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I I I I I I I I I I I I II I I I I I I STREAM CHANNEL GEOMETRY The geometry of a stream channel is described by its alignment (sinuosity), width (distance between stream banks), and depth (distance from top of bank to stream bed). Stream geometry is determined by the sediment and water moving through the channel. As with stream pattern, there are empirical relationships that have been developed that relate water and sediment discharge to stream geometry. SINUOSITY Schumm (1968) found that meander wavelength (L in feet) is related to mean annual discharge (Qm in cfs) and the mean percentage of silt and clay (particle sizes smaller than the No. 200 sieve, 0:074 mm) forming the channel perimeter, M. L _ 1890 Qm 0.34 M-D.74 EQA The relationship of channel width to meander wavelength (Leopold and Wolman, 1960) is approximately: L- 41tW EQ.5 This is closely related to riffle-pool wavelength (21tW) , because in a regular meander bend there are two riffle-pool cycles to one bend with pools at the apices and riffles at the inflections. Meander wavelength and radius, r" are also related: L _ 4.70 r,O,98 EQ,6 (Leopold and Wolman, 1960), and therefore r, - 2 - 3 W. The general alignment of meandering channels is a complex succession of irregular and compound bends. There are usually numerous topographic and geologic effects on the alignment. WIDTH AND DEPTH All available evidence indicates that the greater the quantity of water that moves through a channel, the larger the cross section of that channel. Schumm (1968) produced the following relationships for channel width and depth (in feet): W _ 37 Q_0.38 M-D.39 d _ 0.60 Q_ 0.29 Mo.34 EQ.7 EQ.8 At a given discharge, channels with a high silt-content in the banks are narrow and deep in cross-section, while those with sandy, erodible banks are wide and shallow. The ratio of channel width to depth is called the channel form ratio, F. From EQ. 7 and 8, the form ratio is given by the following relationship: 10