HomeMy WebLinkAbout2020 Boeing North Bridge Monitoring Memo_Year 5.docxMemo
Sent via e-mail: mark.d.clement@boeing.com
jon.l.larscheid-iii@boeing.com
To:
Mark Clement
Jon Larscheid
The Boeing Company
Renton, Washington
Project:
PS2018142E
From:
Diana Halladay
Jon Chalfant
cc:
Project File
Tel:
(425) 368-1000
Fax:
(425) 368-1001
Date:
October 27, 2020
Subject:Shoreline Restoration Monitoring—Year 5
North Bridge Replacement Project
Renton, Washington
USACE Reference Number: NWS-2011-110
This memorandum presents the results of the fifth and final annual monitoring event for the North Bridge Replacement Project’s shoreline restoration. The purpose of the monitoring was
to document conditions during the fifth year following site installation, including a review of the heath and vigor of planted vegetation, and to assess the performance of the restoration
based on established standards. Wood Environment & Infrastructure Solutions, Inc. (Wood), conducted the Year 5 monitoring during a site visit on October 23, 2020.
This memorandum is intended to provide the following information for the Year 5 restoration monitoring:
Monitoring methods;
Monitoring results;
Compliance with performance standards;
Previous actions taken to meet performance standards and implement maintenance recommendations;
Maintenance recommendations for continued success; and
Overall conclusions for the site based on results and observations during the five-year monitoring period.
1.0 Year 5 monitoring methods
The shoreline restoration area (Figure 1) is located immediately south of the new bridge and comprises two separate planted areas on the east and west banks of the Cedar River where
it outfalls to Lake
Washington. Monitoring plots were not established during the Year 1 monitoring in 2016, because the planted sections of the restoration area are small (approximately 1,795 square feet
total), and there were concerns regarding the height and potential stability of plot markers used in proximity to the adjacent Renton Municipal Airport runway (Amec Foster Wheeler 2016).
Instead, monitoring was conducted over the entire restoration area and included a survey of species planted (listed on Figure 2) and volunteer species.
Monitoring during Year 1 and Year 2 (Amec Foster Wheeler 2016 and 2017) included a count of individual plants (alive and dead) over the entire restoration area for each species planted.
Individual plant counts were not performed in the subsequent monitoring years (Wood 2018 and 2019), including Year 5, due to the robust growth and density of planted and volunteer vegetation.
An attempt to count all individual plants would likely produce inaccurate results due to (1) the dense nature of the vegetation, especially for the willow species along the shoreline,
and (2) the fact that volunteer grass and other herbaceous species, as well as individual volunteers of planted species, had become well established in areas between the plantings.
As an alternative technique, Wood scientists recorded any dead planted vegetation and observed the overall health and diversity of the native vegetation (planted and volunteer). Observations
included the absolute aerial cover provided by the native vegetation overall, by visual estimate. The intent was to let the native vegetation (planted or volunteer) grow and expand
naturally, while maintaining the current diversity and health of the planted species.
Invasive species present both within and adjacent to each area were also recorded, along with the overall absolute aerial cover by visual estimate for each invasive species located inside
the restoration area boundaries. Any other undesirable species within and outside of the areas were also noted. Photographs were taken from the photo points shown on Figure 1 and are
provided in Attachment A, along with other photographs of the restoration area.
2.0 Year 5 monitoring results
The Year 5 monitoring results for planted and invasive species are provided in Tables 1 and 2, respectively. The results for overall aerial cover by cover type are provided in Table
3.
Table 1: YEAR 5 RESULTS—PLANTED SPECIES
Scientific Name
Common Name
Total Count (#)1
Species Present (Yes/No)
Dead Plants (#)
Deschampsia cespitosa
Tufted hairgrass
56
Yes
Yes
0
Lupinus polycarpus
Small flowered lupine
38
Yes
0
Lupinus polyphyllus
Large leaf lupine
30
Yes
0
Philadelphus lewisii
Mock orange
7
Yes
0
Physocarpus capitatus
Pacific ninebark
7
Yes
0
Salix hookeriana
Hooker’s willow
250
Yes
0
Salix sitchensis
Sitka willow
7
Yes
0
Spirea betulifolia
Shiny-leaf spirea
15
Yes
0
Spirea douglasii
Douglas spirea
21
Yes
0
Note:
Plant counts as of the Year 2 monitoring event (Amec Foster Wheeler 2017).
