Identification of Washington coastal dune systems and associated wetlands

[From the U.S. Government Printing Office, www.gpo.gov]

IDENTIFICATION OF WASHINGTON COASTAL

NOV 25 1967 DUNE SYSTEMS AND ASS0CIATED WETLANDS

By Louis W. Messmer and James B. Phipps

Grays Harbor College
Aberdeen, Washington

September 1984

State of Washington

Department of Ecology

Olympia, Washington

U.S. DEPARTMENT OF COMMERCE NOAA
Department of Ecology COASTAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
Contract No. C85-025 CHARLESTON, SC 29405-2413

QH
541.5
.S26
M4
1984

TABLE OF CONTENTS

Page

Introduction . . . . .. . . . . . . . . . . . . . . . 1

Methods . . . . . . . . . . . . . . . . ... . . . . . 1

General Geomorphic Conditions and Processes. 2

General Botanical Conditions and Processes 4

The Primary Dunes . . . . . . . . . . . . . . . . . . 5

The Wetlands . . . . . . . . . . . . . . . . . . . . 6

The Dry Dune Meadows . . . . . . . . . . . . . . . . 7

Review of Shoreline Act Criter:La . . . . . . . . . . 9

Bibliography . . . . . . . . . . . . . . . . . . . . 11

IDENTIFICATION OF TIM WASHING-rON MASTAL DUYNE SYSM AIZ ASSOCIATED 7,%rETLVMS

Introduction

The sand dune areas adjacent to the sea in southwestern

Washington can be divided into three distinct 'areas on the

basis of geomorphology and vegetation: Primary dunes; dry

dune meadows and dune ridges; and wetlands. In the following

report these areas are described and napped. The report Also

includes a review of the'pertinent legislative and regulatory

criteria for wetlands associated with the dune system.

Methods

The specific areas were mapped in the field, using

1:24,000 scale air photos as a base. The data from these

photos.were tTans'Leyred to the same scale orthophoto maps

(where available) for the final map.. The field work was done

during July and August, a time when the vegetation was most

recognizable from the aerial view, because the plants of the

drier areas have not ceased growing and the wetland plants

have emerged enough to commence their growing season. Also

during this time, the wetland soils are still noticeably damper

than the adjoining dry areas.

In this report, the vegetation in each area was characterized

by a few index species rather than an exhaustive list of

plants.

General Geomorphic Conditions and Processes

The beaches of southwestern Washington are accretional

features composed of sand, primarily from the Columbia River.

Most of this sand-accreted behind '11orth Head.- forning the Long

Beach PeninsulaP while to the north, lesser accumulations formed

at Twin Harbors and the North Beaches (with additional sand

from sea cliff erosion).

Dune ridges grew as part of this beach building process.-

These dune ridges are formed by wind-blown sand entrapp ed by

dune grasses and other vegetation. Over the centuries, many

dune ridges were formed as the beach prograded and the sea

-regressed. The lower areas between the ridges became dry

meadows or wetlands.

Since the introduction of marram grass from Europe, in

plantinas since 1910, the natural vegetation has been altered

considerably. Even so, the existence of the many older dune

ridges suggests that the original vegetation was capable of

producing ridges. The processes described in this report
pertain to the formation of older dune ridges as well as the
modern ones. IL

The marram grass tends-to grow in clumps and thus,

initially, the dunes are a series of clumps or hummocks that
are aligned with the existing water line. If the water line

does-not move for some time, these hummocks will gradually

coalesce into a continuous ridge (Cooper, 1958).

If the shoreline moves outward slowly, a series of parallel

ridges will be formed, as at Ocean Park on Long Beach. If the

shoreline moves seaward in a series of jumps,'then ridges with

intervening wider-troughs will be formed, as at Grayland on

Twin Harbors Beach. If the shoreline prOgTades rapidly, it

will develop a series of dune clumps without appreciable ridge

lines, as just north of Connor Creek.

'Little or no beach sand is blown past the first dune. ridge',

once it is established. Under present conditions on the local

beaches, only the first ridges are nourished by the beach sand.

The older ridges, landward of the initial ones,have apparently

not changed significantly. In fact, it was our observation*that

generally there were no natural changes in the dune topography

beyond the initial dune ridge. With minor exceptions, we would

like to emphasize that the land forms of the dune systems of

south western Washington are aggradational rather than erosional.
C@

As adjacent dune ridges are built, intervening low areas or

troughs are formed. If these troughs are low enough to inter-
Z

sect the ground water table for part of the year,.they develop

a distinctive wetland vegetational community. If the areas be-

tween dune ridges are high enough to remain above the water

table, they develop a distinctive dry meadow vegetation.. It

should be noted that the level of the water table is naturally

dynamic, and that man-made perturbations can also increase or

0 decrease the wetland areas. Low areas may also fill by down-

slope movement from large dune ridges or dune hummocks.

General Botanical Conditions and Processes

The plant communities are good indicators.of tile different

dune areas described in this report, because they reflect the

micro-climatic and edaphic factors that characterize each of

these areas. In fact the major boundaries for the three areas

described in this report can perhaps best be defined in terms
of the plant communities'.

