Laserfiche WebLink
<br />$TEP 10 (continued) <br /> <br />METHOJ[) 2 . TABLE OF HYDRAULIC ROUGHNESS CONDITIONS <br /> <br />(Manning's n Value) <br /> <br />Estimate the portions of the channel and adjacent overbanks subject to flood <br />flows <br /> <br />Note the conditions of the channel and the overbanks with respect to <br />vegetation, soil, rocks, and anything that might affect roughness <br /> <br />If there is a substantial difference between the channel, the right overbank, <br />and the kit overbank, plan on anrage roughness values based on the <br />proportion of total flow ill each portion of the total cross-section <br /> <br />Select the description which best represents the conditions of the area you are <br />examining and note the Jroughness value in the Table of Roughness Conditions <br /> <br />If m:cessary, average the roughness values of the various parts of the cross- <br />section to get an overaUl value <br /> <br />,-- <br />,-- <br /> <br />Description of Channel and Overbank Conditions <br /> <br />n Value* <br /> <br />Heavily Vegetated <br />Rocky <br />Gravelly <br /> <br />,070 <br /> <br />,050 <br /> <br />,035 <br /> <br />Sandy or grassy ,030 <br /> <br />Concrete ,014 <br /> <br />, Ihese are average values. <br /> <br />.- ---- <br />,------------ <br /> <br />Note that the roughness values listed above are approximate, Roughness values can vary <br />according to depth of flow, water velocity, and the degree of maintenance performed among other <br />factors. These values are only intended to provide general guidance in the performance of an <br />approximate hydraulic analysis. <br />