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19 Supply Irrigating Ditch Co, January 24-25,2001, Agenda Item 11 b, Water Rlahts The water rights owned by the SIDC Include a dlre~t flow right in amount of 92.2 CFS from St. Vraln Creek, and a 51 % interest in the Beaver Par~ Reservoir. The Beaver park Interest delivers approximately 800 acre-feet per year. RecQrds of the State Engineer's Office (1997 - 1999) indicate that the average annual volume diverted by the Supply Ditch has been about 9,500 acre-feet. i; . Protect Description During the study of Knoth Reservoir and Dam, the following alternatives were evaluated: No action alternative 1) Complete rehabilitation of the two dams to Gage Height 20 feet ($590,200) 2) Complete rehabilitation of the two dams to Gage Height 25 feet ($1,233,700) 3) Complete rehabilitation of the two dams to Gage Height 30 feet ($1,898,000) Following is a summary of each alternative: No ActIon Alternative. This alternative was rejected because the need is apparent for some storage within the system to increase the usable yield and to allow for more efficient operation of the ditch Alternative 1 - Rehabilitate the dam to its current capacity (Gage Height 20 feet) This alternative involves rehabilitation of the dam to approximately its current height and size which will store approximately 220 acre-feet. The total project cost is $590,200. This alternative . would not allow storage of the full conditional decree, and was rejected for that reason. Alternative 2 . Raise Dam Crest To Gage Height 25 feet. This alternative is similar to Alternative 1 in all respects except the crest of the dam will be raised approximately five feet in elevation from gagci height 20 feet to gage height 25 feet. This increases the reservoir storage to approximately 360 'acre-feet. The total project cost is $1,233,700, This alternative would not allow storage of the full conditional decree, and was rejected for that reason. Alternative 3 . Raise Dam Crest To Gage Height ~O feet. Thus alternative is similar to Alternatives 1 and 2 in 'all respects except the crest of the dam will be raised approximately ten feet in elevation from gage height 20 feet to gage height 30 feet. This increases the reservoir storage to approximately 540 acre-feet. The total project cost is $1,898,000. This alternative would allow storage ofihe full conditional decree, and is the preferred alternati ve. Selected Alternative 3 involves I. Reshaping the upstream face of both dams and placement of a compacted clay liner over the upstream face to inhibit seepage. Excavation of a cutoff trench tied into the clay liner indicated above. Installation of a toe drain along the mirth dam . Construction of a 200 foot spillway at the right abutment of the south darn 2 . 2. 3. 4.