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<br />Biologic Flow Recommendation <br />The summer flow recommendation, which meets 3 of 3 criteria and is within the accuracy range <br />of the R2CROSS model is 3.5 cfs (See Table I). The winter flow recommendation, which meets <br />2 of3 criteria and is within the accuracy range of the R2CROSS model is 2.8 cfs (See Table I). <br />It is our belief that recommendations that fall outside of the accuracy range of the model, over <br />250% of the measured discharge or under 40% of the measured discharge may not give an <br />accurate estimate ofthe necessary instream flow required. <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. The hydro graph below was derived from data collected by the <br />USGS stream gage for Halfmoon Creek near Malta, CO (ID #07083000), which has a drainage <br />area of 23.6 square miles (See Gage Summary in Appendix C). The total drainage area of the La <br />Plata Gulch Drainage is approximately 5.1 square miles. The period of record for this gage was <br />1946-1998, the period of record used by staff in their analysis was 1946-1998, or 52 years of <br />record. Table 2 below displays the estimated stream flow of La Plata Gulch, in terms of a <br />percentage of exceedence. <br /> <br />Table 2: Estimated flow La Plata Gulch. <br /> <br />Exceedences <br />1% <br />5% <br />10% <br />20% <br />50% <br />80% <br />90% <br />95% <br />99% <br /> <br />Januarv Februarv March Aoril Mav June Julv Auaust September October November December <br />1.94 1.73 2.38 5.62 34.55 63.32 63.97 28.96 10.83 5.62 4.11 2.16 <br />1.49 1.34 1.51 3.46 25.50 51.86 42.87 17.72 7.35 4.32 2.81 1.90 <br />1.21 1.12 1.30 2.81 19.67 45.38 35.01 13.33 6.27 3.89 2.38 1.64 <br />1.08 0.97 0.97 1.86 15.13 38.68 25.50 9.94 5.19 3.03 1.99 1.38 <br />0.82 0.76 0.76 1.21 8.00 25.50 15.13 6.48 3.46 2.16 1.49 1.04 <br />0.65 0.58 0.56 0.76 3.03 17.07 9.08 4.32 2.59 1.62 1.17 0.84 <br />0.54 0.52 0.50 0.58 1.99 13.83 6.92 3.67 2.16 1.45 1.06 0.76 <br />0.45 0.43 0.32 0.52 1.49 11.67 5.62 3.24 1.90 1.32 0.95 0.69 <br />0.32 0.37 0.26 0.37 1.06 7.48 4.13 2.59 1.51 1.10 0.73 0.58 <br /> <br />La Plata Gulch Estimated Stream Flow <br /> <br /> 5 <br /> 4 <br /> 3 <br />J!! <br />u <br /> 2 <br /> 1 :--~, ,. <br /> 0 <br /> cAN <br /> <br /> <br />em <br /> <br />",^R <br /> <br />Affi <br /> <br />",^y <br /> <br />cUN <br /> <br />cue <br /> <br />AUG <br /> <br />ecp <br /> <br />OCT <br /> <br />NOV <br /> <br />DCe <br /> <br />Month <br /> <br />-4- <br />