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HomeMy WebLinkAboutBarbie Mill Tree Violation_Biologists StudyTechnical Memorandum 11241Willows Road NE Suite 200 Redmond, WA 98052 Phone (425) 822-4446 Fax (425) 827-9577 Introduction This technical memorandum is provided as the Biologists Report for City of Renton (City) code violation #CODE16-000749 that occurred at 4205 Williams Avenue N in Renton, Washington. The Barbee Mill Community Organization (BMCO) was issued a warning of violation by the City on November 11, 2016 for unauthorized tree topping along May Creek that violated Renton Municipal Code (RMC) 4-3-050 (Critical Areas) and RMC 4-4-130 (Tree Retention and Land Clearing Regulations). This technical memo documents the existing environmental baseline conditions, evaluates the impacts of the tree topping to regulated critical areas and functions, and recommends a mitigation planting plan to offset these impacts. The mitigation planting plan is described in this memo. A five year monitoring plan is proposed to ensure survival of the planted native trees and shrubs. The tree topping and mitigation planting area occur within the vegetation conservation buffer and shorelands associated with May Creek as designated in the City’s Shoreline Master Program (SMP) (RMC 4-3-090). Shorelands are identified as areas within 200 feet of Type S (Shoreline) waters. May Creek is identified as a Type S water from Lake Washington upstream to the intersection with NE 31st Street (RMC 4-3-090B.2). Any activities in areas regulated by the SMP must achieve a no net loss of ecological functions per RMC 4-3-090D.2 (Environmental Effects). The proposed planting plan includes enhancing the stream buffer on the opposite bank from where the tree topping occurred to replace and improve the riparian functions along this portion of May Creek. To: Angelea Weihs, Assistant Planner Community and Economic Development City of Renton From: Jeff Gray, Senior Wetland Biologist Copies: File Date: July 12, 2017 Subject: Biologists Report for Violation #CODE16- 000749, and Mitigation Planting Plan Project No.: 32866 Angelea Weihs, Assistant Planner, City of Renton Page 2 Biologists Report for Violation #CODE16-000749 July 12, 2017 2 The BMCO has been directed by city staff to apply for a Shoreline Exemption to authorize the mitigation planting in the buffer of May Creek regulated under the City’s SMP. This technical memo is also intended to support the Shoreline Exemption application for the mitigation planting plan. Project Location The unauthorized tree topping and proposed mitigation planting plan occurs on tax parcel #051850TR-A in the Barbee Mill housing community west of Interstate 5 along the eastern shore of Lake Washington in Renton, Washington. In the Public Land Survey System, the site is located within Township 24 North, Range 05 E in the northwest quadrant of Section 32. The tree topping occurred along both banks of May Creek just downstream from the North 40th Place bridge approximately 300 linear feet upstream from the Lake Washington shoreline, identified herein as the project area. Existing Conditions and Landscape Setting May Creek flows in an approximately 75 to 100-foot wide forested riparian corridor upstream of the North 40th Place bridge to the BNSF railroad and Lake Washington Boulevard North crossing. Downstream of the North 40th Place bridge, riparian tree cover is not as wide and sometimes absent as the May Creek channel broadens before discharging into Lake Washington. The stream ordinary high water mark (OHWM) and existing vegetative cover is shown on the attached Tree Restoration Planting Plan. Vegetation in the riparian corridor includes a mix of deciduous and conifer tree species and a shrub understory, including: black cottonwood (Populous balsamifera spp. trichocarpa), big leaf maple (Acer macrophyllum), Douglas-fir (Psuedostuga menziesii), red alder (Alnus rubra), willow (Salix sp.), and salmonberry (Rubus spectabilis). Small patches of Himalayan blackberry (Rubus armeniacus) and Japanese knotweed (Polygonum cuspoidatum) also occur along the left bank in the understory in the vicinity of the tree topping area. The BMCO has an ongoing invasive species management plan that includes treating knotweed infestations. In the project area, May Creek flows in a confined channel through the crossing and downstream of the bridge. The left bank has a dense shrub vegetation community with canopy cover. The right bank of May Creek is hardened with large stones and boulders. The top of the bank is sparsely vegetated with trees and shrubs, and includes large areas of lawn grasses. Ecological functions (e.g., water temperature maintenance through shading, food chain support, organic matter input) provided by the right bank are low due to the lack of woody plants adjacent to the top of bank. Small riverine wetlands are located in pockets along the stream banks below the bankfull height elevation of May Creek downstream of the project area. See figure 1. Angelea Weihs, Assistant Planner, City of Renton Page 3 Biologists Report for Violation #CODE16-000749 July 12, 2017 3 Figure 1. View looking upstream of May Creek and the stream buffer areas downstream of the bridge crossing on North 40th Place. The approximate ordinary high water mark (OHWM) along the right bank of May Creek is represented by the blue line. The OHWM along the left bank is hidden under the overhanging vegetation and not shown. Photo taken May 5, 2017. Resource Classifications and Regulatory Context Critical areas within shoreline jurisdiction are regulated in accordance with the provisions of RMC 4- 3-050 (Critical Areas Regulations). May Creek is classified as a Type S (Shoreline) stream according to RMC 4-3-090B.2. The project area is designated a Class 1 Fish Habitat Conservation Areas in the Urban Conservancy Overlay District per the SMP, and is also located within the standard vegetation conservation buffer width (100’) as