Laserfiche WebLink
<br />0022~3 <br /> <br />. <br /> <br />Maps and Charts. The upper end of this reach is 12 miles below <br />the dam, and the resch included three of the established degrada- <br />tion ranges. In addition, 17 temporary ranges were laid out acrOBS <br />the channel from bank to bank. Along 6 of these, a swath was cut <br />across the channel through the willows, wide enough to permit <br />access for streamflow measurements. Along the other rsnges, only <br />enough clearing was done to permit surveying. Staff gages were <br />set for the observation of streamflow stages and water surface <br />profile data. <br /> <br />(2) Test operation. Controlled releases were made from <br />the dam to furnish constant discharges through the test reach of <br />streamflows up to 3,500 second-feet. Constant flow measurement a <br />were made on five succesaive days beginning 15 May 1961, with <br />observations covering a seven-day period. During these constant <br />flows, measurements and observations were made of the velocities; <br />water surface elevations and depths; location, size and density of <br />willow growth; and the channel configuration. <br /> <br />(3) Analysis of data. Using the observed data from the <br />test reach, computations were made of the coefficients of roughness <br />(resistance to flow) in the clear channel and through the willows. <br />Profiles through the test reach, showing the observed streamflow <br />and also the reconstructed profiles using the computed coefficients <br />of roughness are shown on plate 14 of appendix I. It was found <br />that the resistance to flow through the willows was roughly 5 times <br />as much as the resistance in those channel areas that were free of <br />vegetation. <br /> <br />20. EXTENT OF WILLOW GROWTH <br /> <br />Aerial photographs of the river between Trenton Dam and Harlan <br />County Reservoir were taken in 1958, and the reach below Harlan <br />County Dam was photographed in 1961. These recent photographs were <br />compared with similar pictures taken in 1951, bank lines approximating <br />those of 1951 were drawn on the recent photographs, and the extent <br />of willow growth within the former channel was measured. Typical <br />aerial photograph mosaics with the 1951 channel lines superimposed <br />are presented in Appendix I: Maps and Charts. The willow growth <br />during the past decade has taken over channel areas to the extent <br />of from 11 to 30 acres per mile in the several river reaches, as <br />shown in table 6. <br /> <br />. <br /> <br />25 <br />