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VIDEO

Introduction

Development along the Big Wood River (​BWR​) has dramatically reduced the river’s normal hydrologic function and damaged its habitat for fish and wildlife. Cottonwoods, willows and other native vegetation and the woody debris that gave the river its name have been removed from the river, eliminating shade and reducing habitat. Over half of the Big Wood River from the Sawtooth National Recreation Area boundary to Stanton Crossing is disconnected from its floodplain. Over 40% of the river’s banks in developed areas have been armored with rip-rap to protect properties. Studies below show bank hardening with rip-rap and disconnection of the BWR floodplain is the most severe limiting factor in reducing survival and productivity of trout populations. This has had the effect of increasing the velocity of the river, altering the natural channelization process, disrupting normal sediment transport and disposition, and preventing the river from accessing its normal floodplain, increasing flood damage potential. Development and forest fires have also adversely impacted the river and its tributary streams, polluting the river and preventing fish from accessing their historic spawning grounds. Finally, increased water withdrawals and recent drought conditions have reduced summer flows and increased water temperatures. The BWR is a wonderful asset for our valley, but its health has been severely impacted. We need to fix it.

The expected outcomes of any major restoration effort must be tempered by recognition of the human constraints -- residences, roads, bridges, irrigation diversions and other infrastructure -- imposed on the BWR by human settlement in the valley. But while we can never restore the BWR to the pristine condition it was before we humans came to enjoy this beautiful valley, the recent studies indicate there is a lot we can do to alleviate the harm we have caused to the river in terms of restoring its natural hydrology and habitat for trout and other wildlife and to mitigate the increased risk of flood damage.

STUDIES

Among the most notable of the numerous studies of the BWR and what can be done to restore it to a healthy stream supporting abundant fish and other wildlife and to mitigate flood damage are the following:

Effects of Stream Alterations on Rainbow Trout in the Big Wood River, Idaho, ​Russell F. Thurow, Fisheries Research Biologist, Idaho Dept. of Fish and Game, 1988.

Thurow’s short (13 pages) study primarily focused on the river as a trout fishery. It relied on surveys researchers from the Idaho Department of Fish and Game (​IDFG)​ performed at seven reaches above Magic Reservoir, including electrofishing and snorkeling. The study found that, while the BWR “may be a shadow of its former fishery”, it still had a respectable wild rainbow population with growth rates comparable to the Henry’s Fork and Silver Creek. A significant finding was that unaltered reaches contained 8 to 10 times the fish densities of stretches where rock revetments (riprap) had been installed and/or cover and woody debris had been removed. The study recommended restricting further stream alterations (especially riprap which destroy fish habitat diversity and “create adverse hydraulic impacts”), maintaining riparian buffer zones and restoring channel stability and “natural floodway overflow channels”, but did not suggest specific projects. The study concludes that the future of fish populations in the BWR will be dependent on our ability to: (1) halt the continued, insidious loss of habitat and (2) restore degraded areas.

Big Wood Fishery Assessment, W​ood River Land Trust, May 23, 2005

This assessment by a staff member of the Wood River Land Trust (​WRLT​) used existing studies and research to identify the factors that limited the health and productivity of the BWR, noting the “vital role” the river has “in our vibrant local economy”. The report describes the history and ecology of the river, the role of its floodplain and the river’s normal hydraulic process and the importance of large woody debris as a component of trout habitat and healthy river function. The assessment suggests the following steps: (1) educating the public and policy makers on the value of the floodplain and factors influencing fish habitat, (2) restoration measures between the Glendale Diversion and the North Fork (specifically mentioning re-vegetation of banks, use of anchored woody debris and monitoring) and (3) adoption of local ordinances and state laws to regulate development of the floodplain, specifically with regard to buffer zones, steps to maintain “natural sheet flooding across the floodplain”, alternatives to riprap, requiring river and bank restoration as part of the subdivision approval process and limiting water withdrawals. The assessment recommended further studies.

