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<br />I <br />I <br />I <br /> <br />STREAM FORM <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Channel pattern can be predicted based on the channel grade, discharge, and bed-material <br />size. The thresholds in channel pattern are slightly different between streams with sand versus <br />gravel bed-material. Sand-bed streams have bed-material gradations that are predominantly in the <br />range of panicle sizes from 0.062 nun to 2.00 nun (greater than a No. 200 sieve and less than a <br />No. 10 sieve). The gradation of gravel-bed streams is in the range of 2.00 nun to 64 nun (greater <br />than a No. 10 sieve and less than 2.5 inches). <br /> <br />Estimation of channel grade and discharge are extremely important issues in channel pattern <br />prediction. Methods for estimation channel grade and discharge are discussed in detail in separate <br />appendices. It is also important to keep in mind that these relationships are empirical and that <br />there is significant scatter <br /> <br />SAND-BED CHANNEL <br /> <br />Lane (1957) studied the characteristics of braiding and meandering streams. He conducted his <br />analysis on sand-bed streams with meandering and braiding pattern, and derived two equations <br />that panition the entire range of channel pattern. For meandering channels, Lane concluded, <br />based on regression analysis, that a threshold relationship between slope and discharge was <br />defined: <br /> <br />S = 0.0017 Q-O,25 <br /> <br />~\,. ~ <br /> <br />EQ.1 <br /> <br />where S is the channel slope, Q is the mean annual discharge in cfs. Streams plotting below this <br />equation should be meandering, <br /> <br />For braided streams, the threshold relationship between slope and discharge was: <br /> <br />S _ 0.010 Q-O.25 <br /> <br />EQ.2 <br /> <br />Streams plotting above this curve should be braided. The area between these two curves is <br />characterized as a zone of transition between braiding and meandering. <br /> <br />GRAVEL-BED CHANNEL <br /> <br />Leopold and Wolman (1957) found a similar relationship for meandering and braided gravel- <br />bed streams as that of Lane for sand-bed channel. Their fit of the threshold between meandering <br />and braided streams was given by the equation: <br /> <br />S _ 0.060 Q -0.44 <br /> <br />EQ.3 <br /> <br />Streams plotting below the curve are considered meandering, and those above the curve <br />braided. <br /> <br />9 <br />