Fish Passage on the Truckee River, NV: Multi-Action Dependent Benefits Quantification

Investigator: Jock Conyngham

The Sacramento District is restoring system-wide fish passage along the main stem Truckee River, which extends 121 miles from Lake Tahoe, California to the system’s terminus at Pyramid Lake, Nevada. This required a scientifically valid technique for comparing benefits of alternative actions at numerous structures that could be completed in a limited time window (approximately 6 months). The project goal is implementation of the most effective measures for fish passage improvement on the Truckee River.

Significance
Benefit dependencies arise when actions taken at one location affect the potential benefits from other actions or at other locations. Dependent benefits exist in most projects involving multiple actions and, although they are often neglected, can have a significant influence upon the preferred alternative array, cost effectiveness, and the project’s actual level of goal attainment. Given the large ranges over which many fish species move, the cumulative effects of multiple structures is critical in assessing the benefits of fish passage improvement.

SPK worked with ERDC EL to develop fish passage alternatives at 17 of 30 structures on the Truckee River. Once alternatives for each structure were developed, dependencies between the structures had to be identified.

Methods
Passage efficiency, expressed as the passage rate at a given structure, must be multiplied by the cumulative passage rate of the adjacent structure in the channel system to identify actual benefits. For upstream movement, this pattern can be shown mathematically as:

%_pass,t,i = %_pass,i %_pass,t,i-1

where %_pass,t,i is the cumulative passage efficiency at structure i, %_pass,i is the efficiency of structure i in isolation, and %_pass,t,i-1 is the cumulative passage efficiency at the next structure downstream. For instance, if 80% of the mobile population reach and pass structure i-1 (%_pass,t,i-1 = 0.8) and passage at structure i is 75% (%_pass,i = 0.75), then the cumulative upstream passage rate at i is 60% of the mobile population (%_pass,t,i = 0.8 * 0.75 = 0.6) (See Figure 1).


Figure 1. Example of cumulative upstream passage efficiency.

Although dependency in passage efficiency captures system-wide effects on a given population, measures of habitat quantity, species home range, and, if possible, habitat quality are needed to define benefits accurately and distinguish between alternatives. Besides passage efficiency, the metrics and algorithm applied in the Truckee River case included:

• Differences in various species use of river habitat
• Non-uniform biological imperative for movement among species
• Fish utilization of intermediate reaches

First, a panel of experts’ scored swimming physiology, behavior, ranges, and life history needs for the 8 reference species in the Truckee basin and provided the basis for quantitatively assessing benefits. (The invited panel included experts from the U.S. Fish and Wildlife Service, Pyramid Lake Paiute Tribe, ERDC EL, Nevada Department of Wildlife, U.S. Geological Survey, and Chinook Engineering). Secondly, the experts were asked to assign a range of scores (minimum, best estimate, and maximum) for passage and screening efficiency at each structure for each species. With the scores from the panel, EL and counterparts determined 54 plans for cost effectiveness and incremental cost comparison. Three distinct scenarios were developed using summed values for each plan: 1) best estimate, to reflect a most probable outcome; 2) minimum, which reflects the worst case and most pessimistic estimate of benefit; and 3) maximum, which reflects the best case and most optimistic estimate of benefit.

Results
When analyzed with cost-effectiveness/incremental cost analysis software 3 plans were consistently Best Buys and a fourth plan was a Best Buy under the maximum output scenario. Working closely with counterparts, EL and SPK were able to formulate a benefits assessment for fish passage alternatives on the Truckee River that is technically defensible and, equally important, acceptable to a diverse group of stakeholders and partners.

Partners

• USACE Sacramento District
• US Army Engineer Research and Development Center Environmental Lab

Opportunities for Modification
Although the complete benefits algorithms are complex, the fundamental mathematical engine is straightforward and can be readily modified as knowledge increases about critical habitats, home ranges, the variables that underlie passage efficiency, and other factors that enable success in fish passage and population restoration projects.

Certification Status
This model is currently being prepared for USACE certification.

Additional Resources

• Environmental Benefits Analysis of Fish Passage on the Truckee River, Nevada: A Case Study of Multi-action Dependent Benefits Quantification. Conyngham, J., McKay, S. K., Fischenich, J. C., Artho, D. (2011)

• Truckee River Fish Passage.

EBA Resources

• Objectives & Metrics
• Modeling & Forecasting
• Decision Making: Alternative Comparison, Ecosystem Response Threshlolds
• Risk & Uncertainty Management