Migration Corridors

Importance to Salmonids

Unimpeded access to spawning and rearing habitats is critical to salmonids during their upstream migration from the ocean, as well as during the out-migration period. Out-migration barriers are especially limiting to coho salmon (Oncorhynchus kisutch), as they do not have the option (as do steelhead trout [O. mykiss]) of remaining in the freshwater environment.

Human Impacts

Migration barriers that limit adult and juvenile salmonid access to historic spawning and rearing habitats characterize many watersheds in San Mateo and Santa Cruz Counties. The following types of barrier are common in the region:

Roads. Road and road support structures create barriers to migration by physical blockage or hydrologic alteration. The most common road-related migration barrier is the culvert.

Culverts. By channelizing stream flow, preventing natural channel migration and modifying the cross section of the channel, culverts can affect hydrology, sediment movement, and stream structure, and may completely block migration corridors. While culverts can be designed and maintained to ensure salmonid passage, undersized, improperly installed, or poorly maintained culverts will result in complete or partial migration barrier (Taylor 2000). Potential problems include hydraulic drops at inlet or outlet, with elevation gain and turbulence preventing migration, excessive water velocity or turbulence at inlet or within culvert, and debris accumulation at inlet or within culvert.

Several barriers to migration of salmonids exist along San Francisquito and Corte Madera Creeks in San Mateo County.

Dams. There are numerous small and large dams in the watersheds of San Mateo and Santa Cruz counties – many of which represent barriers to salmonid migration, effectively preventing access to substantial areas of high quality habitat. There are 30 jurisdictional dams in the study area. Jurisdictional dams are defined as "artificial barriers, together with appurtenant works, which are 25 feet or more in height or have an impounding capacity of 50 acre-feet or more.  Any artificial barrier not in excess of 6 feet in height, regardless of storage capacity, or that has a storage capacity not in excess of 15 acre-feet, regardless of height, is not considered jurisdictional." (California Department of Water Resources 1994). The Department of Dams in the Department of Water Resources regulates jurisdictional dams.

Debris Barriers. Debris barriers can form during storm events from natural or human-induced causes. While once thought to be a migration barrier, most debris, especially large wood, is now recognized as an important component to coastal stream habitat and not a true migration barrier. However, debris jams may occasionally create migration barriers. Large, semi-permanent debris jams may form across stream channels, and then change stream flow and block downstream sediment movement. Sediments accumulate upstream of the blockage, while channel incision occurs downstream. While this process can result in improved salmonid habitat, downstream channel incision may result in a barrier that is too high to jump or a shallow downstream staging pool. Debris barriers are generally short lived with decay and strong water forces causing the barrier to collapse and move over time.

Low water flow. Water diversions, groundwater removal, and dams all reduce the quantity and change the timing of water within the watershed. The amount and timing of water flows affect salmonid passage across barriers. Migration may be partially or fully stopped at certain flow regimes. Consideration of migration needs for each life stage (adult, juvenile, and smolt) should be assessed to determine instream flow requirements, as discussed above in Water Quantity).

Thermal Barriers. The preferred migration water temperature is 7.2–15.6 °C for coho, and 10-13 °C for steelhead (Berman 1998). Areas of excessively high temperature may represent a migration barrier for certain species or life stages.

References

California Department of Water Resources. 1994. ESRI Shape File: Dams within the jurisdiction of the State of California. From California Department of Water Resources, Division of Safety of Dams Bulletin 17-93.

Taylor, R.N. 2000. "Culvert Inventory and Fish Passage Evaluation of the Humboldt County Road System." California Deptartment Fish and Game. Final Report.

Berman, C. 1998. "Summary of Temperature Preference Ranges and Effects for Life States of Seven Species of Salmon and Trout (Appendix A)." US EPA Region 10.

Local References

Chartrand, S., B. Hecht, D. Alley, and T. Danzig. 2002. "Arana Gulch Watershed Enhancement Plan Phase 1: Steelhead and Sediment Assessments, Santa Cruz County, California." Balance Hydrologics, Inc., D. W. Alley & Associates, Coastal Watershed Council. Prepared for Arana Gulch Watershed Alliance with funding from California Coastal Conservancy and California Department of Fish and Game, 115 pp.

Ross Taylor and Associates. 2004. "County of Santa Cruz Stream Crossing Inventory and Fish Passage Evaluation." Prepared for the County of Santa Cruz Public Works Department.

General References

Fish Xing Development Team. 2004. Software and learning systems for fish passage through culverts [software program]. U.S. Forest Service [cited 2004]. View on-line source.

NOAA National Marine Fisheries Service (NMFS). 2000. "Guidelines for Salmonid Passage at Stream Crossings." NMFS Southwest Regional Office.

Powers, P.D. , and J.F. Orsborn. 1985. "Analysis of Barriers to Upstream Fish Migration: An Investigation of the Physical and Biological Conditions Affecting Fish Passage Success at Culverts and Waterfalls." Albrook Hydraulics Laboratory, WSU. Final Project Report Part 4 of 4, Contract No. 198BP36523, Project No. 198201400 (BPA Report DOE/BP-36523-1), 134 electronic pp. View on-line document.

Taylor, R.N. and M. Love. 2003. "California Salmonid Stream Habitat Restoration Manual, Part IX: Fish Passage Evaluation at Stream Crossings." California Department of Fish and Game. 100 pp. View document (PDF).

Washington Department of Fish and Wildlife. 2004. Fish Passage Technical Assistance [Web site] [cited 2004]. View on-line source.

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