DESIGN REPORT

BIG WOOD RIVER RESTORATION PROJECT

BROADFORD FISHERMAN’S ACCESS AREA

BLAINE COUNTY, IDAHO

1.0 INTRODUCTION

Biota Research and Consulting, Inc. (Biota) has been retained by Blaine County to complete a site assessment, restoration design, and permitting for the Broadford Fisherman’s Access Area of the Big Wood River. This project was completed as follow-up work to the Emergency Stream Alteration Permit (ESAP 17-067) issued to Blaine County for the Broadford Road Fisherman’s Access Area.

This project was completed to identify specific treatments to be implemented in order to protect proximate land uses and recreational opportunities from severe erosion while maximizing ecological values of the fluvial system. The primary strategy to meet project objectives was to restore function through application of in-channel treatments that enable the river to convey hydrologic and sediment inputs without severe erosion or deposition.

The design report presents analyses completed during the design development process including hydrologic investigations, geomorphic assessment, hydraulic modeling, sediment transport analyses, and restoration treatments and strategies. Hydraulic modeling has been conducted to demonstrate regulatory compliance. The design plans for the Broadford Fisherman’s Access Area include construction-ready drawings, construction implementation details, and specifications.

1.1 PROJECT AREA The project area includes an approximately 1,100-foot segment of the Big Wood River near Bellevue, Idaho, adjacent to the Fisherman’s Access on Broadford Road (design drawing Sheet 1). The project reach encompasses private properties and a 4-acre parcel owned by Blaine County that provides public access to the river corridor.

1.2 PROJECT BACKGROUND The Big Wood River mainstem has been directly altered by anthropogenic activities that include development encroachment on the floodplain; clearing of riparian vegetation; removal of instream woody debris; construction and maintenance of flood control levees; installation of rip rap and bank armoring; and the establishment of transportation crossings. Related resource concerns include unstable channel braiding, widening or enlargement, and severe lateral instability (bank erosion). The large magnitude flood experienced in the Big Wood River in 2017 resulted in widespread changes in the river corridor, and dramatic alteration of sub-reaches that were previously impaired by land use activities. The US Geological Survey (USGS) has maintained a stream gauge in Hailey (#13139510) for more than 100 years, and flow data obtained from the gauge reveal that the Big Wood River experienced a flood in 2017 that had a greater than 50-year return interval. Mean daily flow data recorded at the gauge indicate that 2017 peak flows were approximately 3 times higher than average, and that the 2017 runoff period experienced multiple distinct flood peaks (Figure 1). The multiple, prolonged, large peaks in flood

Broadford Fisherman’s Access Design Report 1 Biota Research and Consulting, Inc. waters caused extensive flooding, river bank and bed erosion, and widespread gravel deposition within the project reach. Private lands and facilities were impacted by erosion, site access and public infrastructure were destroyed, flood protection levees were compromised, and there was concern that Broadford Road itself could be impacted. During the 2017 flood event, emergency actions were undertaken by Blaine County in response to rapid localized lateral river migration, and the destruction of the Fisherman’s Access parking area. Emergency actions included the discharge of rock rip rap to harden the river right bank. This restoration design was completed to identify a long-term solution to local river instability.

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Figure 1. Mean daily flows from the period of record and from 2017 at the USGS Big Wood River gauge in Hailey (#13139510).

Conceptual restoration and enhancement designs have been developed for the entire Broadford Reach of the Big Wood River (from Broadford Road Bridge to Star Bridge). This project will refine those conceptual designs into a final design plan set for the Fisherman’s Access project area. Design treatments are intended to protect infrastructure and facilities proximate to the river while restoring fluvial processes of sediment transport and flood water conveyance.

The project was informed by site observation and assessment, local hydrologic and topographic data, including LiDAR flown in the fall of 2017 (QSI 2017), and the previously completed Geomorphic Assessment Report, Big Wood River, Blaine County, Idaho (Biota, 2016) which studied the associated sub-reach of the Big Wood River and presented localized predictions related to channel stability and sediment transport.

