HR: 1330h
AN: NB33G-15    [Abstracts]
TI: Downstream Effects on Water Quality From Reservoir Drawdown in Southeast Idaho
AU: * Mladenka, G C
EM: gmladenk@deq.state.id.us
AF: Idaho Department of Environmental Quality, 444 Hospital Way #300, Pocatello, ID 83201 United States
AU: Van Every, L R
EM: lvanever@deq.state.id.us
AF: Idaho Department of Environmental Quality, 444 Hospital Way #300, Pocatello, ID 83201 United States
AB: During normal operations in agricultural water delivery, water levels in American Falls (Snake River) and Blackfoot (Blackfoot River) reservoirs decline in late summer and fall. When reservoir volumes reach certain low levels, water released downstream has increased suspended sediment concentrations. This sediment-laden water potentially impacts coldwater aquatic life and salmonid fisheries. To assess impacts to downstream water quality, we collected water quality data above and below the reservoirs. Turbidity below reservoirs was elevated over inflow background levels and was influenced primarily by reservoir level. Turbidity during these periods exceeded both instantaneous and 10 consecutive day average numeric criteria of 50 and 25 NTU, respectively. Downstream phosphorus and nitrogen were significantly elevated compared to upstream sites. Dissolved oxygen in Blackfoot River below Blackfoot reservoir did not meet cold water criteria of 6 mg/L numerous instances during the monitoring period. Our data suggests maintaining minimum reservoir pools would help meet water quality standards and maintain beneficial uses in downstream reaches of these rivers. Failure to maintain minimum reservoir levels in light of increasing demand and extended drought cycles will continue to negatively impact water quality and beneficial uses in these important river reaches.
DE: 1803 Anthropogenic effects
DE: 1857 Reservoirs (surface)
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly