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C. Administration of Existing Senior Water Rights Basic Concept The two main calling water rights on the main stem of the Colorado River are the Shoshone Rights and a group of rights known as the Grand Valley rights or the Cameo Call, actually 3 different structures. The Shoshone rights are capable of calling for water year round (1250 to 1408 cfs), while the Grand Valley rights are irrigation rights which can only call for water April through October. These are absolute water rights, which under dry to average hydrologic conditions may govern the flows on the Colorado River through Glenwood Canyon during portions of the year. The Shoshone senior right is the focal point of this concept as it is the most senior water right and located at the bottom of the study area. However the Grand Valley rights do receive the delivery of the supplies from the Green Mountain Reservoir Historic Users Pool(HUP). II. Benefit to Stream Segments The year round utilization of the Shoshone right has the ability to keep flows of around 1250 cubic feet per second (cfs) in the Colorado River at the Dotsero gage. The Shoshone right is more protective for the Glenwood Canyon segment. The Grand Valley rights call for water from all upstream junior rights. During portions of the year, flows on the Colorado River have historically been maintained by the operation of the Shoshone rights, and to a lesser extent the Grand Valley rights. III. Permanent Flow Protection When operating at full capacity, the Shoshone rights offer year round protection in the operation of existing water rights administration. The administration of these rights has largely shaped the historic hydrograph. The Grand Valley rights accept delivery of HUP supplies, generally from August through October, but the Grand Valley Project Power Plant water rights may have the potential to affect the existing water rights administration year round. IV. Pros and Cons Pros • These are established water rights in place to call for water under dry to average hydrologic conditions and that can help maintain ORV's during portions of the year. • Reliance on these existing rights allows for upstream operational flexibility to deliver water to calling rights provided replacements are made upstream of Segment 4. • Grand Valley HUP deliveries take place during drier conditions and therefore benefit the study area reaches when other concepts may not provide physical supply. • Segments 4 through 7 are downstream of Green Mountain and therefore would benefit from HUP releases. Page 3 of 6