ida-bonner841-1_HydraulicsMemo.pdf

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

TO: Brandon Stokes, WFLHD Project Manager FROM: Jennifer Mora, WFLHD Hydraulics Engineer DATE: December 08, 2023 SUBJECT: Trestle Creek Rd., MP 100 to 103 – ID BONNER 841(1)

Bank Stabilization Report

Background

Trestle Creek Road, United States Forest Service (USFS) Route 275, is a popular access for recreational and commercial visitors to the Trestle Creek area of the Kaniksu National Forest, part of the Idaho Panhandle National Forests. The existing roadway, a gravel logging road with a varying width (14 – 27 feet), parallels Trestle Creek, a 9.9 mile tributary that outfalls to Lake Pend Oreille, providing access to more than 88,000 acres of Forest Service lands. Trestle Creek is an important bull trout spawning stream in the Pacific Northwest, hosting annual spawning runs for adult fish from Lake Pend Oreille. The scope of this project is to reconstruct, and pave, the existing gravel road to match existing width and widen, where feasible, to install vehicle turnouts. Work will also include subgrade stabilization, streambank stabilization, and safety improvements.

High flow events along Trestle Creek have resulted in damage to multiple roadway sites which will be repaired under this project. This report covers bank stabilization design assumptions and recommendations at Trestle Creek Rd, MP 100 to 103.7. Western Federal Lands Highway Division (WFLHD) will complete the design and administer the construction contract in partnership with USFS. Recommendations for locating and stabilizing the new road embankment as well as design assumptions are presented.

Recommended Repairs

Bank stabilization is recommended for controlling erosion along the toe of the new road embankment (see attached drawings). Stabilizing the roadway embankment, utilizing buried riprap revetments and buried log revetments, will require filling into the active channel at each of these locations. Channel encroachments are limited to facilitate construction and promote improved hydraulic conditions for fish after construction.

Site Conditions

Trestle Creek is a small perennial stream characterized by a moderate slope (3.5 – 7.8 percent), coarse non‐cohesive bed material, composite banks and step‐pool and cascade profile. Trestle Creek flows southwest and is paralleled by Trestle Creek Rd., NF‐275, to the west. The project begins at the intersection of SH‐200 (MP 100.00) and ends at the USFS boundary (MP 103.70).

The active channel width of Trestle Creek is approximately 30 to 60 feet wide and 2.5 feet deep.

Bank material deposited in the stream consists of non‐cohesive material, gravel, cobbles, boulders, and large wood. Woody vegetation is present along bank lines in most sections.

Memo to: Brandon Stokes, WFLHD Project Manager December 08, 2023

Unstable banks, with mild to high erosion rates, are characterized by fallen trees, sparse vegetation along bank lines, steep cut slopes, point bars immediately downstream of eroding sections and irregular indentations along bank lines.

Idaho Fish and Game (IDFG) completed construction of in‐stream restoration features along Trestle Creek during the summer of 2021. Installations consisted of large boulder placement, felled trees, log deflection barbs and channel spanning log jams, in addition to excavating a new channel to redirect main channel flow to a primary channel, away from the road, at two sites (Site 2 and 4).

Shifting the active channel away from the road would require filling‐in the old channel, effectively creating a floodplain bench along the road embankment, and incorporating additional measures to prevent channel migration and eliminate the need for bank protection. Without these measures, the potential for the creek to migrate back into the original channel and along the road embankment, posing a risk to the roadway matrix, would still exist. As such, bank protection of the embankment will need to be installed along each site. Understanding that the site is an important Bull Trout spawning stream, care has been taken to limit proposed encroachments into the existing channel, add roughness in the form of large wood and roughened toe along proposed bank stabilization sites, and use of design/construction methods consistent with stream simulation and fish passage design. The goal of proposed bank stabilization along Trestle Creek is to protect the road, and maintain similar habitat benefits for Bull Trout, while ensuring roadway stability and user safety along this important access.

The naming convention, 1‐4, used to reference and describe proposed bank stabilization sites follows the proposed road alignment stationing, in increasing order, with Site 1 downstream and Site 4, upstream. The naming convention, consistent with the naming convention used by IDF&G in‐stream restoration plans (2021), was maintained for this project to facilitate identification of sites where bank stabilization needs were identified early in scoping. The naming convention, 1‐ 4, used to identify sites by reach is further discretized (e.g. 1A, 1B, 2A, 2B, 3A‐1, 3A‐2, 3B, etc.), in the plans and this report, to reflect site conditions and proposed design layout.

Site conditions, and proposed designs, are presented below, upstream to downstream, Site 4 to Site 1, to effectively capture hydraulic conditions and up/downstream reach interactions that were used to inform design.

‐ Site 4: STA. 130+15.35 – 131+39.60 ‐ Site 3: STA. 82+72.22 – 82+98.35; 84+27.61 – 85+73.18; 86+53.86 – 88+35.25 ‐ Site 2: STA. 81+00.00 – 81+85.00; 81+85.00 – 82+72.22 ‐ Site 1: STA. 73+74.00 – 75+05.90; 76+08.00 – 77+28.00

Site #4, Sta. 130+15.35 – 131+39.60 Site 4 is the most upstream bank stabilization site, located at Sta. 130+15.35 – 131+39.60, where Trestle Creek flows northeast to southwest along the east side of Trestle Creek Rd. Residential land use along the west side of the road makes shifting the road away from the creek impractical.

The existing road alignment is fairly straight, running parallel to the existing channel, immediately downstream of a highly dynamic channel section, characterized by wide shallow flow condition, before splitting into two channels and reconnecting approximately 210 feet downstream. The low flow (north) channel is constrained by the existing alignment on the right and a small well‐ vegetated floodplain bench on the left, immediately north of the main (south) channel. The existing road alignment immediately upstream of Site 4 is observed to experience overtopping at the 5‐yr event through sections where the road is approximately 3‐4 feet above the existing channel bottom.

Site 4 is located at the outside of a small meandering bend, along the proposed low flow channel where Trestle Creek flows are split between a low flow (north) and primary (south) channel. In‐ stream improvements, installed by IDFG (2021), consist of excavation of a primary (south) channel, a loosely constructed log jam upstream of Site 4, (i.e. placement of large wood, and rootwads, along the wide, shallow, upstream section), and small barb located immediately upstream of the existing well, meant to redirect flow towards the well, after in‐stream improvements worked to divert flows away from the structure. Recent (12/2022) observations by IDFG indicate that felled trees, racking of wood and debris along the primary (south) channel worked to redirect main channel flows towards the proposed low flow (north) channel along the steep embankment, confirming a need for additional protection and bank stabilization through this section. A small pool, approximately 1 foot depth, was observed immediately downstream of the in‐stream barb, installed to redirect flow towards the well.

