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~~ <br />~~ <br />P1r. Johnson - 2 - December 14, 1987 <br />'~~ Incision can be expected, especially at the 10.3% slope section (assuming <br />properly designed riprap installation on the steeper areas). Such incision <br />would cause excessive sediment transport, resulting in additional <br />contributions of suspended solids to streamflow and runoff. <br />Erosive flows will occur at the 10.3 channel section. Based on the peak flow <br />figure of 95 c.f.s., and the channel geometry parameters provided in Table <br />TR-87-12-1, calculated velocities of 9.7 f.p.s. and 8.2 f.p.s will result when <br />n values of 0.035 and 0.045 are used, re spec tively as calculated by the staff <br />(method used: Oklahoma Technical Press computer program; based on Applied <br />Hydrology and sedimentology; Barfield, Warner and Haan). <br />The velocity figures provided in Table TR-87-12-1 for the Area 41 fi]1 (upper <br />reach, 13.5b slope) and Area 41 fill (lower reach, 21 .4A slope) are low when <br />compared to the staff's results, using the Oklahoma Technical Press Program. <br />Our results are summarized as follows: <br /> Peak Bottom <br /> Discharge Slope Width Depth Velocity <br /> (c.f.s.) % (f t.) Z (H:1V) N (f t.) (f.p.s.) <br />Area 41 Fili 95 13.5 12 3 .035 .64 i0.6 <br />(upper reach) 95 13.5 12 3 .045 .75 9.0 <br />Area 41 Fill 95 21.4 12 3 .035 .56 12.3 <br />(lower reach) 95 2T .4 12 3 .045 .65 10.5 <br />Additionally, the proposed riprap size may not be adequate. The riprap sizing <br />methods provided in Applied Hydrology and Sedimentology for Disturbed Lands; <br />Barfield, Warner and Maan, 1981, pages 185-194, yield the follo~ding numbers: <br /> Peak Flow Rirap D50 <br /> (c.f.s.) (f t.) Safety Factor <br />Area 41 fill 95 1.5 .77 <br />(upoer reach) <br />Area 41 Fill 95 1.8 .62 <br />(lower reach) <br />(NOTE: Riprap specific gravity of 2.23 was used, based upon your submittal <br />from CTL/Tnompson, Inc. of January 12, 1987; however, riprap should possess a <br />minimum specific gravity of 2.5). <br />Based on our calculations, the velocity and riprap calculations provided in <br />Table TR-87-12-1 would result in an under designed and potentially unstable <br />channel configuration. <br />