Upper Snake River Wyoming Operations Update

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Upper Snake River Wyoming Operations Update

Upper Snake River Wyoming Operations Update

April 12, 2019

Subject:  2019 Upper Snake River Wyoming Operations Update

Purpose:  The purpose of these Operation Updates is to provide information regarding Reclamation’s operations as the season progresses.  The operations outlined in this update are based on the best data available at the time and are subject to change as new information becomes available.  For additional information and resources, please visit our website at:  https://www.usbr.gov/pn/hydromet/uppersnake/ .

Summary

The Upper Snake reservoir system is currently 83% full (3,336,211 acre-feet out of 4,045,695 acre-feet). Official water supply forecast for the April-July runoff period have been finalized and the information is included in the table below. April precipitation to date has been well above normal and accompanied by overall near-normal seasonal temperatures. The observed precipitation early this week caused stream-flow to briefly surge, but the subsequent cooling trend has caused runoff to trend to just above last week’s levels. The wet and cool trend is expected to continue through Wednesday, with a potential warm up Thursday and into Friday before another cooler system moves through the region.

 

Jackson Lake’s discharge target was maintained at 700 cubic feet per second (cfs) and is projected to remain steady for this week as well.

 

Palisades’ releases were increased by approximately 2,800 cfs during the week, and the current discharge target is approximately 9,800 cfs. The reservoir is drafting on a trajectory consistent with current estimates for required flood control levels in early May. Additional increases to discharge are likely next week.

 

Ririe’s discharge target was maintained at 125 cfs this week. Ririe’s release is expected to remain at the current magnitude until the reservoir reaches approximately 60,000 AF.

 

Island Park’s discharge target was held steady this week. Island Park’s discharge is expected to remain at the current target until the reservoir reaches approximately 112,000 AF.

 

American Falls Reservoir’s releases were adjusted downwards early this week to fill the reservoir to acceptable levels. Beginning Thursday, releases were increased to approximately 8,750 cfs. Additional increases are likely for the next week.

 

Little Wood Reservoir is projected to maintain the current release for the next 3-7 days.

 

Facility

% Full

Storage

 (acre-feet)

April – July Runoff Forecast

% of Normal

 Yesterday’s

Inflow

 (cfs)

Estimated Outflow (cfs)

Next anticipated discharge change

Jackson Lake

78%

661,231

104%

698

700

Not scheduled

Palisades

73%

875,835

99%

6,426

9,800

Potential increases in the next 3-7 days

Ririe

67%

54,092

121%

279

125

At content of ~ 60,000

Island Park

80%

108,212

115%

613

648

At content of ~ 112,000

Grassy Lake

88%

13,314

9

0

Not scheduled

American Falls

94%

1,566,029

10,197

8,750

Potential increases in the next 3-7 days

Minidoka

94%

89,591

5,801

7,000

+1,250 cfs 

to 8,250 cfs tomorrow

Milner

1.1 feet below full

5,355

 3,500*

*River QD

          +1,000 cfs

 to 4,500 cfs tomorrow

Little Wood

44%

13,228

141%

1,119

625

Not scheduled

 

Reservoir levels, reservoir discharge and river flows can be monitored on the USBR Hydromet page here: https://www.usbr.gov/pn/hydromet/

 

The Upper Snake “teacup” diagram which provides a graphical overview of system conditions can be accessed here:  https://www.usbr.gov/pn/hydromet/burtea.html

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