate-to-high velocities. Not many sites meet this criterion 

within the Yazoo Basin because channel incision and levees have disconnected 

most streams from their adjacent historic floodplains. Riverine Overbank wetlands occur primarily along banks and on small bars within the incised channels 

of streams and on the limited floodplain surfaces adjacent to some channels. 

Sites subject to overbank flow are commonly on point bar or backswamp 

deposits, usually with a natural levee veneer. Off-channel areas subject to overbank flows may be similar to Flats in composition, though usually with a larger 

component of species with broad tolerance to sedimentation, such as box elder 

(Acer negundo) and sugarberry (Celtis laevigata). Certain communities and 

species are very characteristic of the riverfront area, such as black willow (Salix 

nigra), cottonwood (Populus deltoides), and sycamore (Platanus occidentalis). 

Included depressional areas may occur in high-flow channels and swales and 

typically support species such as swamp privet (Forestiera accuminata). 

Isolated Depression 

 Depressions (both isolated and connected) are distinguished from included 

depressional phases of the Flats and Riverine Subclasses in several ways. 

Depressions tend to occur in abandoned channels, abandoned courses, and large 

point bar swales, while included depressions in Flats and Riverine wetlands occur 

in minor swales or in areas bounded by natural levee deposits. Depressions hold 

water for extended periods due to their size, depth, and ability to collect surface 

and subsurface flows from an area much larger than the depression itself. They 

tend to fill during the winter and spring and dry very slowly. Prolonged rains 

may fill them periodically during the growing season, after which they again dry 

very slowly. Included depressions (vernal pools) in Flats and Riverine settings, 

in contrast, fill primarily due to direct precipitation inputs and dry out within 

days or weeks. Depression Subclass wetlands usually exhibit two or more of the 

following characteristics: 

a. Hydric soil indicators F2 (Loamy Gleyed Matrix) or A4 (Hydrogen 

Sulfide) (U.S. Department of Agriculture, NRCS 1998a). 

b. A topographic depression with Dowling or Tunica soils (flooded phase). 

 Dowling soils are not recognized in the current classification of soils in 

the Yazoo Basin, but they appear on the existing soil surveys and have 

proven to be useful in HGM classification. 

c. Vegetation includes a significant component of one or more of the 

following species: baldcypress (Taxodium distichum), swamp tupelo 

(Nyssa aquatica), swamp privet (Forestiera accuminata), water elm 

(Planera aquatica),and buttonbush (Cephalanthus occidentalis). 

 Depressions may be dominated or fringed by species such as overcup oak 

(Quercus lyrata) and water hickory (Carya aquatica), but will otherwise meet the 

criteria above. The Isolated Depression Subclass is not affected by overbank or 
42 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

backwater flooding during floods occurring at 5-year or more frequent return 

intervals. 

Connected Depression 

 The characteristics of Isolated Depressions described above apply equally to 

Connected Depressions. However, Connected Depressions have an additional 

water source due to periodic inundation by floodwaters. 

Isolated Fringe 

 Fringe wetlands occur along the perimeter of water bodies that maintain an 

open water zone at least 2 m deep in most years. The fringe wetland is in the 

fluctuation zone of the water body. Typical examples within the Delta include 

the baldcypress (Taxodium distichum) fringe common on oxbow lakes or the 

black willow (Salix nigra) fringe often associated with borrow pits. Isolated 

Fringe wetlands are disconnected from river flooding (5-year event), although 

they may have small inlet and outlet streams, at least during periods of high 

rainfall. 

Connected Fringe 

 Connected Fringe wetlands are similar in most respects to Isolated Fringe 

systems, but in addition have a direct connection to major stream systems during 

flood events. 

Identifying HGM Wetland Classes and Regional 

Subclasses 

 Identifying the regional wetland subclass for occurs at a particular site can be 

difficult at times because of the complexity of the landscape and hydrology 

within the Yazoo Basin. In order to facilitate this process, we developed 

classification criteria and keys for identifying the wetland class and regional 

subclasses to which a particular site belongs. The classification criteria are based 

on existing map data such as flood frequency, soils, and geomorphology. 

However, in some cases, the classification process will require field evaluation of 

additional factors to correctly ascertain the most appropriate designation for a 

particular site. 

 One of the primary criteria used to identify regional wetland subclasses in the 

Yazoo Basin is flood return interval. A 5-year or less flood return interval is 

regarded as sufficient to support major functions that involve periodic connection 

to stream systems. Sites with a flood return interval of 5 years or less are placed 

in the Riverine, Connected Depression, or Connected Fringe subclasses, while 

sites with a flood return interval greater than 5 years are placed in the Flats, 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 43

Isolated Depression, or Isolated Fringe subclasses. The 5-year threshold was 

selected for practical reasons, namely that the hydrologic models used to develop 

flood return interval maps in the Yazoo Basin have been verified using photography taken during specific 5-year flood events (Figure 9). Adopting this 

criterion necessarily implies that the baseline hydrologic condition in the basin 

includes the changes that have occurred as a result of the MR&T flood control 

project as it existed at the time the data were assembled for this document in 

1997. 

 The Fringe and Depression Classes are distinguished from the Flat and 

Riverine Classes by the fact that they occur in topographic depressions. The 

Fringe Class is distinguished from the Depression Class based on the depth of 

permanent water, and the Flat Class is distinguished from the Riverine Class 

based on the presence or absence of overbank flooding and backwater areas. 

 At the regional wetland subclass level, the classification recognizes that 

certain sites that function primarily as Fringe or Depression wetlands are 

periodically affected by stream flooding, and therefore have a Riverine functional 

component. This is incorporated in the classification system by establishing 

“river-connected” subclasses within the Fringe and Depression Classes. Sites 

that function primarily as Riverine or Flats wetlands often incorporate small, 

shallow depressions sometimes characterized as vernal pools and microdepressions, which are regarded as normal components of the Riverine and Flats 

ecosystems, and are not separated into the Depression Class unless they meet 

specific criteria. Connected Fringe and Depression Classes are distinguished 

from the Isolated Fringe and Depression Classes based on whether or not a site is 

within the 5-year floodplain. The Riverine Overbank and Riverine Backwater 

Classes are distinguished based on whether or not floodwater moves at a 

relatively high velocity in a direction parallel to the channel or has little flow and 

enters a site by moving laterally or backing up from the channel. 

 Figures 10 and 11 provide dichotomous keys that incorporate the foregoing 

criteria to identify the appropriate wetland class or regional wetland subclass for 

a particular site in the Yazoo Basin of the of the Lower Mississippi River 

Alluvial Valley. To use either key, begin at Number 1 and follow the leads to the 

appropriate wetland class or regional wetland subclass. 
44 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

Figure 9. Areas inundated during a 5-year flood event in the Yazoo Basin (from USACE Vicksburg 

District 1997) 
Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 45

Key To Wetland Classes in the Yazoo Basin of the Lower Mississippi River Alluvial Valley 

Key Characteristics (see discussions on criteria for individual subclasses in 

Chapter 3) Class 

1. Wetland is not within the 5-year floodplain of a stream (including both overbank and 

backwater areas) Go To #2 

 2. Wetland is associated with a topographic depression with extended (permanent 

or 

 seasonal) ponding 

Go To #3 

 2. Wetland not associated with a depression as above, but may include depressional 

 areas subject to short-term ponding of precipitation or floodwaters Flat 

1. Wetland is within the 5-year floodplain of a stream Go To #3 

 3. ...... Wetland is associated with a topographic depression with extended 

(permanent 

 or seasonal) ponding 

Go To #4 

 4. Wetland is associated with a depression with permanent water at least 

 2 m deep Fringe 

 4. Wetland is associated with a depression with permanent water less than 

 2 m deep, or with seasonal ponding Depression 

 3. Wetland not associated with a depression as above, but may include 

 depressional areas subject to short-term ponding of precipitation or 

 floodwaters 

Riverine 

 Figure 10. Key to the wetland classes in the Yazoo Basin 
46 Chapter 3 Characterization of Regional Wetland Subclasses in the Yazoo Basin 

Key To Regional Wetland Subclasses of the Yazoo Basin of the Lower Mississippi River Alluvial 

Valley 

Key Characteristics (see discussions on criteria for individual subclasses in 

Chapter 3) Subclass 

1. Wetland is a topographic depression with permanent water or seasonal ponding Go To #2 

 2. Wetland is a topographic depression with permanent water at least 2 m deep Go To #3 

 3. Wetland is within the 5-year floodplain of a stream Connected 

Fringe 

 3. Wetland is not within the 5-year floodplain of a stream Isolated Fringe 

 2. Wetland is a topographic depression with permanent water <2 m deep or 

 seasonal ponding (see additional criteria under isolated and connected 

 depression discussions) 

Go To# 4 

 4. Wetland is within the 5-year floodplain of a stream Connected 

Depression 

 4. Wetland is not within the 5-year floodplain of a stream Isolated 

Depression 

1. Wetland not a topographic depression as above, but may include small 

depression 

 areas subject to short-term ponding of precipitation or floodwaters 

Go To #5 

 5. Wetland is not within the 5-year floodplain of a stream Flat 

 5. Wetland is within the 5-year floodplain of a stream Go To #6 

 6. Floodwaters typically flow parallel to channel during a 5-year event 

 (moderate- to high- velocity downstream flow predominates) 

Riverine 

Overbank 

 6. Floodwaters typically back up into wetland due to high water 

 downstream during a 5-year event (slack-water conditions and slow 

 drainage predominate) 

Riverine 

Backwater 

 Figure 11. Key to the regional wetland subclasses in the Yazoo Basin 
Chapter 4 Wetland Functions and Assessment Models 47

4 Wetland Functions and 

Assessment Models 

 A variety of functions are performed by wetlands in the Yazoo Basin of the 

Mississippi Alluvial Valley. This Regional Guidebook contains models for 

assessing five of the seven regional wetland subclasses identified in the Yazoo 

Basin including the Flats, Riverine Overbank, Riverine Backwater, Isolated 

Depression, and Connected Depression regional wetland subclasses. Note that 

no assessment models were developed for the Isolated Fringe and Connected 

Fringe subclasses. This is because these subclasses are subjected to little impact 

in the Yazoo Basin. The following functions were selected for assessment in the 

five regional wetland subclasses: 

a. Detain Floodwater. 

b. Detain Precipitation. 

c. Cycle Nutrients. 

d. Export Organic Carbon. 

e. Remove Elements and Compounds. 

f. Maintain Plant Communities. 

g. Provide Fish and Wildlife Habitat. 

It should be noted that not all functions are assessed for each regional wetland 

subclass, and the form of the assessment model that is used to assess functions 

can vary from subclass to subclass. 

 In this chapter, each of the functions identified above is discussed generally 

in terms of the following topics: 

a. Definition and Applicability: This section defines the function, 

identifies the subclasses where the function is assessed, and identifies an 

independent quantitative measure that can be used to validate the 

functional index. 
48 Chapter 4 Wetland Functions and Assessment Models 

b. Rationale for Selecting the Function: This section provides the 

rationale for why a function was selected and discusses onsite and offsite 

effects that may occur as a result of lost functional capacity. 

c. Characteristics and Processes that Influence the Function: This 

section describes the characteristics and processes of the wetland and the 

surrounding landscape that influence the function and lay the 

groundwork for the description of assessment variables. 

d. General Form of the Assessment Model: This section presents the 

structure of the general assessment model and briefly describes the 

constituent variables. 

 In Chapter 5, detailed descriptions of assessment variables and the methods 

used to measure or estimate their values are presented. In addition, the specific 

form of the assessment models used to assess functions for each regional wetland 

subclass, and the functional capacity subindex curves are presented in Chapter 5. 

Function 1: Detain Floodwater 

Definition and applicability 

 This function reflects the ability of wetlands to store, convey, and reduce the 

velocity of floodwater as it moves through a wetland. The potential effects of 

this reduction are a damping of the downstream flood hydrograph, maintenance 

of postflood baseflow, and deposition of suspended sediments from the water 

column to the wetland. This function is assessed for the following regional 

wetland subclasses in the Yazoo Basin: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Connected Depression

 The recommended procedure for assessing this function involves estimation 

of “roughness” within the wetland, in addition to flood frequency. A potential 

independent, quantitative measure for validating the functional index is the 

volume of water stored per unit area per unit time (m3

/ha/time) at a discharge 

equivalent to the average annual peak event. 

Rationale for selecting the function 

 The capacity of wetlands to temporarily store and convey floodwater has 

been extensively documented (Dewey and Kropper Engineers 1964; Campbell 

and Johnson 1975; Dybvig and Hart 1977; Novitski 1978; Thomas and Hanson 

1981; Ogawa and Male 1983, 1986; Demissie and Kahn 1993). Many benefits 

related to the reduction of flood damage occur as a result of wetlands performing 
Chapter 4 Wetland Functions and Assessment Models 49

the function. Generally, floodwater interaction with wetlands tends to dampen 

and broaden the flood wave, which reduces peak discharge downstream. 

Similarly, wetlands can reduce the velocity of water currents and, as a result, 

reduce erosion (Ritter, Kochel, and Miller 1995). Some portion of the floodwater 

volume detained within floodplain wetlands is likely to be evaporated or 

transpired, reducing the overall volume of water moving downstream. The 

portion of the detained flow that infiltrates into the alluvial aquifer, or which 

returns to the channel very slowly via low-gradient surface routes, may be 

sufficiently delayed that it contributes significantly to the maintenance of 

baseflow in some streams long after flooding has ceased (Saucier 1994, O’Hara 

1996). Retention of particulates also is an important component of the flood 

detention function because sediment deposition directly alters the physical 

characteristics of the wetland (including hydrologic attributes) and influences 

downstream water quality. 

 This function deals specifically with the physical influences on flow and 

sediment dynamics described earlier. Floodwater interaction with floodplain 

wetlands influences a variety of other wetland functions in the Yazoo Basin, 

including nutrient mobility and storage and the quality of habitat for plants and 

animals. The role of flooding in maintenance of these functions is considered 

separately in other sections of this chapter. 

Characteristics and processes that influence the function 

 The capacity of a wetland to detain and moderate floodwaters is related to 

antecedent conditions, the characteristics of the particular flood event, the 

configuration and slope of the floodplain and channel, and the physical 

obstructions present within the wetland that interfere with flows. The intensity, 

duration, and spatial extent of precipitation events affect the magnitude of the 

stream discharge response. Typically, rainfall events of higher intensity, longer 

duration, and greater spatial extent result in greater flood peaks. Watershed 

characteristics such as size and shape, channel and watershed slopes, drainage 

density, and the presence of wetlands and lakes have a pronounced effect on the 

stormflow response (Brooks et al. 1991; Dunne and Leopold 1978; Ritter, 

Kochel, and Miller 1995; Leopold 1994; Patton 1988). The larger the watershed, 

the greater the volume and stream discharge peak that result from a rainfall event. 

 Watershed shape affects how quickly surface and subsurface flows reach the 

outlet to the watershed. For example, a round-shaped watershed concentrates 

runoff more quickly than an elongated one and will tend to have higher peak 

flows. Steeper hillslopes and channel gradients also result in quicker response 

and higher peak flows. The higher the drainage density (i.e., the sum of all the 

channel lengths divided by the watershed area), the faster water is concentrated at 

the watershed outlet and the higher the peak discharge. As the percentage of 

wetland area and/or reservoirs increases, the greater the flattening effect (i.e., 

attenuation) will be on the stormflow hydrograph. In general, these climatic and 

watershed characteristics are consistent within a given region and are considered 

constant for the purposes of rapid assessment. 
50 Chapter 4 Wetland Functions and Assessment Models 

 The physical characteristics of the floodplain and the stream channel also are 

important determinants of floodflow interactions. The morphology of the stream 

channel and its floodplain reflects the discharges and sediment loads that have 

occurred in the past. Under stable flow and sediment conditions, the stream and 

its floodplain will eventually achieve equilibrium. Alteration to the stream 

channel or its watershed may cause instability that results in channel aggradation 

or degradation and a change in depth, frequency, and duration of overbank flow 

events (Dunne and Leopold 1978; Rosgen1994). As the stream channel 

aggrades, available water storage in the channel decreases, resulting in greater 

depth, frequency, and duration of flooding (on the floodplain) and an increase in 

amount of surface water stored in the wetland over an annual cycle. Conversely, 

as the stream channel degrades, available water storage in the channel increases, 

resulting in less depth, frequency, and duration of flooding and a decrease in the 

amount of surface water stored in the wetland over an annual cycle. The duration 

of water storage is secondarily influenced by the slope and roughness of the 

floodplain. Slope refers to the gradient of the floodplain across which 

floodwaters flow. Roughness refers to the resistance to flow created by 

vegetation, debris, and topographic relief. In general, duration increases as 

roughness increases and slope decreases. 

 Of all of the characteristics described above, only flood frequency and the 

roughness component can be reasonably incorporated into a rapid assessment. 

The extensive channel modifications and levee construction that have taken place 

in the region make it difficult to ascribe detailed flood characteristics to any 

particular point on the ground, particularly if it is not directly adjacent to a 

channel and near a stream gage. At best, we can estimate flood frequency for 

some sites, at least to the extent needed to classify a wetland as Riverine or 

Connected (i.e., within the 5-year floodplain). In cases where flood frequency 

can be estimated more specifically, that information can be used in the 

assessment of this function. Otherwise, the only element of the Floodwater 

Detention function that is assessed is roughness. 

General form of the assessment model 

 The model for assessing the Detain Floodwater function includes the 

following assessment variables that are discussed in greater detail in Chapter 6: 

 VFREQ : Frequency of flooding 

 VLOG : Log density 

 VGVC : Ground vegetation cover 

 VSSD : Shrub-sapling density 

 VTDEN : Tree density 
Chapter 4 Wetland Functions and Assessment Models 51

 The general form of the assessment model is: 

( )



 



 + + + = ×

4

LOG GVC SSD TDEN

FREQ

V V V V FCI V (2) 

 The assessment model has two components: frequency of flooding (VFREQ) 

and a compound expression that represents flow resistance (roughness) within the 

wetland. The flood frequency variable is employed as a multiplier, such that the 

significance of the roughness component is proportional to how often the wetland 

is inundated. 

 The compound expression of flow resistance includes the major physical 

components of “roughness” that can be characterized readily at the level of a 

field assessment. They include elements that influence flow velocity differently 

depending on flood depth and time of year. For example, ground vegetation 

cover (VGVC) and log density (VLOG) can effectively disrupt shallow flows, while 

shrub and sapling density (VSSD) have their greatest influence on flows that 

intercept understory canopies (usually 1-3 m deep), and tree stems (VTDENS) 

interact with a full range of flood depths. Both tree stems and logs are equally 

effective in disrupting flows at all times of the year, while understory and ground 

cover interactions are less effective during winter floods than during the growing 

season. Other components of wetland structure contribute to roughness, but are 

not assessed here (e.g. surface micro-relief) because they cannot be estimated 

rapidly and reliably or they do not commonly influence flows to the same degree 

as the components described above (e.g., snag density). 

Function 2: Detain Precipitation 

Definition and applicability 

 This function is defined as the capacity of a wetland to prevent or slow 

runoff of rainfall to streams. This is accomplished chiefly by micro-depression 

storage and infiltration and absorption by organic material and soils. Both floodprone (riverine) wetlands and nonflooded wetlands (flats) are assessed for this 

function. Depression wetlands also perform a precipitation storage function, but 

are not assessed for that function within the Yazoo Basin. This is partly because 

it is difficult to consistently define source areas and available storage volumes in 

the context of a rapid field assessment; but more simply, impacts to this function 

in depression wetlands generally are directly reflected in lost wetland acreage. 

Wetland subclasses that are assessed for the precipitation detention function in 

the Yazoo Basin include: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Flat 
52 Chapter 4 Wetland Functions and Assessment Models 

 The recommended procedure for assessing this function in the Yazoo Basin 

is estimation of available micro-depression storage and characterization of the 

extent of organic surface accumulations available to improve absorption and 

infiltration. A potential independent direct measure would be calculation of 

onsite storage relative to runoff predicted by a storm hydrograph for a given 

rainfall event. 

Rationale for selecting the function 

 Like the Floodwater Detention function, capture and detention of 

precipitation prevents erosion, dampens runoff peaks following storms, and helps 

maintain baseflow in streams. The stream hydrograph has a strong influence on 

the development and maintenance of habitat structure and biotic diversity of 

adjacent ecosystems (Bovee 1982, Estes and Orsborn 1986, Stanford et al. 1996). 

 In addition, onsite storage of precipitation may be important in maintaining 

wetland conditions on the site, independent of the influence of flooding. The 

presence of ponded surface water and recharge of soil moisture also have 

implications for plant and animal communities within the wetland, but these 

effects are assessed separately.

Characteristics and processes that influence the function 

 Flats and riverine wetlands capture precipitation and local runoff in microdepressions, vernal pools, and ridge and swale topography. Micro-depressions 

are usually formed by channel migration processes and tree windthrow, which 

creates small, shallow depressions when root systems are pulled free of the soil. 

In addition, the presence of surface organic accumulations reduces runoff and 

promotes infiltration. Therefore, sites with large amounts of micro-depression 

storage and a thick, continuous litter or duff layer will most effectively reduce the 

movement of precipitation as overland flow. Instead, the water is detained 

onsite, where it supports biological processes and contributes to subsurface water 

storage and, eventually, to maintenance of baseflow in nearby streams. Clearing 

of natural vegetation cover will remove the source of litter and the mechanism for 

developing new micro-depressions. Land use practices that involve ditching or 

land leveling can eliminate existing micro-depression storage and promote rapid 

runoff of precipitation. 

General form of the assessment model 

 The assessment model for the Detain Precipitation function includes the 

following assessment variables that are discussed in greater detail in Chapter 6: 

 VPOND : Micro-depressional ponding 

 VOHOR : "O" horizon thickness 

The general form of the assessment model is: 
Chapter 4 Wetland Functions and Assessment Models 53

( )

2

VPOND VOHOR FCI + = (3) 

The assessment model has two components, which are equally weighted. The 

percentage of the assessment area subject to ponding (VPOND) is based on a field 

estimate. The thickness of the O horizon (VOHOR) is directly measured in the 

field. 

Function 3: Cycle Nutrients 

Definition and applicability 

 This function refers to the ability of the wetland to convert nutrients from 

inorganic forms to organic forms and back through a variety of biogeochemical 

processes such as photosynthesis and microbial decomposition. The nutrient 

cycling function encompasses a complex web of chemical and biological 

activities that sustain the overall wetland ecosystem, and it is assessed in all 

wetland subclasses. Within the Yazoo Basin, the applicable subclasses discussed 

within this document include the following: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Connected Depression 

d. Isolated Depression 

e. Flats 

 The assessment procedure described here utilizes indicators of the presence 

and relative magnitude of organic material production and storage, including 

living vegetation strata, dead wood, detritus, and soil organic matter. Potential 

independent, quantitative measures for validating the functional index include net 

annual primary productivity (gm/m2

), annual litterfall (gm/m2), or standing stock 

of living and/or dead biomass (gm/m2

). 

Rationale for selecting the function 

 In functional wetlands, nutrients are transferred among various components 

of the ecosystem, such that materials stored in each component are sufficient to 

maintain ecosystem processes (Ovington 1965, Pomeroy 1970, Ricklefs 1990). 

For example, an adequate supply of nutrients in the soil profile supports primary 

production, which makes it possible for the plant community to develop and be 

maintained (Bormann and Likens 1970, Whittaker 1975, Perry 1994). The plant 

community, in turn, provides a pool of nutrients and source of energy for 

secondary production and also provides the habitat structure necessary to 
54 Chapter 4 Wetland Functions and Assessment Models 

maintain the animal community (Fredrickson 1978, Crow and MacDonald 1978, 

Wharton et al. 1981). Plant and animal communities serve as the source of 

detritus, which provides nutrients and energy necessary to maintain a 

characteristic community of decomposers to break down organic material into 

simpler elements and compounds that can then reenter the nutrient cycle (Reiners 

1972; Dickinson and Pugh 1974; Pugh and Dickinson 1974; Schlesinger 1977; 

Singh and Gupta 1977; Hayes 1979; Harmon, Franklin, and Swanson 1986; 

Vogt, Grier, and Vogt 1986). 

Characteristics and processes that influence the function 

 In wetlands, nutrients are stored within, and cycled among, four major 

compartments: (a) the soil, (b) primary producers such as vascular and 

nonvascular plants, (c) consumers such as animals, fungi, and bacteria, and 

(d) dead organic matter, such as leaflitter or woody debris, referred to as detritus. 

The transformation of nutrients within each compartment and the flow of 

nutrients between compartments are mediated by a complex variety of 

biogeochemical processes. For example, plant roots take up nutrients from the 

soil and detritus and incorporate them into the organic matter in plant tissues. 

Nutrients incorporated into herbaceous or deciduous parts of plants will turn over 

more rapidly than those incorporated into the woody parts of plants. However, 

ultimately, all plant tissues are either consumed or die and fall to the ground 

where they are decomposed by fungi and microorganisms and mineralized to 

again become available for uptake by plants. 

 Many of the processes involved in nutrient cycling, such as primary production and decomposition, have been studied extensively in wetlands (Brinson, 

Lugo, and Brown 1981). In forested riverine wetlands of the Southeast specifically, there is a rich literature on the standing stock, accumulation, and turnover of 

aboveground biomass in successional and mature stages (Brinson 1990). For 

example, the annual production of leaves is well documented through litterfall 

studies (Conner and Day 1976, Day 1979, Mulholland 1981, Elder and Cairns 

1982, Brown and Peterson 1983, Conner and Day 1992). Until recently, less 

attention has been paid to woody (Harmon, Franklin, and Swanson 1986; 

Symbula and Day 1988) and belowground components (Raich and Nadelhoffer 

1989, Nadelhoffer and Raich 1992) of these systems. 

 The ideal approach for assessing nutrient cycling would be to measure the 

rate at which nutrients are transformed and transferred between compartments 

over the period of a year (Kuenzler et al. 1980; Brinson, Bradshaw, and Kane 

1984; Harmon, Franklin, and Swanson 1986). However, the time and effort 

required to make these measurements are well beyond a rapid assessment 

procedure. The alternative is to estimate the standing stocks of living and dead 

biomass in each of the four compartments and assume that nutrient cycling is 

taking place at a characteristic level if the biomass in each compartment is similar 

to that in reference standard wetlands. In this case, estimation of consumer 

biomass (animals, etc.) is too complex for a rapid assessment approach, thus, the 

presence of these organisms is assumed based on the detrital and living plant 

biomass components. 
Chapter 4 Wetland Functions and Assessment Models 55

General form of the assessment model 

 The model for assessing the Cycle Nutrients function includes the following 

assessment variables that are discussed in greater detail in Chapter 6: 

 VTBA : Tree basal area 

 VSSD : Shrub-sapling density 

 VGVC : Ground vegetation cover 

 VOHOR : O horizon thickness 

 VAHOR : A horizon biomass 

 VWD : Woody debris biomass 

 VSNAG : Snag density 

 The general form of the assessment model is: 

( ) ( )

2

3 4 



 



 + + +

+

+ +

=

VTBA VSSD VGVC VOHOR VAHOR VWD VSNAG

FCI (4) 

 The two constituent expressions within the model reflect the two major 

production and storage compartments: living and dead organic material. The first 

expression is comprised of indicators of living biomass, expressed as tree basal 

area (VTBA), shrub and sapling density (VSSD), and ground vegetation cover (VGVC). 

