Enhancing hydrological data management and exchange procedures

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1 Enhancing hydrological data management and exchange procedures The Sava River Hydraulic Model Dr Mark R Jourdan, PE Research Hydraulic Engineer U.S. Army Engineer Research and Development Center Vicksburg, MS US Army Corps of Engineers

2 Sava River Watershed Site Map

3 Study Goals Utilize best available data to produce an HEC-RAS steady flow model that could be handed off to the ISRBC for further development Develop a methodology for inundation mapping tied to the hydraulic modeling

4 Study Goals Workshop SEP 2010 Train ISRBC on modeling and mapping software (HEC products) Demonstrate how to use these products Train what information and what steps need to be taken to improve these products Demonstrate various flood risk programs in the US FEMA Flood Insurance Program (DFIRM) Modeling, Mapping, and Consequences Production Center FEMA RiskMAP Discuss the future of floodplain risk management in the Sava River

5 Hydraulic Modeling (HEC-RAS) Approach Model Sava River using a steady flow HEC- RAS Model Extend XSs provided by ISRBC using DEM to transect the entire floodplain Levee stations added to represent levee locations and overtopping elevations Allow flow to be contained within the levee stations until overtopping of the levees Conceptually, this approach does not work w Floodplains are too wide. When overtopping of the levees occur steady flow solution becomes invalid w Gate structure is difficult to simulate in steady flow model

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7 Hydraulic Modeling (HEC-RAS) Approach Ultimately, A steady flow HEC-RAS model, An HEC-HMS model, and An unsteady flow HEC-RAS model was developed using the approach of modeling the Sava River with the gated flow diversion structures in the Central Posavina flood protection system Major Limitation: Flooding information can not be developed outside of the levee system except in the area of the Central Posavina flood protection

8 Hydraulic Modeling (HEC-RAS) HEC-RAS Model Development Cross section geometry Developed using DEM in HEC-GeoRAS ISRBC cross sectional data merged into the XSs cut from DEM Storage Areas Originally, storage curves derived from DEM Post-workshop, storage curves provided by ISRBC were used for the Central Posavina flood protection system storage areas Bridges Only a single bridge added as an example Determined that most bridges on the Sava River do not cause major backwater effects

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10 Hydraulic Modeling (HEC-RAS) HEC-RAS Model Development Levees Most difficult component to model 4 Sources for Levee Information w Levee centerline shapefile provided by ISRBC Provided location of levee w XS data from ISRBC HEC-RAS model Provided location and elevation w Aerial Imagery w DEM Provided location Provided location and elevation Sources did not always match Engineering judgment necessary

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12 Hydraulic Modeling (HEC-RAS) HEC-RAS Model Development Central Posavina Flood Protection System Important from a modeling standpoint to correctly account for flow diversion during high flow events Incorporates a system of levees, diversion channels and storage areas Difficult to model conceptually not having the opportunity to visit the site

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14 Hydraulic Modeling (HEC-RAS) HEC-RAS Model Results Calibration Calibrated to the DEC 2009 and SEP 2010 flood events Calibration at the lower end is reasonable Unsatisfactory calibration in the region around the Central Posavina Flood Protection System. w Poor calibration could be due to several issues Incorrect stream flow inputs based on the observed discharge gages. Gages do not align with confluences of major tributaries Incorrect representation of the Central Posavina Flood Protection System w The modeling approach to simulating the flood protection system needs to be re-evaluated

15 140 Sava 6 Sava River Model December 2009 Event Croatia/Slovenia Border 120 Central Posavina FPS Elevation (m) 100 Belgrade Sremska Mitrovica Slavonski Brod Sremska Mitrovic Raca Jamena Brcko Zupanja Slavonski Brod Srbac Davor Main Channel Distance (m) Mackovac Ustava Stara Gradiska Jasenovac Trebez Sava Gusce Crnac Dubrovak Prevlaka Sava Rugvica Zagreb Preljev Jankomr Jessenice Na Dol

16 September 2010 Event Croatia/Slovenia Border Central Posavina FPS Belgrade Sremska Mitrovica Slavonski Brod

17 Hydraulic Modeling (HEC-RAS) Inundation Mapping Developed inundation mapping for the DEC 2009 and SEP 2010 flood events Poor quality DEM prohibits the development of usable inundation mapping New LiDAR or other DEM could greatly benefit the development of inundation mapping and hydraulic model geometry Examples

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21 Modeling Limitations Levee Information Very difficult to determine proper location and elevations of levees Central Posavina Flood Protection System Difficult to conceptualize without seeing the system Unclear on operational plan for the system DEM Probably the most critical limitation of the modeling Very expensive to have the necessary area flown for the Sava River and its tributaries

22 Model Improvements and Uses Further geometry improvement and calibration of the base HEC-HMS and HEC-RAS model using the updated models since the Phase 1 model development Calibrate to more historic events and a flood frequency based analysis Additional Tributary Modeling Focus on tributaries with adequate available data Utilize HEC-HMS model for flow input Improved inundation mapping using better digital terrain information If not available, demonstrate inundation mapping capability in a pilot area 2-D Modeling using the new 2-D features in HEC- RAS or another 2-D modeling software Depends on better DTM and release of HEC-RAS

23 Model Improvements and Uses (continued) Consequence Estimation Utilizing HEC-FIA Depends on better DTM and development of a structure database with necessary information Flood Warning Products Based on scenario or statistically-based events Link to stream gage elevations Depends on better DTM Flood Forecasting using a system HEC-HMS and HEC-RAS model. Dam Failure Breach Analysis Develop mapping and emergency action plans

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28 Conclusions Overall the goal of developing a base hydraulic model that can be improved upon by the ISRBC was accomplished Included was a base HEC-HMS and unsteady flow HEC-RAS model However, the modeling is incomplete at this point and requires more refinement Focusing on developing a robust HEC-HMS model Using HEC-HMS flow hydrographs as input into the HEC-RAS model With additional effort, an HEC-HMS model could be calibrated and utilized to develop discharge inputs to the HEC-RAS model Develop a process for HEC-DSSVue to digest the stage, flow and precip information from each country The flow inputs from a calibrated HEC-HMS model could allow for more detailed calibration of the HEC-RAS model A system for creating inundation mapping was not achieved primarily due to low quality DEM In the future, the modeling of the tributaries to the Sava River could be more critical than the Sava River in terms of evaluating flood risk considering the tributaries have less extensive levee system and more channel-floodplain interaction

29 Thank you