Broadford Fisherman’s Access Design Report 2 Biota Research and Consulting, Inc. 1.3 PROJECT GOALS AND OBJECTIVES Project objectives were identified based upon existing site conditions, previous geomorphic assessment, land use constraints, and fluvial system potential. Project objectives include the following: 1. Identify the stable functional channel form appropriate under the current (anthropogenically altered) hydrologic regime; 2. Restore sufficient capacity to transport the sediment load while providing opportunities for storage of surplus sediment; 3. Increase lateral channel stability; 4. Reduce aggradation, or severe localized deposition; 5. Reduce channel enlargement potential; 6. Reduce sediment input to the watershed resulting from bank erosion; 7. Implement fluvial enhancement treatments that reduce, or leave unaltered, the flood hazard proximate to development; 8. Identify self-maintaining treatments that maximize the ecological and recreational values of the Big Wood River.

2.0 FLUVIAL CONDITIONS The project area has a catchment, or watershed, characterized by the following: drainage area of 695 square miles, mean basin elevation of 7,550 ft, maximum basin elevation of 12,000 ft, average annual precipitation of 27.9 inches, about 40% forested land cover, and land slopes of 30% or greater across 75% of the basin. Hydrologic and geomorphic conditions within the project reach are summarized in the following sub-sections.

2.1 HYDROLOGIC REGIME The 2016 Geomorphic Assessment identified the project area bankfull discharge, which was the design discharge used for site assessment and analysis. Bankfull discharge is the flow rate, and bankfull stage is the corresponding water surface elevation, at which instream water escapes the active channel and inundates the floodplain (when incipient flooding occurs). There is natural variability in the recurrence interval of bankfull discharge between sites, but a reasonable estimate of bankfull discharge recurrence interval in the project area is 1.1-1.5 years. Bankfull discharge was selected as the primary hydrologic parameter for assessment purposes because it can be identified and corroborated through field investigations, as opposed to potential alternate parameters of dominant discharge (e.g., the flow rate responsible for the stable morphology) or effective discharge (e.g., the flow rate that transports the greatest fraction of the annual sediment load) that are primarily derived through analytical processes, without empirical corroboration.

Estimation of bankfull discharge was performed using hydraulic modeling of open channel flow conditions based upon field-measured morphologic and sediment data (floodplain elevation, bankfull indicators, channel dimension and profile, sediment size class distribution, hydraulic roughness). Analyses indicate that the bankfull discharge in the project area is 560 cfs.

Peak flow characteristics within the project area were quantified in order to inform analysis of channel function and sediment transport. The closest USGS gauge on the Big Wood River is approximately 2 miles upstream of the project area at the Bullion Bridge in Hailey (#13139510). A geomorphic channel

Broadford Fisherman’s Access Design Report 3 Biota Research and Consulting, Inc. survey was conducted through the stream gauge reach, and included measurement of local gauge datum, riffle cross sectional geometry, bankfull indicators, and channel profile (slope). The active stage-discharge rating curve was obtained from the USGS and was used to determine the discharge corresponding to the local bankfull indicators. Analysis of the gauge period of record indicates that the bankfull discharge has a recurrence interval of 1.2 years within the project reach.

The USGS gauge at Hailey (#13139510) was also used to calculate project area peak flows. There are currently over 100 years of peak flow data for the gauge, which has been in operation since 1915. Peak flow recurrence intervals for the gauge were calculated using the Log-Pearson Type III technique and adjusted for drainage area differences between the gauge location and project area following the methods recommended by the USGS (Wood et al. 2016). Table 1 contains the bankfull and peak flow discharges that were used during hydraulic modeling and design development.

Table 1. Peak flow recurrence intervals for the project area. Discharge Recurrence Interval (cfs) Bankfull 560 10-Year 4,949 50-Year 6,989 100-Year 7,835

2.2 GEOMORPHIC ASSESSMENT A geomorphic assessment of the project reach was completed in order to establish baseline conditions and inform the design development process. The assessment included the following:  Incorporation of previous geomorphic assessment results (Biota 2016);  Historic and current aerial imagery interpretation;  Sediment transport modeling;  Stream stability analyses;  LiDAR interpretation including relative elevation model; and  Geomorphic change detection.

The Fisherman’s Access project area is located in an alluvial valley with bounding features composed of alluvial deposits. The river channel has high width/depth ratio and has moderate sinuosity. The reach- wide bankfull channel slope is approximately 0.55%. The reach has an average bankfull channel width of 113 ft, mean depth of 1.6 ft, and width/depth ratio of 70. The entrenchment ratio (the relation of the width at twice the riffle maximum depth [floodprone width] to that of the bankfull channel) is 1.1 ft/ft

The river planform is comprised of irregular meanders and sediment storage occurs in lateral bars, point bars, transverse bars, and mid‐channel bars. Lateral channel migration occurs through irregular lateral activity and avulsion processes. Side channels are frequent. The channel is locally braided with extensive sediment storage in active bars and floodplain bars. The channel banks largely are comprised of alluvium (except in areas with bank protection) and are highly erodible. As exhibited in 2017, channel adjustments are frequent, rapid, and can result in complete realignment of the main channel.

