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C-6 I I I I I I il I I I I I I I I I I I I natural gains occurring within their associated river reach, this problem was avoided. Other refinements included compensation for phreatophyte depletions along the mainstem and adjustments to lag return flows. The San Juan-Chama project was simulated following the rules of the Authorization Act. Daily bypass flow requirements in the Rio Blanco, little Navajo, and Navajo rivers were maintained. The maximum single year diversion (270,000 af), maximum total10-year diversion (1,350,000 af), and capacity of the diversion tunnels were also respected. The diverted water was stored and released from Heron Reservoir, which was also simulated in the San Juan RiverWare model. The release pattern from Heron Reservoir followed the mean call pattern of the current San Juan-chama contracts. The ALP Project impacts were simulated in RiverWare by explicitly entering the various project features and defining their operation in the system. To meet daily minimum flow requirements in the Animas River, a daily operation loop was employed to determine allowable pumping to Ridges Basin reservoir. All other computations were completed on a monthly time step. Before using the San Juan RiverWare model for project analysis, it had to be validated, verified, and calibrated like any model. The configuration of the model was validated by having the model simulate gaged flows from the natural flows and the historical depletions, reservoir releases, and flow routing used to compute the natural flows. . This was essentially a back-calculation of the gaged flows from the natural flows. The model configuration was determined to be valid once the simulated flows at all gage points matched the gaged flows. Once the model configuration was validated, reservoir operation rules were substituted for the historic releases, and the model was rerun. The reservoir operating rules were calibrated so that the end of month reservoir contents closely matched the historical observed contents. Once this match was obtained, rules designed to simulate the Type I shortage were imple- mented and the full irrigation demands substituted for the historical shorted demands. Again the rules were adjusted until the simulated flows at all gaging stations closely matched the observed gaged flows. Once this was achieved the model was assumed calibrated and verified. Simulation of reservoir operations, particularly operation to "mimic" natural flows, requires forecasts of reservoir inflows. For forecasting inflows to Vallecito and Lemon reservoirs, the fraction of the deviation of the actual inflow from the mean inflow is added to the mean inflow. The deviation fraction starts small early in the year and approaches 100% when close to the peak runoff month. For the Navajo Reservoir operation simulation, a forecast error approach is used, whereby the mean historical forecast error for each month is pre- determined and applied. Operation of Navajo Dam to maximize peak flows also requires forecasting the time of peak runoff for the Animas River, allowing releases from Navajo Dam to match the Animas peak. At this time, a constant peak release date has been utilized, since no significant relationship could be developed for predicting timing of the Animas peak. The required timing of the peak release from Navajo Dam was adjusted to optimize the hydrograph statistics to mimic the 1929 to 1993 period of analysis.