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<br />~TEP 10 (continul:Ql <br /> <br />METHOD 1 - TABLE OF CHANNEL CROSS-SECTIONAL SHAPES <br />(Determining Hydraulic Radius) <br /> <br />Be aware that this is a trial and error plrocedul'e, <br /> <br />Estimate the portion of the cross-sectiolll which would carry water during a flood, <br /> <br />From the approx:mate high water line on one s,ide of the cross-section to the <br />approximate high water line on the other side estim.,te the: distance in feet; this is the <br />Wetted Perimeter (P). After the first tim<~ through the procedure you ean come back and <br />try again with a c!.)ser approximation. <br /> <br />Estimate the cross.sectional ar<!a carrying floodwaters (A). <br /> <br />Select the c:onfiguration below which most dosely approximates the channel cross- <br />section shape that you expect at your location, <br /> <br />Note the Hydraulic Radius (R) which corresponds to the cross-section shape you have <br />selected. R is simply the area <A) divided by the Wetted Perimeter CP), <br /> <br />Cross Section <br /> <br />DescriPthm <br /> <br />Hydrnulic Radius <br /> <br />D <br /> <br />Rectangular, deep, wide at <br />bottom and top <br /> <br />3,3 <br /> <br />v <br /> <br />Triangulal, deep, narrow at <br />bottom, wide at top <br /> <br />1.8 <br /> <br />\~ <br /> <br />'7 <br /> <br />Trapezoidal, moderately wide, <br />relatively shallow <br /> <br />1.3 <br /> <br />C::::"- <br /> <br />- <br /> <br />-~ <br /> <br />Rectangular, very wide, <br />extremely shallow <br /> <br />1.0 <br /> <br />Use this table with care. It simply provides a means for comparing th,c cross..sectional area (A) <br />to the Wetted Perimeter (P). If P is small relative to A, the value w:ill be larger; if P is large <br />relative to A, the value will be smaller. <br />