Environmental Checklist
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Beaver Dam Management SEPA Environmental Checklist SEATTLE PUBLIC UTILITIES SEPA ENVIRONMENTAL CHECKLIST This SEPA environmental review of Seattle Public Utilities’ (SPU) Beaver Dam Management Project has been conducted in accord with the Washington State Environmental Policy Act (SEPA) (RCW 43.21C), State SEPA regulations (Washington Administrative Code [WAC] Chapter 197-11), and the City of Seattle SEPA ordinance (Seattle Municipal Code [SMC] Chapter 25.05). A. BACKGROUND 1. Name of proposed project: Beaver Dam Management 2. Name of applicant: Seattle Public Utilities (SPU) 3. Address and phone number of applicant and contact person: Steve Damm, Project Manager Seattle Public Utilities P.O. Box 34018 Seattle, WA 98124-4018 206-713-8648; [email protected] 4. Date checklist prepared: May 10, 2021 5. Agency requesting checklist: Seattle Public Utilities (SPU) 6. Proposed timing or schedule (including phasing, if applicable): The project would be constructed in 2021 and is expected to take up to three working days per each of the two project sites. The constructed project would be maintained for the life span of the subject beaver dams, which could be many years. SPU and the Seattle Department of Parks and Recreation (SPR) would periodically remove debris from the constructed project at the Thornton Creek dams and the Longfellow Creek dams, respectively. SPU would repair the constructed project at all sites for as long as required. 7. Do you have any plans for future additions, expansion, or further activity related to or connected with this proposal? If yes, explain. SPU periodically installs other beaver deterrence structures elsewhere within the municipal limits of the City of Seattle and in the City’s South Fork Tolt and Cedar River municipal watersheds. Those projects have not been identified at this time and would not be related to this proposal. SEPA Checklist Beaver Dam Mgmt 051221 May 12, 2021 Page 1 of 22 Beaver Dam Management SEPA Environmental Checklist 8. List any environmental information you know about that has been prepared, or will be prepared, directly related to this proposal. No environmental information has been prepared or will be prepared. 9. Do you know whether applications are pending for governmental approvals of other proposals directly affecting the property covered by your proposal? If yes, explain. No applications are pending for governmental approvals of other proposals directly affecting the property covered by this proposal. 10. List any government approvals or permits that will be needed for your proposal, if known. Hydraulic Project Approvals(Washington State Department of Fish and Wildlife [WDFW]) 11. Give a brief, complete description of your proposal, including the proposed uses and the size of the project and site. There are several questions later in this checklist that ask you to describe certain aspects of your proposal. You do not need to repeat those answers on this page. Beavers have recently constructed two dams immediately upstream of the pedestrian footbridge over Longfellow Creek near 2512 SW Graham Street, in the High Point neighborhood of West Seattle in the City of Seattle, King County, Washington (Attachment A). The dams pose an imminent threat to integrity of the pedestrian footbridge footings by altering the path and velocity of stream flows (Attachment B). The dams may also lead to localized flooding of nearby residential properties during the rainy season. In addition, beavers have routinely constructed two dams in SPU’s Meadowbrook Pond Stormwater Detention and Flood Control Facility in the Meadowbrook neighborhood of the City of Seattle (Attachment C). This constructed stormwater management facility in northeast Seattle is located immediately downstream of the confluence of the north and south branches of Thornton Creek. It contains the 2.0 to 2.7 acre (depending on water level) Meadowbrook Pond that captures and detains some of the stormwater runoff from about 6,840 acres of the upstream watershed. In recent years, resident beavers have constructed dams at the Pond outlets near 39th Ave NE and NE 105th St (Attachment C), which diminish flows to the lower two miles of Thornton Creek during summer low flow periods and endanger resident fish and impede migration of anadromous fish. This proposal would deploy beaver dam management interventions at both dams at both sites. Specifically, the proposed work would install four pond levelers by notching the dams and then installing exclusion fences (Attachment D). The notched opening would be approximately 3 feet wide and 1.5 feet deep. Once the notch is created, workers would install exclusion fencing such that it forms a box around the notch. The fencing would extend 16 feet upstream from the top of the dam. Notching assists in preventing beavers from detecting stream flow through the dam and the fencing prevents them from effectively plugging the notch. The welded-wire fencing has a mesh size of 4 inches by 6 inches