measured from the OHWM of May Creek. Vegetation clearing (i.e., tree topping) or maintenance activities within these regulated areas require prior authorization from the City. As such, the proposed buffer enhancement plan included at the end of this memo also requires authorization from the City. Buffer enhancement plans using native vegetation that improve buffer functioning are allowed per RMC 4-3-090F1.g (Buffer Enhancement). Site Inspection, Impacts, and Mitigation Requirements A site inspection was completed on May 5, 2017 to evaluate the impacts to the riparian and buffer functions along May Creek that resulted from the tree topping. The trunks of seven small-diameter Angelea Weihs, Assistant Planner, City of Renton Page 4 Biologists Report for Violation #CODE16-000749 July 12, 2017 4 red alder trees were cut between approximately 14 to 16 feet above ground surface. Tree diameters ranged from to 5.4 to 8.2 inches at breast height. Tree limbs below 14 to 16 feet above ground surface were not removed. On the right bank, two alder trees were topped approximately 15 feet from the stream OHWM. On the left bank, five alder trees were topped at or within five feet of the OHWM. The alder trees had leafed-out by the time of the site inspection, and the remaining tree limbs on the left bank continued to provide cover over May Creek. Cover on the left bank did not appear to be reduced as the lower limbs were not removed. However, shading from the morning sun during summer and fall was likely reduced along the opposite (right) bank because the tree shade profiles were reduced. Reducing the amount of vegetative mass also reduces the amount of organic detritus that could potentially enter May Creek along this stream stretch. The two alders that were topped on the right bank previously provided minimal shading of May Creek and few organic inputs because they’re set back from the stream channel. However, shading from late day sun was reduced because these trees are located northwest of May Creek. The red alders that were topped are expected to survive according to the arborists report completed for the violation. As a response to this type of cutting, the red alders are expected to grow approximately 3 to 5 feet in height per year and eventually recover their previous profile. In the short term, the topped trees will redistribute their energy to the remaining limbs and will result in above normal horizontal growth. The red alders are expected to continue to provide the same level of riparian functions prior to the cuttings during the next growing seasons. The temporal loss of shading and organic input functions should be mitigated to achieve a no net loss of ecological functions over time as required per RMC 4-3-090D2. Per RMC 4-4-130 (Tree Code), the project is required to replace 73 caliper inches of trees that were cut. At a minimum, the replacement plantings required by the tree code should be located along the right bank of May Creek immediately downstream of the bridge to increase riparian functions in this sparsely vegetated area. Proposed Mitigation to Offset Unauthorized Tree Topping The proposed mitigation to offset the unauthorized tree topping includes planting native trees and shrubs in existing lawn-dominated areas to improve the riparian functioning along this reach of May Creek. The Tree Restoration Planting Plan is included with this memo. The proposed plantings will increase tree and shrub cover in the riparian vegetation conservation buffer, which will improve thermal regulation of stream temperatures and increase organic input into the stream system. The proposed plantings will occur upstream and downstream of NE 40th Place bridge in the immediate vicinity of the tree topping. Angelea Weihs, Assistant Planner, City of Renton Page 5 Biologists Report for Violation #CODE16-000749 July 12, 2017 5 The planting plan includes 10 shore pine (Pinus contorta) and 9 cascara (Rhamnus purshiana) trees, and 9 each of vine maple (Acer circinatum), serviceberry (Amalanchier alnifolia), and Pacific dogwood (Cornus nuttallii) shrubs. The cascara, Pacific dogwood, serviceberry, and vine maple will be planted at a minimum of 2” caliper size, and the shore pines will be planted at a minimum of 6 feet tall above ground surface. Monitoring Plan, Performance Standards, and Reporting Schedule Performance monitoring is proposed to ensure that the goals of the mitigation planting are achieved. Monitoring and reporting will occur for three full growing seasons following installation. An As- Built document will be provided to the city stating when the plant installation occurred, the numbers and species planted, and their locations. The As Built document will be provided within 2 weeks following the plant installation. Installed plants will be flagged to identify them for future site inspections and maintenance. The following performance standards are proposed for this project: 1) 100% survival for three monitoring years, and 2) less than 10% cover by invasive species as determined by visual observation. Replacing any dead plants will achieve 100% survival for any monitoring year. Brief monitoring reports will be provided to the City each monitoring year. During the summer growing season, the project proponent or their representative will assess survivability and health of the planted trees and shrubs, prescribe any maintenance or adaptive management measures as necessary, and report any corrective measures taken such as replacement plantings or invasive plant removal. Monitoring reports will be provided in the fall after each monitoring event. The proposed monitoring and reporting schedule includes installation in fall 2017 (Monitoring Year 0), 2018 (Monitoring Year 1 and report), 2019 (Monitoring Year 2 and report), and 2020 (Monitoring Year 3 and report). If 100% survival at the end of Year 3 is achieved, then the mitigation planting will be deemed successful with no further monitoring requirements.