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Linking Marine Ecosystem Response to Shoreline Armor Removal and Large Dam Removals in the Elwha River and Nearshore, Washington, USA

Authors:
  • Coastal Watershed Institute/ Western Washington University College of Environment Salish Sea Region
  • Coastal Watershed Institute (CWI) Port Angeles
  • The University of Victoria

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Shaffer, J.A.; Oxborrow, B.; Parks, D.S.; Maucieri, D.G., and Michel, J., 0000. Linking marine ecosystem response to shoreline armor removal and large dam removals in the Elwha River and nearshore, Washington, USA. Journal of Coastal Research, 00(00), 000-000. Charlotte (North Carolina), ISSN 0749-0208. Large in-river dams and shoreline armor have a significant negative effect on coastal hydrodynamic and ecosystem processes. Armor removal (AR) is a well-documented shoreline restoration tool, and removal of large dams is proving to be an extremely effective tool to restore riverine ecosystem processes. However, nearshore ecosystem restoration associated with dam removals (DRs) is incomplete when shoreline impediments, including shoreline armoring and lower river alterations, remain, and linkages between dam and shoreline ARs are not well understood. In this study, near-shore ecosystem processes and function restoration response to large DRs and shoreline AR are assessed. Two nearly century-old large dams in the Elwha River watershed in the NW United States were removed during 2011-14, which liberated upward of 18 million tonnes (Mt) or approximately~9 million m 3 of silt, sand, and gravel to sediment-starved, armored, and unarmored shorelines. Within 1 year of the initiation of DR, unarmored shorelines in the drift cell broadened, flattened, sediment fined, and large woody debris (LWD) volumes significantly increased. Armored shorelines continued to be steep and coarse grained. In 2016-17, approximately 4700 m 3 of large riprap (shoreline armor) was removed from more than 650 m of the armored Elwha River east delta reach drift cell. Following AR, previously eroding shorelines broadened, sediment fined, LWD volumes increased significantly, and beach wrack metrics resembled non-armored beaches. These changes followed AR and did not occur at unarmored DR or control treatments. Invertebrate communities also responded to dam and armor removal (DAR) and showed increasing trends every year for 3 years after the project. It is concluded that only partial nearshore ecosystem restoration occurs from large DR when shoreline armoring that impairs nearshore hydrodynamic processes remains and that full ecosystem restoration of the nearshore associated with large DRs is obtained by restoring impaired shorelines along with DRs.
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Linking Marine Ecosystem Response to Shoreline Armor
Removal and Large Dam Removals in the Elwha River
and Nearshore, Washington, USA
J. Anne Shaffer
†‡
*, Bob Oxborrow
§
, David S. Parks
, Dominique G. Maucieri
,
and Jamie Michel
Coastal Watershed Institute
Port Angeles, WA 98362, U.S.A.
Western Washington University
Poulsbo, WA 98370, U.S.A.
§
School of Aquatic and Fishery Sciences
University of Washington
Seattle, WA 98195, U.S.A.
Department of Biological Sciences
University of Victoria
Victoria, BC, Canada, V8P 5C2
ABSTRACT
Shaffer, J.A.; Oxborrow, B.; Parks, D.S.; Maucieri, D.G., and Michel, J., 0000. Linking marine ecosystem response to
shoreline armor removal and large dam removals in the Elwha River and nearshore, Washington, USA. Journal of
Coastal Research, 00(00), 000–000. Charlotte (North Carolina), ISSN 0749-0208.
Large in-river dams and shoreline armor have a significant negative effect on coastal hydrodynamic and ecosystem pro-
cesses. Armor removal (AR) is a well-documented shoreline restoration tool, and removal of large dams is proving to be
an extremely effective tool to restore riverine ecosystem processes. However, nearshore ecosystem restoration associ-
ated with dam removals (DRs) is incomplete when shoreline impediments, including shoreline armoring and lower
river alterations, remain, and linkages between dam and shoreline ARs are not well understood. In this study, near-
shore ecosystem processes and function restoration response to large DRs and shoreline AR are assessed. Two nearly
century-old large dams in the Elwha River watershed in the NW United States were removed during 2011–14, which
liberated upward of 18 million tonnes (Mt) or approximately ~9 million m
3
of silt, sand, and gravel to sediment-
starved, armored, and unarmored shorelines. Within 1 year of the initiation of DR, unarmored shorelines in the drift
cell broadened, flattened, sediment fined, and large woody debris (LWD) volumes significantly increased. Armored
shorelines continued to be steep and coarse grained. In 2016–17, approximately 4700 m
3
of large riprap (shoreline
armor) was removed from more than 650 m of the armored Elwha River east delta reach drift cell. Following AR, previ-
ously eroding shorelines broadened, sediment fined, LWD volumes increased significantly, and beach wrack metrics
resembled non-armored beaches. These changes followed AR and did not occur at unarmored DR or control treatments.
Invertebrate communities also responded to dam and armor removal (DAR) and showed increasing trends every year
for 3 years after the project. It is concluded that only partial nearshore ecosystem restoration occurs from large DR
when shoreline armoring that impairs nearshore hydrodynamic processes remains and that full ecosystem restoration
of the nearshore associated with large DRs is obtained by restoring impaired shorelines along with DRs.
ADDITIONAL INDEX WORDS: Erosion, bulkheading, beach wrack, large woody debris, Elwha, estuary, ecosystem
restoration, conservation.
