Bureau of Reclamation Banner, Upper Colorado Region

Navajo Reservoir from the air

 

Navajo Reservoir –Navajo is currently releasing 350 cfs.  Releases are made for the authorized purposes of the Navajo Unit, and to attempt to maintain a target base flow through the endangered fish critical habitat reach of the San Juan River (Farmington to Lake Powell). The San Juan River Basin Recovery Implementation Program recommends a target base flow of between 500 cfs and 1,000 cfs through the critical habitat area.  The target base flow is calculated as the weekly average of gaged flows throughout the critical habitat area.
Navajo was at 6064.4 ft of pool elevation and 1,404,661 acre-ft of storage by the end of February, which was 109% of average for the end of the month. Modified unregulated inflow into Navajo was 41,518 af, which was 137% of average for the month. Calculated evaporation for the month was 861 acre-ft.  NIIP diverted a total of 1,457 acre-ft. The release averaged out to 480 cfs throughout the month.  Precipitation at the dam totaled 0.33 inches (31% of average).
As of March 3rd, the release at Navajo was 450 cfs,  (USGS at Archuleta gage is showing 484 cfs) and the observed inflow is 1,387 cfs.  NIIP is diverting 149 cfs. The reservoir elevation is 6064.68 ft and the content is 1,408,495 acre-ft, or 83% full (72% of Active).  The San Juan River at Four Corners USGS gage is at 1,180 cfs, and the Animas River at Farmington USGS gage is at 828 cfs (Animas at Farmington is estimated as there is a gage malfunction).  Snotel sites above Navajo are showing 15.7 inches of SWE (93% of median on this date).
The most probable modified-unregulated inflow forecast for March at Navajo is 82,000 acre-ft (89% of average), for April is 150,000 acre-ft (88% of average), and for May is 265,000 acre-ft (96% of average).  The April-July modified unregulated inflow forecasts are as follows: 

Min Probable: 380,000 acre-ft (52% of average, a decrease of 100,000 af from the last forecast).  Under this forecast, no spring peak release is expected.
Most Probable: 650,000 acre-ft (88% of average, a decrease of 85,000 af from the last forecast).  Under this forecast, a spring peak release of 5,000 cfs for 40 days is expected beginning in early May.
Max Probable: 910,000 acre-ft (123% of average, a decrease of 140,000 af from the last forecast).  Under this forecast, a spring peak release of 5,000 cfs for 60 days is expected beginning in late April.
The shape of the spring peak release has been coordinated with the SJRIP and will be an attempt to maximize the number of days at 5,000 cfs by reducing the ramp-up to three days. The ramp down will be 2-weeks to prevent fish stranding.  Note that the final shape and volume of these hydrographs are subject to change.

Susan Behery

March 10, 2016

 

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