Results of the Sava River Model Jamie G. James, P.E. Nashville District September 2010 US Army Corps of Engineers BUILDING STRONG
Discussion Outline Study Goals Model Limitations HEC-RAS Model Results Inundated Areas Applying the Models and Inundation Maps Administrative Considerations
Study Goals Single Continuous River Model Frequency Flood Profiles Inundation Mapping Depth Grid Mapping
Model Limitations One Dimensional Affects profile calculation in areas of side-flow Affects water surface elevation calculations for areas behind levees in over-topping scenarios Gradually Varied Flow (steady flow model) Assumes that the peak flow exists at all flow change locations at the same time not really how the flood wave propagates downstream Stability Issues (unsteady flow model) Steep slopes, sudden drops, flat slopes (used pilot channels) DEM - DSM
HEC-RAS Model Results General Very broad floodplains behind the levees challenge the model capability when using steady flow. The very broad floodplains also challenge the unsteady flow model, but results are better in overtopping scenarios. Flow velocity varies across the cross section as expected with highest velocities experienced in the channels. Post-RAS Processing Converts the model results to a projection onto the DEM. Process as detailed in earlier presentation on developing Flood Inundation Maps in GIS
HEC-RAS Model Results Steady Flow Results Unsteady Flow Results Location Water Surface Elevation (m) Max. Avg. Velocity Channel/floodplain (m/s) Location Water Surface Elevation (m) Max. Avg. Velocity Channel/floodplain (m/s) Zagreb 690337 114.45 3.55/1.35 Crnac 599660 98.07 1.27/0.65 Mackovac 454298 92.58 1.31/0.21 Sl. Kobas 410859 91.31 0.73/0.40 Zupanja 263364 85.37 1.36/0.49 Zagreb 690337 115.27 2.85/1.33 Crnac 599660 99.26 1.41/0.72 Mackovac 454298 92.00 0.23/- Sl. Kobas 410859 91.62 0.40/0.22 Zupanja 263364 85.95 0.88/0.35 Sremska Mitrovica 139310 80.21 1.40/0.34 Sremska Mitrovica 139310 79.70 1.04/0.23 Belgrade 2506 74.49 1.90/0.28 Belgrade 2506 75.02 1.95/0.35
HEC-RAS Model Results
BUILDING STRONG
BUILDING STRONG
Flooded Area Maps Development and Extent Inundated Areas Developed using post-ras processing that projects the water surface elevation on the grid for the flood profile modeled Mapping extends from the confluence with the Danube River at Belgrade to Zagreb Some processing work remaining to resolve holes Limitations Similar to limitations of the DEM (accuracy +/- 3m) and the model (finite element analysis) It is an approximation Recommended Uses Floodplain regulation and planning Can aid in determining the extents of the floodplain, or whether a structure is in the floodplain, but field run surveys should be the decisive factor
Applying the Models and Inundation Maps Model Flooding Scenarios Flood events other than the base flood Different storms locations, intensities, timings, historical storms Model Flood Mitigation Alternatives Channelization, dams, levee modifications, storage changes Floodplain Management Various strategies dependent upon depth and velocities (floodproofing), floodplain evacuation in most severe areas Flood Warning and Emergency Evacuation Plans
Administrative Considerations Recommendations Users should produce a study report for each new stream, models and flood inundation mapping we will provide the SRC with written documentation of what we ve done Utilize a central holder of the models, GIS data and maps Participants could get the data from the central holder, perform analyses, and return revised (up-to-date) models, GIS data and maps to the central holder The central holder would review and approve/revise the submitted data Prevents numerous versions of the model, data and maps
Questions?