INTRODUCTION
Large dams are well documented to have wide-scale ecosystem
effects, and, as such, large dam removals (DRs) have become an
essential ecosystem restoration tool that can have direct influence
onthemarinenearshorezone(Ezcurra et al., 2019;Maavara
et al., 2020). However, DR plans often give little consideration to
nearshore ecosystem function, which can lead to omission of basic
nearshore functional elements that are critical to ecosystem resto-
ration associated with large DR and, ultimately, incomplete eco-
system restoration (Shaffer et al., 2008,2009,2017a,b).
Similarly, ecosystem impairment from shoreline armor,
including rock or concrete, installed to protect shorelines from
erosion and ecosystem restoration through shoreline armor
removal (AR), has been well documented (Dethier et al.,2016;
Heerhartz et al.,2014,2016;Lee et al.,2018;To f t et al.,2013).
However, no information exists on the relationship of large
DRs, shoreline armor and removal, and associated shoreline
restoration of armored and unarmored beaches affected by in-
river dams and DRs. Globally, shoreline armoring continues to
occur, whereas large DRs, often at the same time, continue to be
implemented with the goal of restoring coastal watershed ecosys-
tems (Boucher, 2022; Dam Removal Europe, 2022). Therefore,
understanding the relationship of the shoreline and riverine eco-
system response to restoration actions provides new and espe-
cially valuable information for nearshore ecosystem function and
management, including large DR restoration priorities.
Located on the north central Olympic Peninsula in Washing-
ton State, the Elwha River had two hydroelectric dams
installed in the main river channel more than 100 years ago.
Most of the Elwha River is located within Olympic National
Park. The Elwha primary drift cell comprises approximately 21
km of shoreline that extends from the west end of Freshwater
Bay east to the tip of Ediz Hook (Shaffer et al.,2008). The
Elwha River DR project, which included the removal of the
DOI: 10.2112/JCOASTRES-D-24A-00007.1 received 20 August 2024;
accepted in revision 9 September 2024; corrected proofs received
28 September 2024; published pre-print online 31 October 2024.
*Corresponding author: anne.shaffer@coastalwatershedinstitute.org
Ó
Coastal Education and Research Foundation, Inc. 2024
Journal of Coastal Research 00 00 000–000 Charlotte, North Carolina Month 2024
32 m high Elwha and 64 m high Glines Canyon dams that sub-
sequently liberated approximately 18 Mt (~9 million m
3
)ofsed-
iment to the watershed, was the world’s largest completed DR
restoration project to date (Warrick et al.,2019). The DR began
in 2011 and ended in 2014.
Approximately one-half the liberated sediment was deliv-
ered to the coast within 5 years of DR and resulted in abrupt
changes to the coastal system (Warrick et al., 2019). During
these dramatic transitions in sediment supply and delivery
to the coastal zone, the unarmored reach of the Elwha
Figure 1. Study region and treatment locations. Control treatment is for sediment, beach profile, large woody debris (LWD), and beach wrack monitoring. An
asterisk (*) indicates sites distal to ecological study (referenced in the “Discussion” section). Inset: broader geographic location in Washington State, USA.
Table 1. Definitions for study treatment and phase categorizations.
Phase Definition
PreDR Pre-dam removal and pre-armor removal
PostDRPreAR After dam removal and before armoring removal
PostDRPostAR After dam removal and after armor removal
Restoration Action Treatment
DR Dam removal
DAR Dam and armor removal treatments
Control Control treatment
Table 2. Parameters for sediment categories used to determine percentage
of coverage as defined by Altizio (2010).
Sediment Category Size (mm)
Cobble 64–256
Pebble 4–64
Granule 2–4
Sand 0.0625–2
Silt 0.002–0.0625
Clay ,0.002
2 Shaffer et al.
Journal of Coastal Research, Vol. 00, No. 00, 2024
nearshore responded almost immediately (Shaffer et al.,
2017b). In contrast, most of the armored Elwha nearshore
continued to be highly erosional, likely because of remaining
alterations in the lower river and shoreline armoring placed
along the east delta, feeder bluffs, and spit of the Elwha drift
cell over the last 100 years (Parks, 2015;Shaffer et al., 2008,
2017b). To address this persistent ecosystem impediment, a
large-scale shoreline restoration project was undertaken.
From 2016–18, the armored portion of the east Elwha Delta
reach was restored through the removal of 4700 m
3
of large
Figure 2. Beach profiles for treatment sites. Treatments include dam removal (DR), dam and armor removal (DAR), down-drift unarmored bluff shorelines,
and control shorelines. PreDR ¼before dam removal and before shoreline armor removal; PostDRPreAR ¼after dam removal and before armor removal;
PostDRPostAR ¼after dam removal and after armor removal.
3Nearshore Ecosystem Response to Shoreline Armor Removal and Large Dam Removals
Journal of Coastal Research, Vol. 00, No. 00, 2024
riprap (shoreline armor) from more than 650 m of the Elwha
nearshore shoreline. This paper compares and quantifies the
nearshore ecosystem response to restoration actions of DR,
shoreline AR, and the cumulative results of both restoration
actions.