Geomorphic Assessment of the Big Wood River, ​Cynthia Rapp, Consulting Geomorphologist, December, 2006, 71 pages with Appendices A (Channel Patterns), B (Aerial Photo Analysis) and C (Photos)

This study prepared for the WRLT describes the transformation of the BWR due to development from “a dominantly anastomosing [a pattern of multiple channels with forested floodplain in between] and meandering system” to a system with a combination of (a) braided channels [multiple channels with bare bars] (49%), (b) straight/sinuous channel patterns (36%), and (3) limited remaining meandering sections (16%). Channels have become more “entrenched” meaning they are restricted with higher flow velocities and limited access to the river’s natural floodplain. Entrenchment increases flood risk. The study advises that bank hardening activities (​e.g​., riprap) “do not provide a long-term solution posed by flood and erosion hazards'', but actually contribute to the problem. The study makes no specific recommendations for renovation projects, but recommends additional studies on channel erosion tendencies, sediment inputs/production, aquatic and riparian habitat and so forth. It does suggest that preserving and restoring straight and sensuous reaches that are not entrenched, have intact riparian cover and connect other braided or meandering sections may provide “the greatest biological benefit for the lowest cost”. Examples are reaches 13 (downstream of Starweather Bridge), 22 and 23 (near Colorado Gulch Bridge). It also suggests the use of engineered log jams in braided sections to enhance long-term sediment storage and multiple channel development and in other sections to reconnect the river to secondary channels that could be active during high flows.

Status and Population Characteristics of Wood River Sculpin Idaho,​ 2007, and​ Distribution, Abundance, and Generic Population Structure of Wood River Sculpin, Cottus Leiopomus​, 2008, IDFG.

These studies report on the distribution of Wood River Sculpin, one of eight sculpin species in Idaho. It is unique to the BWR, Little Wood and Camus Creek. The studies indicate that while these fish (a favorite trout food) are only plentiful in certain areas, “abundance has not been reduced to a critical level”.

Final ​Geomorphic Assessment Report, Big Wood River, Blaine County, Idaho, ​Biota Research and Consulting, Inc. (​Biota​), February 1, 2016, 122 pages with Figures and Exhibit​s

This major study commissioned by Trout Unlimited (​TU​) along with WRLT, the Bureau of Land Management (​BLM​) and others, describes the functioning and impaired channel conditions in the main stem of the BWR from the North Fork (which enters the BWR at the Sawtooth National Recreation Area (​SNRA​)) to Magic Reservoir. Measurements were taken in each reach studied of the geomorphic conditions (channel width, bankfull depth, sinuosity, stream erosion rate, channel type, etc.) and each reach is rated in terms of Sediment Transport Capacity, Lateral Stability, Vertical Stability, Channel Enlargement Potential and Sediment Supply. The study found that sections of the river have experienced “various degrees of morphologic impairment” that have adversely affected sediment movement, lateral channel stability and aquatic ecosystems, and recommends 13 design guidelines designed to reduce highly entrenched channels, reduce sediment input and improve sediment transport, increase lateral channel stability, enhance trout habitat, reduce flood hazard and maximize ecological and recreational values. The study then goes on to specify various approaches that can be utilized throughout the river to improve “flood attenuation” and thereby reduce flood hazard, improve the continuity of sediment movement, increase channel stability and reduce bank erosion, including improving functional channel geometry, utilizing wood revetment bank stabilization techniques instead of riprap, installing rock stabilization with willow bundles where suitable, floodplain improvements, grade control by constructing “hardened riffles” and installing “rock cross vane treatments” to promote scowl pools for energy dissipation and depth and turbulence cover for fish, and establishing set-back requirements for new development. The report does not recommend any particular projects, but identifies seven sections of the river as “conservation opportunities” where restoration measures should be prioritized:

