sr 532 corridor improvements – design-build – davis slough

2019 WETLAND MONITORING REPORT

SR 532 Corridor Improvements – Design-Build – Davis Slough Bridge (Dugualla Bay) Compensatory Mitigation Site

USACE IP NWS-2010-968

Northwest Region

Wetlands Program Issued March 2020

Prepared By: Sean Patrick

Editor:

Kristen Andrews

For additional information about this report or the WSDOT Wetlands Program, please contact:

Kristen Andrews, Wetlands Program WSDOT, Environmental Services Office

P. O. Box 47332, Olympia, WA 98504 E-mail: [email protected]

Phone: 360-570-2588

Monitoring reports are published on the web at: http://www.wsdot.wa.gov/environment/technical/disciplines/wetlands/monitoring-reports

mailto:[email protected]

http://www.wsdot.wa.gov/environment/technical/disciplines/wetlands/monitoring-reports

http://www.wsdot.wa.gov/environment/technical/disciplines/wetlands/monitoring-reports

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532 Dugualla Bay 2019 Monitoring Report i

Site Summary SR 532 Corridor Improvements – Design-Build – Davis Slough Bridge (Dugualla Bay) Compensatory Mitigation Site USACE IP NWS-2010-968

General Site Information

USACE IP Number NWS-2010-968

Ecology WQC 10352

Mitigation Location On Whidbey Island south of Deception Pass, just east of Highway 20

LLID Number 1225936483547

Construction Date 2014-2016

Monitoring Period 2017-2023

Year of Monitoring 3 of 7

Type of Impact Wetland Buffer

Area of Project Impact1 3.23 acres 1.84 acres

Type of Compensation

Wetland Re-Establishment

Mudflat Re-Establishment

Buffer Enhancement

Planned Area of Compensation1 3.47 acres 0.91 acre 9.51 acres

1 Impact and compensation area numbers were sourced from the Wetland and Stream Mitigation Report Addendum SR 532 Davis Slough Bridge Replacement and Widening for Flood Protection dated March, 2015 (WSDOT 2015a). The numbers above include the acreage required for this project’s impact as well as additional acreage present on site for future mitigation.

532 Dugualla Bay 2019 Monitoring Report ii

Table of Contents Site Summary........................................................................ i

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

1.1. Summary ........................................................... 1

1.2. Monitoring Results and Management Activities .. 1

2. Site Description ......................................................... 2

2.1. Location ............................................................. 2

2.2. Purpose and Description ................................... 2

2.3. Study Area ......................................................... 3

3. Performance Standards and Methods ....................... 4

3.1. Performance Standards ..................................... 4

3.2. Methods............................................................. 5

4. Discussion ................................................................. 6

4.1. Site Development .............................................. 6

4.2. Results .............................................................. 7

4.3. Adaptive Management ..................................... 10

5. References .............................................................. 11

Figures Site Sketch ........................................................... 3

Sample Design ..................................................... 5

Marshland Test Seeding ..................................... 10

Appendices Appendix A. As-Constructed Planting Plan ................... 12

Appendix B. Photo Points ............................................. 15

Appendix C. Data Tables .............................................. 20

532 Dugualla Bay 2019 Monitoring Report 1

1. Introduction 1.1. Summary This report summarizes third-year (Year-3) monitoring activities at the 532 Dugualla Bay Compensatory Mitigation Site. Included are a site description, the performance standards, an explanation of monitoring methods, and an evaluation of site development. Monitoring activities included vegetation surveys, photo-documentation, and an assessment of wetland hydrology on August 6 and 7, 2019.

