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+' TRAPEZOIDAL AND CIRCULAR CHANNEL ANALYSIS HYDROCALC HYDRAULICS MANUAL. PAGE 1J <br />• <br />2.1.1.3 Manning's Roughness CoeHlclent <br />~ This program uses Manning's Equation to analyze open-channel IIow. The roughness of the <br />channel >s represented by Manning's Roughness Coefficient, commonly called the "n-value". <br />Suggested values for Manning's n-value are listed in APPENDIX H of this manual, and in many <br />j hydraulics reference books. Roughness coefficients should be adJusted according to experience <br />f in your geographic area. <br />2.1.1.4 Trapezoidal Channel Slde Slopes <br />The slope of each bank of a trapezoidal channel 1s illustrated in Section 2.1 of this manual. The <br />program expects the side slopes to be represented as the "Z-Ratio'", which 1s the ratio of horizontal <br />distance to vertical rise in the channel bank_ For example, a channel bank which rises 1 foot for <br />each three feet of horizontal distance would have a side slope of 3:1, and a Z-Ratio of 3. Z-Ratios <br />of 3 or 4 are common for earthen channels. Concrete-lined channels may have steeper banks, <br />with Z-Ratios of 1.5 or 2. <br />TheTrapezoidal ChannelAnalysis program has the capability of analyzing channelswith a different <br />side slope for each channel bank. For example, IIow to a street gutter can be analyzed using this <br />program. The vertical curb would cause the side slope to be 0 on one side. On the other side, a <br />6-inch difference between the pavement crown elevation and the gutter elevation, divided by a <br />12-foot lane width, would yield a side slope of 24. <br />2.1.1.5 Trapezoidal Channel Bottom Width <br />Section 2.2 of this manual illustrates the bottom width of the trapezoidal channel section. The <br />bottom width >s measured between the toes of each channel bank. <br />2.1.1.6 Circular Channel Diameter <br />ff the channel Is a circular pipe, then the channel diameter 1s simply the inside diameter of the <br />pipe. Itthe channel is a semicircular flume, then the channel diameter is the diameter of the circle <br />circumscribing the flume. <br />t 2.1.2 DESCRIPTION OF RESULTS OF NORMAL DEPTH PROCEDURE <br />j 11ke all procedures of HYDROCALC° Hydraullp, the Normal Depth procedure can provide a complete <br />' printed report of each computation. Section 1.7 of this manual describes how to print reports. <br />2.1.2.1 Normal Depth in a Trapezoidal Channel <br />Forboth trapezoidal and circular channels, the program computes Normal Depth using an iterative <br />approach to arrive at a value which satisfies Manning's Equation: <br />1.486 ~ <br />`' Q =--AR <br />1n which: <br />Q =Flow Rate in the channel (cfs) <br />n = Manning's Roughness Coefficient <br />A =Area of Flow (square feet) <br />R =Hydraulic Radius (feet) _ (Flow Area)/(Wetted Perimeter) <br />S =Slope of Energy Grade Line (feet per foot) <br />f• <br />® 1989 Dodson & Associates. Inc.. 5629 FM 1960 West, Suite 314. Houton, Texos 77069. (713) 440.3187. All Rlehts Reserved <br /> <br />