The dune areas described also provide elegant examples

of plant successions. As the sand upon which the communities

gro w gets older eastward, so does the vegetation. Thus the

entire process of one plant community replacing another can be

observed from a suitable vantage point in the dunes.

Two different successional series develop landward depend-

ing upon the presence or absence of saturated soil. These
series are described as a dry dune meadow sucEession and a

wetland succession. M.

In the first, the pioneer plan4o-s are the dune grasses and

a few forbs that inhabit the primary dune. These are replaced

by non-dune grasses, mosses, lichens and other upland plants

that can tolerate sharp drainage of the dry dune meadows or

older dune ridges. These, in turn, are gradually replaced by M_

shrubs and trees to form a dry or mesic climax or sub-climak
M
forest.

In the second series, the wetland successions, sedges

rushes, silverweed and other pioneers that can withstand

prolonged saturation form in.the wet areas beh.ind the pri mary

dunes. Farther back, these plants are gradually replac ed by

wetland shrubs and trees to form a swampy forest.

The Primary Dunes

The primary dunes are the first series of dunes east.of

the bare sand of-the beach. They are formed by wind-bloWn. sand

from the beach that is trapped by vegetation. These' dunes may
C,

be built into a-single continuous high ridge or more commonly,

a series of dune hummocks that only vaguely resemble a ridge.

The landward (eastern) boundary of this area is identified-by

several Criteria: First, the break in'the slope at the bottom

of the,dune ridge; or second, the change in v6getation from dune

to wetiand; and third where the above criteria are absent, the

subtle change in vegetation from primary dune to dry dune meadow

can be used.

The plants that characterize the primary dune can include

A several species. They all must tolerate moving sand, high wind

velocities, salt spray, and; in the late summer months, little
X* 31

preciptation. Two dune grasses doninate and typify this communi-

ty. 11.1arram grass (Ammophila arenaria) is a tall plant that pro-

liferates by underground stems and tends to produce clumps.

Sea-lyme grass (Elymus mollis) 'is a tall, broader-leaved, native

plant that is second only to marram grass in its soil-binding

ability.

Seaward of the primary dune, berms and hum@ocks (embryo
dunes) may be populated by either of two species of sea rocket
(Cakile spp.) or by silver beach-weed (Ambrosia* chamissonis)..
These broad-leaved plants may be removed by winter storms or

may prepare the way for the more permanent dune grasses by

accumulating additional sand.

Landward of the primary dune, the usual transition is

to wetland. This transition is marked by vegetation that
change s dramatically within a few inches' of elevation. Some

primary dune areas may not be bounded landward by i-.,etland,

but may merge gradually into the dry dune meadow community.

The Wetlands

The wetland areas lie east of the primary dune area and

are low enough to be covered with water for a-large part of

the year. They are formed in the troughs between successive

primary dune ridges. The wetlands are easily marked by a dis-
c,
tinctive vegetation which can be used to denote the boundaries ML_
of this.area. 16%
The plants in the wetlands reflect the fact that submergence

or wet soils precludes the growth of typical primary dune plants

or typical dry dune meadow plants. I%Tetland plants must be able

to tolerate submergence for up to several months each year,

either.by seeds or vegetative parts. Plants that are only found

in this area and are widespread ar-e:- the sichle-leaved rush

(Juncus falcatus), the slough sedge (Carex obnupta), Pacific

silverweed (Potentilla pacifica), and the coast willow (Salix*

hookeriana). Other species occur in the wetlands but are less

widespread, or may also inhabit drier areas. --There is some

indication that low, but dry areas in the primary dunes are

becoming "wet". Dead or dying marram grass was present at the
edges of flat, wet spots within the primary dune area. This

is an indication that vegetational communities chance from dry

to wet successions as hydrologic conditions change.

Dry Dune Meadow's

In the absence of wetlands dry dune meadows occur east

of the primary dune area. These meadows are relatively flat

with only a few hummocks on.them, which can be formed in several

ways. Generally these areas appear to'be fields of hummock

dunes that have been cut off from their sand @upply (the beach)

by a newer primary dune ridge. These areas may also be simply

a dune trough that is not low enough to be flooded Dart of the

year.

Thus, dry dune meadows occur in the same general geomOrDhic

location as the wetla nd; that is, in the troughs between succes-

sive dune ridges. The basic difference between them (wetlands

and dry dune meadows) is that the wetlands are slightly lower.

This component of the dune systems is termed "dry" to

distinguish it from adjacent flat, but lower, wetlands that

can also take on a meadow-like 'appearance.

This vegetational community varies sharply'from the wetlands

community. The lack of prolonged submergence allows plants with

drier preference or requirements to dominate,-,---.'-More typical.

grasses, such as: red fescue (Festuca rubra), little hair grass

(Aira praecox), and sweet vernal grass (Anthoxanthum odoratum.

are common indicators. Additionally, herbs such as seaside

tansy (Tanacetum douglasil), seashore lupine (Lupinus littorallis)

are found in these drier areas.

