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<br />,~Ja139
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<br />was 351,000 acre-feet, or 40 percent of the long-term average. However, since
<br />combined storage at the end of 1989 was 1,706,000 acre-feet, or 201 percent of the
<br />long-term average, a full supply to all water users was available for the year,
<br />
<br />The January 1, 1990, forecast for San Marcial Reservoir was 155,000 acre-feet, or
<br />32 percent of normaL Each month thereafter, from February through May, the
<br />forecast was lower than 32 percent, The final forecast of June 1, 1990, ended at
<br />34 percent, The forecast had very little impact on reservoir operations for 1990
<br />because of the large amount of storage carried over from previous years.
<br />
<br />Summer moisture also aided projects on the Pecos River; however, nearly all
<br />predicted use of reservoir storage was realized in 1990, Early predictions for
<br />streamflow runoff were very low (30-40 percent) throughout the basin. As the
<br />season progressed, late spring moisture increased the forecasts slightly, but heavy
<br />use of reservoir storage was anticipated, Beginning in early July, monsoonal type
<br />conditions in the basin developed and irrigation demand for reservoir storage
<br />decreased significantly, Good moisture conditions continued through September,
<br />resulting in good reservoir storage carryover potential for the 1991 season,
<br />Smaller Reclamation projects within the basin will require normal to above
<br />normal runoff to replenish reservoir storage used in the past 3 years,
<br />
<br />Projected Conditions for 1991
<br />
<br />In planning for 1991 Colorado River operations, three reservoir inflow scenarios
<br />were developed and analyzed. Statistically, inflows for these scenarios are
<br />approximately the upper quartile (equalled or exceeded 25 percent of the time),
<br />lower quartile (equalled or exceeded 75 percent of the time), and lower decile
<br />(equalled or exceeded 90 percent of the time), They have been respectively labeled
<br />the probable maximum, most probable, and probable minimum inflows,
<br />
<br />The inflow volumes resulting from these assumptions were used as input data in
<br />Reclamation's monthly reservoir operation planning computer model, which is
<br />used to plan reservoir operations for the upcoming 12-month period. With the
<br />three levels of assumed water year 1991 inflow and reservoir storage conditions,
<br />studies showed that no project shortages would occur under any inflow scenario,
<br />
<br />For the Rio Grand Project, projections for 1991 project operations were made for
<br />each of three water supply scenarios: the most probable (lOO percent of normal),
<br />the reasonable minimum (25 percent of normal), and the reasonable maximum
<br />(200 percent of norma\),
<br />
<br />With the most probable runoff, a full supply of water would be available to most
<br />users along the lower Rio Grande. Further, this condition would result in a near
<br />full supply for the larger projects on the upper Rio Grande, Smaller projects in
<br />the upper Rio Grande would experience minor shortages,
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