The embankment along Site 4 is a cobble and gravel dominated reach characterized by steep cut slopes that vary between 1V:1.5H to 1V:2H. The proposed low flow (north) channel extends towards the roadway at a wide pool, immediately downstream of a small cascade. Small wood has racked, or collected, upstream of the pool along the existing embankment immediately upstream of a steep cut (highly eroded bank), where riprap is regularly repaired/installed to maintain existing slopes. The existing edge of shoulder is approximately 2.5 feet from the highly eroded bank near an existing well. The floodplain along the south side of the low flow channel is narrow with well‐established trees and dense vegetation. Maintenance, local residents, and IDFG, have communicated difficulties, and the need for on‐going repairs, at this site located immediately downstream of a highly dynamic channel section where the embankment is steep, low, and susceptible to ongoing erosion. Racked wood observed upstream of the small pool, and along the embankment, is considered to have low stability due to poor embedment and observed scour at the toe of the existing slope. Active channel width is approximately 30 to 40 feet, along the low flow (north) channel, and 25 to 30 feet, along the main (south) channel, and 2 to 3 foot depth. Flood prone width is approximately 105 to 110 feet, 3.5 to 4 foot depth. Site constraints, as identified above, limit placement of large wood in the channel to avoid encroachments and upstream impacts.

Recommendations for Site 4 consist of the following:

‐ Buried riprap revetment, 1V:1.5H, to limit channel encroachment.

‐ Removal of existing well, and log sill, to install bank protection through dynamic channel section.

‐ Set the top of the revetment at shoulder elevation to provide protection during high flow events.

‐ Set the top of the revetment toe below historic scour elevation, or to refusal, to limit excavation impacts.

‐ Backfill placed riprap (coarse sediment particles) with conserved streambed material, washing in with smaller gradation streambed material, to fill voids in subsurface layer, consistent with observed site conditions and Stream Simulation Fish Passage design methodology (Bunte and Abt, 2001).

‐ Install roughened toe (i.e. boulder clusters) to increase roughness, and flow diversity along proposed (streambed material) backfilled embankment toe.

‐ Tree plantings/seedings along buried revetment, where applicable.

Site #3, STA. 82+72.22 – 88+35.25:

Site 3, located approximately 0.8 miles downstream of Site 4, immediately upstream of Site 2, is a confined, boulder and cobble dominated reach, characterized by a straight channel pattern, high gradient/energy, with minimal floodplain development and high slope/channel interactions.

The reach is characterized by step‐pool morphology, and steep cuts along the existing embankment. Trestle Creek flows east to west through this reach, constrained by the existing road alignment on the right and steep slopes, with limited access to a narrow vegetated floodplain, on the left. Signs of active erosion, (i.e. sparsely vegetated embankment, undercut large boulders, felled trees, installed riprap, irregular indentations, and scour of fines between larger particles, etc.), are observed along the existing embankment. In‐stream improvements, installed by IDFG (2021), consist of placement of large boulders, and small wood, along toe of existing embankment through this section.

Site 3, located immediately upstream of Site 2, is separated into three sections, 3A‐1, 3A‐2 and 3B, based on site conditions and proposed bank stabilization.

Site #3B, STA. 86+53.86 – 88+35.25:

Site 3B is the upstream (Site 3) site, characterized by a steep slope, 4% – 7.8%, sections of steep, irregular indentations and signs of erosion along the embankment, large 8’+ boulders along banks that constrict the channel and contribute to tight channel geometry.

Active channel width is approximately 25 to 40 feet, 1.2 to 2.5 feet deep. Floodprone width is approximately 36 to 60 feet, 3.0 to 3.5 foot depth.

Site constraints, (i.e. tight channel geometry and high gradient/energy reach), limit opportunities for placement of large wood in the channel to avoid encroachments and upstream impacts.

Recommendations for Site 3B consist of the following:

‐ Buried riprap revetment, 1V:1.5H, to match existing slopes and limit channel encroachment.

‐ Set the top of the revetment below shoulder elevation, above 100‐year water surface elevation, to provide protection during high flow events.

‐ Set the top of the revetment toe below historic scour elevation, or to refusal, to limit excavation impacts.

‐ Backfill placed riprap (coarse sediment particles) with conserved streambed material, washing in smaller gradation streambed material, to fill voids in subsurface layer, consistent with observed site conditions and Stream Simulation Fish Passage design methodology (Bunte and Abt, 2001).

‐ Move, conserve and protect large (5’ ‐ 8’+) boulders encroaching and constricting channel on left bank, towards upstream end of proposed revetment, to open channel, allow flow diversion during construction, and provide resting opportunity for fish after construction.

‐ Install roughened toe (i.e. boulder clusters) to increase roughness, and flow diversity along proposed (streambed material) backfilled embankment toe.

‐ Tree plantings/seedings along buried revetment, where applicable.

Site #3A‐2, STA. 84+27.61 – 85+73.18:

Site 3A‐2, located immediately downstream of Site 3B and upstream of Site 3A‐1, is characterized by a steep slope, 3.5% – 6.3%, sections of steep, irregular indentations and signs of erosion along the embankment, large 5’ ‐ 8’+ boulders along banks that constrict the channel, and contribute to tight channel geometry. Active channel width is approximately 28 to 40 feet, 1.2 to 3.4 feet deep. Floodprone width is approximately 36 to 57 feet, 3.1 to 5.6 foot depth.

Site constraints, (i.e. tight channel geometry and high gradient/energy reach), limit opportunities for placement of large wood in the channel to avoid encroachments and upstream impacts.

Recommendations for Site 3A‐2 consist of the following:

‐ Buried riprap revetment, 1V:1.5H, to match existing slopes and limit channel encroachment.

‐ Set the top of the revetment below shoulder elevation, above 100‐year water surface elevation, to provide protection during high flow events.

‐ Set the top of the revetment toe below historic scour elevation, or to refusal, to limit excavation impacts.

‐ Backfill placed riprap (coarse sediment particles) with conserved streambed material, washing in smaller gradation streambed material, to fill voids in subsurface layer, consistent with observed site conditions and Stream Simulation Fish Passage design methodology (Bunte and Abt, 2001).

‐ Install roughened toe (i.e. boulder clusters) to increase roughness, and flow diversity along proposed (streambed material) backfilled embankment toe.

‐ Tree plantings/seedings along buried revetment, where applicable.

‐ Remove existing culvert, characterized by performance problems including buried outlet, and replace with 18‐inch pipe culvert and riprap apron at outlet, to improve drainage.

