Feasibility of Fish Passage at Alameda Creek Diversion Dam

Feasibility of Fish Passage at Alameda Creek Diversion Dam■■Screened Diversion with Schedule B Bypass Flows represents the estimated amount of water thatcould have been diverted under simulated flows if bypass flows consistent with the SFPUCproposednormal water year instream flow schedule were bypassed downstream at ACDD, whileother flows up to 370 cfs were diverted during the November-through-April time period.Lost Water Diversion Opportunity due to Screening compares the two different diversionscenarios (i.e., unscreened and screened) and quantifies the volume of water that wouldpotentially not be diverted after screen implementation. Consistent with the order-of-magnitudecost estimating in this conceptual feasibility study, the SFPUC-proposed “normal water year”instream flow schedule (Schedule B) was used in this diversion comparison scenario.The estimates depicted in Table 5-2 indicate that on average, use of screens results in an annualdiversion reduction of approximately 1,510 acre-feet of water that could have been diverted in anunscreened diversion condition. Annual reductions in diversion for both a wet and a dry water year areillustrated in Figure 5-2. For the purposes of this analysis, the average annual diversion reduction ofapproximately 1,510 acre-feet of water was used to estimate the annual diversion reduction due toscreening facility operation. An estimated 2016 water rate of $1,500 per acre-foot 11 was used in thisanalysis because it accounts for the time differential of up to several years between this estimate and theactual construction and operation of a potential fish ladder. Therefore, the annual lost diversionopportunity cost due to reduced diversion capacity with screening is approximately $2,265,000. Thiswater cost is added to the annualized screen component cost in Section 5.3.5.2.2 FISH SCREEN BYPASS FLOWSFish screening would require bypass flows at the downstream end of the screens, to maintain sweepingvelocity and prevent fish and small debris from being impinged on the screens, and to provide safedownstream passage for fish (NMFS, 2008a). The volume of water available for diversion toCalaveras Reservoir would be reduced due to this requirement.For purposes of cost estimation it is assumed that the fish screen bypass would require 5 cfs of flow,whenever flows sufficient are available, during the entire diversion period. The estimated annual watercost calculation (Section 5.2) assumes that the SFPUC-proposed normal water year instream flowschedule bypass flows (Section 2.3.2.2) will be used to operate the fish screen bypass when they areavailable. Because the SFPUC-proposed flows (dry, normal, and wet years) would always be sufficientfor operation of a fish screen bypass (5 cfs minimum), it is assumed that there is no additional annualwater cost associated with the operation of the fish screen bypass alone. The entire water costassociated with screening is due to the potential reduction in the maximum rate of diversion withscreening, as described in Section 5.2.1.5.2.3 FISH LADDER OPERATION FLOWSOperation of a fish ladder at ACDD would require a prescribed set of minimum flows, whenavailable, to be maintained prior to any water diversion during certain months of the year when theladder would be in operation, December through April (Table 4-1). Therefore, the volume of wateravailable for diversion to Calaveras Reservoir would also likely be reduced if a fishway wasimplemented. The degree to which SFPUC-proposed instream flows (Section 2.3.2.2) would besufficient to operate a fishway, and the cost of the water in excess of the proposed flows that wouldbe required for that purpose is addressed in this section.11Cost of water cited may be a minimum cost of replacement water (water lost from storage) as it will depend on whereand how SFPUC is able to replace the water. For example, recycled water development in San Francisco is estimatedto cost approximately $3,900 per acre-foot. Thus, the actual cost of replacement water will depend on replacementsources available at the time replacement water is needed.ACDD Passage June 2009 Page 5-6