  • 3500 ft. above and below Fox Creek Bridge (Exh 98)

  • 6000 ft. (the “Training Channel Reach”) starting at Glassford Heights to below the

  • pedestrian bridge at Lake Creek (Exh 99)

  • 8000 ft (the “Highway 75 Reach”) from above Sheep’s Bridge to Red Cliffs (Exh 100)

  • 7000 ft. from Gimlet to above the East Fork Bridge (Exh 101)

  • 27,000 ft. from below Golden Eagle to below the Deer Creek Bridge (Exh 102)

  • 4000 ft. below the Bullion Bridge (Exh 103)

  • 22,000 ft from above Colorado Gulch Rd in Hailey to below the lower Broadford Road

  • Bridge in Bellevue (Exhs 104 and 105)

The study concludes with the recommendation that specific river treatments should be applied “in concert to address underlying causes of fluvial system instability” as opposed to applying “the typical Band-Aid approach” of addressing only the “symptoms of system degradation”.

Preliminary Estimates of the Economic Effects of Stream Restoration on the Big Wood Valley, Idaho, ​Philip S. Cook and Dennis R. Becker of the University of Idaho College of Natural Resources, August, 2016

This study estimated the economic effect of restoring the BWR to “its historic vibrant fishery”. It focused solely on the increased number of days non-resident anglers would spend fishing on the river once restored. The proposed “restoration treatments” were those proposed by Biota in its 2015 study for seven reaches in and around Fox Creek, Hulen Meadows, Hospital Bridge, East Fork, Deer Creek, downstream of Bullion St. Bridge, Colorado Gulch and lower Broadford Rd Bridge, assumed to cost $15 million. It estimates that improved fishing alone would increase non-resident angler spending by $69,000 in year 1 to almost $1.3 million in years 15-20. The benefits from reduced flood risk, improved water quality and increased aesthetic appeal were not considered, nor was the benefit to resident anglers.

Big Wood River Atlas, ​Cardno and Ecosystem Sciences (​Cardno​), 2020, 93 pages with multiple Exhibits

This major study, which was commissioned by Blaine County and covers the 42 miles from the SNRA to Stanton Crossing, was designed to accomplish five objectives:

  • Build community trust and collaboration over river management issues

  • Understand historic and current processes

  • Develop a flood risk management framework that supports the connectivity of floodplains

  • Develop a decision-making framework to identify and evaluate projects that work to

  • restore natural river processes, and encourage aquatic habitat formation

  • Assist river managers with identifying best management practices for development within

  • the river

The study points out that, as a trout fishery, the BWR is “ a significant contributor to the economic health of the valley”. The most critical factor limiting the trout population is the amount and quality of fish habitat, with trout densities in unaltered reaches 8 to 10 times greater than altered reaches (cover impaired or having rock revetments). The study emphasizes the importance of large woody debris in providing good habitat for trout and improving the river’s hydrology. Large stable log jams played a major role in the development and maintenance of the pre-development “anastomosing” channel system described in the Rapp study. This type of channel system is more resilient to disturbances such as flood, fire and large sediment events and creates a more complex mosaic of habitat types that support fish. The study recommends reintroducing large wood to the river but only after proper geomorphic and engineering analysis (see Appendix A). Other factors noted in the study as influencing channel form behavior and habitat are (a) sedimentation, (b) riparian vegetation (which reduces the risk of flood, erosion and bank failure and improves aquatic habitat and water quality), and (3) rock revetments or “riprap” (which adversely affects stream morphology, degrades fish populations and exacerbates flooding and erosion). The study recommends removal of riprap where deemed not critical, modification of existing riprap to achieve greater hydraulic complexity and limiting construction of new riprap, warning that riprap “does not eliminate the potential of an area to be re-captured by the river or be subject to future bank loss.” In terms of steps to be taken to maintain and restore the river, the study recommends projects in the following priority:

  • Protect remaining intact functional floodplain through acquisition, easements or legislation

