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<br />" . <br /> <br />'" <br /> <br />001558 <br /> <br />. <br /> <br />. <br /> <br />It, <br /> <br />With the recommended channel.. maintenance flow hydro graph a maximum' <br />monthly release of 3384 .acre-feet would be required. However" if the <br />average discharge released for other purposes in a given month were (for <br />'example) 60 cfs, the total volume released would be about 3570 acre-feet, <br />or about 186 acre-feet more than channel maintenance flow requirements. <br />This release would be relatively constant through the month (Fig. 7), in <br />contrast to the variable releases required by the channel maintenance <br />hydrograph. Assuming that the 60 cfs generated by these "other" releases <br />satisfied the discharge equal to or less than 60 cfs required in the <br />channel maintenance hydrograph. the channel maintenance flow demand on the <br />reservoir would be that volume of the channel maintenance hydro graph above <br />60 cfs, o,r 1527 acre-feet (see Fig. 7). This volume would have to be <br />released in the prescribed manner in order to satisfy channel maintenance <br />flow' requiremen tse. -- e - , ' <br /> <br />Based, on this procedure, the channel maintenace flow requirements were <br />integrated into the. operational' model. Results indicated that over a <br />30-year period for which historical data are available, the average annual <br />channel maintenance flow requirement would be 995 acre-feet under a West, <br />Slope water marketing scenario, or 686 acre-feet under an EastS!ope'wa~er <br />marketing scenario (a potential short-term condition), compared to' an <br />average annual yield of 23,890 acre-feet. <br /> <br />CONCLUSIONS <br /> <br />Development of the channel maintenance hydrograph, as outlined above, <br />provides a reasonable solution considering site characteristics and the <br />site specific sediment transport conditions of the Rock Creek Project. <br />Both the existing supply limited condition of Rock Creek, particularly for <br />'finer' particle' sizes, arid reduced' downstream sediment supply for post- <br />project conditions have been accounted for in the analysis. The analysis <br />is considered conservative since only gravel sized particles were assumed <br />to be trapped in the reservoir; consequently, the post-project downstream <br />. flows -- were 'required to transport the pre-proj ect supply of medium and <br />coarse sands, a large'portiori of which will most likely also be trapped in <br />'the reservoir. The conservative nature of this assumption is further com- <br />pounded by lack of a significant sediment supply to reaches downstream of <br />the proj ect'.'. From' the project downstream to' the confluence of Egeria' <br />Creek, which is nearly to the, confluence. of Rock Creek with the Colorado <br />'Rive'r';rici -major "sedlment' producing tributaries enter Rock' Creek. Conse- <br />quently, pre-proj ect sediment supply is not achieved at -- any: point down- <br />stream of the proj ect. -- <br /> <br />Vegetation encroachment concerns have also been addressed by the <br />analysis procedure. The peak discharge recommended to meet sediment <br />transport requirements was evaluated considering maximum velocity and <br />inundation depth. It should be noted that the maximum daily drawdown rate <br />calculated from a strict application of the Chapter 30 procedure was <br />adopted in developing the recommended channel maintenance hydrograph; <br />therefore, the resulting procedure capitalizes on certain elements of the <br />basic USFS procedure and modifies other elements to more accurately address <br />site specific conditions. <br />