and is typically anchored with metal t-posts. These interventions are intended to control water levels and flows in Longfellow and Thornton creeks and are preferred alternatives to relocating the beavers or removing or breaching an established beaver dam that maintains hydrology of a nearby wetland or pond. SEPA Checklist Beaver Dam Mgmt 051221 May 12, 2021 Page 2 of 22 Beaver Dam Management SEPA Environmental Checklist These pond levelers would be installed at the intended depth, extending upstream and downstream of each dam. The pond levelers would maintain water levels in adjacent wetlands and ponds such that risk of future localized flooding would be minimized. The proposed design provides unimpeded fish passage while preventing beavers from constructing effective dams at the pedestrian bridge at the Longfellow Creek site and in Meadowbrook Pond at the Thornton Creek site. 12. Location of the proposal. Give sufficient information for a person to understand the precise location of your proposed project, including a street address, if any, and section, township, and range, if known. If a proposal would occur over a range of area, provide the range or boundaries of the site(s). Provide a legal description, site plan, vicinity map, and topographic map, if reasonably available. While you should submit any plans required by the agency, you are not required to duplicate maps or detailed plans submitted with any permit applications related to this checklist. The Longfellow Creek site is in the City of Seattle street right-of-way for SW Graham St near 2512 SW Graham St in the High Point neighborhood of West Seattle (T24N, R03E, S24). Work may also occur on parcels 3438501370 and 3438501360 owned and managed by SPR. The first dam is located at latitude 47.546462, longitude -122.364286. The second dam is located 150 feet downstream of the first dam (47.546878, -122.3644265). The Thornton Creek site at Meadowbrook Pond is on SPU-owned parcel 2726049129 at 3600 NE 105th St in the Meadowbrook neighborhood of the City of Seattle (T26N, R04E, S27) (47.705080, -122.287960). B. ENVIRONMENTAL ELEMENTS 1. Earth a. General description of the site: Flat Rolling Hilly Steep Slopes Mountainous Other: b. What is the steepest slope on the site (approximate percent slope)? Both project locations are generally flat. Steep slopes (less than 40%) are associated with the banks of Longfellow and Thornton Creeks. c. What general types of soils are found on the site (for example, clay, sand, gravel, peat, muck)? If you know the classification of agricultural soils, specify them and note any agricultural land of long-term commercial significance and whether the proposal results in removing any of these soils. The general geologic condition of the Puget Sound region is a result of glacial and non- glacial activity that occurred over the course of millions of years. Review of the geologic map covering the project location (Troost et al. 2005, available at http://pubs.usgs.gov/of/2005/1252/ ) indicates both project sites are underlain primarily by Vashon till, and advance outwash deposits. Glacial till is a mix of poorly sorted silt, sand, and sub-rounded to well-rounded gravels and cobbles that are transported by the glacier and deposited under the ice resulting in a very dense to over consolidated deposit. Advance outwash consists of well sorted sand and gravel that was transported SEPA Checklist Beaver Dam Mgmt 051221 May 12, 2021 Page 3 of 22 Beaver Dam Management SEPA Environmental Checklist by meltwater channels emanating from the toe of the advancing glacier and subsequently overridden by the glacier. However, urban development at and near both project sites over the last 100 years has resulted in a predominance of disturbed native soils/sediments, cut slopes, and large placements of fill material. d. Are there surface indications or history of unstable soils in the immediate vicinity? If so, describe: Portions of the Longfellow Creek site are mapped by the City of Seattle as Potential Slide Environmentally Critical Areas (https://www.arcgis.com/apps/webappviewer/index.html?id=f822b2c6498c4163b0cf90 8e2241e9c2). There are no visible indications of unstable soils on or near this project site or at the Thornton Creek site. e. Describe the purpose, type, total area, and approximate quantities and total affected area of any filling, excavation, and grading proposed. Indicate the source of fill. The proposal would not require any filling, excavation, or grading. f. Could erosion occur as a result of clearing, construction, or use? If so, generally describe: The proposed work would create no potential for erosion. g. About what percent of the site will be covered with impervious surfaces after project construction (for example, asphalt or buildings)? The proposed work would neither create new impervious surfaces nor demolish existing impervious surfaces. h. Proposed measures to reduce or control erosion, or other impacts to the earth, if any: No filling or excavation would take place in or near watercourses or wetlands.