Site #3A‐1, STA. 82+72.22 – 82+98.35:

Site 3A‐1, located immediately downstream of Site 3A‐2 and upstream of Site 2, is a lower gradient section, 3.0% – 3.5%, immediately downstream of tight, steep channel geometry and high energy/gradient reach (3A‐2 and 3B) before transitioning into a wider flow condition, where the stream is constrained by the existing road alignment on the right, at the outside of a wide meandering bend. Site 3A‐1 is immediately upstream of a fixed log jam, installed as part of in‐stream work completed by IDFG in 2021, that works to constrict and divert main channel flows toward the primary (south) channel, away from the existing embankment and proposed low flow (north) channel, during low flow conditions. During high flow, the log jam is overtopped and flows impinge over the structure onto steep cut, 1V:1H, slopes along the existing downstream embankment at Site 2.

The bend immediately upstream of Site 2, is characterized by a narrow shallow floodplain slope, with established large trees, that sit approximately 1 to 2 feet above ordinary high water. Though there is a small vegetated buffer, characterized by milder slopes and trees through this section, site conditions, up and downstream of Site 3A‐1, inform the need to incorporate stream training along bend to protect trees (3A‐1) and downstream (Site 2) embankment from impinging flows and ongoing erosion during high flow conditions.

Active channel width is approximately 30 to 45 feet, 1.3 to 1.5 feet deep. Floodprone width is approximately 42 to 55 feet, 2.0 to 3.2 foot depth.

Recommendations for Site 3A‐1 consist of the following:

‐ Backfill launchable riprap, above ordinary high water, along existing bank to launch into the channel if erosion continues along toe of existing right bank embankment between site of buried log revetment at 3A‐1 and Site 3A‐2.

‐ Buried root wad log revetment, backfilled along existing embankment, along outside meander bend through clearing used as access for construction of in‐ stream improvements (i.e. log jam) to incorporate stream training, add roughness, dampen energy/velocities along high energy bend and shift channel energy away from road embankment. Logs are proposed to be buried in bank, with root wads protruding into channel, to protect low banks by reducing shear stress acting on bank toe, and promote scalloping between logs along face of constructed floodplain bench and formation of scour pools along toe with woody cover.

Use root wads with 22 – 26 foot minimum trunk length and 18 to 24‐inch diameter with root wad attached.

Use root wads with root fans having a minimum diameter of 5 feet and minimum area of 25 square feet.

Place root wads spaced approximately 5‐10 feet apart O.C., trunk to trunk Embed root wads in the revetment with a maximum of 8.5 feet projecting, angled at 23 degrees, root fans oriented upstream, from the embankment slope.

‐ Set the top of the revetment at shoulder elevation to provide protection during high flow events.

‐ Set the top of the revetment toe below historic scour elevation, or to refusal, to limit excavation impacts.

‐ Backfill placed riprap (coarse sediment particles) with conserved streambed material, washing in smaller gradation streambed material, to fill voids in subsurface layer, consistent with observed site conditions and Stream Simulation Fish Passage design methodology (Bunte and Abt, 2001).

‐ Install roughened toe (i.e. boulder clusters) to increase roughness, and flow diversity along proposed (streambed material) backfilled embankment toe.

‐ Conserve and protect existing trees along embankment.

‐ Tree plantings/seedings along buried revetment, where applicable.

Site #2, STA. 81+00.00 to 82+72.22:

Site 2, located immediately downstream of Site 3, consists of fixed log jam at upper limits of reach, installed as part of in‐stream work completed by IDFG in 2021. In‐stream work also consisted of excavation of primary (south) channel, to redirect flows to a primary channel away from road, leaving existing channel along embankment as low flow (north) channel.

Trestle Creek flows northeast to southwest along the east side of Trestle Creek Rd. The existing road alignment is characterized by a horizontal curve that extends towards a steep fill slope north of the existing alignment that makes shifting the alignment away from the creek impractical.

Trestle Creek follows the horizontal curve of the existing alignment through a low flow channel downstream of a fixed log jam diversion at the upstream end of the reach. The existing road embankment along Site 2, located at the outside meandering bend, is characterized by steep cut, 1V:2H to 1V:1H, slopes, sparse/fallen vegetation, exposed roots, large leaning, undercut and/or fallen trees, and leaning roadway markers, all of which are indicators of active bank erosion. The existing edge of shoulder opposite of the fixed log jam, STA. 82+00.00, is approximately 1 foot from the steep cut slope embankment.

Site 2, located immediately downstream of Site 3, is characterized by a milder stream gradient, 1.8% to 4.8%, coarse gravel, cobble and boulder dominated reach. The site is downstream of a fixed log jam, that works to divert main channel flow towards the main (south) channel and a small low flow diversion for the proposed low flow (north) channel during low flow conditions.

The low flow channel is accessible upstream of the log jam and through openings across a low elevation vegetated buffer that separates the primary (south) and low flow (north) channel.

Flows are effectively diverted towards the primary (south) channel during low flow, but the tight geometry along the low flow channel create high velocity/shear zone during high flow events.

The existing log jam and vegetated buffer, separating primary and low flow channel, contribute to flow impingement on existing steep cut embankments that put the existing roadway at risk.

Lack of bank stabilization along this section can promote loss of already undercut trees along bank lines, identified as protecting/buttressing the existing roadway embankment, and contribute to ongoing bank instability and risk to the existing embankment.

Active channel width is approximately 42 to 70 feet, 0.8 to 1.4 feet deep. Floodprone width is approximately 97 to 105 feet, 1.4 to 2.4 foot depth.

Recommendations for Site 2B (STA. 81+85.00 – 82+72.22) and Site 2A (STA. 81+00.00 – 81+85.00) consist of the following:

‐ Site 2B (STA. 81+85.00 – 82+72.22): Backfilled riprap protection, 1V:1.5H, without toe to protect embankment at and downstream of existing log jam along low flow channel. Care will be taken to key‐in riprap, north of existing log jam, to protect existing embankment from impinging flows without encroaching onto low flow channel.

‐ Site 2A (STA. 81+00.00 – 81+85.00): Backfilled riprap with roughened toe to build back embankment, along steep cut slopes, taking care to protect and preserve existing trees along bank. Undercut trees will be backfilled to provide support and protect from ongoing erosion. Set the top of the revetment toe below historic scour elevation, or to refusal, to limit excavation impacts.

‐ Set the top of the revetment at shoulder elevation to provide protection from impinging flows during high flow events.

‐ Backfill placed riprap (coarse sediment particles) with conserved streambed material, washing in smaller gradation streambed material, to fill voids in subsurface layer, consistent with observed site conditions and Stream Simulation Fish Passage design methodology (Bunte and Abt, 2001).

