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. . Mr. J. William McDonald October 17, 1989 Page 3 of what is likely to occur in the future. then it appears that it may be desirable to recalibrate the relationship between the flows recorded at the Vail Gage and flows below the well field. It appears that it would be beneficial to streamflow below the well field, if releases from storage at Black Lakes could be triggered by a higher flow or some other mechanism that would provide for releases of augmentation water in a manner that would better mitigate potential impacts to the segment of Gore Creek which is most impacted by the wells. The benefits of such releases would also accrue to the Gold Medal reach of Gore Creek below Red Sandstone Creek. In addition to the recent stream flow data outlined above, Paul Holden (BIO/WEST, Inc.), has been conducting studies to more specifically identify potential fishery impacts (see Table 1 attached). Mr. Holden has observed that in some years. using the synthetic hydrology and the flPeration. al crite.ria proposed in the Augmentation Plan, too much water would be released from Black Lakes in the fall and early winter months (September through December). As a result of such early releases, the vailable storage in Black Lakes would often be depleted by mid-winter. resulting in possible reductions in fish habitat during the late winter I', tmonths ~ of February anci-eariyUMar-ch~-- Holden' s report~ concludes that there is plenty of spawning habitat in Gore Creek throughout the fall and early winter without flow augmentation from Black Lakes. The critical factor is adult habitat during the mid-winter low flow period. Thus, it appears that it would be most beneficial to the fishery to always operate Black Lakes so as to augment streamflows during December through and early- March. Proposed Modifications in Operation In consideration of the biological and hydrological factors outlined above, the District proposes adoption of a more flexible approach to operation of Black Lakes. The overall goal would be to manage the water available for release from Black Lakes so as to achieve maximum benefits for the Gore Creek fishery while retaining sufficient flexibility to make refinements as more data becomes available. I have described below the approach we are recommending, which is tied to the historical pattern of water diversions by the District during the winter months: 1. The District will continue to monitor streamflow in Gore Creek at the Vail Gage. 2. On or after December 1, when the stream flow at the Vail Gage drops to 10 cfs or less, begin releasing water from Black Lakes.