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<br />. <br /> <br />. <br /> <br />. <br /> <br />R2CROSS model (See Table I). It is our belief that recommendations that fall outside of the <br />accuracy range of the model, over 250% of the measured discharge or under 40% of the, <br />measured discharge may not give an accurate estimate of the necessary instream flow required.-: <br />In these cases, CWCB staff relies upon the biological expertise of the cooperating agencies to <br />develop a biologic instream flow recommendation. <br /> <br />The CD OW has indicated that this is a high priority stream segment to them. However, because <br />the winter recommendation falls outside the accuracy range of the R2CROSS model, staff <br />believes that more data needs to be collected to accurately predict the winter flow <br />recommendation. To determine the winter flow recommendation, staff considered the proposed <br />winter recommendation for the upper reach of 1.5 cfs, and the average of the two <br />recommendations of the lower reach, 3.0 cfs. After consulting with the Colorado Division of <br />Wildlife, staff believes 3.0 cfs will be sufficient to protect the natural environment to a <br />reasonable degree. (See Table 1). <br /> <br />Hydrologic Data <br /> <br />After receiving the cooperating agency's biologic recommendation, the CWCB staff conducted <br />an evaluation of the stream hydrology to determine if water was physically available for an <br />instream flow appropriation. There are no currently operated or historically operated <br />streamflow gages for this reach. The closest gage CWCB staff found was the gage located on the <br />San Miguel River 5.7 miles north of the Howard's Fork San Miguel River drainage. The <br />hydro graph below was derived from data collected by the USGS stream gage for the San Miguel <br />River near Telluride, CO (ill #09171200), which has a drainage area of 42.8 square miles. The <br />drainage area of Howard's Fork San Miguel River is approximately 15 square miles. Staff used <br />a basin apportionment method to estimate stream flows for Howard's Fork San Miguel River <br />(See Gage Summary in Appendix C). The period of record for this gage was 1959 to 1965, the <br />period of record used by staff in their analysis was 1959 - 1965, or six years of record. Table 2 <br />below displays the estimated flow of Howard's Fork San Miguel River above Waterfall Creek, in <br />terms of a percentage of exceedence. <br /> <br />Figure 2: <br /> <br />Estimated Upper Howard's Fork Stream Flow (w/o Waterfall Creek) <br />Exceedences J F b M h A" <br />1% <br />5% <br />10% <br />20% <br />50% <br />80% <br />90% <br />95% <br />99% <br /> <br />s <br /> <br />anuarv e ruarv arc ,pn May June July Auaust eDtem ber October November December <br />3.29 3.66 9.25 19.09 74.00 85.67 76.25 37.60 16.94 8.83 6.11 4;21 <br />3.11 3.48 5.61 16.46 63_83 75.90 65.55 22.08 13.35 7;26 5;30 3.66 <br />2.93 3.48 4.28 14.27 43.68 65.84 49.16 17.23 11.89 6.95 5.12 ,', ,3:48 <br />2.93 3.29 3;66 11.16 33.80 56.70 36.80 13.90 10.24 6.04 4.76 3;29 . <br />2.74- "'2.74 "2;93 8.40 21.76 42.43 17.74 9.33 6.11 4.94 4.02 3;11' <br />2.56 2.56 2.56 4.02 12.80 24.14 10.06 7.13 4.94 4;21 3_68 2.93 <br />2.38 2.56 2.56 2.93 7.97 21.22 8.16 6.04 4.76 4.02 3.48 2.93 <br />2;38 '2.56 2.56 2.93 6.64 18.29 7.37 5.30 4;57 4:02 3.48 2.38 <br />2.38 2.56 2.19 2.89 5.30 14.74 5.98 4.94 4.39 3.84 3;29 2.38 <br /> <br />- 6 - <br />