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<br />. <br /> <br />is a pre-Compact reservoir located on the main stem of the Rio Grande. <br />Large quantities of water can be stored and released without being <br />subjected to Compact storage limitations. This is a unique situation, <br />since no other reservoir has such an advantage. For all practical <br />purposes, water cannot be stored in reservoirs constructed after 1929 <br />because of Compact limitations. <br />Whenever the State Engineer determines that the Compact stored <br />water is not required to meet Colorado's Compact delivery obligation, <br />50 percent of stored "Compact water" is released for the benefit of <br />the San Luis Valley Irrigation District and 50 percent of this water <br />is released for the benefit of all other water users on the Rio Grande <br />in Colorado. Since this administrative procedure was developed in <br />1979,58,000 acre-feet of Compact stored water has been delivered to <br />the Rio Grande water users. Without utilization of Rio Grande Reser- <br />voir for Compact administration purposes, this water would have flowed <br />into New Mexico and would not have been beneficially used within <br />Colorado. <br />Since the Rio Grande Dam cannot safely pass large floods, use of <br />the reservoir by the SLVID and by the State of Colorado for Compact <br />administration purposes is in jeopardy. As a result of the flood <br />hydrology study, it was determined that the existing dam could not <br />pass the probable maximum or the one-half probable maximum flood with <br />the reservoir full at the beginning of the storm. According to the <br />Corps of Engi neers cr iter i a, the dam is cons i dered "seri ous 1 y i nade- <br />quate" and "unsafe." If a flood were to occur at the reservoir site <br />with a magnitude of one-half probable maximum or greater with a full <br />reservoir, the existing dam would overtop and, in our opinion, the <br />dam would fail. The resulting dam failure would cause extensive <br />property damage downstream and probably would result in loss of life. <br />Because of the serious problem of potential overtopping of Rio <br />Grande Dam, alternate ways of passing the large floods were investi- <br />gated. For smaller floods with a frequency of occurrence greater than <br />once in 500 years, the existing dam could safely pass these floods. <br />In order to safely pass the probable maximum flood, it would be neces- <br /> <br />. <br /> <br />. <br /> <br />-4- <br />