  • Reconnect channels where evidence shows that removing confinements such as riprap and levees would open up “prior channel occupation”

  • Reconnect floodplain processes in areas where development has encroached into the floodplain and embankments have been constructed restricting access to the floodplain

  • Restore riparian vegetation where it has been removed or modified to the point of compromised function

  • Use flood fence and engineered ​LWD​ [large woody debris] jams to stabilize “dynamic channel planform” (control sediment in a way that reduces flooding and channel erosion while improving habitat)

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The study lists the criteria used by Blaine County in permitting stream alterations (​SAP​) and states that, while providing “some key guiding principles”, these criteria lack engineering standards to demonstrate adherence to the criteria. The study recommends that future applications include (a) analysis of hydraulic modeling to demonstrate no adverse impacts on flood elevations and velocities (using guidance provided by FEMA, USACE, NORFMA (the Northwest Regional Floodplain Management Association) and others, (b) review by a qualified geomorphologist of the impact of the project on erosion, sediment, transport and migration potential, (c) an assessment by a qualified fisheries biologist of the impact of the project on fish habitat and how to mitigate these impacts, and (d) in the case of projects involving the installation of LWD, an evaluation of the risks of the installation on river hydraulics in accordance with established guidelines. The study goes on to describe each of 22 reaches of the river between the SNRA and Stanton Crossing in terms of sinuosity, gradient, width, bankloss (between 2004-2015 and 2015-2017) and bank stabilization, includes one map depicting the current channel, the historic channel migration zone (​HCMZ​), flood zones and the location of rock armoring, levees, bridges and irrigation diversions, and another map showing zones of recent and potential erosion, and also evaluates the reach in terms of of restoration potential.

Reach #

1. SNRA to Eagle Creek​ A relatively steep 2 mile narrow stretch characterized by low channel migration and little bank stabilization due to low-density residential development. The undeveloped areas in the flood hazard zones, especially forested zones, should be protected.

  1. Eagle Creek to Fox Creek​ A short (-1 mile) low-density, narrow width and high gradient section with a relatively stable channel system and the onlyriparian and floodplain habitat needs to be protected and maintained.

  2. reach with no bank stabilization. Performing well. The undeveloped

  3. Fox Creek to Lake Creek​ A 2.7 mile section with a steep gradient and

  4. USFS land along its western side and low-density residential development on its east. Has high migration potential with a major shift in channel position between 2005 and 2015. A priority should be to limit further development within its HCMZ to maintain floodplain and channel migration functions and complex habitat features.

  5. Lake Creek to Adams Gulch​ A 2-mile steep gradient (highest of all reaches) section with widespread bank armoring (30%) to protect residential development on the western bank (​e.g​., Hulen Meadows) and Hwy 75 on the east. This riprap deflects flows, confines channels and prevents the river from accessing its floodplain on the west side. Reach needs channel restoration and access to the available floodplain. The study suggests placing engineered log jams to redirect flows

  6. into the western floodplain. This would reduce the need for riprap on the east bank and increase habitat availability. A project which addresses some of the problems in this stretch, the Hulen Meadows/Sun Peak Preserve Project (see below), is currently in planning.

  7. Adams Gulch to Warm Springs Creek​ A 1.8 mile section in north Ketchum which has largely maintained uniform channel position except in the Hemingway/Northwood Natural Area above Warm Springs Bridge. This natural undeveloped area has a high value in floodplain function since it is upstream of a highly developed zone. Side channels in this area offer excellent opportunities for reconnection. The section has significant bank armoring, especially along the east bank above Warm Springs Bridge.

