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, Wood 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”.
DOWNLOAD THE 2007 REPORT DOWNLOAD THE 2008 REPORT
Final Geomorphic Assessment Report, Big Wood River, Blaine County, Idaho, Biota Research and Consulting, Inc. (Biota), February 1, 2016, 122 pages with Figures and Exhibits
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)