1.2. Monitoring Results and Management Activities

Current (Year-3) Performance Standards 2019 Results2 Management Activities

Documentation of tidal inundation Documented (see Appendix B, Photo Points 5 and 6) Test area seeding to be completed

5/2020-8/2020 during low tide Minimum 30% cover of native salt marsh species in the salt marsh zones Less than 5% cover (visual estimate)

Minimum native woody density of 4 plants/100ft2 in the buffer 9 plants/100ft2 (visual estimate) Additional native woody plantings

installed on 10/14–10/15/2019

Eradicate Class A- and B-designate noxious weeds and maximum cover of 20% for all noxious weeds

Class B-designate noxious weed spurge laurel (Daphne laureola) present in the buffer Less than 5% cover of noxious weeds across the site

9 weed control visits in 2019 (spurge laurel removed/treated on 8/13)

Final (Year-7) Performance Standards

Minimum 40% native woody cover in the buffer 76% cover (CI95% = 68-85%)

2 Estimated values are presented with their corresponding statistical confidence interval. For example, 76% cover (CI95% = 68-85%) means we are 95% confident that the true cover value is between 68% and 85%.


2. Site Description 2.1. Location This 37-acre compensation site is re-established and rehabilitated wetland and mudflat located on Whidbey Island, south of Deception pass and across the bay from the mouth of the Skagit river. (Figure 1).

Driving Directions: From Interstate 5, take Exit 230 towards Anacortes/Burlington. Travel west on State Route (SR) 20 for about 12 miles. Turn left to continue on SR 20 once you reach Whidbey Island. Travel south on SR 20 for another 10 miles. Turn left onto Jones Road and travel for approximately one mile then bear right onto Dike Road. In a half a mile, there is a pull out on the left side of the road where you can park.

2.2. Purpose and Description This site was created to compensate for the loss of 3.23 acres of wetlands due to the replacement of the Davis Slough Bridge and road improvements along SR 532 as well as the Leque Island Slope Protection project. Additional compensation is available for future projects. The wetland and mudflat re-establishment and rehabilitation areas are designed to provide compensation for lost wetland functions including wildlife habitat, water quality, and restoration of estuarine functions.


2.3. Study Area The 532 Dugualla Bay Compensatory Mitigation Site (Figure 1) contains a large area of wetland rehabilitation interspersed with wetland re-establishment, mudflat, and preservation areas. Buffer enhancement is located up-gradient of the wetland.

Site Sketch


3. Performance Standards and Methods 3.1. Performance Standards Year 3 Performance Standard 1 The site will be evaluated annually during a high tide event (as predicted by NOAA for the day of monitoring). Photographs will be taken at select locations (possible permanent photo points) to document the extent of tidal inundation across the wetland re-establishment and rehabilitation portions of the site.

Performance Standard 2 Native salt marsh species will achieve a minimum 30 percent coverage in the high and low salt marsh zones. Native colonizing vegetation will be included in this coverage calculation.

Performance Standard 3 Native woody species (planted and volunteer) will achieve an average density of at least 4 plants per 100 square feet in the buffer planting areas.

Performance Standard 4 WSDOT will attempt to eradicate Washington State-listed or county-listed Class A weeds and Class B weeds designated for control by Island County. In accordance with this commitment, the presence of knotweeds and purple loosestrife will not be tolerated. All occurrences of Class A or Class B noxious weeds, including knotweeds and purple loosestrife, will be immediately reported to the site manager and an eradication program will be initiated within 30 days of the report.

In addition, invasive species listed in [Appendix C, Table 1] and any other species that competes with desirable vegetation will be controlled across the mitigation site until performance standards for native vegetation have been achieved in the wetland and buffer zones.

Island County Class A, Class B, Class B non-designated, and Class C noxious weeds will not exceed 20 percent aerial cover. The presence of purple loosestrife or non-native knotweeds will trigger invasive species contingency measures.

Year 7 (Final Year) Performance Standard 5 Cover of native woody species (planted and volunteer) will be at least 40 percent in the buffer planting areas.

Appendix A shows the as-constructed planting plan (WSDOT 2017).


3.2. Methods Photographs were taken from permanent photo point locations during a high tide event to document the extent of tidal inundation in the wetland (Performance Standard 1). The table below documents the sample methods used for the remaining performance standards (PS) required by the mitigation plan or permits. Additional details on our methods are located here: WSDOT Wetland Mitigation Site Monitoring Methods Paper (WSDOT 2008).

Sample Design

Placement of Baseline: A 504-meter-long baseline was placed through the buffer at a bearing of 83 degrees (Figure 2).

