This project entails placing large woody material (LWM) along the mainstem Upper Wenatchee River in crib-like structures. The length of the treatment will be for approximately 100 yds. however; the treatment will be non-continuous in favor of utilizing gaps in the riparian canopy as well as further minimizing disturbance to riparian bank vegetation for exact structure placement.
The structures will extend waterward from the bank and provide cover and complexity in-water habitat. There are two types of structures proposed: a mainstem cover jam to provide cover and complexity at various river levels and a mainstem complexity jam to provide cover and complexity through the plane bed glide features at this location.
The larger structure will contain approximately 20 coniferous logs, the majority with rootwads. The non-rootwad LWM, or rather sticks, will be used as bumper/deflector logs intended to deflect floating objects. The LWM will be embedded 30’ into the bank and backfilled with no less than 3’ of imported gravel and cobble at a 3:1 slope. In addition, there will be vertical pile logs installed using a vibrasonic pile driving implement (HMC Movac Sonic Side- Grip, SP80-100 or equivalent). These piles will act as additional stability for the structures. They too will be embedded a minimum of 15’ with approximately 10-15’ above ground. The structures will be located on the upstream end of the project location. The smaller of the structures, approximately 6, will be installed identically as the larger structures discussed above, but with fewer logs. These structures will consist of two logs with root-wads and one bumper/deflector log across the face. These too will have vertical piles associated with them for stability.
In addition to the structures, approximately 100’ of bank will have a three tier Fabric Encapsulated Soil Lifts (FESLs) as part of the treatment option. The larger structure will have approximately 35’ of FESL, 3 tiers deep and the other smaller structures will have approximately 15’ of FESL three tiers deep.
These FESLs will be constructed out of coir fabric consisting of an outer layer and an inner layer. The outer layer will be (700 weight woven coir fabric and the inner layer will be North American Green C125BN Non-Woven Coir or equivalent). The fabric will be staked with a 2 X4 stud cut diagonally at 18in. in length.
In addition to the fabric and stakes the contractor will need to import a gravel/cobble topsoil fill mix from the local quarry to fill each tier of the FESL to a compacted depth of 12". A 3" topsoil layer will also need to be imported to be placed across each tier for future planting by a separate contractor. The appropriate riparian seed mix shall be placed on soil and beneath fabric on all exposed surfaces.
An extensive road network currently exists on the property, so as a result no new roads or temporary access routes will be created. The only new disturbance will be along the face of the proposed LWM treatment locations. This existing road network will be utilized for all construction and revegetation activities. The area where the structures will be located will be cleared to a minimal degree. All Best Management Practices for riparian disturbance will be strictly adhered to.
The purpose of the project is to provide some cover and instream complexity for listed salmonids in the Upper Wenatchee River: (Upper Columbia River Spring Chinook salmon and Upper Columbia River steelhead). This mainstem complexity is intended to support and provide holding and rearing habitat for Chinook and steelhead by increasing cover and complexity.
These structures will promote scour pools at the toe of the structures as well as provide cover habitat in the form of shade and predation refugia.
The locations for the LWM structures were chosen based upon several factors: 1.) the Natapoc site is limited in LWM retention, key pieces of LWM that once persisted through this reach are no longer available due to past logging practices, 2.) this part of the Wenatchee River has a clean line of sight for 400+ feet for any boaters to avoid the LWM, 3.) lastly, the structures placement will take advantage of gaps in the riparian canopy to lessen the riparian footprint. Additionally, the majority of the thalweg in this reach of the Wenatchee River is located along the left bank away from the project location. This is due in part to the river making a hard 90 degree right prior to the proposed project location.
Project Rationale:
In August of 2012 the Yakama Nation Fisheries worked with Interfluve Inc. (IFI) to develop the “Upper Wenatchee River Steam Corridor Assessment and Habitat Restoration Strategy.” This detailed assessment was broken into 11 reaches from River Miles (RM) 35.5-54.2. The Natapoc project lies between RM 50.76-52.75. Included in this reach assessment was a project appendix that listed potential projects within each reach. The Natapoc project lies within reach 10. After creating the project appendix the projects were ranked based upon multiple criteria to arrive at a total biological benefit score. The Natapoc project ranked in the top five projects to implement.
The Regional Technical Team’s (RTT) Revised Biological Strategy lists the Upper Wenatchee area as a “priority 1” for restoration activities. As a priority 1 the restoration action type that is recommended is “Increase LWM retention and recruitment to increase complexity in a manner that is consistent with natural channel structure and function. Channel structure and form is ranked as the number one “Ecological Concern” for the Upper Wenatchee River.
Additionally, the “Upper Columbia Spring Chinook Salmon and Steelhead Recovery Plan” indicates that LWM recruitment and retention is an issue in the Upper Wenatchee and that project actions that focus on this type of habitat enhancement treatment will benefit listed salmonids species in this watershed.
Project Plan:
All project elements described above will be directly adjacent to the mainstem Upper Wenatchee River. All of the project elements are within the 100-yr. floodplain. In addition, the extensive existing road network will be utilized to access all project areas.
All trees and slash removed for construction activities shall temporarily stockpiled and reincorporated into the finished product as slash. Any removed vegetation greater than 6 inches in diameter and 15 feet long shall be incorporated into the structures to add roughness and further stability. All trees removed within clearing limits shall be removed whole with rootwad and utilized for in-water structures where deemed appropriate by project engineer.
The proposed project will be constructed during the approved Department of Fish and Wildlife (WDFW) in-water work window. For this project area the approved in-water work window is from July 15th - August 15th, 2015.
During in-water work a bulk bag cofferdam shall be constructed of several units of bulk bags abutted side by side to create a row that isolates the construction. Bulk bag cofferdams shall be sealed using plastic sheeting and held in place with individual sandbags. The bulk bags will be filled with washed WDFW approved fish-mix and if advised spread on-site in the mainstem upon cofferdam removal. The general approved spec. for this gravel is 3-” round, washed rock. The plastic sheeting shall be draped along the channel bottom on both sides of the cofferdam with outward edge of sheeting minimum 4-feet from toe of cofferdam. The draped portion of plastic sheeting shall be pinned to the channel bed by minimum of two rows of standard sandbags. The construction side edge of plastic sheeting shall be toed into the channel bed minimum 1-ft. toeing in the outward edge of plastic sheeting shall occur after the cofferdam is closed to prevent turbidity to the aquatic environment. Upon individual structure completion the cofferdam will be removed, but not prior to turbidity removal through settlement.Turbidity monitoring probes will be placed prior to any in-water work at both upstream and downstream locations. Monitoring standards will be per Washington State Department of Ecology’s (DOE) turbidity monitoring protocol.
Silt fencing will be employed at locations shown in that attached planset by the contractor. Fencing will installed along the downhill perimeter of the construction areas. Silt fencing shall only be removed when they have served their useful purpose, but not before the upslope area has been permanently protected and stabilized. Silt fencing will also be inspected daily to ensure its effectiveness. In addition, the staging area adjacent to the river will also be contained with silt fencing during construction activities.
The large woody material structures will be constructed by excavating a trench along the face of the bank and embedding the lateral pieces of wood into the bank. This will be the method used for both the complexity jams and the larger cover jam. The vertical piles will be installed using a vibrasonic pile driver; no impact driver will be allowed to be used.
This property was purchased by the Yakama Nation several years ago with the intent of restoring a relic disonnected side-channel located on the property. Unfortunately during soil investigations it was determined that the soils were too unconsolidated, fines, to be feasibly be able to construct the channel. A success of this is that now this wetland complex that currently exists on the property will now be protected under a land management plan so that no further development will be allowed on the site.