 These various living components also reflect varying levels of nutrient 

availability and turnover rates, with the aboveground portion of ground cover 

biomass being largely recycled on an annual basis, while understory and tree 

components incorporate both short-term storage (leaves) and long-term storage 

(wood). Similarly, the second expression includes organic storage compartments 

that reflect various degrees of decay. Snag density (VSNAG) and woody debris 

volume (VWD) represent relatively long-term storage compartments that are 

gradually transferring nutrients into other components of the ecosystem through 

the mediating activities of fungi, bacteria, and higher plants. The thickness of the 

O horizon (VOHOR) represents a shorter-term storage compartment of largely 

decomposed, but nutrient rich, organics on the soil surface. The thickness of the 

A horizon (actually, the portion of the A where organic accumulation is apparent) 

(VAHOR) represents a longer-term storage compartment, where nutrients that have 

been released from other compartments are held within the soil and are available 

for plant uptake but are generally conserved within the system and not readily 

subject to export by runoff or floodwater. All of these components are combined 

here in a simple arithmetic model that weights each element equally. 
56 Chapter 4 Wetland Functions and Assessment Models 

Function 4: Export Organic Carbon 

Definition and applicability 

 This function is defined as the capacity of the wetland to export dissolved 

and particulate organic carbon, which may be vitally important to downstream 

aquatic systems. Mechanisms involved in mobilizing and exporting nutrients 

include leaching of litter, flushing, displacement, and erosion. This assessment 

procedure employs indicators of organic production, the presence of organic 

materials that may be mobilized during floods, and the occurrence of periodic 

flooding to assess the organic export function of a wetland. An independent 

quantitative measure of this function is the mass of carbon exported per unit area 

per unit time (g/m2

 /yr). 

 This function is assessed in river-connected wetlands, which includes the 

following subclasses in the Yazoo Basin: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Connected Depression

Rationale for selecting the function 

 The high productivity and close proximity of river-connected wetlands to 

streams make them important sources of dissolved and particulate organic carbon 

for aquatic food webs and biogeochemical processes in downstream aquatic 

habitats (Vannote et al. 1980; Elwood et al. 1983; Sedell, Richey, and Swanson 

1989). Dissolved organic carbon is a significant source of energy for the 

microbes that form the base of the detrital food web in aquatic ecosystems (Dahm 

1981, Edwards 1987, Edwards and Meyers 1986). Evidence also suggests that 

the particulate fraction of organic carbon imported from uplands or produced in 

situ is an important energy source for shredders and filter-feeding organisms 

(Vannote et al. 1980). 

Characteristics and processes that influence the function 

 Wetlands can be characterized as open or closed systems depending on the 

degree to which materials are exchanged with surrounding ecosystems (Mitsch 

and Gosselink 1993). River-connected wetlands normally function as open 

systems, primarily for two reasons. First, they occur in valley bottoms adjacent to 

stream channels. Since stream channels are the lowest topographic position in the 

landscape, water and sediments pass through the adjacent wetlands as gravity 

moves them toward the stream channel. Second, under natural conditions, low 

gradient, riverine and river-connected depression wetlands are linked to the 

stream channel through overbank and backwater flooding. In the case of the 

Export of Organic Carbon function, the latter reason is of greatest importance. 
Chapter 4 Wetland Functions and Assessment Models 57

 Watersheds with a large proportion of Riverine and other wetland types have 

generally been found to export organic carbon at higher rates than watersheds 

with fewer wetlands (Mulholland and Kuenzler 1979; Brinson, Lugo, and Brown 

1981; Elder and Mattraw 1982; Johnston, Deten-beck, and Niemi 1990). This is 

attributable to several factors, including: (a) the large amount of organic matter in 

the litter and soil layers that comes into contact with surface water during 

flooding, (b) relatively long periods of inundation and, consequently, contact 

between surface water and organic matter, thus allowing for significant leaching, 

(c) the ability of the labile carbon fraction to be rapidly leached from organic 

matter when exposed to water (Brinson et al. 1981), and (d) the ability of 

floodwater to transport dissolved and particulate organic carbon from the 

floodplain to the stream channel. 

General form of the assessment model 

 The model for assessing the Export Organic Carbon function includes the 

following assessment variables that are discussed in greater detail in Chapter 6: 

 VFREQ : Frequency of flooding 

 VOHOR : O horizon thickness 

 VWD : Woody debris biomass 

VSNAG : Snag density 

 VTBA : Tree basal area 

VSSD : Shrub-sapling density 

VGVC : Ground vegetation cover 

The general form of the assessment model is: 

( )

2

3 3 



 



 + +

+



 



 + +

= ×

OHOR WD SNAG TBA SSD GVC

FREQ

V V V V V V

FCI V (5) 

 This model is similar to the model used to assess the Internal Nutrient 

Cycling function in that it incorporates most of the same indicators of living and 

dead organic matter. The living tree, understory, and ground cover components 

(VTBA, VSSD, and VGVC) primarily represent organic production, indicating that 

materials will be available for export in the future. The dead organic fraction 

comprises the principal current sources of exported material, represented by 

snags, woody debris, and accumulation of the O horizon (VSNAG, VWD, and VOHOR). 

 This model differs from the Nutrient Cycling model in that materials stored in 

the soil are not included due to their relative immobility, and periodic flooding is 
58 Chapter 4 Wetland Functions and Assessment Models 

a required component of this model, because the export function is largely 

dependent on inundation and continuity with river flows. 

Function 5: Remove Elements and Compounds

Definition and applicability 

 This function is defined as the ability of the wetland to permanently remove 

or temporarily immobilize nutrients, metals, and other elements and compounds 

that are imported to the wetland from various sources, but primarily via flooding. 

 In a broad sense, elements include macronutrients essential to plant growth 

(nitrogen, phosphorus, and potassium) as well as heavy metals (zinc, chromium, 

etc.) that can be toxic at high concentrations. Compounds include pesticides and 

other imported materials. The term “removal” means the permanent loss of 

elements and compounds from incoming water sources (e.g., deep burial in 

sediments, loss to the atmosphere), and the term “sequestration” means the shortor long-term immobilization of elements and compounds. A potential 

independent, quantitative measure of this function is the quantity of one or more 

imported elements and compounds removed or sequestered per unit area during a 

specified period of time (e.g., g/m2

 /yr). 

 All wetlands in the Yazoo Basin are likely to perform this function to some 

degree. However, the indicators available to support a rapid field assessment are 

concerned primarily with contact between soil materials and floodwaters carrying 

dissolved materials. Removal of materials delivered to an area via local runoff or 

atmospheric sources is not considered as part of this assessment. However, 

materials transported to the area being assessed via the stream channel are part of 

the assessment. Therefore, this function is assessed in river-connected wetlands, 

which includes the following subclasses in the Yazoo Basin: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Connected Depression

Rationale for selecting the function 

 The role of wetlands as interceptors of elements and compounds from upland 

or aquatic non-point sources is widely documented (Mitsch, Dorge, and 

Wiemhoff 1979, Lowrance et al. 1984; Peterjohn and Correll 1984; Cooper, 

Gilliam, and Jacobs 1986; Cooper et al. 1987). The primary benefit of this 

function is that the removal and sequestration of elements and compounds by 

wetlands reduce the load of nutrients, heavy metals, pesticides, and other 

pollutants in rivers and streams. This often translates into better water quality 

and aquatic habitat in rivers and streams through burial or facilitated processing 

of elements and compounds (e.g. denitrification). 
Chapter 4 Wetland Functions and Assessment Models 59

Characteristics and processes that influence the function 

 Elements and compounds are imported to wetlands by a variety of 

mechanisms and from a variety of sources. They include dry deposition and 

precipitation from atmospheric sources, stream flooding, overland flow, 

channelized flow, interflow, shallow groundwater flow, and colluvial material 

from upland sources. Some of the mechanisms, such as dry deposition and 

precipitation, typically account for a small proportion of the total quantity of 

elements and compounds imported to the wetland. The mechanisms that bring 

nutrients and compounds to the wetland from fluvial and terrestial sources are 

more significant in terms of quantities of materials imported. Once nutrients and 

compounds arrive in the wetland, they may be removed and sequestered through 

a variety of biogeochemical processes. Biogeochemical processes include 

complexation, chemical precipitation, adsorption, denitrification, decomposition 

to inactive forms, hydrolysis, uptake by plants, and other processes (Kadlec 

1985, Faulkner and Richardson 1989, Johnston 1991). 

 A major mechanism that contributes to removal of elements and compounds 

from water entering a wetland is reduction. Denitrification will not occur unless 

the soil is anoxic and the redox potential falls below a certain level. When this 

occurs, nitrate (NO2

 ) removed by denitrification is released as nitrogen gas to the 

atmosphere. In addition, sulfate is reduced to sulfide, which then reacts with 

metal cations to form insoluble metal sulfides such as CuS, FeS, PbS, and others. 

 Another major mechanism for removal of elements and compounds is by adsorption to electrostatically charged soil particles. Clay particles and particulate 

organic matter are the most highly charged soil particles and contribute the most 

to the cation exchange capacity (CEC) of the soil. Cation exchange is the 

interchange between cations in solution and other cations on the surface of any 

active material (i.e., clay colloid or organic colloid). The sum total of exchangeable cations that a soil can adsorb is the CEC. The CEC of a soil is a function of 

the amount and type of clay and the amount of organic matter in the soil. 

Further, organic matter is a food source for microbes involved in various 

microbial processes (i.e., reduction-oxidation reactions, denitrification, microbial 

pesticide degradation, etc.). Nitrogen in the ammonium form (NH) may be 

sequestered by adsorption to clay minerals in the soil. Phosphorus can only be 

sequestered, not truly removed. The soluble orthophosphate ion (PO4

) may be 

specifically adsorbed (“fixed”) to clay and Fe and Al oxide minerals (Richardson 

1985), which are generally abundant in riverine wetlands. Likewise, heavy 

metals can be sequestered from incoming waters by adsorption onto the charged 

surfaces (functional groups) of clay minerals by specific adsorption onto Fe and 

Al oxide minerals or by chemical precipitation as insoluble sulfide compounds. 

Direct measurement of concentrations of these soil components is beyond the 

scope of rapid assessment. However, soils with pH of 5.5 or less generally have 

Al oxide minerals present that are capable of adsorbing phosphorus and metals. 

Fe oxides are reflected in brown or red colors in surface or subsoil horizons, 

either as the dominant color or as redox concentrations. If the Fe oxide minerals 

become soluble by reduction, adsorbed phosphorus is released into solution. 

Annual net uptake of phosphorus by growing vegetation, although significant, 

usually represents a small quantity relative to other soil/sediment sinks of 

phosphorus (Brinson 1985). Riverine wetlands also retain nutrients and 
60 Chapter 4 Wetland Functions and Assessment Models 

compounds by storing and cycling them among the plant, animal, detrital, and 

soil compartments (Patrick and Tusneem 1972; Kitchens et al. 1975; Brinson 

1977; Day, Butler, and Conner 1977; Mitsch, Dorge, and Wiemhoff 1979; 

Yarbro 1983; Brinson, Bradshaw, and Kane 1984; Yarbro et al. 1984; Kleiss 

1996). 

General form of the assessment model 

 The model for assessing the Remove Elements and Compounds function 

includes the following assessment variables that are discussed in greater detail in 

Chapter 6:

VFREQ : Frequency of flooding 

 VCEC : Cation exchange capacity 

 VOHOR : O horizon thickness 

 VAHOR : A horizon biomass 

 The general form of the assessment model is: 

( )



 



 + + = ×

3

CEC OHOR AHOR

FREQ

V V V FCI V (6) 

 The variables employed in the model reflect the importance of soil 

characteristics and organic matter in the complex interactions that influence 

removal or immobilization of materials from floodwaters. The clay component 

of soil CEC (VCEC) is estimated by indirect means, and the organic fraction is 

estimated as the thickness of the portion of the A horizon with organic matter 

accumulation (VAHOR). In addition, the role of direct interaction with surface 

organic accumulations and associated microbial activity is indicated by a field 

estimate of the thickness of the O horizon (VOHOR). As noted above, although 

these ecosystem elements influence the fate of materials arriving in the wetland 

from a variety of sources, this model is intended only to assess the removal and 

sequestration of materials arriving in floodwaters. Therefore, the flood frequency 

variable (VFREQ) is employed as a multiplier of the compound expression that 

describes soil and organic matter conditions. 

Function 6: Maintain Plant Communities

Definition and applicability 

 This function is defined as the capacity of a wetland to provide the 

environment necessary for a characteristic plant community to develop and be 

maintained. In assessing this function, one must consider both the extant plant 

community as an indication of current conditions and the physical factors that 
Chapter 4 Wetland Functions and Assessment Models 61

determine whether or not a characteristic plant community is likely to be 

maintained in the future. A variety of approaches have been developed to 

describe and assess plant community characteristics that might be appropriately 

applied in developing independent measures of this function. These include 

quantitative measures based on vegetation composition and abundance such as 

similarity indices (Ludwig and Reynolds 1988), indirect multivariate techniques 

such as detrended correspondence analysis (Kent and Coker 1995), and 

techniques that employ both vegetation and environmental factors, such as 

canonical correlation analysis (ter Braak 1994). However, none of these 

approaches alone provides a “direct independent measure” of Plant Community 

function because they are tools that are employed in a more complex analysis 

that requires familiarity with the regional vegetation and collection of appropriate 

sample data. 

 This function is assessed in the following subclasses in the Yazoo Basin: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Connected Depression 

d. Isolated Depression 

e. Flats 

Rationale for selecting the function 

 The ability to maintain a characteristic plant community is important because 

of the intrinsic value of the plant community and the many attributes and 

processes of wetlands that are influenced by the plant community. For example, 

primary productivity, nutrient cycling, and the ability to provide a variety of 

habitats necessary to maintain local and regional diversity of animals are directly 

influenced by the plant community (Harris and Gosselink 1990). In addition, the 

plant community of a river-connected wetland influences the quality of the 

physical habitat, nutrient status, and biological diversity of downstream systems 

(Bilby and Likens 1979; Hawkins, Murphy, and Anderson 1982, Elder 1985; 

Gosselink, Lee, and Muir 1990). 

Characteristics and processes that influence the function 

 Numerous studies describe the environmental factors that influence the 

occurrence and characteristics of plant communities in lowland hardwood 

wetlands (Robertson, Weaver, and Cavanaugh 1978; Robertson, McKenzie, and 

Elliot 1984; Wharton et al. 1982; Robertson 1992; Smith 1996; Messina and 

Conner 1997; Hodges 1997). Hydrologic regime is usually cited as the principal 

factor controlling plant community attributes. Consequently, this factor is a 

fundamental consideration in the basic hydrogeomorphic classification scheme 
62 Chapter 4 Wetland Functions and Assessment Models 

employed in this document. Soil characteristics are also significant determinants 

of plant community composition (see Soils Section in Chapter 3). In addition to 

physical factors, system dynamics and disturbance history are also important in 

determining the condition of a wetland plant community at any particular time. 

These include past land use, timber harvest history, hydrologic changes, sediment 

deposition, and events such as storms, fire, beaver activity, insect outbreaks, and 

disease. Clearly, some characteristics of plant communities within a particular 

wetland subclass may be determined by factors too subtle or variable to be 

assessed using rapid field estimates. Therefore, this function is assessed 

primarily by considering the degree to which the existing plant community 

structure and composition are appropriate to site conditions and the expected 

stage of maturity for the site. Secondarily, in some subclasses, soil and 

hydrologic conditions are assessed to determine if fundamental requirements are 

met to maintain wetland conditions appropriate to the geomorphic setting. 

General form of the assessment model 

 The model for assessing the Maintain Plant Communities function includes 

the following assessment variables that are discussed in greater detail in 

Chapter 6:

VTBA : Tree basal area 

 VTDEN : Tree density

 VCOMP : Composition of tallest woody stratum 

 VSOIL : Soil integrity 

 VPOND : Micro-depressional ponding 

The general form of the assessment model is: 

( )

( )

2

1

2 2

2





 



 + ×

































 





+

+

= SOIL POND

COMP

TBA TDEN

V V

V

V V

FCI (7) 

 The first expression of the model has two components. One component 

describes the structure of the overstory stratum of the plant community in terms 

of tree basal area and density (VTBA and VTDENS). Together these indicate whether 

the stand has a structure typical of a mature forest with "gap" regeneration 

processes in place. The second term of the expression (VCOMP) considers the 

species composition of the dominant stratum, which will be the overstory in most 

instances, but which may be the shrub or ground cover layers in communities that 

are in earlier (or arrested) stages of development. This allows recognition of the 

faster recovery trajectory likely to take place in planted restoration sites (versus 

abandoned fields). 
Chapter 4 Wetland Functions and Assessment Models 63

 The second expression of the model considers two specific site factors that 

may be crucial to plant community maintenance under certain conditions. VSOIL

is a simple comparison of the soil on the site to the mapped or predicted soil type 

for the area and geomorphic setting. As described in Chapter 3, plant 

communities of the Yazoo Basin are strongly affiliated with particular soil types, 

which in turn are the product of distinct alluvial processes. The VSOIL variable 

allows recognition of sites where the native soils have been replaced or buried by 

sediments inappropriate to the site, or where the native soils have been damaged 

significantly, as by compaction. The VPOND variable focuses on a specific aspect 

of site alteration, the removal of microtopography and related ponding of water 

on flats and riverine wetlands. As described previously, ponding of precipitation 

is a crucial mechanism for maintaining wetland character in many wetlands in the 

Yazoo Basin. Flooding is also critical for the maintenance of many plant 

communities within the basin, but this relationship is considered separately as a 

basic classification factor. As noted elsewhere, characterization of flood 

frequency and duration in the Yazoo Basin is difficult and cannot often be 

interpreted in a way that would add meaningfully to the assessment of plant 

community maintenance. 

Function 7: Provide Fish and Wildlife Habitat 

Definition and applicability 

 This function is defined as the ability of a wetland to support the fish and 

wildlife species that utilize wetlands during some part of their life cycles. 

Potential independent, quantitative measures of this function are animal 

inventory approaches, with data analysis usually employing comparisons 

between sites using a similarity index calculated from species composition and 

abundance (Odum 1950, Sorenson 1948). 

 This function is assessed in the following subclasses in the Yazoo Basin: 

a. Riverine Backwater 

b. Riverine Overbank 

c. Connected Depression 

d. Isolated Depression 

e. Flats 

Rationale for selecting the function 

 Terrestrial, semi-aquatic, and aquatic animals use wetlands extensively. 

Maintenance of this function ensures habitat for a diversity of vertebrate 

organisms, contributes to secondary production, and maintains complex trophic 
64 Chapter 4 Wetland Functions and Assessment Models 

interactions. Habitat functions span a range of temporal and spatial scales and 

include the provision of refugia and habitat for wide-ranging or migratory 

animals as well as highly specialized habitats for endemic species. However, 

most wildlife and fish species found in wetlands of the Yazoo Basin depend on 

certain aspects of wetland structure and dynamics, such as periodic flooding or 

ponding of water, specific vegetation composition, and proximity to other 

habitats. 

Characteristics and processes that influence the function 

 The quality and availability of habitats for fish and wildlife species in 

wetlands of the Yazoo Basin are dependent on a variety of factors operating at 

different scales. Habitat components that can be considered in a rapid field 

assessment include vegetation structure and composition, detrital elements, 

availability of water, both from precipitation and flooding, and spatial attributes 

such as patch size and connectivity. 

 Forested wetlands typically are floristically and hydrologically complex 

(Wharton et al. 1982). Structural diversity in the vertical plane generally 

increases with vegetation maturity (Hunter 1990). Complexity of vegetation 

diversity on the horizontal plane derives from the patterns of alluvial deposition 

that form the substrate, resulting in a high interspersion of low ridges, swales, 

abandoned channel segments, and other features that differentially flood or pond 

rainwater, and support distinctively different plant communities (see Chapter 3). 

 This structural diversity provides a myriad of habitat conditions for animals and 

allows numerous species to coexist in the same area (Schoener 1986). The 

composition of the various plant communities found in these wetlands is also an 

important factor relative to utilization by some wildlife species. Lowland forests 

commonly are highly diverse and may contain hundreds of plant species, but 

members of the genus Quercus (the oaks) often are particularly valuable to many 

species of wildlife. This significance is due to the importance of acorns as a 

major dietary component for many wildlife species. While oaks provide the bulk 

of the hard mast utilized by wildlife in forested wetlands of the southeast, 

hickories (Carya spp.) are very important also, especially to squirrels (Allen 

1987). 

 Detrital components of the ecosystem are of considerable significance to 

animal populations in lowland hardwood wetlands. Litter provides ideal habitat 

for small animals such as salamanders (Johnson 1987) and has a distinctive 

invertebrate fauna (Wharton et al. 1982) that is vital to some of the more visible 

members of the community. For example, prior to laying eggs, wood ducks 

forage extensively on macro-invertebrates found in the floodplain. Similarly, 

mallards heavily utilize the abundant litter invertebrate populations associated 

with flooded bottomland forests during winter (Batema, Henderson, and 

Fredrickson 1985). Logs and other woody debris provide cover and a moist 

environment for many species including invertebrates, small mammals, reptiles, 

and amphibians (Hunter 1990). Animals found in forested wetlands use logs as 

resting sites, cover, feeding platforms, and sources of food (Harmon, Franklin, 

and Swanson 1986, Loeb 1993). Standing dead trees (snags) are used by 
Chapter 4 Wetland Functions and Assessment Models 65

numerous bird species, and several species are dependent on snags for their 

existence (Scott et al. 1977). Stauffer and Best (1980) found that most cavitynesting birds, particularly the primary cavity nesters such as woodpeckers, preferred snags versus live trees. Mammals such as bats, squirrels, and raccoon also 

are dependent on snags to varying extents (Howard and Allen 1989), and most 

species of forest-dwelling mammals, reptiles, and amphibians, along with numerous invertebrates, seek shelter in cavities, at least occasionally (Hunter 1990). 

 In wetlands of the Yazoo Basin, hydrology is one of the major factors 

influencing wildlife habitat quality. A significant hydrologic component is 

precipitation, particularly where it is captured in vernal pools and small puddles. 

These sites are a source of surface water for various terrestrial animals and 

provide reproductive habitat for insects and amphibians, many of which are 

utilized as a food source by other animals (Wharton et al. 1982, Johnson 1987). 

Ponded breeding sites without predatory fish populations are very important for 

some species of salamanders and frogs (Johnson 1987). 

 While temporary ponding of precipitation is important to many species 

precisely because it provides an aquatic environment that is isolated from many 

aquatic predators, wetlands that are periodically river-connected also provide 

vital habitat for some species. Wharton et al. (1982) provided an overview of 

fish use of bottomland hardwoods in the Piedmont and eastern Coastal Plain and 

stated that at least 20 families and up to 53 species of fish use various portions of 

the floodplain for foraging and spawning. Baker and Killgore (1994) reported 

similar results from the Cache River drainage in Arkansas, where they found that 

most fish species exploit floodplain habitats at some time during the year, many 

for spawning and rearing. In addition to flooding itself, the complex environments of floodplains are of significance to fish. Wharton et al. (1982) listed 

numerous examples of fish species being associated with certain portions of the 

floodplain. Baker, Killgore, and Kasul (1991) noted that the different microhabitats on the floodplain typically supported different fish assemblages from 

those of the channel. Baker and Killgore (1994) stated that “the structurally complex environment of irregularly flooded oak-hickory forests provide optimum 

habitat for many wetland fish.” 

 Just as topographic variations provide essential wetland habitats such as 

isolated temporary ponds and river-connected backwaters, they also provide sites 

that generally remain dry. Such sites are important to ground-dwelling species 

that cannot tolerate prolonged inundation. Wharton et al. (1982) stated that old, 

natural levee ridges are extremely important to many floodplain species, because 

they provide winter hibernacula and refuge areas during periods of high water. 

Similarly, Tinkle (1959) found that natural levees were used extensively as egglaying areas by many species of reptiles and amphibians. 

 Landscape-level features such as forest patch size, shape, connectivity, and 

surrounding land use are also important attributes that affect the lowland wildlife 

community (Hunter 1990; Morrison, Marcot, and Mannan 1992). It is generally 

assumed that reduction and fragmentation of forest habitat, coupled with changes 

in the remaining habitat, resulted in the loss of the ivory-billed woodpecker 

(Campephilus principalis), Bachman’s warbler (Vermivora bachmanii), and the 
66 Chapter 4 Wetland Functions and Assessment Models 

red wolf (Canis rufus) and severe declines in the black bear (Ursus americanus) 

and Florida panther (Puma concolor). The extent to which patch size affects 

animal populations has been most thoroughly investigated with respect to birds, 

with inconsistent results (Stauffer and Best 1980, Blake and Karr 1984, Howe 

1984, Lynch and Whigham 1984, Askins, Philbrick, and Sugeno 1987, 

Sallabanks, Walters, and Collazo 1998, Keller, Robbins, and Hatfield 1993; 

Kilgo et al. 1997). However, the negative effects of forest fragmentation on 

some species of birds have been well documented (Finch 1991). These species, 

referred to as “forest interior” species, apparently respond negatively to 

unfavorable environmental conditions or biotic interactions in fragmented forests 

(Ambuel and Temple 1983). The point at which fragmentation effects begin to 

be realized has yet to be defined, and study results have been inconsistent (e.g. 

Temple 1986, Wakeley and Roberts 1996). Thus, the area needed to 

accommodate all the species typically associated with large patches of forested 

wetlands in the region can only be approximated. One such approximation 

(Mueller, Loesch, and Twedt 1995) identified three groups of birds that breed in 

the Mississippi Alluvial Valley with (presumably) similar needs relative to patch 

size. They suggested that to sustain source breeding populations of individual 

species within the 3 groups, that 44 patches of 4,000 - 8,000 ha, 18 patches of 

8,000 - 40,000 ha, and 12 patches larger than 40,000 ha are needed. Species such 

as the Swainson’s warbler are in the first group; more sensitive species such as 

the cerulean warbler (Dendroica cerulea) are in the second group; and those with 

very large home ranges (e.g., raptors such as the red-shouldered hawk (Buteo 

lineatus) are in the third group. 

 The land-use surrounding a tract of forest also has a major effect on avian 

populations. Recent studies (Thompson et al. 1992; Welsh and Healy 1993; 

Sallabanks, Walters, and Collazo 1998; Robinson et al. 1995) suggest that bird 

populations respond to fragmentation differently in forest-dominated landscapes 

than in those in which the bulk of the forests have been permanently lost to 

agriculture or urbanization. Generally, these studies indicate that as the mix of 

feeding habitats (agricultural and suburban lands) and breeding habitats (forests 

and grasslands) increases, predators and nest parasites become increasingly 

successful, even if large blocks of habitat remain. Thus, in more open 

landscapes, block sizes need to be larger than in mostly forested ones. 

Conversely, Robinson (1996) estimated that as the percentage of the landscape 

that is forested increases above 70 percent (approximately), the size of the forest 

blocks within that landscape becomes less significant to bird populations. 

 In landscapes that are fragmented, corridors have been suggested as a means 

of ameliorating many of the anticipated negative effects of fragmentation (Harris 

1985, Noss and Harris 1986), although there is disagreement over the benefits of 

corridors (Simberloff et al. 1992). In bottomland forest communities, probably 

the most significant habitat connection for many species is between flood-prone 

areas and nonflooded habitats of similar structure in the adjacent uplands, which 

allows terrestrial species to seek refuge during periods of high water (Wharton 

et al. 1982). In general, connections between different wetland types, and 

between uplands and wetlands, help maintain higher animal and plant diversity 

across the landscape than if habitats were more isolated from one another (Sedell 

et al. 1990). 
Chapter 4 Wetland Functions and Assessment Models 67

General form of the assessment model 

 The model for assessing the Provide Fish and Wildlife Habitat function 

includes the following assessment variables that are discussed in greater detail in 

Chapter 6:

VFREQ : Frequency of flooding 

 VPOND : Micro-depressional ponding 

 VTCOMP : Tree composition 

 VSNAG : Snag density 

 VTBA : Tree basal area 

VLOG : Log density 

VOHOR : O horizon thickness 

 VTRACT : Wetland tract size 

 VCONNECT : Habitat connections 

 VCORE : Core area 

The general form of the assessment model is: 

( ) ( ) ( ) ( ) 1

4

232 3

FREQ POND T SNAG TBA COMP LOG OHOR TRACT CONNECT CORE V V V VV VV V V V

FCI

+ + + + ++ = × ××

                         (8) 

The expressions within the model reflect the major habitat components described 

above. The first expression concerns hydrology and includes indicators of both 

extensive seasonal inundation and river access by aquatic organisms (VFREQ) as 

well as the periodic occurrence of temporary, isolated aquatic conditions (VPOND). 

