Feasibility of Fish Passage at Alameda Creek Diversion Dam

Feasibility of Fish Passage at Alameda Creek Diversion DamFor the cost of water associated with operating the fish ladder design component, the estimated annualwater cost assumes that the SFPUC-proposed normal water year instream flows will be used when theyare available at ACDD during the adult immigration period of December through April. Assuming that aflow of 10 cfs is sufficient to operate the fish ladder, 12 opportunity costs would not be incurred when theSFPUC-proposed normal water year instream flows are bypassed between approximately January 11 andApril 30. During this time period, the fish ladder flow (10 cfs) combined with the fish screen bypass flows(5 cfs) would be less than the SFPUC-proposed normal water year instream flows (Table 2-3). The waterthat would be bypassed at ACDD and assumed to be available for operation of screens and ladders withoutincurring additional cost, is shown in green on Figure 5-3.However, from December 1 to approximately January 11, the SFPUC-proposed normal water yearinstream flows, along with WSIP Final PEIR mitigation flows of 10 cfs, are estimated to be insufficient tooperate both a fish ladder and fish screen bypass. In that case, the water cost estimated for operation ofscreens and ladders includes the cost of these additional flows (shown in pink in Figure 5-3). The cost ofthe additional flows of up to 5 cfs that would be required from December 1 through approximatelyJanuary 11, when sufficient flows are available, are applied to the annual cost of operating a fish ladder.Similar to the analysis of reduction in diversion capacity due to screening described in Section 5.2.1,predicted daily average flows from the model described in Appendix B were used to estimateunimpaired flow for each day in the simulated period. These unimpaired flows were then used tocalculate the daily difference between SFPUC-proposed normal water year instream flows and flowsrequired for operation of a fish screen bypass and fish ladder combined, for the period fromDecember 1 through approximately January 11 when the proposed flows would not be sufficient foroperating these two design components. Based on this analysis, the additional volume of waterrequired to operate a fish ladder at ACDD (potentially required from December 1 throughapproximately January 11, only when sufficient flows are available) during the simulated period ofrecord (1969-1985 and 1996-2004) would range annually from 0 to 440 acre-feet. The estimatedvolume of water that would be required to operate a fish ladder is illustrated in Figure 5-3 for both awet year and a dry year. The average annual volume of water required to operate a fish ladder, inexcess of the SFPUC-proposed normal water year instream flows, is approximately 130 acre-feet.Based on the estimated 2016 water rate of $1,500 per acre-foot, the average annual lost diversionopportunity cost associated with operation of a fish ladder to facilitate steelhead immigration isapproximately $195,000. This water cost is added to the annualized fish ladder cost in Section 5.3.5.2.4 LIMITATIONS OF WATER DIVERSION ESTIMATIONSA number of limitations are associated with the lost water diversion opportunity costs for both screensand fishways, some of which may affect the accuracy of the estimates. Limitations with this analysisare listed below:■Daily averages were used to model flows in Alameda Creek because those data were available,but daily average flow does not accurately represent the flashy nature of flows in Alameda Creek.Because the daily average reduces the height of the short peaks that occur in the hydrographimmediately after precipitation events, use of these data underestimates the quantity of water inexcess of the diversion capacity of the ACDT that flows down Alameda Creek and over theACDD. Use of shorter time-step data, such as 15-minute interval real-time flow data, would12 This estimate is based on a preliminary review of the Alameda Creek hydrograph and the Long Fishway described inSection 4.1. A more accurate estimate of flows through a fishway at ACDD would require a flow duration analysis, astorm peaking analysis, design work, and a stage discharge evaluation.ACDD Passage June 2009 Page 5-8