  8. Warm Springs Creek to Trail Creek​ A 1.6 mile stretch running through highly developed west Ketchum that is confined by riprap along almost its entire east bank. Here the river transitions into a lower energy river which typically would have a tendency for high channel migration and sinuosity (were it not for the riprap). The stretch experienced high sediment deposition as a result of the 2007 Castle Rock and 2013 Beaver Creek Fires. The study suggests removal or modification of rock armoring as a restoration opportunity. Also, the area around the Trail Creek confluence may offer opportunities for stream channel or floodplain process reconnection.

  9. Trail Creek to Hwy 75 Hospital Bridge​ This 1.5 mile reach is a dynamic section subject to rapid channel movement. It provides excellent opportunities for channel and floodplain restoration, such as reconnecting the channel across from Ketchum’s Wastewater Treatment Plant to its historic 1943 location. The study recommends restoring channel processes upstream of the Hospital Bridge. A project (“Bridge-to-Bridge”) was designed by Biota to address some of the problems in this stretch and TU filed a SAP and was seeking funding to finance it. TU recently determined not to pursue this project, at least at this time, based on a reevaluation indicating improved fish habitat conditions and predicted natural realignment of the river’s main channel without intervention.

  10. Hwy 75 Hospital Bridge to Gimlet Bridge​ This is another highly dynamic reach (2.1 miles in length) subject to rapid channel migration into former channel locations and expansion beyond the HCMZ into residential areas. The study recommends reconnection of the river to areas of former channel occupation along the western floodplain which would expand zones for flooding and sediment conveyance/deposition and modifying armored banks to incorporate bioengineering techniques. A project (the “Cooper Project”) which will address some of these issues in the upper stretch of this reach has recently received SAP approval.

  11. Gimlet Bridge to East Fork Bridge ​This 2-mile section also has an active migration pattern and continued lateral movement and erosion is likely. Several residences have been built directly in the floodplain and are regularly threatened by high water. The river here is highly confined by riprap (40% of total bank length). The study recommends that channel migration into large undeveloped areas in the lower section be encouraged with engineered log jams and regrading. It also suggests removal or setback of riprap to limit channel confinement and the implementation of in-channel structures to assist in maintaining riparian forests, manage sediment and provide habitat.

  12. East Fork Bridge to Hwy 75​ This short .06 mile section has maintained its channel position since 1943, although its entire west bank is currently riprapped. The greatest project potential is to restore the native riparian buffer.

  13. Hwy 75 to End of Golden Eagle​ Similar to the immediate upstream reach, this short reach (0.5 miles) has displayed consistent channel position since at least 1943. While only 20% of the banks have been hardened, properties along the west side of the river (Golden Engle) have cleared the riparian zones (and replaced it with lawns down to the river). The study points out that cover and shade are essential for trout and recommends re-establishing these buffer zones.

  14. Golden Eagle to Zinc Spur​ Reaches 12 and 13 are the two most sinuous reaches in the study area and also contain the least amount of riprap in the developed reaches of the river. The channel has frequently migrated in this section, developing a network of side channels that are hydraulically connected at varying flow levels, creating complex habitat for trout. The 2011 Beaver Creek and 2006 Castle Rock fires contributed large sediment deposits in this reach.The Hiawatha Canal (const. 1983) diversion dam is in this section. The study suggests in-stream structures could play a key role in trapping sediment and maintaining island braided platforms.

  15. Zinc Spur to Deer Creek Rd​. This stretch has many characteristics of a naturally functioning stream capable of supporting healthy aquatic ecosystems. It experienced the greatest amount of channel movement during the 2017 flood and has experienced this kind of dynamic channel movement for decades. The study suggests stabilizing riparian islands with flood fencing or log jams to provide shade and cover.

  16. Deer Creek Rd. to Flying Heart Ranch​ As a result of significant channel changes during the 2017 flood (16 acres of channel migration), this reach contains many large, stable log jams creating deep scour pools. The reach has very unstable banks and exhibits dynamic behavior. Exposed (no vegetation) bars and scoured banks could be stabilized to form vegetated islands and LWD habitat features.

