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Technical Revision No. 54 <br />Reclaimed Ditch 7 Channel lining <br />Page 6a of 9 <br />The peak flows used to size riprap for Ditch 7 were calculated on pages 5 and 6. <br />Since flow from point B flows into point C as shown on Map 6A -5D, the peak flow <br />used for riprap sizing in Ditch 7 is the summation of flow from points B and point <br />C, resulting in a peak flow of 15.3 cfs. A Manning's n of 0.035 will be used for <br />consistency. <br />Ditch 7 varies in grade from approximately 12 -45 %, as shown on page 6e (Figure <br />1). The 12% section parallels the road and the design will remain valid; no <br />changes will be made to the specified riprap size. <br />After the ditch segment leaves the road, it becomes very steep, approximately <br />40% for 200'. In this segment, D50 = 18" will be used. <br />In the main (middle) segment of Ditch 7, the grade varies from approximately 25- <br />35%. Therefore, 35% will be used to size the riprap. <br />The lower segment of Ditch 7 varies in grade from approximately 38 -45 %. <br />Therefore, 45% will be used to size the riprap. Using a Manning's n of 0.035 <br />would specify a D50 =19 ". Using a Manning's n of 0.030 would specify a D50 <br />=27 ". Therefore, D50 = 19" to 27" is acceptable. D50 = 26 -30" is currently in <br />place and performing well. The voids between the rocks have begun to fill in with <br />sediment which is key to long -term channel stability. Using a larger D50 riprap <br />will provide a more conservative design. <br />