‐ Install roughened toe (i.e. boulder clusters) to increase roughness, and flow diversity along proposed (streambed material) backfilled embankment toe.

‐ Conserve and protect existing trees along embankment.

‐ Place (3) 5‐ft diameter rootwad logs, and large boulder ballast, along transition between

Site 2 and 3, taking care not to fill low flow channel. Rootwad logs are proposed to add roughness and protect downstream embankment from flow impingement during high flow events.

‐ Tree plantings/seeding along buried revetment, where applicable.

Site 1, STA. 73+74.00 – 75+05.90, 76+08.00 – 77+28.00:

Site 1 is the furthest downstream reach, located immediately downstream of Site 2 as the channel bends away from the existing road alignment before meandering back towards embankment through a tight section where the channel is constrained between the existing road alignment on the right, and a low elevation floodplain bench on the left. The channel is characterized by a low to moderate gradient, 1.8% ‐ 6%, dominated by gravel, cobbles and boulders through varying channel geometry, transitioning between steep riffles and step‐pool morphology. A steep fill slope immediately west of the existing road alignment makes shifting the road away from the creek impractical. The channel opens up immediately after the tight section (1B), to a wide, expanded section (1A) where two 12‐inch diameter culverts, conveying flow from a roadway ditch and hillside seep, outfall at a low elevation bench along the bank.

The existing culverts, a 12‐inch concrete pipe culvert and buried HDPE installation, are characterized by performance problems including buried inlet, and localized scour at the outlet.

The existing edge of shoulder is approximately 2 feet from the steep vertical cut in the embankment where maintenance has communicated an ongoing need for placement/repair of riprap protection along shoulder.

In‐stream restoration completed by IDFG (2021) consists of placement of cobbles, boulders, and large woody debris as a buffer along the toe of the existing bank, and associated formation of shallow pools, along wide section (1A), and a long log barb placed downstream of the tight section along the toe of the existing embankment (1B).

The active channel width through this segment is approximately 26 to 60 ft, 1 – 2 feet deep.

Floodprone width ranges from 34 – 72 feet, 1.8 to 5.1 feet deep.

Recommendations for Site 1B (STA. 76+08.00 – 77+28.00) and Site 1A (STA. 73+74.00 – 75+05.90) consist of the following:

‐ Site 1B (STA. 76+08.00 – 77+28.00): Backfilled riprap protection, 1V:1.5H, buried with conserved streambed material and large roughness features along toe, to protect steep cut embankment and large trees along banks.

o Set the top of the revetment toe below historic scour elevation, or to refusal, to limit excavation impacts.

o Set the top of the revetment at shoulder elevation to provide protection from impinging flows during high flow events.

o Backfill placed riprap (coarse sediment particles) with conserved streambed material, washing in smaller gradation streambed material, to fill voids in subsurface layer, consistent with observed site conditions and Stream Simulation Fish Passage design methodology (Bunte and Abt, 2001).

o Install roughened toe (i.e. boulder clusters) to increase roughness, and flow diversity along proposed (streambed material) backfilled embankment toe.

o Tree plantings/seeding along buried revetment, where applicable.

‐ Site 1A (STA. 73+74.00 – 75+05.90): Backfill launchable riprap, above ordinary high water, along existing bank to launch into the channel if erosion continues along toe of existing right bank embankment. Care will be taken to protect and preserve installed large wood and roughness features along toe of existing bank.

o Remove (2) existing minor drainage 12‐inch culverts and replace with (2) 18‐inch concrete pipe installations, riprap headwalls at inlet and outlet, and riprap infiltration trench/riprap pad at outlet.

‐ Conserve and protect existing trees along embankment.

Stream Impacts

The reconstructed road embankment, and proposed bank stabilization, will shift the current bank toe 4 – 12 feet into the active channel. The embankment and riprap revetment will armor and roughen the toe of the laterally migrated bank line. Water surface elevations and average channel flow velocities vary along the length of the restored embankment. (See Tables 2 ‐ 8).

Predicted changes in water surface elevations and average channel flow velocities are not large enough to noticeably diminish current wood and sediment transport processes, or increase the north stream bank migration rate. The water surface elevation may increase slightly from existing conditions, due to added roughness features, and velocities should decrease for the same reason.

The riprap revetment ties into natural bank conditions and natural erosion controls in channel.

The active channel is expected to continue to migrate freely across the limited floodplain in response to sediment deposition and large woody debris accumulation.

Construction

A flow diversion structure may or may not be needed for separating the stream from the work area. If an attempt is made to dewater the work area, the permeability of the streambed material and hydraulic gradient across the barrier will allow water to freely flow from the stream under the barrier and into the work area. The flow rate will likely be too great for pumping. Anticipate excavating for riprap placement and placing riprap in standing water.

Flow diversion structure material and installation, maintenance, and removal activities must comply with environmental permit requirements and minimize fish from entering the work area.

Perform in‐water work from July 1 through August 31 (dates inclusive) to ensure protection of redds, given delicate habitat. Terminate the diversion structure outside of the stream in the overbank areas as necessary to prevent water flowing around the structure ends. Before closing the structure, remove fish from the work area to the level specified in the environmental permits using methods approved by the US Fish and Wildlife Service (USFWS).

Provide, install, and maintain diversion screens at pump intakes consistent with the Idaho Department of Fish and Game (IDFG) screening requirements for water diversion.

IDFG, Idaho Department of Water Resources, Idaho Department of Environmental Quality, U.S.

Environmental Protection Agency, and USFWS will restrict the release of turbidity from the work area into the stream. The agencies may require turbidity control and monitoring, and should be contacted for specific requirements and allowable discharge limits. The agencies may require pumping the turbid water from the work area before the flow barriers are removed. Pumping will need to continue until the turbidity discharge limitations can be met. The work area water should be discharged at an upland settlement area. Flow barriers and erosion controls may be needed at the settlement area.

Peak Discharges Peak discharges were estimated using U.S.G.S. StreamStats and corroborated using IDFG recorded flows and provided HEC‐RAS model and Rating Curve. The Trestle Creek watershed is characterized by a total drainage area of 19.6 square miles and mean annual rainfall of 45.5 inches. The watershed is densely forested (92 percent) with large mature trees, and mountainous, with 4280 feet of relief. The mean basin slope is 46 percent, with more than 80% of slopes greater than 30 percent.

Water Surface Elevations and Flow Velocities Water surface elevations and flow velocities were estimated using a 2D HEC‐RAS Hydraulic Model, a program that performs two dimensional hydraulic calculations. Cross sections were generated using ground survey data and proposed surface data. Three individual 2D meshes were used to model sites of interest. All three meshes were setup in a single geometry and computed.

