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).