Sound wetland management depends on an accurate comprehensive assessment of functional ...

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AN ABSTRACT OF THE RESEARCH PAPER OF
John T. Gabriel for the degree of Master of Science in Geography presented on
September 20. 1993.
Title: A Modified Synoptic Analysis of the Status of Oregon's Willametté
Valley Wetlands
Sound wetland management depends on an accurate comprehensive
assessment of functional wetland values. This management should account
for the cumulative impacts to regions and landscapes resulting from
piecemeal destruction and degradation of wetland resources. A regional or
watershed evaluation of wetland values can also make site-specific
assessments more efficient. The purpose of this paper is to conduct a regional
landscape assessment of Oregon's Willamette Valley wetlands. The
information in this report is designed to augment site-specific wetland
evaluations with information on 1) wetland loss, 2) habitat for listed
wetland species and special wetland communities, 3) development threat, 4)
threat to habitat, and 5) wetland restoration potential. I use a modified
version of the U.S. Environmental Protection Agency's synoptic approach
methodology to evaluate Willamette Valley wetlands based on these five
"synoptic indices."
The Willamette Valley was divided into seven subunits, each ranked relative
to the synoptic indices. Based on current wetland area and the historic area of
wetland soils, wetlands occupy between 8 and 13% of the area of each
subunit; historically wetlands were not distributed so uniformly. Altogether,
the Willamette Valley has lost about 41% of its original wetland area.
Wetlands in urban subunits are under the greatest development pressure and
disproportionately contribute habitat for threatened and endangered species.
A Modified Synoptic Analysis
of the Status of Oregon's Willamette Valley Wetlands
John T. Gabriel
A RESEARCH PAPER
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed September 20, 1993
Commencement June 1994
Research Paper Directed by Dr. Frenkel
ACKNOWLEDGMENTS
I wish to thank the U.S. Environmental Protection Agency and the Oregon
Division of State Lands for funding this research. I would also like to express
my appreciation to Ken Bierly, Scott Leibowitz, and Robert Frenkel for their
review, comments and suggestions on drafts of this paper. Their comments
have substantially improved and refined this research. A special thanks goes
to Karen Gabriel for her support and encouragement.
Although the research described in this report has been funded inpart by the
U. S. Environmental Protection Agency agreement 1BO792NTTA to John T.
Gabriel, it has not been subject to the Agency's review and, therefore, does not
necessarily reflect the views of the Agency, and no official endorsement
should be inferred.
TABLE OF CONTENTS
Introduction 1
Background 2
The Willamette River Watershed 2
Settlement History 4
Prehistoric landscape 4
Willamette Valley Wetlands 6
Wetland Ecological Functions 11
Water Quality 12
Biodiversity/ Habitat 13
Hydrologic Function 13
Wetland Management 15
State Wetland Management 15
Wetlands Defined 15
Oregon's Removal-Fill Law 15
Statewide Planning 16
Local Wetland Management 17
Oregon's Wetland Conservation Strategy 18
Federal Wetland Regulation 19
Summary 20
The Synoptic Approach 21
EPA Methodology 21
Define Goals and Criteria 24
Define Synoptic Indices 24
Select Landscape Indicators 25
Conduct Assessment 26
Prepare Synoptic Reports 26
Summary of EPA Methodology 27
Criticism of Synoptic Approach 27
Delineating the study area 27
Oversimplification of complex ecological relationships 29
Methodology 32
Research Question 33
The Study Unit and Subunits 36
Long Tom Subunit 36
Molalla Subunit 37
Rickreal Subunit 37
Santiam Subunit 37
Scappoose Subunit 38
Tualatin Subunit 38
Yamhill Subunit 40
Landscape Indicators 40
Historic Wetland Area 40
Current Wetland Area 42
Listed Wetland Species and Special Wetland Communities 46
Removal-Fill Permit Applications 47
Unallocated Stream Water 49
Results and Discussion 51
Synoptic Indices 51