PS 2 PS 3 PS 4 PS 5

Attribute Cover Density Presence/ Absence Cover

Target population

Native salt marsh

species

Native woody species

Noxious weeds

Native woody species

Zone Wetland Buffer Entire site Buffer

Sample method Qualitative Qualitative Qualitative Line

intercept

SU length n/a n/a n/a 15 m

Total # of SU n/a n/a n/a 18

https://www.wsdot.wa.gov/sites/default/files/2018/02/22/Env-Wet-MonitoringMethods.pdf



4. Discussion 4.1. Site Development Overall, this site is developing very well. The buffer is well ahead of schedule in its development and was sampled for cover this year instead of the current-year performance standard of density. A robust and diverse native woody plant community has developed and it is easily exceeding the final-year performance standard.

The cover of noxious weeds across all areas of the site is very low, though an infestation of the Class B-designate noxious weed spurge laurel was observed in the NE part of the buffer. Site managers were notified and it was treated less than a week after monitoring was concluded. It will almost certainly require follow-up control, however, to successfully eradicate it from the site.

The salt marsh areas are getting inundated regularly and colonization by native salt marsh species is progressing, but more slowly than planned. Only one native salt marsh species, pickleweed (Salicornia depressa), is currently providing a significant amount of cover in these areas. The most dominant species in these areas is a non-native salt marsh species, common brassbuttons (Cotula coronopifolia). It is not entirely clear if the slow development of this community is due to a lack of seed sources, a lack of diversity of topography, and/or other factors. WSDOT is planning to seed three test areas (see Figure 3) with a mix of six native salt marsh species: meadow barley (Hordeum Brachyantherum), saltgrass (Distichlis spicata), Puget Sound gumweed (Grindelia integrifolia), saltmarsh bulrush (Scirpus maritimus), Lyngbye’s sedge (Carex lyngbyei), and Baltic rush (Juncus balticus) to help this community develop faster and with more diversity. Expanded seeding area application or alternate method of adaptive management will be implemented following germination assessment.


4.2. Results Performance Standard 1 (Documentation of tidal inundation)

The wetland re-establishment and rehabilitation portions of the site were mostly inundated during a predicted 8.33-foot high tide event at about 10:00 am on August 6, 2019. See Appendix B, Photo Points 5 and 6 for photo documentation.

Performance Standard 2 (Minimum 30% cover of native salt marsh species in the salt marsh zones)

The cover of native salt marsh species in the salt marsh zone (Photo 1) was visually estimated at less than 5%. Virtually all of this cover was of pickleweed (Salicornia depressa). There was some inland saltgrass (Distichlis spicata) present along the lower edge of the berm, but this was present in 2017 as well and so far does not seem to be colonizing into the rest of salt marsh areas. Non-native salt marsh species common brassbuttons (Cotula coronopifolia) was also present along with an unknown species of goosefoots (Chenopodium sp.) that was not definitively identified to species and whose nativity, therefore, remains unknown at this time.

Photo 1. Herbaceous cover in the salt marsh (August 2019)


Performance Standard 3 (Minimum native woody density of 4 plants/100ft2 in the buffer)

Because of the rapid development of the native woody plant community in the buffer, this area was sampled for cover rather than density in 2019. When sampled in 2017, native woody density in the buffer was estimated at 9.5 plants/100ft² (CI80% = 8.8-10.1). In 2019, the density was visually estimated to be about the same.

Performance Standard 4 (Eradicate Class A- and B-designate noxious weeds and maximum cover of 20% for all noxious weeds)

The cover of all noxious weeds across the site was visually estimated at less than 5%. An infestation of Class B-designate noxious weed spurge laurel was observed in the northeast part of the buffer. Many of the plants were flagged and GNSS locations were taken (Photo 2). Site managers were notified of its presence and location on August 8, and on August 13 a crew visited the site to hand remove the spurge laurel and treat it with herbicide (bag and daub).