Broadford Fisherman’s Access Design Report 4 Biota Research and Consulting, Inc. Hydraulic analysis recently completed (2016 Geomorphic Assessment) within the project reach indicates that local hydraulic conditions during bankfull flow result the mobilization of a 99 mm particle on the river bed. The largest particle size of the local bedload supply is about 80 mm, and the largest particle size of the surface grains on the river bed is about 200 mm. These conditions indicate that the river reach is capable of transporting the largest particles in the available bedload, but is capable of mobilizing up to only the D65 (65th percentile) of the surface grains based upon material size class distribution. These analyses indicate that the reach is competent to transport the available bedload but that the existing surface grains on the river bed promotes vertical channel stability.

Sediment transport analyses conducted within the project reach indicate that the annual sediment supply is comprised of 705 tons of suspended sediment and 3,485 tons of bedload. Modeling indicates that the reach has capacity to transport 702 tons/year of suspended sediment and 2,551 tons/year of bedload. The reach therefore has capacity to transport all of the supplied suspended sediment, but the reach does not have capacity to transport the supplied bedload (net capacity of -27%). These sediment transport conditions result in excess sediment deposition that occurs in the form of point bars, lateral bars, and transverse bars. Stream stability analyses indicate that the reach has insufficient sediment transport capacity, is highly unstable laterally, demonstrates aggradation, is slightly incised, has extensive channel enlargement potential, and is a very high supply of sediment. Stream stability findings are summarized in Table 2. Typical conditions within the project area are depicted in Figures 2 through 4.

Table 2. Summary of stream channel stability indices.

Channel Parameter Rating Sediment Transport Capacity Insufficient Capacity Lateral Stability Highly Unstable Vertical Stability (Aggradation) Aggradation Vertical Stability (Degradation) Slightly Incised Channel Enlargement Potential Extensive Sediment Supply (Channel Source) Very High

Figure 2. Photograph depicting rock rip rap installed near the Fisherman’s Access site during the flood of 2017 to combat severe bank erosion and lateral channel migration.

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Figure 3. Photograph depicting recent lateral channel migration (bank erosion) that occurred near the Fisherman’s Access site during the flood of 2017.

Figure 4. Photograph of transverse and lateral depositional bars in the project reach.

Broadford Fisherman’s Access Design Report 6 Biota Research and Consulting, Inc. Relative Elevation Model

A relative elevation model with the slope of the valley removed (i.e., detrended) was developed following the methods of Olson et al. (2014) to reveal attributes of floodplain topography. Sheet 2 of the design drawings (Appendix A) depicts the 2017 LiDAR surface topography and relative elevation model. The relative elevation model visually depicts the difference between grade elevations and the water surface elevation at the time of the LiDAR survey, which occurred during an average discharge of 339 cfs (September 28; October 1 and 14, 2017).

Geomorphic Change Detection

Channel dynamics were evaluated within the project area, in part, using Geomorphic Change Detection (GCD) software (Wheaton et al 2010). The GCD software was used to quantify erosion and deposition in the project reach between the 2015 and 2017 LiDAR surveys (QSI 2016; 2017). The analysis provides detailed information used to evaluate sediment routing and sorting processes and evaluate potential restoration alternatives. Sheet 3 of the design drawings (Appendix A) shows the pattern of erosion and deposition in the project area and associated elevation changes. Table 3 and Figure 5 summarize the erosion and deposition areas, depths, and volumes. The results indicate that geomorphic changes occurred within approximately 60% of the project area. Results also indicate that there was a greater volume of erosion (approximately 11,259 cy) than there was of deposition (approximately 6,754 cy), which suggests that approximately 4,506 cy of material was mobilized from the project area during the 2017 runoff event. .