 The second expression is comprised of three indicators of forest structure and 

diversity, specifically overstory basal area (VTBA), overstory tree species 

composition (VTCOMP), and snag density (VSNAG). Together these variables reflect 

a variety of conditions of importance to wildlife, including forest maturity and 

complexity and the availability of food and cover. Habitat structure for animals 

associated with detrital components is indicated by two variables: the volume of 

logs per unit area (VLOG) and the thickness of the O horizon (VOHOR). Landscapelevel variables are incorporated within the model to reflect the importance of 

habitat fragmentation and interhabitat continuity as considerations in determining 

habitat quality for a large percentage of wildlife species within the Yazoo Basin. 

These variables include: the size of the overall wetland complex independent of 

the boundaries of the assessment area (VTRACT); the proportion of the assessment 

area that is buffered from surrounding land uses and edge effects (VCORE); and the 

proportion of the assessment area boundary that is connected to other suitable 

habitat types via appropriate movement corridors (VCONNECT).
68 Chapter 5 Model Applicability and Reference Data 

5 Model Applicability and 

Reference Data 

 The assessment models described in Chapter 4 are applied to individual wetland subclasses in different ways. This is because not all the assessment models 

and variables are applicable to all of the regional wetland subclasses. For 

example, the Export Organic Carbon function is applicable only to the Overbank 

and Backwater Riverine and Connected Depression subclasses and is not 

assessed in subclasses having no export mechanism (flooding) or channel 

outflow exits (i.e. Isolated Depressions and Flats). Similarly, some variables are 

not used in assessment models for subclasses where they cannot be consistently 

evaluated. For example, ground vegetation cover (VGVC) and thickness of the O 

and A horizons (VOHOR and VAHOR) are not included in models that are otherwise 

applicable to the depression subclasses (e.g., the Nutrient Cycling function), 

because depresssional sites are often flooded and the variable metrics that require 

the observation of soil and ground-level conditions often cannot be assessed 

consistently. 

 Assessment models also differ among subclasses with regard to their associated reference data. Each subclass was the focus of detailed sampling during 

development of this guidebook, and the reference data collected for each subclass 

have been independently summarized for application. The following sections 

present information for each wetland subclass with regard to model applicability 

and reference data. For each subclass, each of the 7 potential functions available 

for assessment is listed, and the applicability of the assessment model is 

described. The model is presented as described in Chapter 4 if it is applicable in 

its general and complete form; it is presented in a modified form if certain 

variables cannot be consistently assessed in certain subclasses; and the function 

is identified as "Not Applicable" in cases where the wetland subclass does not 

perform the function as described in Chapter 4. For each wetland subclass, 

functional capacity subindex curves are presented for every assessment variable 

used in the applicable assessment models, based on reference data. 

Subclass: Flats 

 Four functions are assessed for this subclass. The applicable assessment 

models have not been changed from the general model form presented in 

Chapter 4. Figure 12 provides the relationship between the variable metrics and 
Chapter 5 Model Applicability and Reference Data 69

 Figure 12. Subindex graphs for Flats (Sheet 1 of 3) 

Cation Exchange Capacity (V CEC )

Variable not used in

assessing this subclass

A Horizon Thickness (V AHOR )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1 2 3 4 5 6 7 8 9 10

Depth of "A" Horizon (cm)

Subindex

Habitat Connections (V CONNECT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Connected Tract Perimeter (%)

Subindex

Composition of Tallest Woody 

Vegetation Strata (V COMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Tallest Strata Concurrence (%)

Subindex

Core Area (V CORE )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Tract within 100m Buffer (%)

Subindex

Frequency of Flooding (V FREQ )

Variable not used in

assessing this subclass
70 Chapter 5 Model Applicability and Reference Data 

 Figure 12. (Sheet 2 of 3) 

Log Biomass (V LOG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100

Log Volume (m3

/ha)

Subindex

Microdepressional Ponding 

(V POND )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Microdepressional Area (%)

Subindex

Ground Vegetation Cover (V GVC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Ground Vegetation Cover (%)

Subindex

"O" Horizon Biomass (V OHOR )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

012345

"O" Horizon Thickness (cm) 

Subindex

Soil Integrity (V SOIL )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Area of Altered Soils (%)

Subindex

Snag Density (V SNAG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 40 80 120

Snags (stems/ha)

Subindex
Chapter 5 Model Applicability and Reference Data 71

 Figure 12. (Sheet 3 of 3) 

Tree Biomass (V TBA )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50

Tree Basal Area (m2/ha)

Subindex

Understory Biomass (V SSD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2500 5000 7500 10000

Shrub/Sapling Density (stems/ha)

Subindex

Tree Density (V TDENS )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800

Tree Density (stems/ha)

Subindex

Dominant Trees (V TCOMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Dominant Tree Concurrence (%)

Subindex

Woody Debris Biomass (V WD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125 150

Woody Debris Volume (m3

/ha)

Subindex

Wetland Tract (V TRACT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1000 2000 3000 4000

Wetland Tract (ha)

Subindex
72 Chapter 5 Model Applicability and Reference Data 

the subindex for each of the assessment models based on the Flats reference data 

(Appendix C). 

Function 1: Detain Floodwater 

 Not applicable. 

Function 2: Detain Precipitation 

( )

2

VPOND VOHOR FCI + = (9)

Function 3: Cycle Nutrients

( ) ( )

2

3 4 



 



 + + +

+

+ +

=

VTBA VSSD VGVC VOHOR VAHOR VWD VSNAG

FCI (10) 

Function 4: Export Organic Carbon 

 Not applicable. 

Function 5: Remove Elements and Compounds 

 Not applicable. 

Function 6: Maintain Plant Communities 

( )

( )

2

1

2 2

2





 



 + ×

































 





+

+

= SOIL POND

COMP

TBA TDEN

V V

V

V V

FCI (11) 

Function 7: Provide Fish and Wildlife Habitat 

( ) ( ) ( ) 1

4

 

32 3

TCOMP SNAG TBA LOG OHOR TRACT CONNECT CORE POND

V V V VV V V V

FCI V

++ + + + =× × ×                  

 (12) 

Subclass: Riverine Backwater 

 All functions are assessed for this subclass using the general form of each 

assessment model presented in Chapter 4. Figure 13 provides the relationship 

between the variable metrics and the subindex for each of the assessment 

variables based on the Riverine Backwater reference data (Appendix C) 
Chapter 5 Model Applicability and Reference Data 73

Figure 13. Subindex graphs for Riverine Backwater (Sheet 1 of 3) 

A Horizon Thickness (V AHOR )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1 2 3 4 5 6 7 8 9 10

Depth of "A" Horizon (cm)

Subindex

Cation Exchange Capacity (V CEC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100

Difference in CEC (%)

Subindex

Habitat Connections (V CONNECT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Connected Tract Perimeter (%)

Subindex

Composition of Tallest Woody 

Vegetation Strata (V COMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Tallest Strata Concurrence (%)

Subindex

Core Area (V CORE )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Tract within 100m Buffer (%)

Subindex

Frequency of Flooding (V FREQ )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

12345

Return Interval (years)

Subindex
74 Chapter 5 Model Applicability and Reference Data 

Figure 13. (Sheet 2 of 3) 

Ground Vegetation Cover (V GVC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Ground Vegetation Cover (%)

Subindex

Log Biomass (V LOG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125

Log Volume (m3

/ha)

Subindex

"O" Horizon Biomass (V OHOR )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

012345

"O" Horizon Thickness (cm) 

Subindex

Microdepressional Ponding 

(V POND )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Microdepressional Area (%)

Subindex

Soil Integrity (V SOIL )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Area of Altered Soils (%)

Subindex

Snag Density (V SNAG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100 120

Snags (stems/ha)

Subindex
Chapter 5 Model Applicability and Reference Data 75

 Figure 13. (Sheet 3 of 3) 

Understory Biomass (V SSD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2500 5000 7500 10000

Shrub/Sapling Density (stems/ha)

Subindex

Tree Biomass (V TBA )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50

Tree Basal Area (m2/ha)

Subindex

Tree Density (V TDENS )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000

Tree Density (stems/ha)

Subindex

Dominant Trees (V TCOMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Dominant Tree Concurrence (%)

Subindex

Wetland Tract (V TRACT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1000 2000 3000 4000

Wetland Tract (ha)

Subindex

Woody Debris (V WD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000

Woody Debris Volume (m3/ha)

Subindex
76 Chapter 5 Model Applicability and Reference Data 

Function 1: Detain Floodwater 

( )



 



 + + + = ×

4

LOG GVC SSD TDEN

FREQ

V V V V FCI V (13) 

Function 2: Detain Precipitation 

( )

2

VPOND VOHOR FCI + = (14) 

Function 3: Cycle Nutrients 

( ) ( )

2

3 4 



 



 + + +

+

+ +

=

VTBA VSSD VGVC VOHOR VAHOR VWD VSNAG

FCI (15) 

Function 4: Export Organic Carbon 

( )

2

3 3 



 



 + +

+



 



 + +

= ×

OHOR WD SNAG TBA SSD GVC

FREQ

V V V V V V

FCI V (16) 

Function 5: Remove Elements and Compounds 

( )



 



 + + = ×

3

CEC OHOR AHOR

FREQ

V V V FCI V (17) 

Function 6: Maintain Plant Communities 

( )

( )

2

1

2 2

2





 



 + ×

































 



 +

+

= SOIL POND

COMP

TBA TDENS

V V

V V V

FCI (18) 

Function 7: Provide Fish and Wildlife Habitat 

( ) ( ) ( ) ( ) 1

4

232 3

FREQ POND T SNAG TBA COMP LOG OHOR TRACT CONNECT CORE V V V VV VV V V V

FCI

+ + + + ++ = × ××

                         (19) 
Chapter 5 Model Applicability and Reference Data 77

Subclass: Riverine Overbank 

 All functions are assessed for this subclass using the general form of each 

assessment model presented in Chapter 4. Figure 14 provides the relationship 

between the variable metrics and the subindex for each of the assessment 

variables based on the Riverine Overbank reference data (Appendix C). 

Function 1: Detain Floodwater 

( )



 



 + + + = ×

4

LOG GVC SSD TDEN

FREQ

V V V V FCI V (20) 

Function 2: Detain Precipitation 

( )

2

VPOND VOHOR FCI + = (21) 

Function 3: Cycle Nutrients 

( ) ( )

2

3 4 



 



 + + +

+

+ +

=

VTBA VSSD VGVC VOHOR VAHOR VWD VSNAG

FCI (22) 

Function 4: Export Organic Carbon 

( )

2

3 3 



 



 + +

+



 



 + +

= ×

OHOR WD SNAG TBA SSD GVC

FREQ

V V V V V V

FCI V (23) 

Function 5: Remove Elements and Compounds 

( )



 



 + + = ×

3

CEC OHOR AHOR

FREQ

V V V FCI V (24) 

Function 6: Maintain Plant Communities 

( )

( )

2

1

2 2

2





 



 + ×

































 



 +

+

= SOIL POND

COMP

TBA TDENS

V V

V V V

FCI (25) 

Function 7: Provide Fish and Wildlife Habitat 

( ) ( ) ( ) ( ) 1

4

232 3

FREQ POND T SNAG TBA COMP LOG OHOR TRACT CONNECT CORE V V V VV VV V V V

FCI + + + + ++ = × ××

                         (26) 
78 Chapter 5 Model Applicability and Reference Data 

 Figure 14. Subindex graphs for Riverine Overbank (Sheet 1 of 3) 

Cation Exchange Capacity (V CEC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100

Difference in CEC (%)

Subindex

A Horizon Thickness (V AHOR )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

012345678

Depth of "A" Horizon (cm)

Subindex

Core Area (V CORE )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Tract within 100m Buffer (%)

Subindex

Frequency of Flooding (V FREQ )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

12345

Return Interval (years)

Subindex

Composition of Tallest Woody 

Vegetation Strata (V COMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Tallest Strata Concurrence (%)

Subindex

Habitat Connections (V CONNECT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Connected Tract Perimeter (%)

Subindex
Chapter 5 Model Applicability and Reference Data 79

Figure 14. (Sheet 2 of 3)

Log Biomass (V LOG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125

Log Volume (m3

/ha)

Subindex

"O" Horizon Biomass (V OHOR )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

012345

"O" Horizon Thickness (cm) 

Subindex

Microdepressional Ponding 

(V POND )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Microdepressional Area (%)

Subindex

Snag Density (V SNAG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125 150

Snags (stems/ha)

Subindex

Soil Integrity (V SOIL )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Area of Altered Soils (%)

Subindex

Ground Vegetation Cover (V GVC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Ground Vegetation Cover (%)

Subindex
80 Chapter 5 Model Applicability and Reference Data 

 Figure 14. (Sheet 3 of 3)

Tree Biomass (V TBA )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50

Tree Basal Area (m2/ha)

Subindex

Understory Biomass (V SSD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2500 5000 7500 10000

Shrub/Sapling Density (stems/ha)

Subindex

Tree Density (V TDENS )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000

Tree Density (stems/ha)

Subindex

Dominant Trees (V TCOMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Dominant Tree Concurrence (%)

Subindex

Wetland Tract (V TRACT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1000 2000 3000 4000

Wetland Tract (ha)

Subindex

Woody Debris Biomass (V WD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125 150

Woody Debris Volume (m3

/ha)

Subindex
Chapter 5 Model Applicability and Reference Data 81

Subclass: Isolated Depression 

 Three functions are assessed for this subclass. All of the applicable models 

have been modified from the general model form presented in Chapter 4. 

Figure 15 provides the relationship between the variable metrics and the 

subindex for each of the assessment variables based on the Isolated Depression 

reference data (Appendix C). 

Function 1: Detain Floodwater 

 Not applicable. 

Function 2: Detain Precipitation 

 Not applicable. 

Function 3: Cycle Nutrients 

 Applicable in the following modified form: 

( )

3

VTBA VSSD VSNAG FCI + + = (27)

Function 4: Export Organic Carbon 

 Not applicable. 

Function 5: Remove Elements and Compounds 

 Not applicable. 

Function 6: Maintain Plant Communities 

 Applicable in the following modified form: 

( ) 2

1

2

2 SOIL

COMP

TBA TDENS

V

V V V

FCI ×

































 



 +

+

= (28) 

Function 7: Provide Fish and Wildlife Habitat 

 Applicable in the following modified form: 

( ) ( ) 2

1

3 3 















 



 + +

×



 



 + + = VTCOMP VSNAG VTBA VTRACT VCONNECT VCORE FCI (29) 
82 Chapter 5 Model Applicability and Reference Data 

 Figure 15. Subindex graphs for Isolated Depression (Sheet 1 of 3) 

A Horizon Thickness (V AHOR )

Variable not used in

assessing this subclass

Cation Exchange Capacity (V CEC )

Variable not used in 

assessing this subclass

Composition of Tallest Woody 

Vegetation Strata (V COMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Tallest Strata Concurrence (%)

Subindex

Habitat Connections (V CONNECT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Connected Tract Perimeter (%)

Subindex

Frequency of Flooding (V FREQ ) 

Variable not used in

assessing this subclass

Core Area (V CORE )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Tract within 100m Buffer (%)

Subindex
Chapter 5 Model Applicability and Reference Data 83

Figure 15. (Sheet 2 of 3)

Ground Vegetation Cover (V GVC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Ground Vegetation Cover (%)

Subindex

Log Biomass (V LOG )

Variable not used in

assessing this subclass

"O" Horizon Biomass (VOHOR)

Variable not used in

assessing this subclass

Microdepressional Ponding 

(V POND )

Variable not used in

assessing this subclass

Snag Density (V SNAG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100 125

Snags (stems/ha)

Subindex

Soil Integrity (V SOIL )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Area of Altered Soils (%)

Subindex
84 Chapter 5 Model Applicability and Reference Data 

Wetland Tract (V TRACT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1000 2000 3000 4000

Wetland Tract (ha)

Subindex

Figure 15. (Sheet 3 of 3) 

Understory Biomass (V SSD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2500 5000 7500 10000

Shrub/Sapling Density (stems/ha)

Subindex

Tree Biomass (V TBA )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50

Tree Basal Area (m2/ha)

Subindex

Tree Density (V TDENS )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 400 800 1200

Tree Density (stems/ha)

Subindex

Dominant Trees (V TCOMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Dominant Tree Concurrence (%)

Subindex

Woody Debris Biomass (V WD )

Variable not use in

assessing this subclass
Chapter 5 Model Applicability and Reference Data 85

Subclass: Connected Depression 

 Six functions are assessed for this subclass. All of the models have been 

modified from the general model form presented in Chapter 4. Figure 16 

provides the relationship between the variable metrics and the subindex for each 

of the assessment variables based on the Connected Depression reference data 

(Appendix C). 

Function 1: Detain Floodwater 

 Applicable in the following modified form: 

( )



 



 + = ×

2

SSD TDEN

FREQ

V V FCI V (30) 

Function 2: Detain Precipitation 

 Not applicable. 

Function 3: Cycle Nutrients 

 Applicable in the following modified form: 

( )

3

VTBA VSSD VSNAG FCI + + = (31)

Function 4: Export Organic Carbon 

 Applicable in the following modified form: 

( )



 



 + + = ×

3

TBA SSD SNAG

FREQ

V V V FCI V (32) 

Function 5: Remove Elements and Compounds 

 Applicable in the following modified form: 

FCI = VFREQ ×VCEC (33) 

Function 6: Maintain Plant Communities 

 Applicable in the following modified form: 
86 Chapter 5 Model Applicability and Reference Data 

( ) 2

1

2

2 SOIL

COMP

TBA TDEN

V

V

V V

FCI ×

































 





+

+

= (34) 

Function 7: Provide Fish and Wildlife Habitat 

 Applicable in the following modified form: 

( ) ( ) 3

1

3 3 















 



 + +

×



 



 + + = × TCOMP SNAG TBA TRACT CONNECT CORE

FREQ

V V V V V V FCI V (35) 
Chapter 5 Model Applicability and Reference Data 87

Frequency of Flooding (V FREQ )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

12345

Return Interval (years)

Subindex

 Figure 16. Subindex graphs for Connected Depression (Sheet 1 of 3) 

Cation Exchange Capacity (V CEC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 25 50 75 100

Difference in CEC (%)

Subindex

A Horizon Thickness (V AHOR )

Variable not used in

assessing this subclass

Habitat Connections (V CONNECT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Connected Tract Perimeter (%)

Subindex

Composition of Tallest Woody 

Vegetation Strata (V COMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Tallest Strata Concurrence (%)

Subindex

Core Area (V CORE )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Tract within 100m Buffer (%)

Subindex
88 Chapter 5 Model Applicability and Reference Data 

Log Biomass (V LOG )

Variable not used in

assessing this subclass

Ground Vegetation Cover (V GVC )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Ground Vegetation Cover (%)

Subindex

"O" Horizon Biomass (VOHOR)

Variable not used in

assessing this subclass

Microdepressional Ponding 

(V POND )

Variable not used in

assessing this subclass

Snag Density (V SNAG )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 40 80 120 160

Snags (stems/ha)

Subindex

Soil Integrity (V SOIL )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

Area of Altered Soils (%)

Subindex

Figure 16. (Sheet 2 of 3) 
Chapter 5 Model Applicability and Reference Data 89

Tree Density (V TDENS )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000

Tree Density (stems/ha)

Subindex

Dominant Trees (V TCOMP )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100

 Dominant Tree Concurrence (%)

Subindex

Woody Debris Biomass (V WD )

Variable not use in

assessing this subclass

Figure 16. (Sheet 3 of 3) 

Understory Biomass (V SSD )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2500 5000 7500 10000

Shrub/Sapling Density (stems/ha)

Subindex

Tree Biomass (V TBA )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50

Tree Basal Area (m2/ha)

Subindex

Wetland Tract (V TRACT )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1000 2000 3000 4000

Wetland Tract (ha)

Subindex
90 Chapter 6 Assessment Protocol 

6 Assessment Protocol 

Introduction 

 Previous chapters of this Regional Guidebook have provided background 

information on the HGM Approach, characterized regional wetland subclasses, 

and documented variables, metrics, and assessment models/functional indices 

used to assess regional wetland subclasses in the Yazoo Basin. This chapter 

outlines the procedures for collecting and analyzing the data required to conduct 

an assessment in the context of a 404 Permit review process or similar 

assessment situation. 

 A typical individual 404 Permit review requires that a comparison be made 

between pre- and postproject conditions of wetlands at the project site. This 

analysis provides a measure of the loss or gain of function as a result of project 

impacts. Both the pre- and postproject assessments should be completed at the 

project site before the proposed project has begun. Data for the pre-project 

assessment represent existing conditions at the project site, while data for the 

post-project assessment are normally based on a prediction of the conditions that 

can reasonably be expected to exist following proposed project impacts. A welldocumented set of assumptions should be provided with the assessment to 

support the predicted postproject conditions used in making an assessment. 

 The tasks required to assess regional wetland subclasses in the Yazoo Basin 

using the HGM Approach include: 

a. Define assessment objectives. 

b. Identify regional wetland subclasses. 

c. Characterize the project area. 

d. Screen for red flags. 

e. Define the wetland assessment areas. 

f. Collect field data. 
Chapter 6 Assessment Protocol 91

g. Analyze field data. 

h. Apply assessment results. 

The following sections discuss each of these tasks in greater detail. 

Define Assessment Objectives 

 Begin the assessment process by unambiguously stating the objective of 

conducting the assessment. This might be as simple as, “The purpose of this 

assessment is to determine how the proposed project will impact wetland 

functions.” Other potential objectives might be to: 

a. Compare several wetlands as part of an alternatives analysis. 

b. Identify specific actions that can be taken to minimize project impacts. 

c. Document baseline conditions at the wetland site. 

d. Determine mitigation requirements. 

e. Determine mitigation success. 

f. Determine the effects of a wetland management technique. 

 Frequently, there will be multiple objectives, and defining these objectives in 

a clear and concise manner will facilitate communication and understanding 

between those involved in conducting the assessment as well as other interested 

parties. In addition, it will help to define the specific approach and level of effort 

that will be required to conduct assessments. For example, the specific approach 

and level of effort will change depending on whether the project is an individual 

404 Permit review, an Advanced Identification (ADID), a Special Area 

Management Plan (SAMP), or some other assessment scenario. 

Identify Regional Wetland Subclasses 

 Identify the regional wetland subclasses that wetlands in the project area 

belong to using the dichotomous key in Figure 11. Depending on the subclasses 

represented, determine which variables must be collected based on the 

information provided in Table 9. 

Characterize the Project Area 

 Characterizing the project area involves describing the project area in terms 

of its project name, location, assessment objectives, hydrogeomorphic and 
92 Chapter 6 Assessment Protocol 

Table 9 

Use of Assessment Variables by Regional Wetland Subclass

Variable 

Code Flat 

Riverine 

Backwater 

Riverine 

Overbank 

Isolated 

Depression 

Connected 

Depression 

VAHOR * * * not used not used 

VCEC not used * * not used * 

VCOMP * * * * * 

VCONNECT * * * * * 

VCORE * * * * * 

VFREQ not used * * not used * 

VGVC * * * * not used 

VLOG * * * not used not used 

VOHOR * * * not used not used 

VPOND * * * not used not used 

VSNAG * * * * * 

VSOIL * * * * * 

VSSD * * * * * 

VTBA * * * * * 

VTCOMP * * * * * 

VTDEN * * * * * 

VTRACT * * * * * 

VWD * * * not used not used 

 

wetland classification, climate, surficial geology, geomorphic setting, surface and 

groundwater hydrology, vegetation, soils, land use, existing cultural alteration, 

proposed impacts, and any other characteristics and processes that have the 

potential to influence how wetlands at the project area perform functions. The 

characterization should be written and should be accompanied by maps and 

figures that show project area boundaries, jurisdictional wetlands, wetland 

assessment areas (see below), proposed impacts, roads, ditches, buildings, 

streams, soil types, plant communities, threatened or endangered species habitat, 

and other important features. Figure 17 provides an example of a project area 

characterization. 

 Some information sources that will be useful in characterizing a project area 

include: 

a. Aerial photographs 

b. Topographic maps 

c. National Wetland Inventory maps 
Chapter 6 Assessment Protocol 93

Project Area Characterization 

Project Name and Location: Little Muddy River access road bridge crossing. 

Four miles west of Valley Park, Issaquena County, Mississippi. Range 5W, 

Township 9N, Section 6. 

Nature of Project: The project will improve a road crossing over the Little 

Muddy River damaged during recent flooding. The road provides year-round 

access to the local boat launch. In addition, one-half acre of forested wetland 

will be cleared in order to construct a boathouse. 

Assessment Objective: The objective is to determine the impact of the proposed 

discharge of dredged or fill material on the functions performed by the 

jurisdictional wetlands in the project area. 

Hydrogeomorphic and National Wetland Inventory Classification Category: 

 Regional Subclass = Riverine Backwater. 

 NWI Class = Palustrine forested, seasonally flooded (PFO1a) 

Description of Project Area and Surrounding Landscape:

 This project is located on the alluvial floodplain of a third order reach of the 

Little Muddy River in Issaquena County, Mississippi. The active, annual floodplain in this reach ranges from one-quarter to one-third mile wide. The main 

channel of the Little Muddy is presently near the center of the annual floodplain. 

The Little Muddy is a tributary of the Yazoo River, and the project area is 

located approximately 4 miles north of the Yazoo River main channel. The area 

normally floods to a depth of 2-3 feet several times during the winter and spring 

each year. 

 Most of the floodplain is forested with the Cypress-Tupelo (Type 102), 

Overcup Oak-Bitter Pecan (Type 96), and Sweetgum-Willow Oak (Type 92) 

cover types dominating (U.S. Forest Service 1982). Terraces (i.e., historical 

floodplains) adjacent to the active floodplain are mostly cleared and dedicated to 

the cultivation of cotton and soybeans. Soils on the active floodplain are hydric 

and belong to the Sharkey Series with a predominance of the Sharkey and 

Dowling Clays (Sr) map unit (U.S. Soil Conservation Service 1961). 

Site Map: 

 Figure 17. Example of project area description 
94 Chapter 6 Assessment Protocol 

d. Geomorphic maps (Kolb et al. 1986) 

e. County Soil Survey 

f. Chapter 3 of this Regional Guidebook

Screen for Red Flags 

 Red flags are features in the vicinity of the project area to which special 

recognition or protection has been assigned on the basis of objective criteria 

(Table 10). Many red flag features, based on national criteria or programs, are 

similar from region to region. Other red flag features are based on regional or 

local criteria. Screening for red flag features determines if the wetlands or other 

natural resources around the project area require special consideration or 

attention that may preempt or postpone conducting a wetland assessment. For 

example, if a proposed project has the potential to impact threatened or 

endangered species habitat, an assessment may be unnecessary since the project 

may be denied or modified based on the impacts to threatened or endangered 

species or habitat. 

Table 10 

Red Flag Features and Respective Program/Agency Authority

Red Flag Features Authority1

Native Lands and areas protected under the American Indian Religious Freedom Act A 

Hazardous waste sites identified under CERCLA or RCRA I 

Areas protected by a Coastal Zone Management Plan E 

Areas providing Critical Habitat for Species of Special Concern B, C, F 

Areas covered under the Farmland Protection Act K 

Floodplains, floodways, or flood-prone areas J 

Areas with structures/artifacts of historic or archeological significance G 

Areas protected under the Land and Water Conservation Fund Act K 

Areas protected by the Marine Protection Research and Sanctuaries Act B, D 

National wildlife refuges and special management areas C 

Areas identified in the North American Waterfowl Management Plan C, F 

Areas identified as significant under the RAMSAR Treaty H 

Areas supporting rare or unique plant communities C, H 

Areas designated as Sole Source Groundwater Aquifers I, L 

Areas protected by the Safe Drinking Water Act I, L 

City, County, State, and National Parks D, F, H, L 

Areas supporting threatened or endangered species B, C, F, H, I 

Areas with unique geological features H 

Areas protected by the Wild and Scenic Rivers Act or Wilderness Act D 1 Program Authority / Agency 

 A = Bureau of Indian Affairs 

 B = National Marine Fisheries Service 

 C = U.S. Fish and Wildlife Service 

 D = National Park Service 

 E = State Coastal Zone Office 

 F = State Departments of Natural Resources, Fish and Game, etc. 

