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42 Each meander 1a described as having t'.,o crossovers (Figure 11) that generally lie near the center of the r1ffl,.. The crossovers occur where the water is of uniform depth and the thalweg (or line of maximum depth) is at its median position while swinging from one side of the channel to the other. The mean depth is less and the velocity is gr,.ater at the crossovers (riffles) than at the bends (po'Jls) under :l1ormal flow conditions. This variation in _aD depth 'JCcurs also in straight channels, in the pool and riffle foraation. I I I I)' I , 1 Cor;CA YE BANI< 2 CROSSOVERS/HEAND!:n S to 7 CHANNEL WIDTHS APART CH.A.'UiEL WIDTH IS KEASlJRED At ritE CEmu. OF 1'HE RIFFLE HIGH WATER KARK Figure 11. Meander ratio.. Meander Ratios Measurements of the horizontal dimensions of meander patterns: show remarkably consistent periodicities shared by streams of all sizes. Numerous observations by a number of workers indicate a constant t'atio of 5 to 1 between the length of the wavelength and the radius of curvature (Figure 12, Leopold and Langbein 1966). The, radius of curvature designates the lenlth of a line that extends from the center of a circle, or in this case, from the center of the bend (curve or loop) to the center of the channel. ,Therefore the wavelength is consistently five times the length of the radius of the curvature. The wavelength has been consistently shown to be 7 to 11 times the stream width when the c,hannel 1smeasured at riffle sites, the cross sectional profile is symmetrical, and the width is taken as the active streambed at bankfull conditions and delineated by the existence of bed IIaterial. When the actual stream length has been measured within the constraints of the wavelength a ,:ons1stant ratio of 11 to 16 has been found.