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Natural Environment Studies The Bureau of Land Management (BLM), United States Forest Service (USFS), Colorado Division of Wildlife (CDOW), and Trout Unlimited (TU) have conducted field surveys of the natural environment resources on these streams and have found natural environments that can be preserved. To quantify the resources and to evaluate instream now requirements, the recommending entities have collected biologic and hydraulic data that were analyzed by CWCB staff. Based on the results of these analyses, staff prepared recommendations of the amount of water necessary to preserve the natural environment to a reasonable degree for each of the streams listed on the attached Tabulations of Instream Flow Recommendations. Water Availability Studies Staff has conducted an evaluation of water availability for the streams listed. To determine the amount of water physically available for the Board's appropriations, staff analyzed available USGS gage records, available streamflow models, and /or utilized appropriate standard methods to develop a hydrograph of median daily flows for each stream flow recommendation. In addition, staff analyzed the water rights tabulation for each stream and has consulted with the Division Engineers' Offices to identify any potential water availability problems. After looking in detail at CWCB Staff s analysis, the Division 4 Engineer and his staff voiced concern over water availability on Tabeguache Creek because they performed an analysis that led them to conclude that less water was available than the amount computed by CWCB staff. By the same token, when USDA Forest Service staff reviewed the CWCB analyses for Tabeguache Creek, Red Canyon Creek and North Fork Tabeguache Creek, they also questioned CWCB staff s numbers. The Forest Service's own water availability analysis for its recommendations indicated that more water was available than was indicated in the CWCB analyses. While CWCB staff computed water availability using its standard method, both the Division 4 Engineer and the USFS employed other methods. Since there is no existing stream gage on any of the three streams in question, each party had to extrapolate, utilize limited data and /or make assumptions in order to estimate and characterize the hydrology of the subject streams. The Division 4 Engineer utilized historic, but limited data, whereas the USFS employed the USGS StreamStats methodology. CWCB staff s results fell between those of the Division Engineer and the USFS. Differences of this sort are not unreasonable, given the many necessary assumptions underlying each approach as well as the need in each case to extrapolate to one degree or another. In view of the foregoing, CWCB staff s values for water availability and its representation of the hydrograph at the lower terminus of the subject reach are reasonable. Based upon its analyses, staff has determined that water is available for appropriation on each stream to preserve the natural environment to a reasonable degree without limiting or foreclosing the exercise of valid water rights. For the Red Canyon Creek and North Fork Tabeguache Creek USFS recommendations, staff lowered or eliminated the flow recommendations during the late season and winter months based upon its estimate of water availability. However, staff and USFS agree that 1) the presence of reproducing trout fisheries on both of these streams suggests that more water may be available than that calculated by CWCB staff, 2) one or more of the streams may have gaining reaches /groundwater input; 3) the available hydrologic data limits the accuracy of any given hydrologic estimation; and 4) CWCB and USFS staff both hypothesize that during extreme low flow events, sufficient interstitial flow exists in the stream substrate to maintain and oxygenate pool habitat where the fish species are surviving until flows increase.