 G = State Historic Preservation Office 

 H = State Natural Heritage Offices 

 I = U.S. Environmental Protection Agency 

 J = Federal Emergency Management Administration 

 K = National Resource Conservation Service 

 L = Local Government Agencies 
Chapter 6 Assessment Protocol 95

Figure 18. A single WAA within a 

 project area 

Figure 19. Spatially separated WAAs 

 from the same regional 

 wetland subclass within a 

 project area

Figure 20. Spatially separated WAAs 

 from different regional 

 wetland subclasses within 

 a project area

Define the Wetland Assessment Areas 

 The wetland assessment area 

(WAA) is an area of wetland within 

a project area that belongs to a 

single regional wetland subclass 

and is relatively homogeneous with 

respect to the criteria used to assess 

wetland functions (i.e., hydrologic 

regime, vegetation structure, topography, soils, successional stage). In 

many project areas, there will be 

just one WAA as illustrated in 

Figure 18. However, as the size 

and heterogeneity of the project 

area increases, it is more likely that 

it will be necessary to define and 

assess multiple WAAs within a 

project area. 

 At least three situations can be 

identified that necessitate defining 

and assessing multiple WAAs 

within a project area. The first 

situation occurs when widely separated areas of wetland, belonging to 

the same regional subclass, occur in 

the project area (Figure 19). 

 The second situation occurs 

when more than one regional 

wetland subclass occurs within a 

project area (Figure 20), and the 

third situation occurs when a 

contiguous wetland area of the same 

regional subclass exhibits spatial 

heterogeneity in terms of hydrology, 

vegetation, soils, or other assessment criteria (Figure 21). 

 The differences may be a result 

of natural variability (e.g., zonation 

on large river floodplains) or cultural 

alteration (e.g., logging, surface mining, hydrologic alterations). Each 

significantly different portion of the contiguous area should be designated as a 

separate WAA and assessed separately. 
96 Chapter 6 Assessment Protocol 

Figure 21. WAA defined based on 

 differences in site-specific 

 characteristics 

 There are elements of 

subjectivity and practicality in 

determining what constitutes 

“significantly different” portions of a 

contiguous wetland area. Field 

experience with the regional wetland 

subclass under consideration should 

provide a sense of the range of 

variability that typically occurs and 

the “common sense” necessary to 

make reasonable decisions in 

defining multiple WAAs. 

 In the Yazoo Basin, recently 

abandoned cropland and land 

harvested for timber will be two common criteria for designating multiple WAAs 

in a project area. Splitting a project area into many WAAs, based on relatively 

minor differences, will lead to a rapid increase in sampling and analysis 

requirements. In general, differences resulting from natural variability should not 

be used as a basis for dividing a project area into multiple WAAs. However, 

zonation caused by different hydrologic regimes or disturbances caused by rare 

and destructive natural events (e.g., hurricanes) should be used as a basis for 

defining WAA. 

Collect Field Data 

 The following equipment is necessary to collect field data. 

a. Plant identification keys 

b. Soil probe/sharpshooter shovel 

c. County Soil Survey 

d. Munsell color book and hydric soil indicator list (U.S. Department of 

Agriculture, NRCS 1998b) 

e. Diameter tape or calipers for measuring tree basal area 

f. 50-m distance measuring tape and meter sticks, stakes, and flagging. 

 Information on the variable and metrics used to assess the functions of 

regional wetland subclasses in the Yazoo Basin is collected at several different 

spatial scales. The Data Form 1 shown in Figure 22 is organized to facilitate data 

collection at each of these spatial scales. For example, the first group of variables, which includes VTRACT, contains information about landscape scale characteristics collected using aerial photographs, maps, and field reconnaissance of the 

area surrounding the WAA. Information on the second group of variables, which 
Chapter 6 Assessment Protocol 97

Data Form 1: Yazoo Basin Regional Guidebook - Variable / Metric Summary 

(Important Note: Use a separate Data Form 1 for each assessment area sampled) 

Assessment Team: Regional Subclass: 

Project Name / Location: Date: 

Quantify the following variables with field recon, aerials, topographic maps, or GIS 

VTRACT Size of forested wetland that is contiguous with the WAA ha 

VCORE Size of wetland tract that is core area % 

VCONNECT Percent of wetland tract that is connected to “suitable habitat” % 

VFREQ Overbank flood recurrence interval in the WAA years 

Sample the following variables based on a walking field reconnaissance of the WAA 

VPOND Percent of the wetland assessment area with topographic micro-depressions that pond water % 

VSOIL Percent of the wetland assessment area with culturally unaltered soils % 

VCEC Percent difference in CEC in WAA (from Data Form 2) % 

Transfer plot values for the following variables to this sheet from the Data Forms 3-6 

VTBA Average tree basal area plot values below (Data Form 3), record at right 

Plot 1 ____ m3/ha Plot 2 ____ m3/ha Plot 3 ____ m3/ha Plot 4 ____ m3/ha m2/ha 

VTDEN

Average tree density plot values below (Data Form 3), record at right 

Plot 1 __ stems/ha Plot 2 __ stems/ha Plot 3 __ stems/ha Plot 4 __ stems/ha stems/ha 

VSNAG

Average snag density plot values below (from Data Form 3), record at right 

Plot 1 __ stems/ha Plot 2 __ stems/ha Plot 3 __ stems/ha Plot 4 __ stems/ha stems/ha 

VTCOMP

Average percent concurrence with dominant trees plot values below (Data Form 4), record at 

right 

Plot 1 ___ % Plot 2 ___ % Plot 3 ___ % Plot 4 ___ % 

% 

VCOMP

Average percent concurrence with dominant species in tallest woody stratum plot values below 

(Data Form 4), record at right 

Plot 1 ___ % Plot 2 ___ % Plot 3 ___ % Plot 4 ___ % 

% 

VWD

Average volume of woody debris plot values below (Data Form 5), record at right 

Plot 1___ m3/ha Plot 2 ___ m3/ha Plot 3 ___ m3/ha Plot 4 ___ m3/ha m3/ha 

VLOG

Average volume of log plot values below (Data Form 5), record at right 

Plot 1___ m3/ha Plot 2 ___ m3/ha Plot 3 ___ m3/ha Plot 4 ___ m3/ha m3/ha 

VSSD

Average density of shrub-sapling strata plot values below (Data Form 6), record at right 

Plot 1 __ stems/ha Plot 2 __ stems/ha Plot 3 __ stems/ha stems/ha 

VGVC

Average ground vegetation cover plot values below (Data Form 6), record at right 

Plot 1 ___ % Plot 2 ___ % Plot 3 ___ % Plot 4 ___ % % 

VOHOR

Average thickness of O horizon plot values below (Data Form 6), record at right 

Plot 1 ___ cm Plot 2 ___ cm Plot 3 ___ cm Plot 4 ___ cm cm 

VAHOR

Average thickness of A horizon plot values below (Data Form 6), record at right 

Plot 1 ___ cm Plot 2 ___ cm Plot 3 ___ cm Plot 4 ___ cm cm 

 Figure 22. Data Form 1: Variable/Metric Summary 

includes VPOND , is collected during a walking reconnaissance of the WAA. Data 

collected for these two groups of variables are entered directly on the Data 

Form 1. Information on the next group of variables is collected in sample plots 

and along transects placed in representative locations throughout the WAA. A 

typical layout for these plots and transects is shown in Figure 23. 

 As in defining the WAA, there are elements of subjectivity and practicality in 

determining the number of sample locations for collecting plot-based and 

transect-based site-specific data. The exact numbers and locations of the plots 

and transects are dictated by the size and heterogeneity of the WAA. For 

example, if the WAA is relatively small (i.e., less than 2-3 acres) and homogeneous with respect to the characteristics and processes that influence wetland 

function, then three or four 0.04-ha plots, with nested transects and subplots in 

representative locations, are probably adequate to characterize the WAA. However, as the size and heterogeneity of the WAA increases, more sample plots are 

required to accurately represent the site. 
98 Chapter 6 Assessment Protocol 

 Figure 23. Sample plot and subplot dimensions and layouts for field sampling 

 The data collected for each of the variable metrics sampled in a plot or along 

a transect are entered on Data Forms 2-6 shown in Figures 24 through 32. Once 

these data have been collected and manipulated on the data form, specific information is transferred to Data Form 1 (Figure 22). Additional manipulation takes 

place on Data Form 1 that consists of taking plot averages. Based on the 

averageing, a final metric value is entered in the box at the right-hand side of the 

page. Detailed instructions on collecting variable metric information are 

provided in the following paragraphs. Variables are listed in alphabetical order 

by variable codes to facilitate locating them. 

 Experience has shown that the time required to complete an assessment at a 

several-acre WAA where 3-4 plots are sampled is 2-4 hr. Training and 

experience will reduce the required time to the lower end of this range. 
Chapter 6 Assessment Protocol 99

Data Form 2: Yazoo Basin Regional Guidebook 

Cation Exchange Capacity (VCEC )

Assessment Team: 

Project Name / Location: Plot: Date: 

Field Procedure 

(1) For each altered area, in the assessment area, record CEC before and after alteration in the 

Columns 2 and 3 below based on the information in the table below or the “feel method” for 

determining soil texture (Figure 33)

(2) For each altered area, calculate the percent of the assessment area that the altered area represents, 

and record in Column 5 as a decimal fraction

Office Procedure 

(1) Subtract Column 2 from Column 3 and enter the absolute value of the result in Column 4 

(2) Multiply Column 4 by Column 5 and record result in Column 6 

(3) Sum the values in Column 6

(4) Record resulting value on the Data Form 1 in the box at the right of the VCEC row 

1 2 3 4 5 6 

Altered Areas 

CEC After 

Alteration 

CEC Before 

Alteration 

Absolute Value 

of Column 3 

minus Column 2 

Percent of 

Assessment 

Area (0-1.0) 

Column 4 

times 

Column 5 

Altered Area 1 . 

Altered Area 2 

Altered Area 3 

Altered Area 4 

Total of Column 6 = __________ 

Soil Texture or Map Unit Symbol 

CEC Range 

meq / 100 grams 

Midpoint of CEC Range 

meg / 100 grams 

Sand 1-5 2.5 

Fine Sandy Loam 5-10 7.5 

Loam 5-15 10 

Silt Loam 5-15 10 

Clay Loam 15-30 22.5 

Clay 30-150 90 

Add other texture classes / map units 

Figure 24. Data Form 2: Cation Exchange Capacity (VCEC ) 
100 Chapter 6 Assessment Protocol 

Data Form 3 (Page 1 of 2): Yazoo Basin Regional Guidebook 

Tree Basal Area, Density, and Snags (VTBA , VTDEN , and VSNAG ) 

Assessment Team: 

Project Name / Location: Plot: Date: 

Sample VTBA , VTDEN , and VSNAG in at least two 0.04-ha circular plots 11.3-m (37-ft) radius 

Field Procedure 

(1) Record the species and dbh (cm) of all trees (i.e., woody stems ≥ 10 cm (4 in.) in the plot in 

 Columns 1 and 2 in the table below. 

1 2 3 4 1 2 3 4 

Species 

Code 

dbh 

 (cm) area (cm2

) area 

(m2) 

Species 

Code 

dbh 

 (cm) area (cm2

) area 

(m2) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(2) Tally standing dead stems (i.e., snags) ≥ 10 cm dbh in each 0.04-ha plot _______________ 

Figure 25. Data Form 3: Tree Basal Area, Density, and Snags (VTBA , VTDEN , and VSNAG ) (Continued) 
Chapter 6 Assessment Protocol 101

Data Form 3 (Page 2 of 2): Yazoo Basin Regional Guidebook 

Tree Basal Area, Density, and Snags (VTBA , VTDEN , and VSNAG ) 

Assessment Team: 

Project Name / Location: Plot: Date: 

Office Procedure (Use Appendix B spreadsheet or calculate manually with steps below) 

(1) Convert dbh values above to cm2 using the equation: (dbh ∗ dbh) ∗ 0.785 = cm2 and record in 

Column 3 of the above table.

(2) Convert cm2 values above to m2 using the equation: cm2 ∗ 0.0001 = m2 and record in Column 4 of 

the above table. 

(3) Sum m2 values in Column 4 above to get tree basal area _______ m2 / 0.04 ha 

(4) Multiply by 25 = tree basal area _______ m2 / ha 

(5) Record m2 / ha on Data Form 1 in the VTBA row as a plot value

(6) Count the number of tree stems recorded in plot from above table to determine tree 

stems / 0.04 ha ___

(7) Multiply tree stems / 0.04 ha by 25 = ____ tree stems / ha 

(8) Record tree stems / ha on Data Form 1 in the VTDEN row as a plot value

(9) Sum the snags tallied in the plot = ____ snags / 0.04 ha 

(10) Multiply snags / 0.04 ha by 25 = ____ snags / ha 

(11) Record snags / ha on Data Form 1 in the VSNAG row as a plot value

Figure 25. (Concluded) 

Procedures for Measuring Assessment Variables 

VAHOR - A horizon biomass 

This variable represents total mass of organic matter in the A soil horizon. 

The A soil horizon is defined as a mineral soil horizon that occurs at the ground 

surface, below the O soil horizon, that consists of an accumulation of unrecognizable decomposed organic matter mixed with mineral soil (U.S. Department of 

Agriculture SCS 1993). In practice, the A horizon is identified in the field as a 

zone of darkened soil. 

 Thickness of the A horizon is the metric used to quantify this variable. 

Measure it using the procedure outlined below. 

 (1) Measure the thickness of the A horizon in each of four, 1-m2

 subplots 

placed in representative areas of each quadrant of the 0.04-ha plot (Figure 23). 

Record measurements on Data Form 6. 

 (2) Average the A-horizon thickness measurements from each of the m2

subplots, and record the average on Data Form 1 in the VAHOR row as a plot value. 

 (3) On Data Form 1, average the A-horizon thickness plot values, and record 

the average value in the box at the right hand side of the VAHOR row. 
102 Chapter 6 Assessment Protocol 

Data Form 4a (Page 1 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Riverine Backwater

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VTCOMP in the 0.04-ha plot 

Field Procedure 

(1) Using the 50/20 rule and the data recorded on the Data Form 3, circle the tree species that are 

dominant in Columns A, B, and C below. If no trees are present, circle nothing. Note: If a dominant 

does not appear on the list, use local knowledge or literature to assign that species to the appropriate 

column. 

A: Common dominants in reference 

standard sites 

B: Species commonly 

present in reference 

standard sites, but 

dominance generally 

indicates heavy selective 

harvest, land abandonment, 

or other disturbances 

C: Uncommon or shrub 

species in reference standard 

sites, but may dominate in 

severely damaged systems 

Carya aquatica Acer drummondii Carpinus caroliniana 

Carya cordiformis Acer rubrum Cornus drummondii 

Carya ovata Carya illinoisensis Cornus foemina 

Carya tomentosa Celtis laevigata Cretaegus spp. 

Fraxinus tomentosa Diospyros virginiana Forestiera acuminata 

Gleditsia aquatica Fraxinus pennsylvanica Ilex deciduas 

Populus heterophylla Liquidambar styraciflua Planera aquatica 

Quercus falcata Salix nigra 

Quercus lyrata Ulmus americana 

Quercus michauxii Ulmus crassifolia 

Quercus nigra 

Quercus nuttallii 

Quercus pagoda 

Quercus phellos 

Quercus stellata 

Taxodium distichum 

Office Procedure 

(1) Using the circled dominant trees in the list of species in Columns A, B, and C above, calculate 

percent concurrence using the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B) + (0.33 * number of circled dominants in Column C)] / total number of circled dominants in all 

columns = _____ % 

(2) Record % concurrence on Data Form 1 in the VTCOMP row as a plot value 

Figure 26. Data Form 4a: Woody Vegetation Composition (VTCOMP and VCOMP ) for Riverine Backwater 

(Continued) 
Chapter 6 Assessment Protocol 103

Data Form 4a (Page 2 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Riverine Backwater

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VCOMP in the 0.04-ha plot 

Field Procedure 

(1) If tree cover is ≥ 20%, use the 50/20 rule and circle the dominant trees in Columns A, B, and C 

below. Note: In this step and Step 2 below, if a dominant does not appear on the list, use local 

knowledge or literature to assign that species to the appropriate column. 

(2) If tree cover is < 20%, identify the next tallest woody stratum with at least 10% cover. Use the 

50/20 rule and circle the dominants in the next tallest woody stratum in Columns A, B, and C below. 

A: Common dominants in 

reference standard sites 

B: Species commonly present in 

reference standard sites, but 

dominance generally indicates heavy 

selective harvest, land abandonment, 

or other disturbances 

C: Uncommon or shrub 

species in reference standard 

sites, but may dominate in 

severely damaged systems 

Carya aquatica Acer drummondii Carpinus caroliniana 

Carya cordiformis Acer rubrum Cornus drummondii 

Carya ovata Carya illinoisensis Cornus foemina 

Carya tomentosa Celtis laevigata Cretaegus spp. 

Fraxinus tomentosa Diospyros virginiana Forestiera acuminata 

Gleditsia aquatica Fraxinus pennsylvanica Ilex decidua 

Populus heterophylla Liquidambar styraciflua Planera aquatica 

Quercus falcata Salix nigra 

Quercus lyrata Ulmus americana 

Quercus michauxii Ulmus crassifolia 

Quercus nigra 

Quercus nuttallii 

Quercus pagoda 

Quercus phellos 

Quercus stellata 

Taxodium distichum 

Office Procedure 

(1) Using the dominants circled in Columns A, B, and C above, calculate percent concurrence using 

the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B) + (0.33 * number of circled dominants in Column C)] / total number of circled dominants in all 

columns = _____ %

(2) Record % concurrence on Summary Data Form 1 in the VCOMP row as a plot value 

Figure 26. (Concluded) 
104 Chapter 6 Assessment Protocol 

Data Form 4b (Page 1 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Riverine Overbank

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VTCOMP in the 0.04-ha plot 

Field Procedure 

(1) Using the 50/20 rule and the data recorded on the Data Form 3, circle the tree species that are 

dominant in Columns A, B, and C below. If no trees are present, circle nothing. If a dominant 

does not appear on the list, use local knowledge or literature to assign that species to the appropriate 

column.

A: Common dominants in reference 

standard sites 

B: Species commonly 

present in reference standard 

sites, but dominance 

generally indicates heavy 

selective harvest, land 

abandonment, or other 

disturbances 

C: Uncommon or shrub 

species in reference standard 

sites, but may dominate in 

severely damaged systems 

Carya aquatica Acer rubrum Acer negundo 

Carya illinoisensis Celtis laevigata Carpinus caroliniana 

Gleditsia aquatica Fraxinus pennsylvanica Forestiera acuminata 

Platanus occidentalis Liquidambar styraciflua Planera aquatica 

Populus deltoids Ulmus americana 

Quercus lyrata 

Quercus nuttallii 

Quercus pagoda 

Quercus phellos 

Salix spp. 

Taxodium distichum 

Office Procedure 

(1) Using the circled dominant trees in the list of species in Columns A, B, and C above, calculate 

percent concurrence using the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B) + (0.33 * number of circled dominants in Column C)] / total number of circled dominants in all 

columns = _____ % 

(2) Record % concurrence on Data Form 1 in the VTCOMP row as a plot value 

Figure 27. Data Form 4b: Woody Vegetation Composition (VTCOMP and VCOMP ) for Riverine Overbank 

(Continued) 
Chapter 6 Assessment Protocol 105

Data Form 4b (Page 2 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Riverine Overbank

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VCOMP in the 0.04-ha plot 

Field Procedure 

(1) If tree cover is ≥ 20%, use the 50/20 rule and circle the dominant trees in Columns A, B, and C 

below. Note: In this step and Step 2 below, if a dominant does not appear on the list, use local 

knowledge or literature to assign that species to the appropriate column. 

(2) If tree cover is < 20%, identify the next tallest woody stratum with at least 10% cover. Use the 

50/20 rule and circle the dominants in the next tallest woody stratum in Columns A, B, and C below. 

A: Common dominants in 

reference standard sites 

B: Species commonly present in 

reference standard sites, but 

dominance generally indicates 

heavy selective harvest, land 

abandonment, or other disturbances

C: Uncommon or shrub 

species in reference 

standard sites, but may 

dominate in severely 

damaged systems 

Carya aquatica Acer rubrum Acer negundo 

Carya illinoisensis Celtis laevigata Carpinus caroliniana 

Gleditsia aquatica Fraxinus pennsylvanica Forestiera acuminata 

Platanus occidentalis Liquidambar styraciflua Planera aquatica 

Populus deltoids Ulmus americana 

Quercus lyrata 

Quercus nuttallii 

Quercus pagoda 

Quercus phellos 

Salix spp. 

Taxodium distichum 

Office Procedure 

(1) Using the dominants circled in Columns A, B, and C above, calculate percent concurrence using 

the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B) + (0.33 * number of circled dominants in Column C)] / total number of circled dominants in all 

columns = _____ %

(2) Record % concurrence on Summary Data Form 1 in the VCOMP row as a plot value

Figure 27. (Concluded) 
106 Chapter 6 Assessment Protocol 

Data Form 4c (Page 1 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Flats

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VTCOMP in the 0.04-ha plot 

Field Procedure 

(1) Using the 50/20 rule and the data recorded on the Data Form 3, circle the tree species that are 

dominant in Columns A, B, and C below. If no trees are present, circle nothing. If a dominant does not 

appear on the list, use local knowledge or literature to assign that species to the appropriate column.

A: Common dominants in 

reference standard sites 

B: Species commonly present in 

reference standard sites, but 

dominance generally indicates 

heavy selective harvest, land 

abandonment, or other 

disturbances 

C: Uncommon or shrub 

species in reference standard 

sites, but may dominate in 

severely damaged systems 

Carya aquatica Acer negundo Cephalanthus occidentalis 

Carya cordiformis Acer rubrum Cornus foemina 

Carya laciniosa Carya illinoisensis Cretaegus spp. 

Carya ovata Celtis laevigata Forestiera acuminata 

Carya texana Diospyros virginiana Maclura pomifera 

Carya tomentosa Fraxinus pennsylvanica Morus rubra 

Nyssa aquatica Fraxinus tomentosa Sassafras albidum 

Platanus occidentalis Gleditsia aquatica Ulmus alata 

Quercus falcata Liquidambar styraciflua 

Quercus lyrata Populus deltoides 

Quercus michauxii Ulmus americana 

Quercus nigra Ulmus crassifolia 

Quercus nuttallii Ulmus rubra 

Quercus pagoda 

Quercus phellos 

Quercus stellata 

Taxodium distichum 

Office Procedure 

(1) Using the circled dominant trees in the list of species in Columns A, B, and C above, calculate 

percent concurrence using the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B) + (0.33 * number of circled dominants in Column C)] / total number of circled dominants in all 

columns = _____ % 

(2) Record % concurrence on Data Form 1 in the VTCOMP row as a plot value 

Figure 28. Data Form 4c: Woody Vegetation Composition (VTCOMP and VCOMP ) for Flats (Continued) 
Chapter 6 Assessment Protocol 107

Data Form 4c (Page 2 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Flats

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VCOMP in the 0.04-ha plot 

Field Procedure 

(1) If tree cover is ≥ 20%, use the 50/20 rule and circle the dominant trees in Columns A, B, and C 

below. Note: In this step and Step 2 below, if a dominant does not appear on the list, use local 

knowledge or literature to assign that species to the appropriate column. 

(2) If tree cover is < 20%, identify the next tallest woody stratum with at least 10% cover. Use the 

50/20 rule and circle the dominants in the next tallest woody stratum in Columns A, B, and C below. 

A: Common dominants in 

reference standard sites 

B: Species commonly present in 

reference standard sites, but 

dominance generally indicates 

heavy selective harvest, land 

abandonment, or other 

disturbances 

C: Uncommon or shrub 

species in reference 

standard sites, but may 

dominate in severely 

damaged systems 

Carya aquatica Acer negundo Cephalanthus occidentalis 

Carya cordiformis Acer rubrum Cornus foemina 

Carya laciniosa Carya illinoisensis Cretaegus spp. 

Carya ovata Celtis laevigata Forestiera acuminata 

Carya texana Diospyros virginiana Maclura pomifera 

Carya tomentosa Fraxinus pennsylvanica Morus rubra 

Nyssa aquatica Fraxinus tomentosa Sassafras albidum 

Platanus occidentalis Gleditsia aquatica Ulmus alata 

Quercus falcata Liquidambar styraciflua 

Quercus lyrata Populus deltoides 

Quercus michauxii Ulmus americana 

Quercus nigra Ulmus crassifolia 

Quercus nuttallii Ulmus rubra 

Quercus pagoda 

Quercus phellos 

Quercus stellata 

Taxodium distichum 

Office Procedure 

(1) Using the dominants circled in Columns A, B, and C above, calculate percent concurrence using 

the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B) + (0.33 * number of circled dominants in Column C)] / total number of circled dominants in all 

columns = _____ %

(2) Record % concurrence on Summary Data Form 1 in the VCOMP row as a plot value 

Figure 28. (Concluded) 
108 Chapter 6 Assessment Protocol 

Data Form 4d (Page 1 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Connected Depression

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VTCOMP in the 0.04-ha plot 

Field Procedure 

(1) Using the 50/20 rule and the data recorded on the Data Form 3 circle the tree species that are 

dominant in Columns A and B below. If no trees are present, circle nothing. If a dominant does not 

appear on the list, use local knowledge or literature to assign that species to the appropriate column. 

A: Common dominants in reference standard sites 

B: Species commonly present in reference 

standard sites, but dominance generally 

indicates heavy selective harvest, land 

abandonment, or other disturbances 

Acer rubrum Celtis laevigata 

Carya aquatica Cephalanthus occidentalis 

Diospyros virginiana Forestiera acuminata 

Fraxinus pennsylvanica Liquidambar styraciflua 

Fraxinus tomentosa Planera aquatica 

Gleditsia aquatica Salix nigra 

Nyssa aquatica Ulmus americana 

Platanus occidentalis Ulmus crassifolia 

Populus heterophylla 

Quercus lyrata 

Quercus nuttallii 

Quercus phellos 

Taxodium distichum 

Office Procedure 

(1) Using the circled dominant trees in the list of species in Columns A and B above, calculate percent 

concurrence using the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in 

Column B)] / total number of circled dominants in all columns = _____ % 

(2) Record % concurrence on Data Form 1 in the VTCOMP row as a plot value 

Figure 29. Data Form 4d: Woody Vegetation Composition (VTCOMP and VCOMP ) for Connected 

Depressions (Continued) 
Chapter 6 Assessment Protocol 109

Data Form 4d (Page 2 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Connected Depression

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VCOMP in the 0.04-ha plot 

Field Procedure 

(1) If tree cover is ≥ 20%, use the 50/20 rule and circle the dominant trees in Columns A and B below. 

 Note: In this step and Step 2 below, if a dominant does not appear on the list, use local knowledge or 

literature to assign that species to the appropriate column.

(2) If tree cover is < 20%, identify the next tallest woody stratum with at least 10% cover. Use the 

50/20 rule and circle the dominants in the next tallest woody stratum in Columns A and B below. 

A: Common dominants in reference standard sites 

B: Species commonly present in reference 

standard sites, but dominance generally 

indicates heavy selective harvest, land 

abandonment, or other disturbances 

Acer rubrum Celtis laevigata 

Carya aquatica Cephalanthus occidentalis 

Diospyros virginiana Forestiera acuminata 

Fraxinus pennsylvanica Liquidambar styraciflua 

Fraxinus tomentosa Planera aquatica 

Gleditsia aquatica Salix nigra 

Nyssa aquatica Ulmus americana 

Platanus occidentalis Ulmus crassifolia 

Populus heterophylla 

Quercus lyrata 

Quercus nuttallii 

Quercus phellos 

Taxodium distichum 

Office Procedure 

(1) Using the dominants circled in Columns A and B above, calculate percent concurrence using the 

following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B)] / total number of circled dominants in all columns = _____ %

(2) Record % concurrence on Summary Data Form 1 in the VCOMP row as a plot value 

Figure 29. (Concluded) 
110 Chapter 6 Assessment Protocol 

Data Form 4e (Page 1 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Isolated Depression

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VTCOMP in the 0.04-ha plot 

Field Procedure 

(1) Using the 50/20 rule and the data recorded on the Data Form 3, circle the tree species that are 

dominant in Columns A and B below. If no trees are present, circle nothing. If a dominant does not 

appear on the list, use local knowledge or literature to assign that species to the appropriate column. 

