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HomeMy WebLinkAbout001063018 Geotech Assessment (Trees) PO Box 2546, Bellingham, Washington 98227 Phone: (360) 714-9409 June 17, 2022 Sonya Baumstein sonya@teamepoch.org Re: Proposed Tree Cutting Jefferson County Parcel 001063018 522 McMinn Road, Port Townsend, WA 98368 Dear Sonya Baumstein: It is our understanding that you are proposing to remove three alder trees and one Douglas fir on the subject property. The four trees that will be removed are shown below in Figure 1. The tree removal will be completed for the purpose of allowing space and sunlight to aid in the development of a new evergreen tree that will be planted to replace a Douglas fir that recently toppled in a windstorm. The proposed tree removal is located within 30 feet of the top edge (crest) of the shoreline bluff. Figure 1. Proposed trees to be removed. Stratum Group previously completed a geologic hazard assessment on the subject property in 2018 (Stratum Group File 6.14.18. Based on our assessment, it is our opinion that the proposed tree removal will have a negligible impact on the risk of landslides and erosion on the shoreline bluff both on and off the subject property. Trees help improve slope stability in two main ways: 1) their root networks provide structure and support to the soil, and 2) they decrease groundwater infiltration through the processes of rainfall interception, evaporation, and transpiration. Both of these are addressed below. 1) Because the mechanics of bluff failure at the site primarily involve deep-seated failure below the rooting depth of trees, the tree roots are not providing any benefit to slope stability. If the trees were within 5 feet of the top edge (crest) of the shoreline bluff, they would work to resist shallow failures and raveling, but that is not the case with the four trees that are proposed to be removed. 2) Three of the trees that are proposed to be removed are deciduous alder trees that drop their leaves during the rainy winter season. Because the alder trees have no leaf cover during the rainy season, they are not effective at reducing groundwater infiltration. Without leaves, there is no rainfall interception and no transpiration. The surface area available for evaporation is also minimal. The fir tree that is proposed to be removed likely does decrease groundwater infiltration. However, its impact on the overall hydrology of the bluff is negligible compared to the large groundwater contribution (recharge) area that encompasses a large upland area extending back to Hastings Avenue 0.5 miles to the southeast. Stratum Group appreciates the opportunity to be of service to you. Should you have any questions regarding this assessment please contact our office at (360) 714-9409. Sincerely yours, Stratum Group Geoff Malick, L.G., M.Sc. Licensed Geologist