Feasibility of Fish Passage at Alameda Creek Diversion Dam

Feasibility of Fish Passage at Alameda Creek Diversion Damabout 18 miles of accessible salmonid habitat (MMWD, 2007). During most years, the watershedsupports 8 to 16 steelhead redds per mile. Redds are concentrated in stream reaches where substrateand flow are favorable. Localized redd densities within favorable reaches have been observed as highas 35 redds per mile during some years. Across different watersheds, redd density is highly variable,depending on individual river and stream characteristics. Maahs and Gilleard (1993) report that foreight coastal Mendocino County streams, redd (assumed to be mostly steelhead) densities in Februaryrange from much less than 1 redd per mile up to approximately 5 redds per mile. Steelhead reddsurveys in the much larger, interior Feather River of California during 2003 indicated redd counts of36 per mile, with nearly all redds concentrated within a few miles of the river system (DWR, 2003).Based on these data, future steelhead redd density above ACDD is estimated to have a potential rangefrom 1 to 35 per mile.Given the above estimate of between 4 and 10 miles of potentially suitable steelhead habitat aboveACDD, and the expectation of between 1 and 35 redds per mile, the habitat above ACDD may becapable of supporting between 4 (1 redd/mile × 4 miles of habitat) and 350 (35 redds/mile × 10 milesof habitat) steelhead redds annually, with the actual value likely lying somewhere in between. Basedon this estimate, it may be possible for habitat above ACDD to sustain a population of steelhead (seeAppendix C). If the quantity and quality of habitat above ACDD are insufficient to independentlysustain a population of steelhead, then it is likely sufficient to sustain a subpopulation large enough tocontribute to a steelhead metapopulation in the Alameda Creek Watershed, if subpopulations are alsoestablished at other locations.6.3 ENVIRONMENTAL CONSIDERATIONSThis section summarizes non-steelhead environmental considerations including biology, wetlands,and cultural resources related to fish passage at ACDD. Construction and operation of fish passagewould result in some unavoidable adverse environmental impacts. Such impacts are typical whenconstructing nearly any type of project in natural lands in California, and should not be consideredprohibitive, but this would certainly add to the overall cost of providing fish passage. In addition toevaluating the design components as in the previous sections, the environmental impacts associatedwith construction and operation of the different design components also should be considered beforeimplementing fish passage. Impacts may require permitting, minimization, and mitigation.While the specific impacts of fish passage as evaluated in this technical memorandum would beaddressed separately in specific permitting documents, the types of impacts that could potentiallyoccur could include:■■■■Interference with the movement of resident fish species;Some localized placement of fill in jurisdictional waters of the United States, including wetlands,that are regulated under the federal Clean Water Act, to construct fish passage facilities andinfrastructure;Limited loss or degradation of riparian habitats regulated by the CDFG under the Fish and GameCode at locations where facilities are constructed; andLimited loss or degradation of habitats that are potentially used by special status species(federally or state-listed, or state species of concern), including the California red-legged frog, thefoothill yellow-legged frog, the California tiger salamander, and at least one species of bat atlocations where facilities are constructed or roadwork is required.ACDD Passage June 2009 Page 6-6