A: Common dominants in reference standard sites 

B: Species commonly present in reference 

standard sites, but dominance generally 

indicates heavy selective harvest, land 

abandonment, or other disturbances 

Acer rubrum Acer negundo 

Carya aquatica Celtis laevigata 

Carya illinoisensis Cephalanthus occidentalis 

Diospyros virginiana Crataegus spp. 

Fraxinus pennsylvanica Forestiera acuminata 

Fraxinus tomentosa Liquidambar styraciflua 

Gleditsia aquatica Planera aquatica 

Nyssa aquatica Salix nigra 

Quercus lyrata Ulmus alata 

Quercus nuttallii Ulmus americana 

Quercus phellos Ulmus crassifolia 

Taxodium distichum 

Office Procedure 

(1) Using the circled dominant trees in the list of species in Columns A and B above, calculate percent 

concurrence using the following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B)] / total number of circled dominants in all columns = _____ % 

(2) Record % concurrence on Data Form 1 in the VTCOMP row as a plot value 

Figure 30. Data Form 4e: Woody Vegetation Composition (VTCOMP and VCOMP ) for Isolated Depressions 

(Continued) 
Chapter 6 Assessment Protocol 111

Data Form 4e (Page 2 of 2): Yazoo Basin Regional Guidebook 

Woody Vegetation Composition (VTCOMP and VCOMP ) for Isolated Depression 

Assessment Team: 

Project Name / Location: Plot: Date: 

Determine VCOMP in the 0.04-ha plot 

Field Procedure 

(1) If tree cover is ≥ 20%, use the 50/20 rule and circle the dominant trees in Columns A, B, and C 

below. Note: In this step and Step 2 below, if a dominant does not appear on the list, use local 

knowledge or literature to assign that species to the appropriate column. 

(2) If tree cover is < 20%, identify the next tallest woody stratum with at least 10% cover. Use the 

50/20 rule and circle the dominants in the next tallest woody stratum in Columns A and B below. 

A: Common dominants in reference standard sites 

B: Species commonly present in reference 

standard sites, but dominance generally 

indicates heavy selective harvest, land 

abandonment, or other disturbances 

Acer rubrum Acer negundo 

Carya aquatica Celtis laevigata 

Carya illinoisensis Cephalanthus occidentalis 

Diospyros virginiana Crataegus spp. 

Fraxinus pennsylvanica Forestiera acuminata 

Fraxinus tomentosa Liquidambar styraciflua 

Gleditsia aquatica Planera aquatica 

Nyssa aquatica Salix nigra 

Quercus lyrata Ulmus alata 

Quercus nuttallii Ulmus americana 

Quercus phellos Ulmus crassifolia 

Taxodium distichum 

Office Procedure 

(1) Using the dominants circled in Columns A and B above, calculate percent concurrence using the 

following formula: 

[( 1.0 * number of circled dominants in Column A ) + ( 0.66 * number of circled dominants in Column 

B)] / total number of circled dominants in all columns = _____ %

(2) Record % concurrence on Summary Data Form 1 in the VCOMP row as a plot value 

Figure 30. (Concluded) 
112 Chapter 6 Assessment Protocol 

Data Form 5 (Page 1 of 2): Yazoo Basin Regional Guidebook 

Woody Debris and Logs (VWD and VLOG )

Assessment Team: 

Project Name / Location: Plot: Date: 

Sample VWD and VLOG along two 15-m transects in each 0.04-ha plot 

Field Procedure 

(1) Count stems in Size Class 1 (0.6-2.5 cm (0.25-1 in.)) that intersect a vertical plane above a 

 6 ft segment of Transect 1 __ and Transect 2 ___ Average these two values ___

(2) Count number of stems in Size Class 2 (2.5 - 7.6 cm (1-3 in.)) that intersect a vertical 

 plane above a 12 ft segment of Transect 1 ___ and Transect 2 ___ 

 Average these two values ____

(3) Record diameter of stems of Size Class 3 (> 7.6 cm (>3 in.)) that intersect a plane above a 50-ft 

section of Transect 1 and Transect 2 in the table below: 

Transect 1 Transect 2 

Stem No. Diameter (cm) Area (cm2) Stem No. Diameter (cm) Area (cm2) 

Stem 1 Stem 1 

Stem 2 Stem 2 

Stem 3 Stem 3 

Stem 4 Stem 4 

Stem 5 Stem 5 

Stem 6 Stem 6 

Stem 7 Stem 7 

Stem 8 Stem 8 

Stem 9 Stem 9 

Stem 10 Stem 10 

Stem 11 Stem 11 

Stem 12 Stem 12 

Stem 13 Stem 13 

Stem 14 Stem 14 

Stem 15 Stem 15 

Stem 16 Stem 16 

Stem 17 Stem 17 

Stem 18 Stem 18 

Stem 19 Stem 19 

Stem 20 Stem 20 

Sum Sum 

Figure 31. Data Form 5: Woody Debris and Logs (VWD and VLOG ) (Continued) 
Chapter 6 Assessment Protocol 113

Data Form 5 (Page 2 of 2): Yazoo Basin Regional Guidebook 

Woody Debris and Logs (VWD and VLOG )

Assessment Team: 

Project Name / Location: Plot: Date: 

Office Procedure (Use Appendix B spreadsheet or calculate using steps below) 

(1) Convert Size Class 1 average value from (1) in Field Procedure above to tons /acre: 

0.187 ∗ number of stems = ______ tons / acre 

(2) Convert Size Class 2 average value from (2) in Field Procedure above to tons / acre: 

0.892 ∗ total number of stems = Size Class 2 tons / acre _____ 

(3) Convert Size Class 3 diameter values to area and enter values on Page 1 of Data Sheet 5: 

diameter2 ∗ 0.785 = cm2

(4) Sum Size Class 3 stem areas (cm2) (for Transect 1 ____ and Transect 2 _____ 

 Average these two values _______ 

(5) Convert Size Class 3 area average to tons / acre using: 

0.0687 ∗ area (cm2

) = Size Class 3 stems tons / acre _____ 

(6) Sum tons / acre for all size classes = tons / acre _______ 

(7) Convert tons / acre for all size classes to ft3 / acre using: 

(32.05 ∗ tons / acre) / 0.58 = ft3

 / acre _____ 

(8) Convert ft3 / acre for all size classes to m3 / ha using: 

cubic feet / acre ∗ 0.069 = m3

 / ha _____ 

(9) Record m3 / ha (all size classes) on the Data Form 1 in the VWD row as a plot value 

(10) Convert tons / acre for Size Class 3 only to ft3 / acre using: 

(32.05 ∗ tons / acre) / 0.58 = ft3

 / acre _____ 

(11) Convert ft3 / acre for Size Class 3 only to m3 / ha using: 

cubic feet / acre ∗ 0.069 = m3

 / ha _____ 

(12) Record m3 / ha on Data Form 1 in the VLOG row as a plot value 

 Figure 31. (Concluded) 

VCEC - Cation exchange capacity 

 The variable represents the change in CEC of a soil as indicated by the total 

change in clay content in the top 50 cm (20 in.) of the soil profile. Most impacts 

do not significantly change the CEC of the soil profile. However, some impacts 

such as the placement of fill material or the excavation and replacement of soil 

can significantly alter CEC and increase or decrease the capacity of a wetland 

area to retain elements and compounds. 

 The percent difference in CEC in the top 50 cm (20 in.) of the soil profile in 

the WAA is used to quantify this variable. Measure it using the following 

procedure. 
114 Chapter 6 Assessment Protocol 

Data Form 6: Yazoo Basin Regional Guidebook 

Shrub-Sapling, Ground Cover, and Organic Horizons (VSSD , VGVC , VOHOR , and VAHOR )

Assessment Team: 

Project Name / Location: Plot: Date: 

Sample VSSD in two 0.004 ha circular subplots (3.6 m or 11.8 ft radius) in the 0.04 ha plot. 

Note: Shrub-Saplings are stems 1.4 m ( 4.5 ft) tall and <10 cm ( 4 in.) dbh 

Field Procedure 

 (1) Count shrub-sapling stems in each subplot and record number of stems below: 

 Subplot 1 ___ Subplot 2 ___

Office Procedure 

(1) Average shrub-sapling stems from the two subplots above: ___ stems / 0.004 ha 

(2) Convert average shrub-sapling units of stems / 0.004 ha to units of stems / ha using: 

stems / 0.004 ha ∗ 250 = _____ stems / ha

(3) Record stem density in stems / ha on Data Form 1 in the VSSD row as a plot value 

Sample VGVC , VOHOR , and VAHOR in four m2

 subplots, with one m2 subplot in each quadrant of 

the 0.04-ha plot. 

Field Procedure 

(1) Estimate the percent cover of ground vegetation in each subplot and record below: 

Subplot 1 ____ % Subplot 2 ____ % Subplot 3 ____ % Subplot 4 ____ % 

(2) Measure the thickness of the “O” Horizon in each subplot and record below: 

Subplot 1 ____ cm Subplot 2 ____ cm Subplot 3 ____ cm Subplot 4 ____ cm 

(3) Measure the thickness of the “A” Horizon in each subplot and record below: 

Subplot 1 ____ cm Subplot 2 ____ cm Subplot 3 ____ cm Subplot 4 ____ cm

Office Procedure 

(1) Average the percent cover of ground vegetation from the four m2 subplots above: ___ %

(2) Record percent cover of ground vegetation on Data Form 1 in the VGVC row as a 

 plot value 

(3) Average the thickness of “O” horizon from the four m2 subplots above: ___ cm

(4) Record average thickness on Data Form 1 in the VOHOR row as a plot value 

(5) Average the thickness of “A” horizon from the four m2 subplots above: ___ cm

(6) Record Average Thickness of “A” horizon on Data Form 1 in the VAHOR row as a 

 plot value

Figure 32. Data Form 6: Shrub-Sapling, Ground Cover, and Organic Horizons (VSSD , VGVC , VOHOR , and

VAHOR ) 
Chapter 6 Assessment Protocol 115

(1) Determine if the native soil in any of the area being assessed has been 

covered with fill material, excavated, replaced, or subjected to any other 

types of impact that significantly change the clay content of the soil 

profile. If no such alteration has occurred, record a zero percent 

difference on the Data Form 1 in the box on the right-hand side of the 

VCEC row. A value of zero, indicates that the CEC of soils in the 

assessment area has not been altered as a result of changes in clay 

content. 

(2) If areas of disturbed soil exist in the WAA, determine what percentage of 

the WAA each area represents, and record the percent of the area as a 

decimal fraction on Data Form 2 in Column 5. If multiple altered areas 

occur, record what percentage of the WAA each area represents on a 

separate row in Data Form 2 (i.e., Altered Area 1, Altered Area 2, etc.). 

(3) Determine what the CEC of the soil in each altered area would have been 

prior to disturbance. Do this based on the map unit identified in the 

county soil survey and the CEC values in Table 11. Record this value on 

Data Form 2 in Column 3 of the appropriate altered area row. 

Table 11 

Values of Cation Exchange Capacity (CEC) for Soil Texture Classes

Soil Texture or Map Unit Symbol 

CEC Range 

meq/100 grams 

Midpoint of CEC Range 

meg/100 grams 

Sand 1-5 2.5 

Fine Sandy Loam 5-10 7.5 

Loam 5-15 10 

Silt Loam 5-15 10 

Clay Loam 15-30 22.5 

Clay 30-150 90 

Conversion to pond or lakes 0 0 

(4) Determine the CEC of the disturbed soil in the altered area. This is 

accomplished by estimating soil texture class based on the “feel” method 

(Figure 33). Record this value on Data Form 2 in Column 2 of the 

appropriate altered area row. 

(5) Calculate the difference in CEC between the natural and disturbed soils 

for each altered area using the following formula. The vertical bars in 

the formula indicate absolute value. 

 Percent difference = | CEC after alteration - CEC before alteration | 

On Data Form 2 this is accomplished by taking the absolute value of 

Column 3 – Column 2. Record this value on Data Form 2 in Column 4 

of the appropriate altered area row. 

(6) Now calculate how each altered area contributes to the percent difference 

in CEC for the entire WAA. On the data form this translates into multiplying Column 4 by Column 5 and recording the results in Column 6. 
116 Chapter 6 Assessment Protocol 

Figure 33. Estimating soil texture by feel (from Thien 1979). Diagram available online at 

http://ltpwww.gsfc.nasa.gov/globe/tbf/tbfguide.htm
Chapter 6 Assessment Protocol 117

(7) Sum the values in Data Form 2, Column 6, to obtain the percent 

difference in CEC for the entire WAA. 

(8) Record the percent difference in CEC on the Data Form 1 in the box on 

the right-hand side of the VCEC row. 

VCOMP - Composition of tallest woody vegetation stratum 

 This variable represents the species composition of the tallest woody stratum 

present in the assessment area. This could be the tree, shrub-sapling, or seedling 

stratum. Percent concurrence with the dominant species in the dominant 

vegetation stratum is used to quantify this variable. Measure it using the 

procedure outlined below. 

(1) Determine percent cover of the tree stratum by visually estimating what 

percentage of the sky is blocked by leaves and stems of the tree stratum, 

or vertically projecting the leaves and stems to the forest floor. If the 

percent cover of the tree stratum is estimated to be at least 20 percent go 

to Step 2. If the percent cover of the tree stratum is estimated to be 

<20 percent, skip Step 2 and go directly to Step 3. 

(2) If the tree stratum has at least 20 percent cover, then the value for VCOMP

will be the same as the value for VTCOMP. In this case, skip the remaining 

steps and simply enter the value on the right-hand side of the VTCOMP row 

on Data Form 1 in the box at the right-hand side of the VCOMP row on 

Data Form 1. 

(3) If the tree stratum does not have at least 20 percent, cover identify the 

dominant species in the tallest woody stratum based on percent cover and 

circle them in Columns A, B, and C on Data Form 4 of the appropriate 

wetland subclass. Apply the 50/20 rule (U. S. Army Corps of Engineers 

1992), and rank species in descending order of percent cover. Identify 

dominants by summing relative dominance in descending order until 

50 percent is exceeded. Additional species with 20 percent relative 

dominance should also be included as dominants. Accurate identification 

of woody species is critical for determining the dominant species in each 

plot. Sampling during the dormant season may require proficiency in 

recognizing plant form, bark, or dormant/dead plant parts. Users who do 

not feel confident in identifying trees should get help. 

(4) Calculate percent concurrence using the following formula: {[ ( 1.0 * 

number of dominants in Column A ) + ( 0.66 * number of dominants in 

Column B) + (0.33 * number of dominants in Column C)] / total number 

of dominant species * 100} = _____ Percent Concurrence 

(5) Record this value as percent concurrence on the Data Form 1 on the 

VCOMP row as a plot value. 
118 Chapter 6 Assessment Protocol 

(6) Average the plot values on the Data Form 1 and record the result in the 

box on the right-hand side of the VCOMP row. 

VCONNECT - Habitat connections 

This variable is defined as the proportion of the perimeter of a forested 

wetland tract that is connected to suitable wildlife habitat such as upland forests 

or other wetlands (Figure 34). Agricultural fields, clear cuts, mined areas, or 

developed areas are examples of unsuitable habitats. 

 Figure 34. Connected wetland forest tract boundary 

 The percentage of the forested wetland tract boundary that is “connected” is 

used to quantify this variable. An adjacent habitat is considered connected if it is 

within 0.5 km (0.31 mile) of the boundary of the forested wetland tract. Measure 

it using the procedure outlined below 

(1) Calculate the length of the forested wetland tract boundary. Use field 

reconnaissance, topographic maps, aerial photography, GIS, or another 

method or tool. 

(2) Calculate the length of the forested wetland tract boundary that is within 

0.5 km (0.31 mile) of suitable habitats like those described above. 

(3) Divide the length of “connected” forested wetland tract boundary by the 

length of the total forested wetland tract boundary, and then multiply by 

100. The resulting number is the percent of the wetland tract boundary 

that is connected. 
Chapter 6 Assessment Protocol 119

(4) Record this percentage on Data Form 1 in the box on the right-hand side 

of the VCONNECT row. 

VCORE - Core area 

 This variable is defined as the portion of a wetland tract that lies inside of a 

100-m (330-ft) buffer inside the boundary of the wetland tract (Figure 35). 

Figure 35. Interior core area and buffer zone 

 The percentage of a wetland tract inside this 100-m (330-ft) buffer zone is 

the metric used to quantify this variable. Determine the value of this metric 

using the following procedure. 

(1) Draw a continuous line 100 m inside the wetland tract boundary. 

(2) Calculate the size of the area inside of this line. This is the core area. 

(3) Divide the size of the core area by size of the wetland tract and then 

multiply by 100. The resulting number is the percent of the wetland tract 

that is core area. 

(4) Record the percentage on Data Form 1 in the box on the right-hand side 

of the VCORE row. 
120 Chapter 6 Assessment Protocol 

VFREQ - Frequency of flooding 

Frequency of flooding refers to the frequency with which overbank or 

backwater flooding from an adjacent stream inundates the assessment area. 

Ideally, characterization of hydrologic regimes would also consider flood depth 

and duration. However, obtaining these data for a particular assessment area 

typically requires considerably more time and effort than is normally available 

under a rapid assessment scenario. Consequently, recurrence interval in years is 

used to quantify this variable. Determine the value of this metric using the 

following procedure. 

(1) Determine recurrence interval using one of the following methods. 

Specific guidelines are provided in Appendix C: 

a. Recurrence interval map 

b. Data from a nearby stream gage 

c. Regional flood frequency curves developed by local and state offices 

of USACE, USGS-Water Resources Division, State Geologic 

Surveys, or NRCS (Jennings, Thomas, and Riggs 1994) 

d. Hydrologic models such as HEC-2 (USACE 1981, 1982), HECRAS 

(USACE 1997), or HSPF (Bicknell et al. 1993) 

e. Local knowledge 

f. A regional dimensionless rating curve 

(2) Record recurrence interval on the Data Form 1 in the box at the right 

hand side of the VFREQ row. 

VGVC - Ground vegetation cover 

 Ground cover is defined as herbaceous and woody vegetation ≤ 1.4 m (4.5 ft) 

in height. Percent cover of ground vegetation is used to quantify this variable. 

Determine the value of this metric using the procedure outlined below. 

(1) Visually estimate the proportion of the ground surface that is covered by 

ground vegetation by mentally projecting the leaves and stems of ground 

vegetation to the ground surface. Do this in each of four 1-m2

 subplots, 

placed in representative portions of each quadrant of a 0.04-ha plot as 

illustrated in Figure 23. Record measurements on Data Form 6. 

(2) Average the percent ground vegetation cover from each of the m2

 subplots, and record the average on Data Form 1 in the VGVC row as a plot 

value. 

(3) On Data Form 1, average the percent ground vegetation cover plot 

values, and record the average value in the box at the right-hand side of 

the VGVC row. 
Chapter 6 Assessment Protocol 121

VLOG - Log biomass 

 See discussion in the Woody Debris (VWD) and Log Biomass (VLOG) section. 

VOHOR - O horizon biomass 

 The O horizon is defined as the soil layer dominated by organic material that 

consists of partially decomposed organic matter such as leaves, needles, sticks or 

twigs < 0.6 cm in diameter, flowers, fruits, insect frass, dead moss, or detached 

lichens on or near the surface of the ground (U.S. Department of Agriculture SCS 

1993). The O horizon does not include recently fallen material or material that 

has been incorporated into the mineral soil. 

 Thickness of the O soil horizon is the metric used to quantify this variable. 

Measure it using the procedure outlined below. 

(1) Measure the thickness of the O horizon at multiple sample points in each 

of the four 1-m2

 subplots placed in representative portions of each 

quadrant of a 0.04-ha plot (see Figure 23) and record measurements on 

Data Form 6. 

(2) Average the O horizon thickness measurements from each of the m2

subplots, and record the average on Data Form 1 in the VOHOR row as a 

plot value. 

(3) On Data Form 1, average the O horizon thickness plot values, and record 

the average value in the box at the right-hand side of the VOHOR row. 

VPOND - Micro-depressional ponding 

 Micro-depressional ponding refers to small topographic depressions that 

collect and hold rainwater for short periods of time. These small depressions are 

usually a result of tree “tip ups” and the scouring of effects of moving water. 

Larger vernal pools occur in the broad swales typical of meander scroll 

topography. These areas are included when estimating micro-depressional 

ponding. 

 This variable is measured as the proportion of the assessment area exhibiting 

micro-depressions. Measure it with the following procedure 

(1) Estimate the percentage of the WAA exhibiting microtopographic 

depressions and vernal pools capable of ponding rainwater. Evidence of 

these depressions may be the presence of water in micro-depression, silt 

on litter, stained leaves, or unvegetated patches. 

(2) Report the percent of the assessment area with micro-depressions on the 

Data Form 1 in the box on the right hand side of the VPOND row. 
122 Chapter 6 Assessment Protocol 

VSNAG - Snag density 

Snags are standing dead woody stems with a dbh ≥ 10 cm (4 in.). The density of 

snag stems per hectare is the metric used to quantify this variable. Measure it 

using the procedure outlined below. 

(1) Count the number of snag stems in at least three 0.04-ha circular plots 

located in representative areas of the WAA. Additional 0.04-ha circular 

plots may be necessary if the WAA is large and heterogenous. Record 

the number of snag stems from the 0.04-ha plot at the bottom of Data 

Form 3. 

(2) Multiply the number of snags by 25 to convert to a per hectare basis. For 

example, if the number of snags from the 0.04-ha circular plot is 2 snags, 

then 2 ∗ 25 = 50 snags / ha. 

(3) Record this value as snags / ha on the Data Form 1 as a plot value on the 

VSNAGS row. 

(4) Average the plot values on the Data Form 1 and record the result in the 

box on the right-hand side of the VSNAGS row. 

VSOIL - Soil integrity 

 It is difficult in a rapid assessment context to assess soil integrity for two 

reasons. First, there are a variety of soil properties contributing to integrity that 

must be measured (i.e., structure, horizonation, texture, bulk density). Second, 

the spatial variability of soils within riverine wetlands makes it difficult to collect 

the number of samples necessary to adequately characterize a site. Therefore, the 

approach used here is to assume that soil integrity exists where evidence of 

alteration is lacking. Stated another way, if the soils in the assessment area do 

not exhibit any of the characteristics associated with alteration, it is assumed that 

soils are similar to those occurring in the reference standard wetlands and have 

the potential to support a characteristic plant community. 

 This variable is measured as the proportion of the assessment area with 

altered soils. Measure it with the following procedure. 

(1) Determine if any of the soils in the area being assessed have been altered. 

 In particular, look for alteration to a normal soil profile, such as 

evidence of excavation or fill, severe compaction, or other types of 

impact that significantly alter soil integrity. Presence of a plow layer 

should not be considered to be a soil alteration. (Note: the influence of 

past tilling is accounted for in the assessment of A horizon thickness.) 

(2) If no altered soils exist, the percent of the assessment area with altered 

soils is zero. This indicates that all of the soils in the assessment area are 

similar to soils in reference standard sites. 
Chapter 6 Assessment Protocol 123

(3) If altered soils exist, determine what percent of the assessment area has 

soils that have been altered. 

(4) Report the percent of the assessment area with altered soils on the Data 

Form 1 in the box on the right of the VSOIL row. 

VSSD - Shrub-sapling density 

 Shrubs and saplings are woody stems < 10 cm (4 in.) dbh and > 1.2 m (4 ft) 

in height. Density of shrub-sapling stems per hectare is the metric used to 

quantify this variable. Measure it using the procedure outlined below. 

(1) Count woody stems < 10 cm (4 in.) and > 1.4 m (4.5 ft) in height in two 

0.004-ha circular plots (radius 3.6 m (11.8 ft)) nested within the 0.04-ha 

plot. If the 0.04-ha plot is heterogeneous, more 0.004-ha plots can be 

sampled. Record the number of stems in each 0.004-ha plot on Data 

Form 6. 

(2) Average the number of stems from the 0.004-ha plots in the 0.04-ha plot. 

(3) Multiply by 250 to convert from the units of stems/0.004-ha to the units 

of stems/ha. For example, if the average of the 0.004-ha plots is 

23 stems, then 23 ∗ 250 = 5,750 stems/ha. 

(4) Record this value as stems/ha on Data Form 1 as a plot value in the VSSD

row. 

(5) Average the plot values on Data Form 1 and record the result in the box 

on the right-hand side of the VSSD row. 

VTBA - Tree basal area 

 Trees are defined as living woody stems ≥ 10 cm (4 in.) dbh. Tree basal area 

is a common measure of abundance and dominance in forest ecology that has 

been shown to be proportional to tree biomass (Whittaker 1975, Whittaker et al. 

1974, Spurr and Barnes 1981, Tritton and Hornbeck 1982, Bonham 1989). Tree 

basal area per hectare is the metric used to quantify this variable. Measure it 

using the procedure outlined below. 

(1) Measure the diameter of all trees (living woody stems ≥ 10 cm or 4 in.) 

at breast height (dbh) in a circular 0.04-ha plot with a radius of 11.3 m 

(37 ft). Record tree species with corresponding diameter measurement in 

the table on Data Form 3. Accurate identification of woody species is 

critical for determining the dominant species in each plot. Sampling 

during the dormant season may require proficiency in recognizing plant 

form, bark, or dormant/dead plant parts. Users who do not feel confident 

in identifying trees should seek assistance. 
124 Chapter 6 Assessment Protocol 

 A spreadsheet is available to complete the calculations in Steps 2-5 below 

(see Appendix B). 

(2) Convert the dbh measurement for each woody stem to square centimeters 

using the following formula: (dbh ∗ dbh) ∗ 0.25 * 3.14 = cm2 . 

(3) Convert the area of each woody stem in cm2

 to square meters using the 

following formula: cm2 ∗ 0.0001 = m2

. 

(4) Sum the m2 measurements of all woody stems from the 0.04 ha plots to 

give m2

/0.04 ha. 

(5) Multiply by 25 to convert to m2

/ha. 

(6) Record this value as basal area/ha on the Data Form 1 as a plot value in 

the VTBA row. 

(7) Average the plot values on the Data Form 1 and record the result in the 

box on the right-hand side of the VTBA row. 

 An alternative rapid method: use an appropriate basal area prism at each plot 

center point to estimate stand basal area and enter as plot values in the VTBA row. 

Average all basal area measurements and record the result in the box on the right 

hand side. 

VTCOMP - Tree composition 

 Tree composition represents the composition of tree species in the forest 

canopy. Percent concurrence with the dominant species in each vegetation 

stratum is the metric used to quantify this variable. Measure it with the 

procedure outlined below. 

(1) Use the data on tree basal area on Data Form 3 and the 50/20 rule to 

identify the dominant species in the tree stratum (U. S. Army Corps of 

Engineers 1992). To apply the 50/20 rule, rank species in descending 

order of dominance. Basal area for each species can be calculated 

manually or accomplished by entering species sequentially in the tree 

basal area spreadsheet. Identify dominants by summing relative 

dominance beginning with the most dominant species in descending 

order until 50 percent is exceeded. Additional species with >20 percent 

relative dominance should also be included as dominants. 

(2) Calculate percent concurrence using the following formula: [( 1.0 * 

number of dominants in Column A ) + ( 0.66 * number of dominants in 

Column B) + (0.33 * number of dominants in Column C)] / total number 

of dominant species = _____ Percent Concurrence 

(3) Record this value as percent concurrence on the Data Form 1 on the 

VTCOMP row as a plot value. 
Chapter 6 Assessment Protocol 125

(4) Average the plot values on the Data Form 1 and record the result in the 

box on the right-hand side of the VTCOMP row. 