Breaklines were implemented to align faces with high ground features and capture high velocities. Models were run using the Diffusion wave equation set, 4 second time step and 5 ft mesh grid size.

Riprap Revetment Design Analysis U.S. Army Corps of Engineers (USACE) procedure (EM 1110‐2‐1601, 1991) Steep Slope Riprap Design, for slopes from 2 to 20 percent, was used to determine riprap size, revetment thickness, and revetment finished slope at both the upstream and downstream revetment sections. Flow velocities and depths used in the procedures were obtained from the HEC RAS analysis.

A higher factor of safety was selected due to the uncertainty and potential for large woody debris jams to deflect flows around and impinge directly on the riprap at each site. This could generate higher than expected flow velocities and turbulence that could damage the revetments. The mean longitudinal slope of the channel, 4.5 percent, and proximity of flows (risk) to the roadway informed the choice to proceed with riprap design guidance. All riprap will be buried and voids filled with fines, to match existing site subsurface site conditions consistent with Stream Simulation Design Methods and practice. Streambed material and vegetation were added to provide additional long term bank stabilization features.

Log Buoyancy Design Analysis The US Department of Agriculture, Forest Service, National Stream & Aquatic Ecology Center tool, Computational Tool For Evaluating the Stability of Large Wood Structures, (Rafferty, M. 2016) was used to evaluate the size, species, configuration, and stability design for log installations proposed for stream enhancement and bank stabilization along Site 3A‐1. Flow velocities and depths used in the procedure were obtained from HEC‐RAS 2D model analysis. Modeled velocities and depths at the site indicate a likelihood for large woody debris to mobilize if not ballasted or secured against shear and buoyant forces. A stability analysis was performed to ensure proposed root wads are designed with sufficient embedment to resist mobilization.

Coarse sediment, and riprap, is proposed as ballast over placed logs to protect against hydraulic erosive forces. Riprap ballast is to be buried, with 2.5 feet of conserved streambed material, to provide additional ballast, fill voids consistent with existing site subsurface conditions and stream simulation design practice, and allow for plantings along newly constructed floodplane bench. A roughened toe, along the face of the root wad revetment, will contribute to added roughness and flow diversity in the channel.

Logs are to be embedded into the bank, so that root wads are pointing upstream, to gain stability as drag forces push them into the bank. A factor of safety of 2.00 was applied to calculations for vertical force balance, horizontal force balance, and moment force balance. Log stability analysis was completed assuming a conservative “worst case scenario” for log, 24‐inch diameter and 26‐ foot length, and ballast, assumed dry unit weight for soil was 133.7 pounds per cubic foot, compared to riprap 165 pounds per cubic foot. The unit weight of wood, green and air‐dried, was assumed to be 38.0 and 33.5 pounds per cubic foot for Douglas Fir, and 27.0 and 22.4 pounds per cubic foot for Western Red Cedar, respectively. Based on conservative assumptions, logs were found to be stable vertically, horizontally and with respect to moment forces. Any log that is shorter, or more narrow diameter, is assumed to remain stable based on stability analysis.

Attachments: Table 1 – Peak Discharge Summary Table 2 – 8 Flow Conditions at Bank Stabilization Sites Figure 1 – Project Location Map Figure 2 – Drainage Area Map Appendix A: HEC‐RAS Model Results Figure 3 – HEC‐RAS 2D Model, Site 1, Buried Revetment Figure 4 – HEC‐RAS Terrain, Site 1, Existing vs. Proposed Figure 5 – 100‐Yr Flow Velocity, Site 1, Buried Revetment Figure 6 – 100‐Yr Flow Depth, Site 1, Buried Revetment Figure 7 – HEC‐RAS 2D Model, Site 2 and 3 Figure 8 – HEC‐RAS Terrain, Site 2‐3, Existing vs. Proposed Figure 9 – 100‐Yr Water Surface Elevation, Site 2, Backfilled Revetment Figure 10 – 100‐Yr Flow Velocity, Site 2, Backfilled Revetment Figure 11 – 100‐Yr Flow Depth, Site 2, Backfilled Revetment Figure 12 – 100‐Yr Water Surface Elevation, Site 2, Backfilled Revetment Figure 13 – 100‐Yr Flow Velocity, Site 3A‐1, Log Revetment Figure 14 – 100‐Yr Flow Depth, Site 3A‐1, Log Revetment Figure 15 – 100‐Yr Water Surface Elevation, Site 3A‐1, Log Revetment Figure 16 – HEC‐RAS Terrain, Site 3, Existing vs. Proposed Figure 17 – 100‐Yr Flow Velocity, Site 3A‐2, Buried Revetment Figure 18 – 100‐Yr Flow Depth, Site 3A‐2, Buried Revetment Figure 19 – 100‐Yr Water Surface Elevation, Site 3A‐2, Buried Revetment Figure 20 – 100‐Yr Flow Velocity, Site 3B, Buried Revetment Figure 21 – 100‐Yr Flow Depth, Site 3B, Buried Revetment Figure 22 – 100‐Yr Water Surface Elevation, Site 3B, Buried Revetment Figure 23 – HEC‐RAS 2D Model, Site 4, Buried Revetment Figure 24 – HEC‐RAS Terrain, Site 4, Existing vs. Proposed Figure 25 – 100‐Yr Flow Velocity, Site 4, Buried Revetment Figure 26 – 100‐Yr Flow Depth, Site 4, Buried Revetment Figure 27 – 100‐Yr Water Surface Elevation, Site 4, Buried Revetment Appendix B: Plan / Profile Layout Drawings F.2 Site 1A Plan and Profile F.3 Site 1B Plan and Profile

F.4 Site 2A Plan and Profile F.5 Site 2B Plan and Profile F.6 Site 3A‐1 Plan and Profile F.7 Site 3A‐2 Plan and Profile F.8 Site 3B Plan and Profile F.9 Site 4 Plan and Profile F.10 Excavation Details Appendix C: Photos Appendix D: Calculations Log Stability Analysis 74+05 Log Stability Analysis 74+23.11 cc: Sven Leon, WFLHD Hydraulics Functional Team Leader

Table 1. Peak Discharge Summary

Drainage Area

Site

Q-Low 2-year 10-year 25-year

50-year

100-year

500-year

(mi2)

Trestle Creek

19.6 35 310 579 715 827 967 1250

Table 2. Flow Conditions at Revetment Site #1B – Buried Riprap and Channel Mitigation.