Photo 2. Flagged spurge laurel in the buffer (August 2019)


Performance Standard 5 (Minimum 40% native woody cover in the buffer)

The cover of native woody species in the buffer planting areas is estimated at 76% (CI95% = 68-85%) (Photo 3). The dominant species are thimbleberry (Rubus parviflorus), salmonberry (Rubus spectabilis), red elderberry (Sambucus racemosa), and bigleaf maple (Acer macrophyllum). A total of 11 native woody species were present in our sample.

Photo 3. Woody cover in the buffer (August 2019)


4.3. Adaptive Management WSDOT crews visited the site nine times to conduct weed control of various noxious weed species and two additional times to plant native woody species (including sweet gale, red elderberry, ocean spray, salmon berry, Hooker’s willow, and snowberry) in buffer planting areas. Work anticipated for 2020 includes seeding installation of three test areas with native salt marsh species, to be completed in late spring/summer during low tide, and continued weed control site-wide (Figure 3).

Marshland Test Seeding


5. References 1. [Ecology] Washington State Department of Ecology. 2013. Water Quality Certification Number 10352.

2. [USACE] US Army Corps of Engineers. 2014. Department of the Army Individual Permit Number NWS-2010-698.

3. [WSDOT] Washington State Department of Transportation. 2008. WSDOT Wetland Mitigation Site Monitoring Methods. https://www.wsdot.wa.gov/sites/default/files/2018/02/22/Env-Wet-MonitoringMethods.pdf

4. [WSDOT] Washington State Department of Transportation. 2013a. Final Wetland and Stream Mitigation Report SR 532 Davis Slough Bridge Replacement – Widening for Flood Prevention (MP 2.50 to MP 3.39). Seattle (WA): Washington State Department of Transportation, Northwest Region.

5. [WSDOT] Washington State Department of Transportation. 2013b. Final Wetland and Stream Mitigation Report Addendum SR 532 Davis Slough Bridge Replacement – Widening for Flood Prevention (MP 2.50 to MP 3.39) September 2013. Seattle (WA): Washington State Department of Transportation, Northwest Region.

6. [WSDOT] Washington State Department of Transportation. 2014. Final Wetland and Stream Mitigation Report Addendum SR 532 Davis Slough Bridge Replacement – Widening for Flood Prevention (MP 2.50 to MP 3.39) April 2014. Seattle (WA): Washington State Department of Transportation, Northwest Region.

7. [WSDOT] Washington State Department of Transportation. 2015a. Final Wetland and Stream Mitigation Report Addendum SR 532 Davis Slough Bridge Replacement – Widening for Flood Prevention (MP 2.50 to MP 3.39) March 24, 2015. Seattle (WA): Washington State Department of Transportation, Northwest Region.

8. [WSDOT] Washington State Department of Transportation. 2015b. Final Wetland and Stream Mitigation Report Addendum SR 532 Davis Slough Bridge Replacement – Widening for Flood Prevention (MP 2.50 to MP 3.39) October 23, 2015. Seattle (WA): Washington State Department of Transportation, Northwest Region.

9. [WSDOT] Washington State Department of Transportation. 2017. SR 532 Davis Slough Bridge Replacement Dugualla Bay Mitigation Site As-Constructed Mitigation Planting Plan.



Appendix A. As-Constructed Planting Plan (from WSDOT 2017)


Appendix B. Photo Points The photographs below were taken from permanent photo-points on August 6-7, 2019 and document current site development.


Photo Point 1a Photo Point 1b

Photo Point 2 Photo Point 3a


Photo Point 3b Photo Point 3c




Photo Point 5c Photo Point 6a


Photo Point 6b Photo Point 6c

Photo Point 6d Photo Point 6e


Appendix C. Data Tables Table 1. Non-native invasive species

Scientific Name Common Name

Buddleia alternifolia fountain butterfly bush

Cytisus scoparius Scotch broom

Rubus armeniacus Himalayan blackberry

Rubus laciniatus cutleaf blackberry

Hedera helix English ivy

Ilex aquifolium English holly

Phalaris arundinacea reed canarygrass

Prunus laurocerasus English laurel

sr 532 corridor improvements – design-build – davis slough

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