 An alternative rapid method: use cover estimation in lieu of basal area 

calculations to determine dominant species. See methodology for determining 

VCOMP above. 

VTDEN - Tree density 

 Tree density is the number of trees (i.e., living woody stems ≥ 10 cm (4 in.)). 

 The density of tree stems per hectare is the metric used to quantify this variable. 

 Measure it using the procedure outlined below. 

(1) Count the number of tree stems in the 0.04-ha plot using the data 

recorded for tree basal area on Data Form 1. If the rapid prism method 

for basal area sampling was employed, then directly count all trees 

within the 0.04-ha plot. 

(2) Multiply the value by 25 to convert to units of stems/ha. 

(3) Record stems/ha on the Data Form 1 as a plot value on the VTDEN row. 

(4) Average the plot values on the Data Form 1 and record the result in the 

box on the right hand side of the VTDEN row. 

VTRACT - Wetland tract 

 This variable is defined as the area of forested wetland that is contiguous and 

directly accessible to the WAA (Figure 36). Wetlands need not be in the same 

regional subclass as the assessment area to be considered. 

 The size of the forested wetland area contiguous with the WAA is the metric 

used to quantify this variable. Determine the value of this metric using the 

following procedure. 

(1) Determine the size of the forested wetland area (ha) that is contiguous 

and directly accessible to wildlife utilizing the WAA. Use field 

reconnaissance, topographic maps, aerial photography, GIS, or another 

method. 

(2) Record the forested wetland area in hectares on the Data Form 1 in the 

box at the right-hand side of the VTRACT row. 

VWD - Woody debris biomass and VLOG - log biomass 

 Woody debris is an important habitat and nutrient cycling component of 

forests. Volume of woody debris and log biomass per hectare is the metric used 
126 Chapter 6 Assessment Protocol 

Figure 36. Wetland tract 

to quantify these variables. Measure them with the procedure outlined below 

(Brown 1974; Brown Oberheu, and Johnston 1982). 

(1) Lay out two 15.24-m (50-ft) east-west transects, originating at the 

0.04-ha plot center point (Figure 23). 

(2) Count the number of nonliving stems in Size Class 1 (≥0.6 and <2.5 cm 

(≥0.25 and <1 in.)) that intersect the vertical plane above the 6-ft 

segment farthest from the plot center point on each 50-ft transect. 

Record the number of Size Class 1 stems on Data Form 5. (Note: all 

stem diameter criteria and the measurements for all size classes refer to 

diameter at the point of intersection with the transect line). 

(3) Count the number of nonliving stems in Size Class 2 (≥2.5 cm and 

< 7.6 cm (≥ 1 and < 3 in.)) that intersect the plane above the 12-ft 

segment farthest from the plot center point on each 50-ft transect. 

Record the number of Size Class 2 stems on Data Form 5. 

(4) Measure and record the diameter of nonliving stems in Size Class 3 

(≥ 7.6 cm (≥3 in.)) that intersect the plane above the entire length of the 

50-ft transect. Record the diameter of individual stems in Size Class 3 

on Data Form 5. 

 A spreadsheet is available to complete the calculations in Steps 5-16 below 

(Appendix B). 
Chapter 6 Assessment Protocol 127

(5) Convert stem counts for Size Classes 1 and 2 using the following 

formulas. 

 Size Class 1: 0.187 ∗ number of stems = _____ tons/acre 

 Size Class 2: 0.892 ∗ number of stems = _____ tons/acre 

(6) Convert stems diameters for Size Class 3 into area using the formula: 

(dbh ∗ dbh) ∗ 0.785 = cm2

. 

(7) Sum the area of the Size Class 3 stems, and convert to tons/acre using 

the formula: area (cm2

) ∗ 0.0687 = tons/acre 

(8) Sum the tons/acre for Size Classes 1, 2, and 3 for Transect 1. 

(9) Repeat Steps 1-8 for Transect 2 

(10) Average the summed tons/acre for all Size Classes Transects 1 and 2 

(11) Convert tons/acre to ft3

/acre using the formula: (32.05 ∗ tons/acre)/ 

0.58 = ft3

/acre 

(12) Convert ft3

/acre to m3/ha using the formula: 0.069 ∗ ft3/acre = m3/ha 

(13) Record m3

/acre on the Data Form 1 as a plot value on the VWD row 

(14) Average tons/acre for Size Class 3 from Transects 1 and 2. 

(15) Convert tons/acre to ft3

/acre using the formula: (32.05 ∗ tons/acre)/ 

0.58 = ft3

/acre 

(16) Convert ft3

/acre to m3/ha using the formula: 0.069 ∗ ft3/acre = m3/ha 

(17) Record m3

/acre on the Data Form 1 as a plot value on the VLOG row 

(18) Average the plot values on the Data Form 1 for VWD and VLOG and 

record the result in the boxes on the right-hand side of the VWD and 

VLOG rows. 

Analyze Field Data 

 The analysis of field data requires two steps. The first step is to transform 

the measure of each assessment variable into a variable subindex. This can be 

done using the graphs at the end of Chapter 5 or in a spreadsheet that has been set 

up to do these tedious calculations (see Appendix B). The second step is to insert 

the variable subindices into the assessment model and calculate the FCI using the 

relationships defined in the assessment models. Again, these tedious calculations 
128 Chapter 6 Assessment Protocol 

can be done manually using the assessment model equations in Chapter 5 or 

using a spreadsheet set up to do the calculations (see Appendix B). 

 Figure 37 shows the spreadsheet that has been set up to do both steps of the 

analysis. The data from the boxes on the right hand side of Data Form 1 are 

entered in the second column labeled “Variable Metric Values” in the lower 

portion of the spreadsheet to the right of the variable names. The calculated 

variable subindex is displayed in the fourth column of the lower half of the 

spreadsheet. The variable subindices are then used to calculate the FCI using the 

appropriate assessment model. The resulting FCI is displayed in the first column 

of the top half of the spreadsheet to the left of each function name. The 

spreadsheet format allows the user to instantly ascertain how a change in the 

metric value of a variable will affect the FCI of a particular function by simply 

entering a new metric value in the bottom half of the spreadsheet. 

Apply Assessment Results 

 Once the assessment and analysis phases are complete, the results can be 

used to: (a) compare the same WAA at different points in time, (b) compare 

different WAAs at the same point in time, (c) compare different alternatives to a 

project, or (d) compare different hydrogeomorphic classes or subclasses (Smith 

et al. 1995). 

Special Issues in Applying the Assessment 

Results

 Users of this document must recognize that not all situations can be anticipated or accounted for in developing a rapid assessment method. In particular, 

users must be able to adapt the material presented here to special or unique situations encountered in the field. For example, most of the reference standard 

conditions identified in the field were mature forests with high species diversity, 

and typically they were dominated by oak species. Sites that deviate from this 

reference condition typically produce low scores for some functions. However, 

there are situations where deviation from the reference standard condition is 

appropriate and should be recognized as such. In most of these cases, alternative 

reference standards have been identified in the discussions of assessment 

variables (such as where cottonwood or willow dominate on new substrates, this 

is recognized as an appropriate VCOMP condition). In other instances, however, 

professional judgment in the field is essential to proper application of the models. 

 For example, some sites with near-permanent flooding are dominated by 

buttonbush. Where this occurs because of water control structures, it should be 

recognized as having arrested functional status, at least for some functions. 

However, where the same situation occurs because of beaver activity or changes 

in channel courses, the buttonbush swamp should be recognized as a functional 

and temporary component of a larger wetland complex. Other such situations that 

require special consideration include areas affected by fire, sites damaged by ice 

storms, and similar occurrences. 
Chapter 6 Assessment Protocol 129

 Another potential consideration in the application of the assessment models 

presented here concerns projection of future conditions. This may be particularly 

important in determining the rate at which functional status will improve as a 

result of restoration actions intended to offset impacts to jurisdictional wetlands. 

The graphs in Figure 38 represent general recovery trajectories for forested sites 

within the Yazoo Basin, based on a subset of the reference data collected to 

develop this guidebook. In selected stands, individual trees were aged using an 

increment corer to develop a general relationship between the age of sampled 

stands and the site-specific variables employed in the assessment models. Thus, 

a user can estimate the overstory basal area, shrub density, woody debris volume, 

and other functional indictors for various time intervals and calculate functional 

capacity indices for all applicable functions. These curves are specifically constructed to reflect wetland recovery following restoration of agricultural land, 

which is the most common restoration scenario in the Yazoo Basin. Thus, they 

assume that the initial site condition includes bare ground that has been tilled 

(hence the deeper initial A horizon). Note that landscape variables are not 

included here, because they require site-specific knowledge to project future 

conditions. Ponding development rates also are not estimated, because ponding 

is the result of both geomorphic and biotic factors and the initial site conditions 

(i.e., extent of land leveling). The degree of microtopographic relief will be 

dependent on the extent of site contouring work done prior to planting, in most 

cases. Similarly, the rates of compositional change (VCOMP and VTCOMP) are 

dependent on initial site conditions; generally, a site planted with appropriate 

species should have an initial FCI score of 1.0 for the compositional variables 

and maintain that fully functional status indefinitely. Estimation of future 

composition for unplanted areas will require site-specific evaluation of seed 

sources and probable colonization patterns. Note also that the graphs in 

Figure 38 are amalgams of data from all wetland subclasses. In situations where 

a site is expected to be unusual in one or more respects (such as a cottonwood 

stand, where basal areas are likely to increase more quickly than in hardwood 

forests), more specific data may exist and should be substituted for these general 

curves as appropriate. 
130 Chapter 6 Assessment Protocol 

FCI Calculation for the Riverine Backwater Regional Subclass in the Yazoo Basin (12-12-00) 

 

Enter quantitative or categorical measure from Field Data Sheet in the shaded cells below 

Variable

Metric 

Value Units Subindex 

1. VTRACT 1 ha 0.0 

2. VCORE 1 % 0.1 

3. VCONNECT 1 % 0.1 

4. VFREQ 5 years 0.3 FCI Function

5. VPOND 1 % 0.1 0.0 Detain Floodwater 

6. VSOIL 1 % 1.0 0.3 Detain Precipitation 

7. VCEC 1 % 1.0 0.2 Cycle Nutrients

8. VTBA 1 m2 / ha 0.0 0.1 Export Organic Carbon 

9. VTDEN 1 stems / ha 0.0 0.2 Remove Elements and 

 Compounds 

10. VSNAG 1 stems / ha 0.0 0.0 

 Maintain Plant 

 Communities

11. VTCOMP 1 % 0.0 0.0 

 Provide Fish and Wildlife 

 Habitat 

12. VCOMP 1 % 0.0 

13. VWD 1 m3 / ha 0.5 

14. VLOG 1 m3 / ha 0.0 

15. VSSD 1 stems / ha 0.0 

16. VGVC 1 % 0.1 

17. VOHOR 1 cm 0.6 

18. VAHOR 1 cm 0.6 

Figure 37. Example of an FCI calculation spreadsheet 
Chapter 6 Assessment Protocol 131

Figure 38. Recovery trajectories for selected assessment variables (Continued) 

Basal Area (V TBA )

0

10

20

30

40

50

0 20 40 60 80 100

Stand Age in Years

Basal Area / ha

Ground Vegetation Cover (V GVC )

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100

Stand Age in Years

% Cover

Tree Density (V TDENS )

0

100

200

300

400

500

600

700

800

900

0 20 40 60 80 100

Stand Age in Years

Stems / ha

Woody Debris (V WD )

0

10

20

30

40

50

0 20 40 60 80 100

Stand Age in Years

m3 / ha

Shrub-Sapling Density (V SSD )

0

1000

2000

3000

4000

5000

6000

7000

8000

0 20 40 60 80 100

Stand Age in Years

Basal Area / ha

Logs (V LOG )

0

10

20

30

40

50

0 20 40 60 80 100

Stand Age in Years

m3 / ha
132 Chapter 6 Assessment Protocol 

Figure 38. (Concluded) 

A Horizon (V AHOR )

0

1

2

3

4

5

0 20 40 60 80 100

Stand Age in Years

Thickness (cm)

O Horizon (V OHOR )

0

1

2

0 20 40 60 80 100

Stand Age in Years

Thickness (cm)

Snags Density (V SNAG )

0

10

20

30

40

50

0 20 40 60 80 100

Stand Age in Years

Stems / ha
References 133

References 

Allen, A. W. (1987). “Habitat suitability index models: Gray squirrel, revised,” 

Biological Report 82(10.135), U.S. Fish and Wildlife Service. 

Ambuel, B., and Temple, S. A. (1983). “Area-dependent changes in the bird 

communities and vegetation of southern Wisconsin forests,” Ecology 64, 

1057-68. 

Askins, R. A., Philbrick, M. J., and Sugeno, D. S. (1987). “Relationship 

between the regional abundance of forest and the composition of forest bird 

communities,” Biological Conservation 39, 129-52. 

Autin, W. J., Burns, S. F., Miller, B. J., Saucier, R. T., and Snead, J. I. (1991). 

“Quaternary geology of the Lower Mississippi Valley.” Quaternary 

nonglacial geology: Conterminous U.S. Vol. K-2, The Geology of North 

America. Morrison, R.B., ed., Geological Society of America, Boulder, CO, 

547-82. 

Baker, J. A., and Killgore, K. J. (1994). “Use of a flooded bottomland hardwood 

wetland by fishes in the Cache River System, Arkansas,” Technical Report 

WRP-CP-3, Wetlands Research Program, U.S. Army Engineer Waterways 

Experiment Station, Vicksburg, MS. 

Baker, J. A., Killgore, K. J., and Kasul, R. L. (1991). “Aquatic habitats and fish 

communities in the lower Mississippi River,” Reviews in Aquatic Sciences 3, 

313-56. 

Barham, A. F. (1964). “As I saw it: The story of the development of drainage 

and flood control in the St. Francis Basin of Arkansas,” Unpublished 

manuscript. 

Barnhardt, M. L. (1988). “Historical sedimentation in west Tennessee gullies,” 

Southeastern Geographer 28, 1-18. 

Batema, D. L., Henderson, G. S., and Fredrickson, L H. (1985). “Wetland 

invertebrate distribution in bottomland hardwoods as influenced by forest 

type and flooding regime.” Proceedings, Fifth Annual Hardwood 

Conference. University of Illinois, Urbana, 196-202. 
134 References 

Bicknell, B. R., Imhoff, J. C., Kittle, J. L., Donigan, A. S., and Johanson, R. C. 

(1993). “Hydrological Simulation Program - Fortran (HSPF): User’s 

manual for release 10.0,” EPA 600/3-84-066, Environmental Research 

Laboratory, U.S. Environmental Protection Agency, Athens, GA. 

Bilby, R. E., and Likens, G. E. (1979). “Effect of hydrologic fluctuations on the 

transport of fine particulate organic carbon in a small stream,” Limnology 

and Oceanography 24, 69-74. 

Blake, J. G., and Karr, J. R. (1984). “Species composition of bird communities 

and the conservation benefit of large versus small forests,” Biological 

Conservation 30, 173-87. 

Bolen, E. G., Smith, L. M., and Schramm, H. L. (1989). “Playa lakes - Prairie 

wetlands of the southern high plains,” Bioscience 39, 615-23. 

Bolton, S. C., and Metzger, J. E. (1998). “The Vicksburg District 1977-1991,” 

U.S. Army Corps of Engineers Vicksburg, District, Vicksburg, MS. 

Bonham, C. D. (1989). Measurements for terrestrial vegetation. John Wiley 

and Sons, New York. 

Bormann, F. H., and Likens, G. E. (1970). “The nutrient cycles of an 

ecosystem,” Scientific American 223, 92-101. 

Bovee, K. D. (1982). “A guide to stream habitat analysis using the in stream 

flow incremental method-ology,” Instream Flow Information Paper No. 12, 

OBS-82/26, U.S. Fish and Wildlife Service. 

Braun, E. L. (1950). Deciduous forests of eastern North America. Hafner Press, 

New York. 

__________. (1964). Deciduous forests of eastern North America. Hafner 

Publishing Company, New York. 

Brinson , M. M. (1977). “Decomposition and nutrient exchange of litter in an 

alluvial swamp forest,” Ecology 58, 601-9. 

__________. (1985). “Management potential for nutrient removal in forested 

wetlands.” Ecological considerations in wetlands treatment of municipal 

wastewaters. P. J. Godfrey et al., ed., Van Nostrand Reinhold, New York, 

405-16. 

__________. (1990). “Riverine forests.” Forested wetlands. A. E. Lugo, M. 

M. Brinson, and S. Brown, ed., Elsevier Scientific Publishers, Amsterdam, 

87-141. 

__________. (1993a). “A hydrogeomorphic classification for wetlands,” 

Technical Report WRP-DE-4, U.S. Army Engineer Waterways Experiment 

Station, Vicksburg, MS. 
References 135

Brinson , M. M. (1993b). “Changes in the functioning of wetlands along 

environmental gradients,” Wetlands 13, 65-74. 

__________. (1995a). “The hydrogeomorphic approach explained,” National 

Wetlands Newsletter, November/December, Environmental Law Institute, 

Washington, DC. 

__________. (1995b). “Assessing wetland functions using HGM,” National 

Wetlands Newsletter, January/February, Environmental Law Institute, 

Washington, DC. 

Brinson, M. M., Bradshaw, H. D., and Kane, E. S. (1984). “Nutrient 

assimilative capacity of an alluvial floodplain swamp,” Journal of Applied 

Ecology 21, 1041-57. 

Brinson, M. M., Bradshaw, H. D, Holmes, R. N., and Elkins, J. B., Jr. (1980). 

“Litterfall, stemflow, and throughfall nutrient fluxes in an alluvial swamp 

forest,” Ecology 61, 827-35. 

Brinson, M. M., Hauer, F. R., Lee, L. C., Nutter, W. L., Rheinhardt, R. D., 

Smith, R. D., and Whigham, D. (1995). “A guidebook for application of 

hydrogeomorphic assessments to riverine wetlands,” Wetlands Research 

Program Technical Report WRP-DE-1, U.S. Army Engineer Waterways 

Experiment Station, Vicksburg, MS. 

Brinson, M. M., Lugo, A. E., and Brown, S. (1981). “Primary productivity, 

decomposition and consumer activity in freshwater wetlands,” Annual 

Review of Ecology and Systematics 12, 123-61. 

Brinson, M. M., Nutter, W. L., Rheinhardt, R., and Pruitt, B. A. (1996). “Background and recommendations for establishing reference wetlands in the Piedmont of the Carolinas and Georgia,” EPA/600/R-96/057, U.S. Environmental 

Protection Agency National Health and Environmental Effects Laboratory, 

Western Division, Corvallis, OR. 

Brinson, M. M., Smith, R. D., Whigham, D. F., Lee, L. C., Rheinhardt, R. D., 

and Nutter, W. L. (1998). “Progress in development of the 

hydrogeomorphic approach for assessing the functioning of wetlands.” 

Proceedings, INTECOL International Wetland Conference. Perth, Australia. 

Brinson, M. M., Swift. B. L., Plantico, R. C., and Barclay, J. S. (1981). 

“Riparian ecosystems: Their ecology and status,” OBS-81/17, U.S. Fish and 

Wildlife Service. 

Brooks, K. N., Ffolliott, P. F., Gregerson, H. M., Thames, J. L. (1991). 

Hydrology and the management of watersheds. Iowa State University Press, 

Ames, IA. 
136 References 

Brown, D. A., Nash, V. E., Caldwell, A. G., Bartelli, L. J., Carter, R. C., and 

Carter, O. R. (1971). “A monograph of the soils of the southern Mississippi 

Valley alluvium,” Arkansas, Mississippi, and Louisiana Agricultural Experiment Stations in Cooperation with the U.S. Department of Agriculture Soil 

Conservation Service. Southern Cooperative Series Bulletin 178, 112 pages 

plus 2 map sheets. 

Brown, J. K. (1974). “Handbook for inventorying downed woody material,” 

General Technical Report INT-16, U.S. Department of Agriculture Forest 

Service. 

Brown, J. K., Oberheu, R. D., and Johnston, C. M. (1982). “Handbook for 

inventorying surface fuels and biomass in the interior west,” General 

Technical Report INT-129, U.S. Department of Agriculture Forest Service 

Inter-mountain Forest and Range Experiment Station, Ogden UT. 

Brown, S., and Peterson, D. L. (1983). “Structural characteristics and biomass 

production of two Illinois bottomland forests,” American Midland Naturalist

110, 107-17. 

Campbell, K. L., and Johnson, H. P. (1975). “Hydrologic simulation of 

watersheds with artificial drainage,” Water Resources Research 11, 120-26. 

Conarro, R.M. (undated). “The beginning: Recollections and comments, 

Bienville, Delta, DeSoto, Homochitto, and Holly Springs National Forests,” 

Unpublished manuscript, U.S. Department of Agriculture Forest Service, 

Southern Region. 

Conner, W. H., and Day, J. W. (1992). “Water level variability and litterfall 

productivity of forested fresh-water wetlands in Louisiana,” American 

Midland Naturalist 128, 237-45. 

Conner, W. H., and Day, J. W., Jr. (1976). “Productivity and composition of a 

baldcypress-water tupelo site and bottomland hardwood site in a Louisiana 

swamp,” American Journal of Botany 63, 1354-64. 

Cooper, J. R., Gilliam, J. W., and Jacobs, T. C. (1986). “Riparian areas as a 

control of nonpoint pollutants.” Watershed research perspectives. D. L. 

Correll, ed., Smithsonian Institution Press, Washington, DC. 

Cooper, J. R., Gilliam, J. W., Daniels, R. B., and Robarge, W. P. (1987). 

“Riparian areas as filters for agricultural sediment,” Soil Science Society of 

America Journal 51(2), 416-20. 

Cowardin, L. M., Carter, V., Golet, F. C., and LaRoe, E. T. (1979). 

“Classification of wetlands and deepwater habitats of the United States,” 

FWS/OBS-79/31, Office of Biological Services Report, U.S. Fish and 

Wildlife Service, Washington, DC. 
References 137

Crow, J. H., and MacDonald, K. B. (1978). “Wetland values: Secondary 

productivity.” Wetland functions and values: The state of our 

understanding. P. E. Greeson, J. R. Clark, and J. E. Clark, ed., American 

Water Resources Association, Minneapolis, MN. 

Dahm, C. M. (1981). “Pathways and mechanisms for removal of dissolved 

organic carbon from leaf leachates in streams,” Canadian Journal of Fish 

and Aquatic Science 38, 68-76. 

Day, F. P. (1979). “Litter accumulation in four plant communities in the Dismal 

Swamp, Virginia,” American Midland Naturalist 102, 281-89. 

Day, J. W., Jr., Butler, T. J., and Conner, W. H. (1977). “Productivity and 

nutrient export studies in a cypress swamp and lake system in Louisiana.” 

Estuarine processes, volume II. M. L. Wiley, ed., Academic Press, New 

York. 

Demissie, M., and Kahn, A. (1993). “Influence of wetlands on streamflow in 

Illinois,” Illinois State Water Survey. 

Dewey and Kropper Engineers. (1964). “Effect of loss of valley storage due to 

encroachment— Connecticut River,” Report to the Water Resources 

Commission, Hartford, CT. 

Dickinson, C. H., and Pugh, G. (1974). Biology of plant litter decomposition, 

volume I. Academic Press, London, England. 

Dickson, J. G. (1991). “Birds and mammals of pre-colonial southern old-growth 

forests,” Natural Areas Journal 11, 26-33. 

Dunne, T., and Leopold, L. B. (1978). Water in environmental planning. W. H. 

Freeman and Company, San Francisco, CA. 

Dybvig, W. L., and Hart, J. R. (1977). “The effects of agricultural drainage on 

flood flows at Moose Jaw.” Proceedings, 1977 Canadian hydrology 

symposium. National Resources Council, 311-21. 

Edwards, R. T. (1987). “Sestonic bacteria as a food source for filtering 

invertebrates in two southeastern blackwater streams,” Limnology and 

Oceanography 32, 221-34. 

Edwards, R. T., and Meyers, J. L. (1986). “Production and turnover of plantonic 

bacteria in two sub-tropical blackwater rivers,” Applied Environmental 

Microbiology 52, 1317-23. 

Elder, J. F. (1985). “Nitrogen and phosphorus speciation and flux in a large 

Florida river-wetland system,” Water Resources Research 21, 724-32. 
138 References 

Elder, J. F., and Cairns, D. J. (1982). “Production and decomposition of forest 

litter fall on the Appalachicola River flood plain, Florida,” Water Supply 

Paper 2196-B, U.S. Geological Survey, Washington, DC. 

Elder, J. F., and Mattraw, H. (1982). “Riverine transport of nutrients and 

detritus to the Apalachicola Bay Estuary, Florida,” Water Resources Bulletin

18, 849-56. 

Elwood, J. W., Newbold, J. D., O’Neill, R. V., and Van Winkle, W. (1983). 

“Resource spiraling: An operational paradigm for analyzing lotic 

ecosystems.” Dynamics of lotic ecosystems. T. D. Fontaine and S. M. 

Bartell, ed., Ann Arbor Science, Ann Arbor, MI. 

Environmental Laboratory. (1987). “Corps of Engineers wetlands delineation 

manual,” Technical Report Y-87-1, U. S. Army Engineer Waterways 

Experiment Station, Vicksburg, MS. 

Estes, C. C., and Orsborn, J. F. (1986). “Review and analysis of methods for 

quantifying instream flow requirements,” Water Resources Bulletin 22, 389-

98. 

Ewel, K. C., and Odum, H. T. (1984). Cypress swamps. University Presses of 

Florida, Gainesville, FL. 

Eyre, F. H. (1980). Forest cover types of the United States and Canada,” 

Society of American Foresters, Washington, DC. 

Fanning, D. S., and Balluff-Fanning, M. C. (1989). Soil morphology, genesis, 

and classification. John Wiley and Sons, New York, New York. 

Faulkner, S. P., and Richardson, C. J. (1989). “Physical and chemical 

characteristics of freshwater wetland soils.” Constructed wetlands for 

wastewater treatment. D. A. Hammer, ed., Lewis Publishers, Chelsea, MI. 

Ferren, W. R., Jr., Fiedler, P. L., and Leidy, R. A. (1996). “Wetlands of 

California. Part I. History of wetland habitat,” Madrono 43, 105-24. 

Ferren, W. R., Jr., Fiedler, P. L., Leidy, R. A., Lafferty, K. D., and Mertes, 

L. A. K. (1996a). “Wetlands of California. Part II. Classification and 

description of wetlands of the central California and southern California 

coast and coastal watershed,” Madrono 43, 125-82. 

__________. (1996b). “Wetlands of California. Part III. Key to the catalogue 

of wetlands of the central California and southern California coast and 

coastal watershed,” Madrono 43, 183-233. 

Finch, D. M. (1991). “Population ecology, habitat requirements, and 

conservation of neotropical migratory birds,” General Technical Report RM205, U.S. Department of Agriculture Forest Service. 
References 139

Fisk, H. N. (1944). “Geological investigations of the alluvial valley of the lower 

Mississippi River,” Mississippi River Commission, Vicksburg, MS. 

Fredrickson, L. H. (1978). “Lowland hardwood wetlands: current status and 

habitat values for wildlife.” Wetland functions and values: The state of our 

understanding. P. E. Greeson, J. R. Clark, and J. E. Clark, ed., American 

Water Resources Association, Minneapolis, MN, 207-306. 

Golet, F. C., and Larson, J. S. (1974). “Classification of freshwater wetlands in 

the glaciated Northeast,” Resource Publication 116, U.S. Fish and Wildlife 

Service. 

Gosselink, J. G., Lee, L. C., and Muir, T. A., ed. (1990). Ecological processes 

and cumulative impacts illustrated by bottomland hardwood wetland 

ecosystems. Lewis Publishers, Chelsea, MI. 

Harmon, M. E., Franklin, J. F., and Swanson, F. J. (1986). “Ecology of coarse 

woody debris in temperate ecosystems,” Advances in Ecological Research

15, 133-302. 

Harris, L. D. (1985). “Conservation corridors: A highway system for wildlife,” 

ENFO Report 85-5, Environmental Information Center of the Florida 

Conservation Foundation, Inc., Winter Park, FL. 

