CIV E 530 - OPEN-CHANNEL HYDRAULICS SPRING 2008 HOMEWORK No. 12:   HEC-RAS APPLICATION The restoration of Tecate Creek calls for the sizing of a 6-point prismatic flood channel (see sample below) to convey the 10-yr flood within the pilot channel (inbank), and the 500-yr and 10,000-yr floods by the entire flood channel (out of bank). The 10-yr flood peak is 268 m3/sec; the 500-yr flood peak is 997 m3/sec; the 10,000-yr flood peak is 1499 m3/sec. 1. Calculate, using HEC-RAS, the water surface profiles for the three flood frequency levels. 2. Report the u/s and d/s cross sections (plotted output). 3. Report the water-surface profile (plotted output). 4. Report the HEC-RAS summary table containing output data for the three flood levels. 5. Report the freeboards for the three design discharges. The freeboard for the 10-yr flood is to the top of the inbank channel. The freeboard for the 500-yr and 10,000-yr floods is to the top of the total channel. Tecate Creek channel design data Reach length: 11,560 m. Use 7 cross-sections, at R.M. 11560, 9560, 7560, 5560, 3560, 1560, and 0. U/S invert elevation: 552 m. D/S invert elevation: 472 m. Channel side slopes (in bank and out of bank): 2 H: 1 V. Pilot channel (in-bank) bottom width: 25 m. Flood plain (out-of-bank) bottom width: 30 m. (Assume a horizontal flood plain). Inbank channel flow depth: 2.5 m. Out-of-bank channel flow depth: 3.5 m. Manning's n in-bank: 0.035. Manning's n for flood plain (out-of-bank): 0.075. Use normal depth as the downstream boundary condition (normal channel slope, taken as the u/s slope). Neglect the differences in reach length between in-bank and out-of-bank flows (Assume low channel sinuosity). An example of a 6-point cross section is given below (Alamar Creek).

Fig. 1   Sample 6-point prismatic flood channel (Alamar Creek).