K. V. Wilson
1973
<p>Extreme changes in velocity, stage, and Manning's roughness coefficient, <i>n</i>, were observed during the first year after canalization of Hanging Moss Creek at Jackson, Miss. Additional changes were observed during the following 8 years. The channel, constructed during the summer of 1963, had a 50-foot-wide bottom, 2:1 side slopes, and 12-foot depth. In March 1964, average velocities of 7.8 feet per second were measured at a 5 1/2-foot depth in the clean channel and Manning's <i>n</i> was computed to be 0.022. In October 1964 the average velocity was<br />3.2 fps at a 5 1/2-foot depth and Manning's <i>n</i> was 0.045. The channel was then lined with fairly thick vegetation consisting of small willows,<br />weeds, and grass. In October 1970 (summer foliage existing) the average velocity was 2.0 fps at a 5 1/2-foot depth and Manning's <i>n</i> was 0.07. Willow trees, 8 to 10 feet high, then lined the channel. In March 1971 (barren foliage), Manning's<i> n</i> was 0.05. In March 1972 (barren foliage), Manning's<i> n</i> was increased to 0.07. These observations indicate that the commonly used values of Manning's <i>n</i> for channel rectification (0.02-0.03) are low and that the carrying capacity of earthen channels may be reduced 50 percent as a result of only 1 year's growth of vegetation and 70 percent as a result of 8 year's growth. The carrying capacity during summer foliage is approximately two-thirds the carrying capacity during barren winter foliage.</p>
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U.S. Geological Survey
Changes in floodflow characteristics of a rectified channel caused by vegetation, Jackson, Mississippi
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