Standard nearshore physical metrics of beach profile topogra-
phy, beach sediment grain size, large woody debris (LWD) com-
position and distribution, and ecological metrics of beach wrack
composition, including invertebrate species composition and
abundance, were used to define nearshore physical restoration
action response to individual actions of DR and shoreline resto-
ration (Rich et al. 2014;Toft, Litle, and Adams, 2015). The met-
ric responses of the two sites that experienced DR (one with
armoring, one without armoring) were then compared with the
control site (no DR, no AR) and analyzed with each restoration
action to define the relative role of DRs, shoreline AR, and the
two actions combined to achieve nearshore ecosystem restora-
tion. These metrics were used to test two hypotheses: (1) that
DR alone does not restore the ecological metrics when shoreline
impediments of shoreline armoring remain and (2) when shore-
line armor is removed, DR shorelines physically and ecologi-
cally fully restore relative to unarmored shorelines.
METHODS
The study area is located along the nearshore of the central
Strait of Juan de Fuca, including the Elwha and Dungeness
River drift cells, on the northern Olympic Peninsula in Wash-
ington State (Figure 1). In the early 1900s, two dams were con-
structed on the Elwha River, and the shoreline of the eastern
Elwha Delta and drift cell was heavily armored repeatedly
until the early 2000s, nearly eliminating river conveyance of
sediment, which previously sustained the beaches in the drift
cell (Shaffer et al., 2008;Ward et al., 2008). Impacts resulting
from in river dams and shoreline armoring included increased
shoreline erosion, decreased habitat extent and complexity,
and decreased connectivity of the shoreline and the lower river
estuary due to sediment starvation and extensive shoreline
armoring (Parks, 2015;Parks, Shaffer, and Barry, 2013). A cen-
tury later, the two in-river dams were removed with the intent
of a complete watershed scale ecosystem recovery; however,
the shoreline armoring impediments remained along much of
the Elwha drift cell following DRs (Shaffer et al., 2017a).
Study Treatments
This study included three treatments and three phases
(Table 1). Two of the three treatments were restoration
actions that were within the Elwha DR drift cell (one with
and one without armoring). The restoration treatment shore-
lines of the Elwha shoreline are described in further detail in
Parks (2015),Parks, Shaffer and Barry (2013), and Warrick
et al. (2019). The third treatment is a control site on the
Dungeness drift cell, well outside the Elwha drift cell, which
served as a comparative treatment unaffected by either the
dam or shoreline armor (Figure 1). These nearshore treat-
ments were classified as follows.
DR Treatment
This treatment experienced only DR response and is the
unarmored area of the west shoreline located in the Freshwater
Bay area of the Elwha drift cell (Figure 1). It is an unarmored
embayed 2000-mm shoreline to the west of the Elwha River
mouth. This stretch of shoreline experienced persistent erosion
because of sediment starvation caused by the Elwha and Glines
in-river dams and significant sediment delivery during DR
(Parks, 2015,Shaffer et al., 2017a,b;Warr i c k et al., 2019). This
segment of the Elwha nearshore was monitored for beach pro-
files and LWD before, during, and after the DR project and also
for beach profiles, LWD, beach wrack, and sediment composi-
tion after the shoreline AR project.
Figure 3. Nonmetric multidimensional scaling plot (NMDS) plot showing beach wrack vegetation composition communities. Each data point is a single
quadrat’s wrack vegetation composition. (a) Correlations between samples and the different components of the quadrat communities. (b) Hulls for phase
and treatment combinations.
4 Shaffer et al.
Journal of Coastal Research, Vol. 00, No. 00, 2024
Figure 4. Box plots showing beach wrack vegetation composition variables (a) Total Cover, and (b) Total Algae Percent, at each restoration action treatment and
phase. Treatments include dam removal (DR), dam and armoring removal (DAR), and Control. The different phases are shown with gray indicating samples taken
after dam removal and before armoring removal (PostDRPreAR). Black boxes indicate samples taken after dam removal after and armor removal (PostDRPostAR).
Figure 5. Nonmetric multidimensional scaling plot (NMDS) plot showing beach wrack sediment communities for the total sediment samples. Each data
point is a single quadrat percentage of covers averaged between the top layer and 5-cm-depth sample. (a) Correlations between samples and the different
components of the quadrat communities. (b) Hulls for phase and treatment combinations.
5Nearshore Ecosystem Response to Shoreline Armor Removal and Large Dam Removals
Journal of Coastal Research, Vol. 00, No. 00, 2024
Dam and Armor Removal Treatments
This treatment experienced both dam and armor removal
(DAR) response. This is the armored area of the east Elwha
shoreline also known as the east delta. This reach of shoreline
experienced persistent erosion due to sediment starvation
from in-river dams and significant shoreline armor over the
last century, including during and after DRs (War r i ck et al.,
2019). To address this persistent ecosystem impediment, a
large-scale shoreline restoration project was undertaken. The
armored portion of the east Elwha Delta reach was restored
through the removal of 4700 m
3
of riprap from more than 650
m of the Elwha nearshore shoreline. In this study, the near-
shore ecosystem response to restoration actions of DR, shore-
line AR, and the cumulative results of both restoration actions
are defined.
Control Treatment
This treatment experienced neither the restoration action of
DR nor shoreline AR. The control located in the Dungeness
Bay region of the Dungeness drift cell is 31 km east of the
Elwha drift cell and included a 600-m long shoreline that has
had no armoring and no alterations over the last 20 years. The
treatment has the same NW orientation and experiences simi-
lar fetch as the Elwha drift cell study treatments but is some-
what protected to the north by Dungeness Spit. It is a county
park and is protected from development. The control is ecologi-
cally dissimilar in some ways from the other study treatment
locations (i.e. shorter, somewhat protected from dominant
wind and fetch by a spit, in a different drift cell). This paper
primarily focuses on the differences in relative changes of the
treatments related to restoration actions and phases, so the
control treatment is an appropriate comparative area to repre-
sent physical and ecological variability in a region where no
restoration actions are occurring. This area was monitored for
beach topography, sediment composition, LWD, beach wrack
composition, and invertebrate composition both before and
after the AR restoration project.
Standard nearshore physical metrics of beach profile
topography, beach sediment grain-size, LWD composition
and distribution, and ecological metrics of beach wrack compo-
sition were used, including invertebrate species composition
Figure 6. Box plots illustrating the percentage of beach wrack sediment variables observed at each treatment, phase, and sediment depth. Treatments
include dam removal (DR), dam and armoring removal (DAR), and Control. The different phases are shown with gray indicating samples taken after dam
removal and before armoring removal (PostDRPreAR). Black boxes indicate samples taken after dam removal after and armor removal (PostDRPostAR).
The top row of panels shows samples from the top layer of sediment, middle row of panels shows samples from 5 cm depth, and the lower row shows the
average cover between the top layer and 5 cm depth.
6 Shaffer et al.
Journal of Coastal Research, Vol. 00, No. 00, 2024
and abundance (Toft, Litle, and Adams, 2015), to define near-
shore physical restoration action response to individual
actions of DR and shoreline restoration. The metric responses
of the two sites that experienced DR (one with armoring, one
without armoring) were compared with the control site (no
DR, no AR) and analyzed with each restoration action to
define the relative role of DRs, shoreline AR, and the two
actions combined to achieve nearshore ecosystem restoration.
These metrics were used to test the two hypotheses: (1) DR
alone does not restore the ecological metrics when shoreline
impediments of shoreline armoring remain, and (2) when shore-
line armor is removed, DR shorelines physically and ecologi-
cally fully restore relative to unarmored shorelines.
The study was divided into three phases: pre-dam removal
(PreDR); post-dam removal and pre-armor removal Post-
DRPreAR; and post-dam removal and post-armor removal
(PostDRPostAR; Table 1).
Beach Profiles
Beach profile data included beach shore face topography
(elevation in meters) and beach shore face, sediment mean,
intermediate-axis, grain-sized diameter in millimeters. Beach
topography was measured normal to the alongshore direction
in a series of topographic profiles extending from the upper-
beach berm or bluff toe, 30 m down to the low-tide water line,
and were spaced approximately 30 m apart parallel to one
another. Transects were truncated to 30 m in length to nor-
malize transect length across the study area. Measurements
of vertical elevation of the beach surface were recorded every
meter along the topographic profile.
Topographic beach profiles were measured within the
study area from a variety of sources. These included aerial
fixed-wing LIDAR digital elevation models (DEMs; Dewberry,
Inc., 2016;Entrix, Inc., 2009;Geomatics Data Solutions, 2015;
Quantum Spatial, 2019;Woolpert, Inc., 2013,2014,2015), real-
Figure 7. Box plots showing the log transformed counts of the six most abundant beach wrack taxonomic groups in each treatment and phase. Treatments
include dam removal (DR), dam and armoring removal (DAR), and Control. The different phases are shown with gray indicating samples taken after dam
removal and before armoring removal (PostDRPreAR). Black boxes indicate samples taken after dam removal after and armor removal (PostDRPostAR).
7Nearshore Ecosystem Response to Shoreline Armor Removal and Large Dam Removals
Journal of Coastal Research, Vol. 00, No. 00, 2024
time kinematic GPS (RTK-GPS) data collected by the U.S. Geo-
logical Survey in 2009 and 2016 (Stevens et al.,2016;Wa r r ick
et al., 2007), and RTK-GPS data collected by the authors in
2017, 2018, and 2019. Beach profiles from 2009, 2012, 2014,
and 2015 were extracted from LIDAR-based DEMs using the
ARC GIS 10.6.1 3D extension tool (ESRI, 2020).
Beach topography was measured using foot surveys in 2017,
2018, and 2019, with an Arrow Gold
TM
RTK-GPS mounted on
either a standard 2-m survey pole or backpack and connected
to the Washington State Reference Network to receive real-
time horizontal and vertical position corrections. Horizontal
survey data were collected in World Geodetic System 1984
coordinates in meters, and vertical data were collected using
the National Vertical Datum of 1988 meters. Horizontal and
vertical accuracy of RTK-GPS measurements was assessed by
occupying survey benchmarks within the sample area. Overall
root-mean-square accuracy of DEMs and RTK-GPS measure-
ments ranged from 65.9 to 610 cm.
Beach Wrack Composition, Sediment, and
Invertebrates
The beach wrack sampling method was used, which was
developed by Heerhartz et al. (2014) andisemployedbythe
Puget Sound Ecosystem Monitoring Program described in Toft
et al. (2017). For both biological and sediment sampling, two 50-
m transects were placed parallel to the shoreline along the
high-tide line with fresh wrack deposition at each of the three
beaches. Transect locations were selected randomly, and at 10
random points along each transect, a 30 cm 330 cm quadrat
was placed for sampling. To determine beach wrack composi-
tion, within each quadrat a visual estimate of the percentage of
composition of algae, eelgrass, terrestrial plant material, and
human debris was conducted for each point. A minimum of
three observers quantified beach wrack composition per quad-
rat, with the same person making observations at all quadrats.
Observations of all observers were averaged for each quadrat.