Wetland Loss 52
Development Threat to Wetlands 55
Habitat for Listed Wetland Species and Special Communities 58
Threat to Listed Wetland Species and Special Communities 61
Restoration Potential 64
Conclusion 67
Long Tom 67
MolaIla 69
Rickreal 69
Santiam 69
Scappoose 70
Tualatin 70
Yamhill 70
Willamette Valley 71
Works Cited 73
Appendices
A. List of National Wetlands Inventory Maps Sampled 80
B. Subunit Area Information 81
C Subunit Shannon Index Data 82
D. Gray Scale Copies of Subunit Maps 83
LIST OF FIGURES
Figure 1. The Willamette River Watershed 3
Figure 2. The Willamette Valley Study Unit and Subunits 39
Figure 3. Area of Hydric Soils 42
Figure 4. Dot-Grid Sampling Techniques 44
Figure 5. Current Wetland Area 45
Figure 6. Sites Supporting Listed Wetland Species and Communities 47
Figure 7. Removal-Fill Applications Per Subunit 48
Figure 8. Synoptic Index: Wetland Loss 53
Figure 9. Synoptic Index: Development Threat to Wetlands 57
Figure 10. Synoptic index: Habitat for Listed Wetland Species and Special 60
Wetland Communities.
Figure 11. Synoptic Index: Threat to Wetland Habitat for Listed Wetland 63
Species and Special Communities.
Figure 12. Synoptic Index: Restoration Potential 65
Figure 13. Summary of Synoptic Indices 68
LIST OF TABLES
Table 1. Wetland Support of Listed Species 13
Table 2. The Synoptic Approach 23
Table 3. Research Questions, Synoptic Indices, Landscape Indicators 33
Table 4. Comparison of Dot-Grid Sampling to GIS 45
Table 5. Water Availability per Subunit 50
The Modified Synoptic Analysis of the Status of Oregon's Willamette Valley
Wetlands
INTRODUCTION
The purpose of this study is to develop baseline information on Willamette
Valley wetlands that can be used to guide wetland management decisions.
Little is currently known about the status of Oregon's Willamette Valley
wetlands; this study is a first attempt to gather regional information on this
natural resource. The goal of the study is to place management decisions
regarding individual wetlands in the context of the regional status of
wetlands. Wetland managers may use information in this study to augment,
rather than substitute for, site-specific wetland evaluations. A modified
version of the synoptic approach methodology developed by the U.S.
Environmental Protection Agency's Wetlands Research Program (EPA) in
Corvallis, Oregon, is used to conduct this study (Leibowitz et al. 1992).
2
BACKGROUND
The Willamette River Watershed
Oregon's Willamette Valley is located in the western third of the state. It
contains two-thirds of the state's total population, the major urban centers,
and it is the state's most productive agricultural region. The valley is a
structural trough which has been partially filled by alluvium from the Coast
and Cascade Ranges and silts deposited by the Bretz or Missoula floods (Dart
1981). The eastern boundary of the Willamette River watershed (Figure 1) is
formed by the Cascade Range, a strongly faulted anticline composed primarily
of igneous rocks. The Cascades rise to a maximum height of about 3500m, but
typical elevations range between 1000 and 1500m. Many of the rivers
draining this range have headwaters in snow fields or glaciers. Snow melt in
the spring and summer is stored in reservoirs and released throughout the
year. This results in less variability in stream flows than prior to dam
development, with lower flood peaks in the spring and higher flows in
summer. The Coast Range forms the western boundary of the Willamette
Valley watershed. It has less topographic relief, with maximum elevations in
the north at Saddle Mt. at l000m and in the south at Marys Peak at 1250m.
Typical elevations range from 550m to 1050m. This range is composed
primarily of uplifted marine sediments. The range is more easily eroded than
the Cascades and has a smaller snow pack and water storage capacity.
The climate is humid temperate with average annual rainfall between 90 to
115 cm, approximately three quarters of it falling between October and March.
The average annual temperature is between 4°C in January and 19°C July and
August (NOAA 1978; Dart 1981).