Yellowtail Dam
Modeling Results Brian Marotz
Hydropower Mitigation Coordinator
Assumptions for this analysis
• Optimize reservoir refill during primary use period.
• Avoid elevations in the Flood Pool above 3640.
• Reduce the extent and duration of spill (>8 kcfs).
• Reservoir draft targets for each month, January through June, were based on water supply (April through July inflow volume).
• Dam discharges during fall based on similar wateryears and shaped to provide stable fisheries flows for primary river species.
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Eva
cuat
ed S
tora
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(KA
F)
April - August Inflow (KAF)
Inflow Water Supply compared to Bighorn Reservoir drawdown
Monthly Elevation Targets
Based on Inflow Water Supply
Example of medium-low wateryear
Not Directly Comparable to GorQ
Comparison of Bighorn Reservoir Elevations
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1960 1970 1980 1990 2000 2010
Elevations: ft. 1968-2009
Var Q Min El.
VarQ Max El
Hist.Min El.
Hist.Max El.
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1960 1970 1980 1990 2000 2010 2020
Outflows: Kcfs 1968-2009
Hist.Min.
Hist.Max.
VarQ Min.
VarQ Max.
Comparison of Bighorn River Discharges
Comparison of Rule Curves Comparison of Rule Curves and Historic Operationsand Historic Operations
• Rule curves reduced reservoir drawdown in all except the highest water years.
• Minimized the use of the flood pool, extent and duration.
• Spill was reduced in volume and duration. On.
• Bighorn River discharges remained more stable.
• Extremely low river flows (<1,500 cfs) were avoided.
Next step:Compare model results andoptimize benefits.