To visually estimate sediment grain size, two random
points along the transect were randomly selected, and the
30 cm 330 cm quadrat was again placed on the transect
line. The percentage of each sediment substrate category
was estimated at the surface and then again after digging
down 5 cm into the sediment (Table 2). These two percent-
age estimates were then averaged to gain a total percentage
of each substrate category. Sediment substrate categories
were identified as per Heerharz et al. (2014): cobble (.6cm),
pebble (4–6 cm), granule (2–4 mm), sand (“gritty” up to 2 mm),
and silt/clay (smooth; Table 2).
Beach wrack invertebrates were collected from five ran-
domly selected points of the 10 points used for composition
estimates. At each point, a 15-cm diameter corer made from
PVC pipe was pushed from the surface of the wrack to the
beach surface. The wrack samples were bagged, labeled with
sample location information (i.e. sample number, GPS coordi-
nates, location along transect), and frozen until processing. In
the laboratory, invertebrate samples were identified by trained
invertebrate specialists to lowest taxa using standard dissect-
ing and microscope techniques and counted per sample.
Large Woody Debris
The LWD monitoring protocols developed by Rich et al. (2014)
were used. A series of 18-m-wide transects were established at
permanent locations parallel to the shore and then sampled
from the bank to the waterline. Three transects each were sam-
pled at the DR and DAR treatment; two transects were sampled
at the control treatment. Transects were sampled once a year in
either June or July 2016–19.
Data were collected within a 4-hour period around the low
tide of the day. Length and width of all LWD greater than 0.5
m in length and 10 cm in diameter within the transect line
were recorded. All LWD pieces less than 0.5 m in length and
diameter less than 10 cm were estimated for percentage of
coverage of total transect area for each transect.
Data Analysis
A PERMANOVA was used to examine the effect of phase and
treatment and also whether an interaction between phase and
treatment occurs on beach wrack composition and beach wrack
sediment categories. The adonis2 function from the vegan pack-
age (version 2.6-4) was used, and data were displayed with a
nonmetric multidimensional scaling plot and Bray-Curtis dissim-
ilarities (Oksanen et al., 2022). Beach wrack sediment was
Figure 8. Interval plots showing the log transformed mean counts
(6SEM) of the four most abundant beach wrack taxonomic groups in each
treatment, phase, and year. Treatments include dam removal (DR), dam
and armoring removal (DAR), and Control. The different taxonomic
groups are shown in color.
8 Shaffer et al.
Journal of Coastal Research, Vol. 00, No. 00, 2024
analyzed separately for the top layer and 5-cm depth, as well as
the averaged total sediment categories.
Generalized additive models were used to model beach wrack
invertebrate total abundance, Hill-Richness, and Hill-Shannon
metrics. Hill-Richness and Hill-Shannon metrics were calcu-
lated using the hillR package (version 0.5.2; Li, 2018). All mod-
els included phase, treatment, an interaction between phase
and treatment as fixed effects, and year as a random effect.
Each metric (invertebrate total abundance, Hill-Richness, and
Hill-Shannon) had two models conducted: total average percent-
age of wrack cover and average percentage of algae cover. The
Akaike Information Criterion model selection was conducted for
each metric to determine which model best fit each metric. Neg-
ative binomial distributions were used to model invertebrate
total abundance, whereas a scat distribution was used for Hill-
Richness and a gamma distribution for the Hill-Shannon mod-
els. The final comparison between the DAR and DR treatments
was determined using a Wilcoxon rank sum test.
A generalized linear mixed model with a negative binomial
distribution was used to examine the effect of phase and
treatment and to determine whether an interaction between
phase and treatment on LWD counts occurred. Additionally,
linear mixed effects models were used to examine the effect
of phase and treatment and to determine whether an interac-
tion occurs between phase and treatment on log-transformed
LWD length and diameter. All three models included year as
a random effect. Pairwise contrasts were examined for each
model using the glht function from the multcomp package
(version 1.4-25; Hothorn, Bretz, and Westfall, 2008).
Assumption checks for models were conducted visually,
and all data analyses were conducted in R (version 4.4.0; R
Core Team, 2024).
RESULTS
Beach profiles of all treatments changed with phase. Lower
elevations of the profiles showed the most change. The DR
treatment with no armor changed positively overall by an
average of 0.3 m PostDR and 0.4 m after the AR period (even
though AR occurred outside this part of the study area); it
had a net change of 0.7 m relative to PreDR, with the major-
ity of the change occurring within the waterward 15–30 m
horizontal distance of the beach profile (Figure 2).
In contrast, the DAR treatment site continued to erode after
DR and before DAR, losing on average 0.5 m after the dams
were removed but before armor was removed. After AR, this
shoreline aggraded, gaining 0.7 m in elevation relative to
PreAR profile. Net gain of the armored shoreline after armor
removal was therefore 0.2 m relative to preDR (Figure 2).
Beach Wrack Vegetation
Beach wrack vegetation communities differed based on
treatment (PERMANOVA; F
2,231
¼30.9; p¼0.001), phase
(PERMANOVA; F
1,231
¼8.4; p¼0.001), and an interaction
between treatment and phase (PERMANOVA; F
2,231
¼10.4;
p¼0.001; Figures 3 and 4). PostDrPreAR phases were more
positively correlated with algae and human debris, whereas
PostDRPostAR phases were more positively correlated with
eelgrass and terrestrial plants in the wrack composition
(Figure 3). Control and DAR treatments were also more pos-
itively correlated with terrestrial and eelgrass than DR
treatments (Figure 3). The DR treatments tended to have
higher wrack cover than DAR treatments in both phases,
similar total wrack cover as the control during the Post-
DRPreAR, and more than the control during PostDRPostAR
(Figure 4).