Table 3. Summary of erosion and deposition quantities in the project area from 2015 to 2017. Geomorphic Potential Attribute Changes Error Total Area of Erosion (acres) 2.5 -- Total Area of Deposition (acres) 2.2 -- Percent of Total Area with Detectable Change (%) 57% -- Volume of Change Total Volume of Erosion (cy) 11,259 +/-2,863 Total Volume of Deposition (cy) 6,754 +/-2,515 Total Net Volume (cy) -4,506 -- Vertical Changes Average Depth of Erosion (ft) 2.8 +/-0.7 Maximum Depth of Erosion (ft) 7.6 -- Average Depth of Deposition (ft) 1.9 +/-0.7 Maximum Depth of Deposition (ft) 4.0 Percentages (by volume) Percent Erosion (%) 63 -- Percent Deposition (%) 38 --

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Figure 5. Erosion and deposition depth and volume for the project area from 2015 to 2017.

Historic Channel Mapping

Historic Big Wood River main channel and side channel locations were mapped from a series of georeferenced historic aerial images including 1943, 1970, 1978, 1992, 2004, 2013 (Sheet 4). The historic aerial images document the process of development and encroachment into the big Wood River floodplain over time which has led to impaired fluvial functions and riverine services. The 1943 channel form in the project area is characterized as anastomosing with multiple channels separated by vegetated floodplain islands. As shown in the 1943 aerial imagery, the river reach had active side channels and multiple crossing structures. There are portions of the project area that currently have a braided channel form, but channel braids meander through barren unconsolidated alluvium instead of through robustly vegetated floodplain islands that existed historically.

2.3 HYDRAULIC MODELING The peak discharges described above were used in a hydraulic model that was developed to determine flood inundation for a range of flows including the 10-year, 50-year, and 100-year flood events. The hydraulic model was developed with the Hydrologic Engineering Centers River Analysis System (HEC- RAS), which is a cross section–based one-dimensional model developed by the U.S. Army Corps of Engineers (USACE 2010) for computing velocity, flow depth, shears stress, and other hydraulic characteristics in riverine systems. Hydraulic model outputs were exported to HEC-GeoRAS (USACE 2009), which is a custom interface between HEC-RAS and GIS for mapping water surface elevations,

Broadford Fisherman’s Access Design Report 8 Biota Research and Consulting, Inc. flow depths, and flood inundation boundaries. The flood inundation tool in HEC-GeoRAS interpolates the water surface elevations from HEC-RAS cross sections to two-dimensional geospatial data.

The flood inundation areas and depths with in the project area during a 50-year flood event are depicted on Sheet 5. Existing roads, dikes, and levees in the project area confine flood waters and limit floodplain connectivity and inundation. The limited dispersal of flood water across the floodplain, and the conveyance bottleneck at the Broadford Road Bridge, result in increased stream power and energy within the active river channel.

Hydraulic modeling was also used to complete a “No-Rise” assessment to ensure that project actions will not cause adverse impacts in the form of increased base flood elevations. The current effective hydraulic model was obtained from FEMA through an Engineering Library Data Request. This revised “No-Rise” is based on the effective hydraulic model for the Big Wood River and surveyed cross sections of the channel at the project site completed by Galena Engineering in March 2018. The 1% recurrence interval event (100-year) was evaluated using the effective discharge of 6,580 cfs for the Big Wood River at this location. The “No-Rise” certificate for the Broadford Road Fisherman’s Access Area is contained in Appendix B.

3.0 RESTORATION AND ENHANCEMENT DESIGN

The dramatic consequences of recent erosion at the Fisherman’s Access site have highlighted the need for systemic improvements that protect private property and public infrastructure while accommodating fluvial processes. Landowners within 300 feet upstream and 1,000 feet downstream from the proposed project area are depicted on Sheet 6. The Project area Federal Emergency Management Area (FEMA) Special Flood Hazard Areas are depicted on Sheet 7.

The restoration strategy for the Fisherman’s Access area is to address the channel instabilities, severe bank erosion rates, and discontinuity in sediment transport regime. The presented restoration designs are intended to enhance fluvial functions while protecting adjacent landowners and land uses from severe erosion.

Project restoration and enhancement designs were developed using an iterative process that identified stable channel morphology based upon existing hydrologic regime, sediment inputs, and site conditions. A “Natural Channel Design” approach was applied to define appropriate morphology for the project area reach using analogy, empirical, and analytical design techniques. Throughout the design development process, constraints that could potentially inhibit restoration were identified, considered, and incorporated into project designs, where needed. Examples of constraints considered for the project area include flood risk, infrastructure (e.g. existing roads and downstream bridge), land use conflicts, and instream construction timeframe restrictions.

