Laserfiche WebLink
<br />38 <br /> <br />Requirements for Methodology Improvements - <br />Single and Multiple Transect R-2 Cross Methods <br /> <br />The single and multiple transect R-2 Cross computer model <br />has several probe1ms that should be corrected. The input para- <br />meter for slope as it is presently used by the Colorado Division <br />of Wildlife can accept only three digits to the right of the <br />decimal. On streams with a slope of less than 1% this only <br />permits the input of one non-zero digit and rounding off errors <br />can be significant. For example, the observed slope across <br />transects 1, 2, 3, 5, and 6 on the East River was 0.00015. <br />Since the lowest number that can be put into the Colorado R-2 <br />Cross Program is 0.001, an input error of 259% results for the <br />slope input value alone. ,The program should be modified to accept <br />a minimum of five, or preferrably six dip-its to the right of the <br />decimal so that when the slope is less than 1% (almost always <br />the case in streams over 50 ft in width) three significant <br />,digits can be used. Bovee and Milhous (1978) alluded to this same <br />problem in reference to single transect methods utilizing the <br />Manning equation. <br /> <br />The tendencv of the R-2 Cross model to overestimate the <br />average velocity by an average of 45% from measured field values <br />in this study indicates that some action should be taken to balance <br />.measured water stage levels and field velocity measurements, i.e., <br />.to better calibrate the model than is presently being done. <br />This would require more manipulation of the data and greater <br />data analysis expense but the improvement in the reliability and <br />accuracy of the velocity component of the output should be worth <br />the effort. <br /> <br />The possibility of increasing the minimum acceptable aver~ge <br />velocity from 1 ft/sec to 1.5 ft/sec should be examined if no <br />~orrection is made for the tendency to overestimate a~~~ag~ <br />velocity in the prediction of output parameters. <br /> <br />Finally, average depth should be the primary criterion 'on <br />which minimum flow recommendations are determined since it is the <br />first factor to become limiting in almost twice as many instances <br />as average velocity and wetted perimeter combined. <br />