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~1 <br />filter and clay zone as specified in the design in the main channel with the <br />rock size range from 1 foot to 3 feet in diameter. The pit at both sides of <br />the restored channel has not been reclaimed by Dorchester; therefore, there <br />~ was no riprap placed at the overbank area at the time of the site visit. <br />1 <br />III. HYDRAULIC ANALYSIS <br />The hydraulic calculation of the designed channel was presented in the <br />September 1981 report (Table 20, p. 74 ). The as-built channel cross section <br />' is shown in Figure 2. The channel dimensions were obtained using the measured <br />dimension and 3-feet riprap was added on top of the gravel filter. Since the <br />' channel slope varies from 3 to 4 percent, a slope of 3 percent is used in <br />these hydraulic calculations. Table 1 presents the dimensions and results of <br />the hydraulic calculations for the designed channel and as-built channel. <br />' Table 1 indicates that the as-built channel is narrower and deeper than the <br />' designed channel. However, the capacity of the as-built channel is greater <br />' than the designed channel. <br />The 100-year, 24-hour peak runoff (9789 cfs) was also used to check the <br />hydraulic characteristics of the as-built channel. An overbank slope of 10 to <br />1 was assumed since the pit has not been totally reclaimed. The overbank area <br />' would have flow depth of 3 feet during a 100-year, 24-hour peak runoff. The <br />floodplain will be approximately 123 feet wide. Atypical cross section of <br />the completely restored Newlin Creek channel is shown in Figure 3. The <br />results of the hydraulic calculations are given in Table 2. <br />' IV. CHANNEL STABILITY <br />The velocities in the as-built channel range from 13 fps to 17 fps for <br />' the peak runoffs of the 10-year, 24-hour and 100-year, 24-hour events. Riprap <br />protectiong at channel bottom and banks is required. For side slope of 2.3 <br />' to 1, riprap with a mean diameter of 1.5 feet is adequate for both channel <br />bottom and banks. The thickness of riprap should be approximately 3 feet. <br />The as-built channel has approximately 3-foot thick riprap with the mean <br />diameter approximately 1.5 feet. The as-built channel also has gravel filter <br />below the riprap to prevent the loss of fine particles and clay liner under <br />' the gravel filter to prevent seepage. <br /> <br />1 <br />