Turtleback Mountain Preserve Wetland Restoration

Over a dozen streams originate within the preserve. These intermittent, non-fish-bearing, first- and second-order tributaries contribute to larger, perennial streams in the surrounding lowlands. Noting frequent washouts and worsening channel incision (i.e., downcutting) in many of these streams likely due to the increasing intensity of winter storms, Land Bank staff commissioned a 2021 evaluation of the Turtleback Mountain Preserve gravel road/trail network. The consultant developed plans for the replacement or addition of multiple culverts to improve conveyance in cross drains and streams and to ensure compliance with Washington forest road requirements (WAC 222-24-0511).

In 2023, after updating the Turtleback Mountain Preserve Stewardship and Management Plan, receiving approval from Washington DNR under WAC 222-16 050(3) and completing a cultural resources assessment in the work areas, a Land Bank contractor replaced 20 undersized steel and concrete culverts with larger, double walled HDPE culverts. These new culverts will help prevent future washouts, reduce maintenance requirements, and bring the forest road/trail network up to Washington forest road standards. Funding for the project was provided by the Land Bank and the San Juan Preservation Trust’s Turtleback Stewardship Endowment.

Although the new culverts addressed artificial flow constrictions across the mountain, the general lack of large and small woody debris in many of these streams has allowed continued scouring of sediments during high flows. As part of ongoing forest thinning and restoration efforts within the preserve, the Land Bank is pursuing plans to dissipate instream energy (i.e., scouring flows) by increasing channel roughness through the addition of large and small wood. When installed, this material will trap sediment and help aggrade the incising channel beds.