Feasibility of Fish Passage at Alameda Creek Diversion Dam

Feasibility of Fish Passage at Alameda Creek Diversion Damdefine the flows under which steelhead are most likely to migrate. Key design requirements for anypassage or screening features would come directly from this analysis.Design components identified that could potentially facilitate adult immigration to spawning habitatsabove ACDD include:■■■Fish laddersFish liftsTrap and haulDesign components to facilitate upstream steelhead migration would be operational from Decemberthrough April (Table 4-1) (information regarding expected numbers of immigrating steelhead can befound in Section 6.2).Passage would also require screening at the ACDT, to prevent entrainment of fish into the diversiontunnel, and Calaveras Reservoir. Screening in accordance with regulatory criteria would require a fishscreen bypass, which would need to be designed in a manner that could safely provide downstream fishpassage at ACDD for both emigrating juvenile and post-spawn adults. Details on future bypass flows atACDD are presented in Section 2.3.2.2. Bypass flows related to future operation of CDRP would beprovided at ACDD via a new outlet structure proposed as part of the CDRP. However, in the analysis inthis memorandum it is assumed that SFPUC-proposed instream flows could also be provided by acombination of a fish ladder (Section 4.1), and/or a fish screen bypass flow conduit operated inconjunction with screening of ACDT (Section 4.4). If upstream passage was provided for immigratingadult steelhead, fish screen bypass flows would be the associated primary mechanism allowing emigratingsteelhead to bypass the dam in a downstream direction.This section describes the adult immigration and fish screen design components and provides apreliminary evaluation of their suitability at ACDD. Design components that are technically feasibleat ACDD and that would meet the basic biological needs of a steelhead population above ACDD areretained for further evaluation. Design components are eliminated from further consideration in thismemorandum if they serve the same purpose as other design components but at a clearly higher cost,with greater engineering challenges, or are otherwise determined to be less suitable than substitutabledesigns.4.1 FISH LADDERSIn this section, fish ladders (sometimes more generally referred to as fishways) are evaluated as aspecific design component for providing passage to immigrating adult steelhead. Following theanalysis, this design component is retained for consideration later in this document.A fish ladder is a structure used to facilitate passage of fish over or around an obstacle, typically adam or other migration barrier (Figure 4-1). Specifically, as defined by NMFS, the fish ladder is thecomponent of a fish passage facility that dissipates hydraulic potential energy into discrete pools orinto a baffled chute to provide passage for upstream migrants (NMFS, 2003). Fish ladders are themethod most commonly used for allowing upstream fish migration past instream barriers. Althoughdesign criteria for fish ladders are primarily based on adult fish immigration, when operating, somefish ladders also can provide for downstream migration.Typically, fish ladders consist of a series of ascending pools that must be “climbed” or jumped by thefish. A series of pools contained within the water passage acts to incrementally divide the height ofthe passage and to dissipate the energy in the water, thereby enabling fish to gradually climb theACDD Passage June 2009 Page 4-2