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" Agenda Item 28 May 16-17, 2006 Board Meeting Page 20f4 Thus, in order for New Mexico to construct the Navajo-Gallup Project and comply with the above Congressional requirement it needs a HD of 6.2 maf, of which it gets 11.25 % or 691,875 AF which is . 22,500 AF more than its apportionment of 669,375 AF under a 6.0 maf HD. Previous Hvdrolol!le Determinations The first HD was done in 1967 and was followed by HDs in 1984 and 1988. We would stress that the Upper Basin States do not agree with some assumptions, in particular the Lower Basin Delivery obligation, and therefore the HOs are mainly planning documents. The previous HOs have been done with annual data using a mass balance equation that considers virgin stream flows, available storage, reservoir bank storage, a specified shortage percentage, and a minimum release to the Lower Basin. The program then computes yield, defines critical period and computes the probability of meeting various demands higher than the firm yield. The 1984 HO concluded that there was enough runoff in the Upper Basin to support a depletion level of at least 5.8 mar. The determination also certified that 69,000 AF of water annually was available through 2039 for marketing from Navajo Reservoir after reserving 3,000 AF per year in perpetuity for the Jicarilla Apache Tribe. The 1988 HO concluded that water depletions in the Upper Basin could reasonably be allowed to rise to 6.0 maf annually. The 1988 HO certified the availability of 94,500 AF of water annually for marketing from Navajo Reservoir. Of this amount, 3,000 AF remained reserved for the Jicarilla Apache Tribe, 69,000 AF was available for marketing through 2039 and an additional 22,500 AF per year from Navajo Reservoir was found to be available for marketing in perpetuity. . The increase resulted from updates to the Upper Basin depletion schedule trough 2040, a longer period of stream flow record, a tolerable shortage to irrigation of 6%, and a 98.5 % probability of being sustained with a 6% shortage. Also, changes to some input data, such as area-capacity tables, occurred. The constants werel) a delivery of 8.25 maf to the Lower Basin, 2) only active storage (power pools protected) in Powell, Flaming Gorge, Aspinall and Navajo was considered, and 3) the average annual evaporation from those four CRSP reservoirs of 546,000 AF was used. 2006 Hvdrolol!lc Determination The current draft HD continues to look at and refine assumptions and evaluate the data used. We would note that the current process for developing the HO has very few variables; it can vary flows, available storage, depletions and shortages or curtailments thereto. The 2006 HO proposal changes the following: . It adjusts certain years in the USBR natural flow database so that natural flow is calculated on a consistent basis, which results in a small increase in stream flows. . It considers and utilizes live storage space in 60 other Upper Basin reservoirs, which makes more storage space available to conserve and utilize high flows that might have otherwise spilled. · It calculates evaporation on an annual basis rather than using an annual average. This results in changes to the evaporation amounts depending on the use assumptions and period of record used and acknowledges that in dry years the reservoir evaporation is less and thus the yield available for other consumptive uses that year can be higher. In other words, the depletion that occurs in a particular year . Flood Protection. Water Project Planning and Finance. Scream and Lake Protection Water Supply Protection. Conservation Planning