Influence of River Level on Temperature and Hydraulic Gradients in Chum and Fall Chinook Salmon Spawning Areas Downstream of Bonneville Dam, Columbia River

Abstract

Chum salmon Oncorhynchus keta and fall Chinook salmon O. tshawytscha segregate spatially during spawning in the Ives Island side channel of the lower Columbia River downstream from Bonneville Dam. Previous research during one spawning season (2000) suggested that these species selected spawning habitats based on differences in hyporheic temperature and vertical hydraulic gradient (VHG). In this study we confirmed the spatial segregation of spawning based on hyporheic characteristics over 4 years (2001)(2002)(2003)(2004) and examined the effects of load-following operations (power generation to meet short-term electrical demand) at Bonneville Dam on hyporheic function and characteristics. We found that during the study period hyporheic temperature and VHG in chum salmon spawning areas were highly variable during periods of loadfollowing operation, when river levels fluctuated. In contrast, hyporheic water temperature and VHG within chum salmon spawning areas fluctuated less when river levels were not changing owing to load-following operation. Variable temperature and VHG could affect chum and fall Chinook salmon spawning segregation and incubation success by altering the cues each species uses to select redd sites. Additional research will be required to fully assess the effects of load-following operations on the hyporheic environment, spawning site selection, and incubation success of chum and fall Chinook salmon downstream from Bonneville Dam.

Temperature and Water Depth Monitoring Within Chum Salmon Spawning Habitat Below Bonneville Dam -- Annual Report -- October 2007-September 2008

“…PT2X sensors record temperature with a resolution of 0.1°C; water level is recorded with an accuracy of ±0.6 cm. In general, temperature patterns observed from October 2007 through June 2008 were similar to those observed during previous years, in that riverbed temperatures were much warmer than the overlying river (Arntzen et al 2006Geist et al 2008). Despite substantial variation between monitoring locations, at each location, mean riverbed temperature was at least 2°C warmer than the river temperatures.…”

“…During 1999, fisheries researchers from the Pacific Northwest National Laboratory (PNNL) identified areas in which relatively warm subsurface water upwelled through chum salmon spawning gravels in the Ives Island spawning complex (Geist et al 2002). Since 1999, PNNL has monitored river and bed temperatures in the Ives Island channel to assist with emergence timing predictions for chum salmon and to assess the impacts of hydrosystem operation on groundwatersurface water interaction within chum salmon spawning locations (Geist et al 2008). PNNL also monitored water surface elevations within these areas to assist with redd dewatering estimates.…”

Hydropower-related pulsed-flow impacts on stream fishes: a brief review, conceptual model, knowledge gaps, and research needs

“…2. Load-following flows: These are pulsed flows created when electricity is generated in response to immediate system load demands (Geist et al 2008). 3.…”

“…In the lower Columbia River (Washington USA), load-following flows caused temperature and vertical hydraulic gradient variations within the chum and Chinook salmon spawning areas. These gradients altered the cues each species uses to select redd sites, presumably leading to salmon spawning segregation and reduced incubation success (Geist et al 2008).…”

Effects of river scale flow regimes and local scale habitat properties on fish community attributes

“…The negative effect of MA60 confirmed the findings from others studies indicating that important shortterm variation of flow can negatively affect fish community attributes. Stranding mortality (Cushman 1985;Bradford et al 1995;Young et al 2011), downstream displacement (Jeffries et al 2005), reduced spawning and rearing success (Geist et al 2008) due to redd/nest dewatering (McMichael et al 2005), and obstructed migration pathways (Montgomery et al 1983) may all underlie the negative influence of short-term variation of flow on fish community attributes. Although short-term variations of flow seem to reduce fish community attributes, the positive effect of the flashiness of hourly high flows (RH2) suggested that for a comparable average hourly flow variation (MA60) it may be less detrimental to subject a river to a small number of larger hourly flow events (large value of RH2) than to a large number of smaller hourly flow events (small value of RH2) within a day.…”