Flaming Gorge Technical Working 

Group

May 21, 2018 Hydrology Summary

Jed Parker, P.E.

This hydrologic update provides information regarding current conditions and fulfills the 

requirements detailed in the 2005 Flaming Gorge Final Environmental Impact Statement (FEIS) 

in Section 2.5.3 related to an operational plan for Flaming Gorge Dam (“Hydrology Summary”). 

The Hydrology Summary is to describe the current hydrologic classification of the Green River 

and Yampa River Basins, including the most probable runoff patterns for the two basins. 

Hydrologic determinations for both the Yampa River Basin and Green River Basin above 

Flaming Gorge have been made and are unlikely to change unless significant, unexpected 

precipitation occurs in either basin. The Green River Basin above Flaming Gorge Reservoir is 

expected to receive 1,120,000 acre-feet in the April through July runoff period (May mid-month 

forecast), placing it in the average (below median) hydrologic classification. The Yampa River 

Basin is expected to receive 841,000 acre-feet for the same April through July runoff period, 

placing it in the moderately dry hydrologic classification. These projections are based off of the 

Colorado River Forecast Center’s May Final Forecast. 

Snow water equivalent (SWE) as of May 20, 2018, for the Upper Green River and Yampa/White 

River Basins are 89 and 48 percent of median, respectively. Flaming Gorge SWE is similar to 

2003 and 2006, while Deerlodge SWE is similar to 2001 and 2017. The Tower snotel site, used 

as a reference point for Yampa snowpack and runoff, currently has 30.5 inches of SWE (64

percent of median). On May 20, 2001 the Tower SNOTEL measured a SWE of 28.9 inches 

during a runoff season where the Yampa yielded 790 kaf (62% of 30-year average, Maybell + 

Lily).

SNOTEL tracking graphs, with analogous years, are provided in Figure 1 for the Upper Green 

River Basin above Flaming Gorge and Figure 2 for the Yampa River at the Deerlodge Park, CO 

gage.
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Figure 1 - Upper Green River Basin SNOTEL Tracking. 1981-2010 percent of median compared against 2018 YTD 

Snow Water Equivalent (SWE), and analog years 2006 and 2003.

Figure 2 - Yampa River above Deerlodge SNOTEL Group. 1981-2010 percent of average SWE compared 

against 2018 YTD, and analog years 2001 and 2017.
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10-Day Streamflow Forecasts

Observed data from the Deerlodge Park gage indicates that the Yampa River saw a peak flow 

of around 9,000 cfs, May 12-13. The following, Figure 3, illustrates 10-day forecasted flow 

values for the Yampa River at the Deerlodge Park gage, May 21 through June 1, 2018. 

Figure 3 - Streamflow forecast for the Yampa River, May 21 – June 1, 2018.

Comparison of 2001 and 2018 Yampa River flows

The following, Figure 4 is intended to provide a comparison between Yampa River flows 

between 2001 and what is anticipated in 2018. The 2018 data includes the CBRFC 15-day ESP 

prediction.
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Figure 4 - Yampa River flow comparison for years 2001 and 2018

A 10-day deterministic flow for the Green River at the Jensen, UT gage is provided in Figure 5. 

Please note that increased flows from Flaming Gorge beyond what is currently planned with 

power plant capacity is not represented here. 

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Flow (cfs)

Yampa River flows, 2001 & 2018

2018 Yampa River Flows

2001 Yampa River Flows
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Figure 5 - Streamflow forecast for the Green River at the Jensen, UT gage for the period May 21 – June 1, 2018.

Jensen target flow scenarios

The following are two figures to demonstrate possible release scenarios from Flaming Gorge 

Dam. This analysis uses the following assumptions:

• CBRFC Yampa River 15-day ESP projection to June 4, 2018

• CBRFC Yampa River - 20% exceedance from daily flow statistics from June 5 – June 

15, 2018

• One day travel time from Deerlodge to confluence

• Two day travel time from Flaming Gorge to Jensen, UT

• Power plant capacity is estimated at 4,400 cfs

Scenario 1 in Figure 6 shows the current power plant capacity at 14 day release schedule. This 

scenario is intended to yield a continuous flow at Jensen at or above 8,300 cfs from 5/23 to 

06/05/2018 (14 days).
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Figure 6 - Current release plan, ~4,400 cfs for 14 days

Scenario 2 in Figure 7 is intended to demonstrate the release needed to maintain flows at 

Jensen above 10,000 cfs from the period 05/24 through 06/06/2018 (14 days). Using current 

projections, this release scenario will require releases as detailed in Table 1.

Figure 7 - Release pattern above power plant capacity to maintain 10,000 cfs at Jensen

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Scenario 1 - 14 days at p.p. capacity

~4,400 cfs release Yampa Projection Jensen Projection

8,300 cfs 10,000 cfs

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Scenario 2 - Maintain 10,000 cfs at Jensen

FG Release Yampa Projection Jensen Projection

8,300 cfs 10,000 cfs
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Table 1 - Flaming Gorge release schedule for Scenario 2

Date Flaming Gorge Release

5/21/2018 2708

5/22/2018 4296

5/23/2018 4400

5/24/2018 4400

5/25/2018 4400

5/26/2018 4400

5/27/2018 4400

5/28/2018 4400

5/29/2018 4400

5/30/2018 4400

5/31/2018 4534

6/1/2018 4896

6/2/2018 5318

6/3/2018 5788

6/4/2018 6326

6/5/2018 6721

6/6/2018 5000

6/7/2018 4000

6/8/2018 3000

6/9/2018 2000

6/10/2018 1700

6/11/2018 1700