Rio Grande - Rio Grande Reservoir Multi-Use Enlargement_Application Addendum

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III Mr. Travis Smith, Superintendent October 16, 2003 Page 3 The records from stream gaging stations operated on the Rio Grande at Thirty Mile Bridge and Del Norte were used in this investigation. The Thirty Mile Bridge gaging station is situated O~7 mile downstream from the dam forming Rio Grande Reservoir. It measures the outflow from the reservoir, consisting of both native water passed through the reservoir and water released from storage in the reservoir. The Del Norte stream .gaging station is situated 6 miles west of Del Norte in Rio Grande County and is the main gage used ~y the Division Engineer and water commissioners in their water right administration~ Table 2 shows the monthly and annual flow at the Thirty Mile Bridge gaging station during water years 1946-2002. The annual flow averaged 146,606 acre-feet and ranged from 31,314 acre-feet in water year 2002 to 262,369 acre-feet in water year 1986. Table 3 shows the monthly and annual flows at the Del Norte gaging station during....water years 1946-2002. The annual flows averaged 599, 199 and ranged from 161 ,352 acre..fe'et in water year 2002 to 1 ~ 047,891 acre-feet in water year 1987. RIO GRANDE COMPACT ADMINISTRATION AND THE TRES RIGS DECREE As you know, the administration of water rights for compliance with the Rio Grande Compact plays an important part in determining the water available for the storage in Rio Grande Reservoir.' Three different approaches to this administration occurred during the analysis period. Water years 1946-1967 was a period essentially without administration for the Rio Grande Compact and Colorado accumulated a substantial debit under the Compact Water years 1968-1985 vyas a period of rigorous administration for the Compact as required by Colorado's 1968 Stipulation with New Mexico and Texas. Colorado met its scheduled delivery every year in this middle period with significant curtailments occurring to Colorado water users in some years. "Project Storage" in Elephant Butte and Caballo Reservoirs spilled in 1985, which cancelled Colorado's accrued debit and allowed Colorado to use the annual and accrued debits that are allowable under the Compact Consequently, water years 1986-2002 was a period of what may be considered the normal administration for the Compact. Curtailments to Colorado water users occurred in this latest periodt but were substantially reduced from those in the middle period because Colorado could use the annual and accrued debits that are allowed under the Compact, and because the Closed Basin Project began operating in 1987 and provided some water to help satisfy Colorado's delivery obligations. We believe the approach to compact administration in the latest period will continue in the future; had it been applied in