Active restoration efforts (Sheets 8 and 9) incorporate grading and earthwork to establish the desired channel form (alignment and cross sectional geometry). The design drawings contain construction stakeout points with design elevations to be utilized during implementation (Sheet 10). Treatments include channel excavation, floodplain creation, bank toe hardening, and the installation of wood structures. Precise wood structure configurations, or designed log jams, are presented in order to establish specific components of channel form and function.

Broadford Fisherman’s Access Design Report 9 Biota Research and Consulting, Inc. 3.1 DESIGN CHANNEL GEOMETRY Design channel geometry was derived based on reference reach conditions. Reference reach channel cross sections were scaled based upon hydraulic geometry to achieve the cross sectional area necessary to convey the bankfull discharge of the project area. Development of design cross sections from hydraulically scaled reference reach conditions preserves critical attributes of channel geometry including an inset channel to consolidate low flows; achievement of the proper ratio of maximum depth to mean depth; and establishment of proper relationship between local stage, stream power, and sediment transport. The project area design channel dimensions are shown in Table 4 and on Sheets 11 and 12.

Table 4. Project areas design channel geometry.

Bankfull Mean Maximum Bankfull Wetted Hydraulic Width/Depth Slope Width Depth Depth Area Perimeter Radius Ratio (%) (ft) (ft) (ft) (sq ft) (ft) (ft) 68 2.7 4.2 25 0.55% 184 69 2.7

3.2 DESIGN CRITERIA FROM DIMENSIONLESS RATIOS The design channel (riffle) geometry was used to specify morphologic attributes of channel pattern and profile based upon dimensionless ratios obtained from reference reach conditions, regional empirical data, and professional experience. Channel dimension, pattern, and profile are designed using dimensionless ratios (below), which describe functional channel form based upon bankfull channel width and depth. For example, multiplication of the dimensionless ratio of riffle length to riffle width by the design bankfull channel width yields a value for suitable design riffle length. The design criteria derived from dimensionless ratios (Table 5) include the average value and the range of observed values for several important morphologic parameters. Inclusion of a range of values (and not just the average condition) within a restoration design prevents the pursuit of a homogeneous channel and ensures that the restored riverine system demonstrates a range of hydraulic and fluvial conditions reflective of natural functional systems. The design drawings (Sheets 8 to 17) contain detailed information describing the morphologic restoration and enhancement actions for the project area.

Table 5. Project area design criteria derived from dimensionless ratios

Design Criteria Parameter Mean Value Min Value Max Value Meander Width Ratio 326 190 680 Riffle Length/Riffle Width 218 170 333 Riffle Dmax/Dmean 6.8 5.9 7.2 Inner Berm Width/Riffle Width 31 27 36 Riffle Slope/Reach Slope 1.21% 0.83% 1.76% Pool Length/Riffle Width 170 136 218 Pool Width/Riffle Width 53 48 75 Pool Dmax/Riffle Dmean 6.5 5.1 9.5 Pool Slope/Reach Slope 0.02% 0.01% 0.03% Pool-Pool Spacing/Riffle Width 558 360 986 Linear Wavelength/Riffle Width 966 680 1224 Stream Meander Length Ratio 1299 1074 1972 Radius of Curvature/Riffle Width 286 211 422

Broadford Fisherman’s Access Design Report 10 Biota Research and Consulting, Inc. 3.3 FLOODPLAIN CONSTRUCTION An inset floodplain will be constructed within the project reach to reestablish channel geometry and address excessively wide channel conditions. The inset floodplain will be constructed at the local bankfull elevation (0.75 ft higher on the outside of meander bends) by placing native alluvial fill material. Establishment of a hydraulically connected floodplain with suitable width is paramount to site restoration. Floodplain width determines channel entrenchment ratio, which dictates channel form and processes associated with sediment transport, stable peak flow hydraulic conditions, and aquatic habitat. Suitable floodplain width also enables flood waters to disperse and dissipate energy while inundating riparian lands, which facilitates sediment deposition and recruitment of woody vegetation adjacent to the river channel. The location of proposed floodplain construction is shown on the design drawings (Sheets 8 to 17).

The floodplain bench construction involves placing consecutive lifts of native alluvium below the ordinary high water mark, compaction of lifts with excavator bucket or similar force, and installation of transplanted woody and herbaceous vegetation mats atop placed fill to achieve the design elevation.