Table 3. Model results for invertebrate abundance, Hill-Richness, and Hill-Shannon diversity metrics. Treatments include DR, DAR, and Control; phases
include PostDRPreAR and PostDRPostAR. Baseline is Control for the treatments and PostDRPreAR for the phase in the generalized linear model. Algae
and total wrack cover were smoothed terms. Final comparison (DAR vs. DR) was determined using a Wilcoxon rank sum test.
Estimate Test Statistic pValue
Invertebrate Total Abundance
PostDRPreAR vs. PostDRPostAR 0.72 61.56 0.64
Control vs. DAR 2.82 61.19 0.018*
Control vs. DR 0.83 60.833 0.32
DAR vs. DR W¼652 0.16
PostDRPostAR:DAR 2.44 61.20 0.04*
PostDRPostAR:DR 0.14 62.23 0.95
Algae Cover v
2
¼3.00 0.20
Hill-Richness
PostDRPreAR vs. PostDRPostAR 0.30 60.55 0.58
Control vs. DAR 2.03 60.88 0.022*
Control vs. DR 1.00 60.73 0.17
DAR vs. DR W¼657.5 0.16
PostDRPostAR:DAR 1.32 60.82 0.11
PostDRPostAR:DR 1.00 61.12 0.37
Total wrack cover v
2
¼20.38 7.87 310
4
***
Hill-Shannon
PostDRPreAR vs. PostDRPostAR 0.0033 60.042 0.94
Control vs. DAR 0.16 60.091 0.079
Control vs. DR 0.29 60.083 6.88 310
4
***
DAR vs. DR W¼647 0.14
PostDRPostAR:DAR 0.0040 60.091 0.96
PostDRPostAR:DR 0.12 60.11 0.28
Total wrack cover F¼3.27 0.012*
9Nearshore Ecosystem Response to Shoreline Armor Removal and Large Dam Removals
Journal of Coastal Research, Vol. 00, No. 00, 2024
Beach Wrack Sediment
Beach wrack sediment communities in the total sediment
samples differed based on treatment (PERMANOVA; F
2,66
¼
30.0; p¼0.001), phase (PERMANOVA; F
1,66
¼4.8; p¼0.015),
and an interaction between treatment and phase (PERMA-
NOVA; F
2,66
¼5.1; p¼0.002; Figures 5 and 6). PostDRPreAR
phase for the DAR and DR treatments was more positively
correlated with sand, whereas the control treatment is more
positively correlated with cobble and pebbles (Figure 5). In the
PostDRPostAR phase, the DAR was more positively correlated
with sand, whereas the DR and control treatments were more
positively correlated with gravel and pebbles (Figure 5). Sand
was the most common sediment type, especially during the
PostDRPreAR phase (Figure 6). The top layer and 5-cm-depth
Figure 9. Box plots showing beach wrack invertebrate (a) total count, (b) Hill-Richness, and (c) Hill-Shannon metrics at each restoration action treatment
and phase. Treatments include dam removal (DR), dam and armoring removal (DAR), and Control. The different phases are shown with gray indicating
samples taken after dam removal and before armoring removal (PostDRPreAR). Black boxes indicate samples taken after dam removal after and armor
removal (PostDRPostAR). Note: One outlier was not plotted—a total count for the DR treatment and PostDRPostAR of 17643.
10 Shaffer et al.
Journal of Coastal Research, Vol. 00, No. 00, 2024
sediment samples showed similar results to the total sediment
samples (Figures 6, S1, and S2; Tables S2 and S3).
Beach Wrack Invertebrates
The most commonly observed taxa were Amphipoda and
Oligochaeta, followed by Acari and Nematodes (Figures 7
and 8). Abundance of most abundant taxa were lower at the
DAR site and increased yearly after AR (Figures 7 and 8).
Individual taxa responses to the AR event were varied and
were different among restoration actions.
The best model for invertebrate total abundance included
total percentage of algae, whereas best models for invertebrate
richness and Shannon diversity metrics included total wrack
percentage (Table S6). For total abundance models, no main
effect of phase occurred; however, a main effect of treatment
was found, with the DAR treatment having lower invertebrate
abundance than the control treatment. Additionally, an interac-
tion between phase and treatment occurred (Table 3,Figure 9).
For the best Hill-Richness model, higher richness at the
control treatment was found, as compared with the DAR
treatment, and no other treatments or phases were signifi-
cantly different (Table 3,Figure 9). A main effect of total
wrack cover on Hill-Richness occurred, with richness declin-
ing to the lowest, around 30% wrack cover, before increasing
with wrack cover (Figure S3a).
For the best Hill-Shannon model, higher evenness was
found at the DR treatment compared with the control; how-
ever, no other treatments or phases were significantly differ-
ent (Table 3,Figure 9). A main effect of total wrack cover was
found on the Hill-Shannon metric, with evenness increasing
to the maximum around 30% wrack cover before decreasing
with wrack cover (Figure S3b).
Large Woody Debris
The LWD count increased in both the PostDRPreAR
and PostDRPostAR compared with PreDR; however, no
difference occurred between both PostDR phases (Table 4 ,
Figure 10). The DR had the highest LWD count, followed by
DAR, with the control treatment having the lowest LWD count
regardless of phase (Tabl e 4,Figure 10).
