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APPENDIX I YAMPA RIVER HISTORIC AND ENVIRONMENTAL BASELINE CONDITION The historic condition for the Little Snake River was derived by using U.S. Geological Survey (USGS) gage data for the Little Snake River near Lily. The historic condition for the Yampa River above the confluence with the Little Snake was derived by using the USGS gage record for Maybell. Gage records for the Yampa River are good except in the winter when the record is fair. At Lily on_the Little Snake River the record is fair except in the winter when the record is poor. Both gages have quite extensive records, dating back to the early 1900's. The historic flow of the Yampa River at Deerlodge Park is also of interest, but no gage existed there until 1978. Deerlodge Park is below the confluence of the Yampa and Little Snake Rivers and generally reflect condition on both Rivers, and is widely accepted as being above important spawning habitat areas. Yampa flow at Deerlodge Park can be accurately estimated by summing the gage record for Little Snake near Lily and Yampa River near Maybell. The data and statistical analysis are presented in Attachment 1. The development of the environmental baseline (baseline) for the Yampa River was accomplished using the Service's HYDROSS computer model. The baseline condition was modeled with all existing and permitted major water development projects on the Little Snake River and Yampa River up to and including Stagecoach Reservoir. These projects are modeled as if they were on line and operating for the entire period of record, 1930 to 1982. On the Yampa River all depletions were modeled up to the year the actual depletion commenced. For example, the operations of the Hayden and Craig thermoelectric power plants were staged to reflect their operations through the entire period of record. The Hayden unit was operated in the model from 1930 to 1965, when the unit actually came on line. Likewise, the Hayden II unit was operated from 1930 to 1976.