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1 Executive Summary Scenario III - Elkhead Enlargement enlargement of Elkhead Reservoir Juniper rights converted to instream flow Juniper rights subordinated only to storage Scenario IV - Stagecoach Enlargement enlargement of Elkhead Reservoir ' enlargement of Stagecoach Reservoir Juniper rights converted to instream flow Juniper rights; subordinated only to storage Scenario V - Williams Fork Project enlargement of Elkhead Reservoir development of Williams Fork Project Juniper rights converted to instream flow ' Juniper rights subordinated only to storage ' Potential reservoirs at the East Fork and Elk Creek sites were not explicitly modeled. These two reservoirs are functionally equivalent, in terms of water deliveries and instream ' flow regimes in reaches of interest, to the Williams Fork and Stagecoach Enlargement alternatives which were modeled ex licitl p y. The "no action" scenario is functionally equivalent to simulation of the exercise of the ' general subordination. This is true because the limits on the general and other subordination exceed the estimated consumption under all existing and future junior demands explicitly represented in the basin model. Thus, subordination of the Juniper rights in the model would make them the most junior right represented, and unable to influence the operation of any other rights represented in the model. Results from model scenarios were used in two ways. First, the model was used to test ' the sensitivity of predicted demands shortages, reservoir contents and intream flows to various operational constraints, new storage facilities and instream flow requirements. Second, model results for each scenario were compared against results of the baseline scenario in order to evaluate which scenario could best meet basin wide water demands while maximizing ' recreational opportunities and helping to protect historical flow regimes in reaches potentially containing endangered fish habitat. Evaluation R lt esu s Scenario I - No Action (Baseline) Scenario I of the Yampa River Basin Model represents physical condition and water rights as they currently exist and are administered in the basin. Three reservoirs were operated ' in this scenario including Stagecoach Reservoir, Steamboat Lake and Elkhead Reservoir. Operations of several other reservoirs presently existing in the basin, such as Lake Catamount, Yamcolo Reservoir and numerous small reservoirs, were not explicitly modeled. Depletive ' effects of these projects, however, were implicit in the gage-based model hydrology or were modeled as separate demands (this was the case with Lake Catamount). Demands are met in the basin model according to assigned ranks; these ranks generally correspond to the relative priorities of basin water rights. In all of the model scenarios, the demand increment to reflect existing senior demands (potential 1989 conditions) were met prior ' to allowing existing reservoirs to fill. While existing reservoir storage decrees are generally junior rights, historically they have been allowed to fill without administrative call by senior 1 S-19