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water interface and comparing the result to an allowable tractive <br />• force determined by an empirical evaluation of the soil materials. <br />While the actual tractive force may be determined if the flow <br />characteristics of the Channel are known (i.e., io YRS), the <br />analysis of the allowable tractive force is not well defined as <br />Smerdon and Beasley (1961), Doubt (1963), and Flaxman (1963) indicate. <br />Therefore, velocity is often accepted as the mast important factor <br />when designing stable earthen channels using the static equilibrium <br />approach. <br />The permissible velocity approach consists of specifying a non- <br />eroding velocity that is sufficient to transport the sediment load <br />entering the channel, yet low enough to prevent scour Cf the bed and <br />banks. Comparison of the actual flow velocities to maximum <br />. permissible velocities normally associated with the type of channel <br />soil materials is made to determine the erosion potential. Several <br />authors have published tables of maximum permissible velocities <br />(Fortier and Scobey, 1926; Lane, 1955; U.S. Army Corps of Engineers, <br />1970; Soil Conservation Service, 1954). In general, for water <br />transporting collodial silts in a channel composed of sandy clays and <br />lined with an average stand of vegetation, the maximum permissible <br />velocity ranges between 5 to 6 feet per second, Comparing this range <br />in permissible velocity with the velocity values in Table 3.2 <br />indicates that the majority of the channels are stable. Channels <br />exceeding this criteria are 41-1, 9/10-1, 7-2(51), 9/10-1(S1E) and <br />9/10-2(S1E). <br />• <br />36 <br />