Background:

Dworshak Dam was built in 1971 by the Army Corps of Engineers.  This 218.8 m (718 ft) high dam irrevocably blocked the North Fork of the Clearwater River for access to hundreds of miles of tributaries for anadromous fish spawning and flooded 86.9 km (54 mi) of riverine habitat for resident fishes.  The resident fisheries that were developed in the reservoir were intended to mitigate for some of these losses.
    
Dworshak Dam is part of the Federal Columbia River Power System (FCRPS), and was constructed primarily to provide flood control and hydropower needs.  Historic operation of Dworshak Dam and Reservoir included full pool operation during summer months, then drafting to meet flood control rule curve objectives during fall and winter (providing artificially elevated discharge for hydropower production) and refill in the spring.  Significant operational changes were instituted at the Dworshak project in 1993.  The majority of reservoir drafting now occurs from July to September.  Approximately 1.2 million acre feet of water stored in Dworshak Reservoir is used to implement summer flow augmentation goals for the Snake River identified in the 2000 FCRPS Biological Opinion (National Marine Fisheries Service 2000).
        
The current operations of Dworshak Dam are a limiting factor to fish populations within Dworshak Reservoir (Clearwater Subbasin Plan, section 8.3.1, pg. 348).  Drawdowns of the reservoir can be a much as 47 m (154 ft) and reduce the surface area by 52%, thereby reducing habitat for fish populations.  Drawdowns also prevent the establishment of productive littoral areas around the shorelines of the reservoir, which affects near-shore spawning and feeding species.
    
Kokanee are a well adapted species for this fluctuating reservoir since they occupy the pelagic, offshore areas and spawn in tributary streams.  Their densities have exceeded 100 adult kokanee per hectare, and harvest of kokanee by anglers has exceeded 200,000 fish in some years.  The population's biggest limiting factor has been entrainment into Dworshak Dam outflows (Clearwater Subbasin Plan, section 8.3.1, pg. 348).  For example, in the spring of 1996, IDFG estimated 1.3 million kokanee were entrained, potentially reducing the kokanee population in the reservoir by 95%.  These losses impacted the kokanee sport fishery for the next three years.  Fickeisen and Geist (1993) noted that the principle bottleneck to the population appeared to be the entrainment losses of fish through the dam, even before the catastrophic 1996 event.
    
The problem of entrainment losses is a major critical limiting factor to Dworshak Reservoir resident fishes and has been researched extensively.  Entrainment losses of resident fish are a major concern in the Columbia Basin.  Entrainment loss of kokanee has been a major problem in both Libby Reservoir (Skarr et al. 1996) and Lake Roosevelt.  Substantial entrainment has been documented at Grand Coulee Dam since 1996 (LeCaire, 1999).  Entrainment losses of kokanee have been shown to be the main factor causing wide fluctuations in the abundance of kokanee in Dworshak Reservoir (Maiolie and Elam 1998).  If these losses could be minimized by a means such as strobe lights, then the operation of dams for flood control, power production, providing anadromous fish flows, etc. could be done with less of an impact on resident species.  Thus, this project could help to increase the flexibility of dam operations, or to allow a better integration of resident and anadromous fish needs.
    
Strobe lights have achieved measurable success at moving fish in a number of different studies.  Patrick (1982) found strobe lights worked well to divert alewife.  Patrick (1980) found that American eels strongly avoided strobe lights with no behavioral adaptation over a 48 hour period.  Nemeth and Anderson (1992) found that juvenile coho and chinook salmon avoided strobe lights.  At the York Haven Hydroelectric Project on the Susquehanna River, American shad were "strongly and consistently" repelled from the turbine intakes (Winchell et al. 1994).  Ploskey and Johnson (1997) found that strobe lights elicited consistent displacement of juvenile salmonids both vertically and horizontally.  Field experiments at the Seton Hydro-Electric station in British Columbia tested the response of sockeye smolts to strobe lights at a current velocity approaching 1 m/sec.  Strobe lights were found to be 56% effective at guiding downstream migrating fish (McKinley and Patrick 1986).  The U.S. Army Corps of Engineers conducted tests with strobe lights at the Hiram M. Chittenden Locks in Seattle during 1998.  They found that smolt entrainment into the locks was reduced by 87% when the lights were turned on, in spite of water velocities of 5.5 ft/sec (Johnson et al. 1998).  Most importantly, our Idaho Department Fish and Game Dworshak Research Project has tested the effectiveness of strobe lights at deterring fish entrainment and found consistently promising results.

FY 06 Contract Summary:

The goal of this project is to improve resident fisheries in Dworshak Reservoir as partial mitigation for Dworshak Dam.  Our project seeks to evaluate then implement strategies to reduce entrainment losses.  In doing so, increases in kokanee abundance will provide for a better fishery.  This year the project will finish our efforts to assess the effectiveness of underwater strobe lights at deterring fish entrainment into Dworshak Dam intakes.  We will conduct tests during higher discharges, reduced water clarity periods, and during any remaining untested dam operation conditions.  We will also perform hydroacoustic surveys to determine the distribution of fish in front of discharging dam intakes while strobe lights are flashing.  This information will provide guidance to the design and construction of permanent installation of strobe lights on Dworshak Dam.  
    
We will also conduct a population survey to monitor Dworshak Reservoir kokanee abundance.  This information will continue to provide a means to evaluate the effect of Dworshak Dam operations on the kokanee population and the ability to meet the management goal of maintaining a population of 30 to 50 adults/ha.  Lastly, we will finish the installation of a fixed-site hydroacoustic transducer inside turbine unit two.  This technology will allow continuous remote assessment of fish entrainment rates and patterns and provide real-time monitoring and evaluation of installed strobe light performance and guide management efforts in the future.