On average there were longer LWD logs in the PreDR phase
compared with the PostDRPostAR as well as longer logs in the
DR treatment compared with the DAR treatment (Table 4 ,
Figure 10). All other phase and treatments did not differ from
each other significantly (Table 4). Additionally, a significant
interaction occurred between treatment and phase (Table 4 ).
Finally, for LWD mean log diameter, the PreDR phase had
larger diameter logs than both PostDR phases, although the
PostDR phases did not differ from each other (Table 4,Figure
10). No difference occurred between the control treatment
and the DAR or DR treatment; however, larger diameter logs
in the DR treatment occurred, as compared with the DAR
treatment (Table 4,Figure 10). A significant interaction also
occurred between phase and treatment (Table 4).
DISCUSSION
This work provides a novel study of the role that shoreline
armoring plays in DR shorelines and illustrates that in the
Elwha system, both dam and shoreline ARs contribute to restore
a degraded shoreline. The study also indicates that when dams
are removed but shoreline armor remains, armored shorelines
within the drift cell continue to function at an impaired state
until armor is removed. After the armor is removed, the physical
and ecological metrics of the beach respond quickly with restora-
tion trends consistent with, but delayed relative to, changes
observed at unarmored shorelines.
Earlier work has documented that shoreline armoring and
in-river dams work synergistically to impair shorelines. Parks
(2015) documented that when the nearshore is sediment
starved because of in-river dams, armored feeder bluff shore-
lines are coarser, and grain size is larger than unarmored
feeder bluff shorelines. This study illustrated that armored
shorelines that experienced DR responded and rapidly became
persistently broad and finer grained—but only after armoring
was removed. This response was not only seen at the AR treat-
ment locations but also farther along the shoreline (Figures 2
and 11;Parks, 2022), illustrating that shoreline armor and its
removal can have both a local and drift cell–wide ecosystem
effect. This is a key consideration for broader geographic impli-
cations for both shoreline armoring and shoreline restoration
through AR.
Table 4. Model results for LWD count, mean log length, and mean log
diameter generalized linear models. Treatments include DR, DA, and
Control; phases include PreDR, PostDRPreAR, and PostDRPostAR.
Baseline is Control for the treatments and PreDR for the phase in the gener-
alized linear model. Additional contrasts (PostDRPreAR vs. PostDRPostAR;
DAR vs. DR) were determined using the multcomp package (Hothorn, Bretz,
and Westfall, 2008).
Estimate pValue
LWD Count
PreDR vs. PostDRPreAR 2.46 60.63 1.04 310
4
***
PreDR vs. PostDRPostAR 2.57 60.36 1.69 310
12
***
PostDRPreAR vs. PostDRPostAR 0.11 60.57 0.98
Control vs. DAR 1.34 60.26 2.61 310
07
***
Control vs. DR 2.62 60.26 ,2.0 310
16
***
DAR vs. DR 1.28 60.22 ,1310
07
***
PostDRPreAR:DAR 0.87 60.59 0.14
PostDRPreAR:DR 0.54 60.58 0.35
LWD Mean Log Length
PreDR vs. PostDRPreAR 0.12 60.33 0.73
PreDR vs. PostDRPostAR 0.74 60.22 0.032*
PostDRPreAR vs. PostDRPostAR 0.63 60.31 0.098
Control vs. DAR 0.13 60.074 0.080
Control vs. DR 0.13 60.070 0.067
DAR vs. DR 0.26 60.032 ,1310
04
***
PostDRPreAR:DAR 0.35 60.19 0.064
PostDRPreAR:DR 0.42 60.17 0.013*
LWD Mean Log Diameter
PreDR vs. PostDRPreAR 0.59 60.21 0.035*
PreDR vs. PostDRPostAR 0.89 60.14 0.0078**
PostDRPreAR vs. PostDRPostAR 0.30 60.20 0.30
Control vs. DAR 0.06 60.056 0.28
Control vs. DR 0.040 60.053 0.46
DAR vs. DR 0.10 60.024 9.29 310
05
***
PostDRPreAR:DAR 0.29 60.14 0.044*
PostDRPreAR:DR 0.31 60.13 0.015*
DAR ¼dam and armoring removal, DR ¼dam removal, LWD ¼large
woody debris, PostDRPostAR ¼after dam removal and after armor
removal, PostDRPreAR ¼after dam removal and before armor removal,
PreDR ¼before dam removal and before armor removal
Boldface ¼statistical significance
a¼0.05; *p ,0.05, **p ,0.01, ***p ,0.001.
11Nearshore Ecosystem Response to Shoreline Armor Removal and Large Dam Removals
Journal of Coastal Research, Vol. 00, No. 00, 2024
When shoreline armor remains down drift of large sediment
restoration events, the armoring will continue to impede ecosys-
tem (functions) restoration, even after significant sediment addi-
tions and farther afield than the shoreline armored treatment.
When the shoreline armoring is removed, ecological response is
varied, indicating shoreline ecological response may take longer
than the timeline of this study. Finally, these changes to the
physical system are also being reflected to higher trophic sys-
tems. CWI et al. (2022) documented that the distribution of surf
smelt spawn expanded exactly concurrent with or mirrored sedi-
ment changes associated with dam and then shoreline AR along
the drift cell.