  17. Flying Heart Ranch to Bullion St Bridge ​The channel position in this 1.4 mile reach has been remarkably stable over the available photographic record, despite only 17% of banks being armored. The reach is “transport dominated”, meaning that sediment moves through and is not deposited. The riparian buffers in this section are “improved” (meaning property owners have retained native vegetation in the buffer). Removing or setting back riprock in areas of low flood risk may offer simple and effective restoration approaches in this reach, “but opportunities are limited”.

  18. Bullion St. Bridge to Colorado Gulch​ This stretch next to the City of Hailey has experienced severe flood problems and excessive sediment deposition. The lower reach has “significant potential for restoration of channel and floodplain processes” by removing riprap and old road grades. The study describes this as a “unique opportunity”. As described below (see Hailey Greenway Project and Colorado Gulch Project), WRLT is embarking on projects that will restore channel processes and mitigate flooding in this reach that has been severely impacted by artificial constraints.

  19. Colorado Gulch To Upper Broadford Rd (Star) Bridge ​The gradient flattens in this relatively straight 1.6-mile reach to less than 0.5% and agriculture dominates the floodplain. The floodplain to the east offers high value to flood conveyance and ecosystem function and reconnecting it to the main channel and protecting and conserving it should be “a high priority”.

  20. Upper to Lower Broadford Road Bridges​ A very dynamic (bank loss, sediment deposition and channel migration) 2.7 mile stretch heavily leveed, “presumably” to protect agricultural lands. The study suggests conservation opportunities in this reach such as “strategic” breach or setback of levees to allow the river to access its normal meander belt and flood fencing and/or engineered log jams to retain sediment and improve aquatic habitat through pool formation and shade/cover. There is a project (see Broadford Fisherman’s Access Project) planned by the County with participation by adjacent landowners for the lower part of this stretch above the bridge to address high erosion.

  21. Broadford Bridge to Townsend Gulch​ A 2-mile stretch with the City of Bellevue to the east and farmland to the west. It includes the District # 45 Diversion and the Howard Preserve. This reach has the second largest FEMA floodplain of all reaches. A large percentage of the banks are either leveed or riprapped (44%) and prevent the evolution of stable riparian islands and disconnect the main channel from side channels and overflow flood pathways. Channel expansion into the floodplain could be accomplished without impacting residences. Restoration work recently took place upstream of the #45 Diversion and more work is planned in this stretch, including altering or removing the diversion dam which is failing and currently restricts fish passage (see Bellevue Reach Projects below).

  22. Townsend Gulch to Glendale Rd​ This reach has very low gradient and a wide floodplain resulting in rapid channel migration. The study suggests stabilizing mid-channel riparian stands with flood fencing or log jams to help capture and maintain sediment and improve habitat. The reach has the second highest percentage of bank stabilization implemented “in attempts to channelize the river”. The study suggests removing bank armoring in this stretch to allow the river to access a wider portion of its natural meander and the installation of flood fencing and/or apex dams to retain sediment and improve aquatic habitat.

  23. Glendale Rd. to Mule Shoe Bend​ The river is diverted into an irrigation canal above Glendale Rd each spring and there is active in-stream sand and gravel mining below Glendale Rd. The study concludes that it is hard to envision restoration of a functioning river ecosystem until a natural flow regime is restored.

  24. Mule Shoe Ln to Stanton Crossing​ This reach is in a primarily agricultural area and, as it too is below the Glendale Diversion, it would not make much sense to restore it. If somehow flows could be restored, there is “great potential” to restore riparian and floodplain habitat within this reach with the installation of large woody debris structures or flood fencing.

The study concludes (pgs 82-91) with recommendations of treatment techniques: no action, restoring the riparian buffer through land management practices, removing infrastructure at risk, native riparian planting and increasing floodplain roughness, employing in-channel structures like rock or large wood and engineered log jams, and includes diagrams and photographs demonstrating how such structures should be designed and constructed.

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