The floodplain bench treatment includes a series of brush trenches located perpendicular to the flow path throughout the floodplain and floodplain wood structures. The intent of the woody material on the surface of the floodplain bench is to reduce the velocity of flow on the floodplain and to encourage deposition of fine sediments. Brush trenches should be constructed perpendicular to flow at a spacing of 1 per 1,000 sq ft. The excavated area for the brush trenches should be approximately 10 ft long by 2 ft wide and 5 feet deep. Woody Material and live dormant woody vegetation cuttings should be placed in the trenches.

Coarse available materials, or imported rock, should be placed on the river side of the fill to achieve increased bank stability. Fine sediments and unclassified fill materials are placed on the landward side of the channel banks. All implemented channel narrowing treatments are oriented and situated to achieve the functional bankfull channel width. Bioengineering techniques to stabilize the channel banks include willow stingers and vegetation bundles incorporated into the bank which will help promote the stability of treatments, enhance instream cover, and provide bank vegetation.

3.4 LARGE WOODY DEBRIS STRUCTURES

The presence of large woody debris (LWD) influences both physical and biological processes and serves many functions. Some benefits of utilizing LWD in restoration plans include: increased erosion resistance; improved aquatic and riparian habitat; sediment sorting and retention (USBR 2014; USBR and ERDC 2016); reduced near bank shear stress and erosive energy; and flood control. Log jam structures were designed to provide specific functions at identified treatment locations (Sheets 8 and 9). Wood treatment designs are based upon professional experience and the principles established in published literature (NRCS Engineering Field Handbook, USFS Soil Bioengineering Guide, various Rosgen publications, etc.). The constructed LWD structures should generally follow the typical design drawing for optimal function and stability but may require field adjustments to address site specific conditions during implementation. Channel Margin Structure The channel margin structures (Sheet 14) are designed to provide bank stability and protection for revegetation treatments, particularly in areas of floodplain construction as well as increase habitat complexity and provide fish cover. These structures also cause flow convergence that maintains localized scour pools and reduces near bank shear stress. These structures are utilized along the channel margins particularly in areas of floodplain bench creation.

Broadford Fisherman’s Access Design Report 11 Biota Research and Consulting, Inc. The channel margin structures are comprised of logs with root wads (greater than 18 inches diameter and 30 ft length), broken logs (greater than 12 inches diameter and 30 ft length), and boulders (greater than 24 inches diameter). Structure logs are anchored in to the river bank with root wads that protrude into the channel and include boulders for ballast to increase structure stability. Buried logs should be backfilled with native alluvium and capped with salvaged vegetation. Racking logs and slash should also be placed irregularly among the exposed root wads of the channel margin structure to provide complexity and roughness.

Meander Bend Structure Meander bend structures (Sheet 15) are intended to limit channel migration in the short term to enable establishment and maturation of woody vegetation installed along the channel margins, particularly in areas of inset floodplain creation. The structures tend to accumulate natural woody debris through time, maintain lateral scour pools, and reduce near bank shear stress. These structures are utilized along the outside of meander bends.

Meander bend structures are comprised of the same materials as channel margin structures but have more logs and are oriented to provide increased bank stability. These structures may also utilize a rock toe treatment for additional bank stability, where needed. The meander bend structures are also comprised of buried key logs anchored in to the river bank with root wads that protrude into the channel. Buried logs should be backfilled with native alluvium and capped with salvaged vegetation. These structures should also incorporate racking logs and slash to provide increased complexity, hydraulic roughness, and fish cover.

At locations where bank erosion potential is high due to near bank shear stress or channel alignment, proposed river bank construction incorporates a rock toe treatment in addition to the meander bend structures in order to provide instantaneous bank stability. The length of the rock toe treatment is estimated to be 660 ft but should be confirmed and staked in the field during implementation (Sheet 13). The rock toe treatment was designed, and material sized using U.S. Army Corps of Engineers technical bulletins and methodologies that incorporated input parameters of design channel geometry, channel slope, mean and maximum channel depths, flow velocity, and radius of curvature.

