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3.0 WATER RIGHT CONSIDERATIONS The demand to lease or acquire reservoir water on the West Slope is strongly influenced by water right considerations. Many in-basin municipal and industrial water users have relatively junior wa'..)r rights. These junior water rights are commonly out-of-priority and unable to legally divert wate :uring a significant portion of the year. In order to divert water on a reliable year-round basis, such .i' ~r users acquire additional water supplies to augment or replace their water depletions. Most of the water currently leased from Green Mountain Reservoir arid Ruedi Reservoir is ued for water right augmentation. We anticipate that a primary demand for Wolford Mountain Reservoir water will be for augmentation purposes. 3.1 SOURCES OF AUGMENTATION WATER Currently, common sources of augmentation water include West Slope facilities such as Green Mountain Reservoir and Ruedi Reservoir. The conversion of senior irrigation water rights and small local storage facilities are also commonly used as a source of augmentation water. Augmentation with irrigation water results in the permanent removal of irrigation water from certain agricultural lands. The water that was previously consumed by crop evapotranspiration is used to augment out-of-priority depletions associated with a junior water right. Unlike the use of reservoir water, augmentation based on irrigation dry-up can occur only during the growing season and cannot exceed the historical consumptive water use associated with the land permanently removed from irrigation. In addition, the administration of many agricultural based augmentation plans is complex and requires the release of water to the stream system during the non-irrigation season. The purpose of these releases is to mimic the historic pattern of irrigation retum flow to a given stream system. Reservoir releases are often a preferred source of water right augmentation. Water from a reservoir can be released to augment out-of-priority depletions that occur during any portion of the year. Further, the use of reservoir water does not require the permanent dry-up of agricuituralland. The engineering and legal costs to adjudicate an augmentation plan utilizing agricultural rights can be significant. If water can be leased from a reservoir, the expense to a water user is often r~duced. 3.2 SENIOR WATER RIGHT DEMANDS The location and the amount of demand for West Slope augmentation water is influenced by the location and timing of senior water right calls. Water right calls primarily originate from two senior demands located on the main stem of the Colorado River: the Shoshone Power Plant demand and the Cameo irrigation demand. The operation of Green Mountain Reservoir also affects the timing and amount of water right calls. In addition, proposed in stream flow rights on the lower Colorado River could affect junior water users in the future. A discussion of these water right considerations is presented below. 5