Sediment and steelhead in the Alameda Creek basin: a review

Gordon Becker, Center for Ecosystem Management and Restoration (CEMAR)

Challenges to steelhead

• Duration of flows (à la “good days”)

• Migration impediments

• High growth rearing habitat

• Ocean survivorship

Juvenile O. mykiss

Steelhead smolt

Elevated sedimentation impacts

• Spawning area degradation

• Migration hinderance

• Reduced rearing capacity

Migration impediments

Direct: Migrating salmonids avoid waters with high silt loads, or cease migration when such loads are unavoidable (Cordone and Kelley 1961)

Likely indirect: Silt dominated substrate of lower Alameda Creek may provide a lesser-defined thalweg and fewer velocity refugia than “natural” bedload channel

Alameda Ck near lower inflatable dam, u/s view

Ladder efficiency?

Arroyo las Positas fishway

Spawning areas

In an OR stream, only about 8 percent of total area suitable for coho spawning (Bjornn and Reiser 1991)

In an Eel River tributary, only 2.2 percent of the channel bed provided spawnable habitat-- largely tails of plunge pools and glides (Trush 1991)

Spawning areas (2)

Scour: “Increased sediment transport as a result of…greater sediment supply should increase the average depth of scour…in channels” (Montgomery et al. 1998)

Smothering: Intrusion and accumulation of fine sediments into redds reduces embryo survival through decreased dissolved oxygen and water exchange and impeded emergence (Swanson et al. 1987; Chapman 1988)

Reduced rearing capacity

Thermal refugia: Reduction of pool area or volume in a small ID stream resulted in a reduction of summer [rearing] capacity proportional to the percentage area or volume lost (Bjornn et al. 1977)

Little Yosemite

pool

Reduced rearing capacity (2)

Foraging efficiency: Juvenile coho salmon… exhibited significant avoidance when turbidity exceeded a threshold that was relatively high (>70 NTU) (Bisson and Bilby 1982)

Velocity refugia: Recent LFAs suggest juveniles “blown out” of San Francisquito and San Geronimo Creeks (J&S 2004; Stillwater 2004)

Stonybrook Creek, u/s view

Reduced rearing capacity (3)

“As interstitial refuges and prey declined, steelhead spent less time sheltering behind or under cobbles and more time actively swimming (Power 2003)”

“…steelhead confined to channels with higher levels of sediment experienced lower food availability… (Power 2003)”

Sedimentation rates are key to steelhead recovery in AC