North Platte River Water Supply Update (3)

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-,. . Wyoming Area Office Page 1 of 2 Bureau of Reclamation North Platte River Water Supply Update April 16, 2008 Figure 1 shows current reservoir storage conditions for Reclamation reservoirs as of April 10, 2008, on the North Platte River and provides a comparison of total inflow, total Guernsey Reservoir outflow, and total September 30 system storage for water years 2005 through 2007, including the "expected" 2008 operations compiled from the April operating plan. The term "kaf ' used in this report represents acre-feet times 1000. The North Platte total system storage of 706.3 kaf at the end of water year 2007 represents a decrease in the system storage of 99.6 kaf over water year 2006 (805.9 kaf). This system storage decrease is attributable to below average runof£ Irrigation releases from Guernsey Reservoir for downstream irrigation demand were discontinued on September 7, 2007. The North Platte Project Irrigation Districts conserved approximately 286.3 kaf of carryover storage. The total system expected inflow for 2008 is estimated at 1,251.0 kaf or 94% of average. The total Guernsey Reservoir expected outflow for 2008 is estimated to be 955.0 kaf. The projected total system expected storage on September 30, 2008, is estimated to be 60% of average (851.3 kaf/1419.2 kaf) or 3 1 % of the total conservation capacity of the system and represents the Scn lowest total system storage in the last 30 years. Figure 2 and Figure 3 provide snow water equivalent (SWE) information expressed in inches of water for the upper and lower North Platte River basins. The SNOTEL information shows the SWE is above average for the upper North Platte River Basin and at average for the lower North Platte River Basin. As of April 14, 2007, the Natural Resources Conservation Service (NRCS) reported the SWE to be 119% and 101% of average (Figure 4) for the upper and lower basin, respectively, thanks to recent snow storms the week of April 7`h. Reclamation's April 1 forecast of the April through July runoff in the basin above Seminoe Reservoir is 750 kaf (107% of average) and 100 kaf (83% of average) for the basin between Alcova and Glendo Reservoirs. The Natural Resource Conservation Service (NRCS) SWE data on March 31, 2008 were 110% and 94% of average for the upper and lower North Platte River basins, respectively, when these forecasts were made. Figure 5 provides a comparison of SWE data for the years 1997, 2006, and 2008, above Seminoe Reservoir. These data show how sensitive the runoff is to late snow storms that extend the SWE curve to a peak beyond May 1. Even with an April-July runoff like water year 1997, the expected total system storage on September 30, 2008, would likely only increase by approximately 300 kaf from 850 kaf to 1150 kaf, which is still well below the 30- year average of 1419.2 kaf. Reclamation's determination of the forecasted supply as of April 1 is above 1,100 kaf (Figure 6), which indicates at this time there is no need to allocate storage. Table 1 shows the actual total system inflows, Guernsey outflow, and end-of-month total system storage for the month of October through March and the projected April through September operations based on minimum, expected, and maximum inflow conditions. These inflow conditions (Table 2) provide the range for Reclamation operating plans in the North Platte River