Results
Water Depth Profile
1D HEC-RAS Model:
2D HEC-RAS Model:
For both the 1D and 2D HEC-RAS models, the most significant change in water surface elevation was near the estuary downstream end. The 2D model, as seen in the plots above for the 20-year flood event, has a much higher resolution (~10-meter length scale) and more detailed results. It shows some differences in the upstream water depth but no significant change. The 1D model results, while less detailed (~1000-meter length scale), act as a confirmation of results found by the 2D model.
The figure on the left compares results from the 1D and 2D HEC-RAS models for the 20-year flood event at the midstream zone (~7 kilometers upstream). This demonstrates the differences in resolution between the models but still reports similar findings regarding magnitude and period of flood peaks.
Inundation Area
1D HEC-RAS Results
2D HEC-RAS Results
20-year Flood Maximum WLE:
With WLOs
Without WLOs
Video: 20-year Storm without WLOs
100-year Flood Maximum WLE:
With WLOs
Without WLOs
Video: 20-year Storm with WLOs
For both the 1D and 2D HEC-RAS models, the scenarios that included water level oscillations had a larger inundation area particularly in the estuary (downstream) zone. As expected, the 100-year storm showed a larger inundation area than the 20-year storm in both models. The 2D model found that the flood may show different flow routes due to different water levels in the estuary zone. When comparing the models, the inundation zones were convincingly similar and the only differences can be credited to the limitations in 1D HEC-RAS resolution.
Effect of Flood Size & Period
2D HEC-RAS Results
The above plots reflect the changes in water depth profile for different flood amplitudes (left) and flood periods (right). The left figure plots water depth over time for both the 20-year and 100-year flood events. The upstream boundary zone and midstream zone show similar results between the two flood events and more oscillation effects at the midstream. At the estuary zone, however, the 100-year flood event shows a salient second flood peak. This comes after a negative reflection in water level oscillations in Chequamegon Bay (downstream boundary zone). Both peaks observed in the 100-year flood event are smaller than the single peak observed in the 20-year flood event. This is caused by the shift in flood routing observed in the 2D model. The right figure plots two different flood periods for the 100-year flood event: 10 and 2.5 hour periods. As expected, the 2.5-hour event has a shorter duration of hazard. This is shown in the estuary zone with roughly the same amplitude in flood peaks. However, considerable differences are observed at the upstream and midstream zones. The peak of the 2.5-hour event is much higher than the 10-hour event. In a shorter duration event, the flood tends to propogate towards the downstream before it interacts (or drowns) lateral boundaries.
1D HEC-RAS Results
The 1D HEC-RAS model results, as expected, show less resolution than the 2D model. Again, this is due to the limitations of 1D HEC-RAS modeling. The results are similar to that of the 2D model. The flood peak occurs at slightly lower amplitudes at the upstream zone, but the results are comparable. The midstream zone data was collected at about 2 kilometers upstream, which is shorter than the data collected in the 2D model results. However, this data is consistent with the trends seen in the 2D results. The flood peak amplitude is shorter and the water level oscillations have more of an impact on water surface elevation. In the estuary zone, only one flood peak was observed for the 100-year flood. This is due to the 1D model limitations with resolution and inability to model flood routing changes. Overall, the 1D model similarly demonstrates the reduced impact of water level oscillations further upstream and lower flood peaks at the downstream.