Table 2: YEAR 5 RESULTS—INVASIVE SPECIES
Invasive Species1
Absolute Aerial Cover (%)
Notes
Scientific Name
Common Name
East Bank
West Bank
Buddleia davidii
Butterfly bush
<1
NA
On the north end of the east bank.
King County Non-Regulated Class B Noxious Weed; control recommended.
Rubus armeniacus
Himalayan blackberry
NA
<1
Adjacent to the south end of the east bank.
On the south end of the west bank.
King County Non-Regulated Class C Noxious Weed; control recommended.
Tanacetum vulgare
Common Tansy
<1
<1
On both banks and adjacent to the south end of the west bank.
King County Non-Regulated Class C Noxious Weed; control recommended.
Total Absolute Aerial Cover (%)
<2
<2
Notes:
Plant species listed as regulated or non-regulated noxious weeds by King County (2020). Cover data on Weeds of Concern were not collected, but their presence was noted and is discussed
in the report narrative.
Abbreviations:
NA = not applicable
Plant mortalities were not observed during the Year 5 monitoring event, and all planted species were present in the restoration area. There were some signs of predation by beaver (Castor
canadensis) or another mammal species on the willow and spirea, but the existing stands appeared healthy, with significant growth since the 2019 survey (Wood 2019), especially on the
east bank. Additional species in the restoration area included a variety of native grasses and common rush (Juncus effusus). The expanded cover by volunteer grass and other herbaceous
species that have become established between the plantings may have outcompeted some of the more upland container plantings, but planted species such as the lupine (Lupinus spp.), were
still observed among the herbaceous plants on both banks.
Table 3: YEAR 5 RESULTS—OVERALL AERIAL COVER
Absolute Aerial Cover (%)
Cover Type
East Bank
West Bank
Average
Native Species
98
98
98
Invasive Species
<2
<2
<2
Open Ground
3
1
2
Three invasive species (compared to eight species in 2019) were present in low amounts in one or both restoration areas:
Butterfly bush (Buddleia davidii),
Himalayan blackberry (Rubus armeniacus), and
Common tansy (Tanacetum vulgare).
Total absolute aerial cover of invasive species was less than two percent for the east bank and less than two percent for the west bank, compared to six and three percent, respectively,
from 2019.
These three invasive species are listed on the 2020 King County Noxious Weed List (King County 2020) as a Non-Regulated Class B or Class C noxious weed, where control is recommended.
Creeping buttercup (Ranunculus repens) was also present in the restoration areas. Although it is a Weed of Concern for King County, with control recommended, a cover estimate was not
collected, as it was present in low amounts and is not on the Washington State Noxious Weed List (Washington State Noxious Weed Control Board 2020). One bittersweet nightshade (Solanum
dulcamara) plant was observed on the north end of the east bank restoration area; it is also a Weed of Concern for King County but is not on the Washington State Noxious Weed List.
Native species (planted and volunteer) provided most of the cover, at an average of 98 percent, followed by invasive species at less than two percent. There were limited areas of little
or no vegetation (two percent average) immediately adjacent to the planted vegetation, and these areas were stabilized with mulch. These areas are expected to fill in further as has
been observed over past monitoring years, especially since they have aerial cover provided by the adjacent planted vegetation. The graveled portions of the restoration area along the
water column were not included in this aerial cover estimate.
3.0 Compliance with performance standards
Specific performance standards for Year 5 are:
80 percent survival of all plants; and
Not more than 10 percent coverage by non-native invasive species.
The Year 5 performance standard of 80 percent survival for all plants was achieved. Plant mortalities were not observed for any of the container or live stake plants. Table 4 provides
the Year 2 (2017) plant count and summarizes the results from the Year 5 (2020) monitoring, including species presence, number of dead plants observed, and the resulting survival rates
for each individual species.
The Year 5 performance standard of not more than 10 percent coverage by invasive species was achieved. Absolute aerial cover by invasive species was recorded at less than two percent
for each bank (Tables 2 and 3).
