| Species |
Drought / low flow
(channel bottom) |
High flow pulse
(up to bankfull) |
Small flood
(overbank, 2–10 year
recurrence interval) |
Large flood
(floodplain maintenance,
>10-year recurrence interval) |
| Aquatic Species—Main Channel and Off-Channel |
| Spring Chinook |
May decrease summer populations of juveniles in upstream tributaries because of habitat reduction.
Spring drought may decrease smolt outmigration or adult upstream migration. |
Small floods will have minor impacts.
Flushing sediment from gravel bars may increase spawning success and decrease storage of pathogens in sediments. |
Intermediate floods will have minor impacts in early fall or late winter.
Spawning success and egg survival in redds may decrease if bed is mobilized.
Juvenile survival may be reduced in simplified river reaches.
Flushing sediment from gravel bars may increase spawning success and decrease storage of pathogens in sediments. |
Large floods will have moderate impacts in early fall or late winter. Spawning success and egg survival in redds may decrease if bed is mobilized.
Juvenile survival may be reduced in simplified river reaches.
Flushing sediment from gravel bars may increase spawning success and decrease storage of pathogens in sediments. |
| Bull Trout |
May decrease summer populations of juveniles in upstream tributaries because of habitat reduction.
Spring drought may decrease smolt outmigration or adult upstream migration. |
Small floods will have minor impacts.
Flushing sediment from sediment may increase spawning success and decrease storage of pathogens in sediments. |
Intermediate floods will have minor impacts in early fall or late winter.
Spawning success and egg survival in redds may decrease if bed is mobilized.
Juvenile survival may be reduced in simplified river reaches.
Flushing sediment from gravel bars may increase spawning success and decrease storage of pathogens in sediments. |
Large floods will have moderate impacts in early fall or late winter.
Spawning success and egg survival in redds may decrease if bed is mobilized.
Juvenile survival may be reduced in simplified river reaches.
Flushing sediment from gravel bars may increase spawning success and decrease storage of pathogens in sediments. |
| Aquatic Species—Off-Channel |
| Oregon Chub |
May decrease summer populations of juveniles in floodplain tributaries because of habitat reduction as streams and ponds dry up. |
Small floods may increase floodplain habitat and increase dispersal. |
Intermediate floods will have minor impacts.
Reconnected floodplain habitats may benefit dispersal.
Negative effects of floods on predators may increase survival of chub. |
Large floods may cause mortality and displacement.
Reconnected floodplain habitats may benefit dispersal.
Negative effects of large floods on predators may increase survival.
If floods increase predators, survival may decrease. |
| Western Brook and Pacific Lamprey |
Less affected than other fish because they rear in intergravel environment.
As stream habitat shrinks, survival of juveniles may decrease. |
Will have minor impacts.
Flushing sediment from sediment may increase survival, food supply, and spawning success. |
May decrease survival if gravel deposits are scoured and eliminated.
Flushing sediment from sediment may increase survival, food supply, and spawning success. |
May decrease survival if gravel deposits are scoured and eliminated. Flushing sediment from gravel bars may increase survival, food supply, and spawning success. |
| Western pond turtle |
May decline if habitat dries up.
Augmented summer flows may decrease available habitat. |
Little effect. |
If flood connects river to deep ponds, could increase abundance.
Possible increased mortality in young.
Adult dispersal and reproduction may increase if wetland habitats increase.
Increased scour may provide nest sites. |
If flood creates floodplain ponds or connects river to deep ponds, could increase abundance.
Possible increased mortality in young.
Adult dispersal and reproduction may increase if wetland habitats increase.
Increased scour may provide nest sites. |
| Red-legged frog |
May decline if habitat dries up. |
Likely to scour habitat and cause mortality. |
Likely to scour habitat and cause mortality.
Survival increased if temporary wetlands created.
Adult dispersal and egg production may increase if wetland habitats increase. |
Likely to scour habitat and cause mortality.
Survival increased if temporary wetlands created, but may also allow bullfrogs to invade.
Adult dispersal and egg production may increase if wetland habitats increase. |
| Riparian/Floodplain Species |
| Black Cottonwood |
Extreme drought decreases seedling survival.
Young tree survival may decrease.
Rate of flow decrease critical to seedling survival. |
New gravel bars create instream colonization sites for next season. |
Seedlings and young trees on floodplain may be eroded.
Sediment deposits may benefit young trees.
New bars and floodplain surfaces create colonization sites for next season. |
Seedlings and young trees on floodplain may be eroded.
Vegetative reproduction increases from tree fall and fragmentation.
Sediment deposits may benefit young trees.
New bars and floodplain surfaces create colonization sites for next season. |
| White Alder (Big-leaf maple) |
Extreme drought decreases seedling survival.
Young tree survival may decrease. |
Little negative effect.
High flow may increase seed dispersa. |
Seedlings and young trees on floodplain may be eroded.
Sediment deposits may benefit young trees. |
Seedlings and young trees on floodplain may be eroded.
Vegetative reproduction increases from tree fall.
Sediment deposits may benefit young trees. |
U.S. Department of the Interior | U.S. Geological Survey