__________. (1988). “Landscape linkages: The dispersal corridor approach to 

wildlife conservation.” Transactions, North American Wildlife and Natural 

Resources Conference 53, 595-607. 

Harris, L. D., and Gosselink, J. G. (1990). “Cumulative impacts of bottomland 

hardwood forest conversion on hydrology, water quality, and terrestrial 

wildlife.” Ecological processes and cumulative impacts illustrated by 

bottomland hardwood wetland ecosystems. J. G. Gosselink, L. C. Lee, and 

T. A. Muir, ed., Lewis Publishers, Chelsea, MI, 259-322. 

Hauer, F. R., and Smith, R D. (1998). “The hydrogeomorphic approach to 

functional assessment of riparian wetlands: evaluating impacts and 

mitigation on river floodplains in the U.S.A,” Freshwater Biology 40, 517-

30. 

Hawkins, C. P., Murphy, M. L., and Anderson, N. H. (1982). “Effects of 

canopy, substrate composition, and gradient on the structure of 

macroinvertebrate communities in Cascade Range streams of Oregon,” 

Ecology 63, 1840-56. 

Hayes, A. J. (1979). “The microbiology of plant litter decomposition,” Scientific 

Progress 66, 25-42. 

Hodges, J. D. (1997). “Development and ecology of bottomland hardwood 

sites,” Forest Ecology and Management 90, 117-25. 
140 References 

Howard, R. J., and Allen, J. A. (1989). “Streamside habitats in southern forested 

wetlands: Their role and implications for management.” General Technical 

Report SE-50, Proceedings of the symposium: The forested wetlands of the 

southern United States. D. D. Hook and R. Lea, ed., U.S. Department of 

Agriculture Forest Service. 

Howe, R. W. (1984). “Local dynamics of bird assemblages in small forest 

habitat islands in Australia and North America,” Ecology 65, 1585-1601. 

Hubbard, D. E. (1988). “Glaciated prairie wetland functions and values: A 

synthesis of the literature,” Biological Report 88, 43, U.S. Fish and Wildlife 

Service, Washington, DC. 

Hunter, M. L. (1990). Wildlife, forests, and forestry: Principles of managing 

forests for biological diversity. Prentice Hall, Englewood Cliffs, NJ. 

Jennings, M. E., Thomas, W. O., Jr., and Riggs, H. C. (1994). “Nationwide 

summary of U.S. Geological Survey regional regression equations for 

estimating magnitude and frequency of floods for ungaged sites, 1993,” 

Water-Resources Investigations Report 94-4002, U.S. Geological Survey. 

Johnson, T. R. (1987). “The amphibians and reptiles of Missouri,” Missouri 

Department of Conservation, Jefferson City, MO. 

Johnston, C. A. (1991). “Sediment and nutrient retention by freshwater 

wetlands: Effects on surface water quality,” Critical Reviews in 

Environmental Control 21, 491-565. 

Johnston, C. A., Detenbeck, N. E., and Niemi, G. J. (1990). “The cumulative 

effect of wetlands on stream water-quality and quantity: A landscape 

approach,” Biogeochemistry 10, 105-41. 

Kadlec, R. H. (1985). “Aging phenomenon in wastewater wetlands,” Ecological 

considerations in wet-land treatment of municipal wastewaters. P. J. 

Godfrey, ed., Van Nostrand Rheinhold Co., New York. 

Kantrud, J. A., Krapu, G. L., and Swanson, G. A. (1989). “Prairie basin 

wetlands of the Dakotas: A community profile,” Biological Report 85 

(7.28), U.S. Fish and Wildlife Service, Washington, DC. 

Keller, C. M. E., Robbins, C. S., and Hatfield, J. S. (1993). “Avian communities 

in riparian forests of different widths in Maryland and Delaware,” Wetlands

13, 137-44. 

Kent, M., and Coker, P. (1995). Vegetation description and analysis, a practical 

approach. John Wiley and Sons, New York. 

Kilgo, J. C., Sargent, R. A., Miller, K. V., and Chapman, B. R. (1997). 

“Landscape influences on breeding bird communities in hardwood fragments 

in South Carolina,” Wildl. Soc. Bull. 25, 878-85. 
References 141

Kitchens, W. M. , Jr., Dean, J. M., Stevenson, L. H., and Cooper, J. M. (1975). 

“The Santee Swamp as a nutrient sink.” Mineral cycling in southeastern 

ecosystems. F. G. Howell, J. B. Gentry, and M. H. Smith, ed., ERDA 

Symposium Series 749513. Washington, DC. 

Kleiss, B. A. (1996). “Sediment retention in a bottomland hardwood wetland in 

Eastern Arkansas,” Wetlands 16, 321-333. 

Klimas, C. V. (1988). “Forest vegetation of the leveed floodplain of the lower 

Mississippi River,” Lower Mississippi River Environmental Program Report 

11. Mississippi River Commission, Vicksburg MS. 

__________. (1991). “Limitations on ecosystem function in the forested 

corridor along the lower Mississippi River.” Proceedings International 

Symposium on Wetlands and River Corridor Management. Assoc. State 

Wetland Managers, Berne, N.Y. 

Kolb, C. R., Steinriede, W. B., Jr., Krinitzsky, E. L., Saucier, R. T., Mabry, P. 

R., Smith, F. L., and Fleetwood, A. R. (1968). “Geological investigation of 

the Yazoo Basin, Lower Mississippi Valley,” Technical Report TR-3-480 

(map folio), U.S. Army Engineer Waterways Experiment Station, Vicksburg, 

MS. 

Kuchler, A. W. (1969). “Potential natural vegetation,” Map Sheet No. 90, 

U.S. Geological Survey, Washington, DC. 

Kuenzler, E. J., Mulholland, P. J., Yarbro, L. A., and Smock, L. A. (1980). 

“Distributions and budgets of carbon, phosphorus, iron, and manganese in a 

floodplain swamp ecosystem,” Report No. 157, Water Resources Institute of 

the University of North Carolina, Raleigh, NC. 

Kurz, H., and Wagner, K. A. (1953). “Factors in cypress dome development,” 

Ecology 34, 157-64. 

Larson, J. S., Bedinger, M. S., Bryan, C. F., Brown, S., Huffman, R. T., Miller, 

E. L., Rhodes, D. G., and Touchet, B. A. (1981). “Transition from wetlands 

to uplands in southeastern bottomland hardwood forests.” Wetlands of 

bottomland hardwood forests. Proceedings of a workshop on bottomland 

hardwood forests of the southeastern United States. Developments in 

Agricultural and Managed Forest Ecology Vol. II. J. R. Clark and 

J. Benforado, ed., Elsevier Scientific Publishing Company, New York. 

Leibowitz, S. G., and Hyman, J. B. (1997). “Use of scale invariance in assessing 

the quality of judgement indicators,” U.S. Environmental Protection Agency 

Laboratory, Corvallis, OR. 

Leopold, L. B. (1994). A view of the river. Harvard University Press, 

Cambridge, MA. 
142 References 

Loeb, S. C. (1993). “The role of coarse woody debris in the ecology of 

southeastern mammals.” Biodiversity and coarse woody debris in southern 

forests. GTR-SE-94, J. W. McMinn and D. A. Crossley, ed., U.S. 

Department of Agriculture Forest Service Southern Research Station, 108-

18. 

Lowrance, R., Todd, R., Fail, J., Hendrickson, O., Leonard, R., and Asmussen, L. 

 (1984). “Riparian forests as nutrient filters in agricultural watersheds,” 

Bioscience 34, 374-77. 

Ludwig, J. A., and Reynolds, J. F. (1988). Statistical ecology: A primer on 

methods and computing. John Wiley and Sons, New York. 

Lynch, J. F., and Whigham, D. F. (1984). “Effects of forest fragmentation on 

breeding bird communities in Maryland, USA,” Biological Conserv. 28, 287-

324. 

Meadows, J. S., and Nowacki, G. J. (1996). “An old-growth definition for 

eastern riverfront forests,” General Technical Report SRS-4, U.S. 

Department of Agriculture Forest Service Southern Research Station. 

Messina, M. G., and Conner, W. H. (1997). Southern forested wetlands: 

Ecology and management. Lewis Publishers, Boca Raton, FL. 

Mississippi River Commission. (1881-1897). “Map of the lower Mississippi 

River from the mouth of the Ohio River to the Head of Passes,” Vicksburg, 

MS. 

Mississippi River Commission. (1970). “Flood control in the lower Mississippi 

River Valley,” Vicksburg, MS. 

Mitch, P. P., and Gosselink, J. G. (1993). Wetlands. Van Nostrand Reinhold, 

New York. 

Mitsch, W. J., Dorge, C. L., and Wiemhoff, J. R. (1979). “Ecosystem dynamics 

and a phosphorus budget of an alluvial cypress swamp in southern Illinois,” 

Ecology 60, 1116-24. 

Moore, N. R. (1972). “Improvement of the lower Mississippi River and 

tributaries 1931-1972,” Mississippi River Commission, Vicksburg, MS. 

Morrison, M. L., Marcot, B. C., and Mannan, R. W. (1992). Wildlife-habitat 

relationships: Concepts and applications. University of Wisconsin Press, 

Madison, WI. 

Mueller, A. J., Loesch, C. R., and Twedt, D. J. (1995). “Development of 

management objectives for breeding birds.” Proceedings, partners in flight 

international workshop. Cape May, NJ. 
References 143

Mulholland, P. J. (1981). “Organic carbon flow in a swamp-stream ecosystem,” 

Ecological Monographs 51, 307-32. 

Mulholland, P. J., and Kuenzler, E. J. (1979). “Organic-carbon export from 

upland and forested wetland watersheds,” Limnology and Oceanography 24, 

960-66. 

Nadelhoffer, K. J., and Raich, J. W. (1992). “Fine root production estimates and 

belowground carbon allocation in forest ecosystems,” Ecology 73, 1139-47. 

National Interagency Implementation Team. (1996). “National action plan to 

implement the hydrogeomorphic approach (NAP),” Federal Register 

Volume 61 Number 160, 42593-42603, Washington, DC. 

National Weather Service. (1998). “Climate data for Mississippi: Selected 

cities,” <http://www.jannws.state.ms.us/climate.html> (August 1, 1998). 

Noss, R. F., and Harris, L. D. (1986). “Nodes, networks, and MUMs: Preserving 

diversity at all scales,” Environmental Management 3, 299-309. 

Novitski, R. P. (1978). “Hydrogeological characteristics of Wisconsin's 

wetlands and their influences on floods, stream flow, and sediment.” 

Wetland functions and values: The state of our understanding. P. E. 

Greeson, J. R. C. Clark, and J. E. Clark, ed., American Water Resources 

Association, Minneapolis, MN, 377-88. 

O’Hara, C. G. (1996). “Susceptibility of ground water to surface and shallow 

sources of contamination in Mississippi,” U.S. Geological Survey 

Hydrologic Investigations Atlas HA-739, U.S. Department of the Interior. 

Odum, E. P. (1950). “Bird populations of the Highlands (North Carolina) 

Plateau in relation to plant succession and avian invasion,” Ecology 31, 587-

605. 

Ogawa, H., and Male, J. W. (1983). “The flood mitigation potential of inland 

wetlands,” Publication Number 138, Water Resources Center, Amherst, MA. 

__________. (1986). “Simulating the flood mitigation role of wetlands,” 

Journal of Water Resources Planning and Management ASCE 112, 114-28. 

Omernik, J. M. (1987). “Ecoregions of the conterminous United States,” Map 

(scale 1:7,500,000), Annals of the Association of American Geographers 77, 

118-125. 

Ovington, J. D. (1965). “Organic production, turnover and mineral cycling in 

woodlands,” Biological Review 40, 772-85. 

Patrick, W. H., Jr., and Tusneem, M. E. (1972). “Nitrogen loss from flooded 

soil,” Ecology 53, 735-37. 
144 References 

Patton, P. C. (1988). “Drainage basin morphometry and floods.” Flood 

geomorphology. V. R. Baker, R. C. Kochel, and P. C. Patton, ed., John 

Wiley and Sons. New York, 51-64. 

Perry, D. A. (1994). Forest ecosystems. Johns Hopkins University Press, 

Baltimore, MD. 

Peterjohn, W. T., and Correll, D. L. (1984). “Nutrient dynamics in an 

agricultural watershed— Observations on the role of a riparian forest,” 

Ecology 65, 1466-75. 

Pomeroy, L. R. (1970). “The strategy of mineral cycling,” Annual Review of 

Ecology and Systematics 1, 171-90. 

Pugh, G., and Dickinson, C. H. (1974). Biology of plant litter decomposition, 

Volume II. Academic Press, London. 

Putnam, J. A. (1951). “Management of bottomland hardwoods,” Occasional 

Paper 116, U.S. Department of Agriculture Forest Service, Southern Forest 

Experiment Station. 

Putnam, J.A., Furnival, G. W., and McKnight, J. S. (1960). “Management and 

inventory of southern hardwoods,” U.S. Department of Agriculture Forest 

Service Agricultural Handbook No. 181. 

Raich, J. W., and Nadelhoffer, K. J. (1989). “Belowground carbon allocation in 

forest ecosystems: Global trends,” Ecology 70, 1346-54. 

Reiners, W. A. (1972). “Terrestrial detritus and the carbon cycle.” Carbon and 

the biosphere. G. M. Woodwell and E. V. Pecan, ed., Conference 

Proceedings 720510, U.S. Atomic Energy Commission. 

Remsen, J. V., Jr. (1986). “Was Bachman’s Warbler a bamboo specialist?” Auk 

103, 216-219. 

Rheinhardt, R. D., Brinson, M. M., and Farley, P. M. (1997). “A preliminary 

reference data set for wet forested flats in North Carolina and its application 

to wetland functional assessment, mitigation, and restoration,” Wetlands 17, 

195-215. 

Richardson, C. J. (1985). “Mechanisms controlling phosphorous retention 

capacity in freshwater wetlands,” Science 228, 1424-27. 

Ricklefs, R. E. (1990). Ecology. 3rd ed., W. H. Freeman and Company, 

New York. 

Ritter, D. F., Kochel, R. C., and Miller, J. R. (1995). Process geomorphology. 

3rd ed. William C. Brown Publishers, Chicago, IL. 
References 145

Robertson, P. A. (1992). “Environmental factors affecting tree growth on three 

wetland sites in southern Illinois,” American Midland Naturalist 128, 218-

326. 

Robertson, P. A., MacKenzie, M. D., and Elliot, L. F. (1984). “Gradient 

analysis and classification of the woody vegetation for four sites in southern 

Illinois and adjacent Missouri,” Vegetation 58, 87-104. 

Robertson, P. A., Weaver, G. T., and Cavanaugh, J. A. (1978). “Vegetation and 

tree species patterns near the northern terminus of the southern floodplain 

forest,” Ecological Monographs 48, 249-67. 

Robinson, S. K. (1996). “Setting objectives in forested habitats.” Presentation, 

partners in flight, midwest and southern Great Plains workshop, April 8, 

1996, St. Louis, MO. 

Robinson, S. K., Thompson, F. R., III, Donovan, T. M., Whitehead, D. R., and 

Faaborg, J. (1995). “Regional forest fragmentation and the nesting success 

of migratory birds,” Science 267, 1987-90. 

Rosgen, D. L. (1994). “A classification of natural rivers,” Catena 22, 169-199. 

Rudis, V. A. (1995). “Regional forest fragmentation effects on bottomland 

hardwood community types and resource values,” Landscape Ecology 10, 

291-307. 

Rudis, V. A., and Birdsey, R. A. (1986). “Forest resource trends and current 

conditions in the Lower Mississippi Valley,” Resource Bulletin SO-116, 

U.S. Department of Agriculture Forest Service Southern Forest Experiment 

Station. 

Sallabanks, R., Walters, J. R., and Collazo, J. A. (1998). “Breeding bird 

abundance in bottomland forests: Habitat, edge, and patch size effects,” 

Condor 102, 748-58. 

Sartain, E. B. “It didn’t just happen,” Mississippi County, Arkansas Drainage 

Districts. 

Saucier, R. L. (1994). “Geomorphology and quaternary geologic history of the 

Lower Mississippi Valley,” Vol I (report), Vol II (map folio), U.S. Army 

Engineer Waterways Experiment Station, Vicksburg MS. 

Schlesinger, W. H. (1977). “Carbon balance in terrestrial detritus,” Annual 

Review of Ecology and Systematics 8, 51-81. 

Schneider, D. C. (1994). Quantitative ecology: Spatial and temporal scaling. 

Academic Press, New York. 
146 References 

Schoener, T. W. (1986). “Resource partitioning.” Community ecology: 

Patterns and processes. J. Kikkawa and D. J. Anderson, ed., Blackwell, 

Melbourne, 91-126. 

Scott, V. E., Evans, K. E., Patton, D. R., and Stone, C. P. (1977). “Cavity 

nesting birds of North American forests,” Handbook 553, U.S. Department 

of Agriculture Forest Service. 

Sedell, J. R., Reeves, G. H., Hauer, F. R., Stanford, J. A., and Hawkins, C. P. 

(1990). “Role of refugia in recovery from disturbances: Modern fragmented 

and disconnected river systems,” Environmental Management 14, 711-24. 

Sedell, J. R., Richey, J. E., and Swanson, F. J. (1989). “The river continuum 

concept: A basis for the expected ecosystem behavior of very large rivers,” 

Canadian Journal of Fisheries and Aquatic Science 46, 49-55. 

Semeniuk, C. A. (1987). “Wetlands of the Darling System: A geomorphic 

approach to habitat classification,” Journal of the Royal Society of Western 

Australia 69, 95-112. 

Shafer, D. J., and Yozzo, D. J. (1998). “National guidebook for application of 

hydrogeomorphic assessment to tidal fringe wetlands,” Technical Report 

WRP-DE-16, Wetlands Research Program, U.S. Army Engineer Waterways 

Experiment Station, Vicksburg, MS. 

Simberloff, D., Farr, J. A., Cox, J., and Mehlman, D. W. (1992). “Movement 

corridors: Conservation bargains or poor investments?” Conservation 

Biology 6, 493-504. 

Singh, J. S., and Gupta, S. R. (1977). “Plant decomposition and soil respiration 

in terrestrial ecosystems,” Botanical Review 43, 449-528. 

Smith, R. D. (2001). “Hydrogeomorphic approach to assessing wetland 

functions: Guidelines for developing regional guidebooks; Chapter 3, 

Developing a reference wetland system,” ERDC/EL TR-01-29, U.S. Army 

Engineer Research and Development Center, Vicksburg, MS. 

Smith, R. D., and Wakeley, J. S. (2001). “Hydrogeomorphic approach to 

assessing wetland functions: Guidelines for developing regional guidebooks. 

 Chapter 4, Developing assessment models,” ERDC/EL TR-01-30, U.S. 

Army Engineer Research and Development Center, Vicksburg, MS. 

Smith, L. M., and Winkley, B. R. (1996). “The response of the Lower 

Mississippi River to river engineering,” Engineering Geology 45, 433-55. 

Smith, L. M., and Patrick, D. M. (1991). “Erosion, sedimentation, and fluvial 

systems,” The heritage of engineering geology: the first hundred years. 

Centennial Special Volume 3. G. A. Kiersch, ed., Geological Society of 

America, Boulder CO. 
References 147

Smith, W. P., Hamel, P. B., and Ford, R. P. (1993). “Mississippi Alluvial Valley 

forest conversion: Implications for eastern North American avifauna.” 

Proceedings of the Annual Conference of Southeastern Fish and Wildlife 

Agencies 47, 460-69. 

Sorenson, T. A. (1948). “A method of establishing groups of equal amplitude in 

plant sociology based on similarity of species content, and its application to 

analyses of the vegetation on Danish commons,” Kongelige Danske 

Videnskabernes Selskab Biologiske Skrifter 56, 1-34. 

Southern Regional Climate Center. (1998). “Electronic climate atlas,” 

<http://www.srcc.lsu.edu/atlas.html> August 1, 1998. 

Spurr, S. H., and Barnes, B. V. (1981). Forest ecology. John Wiley and Sons, 

New York. 

Stanford, J. A., Ward, J. V., Liss, W. J., Frissell, C. A., Williams, R. N., 

Lichatowich, J. A., and Coutant, C. C. (1996). “A general protocol for 

restoration of regulated rivers,” Regulated Rivers Research and Management

12, 391-413. 

Stauffer, D. F., and Best, L. B. (1980). “Habitat selection by birds of riparian 

communities evaluating effects of habitat alterations,” Journal of Wildlife 

Management 44, 11-15. 

Stewart, R. E., and Kantrud, H. A. (1971). “Classification of natural ponds and 

lakes in the glaciated prairie region,” Resource Publication 92, U.S. Fish and 

Wildlife Service, Washington, DC. 

Symbula, M., and Day, F. W. (1988). “Evaluation of two methods for 

estimating belowground production in a fresh-water swamp forest,” 

American Midland Naturalist 120, 405-15. 

Temple, S. A. (1986). “Predicting impacts of habitat fragmentation on forest 

birds: A comparison of two models.” Wildlife 2000: Modeling habitat 

relationships of terrestrial vertebrates. J. Verner, M. L. Morrison and C. J. 

Ralph, ed., University of Wisconsin Press, Madison, WI, 301-04. 

ter Braak, C. J. F. (1994). “Canonical community ordination. Part 1: Basic 

theory and linear methods,” Ecoscience 1, 127-140. 

Thien, S. (1979). “A flow diagram for teaching texture-by-feel analysis,” 

Journal of Agronomic Education 8, 54-55. 

Thomas, D. M., and Hanson, M. A. (1981). “Generalization of streamflow 

characteristics from drainage-basin characteristics,” Water Supply Paper 1-

55, U. S. Geological Survey, Washington, DC. 
148 References 

Thompson, F. R., III, Dijak, W. D., Kulowiec, T. G., and Hamilton, D. A. 

(1992). “Breeding bird populations in Missouri Ozark forests with and 

without clearcutting,” Journal of Wildlife Management 56, 23- 30. 

Tinkle, D. W. (1959). “Observations of reptiles and amphibians in a Louisiana 

swamp,” American Midland Naturalist 62, 189-205. 

Tritton, L. M., and Hornbeck, J. W. (1982). “Biomass equations for major tree 

species the northeast,” General Technical Report NE-69, U.S. Forest Service, 

Northeast Forest Experiment Station. 

Tuttle, J. R., and Pinner, W. (1982). “Analysis of major parameters affecting the 

behavior of the Mississippi River,” Potamology Program Report 4, U.S. 

Army Engineer Lower Mississippi Valley Division, Vicksburg, MS. 

U.S. Army Corps of Engineers. (1973). “Mississippi River & tributaries postflood report-1973,” Lower Mississippi Valley Division and Mississippi River 

Commission, Vicksburg, MS. 

__________. (1981). “HEC-1 flood hydrograph package. Users manual,” 

Hydrologic Engineering Center, Davis, CA. 

__________. (1982). “HEC-2 water surface profiles. Users manual,” 

Hydrologic Engineering Center, Davis, CA. 

__________. (1992). Memorandum on the “Clarification of Use of the 1987 

delineation manual,” Office of the Chief of Engineers, Washington, DC. 

__________. (1997). “HEC- RAS river analysis system. User manual,” 

Hydrologic Engineering Center, Davis, CA. 

U.S. Army Corps of Engineers, Mississippi Valley Division. (1998). “The 

Mississippi River and tributaries flood control project,” text of a briefing for 

the Disaster Response Focus Meeting, 18 June 1988. 

U.S. Army Corps of Engineers, Vicksburg District. (1997). “Yazoo Basin 

reformulation study: background information,” Unpublished file document. 

U.S. Department of Agriculture, Natural Resources Conservation Service. 

(1998a). “Field indicators of hydric soils in the United States, Version 4.0,” 

Fort Worth, TX. 

__________. (1998b). “Keys to soil taxonomy, eighth edition,” 

http://www.statlab.iastate.edu/soils/keytax/RevKeysSoilTax5_00.pdf

U.S. Department of Agriculture, National Resources Conservation Service, Soil 

Survey Division. (1998). “Official soil series descriptions,” 

<http://www.statlab.iastate.edu/soils/osd/> August 1, 1998. 
References 149

U.S. Department of Agriculture, Soil Conservation Service. (1993). “Soil 

survey manual,” U.S. Department of Agriculture Handbook 18, U.S. 

Government Printing Office, Washington, DC. 

U.S. Department of Agriculture, Soil Conservation Service and Mississippi 

Agricultural and Forestry Experiment Station (MAFES). (1974). “General 

soil map –state of Mississippi,” Mississippi State Department of Agriculture 

and Commerce. Jackson, MS. 

U.S. Environmental Protection Agency. (1998). “Level III ecoregions of the 

continental United States (map),” National Health and Environmental 

Effects Laboratory, Corvallis, OR. 

U.S. Forest Service. (1982). “Wildlife habitat management handbook, southern 

region,” FSH- 2609.23R, U.S. Forest Service. 

Vannote, R. L., Minshall, G. W., Cummins, K. W., Sedell, J. R., and Cushing, C. 

E. (1980). “The river continuum concept,” Canadian Journal of Fisheries 

and Aquatic Sciences 37, 130-37. 

Vogt, K. A., Grier, C. C., and Vogt, D. J. (1986). “Production, turnover, and 

nutrient dynamics of above and belowground detritus of world forests,” 

Advances in Ecological Research 15, 303-77. 

Wakeley, J. S., and Roberts, T. H. (1996). “Bird distribution and forest zonation 

in a bottomland hardwood wetland,” Wetlands 16, 296-308. 

Wakeley, J. S., and Smith, R. D. (2001). “Hydrogeomorphic approach to 

assessing wetlands functions: Guidelines for developing regional 

guidebooks; Chapter 7, Verifying, field testing, and validating assessment 

models, ERDC/EL TR-01-31, U.S. Army Engineer Research and 

Development Center, Vicksburg, MS. 

Welsh, C. J. E., and Healy, W. M. (1993). “Effect of even-aged timber 

management on bird species diversity and composition in northern 

hardwoods of New Hampshire,” Wildlife Society Bulletin 21, 143-54. 

Wharton, C. H., and Brinson, M. M. (1978). “Characteristics of southeastern 

river systems.” General Technical Report WO-12, Strategies for protection 

and management of floodplain wetlands and other riparian ecosystems. 

R. R. Johnson and J. F. McCormick, ed., U.S. Forest Service. 

Wharton, C. H., Kitchens, W. M., Pendleton, E. C., and Sipe, T. W. (1982). 

“The ecology of bottomland hardwood swamps of the Southeast: A 

community profile,” Report FWS/OBS-81/37, Office of Biological Services, 

U.S. Fish and Wildlife Service, Washington, DC. 
150 References 

Wharton, C. H., Lambou, V. W., Newson, J., Winger, F. V., Gaddy, L. L., and 

Mancke, R. (1981). “The fauna of bottomland hardwoods in the 

southeastern United States.” Proceedings, workshop on bottomland 

hardwood forest wetlands of the southeastern United States. J. R. Clark and 

J. Benforado, ed., Elsevier, New York, 87-160. 

Whittaker, R. H. (1975). Communities and ecosystems. MacMillan Publishing 

Company, New York. 

Whittaker, R. H., Bormann, F. H., Likens, G. E., and Siccama, T. G. (1974). 

“The Hubbard Brook Ecosystem Study: Forest biomass and production,” 

Ecological Monographs 44, 233-54. 

Wiseman, J. B. (1982). “A study of the composition, successional relationships, 

and floristics of Mississippi River floodplain forests in parts of Washington, 

Bolivar, and Sharkey Counties, Mississippi,” Ph.D. dissertation, Mississippi 

State University. 

Yarbro, L. A. (1983). “The influence of hydrologic variations on phosphorus 

cycling and retention in a swamp stream ecosystem.” Dynamics of lotic 

ecosystems. T. D. Fontaine and S. M. Bartell, ed., Ann Arbor Science, Ann 

Arbor, MI, 223-46. 

Yarbro, L. A., Kuenzler, E. J., Mulholland, P. J., and Sniffen, R. P. (1984). 

