CE4723 Hydraulics Final Exam
— David Wagner 2007/12/11 12:44
HEC-RAS Model
The problem represented in HEC-RAS is illustrated by the following schematic and xyz profile plot.
The following HEC-RAS summary was produced using a mixed flow regime. The same values result from a subcritical flow regime.
| Reach | River Sta | Profile | Q Total | Min Ch El | W.S. Elev | Crit W.S. | E.G. Elev | E.G. Slope | Vel Chnl | Flow Area | Top Width | Froude # Chl |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (cfs) | (ft) | (ft) | (ft) | (ft) | (ft/ft) | (ft/s) | (sq ft) | (ft) | ||||
| 1 | 58080 | PF 1 | 100000.00 | 60.00 | 78.68 | 71.41 | 79.94 | 0.001116 | 9.03 | 11073.42 | 700.00 | 0.40 |
| 1 | 55440 | PF 1 | 100000.00 | 55.00 | 75.18 | 76.33 | 0.001681 | 8.60 | 11626.53 | 700.00 | 0.37 | |
| 1 | 54120 | PF 1 | 100000.00 | 52.50 | 72.81 | 73.99 | 0.001862 | 8.72 | 11468.58 | 700.00 | 0.38 | |
| 1 | 52800 | PF 1 | 100000.00 | 50.00 | 70.00 | 62.84 | 71.28 | 0.002256 | 9.09 | 11000.00 | 700.00 | 0.40 |
As expected, the water surface slope between river miles 10 and 10.5 differs from the slope between 10.5 and 11 as primarily as a result of the change in roughness.
| W.S. Elev (ft) | ||
|---|---|---|
| River Sta | Table 6.10 | HEC-RAS |
| 58080 | 78.4 | 78.68 |
| 55440 | 74.5 | 75.18 |
| 54120 | 72.4 | 72.81 |
| 52800 | 70.0 | 70.00 |
Table 6.10 and HEC-RAS
The HEC-RAC values are higher than the values of table 6.10. However, a warning in the detailed report indicated there may be a need for more cross sections.
Revised HEC-RAS Model
Additional cross-sections do effect the results of the HEC-RAS model, especially at the upstream portion of the reach. Note when HEC-RAS interpolated the cross-section geometry it also interpolated roughness values, so the Manning's n values needed to be manually restored to their given values.
| W.S. Elev (ft) | ||
|---|---|---|
| River Sta | Table 6.10 | HEC-RAS |
| 58080 | 78.4 | 78.20 |
| 55440 | 74.5 | 75.17 |
| 54120 | 72.4 | 72.80 |
| 52800 | 70.0 | 70.00 |
Table 6.10 and HEC-RAS
| Reach | River Sta | Profile | Q Total | Min Ch El | W.S. Elev | Crit W.S. | E.G. Elev | E.G. Slope | Vel Chnl | Flow Area | Top Width | Froude # Chl |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (cfs) | (ft) | (ft) | (ft) | (ft) | (ft/ft) | (ft/s) | (sq ft) | (ft) | ||||
| 1 | 58080 | PF 1 | 100000.00 | 60.00 | 78.20 | 71.41 | 79.55 | 0.001229 | 9.31 | 10739.35 | 700.00 | 0.42 |
| 1 | 57640.* | PF 1 | 100000.00 | 59.17 | 77.69 | 79.00 | 0.001199 | 9.19 | 10880.23 | 700.00 | 0.41 | |
| 1 | 57200.* | PF 1 | 100000.00 | 58.33 | 77.20 | 78.47 | 0.001165 | 9.06 | 11039.40 | 700.00 | 0.40 | |
| 1 | 56760.* | PF 1 | 100000.00 | 57.50 | 76.72 | 77.95 | 0.001133 | 8.93 | 11201.24 | 700.00 | 0.39 | |
| 1 | 56320.* | PF 1 | 100000.00 | 56.67 | 76.25 | 77.45 | 0.001099 | 8.79 | 11373.55 | 700.00 | 0.38 | |
| 1 | 55880.* | PF 1 | 100000.00 | 55.83 | 75.77 | 76.94 | 0.001186 | 8.66 | 11544.03 | 700.00 | 0.38 | |
| 1 | 55440 | PF 1 | 100000.00 | 55.00 | 75.17 | 76.32 | 0.001685 | 8.61 | 11616.76 | 700.00 | 0.37 | |
| 1 | 55000.* | PF 1 | 100000.00 | 54.17 | 74.41 | 75.56 | 0.001735 | 8.63 | 11582.46 | 700.00 | 0.37 | |
| 1 | 54560.* | PF 1 | 100000.00 | 53.33 | 73.62 | 74.79 | 0.001792 | 8.67 | 11537.10 | 700.00 | 0.38 | |
| 1 | 54120 | PF 1 | 100000.00 | 52.50 | 72.80 | 73.98 | 0.001867 | 8.73 | 11458.82 | 700.00 | 0.38 | |
| 1 | 53680.* | PF 1 | 100000.00 | 51.67 | 71.93 | 73.14 | 0.001963 | 8.81 | 11348.71 | 700.00 | 0.39 | |
| 1 | 53240.* | PF 1 | 100000.00 | 50.83 | 71.01 | 72.24 | 0.002085 | 8.92 | 11206.13 | 700.00 | 0.39 | |
| 1 | 52800 | PF 1 | 100000.00 | 50.00 | 70.00 | 62.84 | 71.28 | 0.002256 | 9.09 | 11000.00 | 700.00 | 0.40 |
The upstream water surface elevations are now predicted to be lower than the previous model indicated, and lower than the data in Table 6.10.
Discussion