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<br /> <br />1 <br /> <br /> <br /> <br /> <br />1 <br /> <br />1 <br /> <br />1 <br />1 <br />1 <br /> <br />~J <br /> <br />1 <br /> <br />COEFFICIENT "x" <br />The value of "x" must fall between 0.0 and 5.0 in order to avoid negative coordinates of the <br />computed downstream hydrograph. <br />Following is a sample calculation for estimating the value of "x": <br />The value of "x"may be estimated by using the formula: <br />x = 1.495'' / nPv' <br />P = wetted perimeter; n = Manning's Roughness Coefficient <br />Currant Creek at a certain location has a channel combined with a wide stream bed. The stream bed <br />and channel are heavily vegetated. <br />"P" is estimated at 30 + 15 + 100 + 100 = 260 feet <br />"n", Manning's Roughness Coefficient, is estimated at 0.10; Slope is O.OI S <br />x=1.49x0.015'rz/O.]Ox260v'=1.49 x0.122/O.lOx40.7=0.03 <br />This value is extremely low and would result in a small run-0ff condition because the stream bed <br />acts as a detention area. The selected values for the "x" coefficient are within the 0 to 5 range. <br />Where the creek beds are wider, the value of "x" is in the 0.20 to 0.25 range; where the stream bed <br />is narrow with typically no vegetation, the value of "x" is between 0.40 and 0.45. Exhibit VIII <br />shows the complete inputs and tabulations of the parameters for each sub-basin. <br />The following equation is used to establish a required cross-sectional area to be uscd in the design <br />of stream crossings. <br /> <br />using V = Q/A establishes the velocity of the flow <br />m = 1.33 is being a generally accepted coefficient <br />K=LJV <br />coefficient "K" is generated by the computer program <br />L =Length of Stream Reach <br />PAGE 10 <br />