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Feasibility Study Trinchera Irrigation Company Smith Dam Repair INTRODUCTION (Need for the Project) The Trinchera Irrigation Company (TIC), located in Costilla County, Colorado owns and operates Smith Reservoir as an irrigation water storage reservoir for the benefit of the shareholders. The Smith Reservoir's priority is dated Apri18 1911 in the amount of 5000 acre feet. Water from Trinchera, Sangre de Cristo and Spring Creeks and their tributaries is adjudged and decreed to be allowed to flow into Smith Reservoir under Priority No. 95, being Reservoir Appropriation Priority No. 2. The earth and rockfill dam was constructed in 1914. Original dam construction included a concrete core wall with a "selected earth" impervious zone on the upstream side. The upstream shell consists of borrow pit run overlaid by "one and two man stones" on the upstream slope. The slope was originally constructed at 1.5:1. In Apri12009 an intense snow storm accompanied by high easterly winds occurred in the area. This storm caused considerable erosion on the upstream slope of the dam. Down slope migration of the boulders and rip rap was a result of under-mining by wave action. The erosion resulted in six foot high vertical scarps with voids between the rockfill, which could be probed several feet horizontally into the embankment. The outlet has upstream and downstream gate valves. Due to operational difficulties with the upstream gate the Trinchera Irrigation Company has controlled the flow with the downstream valve. This was considered an undesirable mode of operation by the Colorado State Engineer's Dam Safety Branch. The upstream gate leaked a considerable amount due to the inability to completely close the gate. These concerns resulted in an unsatisfactory rating on the dam. The Dam Safety Field Engineer recommended a restriction to a level2 feet below the emergency spillway crest on Apri122, 2009. The TIC received notice from the Office of the State Engineer dated June 1, 2009 restricting the reservoir to a level2 feet below the emergency spillway crest (gage height 26.5') resulting in a loss of water storage of approximately 1,100 acre-feet. Trinchera Irrigation Company was compelled to make the necessary repairs due to safety concerns and the need to restore the reservoir to full capacity rather than risk losing storage and exchange water. Letters from the Division of Water Resources and a Dam Safety Report are included in Appendix A. Water records indicate there is a great need to carry over water from year to year due to the variable nature of rainfall and runoff in the basin. In a dry year the water that may be carried over in the reservoirs is very important and may be the difference between