“Effects of stream channelization on exports of nitrogen and phosphorus 

from North Carolina coastal plain watersheds,” Environmental Management

8, 151-60. 

Young, G. L. (1998). “Environmental design and mitigation for water resource 

projects, Yazoo Basin, Mississippi (abstract),” Presentation summaries, D. F. 

Hayes, ed., American Society of Civil Engineers Wetlands Engineering and 

Restoration Conference, 1988. American Society of Civil Engineers, Reston, 

VA. 

Zedler, P. H. (1987). “The ecology of southern California vernal pools: A 

community profile,” Biological Report 85 (7.11), U.S. Fish and Wildlife 

Service, Washington, DC. 
Appendix A 

Glossary 

“A” horizon: A mineral soil horizon at the soil surface or below an “O” horizon 

characterized by accumulation of humified organic matter intricately mixed with 

the mineral fraction. 

Assessment model: A simple model that defines the relationship between 

ecosystem and landscape scale variables and functional capacity of a wetland. 

The model is developed and calibrated using reference wetlands from a reference 

domain. 

Assessment objective: The reason that an assessment of wetland functions is 

being conducted. Assessment objectives normally fall into one of three 

categories. These include: documenting existing conditions, comparing different 

wetlands at the same point in time (e.g., alternatives analysis), and comparing the 

same wetland at different points in time (e.g., impact analysis or mitigation 

success). 

Assessment team (A-Team): An interdisciplinary group of regional and local 

scientists responsible for classification of wetlands within a region, identification 

of reference wetlands, construction of assessment models, definition of reference 

standards, and calibration of assessment models. 

Channel: A natural stream or river, or an artificial feature, such as a ditch or 

canal, that exhibits features of bed and bank and conveys water primarily

unidirectionally downgradient. 

Colluvial: Colluvium is a heterogeneous mixture of soil and parent material that 

has moved down a slope and settled at its base as a result of gravitational action. 

Direct impacts: Project impacts that result from direct physical alteration of a 

wetland, such as the placement of dredge or fill. 

Direct measure: A quantitative measure of an assessment model variable. 

Appendix A Glossary A1
Functional assessment: The process by which the capacity of a wetland to 

perform a function is measured. This approach measures capacity using an 

assessment model to determine a functional capacity index. 

Functional capacity: The rate or magnitude at which a wetland ecosystem

performs a function. Functional capacity is dictated by characteristics of the 

wetland ecosystem, the surrounding landscape, and the interaction between the 

two. 

Functional capacity index (FCI): An index of the capacity of a wetland to 

perform a function relative to other wetlands from a regional wetland subclass in 

a reference domain. Functional capacity indices are by definition scaled from 0.0 

to 1.0. An index of 1.0 indicates that a wetland performs a function at the highest 

sustainable functional capacity, the level equivalent to a wetland under reference 

standard conditions in a reference domain. An index of 0.0 indicates the wetland 

does not perform the function at a measurable level and will not recover the 

capacity to perform the function through natural processes. 

Frass: Dead insect biomass and insect secretions. 

Highest sustainable functional capacity: The level of functional capacity

achieved across the suite of functions by a wetland under reference standard 

conditions in a reference domain. This approach assumes that the highest 

sustainable functional capacity is achieved when a wetland ecosystem and the 

surrounding landscape are undisturbed. 

Hydrogeomorphic wetland class: The highest level in the hydrogeomorphic 

wetland classification. There are five basic hydrogeomorphic wetland classes, 

including depression, fringe, slope, riverine, and flat. 

Indicator: Indicators are observable characteristics that correspond to 

identifiable variable conditions in a wetland or the surrounding landscape. 

Indirect measure: A qualitative measure of an assessment model variable that 

corresponds to an identifiable variable condition. 

Indirect impacts: Impacts resulting from a project that occur concurrently, or at 

some time in the future, away from the point of direct impact. For example, 

indirect impacts of a project on wildlife can result from an increase in the level of 

activity in adjacent, newly developed areas, even though the wetland is not 

physically altered by direct impacts. 

In-kind mitigation: Mitigation in which lost functional capacity is replaced in a 

wetland of the same regional wetland subclass. 

Interflow: The lateral movement of water in the unsaturated zone during and 

immediately after a precipitation event. The water, moving as interflow, 

discharges directly into a stream or lake. 

A2 Appendix A Glossary
Jurisdictional wetland: Areas that meet the soil, vegetation, and hydrologic 

criteria described in the “Corps of Engineers Wetlands Delineation Manual” 

(Environmental Laboratory 1987) or its successor. 

Mitigation: Restoration or creation of a wetland to replace functional capacity

that is lost as a result of project impacts. 

Mitigation plan: A plan for replacing lost functional capacity resulting from

project impacts. 

Mitigation wetland: A restored or created wetland that serves to replace 

functional capacity lost as a result of project impacts. 

Model variable: A characteristic of the wetland ecosystem or surrounding 

landscape that influences the capacity of a wetland ecosystem to perform a 

function. 

“O” horizon: A layer with more than 12 to 18 percent organic C (by weight; 50 

percent by volume). Form of the organic material may be recognizable plant parts 

(Oi) such as leaves, needles, twigs, moss, etc., partially decomposed plant debris 

(Oe), or totally decomposed organic material (Oa) such as muck. 

Off-site mitigation: Mitigation that is done at a location physically separated 

from the site at which the original impacts occurred, possibly in another 

watershed. 

Out-of-kind mitigation: Mitigation in which lost function capacity is replaced 

in a wetland of a different regional wetland subclass. 

Project alternatives: Different ways in which a given project can be done. 

Alternatives may vary in terms of project location, design, method of 

construction, amount of fill required, and other ways. 

Project area: The area that encompasses all activities related to an ongoing or 

proposed project. 

Project target: The level of functioning identified for a restoration or creation 

project. Conditions specified for the functioning are used to judge whether a 

project reaches the target and is developing toward site capacity. 

Red flag features: Features of a wetland or the surrounding landscape to which 

special recognition or protection is assigned on the basis of objective criteria. 

The recognition or protection may occur at a Federal, State, regional, or local 

level and may be official or unofficial. 

Reference domain: The geographic area from which reference wetlands are 

selected. A reference domain may, or may not, include the entire geographic 

area in which a regional wetland subclass occurs. 

Appendix A Glossary A3
Reference standards: Conditions exhibited by a group of reference wetlands 

that correspond to the highest level of functional capacity (highest, sustainable 

level of functioning) across the suite of functions performed by the regional 

wetland subclass. The highest level of functional capacity is assigned an index 

value of 1.0 by definition. 

Reference wetlands: Wetland sites that encompass the variability of a regional 

wetland subclass in a reference domain. Reference wetlands are used to establish 

the range of conditions for construction and calibration of functional indices and 

establish reference standards. 

Region: A geographic area that is relatively homogeneous with respect to largescale factors such as climate and geology that may influence how wetlands 

function. 

Regional wetland subclass: Wetlands within a region that are similar, based on 

hydrogeomorphic classification factors. There may be more than one regional 

wetland subclass identified within each hydrogeomorphic wetland class, 

depending on the diversity of wetlands in a region and the assessment objectives. 

Site potential: The highest level of functioning possible, given local constraints 

of disturbance history, land use, or other factors. Site capacity may be equal to 

or less than levels of functioning established by reference standards for the 

reference domain, and it may be equal to or less than the functional capacity of a 

wetland ecosystem. 

Soil horizon: A layer, approximately parallel to the surface of the soil that is 

distinguishable from adjacent layers by a distinctive set of properties produced 

by soil forming processes (Soil Survey Staff 1981 cited in Fanning and BalluffFanning 1989). 

Solum: A set of related soil horizons (Soil Survey Staff 1981 cited in Fanning 

and Balluff-Fanning 1989). 

Throughflow: The lateral movement of water in an unsaturated zone during and 

immediately after a precipitation event. The water from throughflow seeps out at 

the base of slopes and then flows across the ground surface as return flow, 

ultimately reaching a stream or lake. See Interflow for comparison. 

Value of wetland function: The relative importance of a wetland function to an 

individual or group. 

Variable: An attribute or characteristic of a wetland ecosystem or the 

surrounding landscape that influences the capacity of the wetland to perform a 

function. 

Variable condition: The condition of a variable as determined through 

quantitative or qualitative measure. 

A4 Appendix A Glossary
Variable index: A measure of how an assessment model variable in a wetland 

compares to the reference standards of a regional wetland subclass in a reference 

domain. 

Wetland: See Wetland ecosystems. 

Wetland assessment area (WAA): The wetland area to which results of an 

assessment are applied. 

Wetland banking: The process of creating a "bank" of created, enhanced, or 

restored wetland to serve at a future date as mitigation for project impacts. 

Wetland ecosystems: In 404: ".......areas that are inundated or saturated by

surface or ground water at a frequency and duration sufficient to support, and 

that under normal circumstances do support, a prevalence of vegetation typically

adapted for life in saturated soil conditions. Wetlands generally include swamps, 

marshes, bogs, and similar areas" (Corps Regulation 33 CFR 328.3 and EPA 

Regulations 40 CFR 230.3). In a more general sense, wetland ecosystems are 

three dimensional segments of the natural world where the presence of water, at 

or near the surface, creates conditions leading to the development of 

redoxomorphic soil conditions, and the presence of a flora and fauna adapted to 

the permanently or periodically flooded or saturated conditions. 

Wetland functions: The normal activities or actions that occur in wetland 

ecosystems, or simply, the things that wetlands do. Wetland functions result 

directly from the characteristics of a wetland ecosystem and the surrounding 

landscape and their interaction. 

Wetland creation: The process of creating a wetland in a location where a 

wetland did not previously exist. Wetland creation is typically done for 

mitigation. 

Wetland enhancement: The process of increasing the capacity of a wetland to 

perform one or more functions. Wetland enhancement can increase functional 

capacity to levels greater than the highest sustainable functional capacity

achieved under reference standard conditions, but usually at the expense of 

sustainability, or at a reduction of functional capacity of other functions. 

Wetland enhancement is typically done for mitigation. 

Wetland restoration: The process of restoring wetland function in a degraded 

wetland. Restoration is typically done as mitigation. 

Wetland tract: The area of forested wetland that is contiguous and directly

accessible to the WAA. 

Wetland values: See Value of wetland functions. 

Appendix A Glossary A5
Appendix B 

Spreadsheets 

This appendix contains information for using the spreadsheet for calculation 

of tree basal area, woody debris and log volume, and functional capacity indices. 

The spreadsheets are available on the HGM website at 

http://www.wes.army.mil/el/wetlands/hgmhp.html 

Tree Basal Area Spreadsheet 

This spreadsheet is used to calculate tree basal areas from the data recorded 

in the table on Data Form 3. Two different spreadsheets are available. One for 

dbh measurements made in centimeters and one for dbh measurements made in 

inches. An example of the spreadsheet for measurements made in centimeters is 

shown in Figure B1. 

To use the spreadsheet, enter the species code and dbh in cm from Columns 1 

and 2 of Data Form 3 into the first two columns of the spreadsheet. The 

spreadsheet will automatically calculate area of each tree in units of cm2

/0.04 ha 

and m2

/0.04 ha, and then convert m2/0.04 ha, to m2/ha in Columns 3, 4, and 5, 

respectively. The spreadsheet sums Column 5 in the bottom right-hand corner to 

give total m2

/ha based on the 0.04-ha plot data. This value should be entered on 

Data Form 1 as a plot value in the VTBA row. 

If species are entered sequentially, the total basal area can be recorded for 

each species and used to determine dominants for the VTCOMP using the 50/20 

rule. For example, enter all FRPE stems and record the m2

/ha from the bottom

right cell. Then enter all the QULY stems and record the m2

/ha from the bottom

right-hand cell, and subtract the m2

/ha of the FRPE stems to get m2/ha for 

QULY. Continue until all species have been entered. Use the m2

/ha values 

recorded for each species, after subtracting previously entered species, to 

determine dominance using the 50/20 rule. 

Appendix B Spreadsheets B1
If you measured tree diameters in centimeters, enter species name in A5-A32 and diameter values 

in the shaded cells B5-B26 

Enter 

individual 

Converts to 

cm2 / 0.04 ha

Converts to 

m2 / 0.04 ha Converts to m2 / ha

tree 

diameters 

(cm) 

Enter individual 

tree species code 

in cells A5-A32 

in cells B5-

B26 

0.25 * 3.14 * tree 

diameter2 = cm2

Column B * 0.0001 = 

m2

Column C * 25 = 

m2/ha 

FRPE 45.00 1589.63 0.16 3.97 

FRPE 20.00 314.00 0.03 0.79 

FRPE 12.00 113.04 0.01 0.28 

FRPE 8.00 50.24 0.01 0.13 

QULY 13.00 132.67 0.01 0.33 

QULY 23.00 415.27 0.04 1.04 

QULY 25.00 490.63 0.05 1.23 

CAAQ 21.00 346.19 0.03 0.87 

CAAQ 14.00 153.86 0.02 0.38 

QUNU 23.00 415.27 0.04 1.04 

QUNU 45.00 1589.63 0.16 3.97 

QUNU 34.00 907.46 0.09 2.27 

QUNU 17.00 226.87 0.02 0.57 

 0.00 0.00 0.00 

 0.00 0.00 0.00 

0.00 0.00 0.00 

 0.00 0.00 0.00 

 0.00 0.00 0.00 

 0.00 0.00 0.00 

 

Total Tree Basal 

Area in m2/ha = 16.86 

 Figure B1. Example of the tree basal area spreadsheet 

Woody Debris and Log Volume Spreadsheet 

This spreadsheet is used to calculate the volume of wood debris (VWD) and 

logs (VLOG ). An example of the spreadsheet is shown in upper portion of 

Figure B2 which includes the cells for data entry of Size Class 1 and 2 and other 

calculations, and the lower portion of Figure B2 which includes the cells for data 

entry of Size Class 3. 

To use the spreadsheet, enter the values Size Class 1 and 2 stem counts from

Data Form 5 in Columns 2 and 5 of the spreadsheet, respectively. The 

spreadsheet calculates the average of Transects 1 and 2 for Size Class 1 stems in 

Column 3, and tons/acre for Size Class 1 stems in Column 4. Similarly, the 

B2 Appendix B Spreadsheets 
spreadsheet calculates the average of Transects 1 and 2 for Size Class 2 stems in 

Column 6, and tons/acre for Size Class 2 stems in Column 7. 

Now, enter the diameter values for Size Class 3 stems from Data Form 5 in 

the appropriate Columns in the lower portion of the spreadsheet. The 

spreadsheet calculates the stem area in the units of cm2

, sums these values at the 

bottom of the column, and inserts this information into Column 8 in the upper 

part of the spreadsheet. Then, as with Size Class 1 and 2, the spreadsheet 

calculates the average of Transects 1 and 2 for Size Class 3 stems in Column 9, 

and tons/acre for Size Class 3 stems in Column 10. The spreadsheet then 

calculates ft3

/acre for Size Class 3 in Column 11, and m3/acre for Size Class 3 in 

Column 13 which is the final variable metric value for VLOG. This value should 

be entered on Data Form 1 as a plot value in the VLOG row. 

The spreadsheet then calculates ft3

/acre for the Size Classes 1 and 2 in 

Columns 14 and 15, respectively. These values are summed with the ft3

/acre 

value for logs in Column 11 and then m2

/ha are calculated for all three size 

classes in Column 17. This is the final variable metric value for VWD and should 

be entered on Data Form 1 as a plot value in the VWD row. 

Functional Capacity Index Spreadsheet

This spreadsheet is used to calculate the functional capacity indices for the 

functions assessed for each regional wetland subclass. Five separate spreadsheets 

are included in the Excel spreadsheet file, one for each regional wetland subclass. 

An example of the spreadsheet is shown in Figure B3. 

To use the spreadsheet, enter values from the boxes on the right-hand side of 

Data Form 1 in the second column labeled “Variable Metric Values” in the lower 

portion of the spreadsheet to the right of the variable names. The sequence of 

variables on Data Form 1 corresponds to the sequence of variables in the 

spreadsheet. 

The calculated variable subindex is displayed in the fourth column of the 

lower portion of the spreadsheet and is based on the relationships defined by the 

graphs in Chapter 5. Variable subindices are then used to calculate the FCI using 

the appropriate assessment model from Chapter 5. The resulting FCI is displayed 

in the first column of the top half of the spreadsheet to the left of each function 

name. The spreadsheet format allows the user to instantly ascertain how a 

change in the metric value of a variable will affect the FCI of a particular 

function by simply entering a new metric value measure in the bottom half of the 

spreadsheet. 

Appendix B Spreadsheets B3
Fill in Size Class 1, Size Class 2, and Size Class 3 in appropriate light green 

shaded areas below. Read VLOG and VWD subindices in yellow shaded areas to the right. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

Size Class 1 No. of Stems/ Transect 

Size Class 2 No. of Stems/ Transect 

Size Class 3 Sum of Stem Area (cm2) 

Transect 1 

Transect 2 

Size Class 1 Average No. Stems/Transect 

Size Class 1 tons/acre 

Transect1 

Transect 2 

Size Class 2 Average No.Stems/ Transect

Size Class 2 tons/ acre 

Transect 1 

Transect 2 

Size Class 3 Average of Stem Area (cm2) 

Size Class 3 tons/acre 

Size Class 3 ft3/acre 

(VLOG) Size Class 3 m3/ha 

Size Class 1, 2, and 3 ft3/acre 

Size Class 1, 2, and 3 ft3/acre 

(VWD) Size Class 1, 2, and 3 m3/ha 

Plot 1 5 9 7 0.6545 2 6 4 1.784 3573.32 9012.59 6292.95 432.33 23889.73 Plot 1 1648.39 434.76 24024.48 Plot 1 1657.69 Plot 2 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 2 0.00 0.00 0.00 Plot 2 0.00 Plot 3 0 0 0 0 3.14 0.00 1.57 0.11 5.96 Plot 3 0.41 0.11 5.96 Plot 3 0.41 Plot 4 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 4 0.00 0.00 0.00 Plot 4 0.00 Plot 5 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 5 0.00 0.00 0.00 Plot 5 0.00 Plot 6 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 6 0.00 0.00 0.00 Plot 6 0.00 Plot 7 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 7 0.00 0.00 0.00 Plot 7 0.00 Plot 8 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 8 0.00 0.00 0.00 Plot 8 0.00 Plot 9 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 9 0.00 0.00 0.00 Plot 9 0.00 Plot 10 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Plot 10 0.00 0.00 0.00 Plot 10 0.00 

B4 Appendix B Spreadsheets Figure B2. Example of the woody debris and log volume spreadsheet showing data entry for Size Classes 1 and 2 and calculations (Continued) 
Appendix B Spreadsheets B5 Size Class 3 Stem Diameters Plot 1 Size Class 3 Stem Area (cm2) Plot 1 Size Class 3 Stem Diameters Plot 2 Size Class 3 Stem Area (cm2) Plot 2 Size Class 3 Stem Diameters Plot 3 Size Class 3 Stem Area (cm2) Plot 3 Size Class 3 Stem Diameters Plot 4 Size Class 3 Stem Area (cm2) Plot 4 Size Class 3 Stem Diameters Plot 5 Size Class 3 Stem Area (cm2) Plot 5 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 Transect 1 Transect 2 4.00 34.00 12.56 907.46 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10.00 4.00 78.50 12.56 0.00 0.00 3.14 0.00 0.00 0.00 0.00 0.00 20.00 56.00 314.00 2461.76 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30.00 78.00 706.50 4775.94 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 56.00 33.00 2461.76 854.87 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3573.32 9012.59 0.00 0.00 3.14 0.00 0.00 0.00 0.00 0.00 Figure B2. (Concluded) 
 

FCI Calculation for Riverine Overbank Regional Subclass in the Yazoo Basin 

 

FCI Function 

 

0.1 Detain Floodwater 

0.3 Detain Precipitation 

0.4 Cycle Nutrients 

0.4 Export organic Carbon 

0.2 Remove Elements and Compounds 

0.6 Maintain Plant Communities 

0.3 Provide Fish and Wildlife Habitat 

 

Enter quantitative or categorical measure from Field Data Sheet in shaded cells 

Variables Variable Metric Value Units Subindex 

1. Vtract 1000 ha 0.3 

2. Vcore 22 % 1.0 

3. Vconnect 22 % 1.0 

4. Vfreq 5 years 0.3 

5. Vpond 100 % 0.0 

6. Vsoil 1 % 0.6 

7. Vcec 25 % 0.8 

8. Vtba 15 m2/ha 0.4 

9. Vtden 1000 stems/ha 0.5 

10. Vsnag 120 stems/ha 0.4 

11. Vtcomp 80 % 0.8 

12. Vwd 120 m3/ha 0.2 

13. Vlog 120 m3/ha 0.6 

14. Vssd 1000 stems/ha 0.5 

15. Vcomp 80 % 0.8 

16. Vgvc 100 % 0.2 

17. Vohor 1 cm 0.6 

18. Vahor 1 cm 0.6 

Figure B3. Example of an FCI calculation spreadsheet for the Riverine Backwater subclass 

B6 Appendix B Spreadsheets 
Appendix C 

Reference Wetland Data and 

Spatial Data 

This appendix provides the information necessary to access the data collected 

from reference wetland stands in the Yazoo Basin reference domain and 

information collected for use in ArcView. 

Reference Wetland Data 

General information on plot numbering, regional subclass, and variables is 

contained in the Excel spreadsheet with the name “lmv-env.xls.” This 

spreadsheet is available on the HGM website 

http://www.wes.army.mil/el/wetlands/hgmhp.html. A list of the fields in this 

spreadsheet is provided below: 

Stand No. 

Plot No. 

Regional Subclass 

Condition class 

Date 

State 

County

7.5 Quad 

Township 

Range 

Section 

1/4 Section 

1/16 Section 

UTM Lat 

UTM Long 

VTRACT

VCORE

VCONNECT

VFREQ 

Ponding 

VPOND

A Horizon 

A Horizon 

VAHOR

LC-1 

LC-2 

LC-3 

LC-4 

LC-1 

LC-2 

LC-3 

LC-4 

VOHOR

VCEC

VSOIL

VCOMP

VTCOMP

VDIVERSITY 

VTBA

VTDEN

VSSD

GC-1 

GC-2 

GC-3 

GC-4 

GC-1 

GC-2 

GC-3 

GC-4 

VGVC

VSNAG 

WD1-1 

WD1-2 

WD1-3 

WD1-4 

WD2-1 

WD2-2 

Appendix C Reference Wetland Data and Spatial Data C1
WD2-3 

WD2-4 

WD3-1 

WD3-2 

WD3-3 

WD3-4 

WD3-1 

WD3-2 

WD3-3 

WD3-4 

VWD

VLOG

Microtopographic Relief 

Vegetation Density

Subsurface Connections 

Depth to RF (cm)

RF Indicator 

Depth SHWT (cm)

Perm. (in/hr) 

Surface Connect. 

Condition Class Original 

Regional Subclass Original 

Stand Age 

Species 

Tree Age 

Diameters (cm)

Notes

ArcView Shape Files 

Numerous spatial data layers were compiled and collected from a variety of 

sources during the course of this project. Most of the coverages are for the entire 

Yazoo Basin. Some of the coverages are for the Lower Mississippi River Valley. 

This information is available on the HGM website 

(http://www.wes.army.mil/el/wetlands/hgmhp.html) in the form of ArcView 

shape files. A list of shape files contents and file names that are available on the 

website is provided below: 

County Boundaries (all_counties.*) 

Geology (all_geology.*) 

100 Year Flood Elevation (base100yr.*) 

10 Year Flood Elevation (base10yr.*) 

5 Year Flood Elevation (base5yr.*) 

2 Year Flood Elevation (base2yr.*) 

1 Year Flood Elevation (base1yr.*) 

Land Use / Land Cover (lulc.*) 

Geomorphology (saucier.*) 

Reference Wetland Plot Locations (smith_plots.*) 

Streets (streets.*) 

Yazoo Basin County Boundaries (yb_county_bound.*) 

Yazoo Basin Streams (yb_streams.*) 

Yazoo Basin STATSGO Soils (yb_statsgo.*) 

C2 Appendix C Reference Wetland Data and Spatial Data 
Yazoo Basin Watershed Boundaries (yb_watersheds.*) 

Hydric Soils (yb_hydric.*) 

Digital Geomorphology Maps 

During the course of this project we relied heavily on the geomorphic 

mapping of the Yazoo Basin summarized by Saucier (1994a, 1994b). The 15-in. 

geomorphic maps developed by Kolb et al. (1968) were found to be an important 

resource for reading the landscape and developing the regional wetland 

subclasses. Copies of these maps are available, but they are rare. We scanned 

the 15-ft quad maps in the Kolb et al. (1968) folio as high-resolution geotiff files 

and are willing to make them available to interested parties. Contact Dan Smith 

by e-mail if you are interested in these digital maps (smithr1@wes.army.mil). 

Appendix C Reference Wetland Data and Spatial Data C3
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing

this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-

4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently

valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY)

April 2002 

2. REPORT TYPE

Final report

3. DATES COVERED (From - To)

 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

4. TITLE AND SUBTITLE

A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland

Functions of Selected Regional Wetland Subclasses, Yazoo Basin, Lower Mississippi River 

Alluvial Valley 5c. PROGRAM ELEMENT NUMBER 

5d. PROJECT NUMBER 

5e. TASK NUMBER 

6. AUTHOR(S) 

R. Daniel Smith, Charles V. Klimas 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT 

 NUMBER

U.S. Army Engineer Research and Development Center 

Environmental Laboratory

3909 Halls Ferry Road

Vicksburg, MS 39180-6199

CVK & Associates 

12301 Second Avenue NE

Seattle, WA 98125

ERDC/EL TR-02-4 

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)

U.S. Army Corps of Engineers 

Washington, DC 20314-1000 

11. SPONSOR/MONITOR’S REPORT 

 NUMBER(S)

12. DISTRIBUTION / AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES

14. ABSTRACT

 The Hydrogeomorphic (HGM) Approach is a method for developing functional indices and the protocols used to apply these indices to

the assessment of wetland functions at a site-specific scale. The HGM Approach was initially designed to be used in the context of the 

Clean Water Act Section 404 Regulatory Program permit review to analyze project alternatives, minimize impacts, assess unavoidable 

impacts, determine mitigation requirements, and monitor the success of compensatory mitigation. However, a variety of other potential 

uses have been identified, including the determination of minimal effects under the Food Security Act, design of wetland restoration 

projects, and management of wetlands. 

 This report uses the HGM Approach to develop a Regional Guidebook for assessing the functions of five regional wetlands subclasses 

that occur in the Yazoo Basin of the Lower Mississippi River Alluvial Valley. The five regional subclasses include Flats, Riverine

Overbank, Riverine Backwater, Isolated Depression, and Connected Depression. The report begins with an overview of the HGM

Approach and then classifies and characterizes these wetland subclasses in the context of the Yazoo Basin reference domain. It then

discusses for each wetland subclass (a) the rationale used to select functions, (b) the rationale used to select model variables, (c) the

rationale used to develop assessment models, and (d) the data from reference wetlands used to calibrate model variables and assessment 

models. Finally, it outlines an assessment protocol for using the model variables and functional indices to assess each of the wetland

subclasses. 

15. SUBJECT TERMS

404 Regulatory Program Classification Ecosystem Function Functional profile 

Assessment Clean Water Act Evaluation Functional assessment Geomorphology (Continued) 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 

OF ABSTRACT

18. NUMBER 

OF PAGES 

19a. NAME OF RESPONSIBLE PERSON

a. REPORT 

UNCLASSIFIED 

b. ABSTRACT

UNCLASSIFIED 

c. THIS PAGE

UNCLASSIFIED 

 

 185

19b. TELEPHONE NUMBER (include area

code)

Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18
15. (Concluded) 

Hydrogeomorphic (HGM) Approach 

Hydrology 

Impact analysis 

Index 

Indicators 

Landscape 

Lower Mississippi Alluvial Valley 

Method 

Mitigation 

Model 

National Action Plan 

Procedure 

Reference wetlands 

Restoration 

Value 

Wetland 

Yazoo Basin