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24-Month Study Reports of Colorado River Operations

January 27, 2015
by John Weisheit

A 24-month report is a document from the Bureau of Reclamation which provides information about the conditions of main reservoirs in the Colorado River basin and projections for the near future. For instance, the report is essential for making a determination about operating criteria for shortage and surplus declarations.

Projection for water year 2017

During the 17-year period 2000 to 2016, the unregulated inflow to Lake Powell, was above average in only 3 out of the past 17 years. The period 2000-2016 is the lowest 17-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.57 maf, or 79% of the 30-year average (1981-2010). (The 1981-2010 total water year average is 10.83 maf.)

The unregulated inflow during the 2000-2016 period has ranged from a low of 2.64 maf (24% of average) in water year 2002 to a high of 15.97 maf (147% of average) in water year 2011.

In water year 2016 unregulated inflow volume to Lake Powell was 9.62 maf (89% of average), which, though still below average, was significantly higher than inflows observed in 2012 and 2013 (45% and 47% of average, respectively).

Under the current most probable forecast, the total water year 2017 unregulated inflow to Lake Powell is projected to be 12.93 maf (119% of average).At the beginning of water year 2017, total system storage in the Colorado River Basin was 30.2 maf (51% of 59.6 maf total system capacity). This is nearly the same as the total storage at the beginning of water years 2015 and 2016 which began at 30.1 maf and 30.3 maf, respectively, both of which were 51% of capacity.

Since the beginning of water year 2000, total Colorado Basin storage has experienced year to year increases and decreases in response to wet and dry hydrology, ranging from a high of 94% of capacity at the beginning of 2000 to a low of 50% of capacity at the beginning of water year 2005.

One wet year can significantly increase total system reservoir storage, just as persistent dry years can draw down the system storage. Based on current inflow forecasts, the current projected end of water year total Colorado Basin reservoir storage for water year 2017 is approximately 33.8 maf (57% of total system capacity).

The actual end of water year 2017 system storage may vary from this projection, primarily due to uncertainty regarding the season's snowpack and resulting runoff and reservoir inflow. Based on the April minimum and maximum probable inflow forecasts and modeling, the range of end of water year 2017 total system capacity is approximately 32.47 maf (54%) to 37.0 maf (62%), respectively.

Upper Colorado River Basin Water Resources Division

Lower Colorado River Basin Water Resources Division

MONTHLY RESERVOIR SUMMARY

ARCHIVE OF 24-MONTH REPORTS

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018


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