Shoreline armoring effects are valuable ecological factors to
shorelines (Dethier et al., 2016;Heerhartz et al., 2014,2016;
Figure 10. Box plots showing large woody debris (LWD) (a) count, (b) length, and (c) diameter at each restoration action treatment and phase. Treatments
include dam removal (DR), dam and armoring removal (DAR), and Control. The different phases are displayed with white indicating samples taken before
the dam removal (PreDR) and gray indicating samples taken after dam removal and before armoring removal (PostDRPreAR). Black boxes indicate sam-
ples taken after dam removal after and armor removal (PostDRPostAR).
12 Shaffer et al.
Journal of Coastal Research, Vol. 00, No. 00, 2024
Lee et al.,2018) but to date have been overlooked when quanti-
fying hydrodynamic response of shorelines affected by DR (War-
rick et al., 2019;Zurbuchen et al., 2020). Our work confirms the
value of including shoreline AR into coastal planning for DRs
and the significance of proper geographic scale in understand-
ing and optimizing the ecological response to them. Lack of rep-
lication of all work in the Elwha system is a strong motivator in
replicating these studies along other DR shorelines.
Nearshore ecosystem function is complex and synergistic,
and it varies with restoration actions. Prior work in the
Elwha nearshore has demonstrated that intact, mature near-
shore habitats are functionally more stable and resilient than
newly restored habitats after large-scale DRs (Shaffer,
Munsch, and Juanes, 2018). Further, nearshore ecosystem
function and restoration have critical seasonal and inter-
annual temporal dimensions (Shaffer et al., 2012), and newly
created habitats may take decades to establish, stabilize, and
become functionally mature. Finally, many of the species
driving restoration action have complex and long life histo-
ries that depend on multiple nearshore habitats seasonally
that collectively make ecosystem restoration a decades’ long
endeavor. It is therefore clearly crucial to prioritize restoring
impaired coastal zones at the proper ecosystem scale (drift
cell) and temporal scales.
CONCLUSIONS
Both large dam and shoreline armoring have significant
and interactive effects to nearshore ecosystem forming and
functional processes. Restoration actions to remedy these
impacts are key for ecosystem recovery; however, DR alone
will not achieve complete nearshore ecosystem restoration
when shoreline impediments remain along the DR shoreline.
Shoreline AR can remedy this gap; it results in significant,
dramatic, and synergistic restoration both at and far distal to
the AR treatment with ecological restoration changes that
Figure 11. Beach profiles for distal unarmored and unarmored bluff shorelines noted in Figure 1 by an asterisk (*). PreDR ¼before dam removal and
before shoreline armoring removal; PostDRPreAR ¼after dam removal and before armoring removal; PostDRPostAR ¼after dam removal and after armor-
ing removal. Data reprinted with permission from Parks (2022).
13Nearshore Ecosystem Response to Shoreline Armor Removal and Large Dam Removals
Journal of Coastal Research, Vol. 00, No. 00, 2024
are translated across many facets of nearshore ecosystem
function.
ACKNOWLEDGMENTS
A number of college collaborators (including faculty and
students) and CWI interns, staff, and volunteers (including
Jenise Bauman, Wesley Greentree, Kirsten Simonsen, Tara
McBride, Sara Schoenemann, Katrina Campbell, David Harvey,
Lindsey Howard, Tony Thompson, Breyanna Waldsmith, Seren
Weber, and Curtis Welker) assisted with the analytical and field
elements of this work. The Lower Elwha Klallam Tribe, Pam
Lowry, the Dudley family, and Malcom and Phoebe Moore
provided collaboration. Bruch and Bruch Construction and 2
Grade LLC provided partnership and removed the armor from
the shoreline. Professional videographers Laura James and
John Gussman provided filming services. Funding for this work
was provided by Patagonia, Inc.; USFWS grant numbers
F16AP000157, F17AC00393, and F18AP00149; and Washington
Recreation and Conservation Office grant numbers 15-1045 and
16-2089 through the Salmon Recovery Funding Board and the
Estuary and Salmon Restoration Program. Thank you all.
An extended summary of this research was originally
published in Shaffer et al. (2024).
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Observations from ground‐penetrating radar, sediment cores, elevation surveys and aerial imagery are used to understand the development of the Elwha River delta in north‐western Washington, USA, which prograded as a result of two dam removals in late 2011. Swash‐bar, foreshore and swale depositional elements are recognized within ground‐penetrating radar profiles and sediment cores. A model for the growth and development of small mountainous river wave‐dominated deltas is proposed based on observation of both the fluvial and deltaic settings. If enough sediment is available in the fluvial system, mouth‐bars form after higher than average river discharge events, creating a large platform seaward of the subaqueous delta plain. Swash‐bars form concurrently or within a month of mouth‐bar deposition as a result of wave action. Fair‐weather waves drive swash‐bar migration landward and in the direction of littoral drift. The signature of swash‐bar welding to the shoreline is landward‐dipping reflections, as a result of overwash processes and slipface migration. However, most swash‐bars are eroded by the river mouth, as only 10 of the 37 swash‐bars that formed between August 2011 and July 2016 survived within the Elwha River delta. The swash‐bars that do survive either amalgamate onto the shoreline or an earlier deposited swash‐bar, forming a single larger barrier at the delta front. In asymmetrical deltas, the signature of swash‐bar welding is more likely to be preserved on the downdrift side of the delta, where formation is more likely and accommodation behind newer swash‐bars preserves older deposits. On small mountainous river deltas, welded swash‐bars may be more indicative of a large sediment pulse to the system, rather than large hydrological events.