Laserfiche WebLink
<br />Biolo~ic Flow Recommendations <br />The CD OW recommended a 1.8 cfs summer/winter flow based on the October 9th, 1996, data <br />collection efforts. <br /> <br />. Staff reviewed the data collected by the CDOW. The summer flow recommendation for the <br />proposed reach, which meets 3 of 3 criteria but is outside the accuracy range of the R2CROSS <br />model is 4.8 cfs. The winter flow recommendation for the proposed reach, which meets 2 of 3 <br />criteria and is within the accuracy range of the R2CROSS model is 1.8 cfs (See Table 1). Staff <br />reviewed the data collected by the CDOW. It is our belief that recommendations that fall <br />outside of the accuracy range of the model, over 250% of the measured discharge or under 40% <br />of the measured discharge may not give an accurate estimate of the necessary instream flow <br />required. In these cases, CWCB staff relies upon the biological expertise of the cooperating <br />agencies to develop a biologic instream flow recommendation. <br /> <br />The CDOW has indicated that this is a high priority stream segment to them. However, because <br />the summer recommendation falls outside the accuracy range of the R2CROSS model, staff <br />believes that more data needs to be collected to accurately predict the summer flow <br />recommendation. Staff has consulted with the recommending agency and believes that it would <br />be appropriate for the Board to file on a year-round flow of 1.8 cfs, if water was available (See <br />Table 1). <br /> <br />. <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 7.3 miles northwest of the Chapman Gulch drainage. The hydro graph below <br />was derived from data collected by the USGS stream gage for the San Miguel River near <br />Telluride, CO (ID #09171200), which has a drainage area of 42.8 square miles. The drainage <br />area of Chapman Gulch is approximately 0.8 square miles. Staff used a basin apportionment <br />method to estimate stream flows for Chapman Gulch (See Gage Summary in Appendix C). The <br />period of record for this gage was 1959 to 1965, the period of record used by staff in their <br />analysis was 1959 - 1965, or six years of record. Table 2 below displays the estimated flow of <br />Chapman Gulch, in terms of a percentage of exceedence. <br /> <br />Table 2: <br /> <br />Estimated Chapman Gulch Stream Flow <br />Exceedences <br />1% <br />5% <br />10% <br />20% <br />50% <br />80% <br />90% <br />95% <br />99% <br /> <br />Jan uarv Februarv March ADril Mav June Julv August SeDtember October November December <br />0.34 0.38 0.96 1.98 7.69 8.90 7.92 3.91 1.76 0.92 0.63 0.44 <br />0.32 0.36 0.58 1.71 6.63 7.89 6.81 2.29 1~39 0.75 0.55 0.38 <br />0.30 0.36 0.44 1.48 4.54 6.84 5.11 1.79 1.24 0.72 0.53 0.36 <br />0.30 0.34 0.38 1.16 3.51 5.89 3.82 1.44 1.06 0.63 0.49 0.34 <br />0.29 0.29 0.30 0.67 2.26 4.41 1.84 0.97 0.70 0.51 0.42 0.32 <br />0.27 0.27 0.27 0.42 1.33 2.51 1.05 0.74 0.51 0.44 0.38 0.30 <br />0.25 0.27 0.27 0.30 0.83 2.20 0.85 0.63 0.49 0.42 0.36 0.30 <br />0.25 0.27 0.27 0.30 0.69 1.90 0.77 0.55 0.48 0.42 0.36 0.25 <br />0.25 0.27 0.23 0.30 0.55 1.53 0.62 0.51 0.46 0.40 0.34 0.25 <br /> <br />. <br /> <br />- 4- <br />