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<br />about the 7111 of the month, the first comprehensive analysis is done to determine what the <br />projected index supply for the year will be. Upper index flows that have occurred through the <br />end of March are added to the forecast (April - September) and to average flows for October <br />through December. This will provide the first estimate of the annual index supply for each river. <br /> <br />From that estimate of the annual index, the obligation for each river is determined using the <br />delivery schedules in Article III. Deliveries through the end of March are added to the normal <br />(average) deliveries for November and December, the anticipated Closed Basin Project deliveries <br />and the appropriate portion of the 10,000 acre-foot credit The sum of those deliveries, subtracted <br />from the projected obligation determines the amount of water needed at the State line during the <br />irrigation season (April - October). Adjustments to the amount needed are made for variables <br />which include Colorado's accrued credits or debits, return flows, tributary inflows or accretions <br />to the rivers. <br /> <br />Once the amount to be delivered during the irrigation season is determined then it is necessary to <br />determine how much of the available index supply must be delivered on a daily basis to achieve <br />the desired delivery. This is accomplished by dividing the amount of delivery required by the <br />amount of index supply available during the irrigation season. This quotient then represents the <br />percentage of the daily available index supply that must bypass the Colorado diverters and be <br />delivered to the Stateline. Again, return flows, tributary inflows and groundwater accretions must <br />be taken into consideration and the curtailment reduced accordingly or substantial over deliveries <br />can result One of the greatest challenges for the administrators is weather conditions that cause <br />substantial changes to the index supply and the forecast which add greatly to the delivery <br />obligation. Late summer or early fall rainfall events can. have very dramatic effects on <br />administration and must be handled in a timely manner to prevent large under deliveries. A study <br />of the delivery schedules show that in higher years like 1999, that the incremental amount of <br />water that has to be delivered when an unexpected event occurs can reach as high as 90 percent of <br />the increased amount of water indexed. Therefore, during the entire irrigation season it is <br />imperative that a continual monitoring of daily administration occurs to ensure that the forecast is <br />indeed tracking as was expected and that deliveries are being made accordingly. <br /> <br />November 1" through December 31" <br /> <br />Diversions on both the Rio Grande and the Conejos River are curtailed 100 percent if necessary <br />to deliver water to the State line to complete the remaining deliveries. Reservoirs are typically <br />allowed to go into storage on November I. Consultation with the water users on both rivers can <br />result in some diversions extending into November if the Compact will be met with the remaining <br />deliveries. In fact, six large ditches on the Rio Grande have obtained decrees to divert water to <br />recharge the aquifers in the San Luis Valley to the extent the water is not needed to meet the <br />Compact obligation. Typically, by no later than Thanksgiving, the winter weather has made <br />diversion of water impossible and all diversions are concluded. Closed Basin Project deliveries <br />are made to the river at the sustainable level necessary and in accordance with winter operations. <br /> <br />Because the Compact is river specific in Colorado, the process for determining curtailment percentages <br />occurs independently for both the Rio Grande and the Conejos River and different curtailment <br />percentages are applied to the two systems pursuant to the analysis described above. It is important to <br />note this process relies heavily on forecasted inflows at least through the end of June. As the snowmelt <br />runoff recedes, the summer thunderstonn activity or lack thereof begins to control the index supply for <br />the remainder oflhe summer and fall seasons. The actual flows are not, and cannot be, known until very <br />late in the calendar year. While Colorado attempts to match the delivery requirement on an annual basis, <br />over and under deliveries can and do result from inaccuracies associated with inflow forecasts and <br /> <br />j <br /> <br />, .,;.,ill' <br />~",.'",~"ti~4. = :; . <br />