The rock toe should have a median (D50) size of 24 inches and a maximum (D100) size of 36 inches with an appropriate gradation. A factor of safety of 1.2 was applied to size the rock because the treatment would protect a newly constructed river bank composed of recently placed unconsolidated alluvium. A gravel or geotextile filter may be required depending on the size class distribution of the material used to construct the channel bank (the material underneath the rock toe); the use of coarse alluvial fill instead of a fine sediment mixture may negate the need to incorporate an intermediate layer under the rock toe. The rock toe should extend from the adjacent floodplain bench elevation down to the local scour depth 3.4 feet below the channel bed elevation. The rock toe will have a horizontal to vertical slope of 2:1 with bundles of live woody cuttings installed on 4-foot spacing. The bundle planting configurations will alternate between vertical bundles and 45-degree bundles. Vertical bundles will be installed parallel with the constructed bank, and 45-degree bundles will be installed at a 45-degree angle to the bank. Details regarding the collection, preparation, and installation of the bundles are provided in Section 4.1 and on Sheet 10. Floodplain Wood Structure The floodplain wood structures (Sheet 16) are intended to reduce the velocity of flow on the floodplain to encourage deposition of fine sediments. These structures tend to accumulate woody debris over time and

Broadford Fisherman’s Access Design Report 12 Biota Research and Consulting, Inc. improve sediment storage processes. They are placed irregularly throughout the floodplain in combination with brush trenches.

Floodplain wood structures are comprised of broken logs greater than 12 inches diameter and 30 ft length and pinning logs greater than 12 inches diameter and 20 ft length. The structure logs placed on the surface are held to the floodplain with forward angled pinning logs to increase structure stability. The pinning logs are buried and angled forward to increase structure stability. The pinning logs should be backfilled with native alluvium and capped with salvaged vegetation. Slash and small wood should be placed irregularly upstream of the structure as racking material.

3.5 REVEGETATION/RECLAMATION Revegetation of the project area will be accomplished via broadcast seeding and bioengineering with dormant hardwood cuttings.

Dormant Hardwood Cuttings Dormant hardwood cuttings will be utilized to facilitate bioengineering efforts within the project area. In order to optimize establishment and long-term persistence, cuttings will be installed in appropriate locations within the riparian zone (i.e., bank zone, overbank zone, transitional zone, and upland zone) based on hydrologic tolerance of each species, and cuttings will be installed to a depth of 1 foot below the lowest water table of the year. Bioengineering techniques to be employed include: vertical bundles, 45- degree bundles, and brush trenches. The vertical bundles and 45-degree bundles will be installed on the constructed banks in conjunction with toe rock, and the brush trenches will be installed on the constructed floodplain benches. The species of hardwood cuttings utilized will be limited to black cottonwood, red osier dogwood, and willows native to the Big Wood River Drainage. Cuttings will be collected from native riparian trees and shrubs, either onsite or at off-site locations approved by the design consultant within the Big Wood River Drainage. Sheet 17 of the design drawings contain preparation and installation procedures for vertical bundles, 45-degree bundles, and brush trenches. Seeding A native transitional seed mix will be dispersed throughout the treatment area after construction has been completed, including all temporary haul roads and equipment and material storage areas. Seed will be applied by hand, with a broadcast seeder, or via a hydroseeder after October 1 and prior to the onset of season-long snow cover. Seed will be applied to a properly prepared, firm seed bed, and will not be broadcast on snow-covered ground. After application of seed, the reclamation areas will be rolled, harrowed, or raked to ensure maximum seed-to-soil contact. Certified weed-free straw will then be distributed over the seeded area. If hydroseeded, seed will be applied with minimal mulch to ensure good seed-to-soil contact. The seed mix in Table 9 will be applied at the specified rate (pounds of pure live seed per acre). Sterile triticale has been added to the seed mix as a nurse crop to provide fast-growing, short- term vegetative growth to assist with erosion control, add standing mulch, provide weed competition, and to facilitate establishment of the slower growing native perennial species. The triticale is sterile and will not produce viable seed. Therefore, it will only be present during the initial growing season. Where available, the reclamation seeding effort will be supplemented with transplanted native herbaceous and woody vegetation salvaged during construction.

