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<br />fIOlJ-"~-1995 I::>: I~ <br /> <br />JOB <br /> <br />P.03 <br /> <br />Leo Lentsch, Paul Thompson, Pat Nelson <br />Page 2 <br />November 13. 1995 <br /> <br />item!.. Interestingly, at the Ouray study reach, the bankfull discharge ranged from about 17,000 <br />to 23.000 cfs with an average value of about 20,000 cfs. The pre-1963 mean annual peak (which <br />should be relatively close to the bankfull discharge) was 24,000 efs. p0S1-l963 the mean annual <br />peak is about 17,300 cfs. So conversely, whereas the Canyonlands srudy reach bankfull <br />discharge has increased dramatically, the Ouray reach bankfull discharge actually decreased <br />since 1963. <br /> <br />The point of this discussion is that it is difficult to assess the overbank discharge required for <br />floodplain inundation. flood stage for opening habitat, or possible restoration by levee removal to <br />certain a elevation, without predicting the water surface clevation. The water surface is a <br />function of downstream constrictions, channel roughness and channel morphology response to <br />high flows. It can just fool you. To proceed with any restoration and levee removal activities, <br />one high flow season is needed to collect the data, perform the depression surveys, etc. as was <br />accomplished at Ouray lasl year. The draft levee removal strategic plan does not allow any <br />opportunity for hydrologiclhydraulic analysis for the 1996 sel~cted sites. Perhaps, any levee <br />removal activities in 1996 should be considered for Ouray fust where the required analysis has <br />been completed. 'The bottomland flooding draft report is essential complete. <br /> <br />The thirty 1996 sites that you have included into the design plan could receive a varying level of <br />aoaIysh. Some sites may be assessed on smaller scale than was performed at Ouray. It may be <br />appropriate to conduct either a qualitative, quantitative or engineering analysis to predict the <br />flood stage (discharge) versus area of inundatiOll at each site. Tne qualitative approach would be <br />more or less a guess making levee removal an experiment. The engineering analysis incorporates <br />the level of work compler.cd at Ouray. You may want to evaluate and schedule restoration at the <br />proposed sites on this basis. <br /> <br />TOTAL t". 03 <br />