Discharge (cfs)

2-Year

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2295.3 2297.5 2297.9

Water Surface Elevation – Proposed Condition (feet)

2295.3 2297.6 2298.0

Average Channel Flow Velocity – Existing Condition (ft/sec)

3.6 5.1 5.8

Average Channel Flow Velocity – Proposed Condition (ft/sec)

3.7 5.3 6.0

Table 3. Flow Conditions at Revetment Site #2A – Backfilled/Buried Riprap.

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2315.7 2317.4 2316.9

Water Surface Elevation – Proposed Condition (feet)

2316.0 2317.5 2317.0

Average Channel Flow Velocity – Existing Condition (ft/sec)

1.6 2.9 3.1

Average Channel Flow Velocity –

1.8 3.5 3.8

Table 4. Flow Conditions at Revetment Site #2B – Backfilled/Buried Riprap at Fixed Log Jam.

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2318.7 2020. 2320.4

Water Surface Elevation – Proposed Condition (feet)

2317.7 2319.6 2321.0

Average Channel Flow Velocity – Existing Condition (ft/sec)

1.8 3.1 3.4

Average Channel Flow Velocity –

1.2 3.2 3.5

Table 5. Flow Conditions at Revetment Site #3A-1 – Rootwad Log Revetment and Channel Mitigation.

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2322.3 2323.4 2323.7

Water Surface Elevation – Proposed Condition (feet)

2322.5 2323.7 2323.9

Average Channel Flow Velocity – Existing Condition (ft/sec)

1.2 2.5 2.8

Average Channel Flow Velocity –

1.4 2.8 3.0

Table 6. Flow Conditions at Revetment Site #3A-2 – Buried Riprap and

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2327.8 2329.6 2330.0

Water Surface Elevation – Proposed Condition (feet)

2327.9 2329.7 2330.1

Average Channel Flow Velocity – Existing Condition (ft/sec)

4.8 6.5 6.8

Average Channel Flow Velocity –

5.2 6.9 7.2

Table 7. Flow Conditions at Revetment Site #3B – Buried Riprap and

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2340.2 2342.6 2343.1

Water Surface Elevation – Proposed Condition (feet)

2340.3 2342.7 2343.2

Average Channel Flow Velocity – Existing Condition (ft/sec)

3.9 5.6 5.9

Average Channel Flow Velocity –

3.7 5.4 5.8

Table 8. Flow Conditions at Revetment Site #4 – Buried Riprap and Channel

Mitigation.

50-Year

100-Year

Water Surface Elevation – Existing Condition (feet)

2497.8 2498.9 2499.4

Water Surface Elevation – Proposed Condition (feet)

2497.3 2498.6 2498.8

Average Channel Flow Velocity – Existing Condition (ft/sec)

3.6 4.8 4.9

Average Channel Flow Velocity –

3.0 4.1 4.2

Appendix A: HEC‐RAS Model Results

Bank Stabilization

Site Location

Project Site Location

Image from ESRI, printed 04/19/2023

Lake Pend Oreille

Site 3

Site 4

Site 1

Site 2

End Project

Start Project

N

FIGURE 1

TRESTLE CREEK ROAD

PROJECT LOCATION

0 1 miles

Image from ESRI, printed 04/19/2023

N

FIGURE 2

TRESTLE CREEK

DRAINAGE AREA

0 2 miles

Lake Pend Oreille

Site 2

Site 1

Site 4

Site 3

HECRAS 6.3 - Two-Dimensional hydraulic model.

US Hydro Boundary Mesh

FIGURE 3

Trestle Creek, Site 1

HECRAS 2-D MODEL

DS Normal Depth Boundary

Site1B

Site1A

FIGURE 4

Trestle Creek, Site 1 HECRAS 2-D Terrain

Existing vs. Proposed

Site1B

Site1A

Flow Velocity (Feet/sec)

1.5-yr

Q-Low

N

Design Value Location - Site 1B

FIGURE 5

Trestle Creek, Site 1B

100-YEAR FLOW VELOCITY

2-yr

500-yr

100-yr 50-yr

25-yr 10-yr

Flow Depth (Feet)

1.5-yr

Q-Low

N

Design Value Location - Site 1B

FIGURE 6

Trestle Creek, Site 1B

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr 50-yr

Water Surface Elevation (Feet)

Q-Low

1.5-yr

N

Design Value Location, Site 1B

FIGURE 7

Trestle Creek, Site 1B

100-YEAR WATER SURFACE

2-yr

500-yr

100-yr 50-yr

US Hydro Boundary Mesh

FIGURE 8

Trestle Creek, Site 2-3

HECRAS 2-D MODEL

DS Normal Depth Boundary Site3B, Buried Revetment

Site3A-2, Buried Revement Site2A, Backfilled Revetment

Site2B, Backfilled Revetment

Site3A-1, Log Revetment

Existing LogJam

FIGURE 9

Trestle Creek, Site 2-3

HECRAS 2-D TERRAIN

EXISTING VS. PROPOSED

Site2B, Backfilled Revetment

Site3A-2, Buried Revement

Site2A, Backfilled Revetment

Site3A-1, Log Revetment

Existing LogJam

Flow Velocity (Feet/sec)

1.5-yr

Q-Low

N

Design Value Location - Site 2

FIGURE 10

Trestle Creek, Site 2

100-YEAR FLOW VELOCITY

2-yr

500-yr 100-yr50-yr25-yr

0.5

1.5

2.5

3.5

4.5

Flow Depth (Feet)

1.5-yr

Q-Low

N

Design Value Location - Site 2

FIGURE 11

Trestle Creek, Site 2

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr 50-yr

2314.5

2315.5

2316.5

2317.5

2318.5

2319.5

Water Surface Elevation (Feet)

Q-Low

1.5-yr

N

Design Value Location, Site 2

FIGURE 12

Trestle Creek, Site 2

100-YEAR WATER SURFACE

2-yr

500-yr

100-yr 50-yr

0.5

1.5

2.5

3.5

4.5

Flow Velocity (Feet/sec)

1.5-yr

Q-Low

N

Design Value Location - Site 3A-1

FIGURE 13

Trestle Creek, Site 3A-1, Log Revetment

100-YEAR FLOW VELOCITY

2-yr

500-yr

100-yr 50-yr

0.5

1.5

2.5

3.5

4.5

Flow Depth (Feet)

1.5-yr

Q-Low

N

Design Value Location - Site 3A-1

FIGURE 14

Trestle Creek, Site 3A-1, Log Revetment

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr 50-yr

2319.5

2320.5

2321.5

2322.5

2323.5

2324.5

Water Surface Elevation (Feet)