Broadford Fisherman’s Access Design Report 13 Biota Research and Consulting, Inc. 3.6 PROJECT IMPLEMENTATION Project implementation should occur in an environmentally sensitive manner, and any incidental damage to the site should be reclaimed. Construction activities should be performed by an experienced contractor under the supervision and direction of the design consultant. Every reasonable effort should be made to complete the proposed restoration and enhancement design plans in a manner that minimizes the potential for adverse impacts to water quality, fish, wildlife, and the environment. Construction activities should comply with all permit conditions and be conducted using industry standard Best Management Practices (BMP) included with the design drawings (Sheet 17). Potential instream construction timing restrictions should be considered for planning project implementation. Past projects on the Big Wood River have had restricted construction operations from the period between March 31th to July 15th. The project design treatments described above have been identified for a number of specific locations shown in the design drawings (Sheets 8 and 9). Construction quantities and structure quantities associated with proposed design treatments are summarized in Table 6. Table 7 contains the log quantities for the LWD structure treatments. Table 8 contains the dormant hardwood cutting quantities and Table 9 contains the seed mix that will be applied at the specified rate (pounds of pure live seed per acre) for revegetation of the project area.

Table 6. Treatment quantities summary Cut Fill Treatment Quantity Volume Volume (cy) (cy) Floodplain Bench Construction Area (acres) 2.48 1,406 5,989 Rock Toe (linear ft) 660 -- 1,643 Riffle Construction (acres) 0.96 1,323 -- Pool Construction (acres) 0.37 3,260 -- Channel Margin Structures (locations) 6 -- -- Meander Bend Structures (locations) 7 -- -- Floodplain Wood Structures (locations) 9 -- -- Parking Area Construction (sq ft) 5,900 -- -- Total 5,989 7,632

Table 7. Large wood treatment log quantities Channel Floodplain Meander Bend Large Wood Treatment Logs Margin Wood Total Structures Structures Structures Logs with root wads (>18 in 24 42 -- 66 diameter, 30 ft length) Broken logs (>12 in diameter, 30 6 35 18 59 ft length) Pinning logs (>8 in diameter, 20 -- -- 18 18 ft length) Ballast Boulders (>24 in 24 42 -- 66 diameter)1 1The estimated 66 cy of ballast boulders may be sourced from on-site excavated materials, as available.

Broadford Fisherman’s Access Design Report 14 Biota Research and Consulting, Inc. Table 8. Dormant hardwood cutting treatment quantities Dormant Total Cuttings Dormant Treatment Spacing Quantity Per Cuttings Treatment Brush Trenches 1,000 sq ft spacing 107 20 2,140 Vertical Bundles 8-ft spacing 249 3 747 45-Degree Bundles 8-ft spacing 249 3 747

Table 9. General seed mix specifications Pounds Common Name Scientific Name Pure Live Seed Per Acre Idaho fescue Festuca idahoensis 1.8 bluebunch wheatgrass Pseudoroegneria spicata 4.8 bluejoint reedgrass Calamagrostis canadensis 0.3 Elymus lanceolatus var streambank wheatgrass psammophilus 7.7 western yarrow Achillea millefolium 0.1 tufted hairgrass Deschampsia cespitosa 0.3 fowl bluegrass Poa palustris 0.4 Quickgaurd sterile triticale 20.0 Total 35.3

4.0 SUMMARY AND CONCLUSIONS

The restoration of the Broadford Fisherman’s Access Area of the Big Wood River provides an opportunity to benefit proximate land uses and riverine conditions. The emphasis for proposed project actions is placed on the importance of addressing the underlying causes of fluvial system instability, as opposed to applying individual treatments that address symptoms of riverine impairment (the typical Band-Aid approach). A detailed understanding of Big Wood River riverine processes has enabled development of a restoration plan that will protect proximate land uses and recreational opportunities from severe erosion while maximizing ecological values of the fluvial system.

The final design plans for the Broadford Fisherman’s Access Area include construction-ready drawings, specifications, and construction implementation details. The final design plans were developed to achieve objectives of reduced flood hazard and improved flood attenuation, improved continuity of sediment movement, increased channel stability, and reduced severe bank erosion.

Broadford Fisherman’s Access Design Report 15 Biota Research and Consulting, Inc. 5.0 REFERENCES

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USBR (US Department of the Interior, Bureau of Reclamation). 2014. Pacific Northwest Region Resource & Technical Services Large Woody Material -Risk Based Design Guidelines. Boise, Idaho.

USBR and ERDC (Bureau of Reclamation and U.S. Army Engineer Research and Development Center). 2016. National Large Wood Manual: Assessment, Planning, Design, and Maintenance of Large Wood in Fluvial Ecosystems: Restoring Process, Function, and Structure. Available: www.usbr.gov/pn/and http://cw-environment.usace.army.mil/restoration.cfm

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