It should be noted that the two commonest pioneer trees

in the dune system, the coast or lodgepole pine (Finus contorta),

and the Sitka spruce (Picea sitchensis) can be found in either

the wetlands or the dry dune meadows, and are thus not good

indicators for either system.

It should be further noted that marram. grass and sea-lyme.

grass can be found in the dry dune meadow community. This
apparently reflects some secondary cause of soil instability such

as wind blowouts, human works, or possibly rodent burrowing.

In certain areas, south of Ocean Park, for instance, the

dry meadow merges seaward with the primary dunes@ area, with no
intervening wetlands. This may reflect a rapidly prograding
beach, with no time for dune hummocks to coalesce into a

continuous primary dune ridge.
.,Dry dune meadow vegetation also is found on older dune W
ridges-. Although the mapping separates dry dune meadows from
older dune ridges, the seDaration is-geomorphic, rather than

botanical.

Review of Shoreline Act Criteria

The wetlands described and mapped in these documents

relate to the criteria and definition in the-Shoreline

Management Act RCW 90.58.030 and accompanying regulation in

several ways.

In Sec. (2)(b) of RCW 90.58.030 wetlands are related to

as "ordinary high-water mark on all lakes, streams, and tidal

waters. (Sec. (2)(b) goes on to define the high water

mark as the line where "the presence and action of water is so
common*and usual as to mark upon the soil a chara cter different

from that of the abutting uplands . . . 11

In the dune wetlands identified in this study, the transi-

tion from primary dune or dry dune meadow vegetation is easily

discernible at all times. Dune wetlands are subject to

seasonal flooding and the vegetation faithfully reflects the

conditions of an "ordinary high water mark." On the other hand,

this is not a high water mark on a lake, stream or tidal water.

So dune wetlands are not specifically mentioned in Section (2)(b).

Section (2)(d) talks about". all the waters of the

state,. and their associated wetlands." Certainly, the

ocean qualifies as a 1twater area" or a "tidal water" of the

state. Since the entire dune system is formed by the ocean,-

owing its origin and existence to it, one might argue that it

is ce rtainly associated. Or as stated in 1VAC 173-22-030,

Sec. 2, they are "influenced and- are in proximity to, any,

or tidal water."

Finally, the dune wetlands can qualify a6. @arshes as

described in RCW 90.SS.040. They are low, flat areas on

which the vegetation consists mainly of herbaceous plants

such as sedges an d other aquatic or semi-aquatic plant s.

Also, shallow water stands upon them for a considerable part

of the year. As in other marshes, they tend to merge or

develop into "swam-os" with trees and shrubs replacing some

of the her baceous wetland plants.

Although the dune wetlands as described in this study

can be construed to fall under the Shoreline Management Act's

criteria, the Act could certainly be written or interpreted to

specifically include dune wetlands as:

a) associated with tidal waters

b) marshes and/or swamps

c) shorelines of statewide significance

d) all of the above

The language could also provide more explicitly for

natural development or changes within the dune system. For
instance, a dry dune meadow area could become wetland due to L

changes in the water table.

BIBLIOGRAPHY

Albright, R., Hirschi, R., Va.nbianchi, R., and.Vita, C.
Coastal Zone Atlas of Washi.ngton,, Land Cover/Land Use
Narratives. Department of Ecology; State of WasFilngton.
Olympia,_Ivashington.

Chapman, V.J. 1976. Coastal Vegetation, 2nd Ed. Pergamon Press
Oxford, England

Cooper, W.S. 1958. Coastal Sand Dunes of Oregon and Washington.
Geological Society of America, D-1emoir 72. New York,
New York.

Crook, C.S. 1979. A Systen, of Classifying and Identifying
Oregon's Beaches and Dunes. Oregon Coastal Zone
Management Association. Newport, Oregon.

Davies, J. L. 1977. Geographical Variation in Coastal Develop-
ment. Longman, Inc. New York, New York.
Hitchcock, C.'L ., Cronquist, A., Ownbey, M., and Thompson, J.Iw'.
1969. Vascular Plants of the Pacific Northwest, 5 vols.
University of Washington Press. Seattle, Washington
Phipps, J.B., and Smith, j.M. 1978. Coastal Accretion and
Erosion in Southwest 11ashington. Department of Ecology,
State of Washington. Olympia, Washington

Ruef, M.H. 1975. Coastal Sand Dunes Stud
y, Pacific and Grays
Harbor Counties, Washington. Department of Ecology,
State of Washington. Olympia, Washington

Sweeney, S.S., Nelson, W.H., and RodTick, E.A. 1982. OCS
Resource Inventory Maps and Manual. Washington Department
of -Game. Olympia, Washington

Wiedemann, A.M., Dennis, L.R., and Smith, F.H. 1969. Plants
of the Oregon Coastal Dunes. Oregon State University
R-ookstOTe, Corvallis, Oregon

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