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<br />4. MODEl PARAMETERS (from model used to revise fOO-year water surface eJevat;on) <br /> <br />1. <br /> <br />Discharges: <br /> <br />Upstream Limit <br /> <br />Downstream Limit <br /> <br />lO-year <br />50-year <br />IOO-year <br />500-year <br /> <br />__.-2!. 500 <br />8,000 <br />--- <br />10,700 <br /> <br />3,500 <br />8,000 <br />10,700 <br /> <br />_----.!2.,000 <br /> <br />19,000 <br /> <br />Attach diagram showing' changes in IOO-year discharge <br /> <br />2. ~;xplain how the starting water surface elevations were determined Vaules were obtained from <br />1973 FEMA data downstream of Ash Avenue for 100-year water surface elevation. <br /> <br />Also model was started a sufficient distance downstream ~ 1500') to obtain accurat <br /> <br />water surface elevations at the new Ash Avenue bridge. <br /> <br />3. <br /> <br />Give range "ffriction loss coefficients (Manning's -N") Channel <br /> <br />0.035 - 0.040 <br /> <br />Overbanks <br /> <br />0.045 - 0.055 <br /> <br />If friction loss coefficients are different anywhere along the rev ised reach from those used to develop the FlltM, <br />give locatiun, value used in the effective FIS, and revised values and an explanation as to how the revised values <br />were determined. <br /> <br />Location <br /> <br />Frs <br /> <br />Hcvised <br /> <br />Downstream Study Limit <br />To Sta 29800 <br /> <br />Channel <br /> <br />0.045 <br /> <br />Over banks <br /> <br />Channel <br /> <br />Over banks <br /> <br />0.050 <br /> <br />0.035 <br /> <br />0.050 <br /> <br />I~xplain: River is a natural channel, irregular ~ide slope, even clean and regular <br /> <br />cobblestone bed, and has little variation in cross section. An n value of <br /> <br />0.45 is unreasonable. Chow's "open channel Hydraulics'! and normal practice <br /> <br />in region would indicate 0.030 - 0.035. <br />4. Describe how the cross section geometry data were determined le.g., field survey, topographic map, tuhf''' (rom <br />previous .";Iudy) and li:il cross sections that were added. <br /> <br />Field surveys and digitized aerial mapping, Sew sections: 25999, 26034, <br /> <br />26054,26074, 26114, 26349, 26787, 27097, 27626, 27427, 27537, 27627, 27647, <br /> <br />27672, 27697, 27702, 27735, 27825, 27915, 28015, 28105, 28320, 28355, 28755, <br />29105, 29175 <br /> <br />Riverine Hydrauli< Analysl~ fOlm <br /> <br />formA <br /> <br />Page 3 of 6 <br />