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<br />Plennlng And Preliminary Design <br /> <br />e <br /> <br />I. Measur ,ment of streamflow <br />A. Direct measurement of stream gaging <br />1. Cwrent meter method <br />2. Measurement by floats <br />3. Ultrasonic method <br />4. Tracer-dilution technique <br />B. Mlasurementthroogh hydraulic devices <br />1. Weirs and notches <br />2. Orifices <br />3. Aumes <br />C. In,lirect measurement of peak flow <br />1. Slope-area method <br />2. Aow-over-structure methods <br />II. Estimation of stream flow <br />A. Application of precipitation data <br />I. Precipitation - runoff relation <br />2. Hydrograph analysis <br />3. Empirical formulas <br />II. Extension of gage sites <br />C. Use of generalized data, charts, tables <br /> <br />Many if liot all of these methods can be found in hydrology and hydraulic text books. <br />These me thods of measurement will not be discussed in this manual, save three, and <br />will be Ie:'! for further investigation by the reader. <br /> <br />The use of a cwrent meter is the most common type of discharge measuremenl. The <br />current meter functions through the use of the revolution of the propeller. Usually the <br />cwrent meter is attached to a counter that progresses each time the propeller completes <br />one revol ution caused by currenl. A stopwatch is used to measure the time over which <br />the revolutions are counted. <br /> <br />Secondly. empirical formulas may be employed through the use of the Manning's <br />Equation. Manning's formula has proven most reliable in practice and is given by <br /> <br />2 I <br />V = (1.486)R'S2 <br />n <br /> <br />(EQ 5-2) <br /> <br />Where: <br />R = hydraulic Radius, ft. <br />S = slope energy line <br />Y = mean velocity, ft/sec <br />n = Manrling's roughness coefficient <br /> <br />Typical values of n are summarized in table 5-2 <br /> <br />e <br /> <br />60 <br /> <br />Colorado Erosion Control Manual <br />