Q-Low

1.5-yr

N

Design Value Location, 3A-1

FIGURE 15

Trestle Creek, Site 3A-1, Log Revetment

100-YEAR WATER SURFACE

2-yr

500-yr 100-yr

50-yr

FIGURE 16

Trestle Creek, Site 3

HECRAS 2-D TERRAIN

EXISTING VS. PROPOSED

Site3A-2, Backfilled Revetment

Site3B, Backfilled Revetment

Flow Velocity (Feet/sec)

1.5-yr

Q-Low

N

Design Value Location - Site 3A-2, Buried Revetment

FIGURE 17

Trestle Creek, Site 3A-2, Buried Revetment

100-YEAR FLOW VELOCITY

2-yr

500-yr 100-yr

50-yr

Flow Depth (Feet)

1.5-yr

Q-Low

N

Design Value Location - Site 3A-2, Buried Revetment

FIGURE 18

Trestle Creek, Site 3A-2

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr 50-yr

Water Surface Elevation (Feet)

Q-Low

1.5-yr

N

Design Value Location, 3A-2, Buried Revetment

FIGURE 19

Trestle Creek, Site 3A-2

100-YEAR WATER SURFACE

2-yr

500-yr 100-yr

50-yr

Flow Velocity (Feet/sec)

1.5-yr

Q-Low

N

Design Value Location - Site 3B, Buried Revetment

FIGURE 20

Trestle Creek, Site 3B, Buried Revetment

100-YEAR FLOW VELOCITY

2-yr

500-yr

100-yr 50-yr25-yr

Flow Depth (Feet)

1.5-yr

Q-Low

N

Design Value Location - Site 3B, Buried Revetment

FIGURE 21

Trestle Creek, Site 3B, Buried Revetment

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr

50-yr

Water Surface Elevation (Feet)

Q-Low

1.5-yr

N

Design Value Location, Site 3B, Buried Revetment

FIGURE 22

Trestle Creek, Site 3B Buried Revement

100-YEAR WATER SURFACE

2-yr

500-yr

100-yr 50-yr

US Hydro Boundary

Mesh

FIGURE 23

Trestle Creek, Site 4

HECRAS 2-D MODEL

DS Normal Depth Boundary

Site4

FIGURE 24

Trestle Creek, Site 4

HECRAS 2-D MODEL

Site4

Flow Velocity (Feet/sec)

1.5-yr

Q-Low

N

Design Value Location - Site 4

FIGURE 25

Trestle Creek, Site 4

100-YEAR FLOW VELOCITY

2-yr

500-yr 100-yr50-yr25-yr

0.5

1.5

2.5

Flow Depth (Feet)

1.5-yr

Q-Low

N

Design Value Location - Site 4

FIGURE 26

Trestle Creek, Site 4

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr 50-yr

2496.5

2497.5

2498.5

2499.5

Water Surface Elevation (Feet)

Q-Low

1.5-yr

N

Design Value Location, Site 4

FIGURE 27

Trestle Creek, Site 4

100-YEAR WATER SURFACE

2-yr

500-yr 100-yr

50-yr

Appendix B: Plan / Profile Layout Drawings

52.8'

12'

63.

1'

.9

12'

.9

P

L A

S T I C O

U T

L E

T

7'

C

M P O

U T

L E

T

C

M P I

N L E

T

P

L A

S T I C I

N L E

T

F I R

10'X10'X10'

C

E D

A R

Placed riprap, Method A, Class 4

Removal of pipe culvert

Existing ground geotextile fabric, Class 1, Type E

Separation-stabilization

OHW (Q1.5 Water Surface Elevation)

Q100 Water surface elevation

28.8 LNFT

18-inch pipe culvert

74+44.30

Placed riprap, Method A, Class 4

Placed riprap, Method A, Class 2

ID

STATESite 1A Profile

Removal of pipe culvert

Removal of pipe culvert

Method A, Class 4

Placed riprap, Method A, Class 4

Placed riprap, geotextile fabric, Class 1, Type E

Separation-stabilization

28.8 LNFT

18-inch pipe culvert

74+44.30

18-inch pipe culvert, 28.8 LNFT

74+48.30

(See Sheet F.3 for details)

Site 1B Profile

Clean and regrade ditch

Site 1B Bank Stabilization

Protect existing trees along embankment

N

7 7

0+30 0+40 0+50 0+60 0+70 0+80 0+90 1+00 1+10 1+20 1+30 1+40 1+50 1+60 1+70

2,275 2,275

2,280 2,280

2,285 2,285

2,290 2,290

2,295 2,295

2,300 2,300

2,305 2,305

2,310 2,310

1.75:1

2'

'1 '1

1.

:1

3.1'

:0

P

M

D e c e m b e r

[S

H E

E T

F

.2

S it e A

P la n P ro fi le c p w

-w o rk \d

\i d a b o n n e r_

B S

M

IT

L A

Y O

U T

S

H E

E T

S

S u rv F t-

D .d g n

SITE 1A 73+74.00 - 75+05.90

TRESTLE CREEK RD.,

BANK STABILIZATION,

PROJECT

NUMBER

SHEET

F.2

FLAP BONNER 841(1)

52.8'

12'

63.

1'

.9

12'

.9

P

L A

S T I C O

U T

L E

T

7'

C

M P O

U T

L E

T

C

M P I

N L E

T

P

L A

S T I C I

N L E

T

10'X10'X10'

Placed riprap, Method A, Class 4

Placed conserved streambed material

Existing ground Cuttings, Flailing alder plant seeding

Class 1, Type E geotextile fabric, Separation-stabilization

OHW (Q1.5 Water surface elevation)

Q100 Water surface elevation

Site 1B Profile

Roughened toe, boulder clusters

Place conserved streambed material

Placed riprap, Method A, Class 4

Site 1B, Buried Revetment

Channel thalweg

(See Sheet F.2 for details)

Site 1A Profile

ID

STATE

Riprap Crest El. 2299.3'

N

N54° 11'

09" E

N70°18'52"E N73°49'29"E

7 7

0+00 0+10 0+20 0+30 0+40 0+50 0+60 0+70 0+80 0+90 1+00 1+10 1+20 1+30 1+40 1+50

2,280 2,280

2,285 2,285

2,290 2,290

2,295 2,295

2,300 2,300

2,305 2,305

2,310 2,310

2,315 2,315

2,320 2,320

Roughened toe, boulder clusters

1.5:1 :1

164 LNFT

5. Place irregular large stone along the revetment toe, 30 ft. o.c., to increase bank line irregularity and habitat complexity.