Table 4: SPECIES, PLANT COUNTS, AND SURVIVAL RATES
Planted Species
2017
2020
Scientific Name
Common Name
Live Plants1 (#)
Species Present (Yes/No)
Dead Plants (#)
Survival Rate2 (%)
Deschampsia cespitosa
Tufted hairgrass
56
Yes
0
100
Lupinus polycarpus
Small flowered lupine
38
Yes
0
100
Lupinus polyphyllus
Large leaf lupine
30
Yes
0
100
Philadelphus lewisii
Mock orange
7
Yes
0
100
Physocarpus capitatus
Pacific ninebark
7
Yes
0
100
Salix hookeriana
Hookers willow
250
Yes
0
100
Salix sitchensis
Sitka willow
7
Yes
0
100
Spirea betulifolia
Shiny-leaf spirea
15
Yes
0
100
Spirea douglasii
Douglas spirea
21
Yes
0
100
Total:
431
0
100
Notes:
Plant counts as of the 2017 Year 2 monitoring event.
Survival rate is based on the number of dead plants observed in 2020 compared to the number of live plants counted in 2017.
4.0 Previous actions taken
On the west bank, vegetation that was once blocking the facility warning/restricted access sign facing the Cedar River has been trimmed so that the sign is visible. Trimming included
full removal of at least one volunteer red alder (Alnus rubra) noted during past surveys, due to the height restrictions for vegetation adjacent to the airport activities.
The supplemental plantings of Pacific ninebark and Douglas spirea installed in July/early August 2019 (Wood 2019) were observed to be alive and healthy during this monitoring event.
5.0 Maintenance recommendations
Given the overall success of the restoration site, maintenance and monitoring activities are not anticipated to continue. However, since the planted vegetation appears to be successfully
established, the temporary irrigation system could be removed. Although few invasive species were observed within the mitigation area and in very limited amounts, King County does recommend
control of the Non-Regulated Class B and Class C noxious weeds that were present.
For vegetation in front of the facility warning/restricted access signs, branches of individual plants will likely need to be routinely trimmed to maintain visibility of these signs,
or the signs may need to be repositioned or replaced with signage more appropriate for the area. Also, routine trimming of vegetation may be needed to maintain plant heights below the
required restrictions for vegetation adjacent to the airport activities. This maintenance activity could also include removal of potential volunteer species that would violate those
height standards, such as red alder.
6.0 Conclusions
Overall, the site has performed well, and considering the overall trends and performance of the site, the expectation remains that native species will continue to survive and provide
increased cover over time, and that the invasive species cover will remain low. Considering the site has reached current conditions after five years, the site is well on its way to
maturing into a restored system.
7.0 References
Amec Foster Wheeler Environment & Infrastructure, Inc. (Amec Foster Wheeler), 2016, Memorandum: Shoreline Restoration Monitoring—Year 1, North Bridge Replacement Project, The Boeing
Company, Renton, Washington, December 1.
———, 2017, Memorandum: Shoreline Restoration Monitoring—Year 2, North Bridge Replacement Project, The Boeing Company, Renton, Washington, October 27.
King County, 2020, King County 2020 Noxious Weed List, accessed October 2020 at: https://your.kingcounty.gov/dnrp/library/water-and-land/weeds/WeedLists/2020-King-County-Noxious-Weed-List.pdf.
Washington State Noxious Weed Control Board, 2020, 2020 Washington State Noxious Weed List, accessed October 2020 at: https://www.nwcb.wa.gov/pdfs/2020-State-Weed-List_Scientific_Name-8.5x11.pdf.
Wood Environment & Infrastructure Solutions, Inc. (Wood), 2018, Memorandum: Shoreline Restoration Monitoring—Year 3, North Bridge Replacement Project, The Boeing Company, Renton, Washington,
October 9.
———, 2019, Memorandum: Shoreline Restoration Monitoring—Year 4, North Bridge Replacement Project, The Boeing Company, Renton, Washington, October 18.
Attachment: Figure 1—Shoreline Restoration Area
Figure 2—Plant List
Attachment A—Year 5 Monitoring Photographs
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