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

ge

(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.