4. Backfill placed riprap with conserved streambed material to the approximate thalweg elevation.

3. Set the top of the revetment toe below historic scour elevation, or to refusal, as described in Sheet F.10.

2. Set the top of the revetment at the shoulder elevation

1. Protect existing trees along embankment.

NOTES:

.5

15.6'

'1

:4 e c e m b e r

[S

H E

E T

F

.3

S it e B

P la n P ro p w

-w o rk \d

\i d a b o n n e r_

B S

M

IT

L A

Y O

U T

S

H E

E T

S

S u rv F t-

D .d g n

SITE 1B 76+08.00 - 77+28.00

TRESTLE CREEK RD.,

BANK STABILIZATION,

PROJECT

F.3

24°

C

M P O

U T L E T

LOG JAM

" C

M P

IN

L E T

C

E D

A R

" C

M P O

U T L E T

7'

5'

C

E D

A R

5' 5'

C

M P

IN

L E T

C

E D

A R

8'X10'

C

M P O

U T L E T

LOG JAM

" C

M P

IN

L E T

C

E D

A R

" C

M P O

U T L E T

7'

5'

C

E D

A R

5' 5'

C

M P

IN

L E T

C

E D

A R

8'X10'

Placed riprap, Method A, Class 4

Placed conserved streambed material

Q100 Water surface elevation

OHW (Q1.5 Water surface elevation)

Class 1, Type E geotextile fabric, stabilization

Separation and

Existing ground

ID

STATE

Site 2A Profile

(See Sheet F.5 for details)

Site 2B

(See Sheet F.6 for details)

Site 3A-1

(See Sheet F.7 for details)

Site 3A-2

Removal of pipe culvert

Place conserved streambed material

Placed riprap, Method A, Class 4

Install backfilled and buried revetment

Site 2A -

Protect existing trees along embankment.

Removal of pipe culvert

Preserve and protect existing log jam

Roughened toe, boulder clusters

Protect existing trees trees existing

Protect

18-inch pipe culvert, 30 LNFT

Ordinary High Water

Backfill riprap between trees above

Placed riprap, Method A, Class 4

Cuttings, flailing alder plant seeding

N

0+80 0+90 1+00 1+10 1+20 1+30 1+40 1+50 1+60 1+70 1+80 1+90 2+00 2+10 2+20

2,300 2,300

2,305 2,305

2,310 2,310

2,315 2,315

2,320 2,320

2,325 2,325

2,330 2,330

2,335 2,335

2,340 2,340

SITE 2A, 81+00.00 - 81+85.00

TRESTLE CREEK RD.,

BANK STABILIZATION,

1.5:1

5. Place irregular large stone along the revetment toe, 30 ft o.c., to increase bank line irregularity and habitat complexity.

4. Backfill placed riprap with conserved streambed material to the approximate thalweg elevation.

3. Set the top of the revetment toe below historic scour elevation, or to refusal, as described in Sheet F.10.

2. Set the top of the revetment at the shoulder elevation

1. Protect existing trees along embankment.

NOTES:

18'

.1

:1

12'

.9

:0 e c e m b e r

S h e e t_

F .4

S it e

A

R e v

S p w

-w o rk \d

\i d a b o n n e r_

B S

M

IT

L A

Y O

U T

S

H E

E T

S

S u rv F t-

D .d g n

PROJECT

NUMBER

F.4

0+60 0+70 0+80 0+90 1+00 1+10 1+20 1+30 1+40 1+50 1+60 1+70 1+80 1+90 2+00

2,300 2,300

2,305 2,305

2,310 2,310

2,315 2,315

2,320 2,320

2,325 2,325

2,330 2,330

2,335 2,335

2,340 2,340

24°

C

M P O

U T L E T

LOG JAM

" C

M P

IN

L E T

C

E D

A R

" C

M P O

U T L E T

7'

5'

C

E D

A R

5' 5'

C

M P

IN

L E T

C

E D

A R

8'X10'

C

M P O

U T L E T

LOG JAM

" C

M P

IN

L E T

C

E D

A R

" C

M P O

U T L E T

7'

5'

C

E D

A R

5' 5'

C

M P

IN

L E T

C

E D

A R

8'X10'

Method A, Class 4

Placed riprap, Placed conserved streambed material

Q100 Water surface elevation

OHW (Q1.5 Water surface elevation)

Class 1, Type E geotextile fabric, Stabilization-separation

(See Sheet F.4 for details)

Site 2A

Place conserved streambed material

Placed riprap, Method A, Class 4

Install buried revetment on embankment opposite of log jam.

Site 2B log jam protect existing

Preserve and

(See Sheet F.6 for details)

Log Revetment

Site 3A-1

(See Sheet F.7 for details)

Buried Revetment

Site 3A-2

Site 2B Profile

ID

STATE

Existing surface

Removal of pipe culvert taking care not to fill low flow channel and boulder ballast (15 CY) along transition, Place Rootwad Logs (3)

Ordinary High Water

Backfill riprap between trees above

Placed riprap, Method A, Class 4

18-inch pipe culvert, 30 LNFT

84+07.00

Protect existing trees

Cuttings, flailing alder seeding

Roughened toe, boulder clusters

N

Protect existing trees along edge of road.

5. Place irregular large stone along the revetment toe, 30 ft. o.c., to increase bank line irregularity and habitat complexity.

4. Backfill placed riprap with conserved streambed material to the approximate thalweg elevation.

3. Set the top of the revetment toe below historic scour elevation, or to refusal, as described in Sheet F.10.

2. Set the top of the revetment at the shoulder elevation

1. Protect existing trees along embankment.

NOTES:

LNFT

6. Rootwad - 18" ± 6" diameter, 22' - 26' length, 5' ± 6" rootwad diameter.

1.5:1

:1

16.9'

.5

:0 e c e m b e r

[S h e e t_

F .5

S it e

B

B a c k fi ll

R e v p w

-w o rk \d

\i d a b o n n e r_

B S

M

IT

L A

Y O

U T

S

H E

E T

S

S u rv F t-

D .d g n

SITE 2B, 81+85.00 - 82+72.22

TRESTLE CREEK RD.,

BANK STABILIZATION,

PROJECT

NUMBER

FLAP BONNER 841(1) F.5

ID FLAP BONNER 841(1)

LOG JAM

" C

E D

A R

C

M P O

U T L E

T

7'

5'

C

E D

A R

5' 5'

C

M P

IN

L E

T

POLE 153700

C

E D

A R

8'X10'

P O

L E

Placed riprap, Method A, Class 4

Place conserved streambed material

Riprap toe control point, 2317.3'

Existing ground

(See Sheet F.7 for details)

Buried riprap revetment

Site 3A-2

(See Sheet F.8 for details)

Buried riprap revetment

Site 3B Rootwads

Place…