Feasibility of Fish Passage at Alameda Creek Diversion Dam

2.0 Settingalmost never submerged; except during extreme high flows, the water surface elevation downstreamof the spillway remains below the invert of the lower sluiceway.During diversion to Calaveras Reservoir, both sluiceways typically remain closed. In general, it isunderstood that standard procedure is to sluice the sediment channel at least once per year (at the endof the diversion season) or as needed to prevent bedload from being transported into the ACDT. Thisentails opening one or both of the sluiceways to flush sediment from behind the ACDD and sedimentchannel.Access to the dam site is via a maintenance road that approaches from the northwest and dead-endsjust east of the right abutment. Access to the left side of the dam in high-flow times is restricted to agallery (approximately 3 feet wide by 6 feet high) that runs through the dam. During low-flowperiods, the left side can be accessed by walking across Alameda Creek upstream of the trash rack, orby walking across the ogee crest spillway when it is not spilling.Modification of ACDD and its operation are proposed in relation to the SFPUC’s Calaveras DamReplacement Project (CDRP). CDRP includes provision of water releases in accordance with aMemorandum of Understanding (MOU) with the CDFG (CDFG, 1997). The flow compliance pointfor this instream flow schedule is immediately below the confluence of Calaveras and Alamedacreeks. To maximize aquatic habitat under future CDRP operations, SFPUC will provide bypassflows from the ACDD whenever flows are available and will supplement flows with releases from thereplacement Calaveras Dam, as needed, to meet the requirements of the MOU (SFPUC, 2008a). TheSFPUC has also proposed an instream flow schedule for future populations of steelhead (SFPUC,2009b). The SFPUC-proposed instream flow schedule would provide differing amounts of flowdepending on annual hydrologic conditions (dry, normal, or wet), as summarized in Table 2-3, andillustrated in Figure 2-6. To provide ACDD bypass flows under the CDRP, SFPUC plans to constructa new tunnel through the left abutment of the ACDD, or like structural components, through whichflows will be bypassed.Additionally, as noted in the programmatic environmental impact report (PEIR) for the SFPUC WaterSystem Improvement Program (WSIP), it is anticipated that the SFPUC, when implementing CDRP,will adopt a mitigation measure to provide a bypass of up to 10 cfs downstream of the ACDD fromDecember 1 to April 30 whenever sufficient flow is present in the stream (SFPD, 2008). For thepurposes of this technical memorandum, it is assumed that both the SFPUC-proposed instream flowschedule and the WSIP mitigation flows would be provided as bypass flows at ACDD whenever suchflows are available.2.4 STEELHEAD PRESENCE IN THE ALAMEDA CREEKWATERSHEDHistoric population estimates of steelhead in the Alameda Creek Watershed are unavailable, butsteelhead were historically present (Leidy, 2007). Based on various anecdotal accounts of steelheadpresence in the watershed from as early as the 1930s, the size of the watershed, the presence ofperennial streams, and various O. mykiss records from surveys since the 1930s, it is likely that in thepast this watershed supported a large steelhead run, relative to other San Francisco Estuary streams(Leidy et al., 2005).ACDD Passage June 2009 Page 2-11