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1. <br />Showed: <br />→ Drainage area: 7 sq miles. <br />→ Discharge: 1,600 cfs. <br />2.Flood zone = Zone A. <br />3. <br />4. <br />Elevation 65.00 <br />Elevation 54.5 <br />10.5' <br />5.Normal depth calculation: <br />Q = 1.49/n x A xR2/3 x S1/2 <br />n =0.03 <br />S =0.0283 <br />Assume water level at 9' high from the bottom of channel at Elev. 63.50. <br />Calculate Q: A = (13.50 + 13.50 + 12 + 12) x 9/2 =229.5 sf. <br />P = 16.22 + 16.22 +12 = 44.44 ft. <br />R = A/P = 229.5/44.44 → R2/3 = 3. <br />With S = 0.00283 → S1/2 = 0.053. <br />Qcal = (1.49/0.03) x 229.5 x 3 x 0.053 =1,812 cfs. <br />Qcal > Q100 = 1,600 cfs → OK. <br />→ Waterlevel for 100 year flood under elevation of 63.5 for safety. <br />- Add 18.2 ft above flood elevation → FF = 81.70' (New Detached ADU). <br />Section II: Post – Construction Hydrology Calculations <br />RATIONAL METHOD HYDROLOGY CALCULATIONS <br />Discharge - Drainage area relationships Flood Insurance Study (FIS), Orange <br />County. <br />Benmark = 74.189', SA-226-70 NAVD88. <br />12' <br />Table 7: discharge of East Garden Grove Wintersburg Channel at Euclid St. <br />East Garden Grove Wintersburg channel (C0-5) at Euclid St. had 10' width & 11.5' <br />high slope 1.5:1. <br />4