Importing HEC-2 Data Into HEC-RAS

1. Importing HEC-2 Data Into HEC-RAS What you need to know… L-1621/Klipsch98

2. What you should know first… • Not all HEC-2 options have a parallel in HEC-RAS • Computation of Manning’s n values from high watermarks. • Archiving (AC) • Free format (FR) These options are ignored by the importer, so data sets which contain them can still be imported. Some HEC-2 options are available, but are not imported • Split flow • Vertical variation of Manning’s n values • Storage outflow for HEC-HMS L-1621/Klipsch98

3. All imported data should be reviewed carefully for accuracy and completeness, especially... • Special bridges (SB) and culverts (SC) • Normal bridges (X2, BT) • Encroachments and floodway determination (X3, ET) • Ineffective flow areas (X3) • Channel improvements and modifications (CI) • How the HEC-2 cross sections are Identified… • By river mile or station? • By an arbitrary numbering scheme? • Are the section ID numbers increasing from downstream to upstream? • Are there duplicate section ID numbers? L-1621/Klipsch98

4. The Import Process – Step 1 • Create a new project … L-1621/Klipsch98

5. Give your new project a title and a unique file name … • Confirm your title and file name… L-1621/Klipsch98

6. The Import Process – Step 2 • After a new project has been opened, select Import HEC-2 data… from the File menu. L-1621/Klipsch98

7. Select the HEC-2 file to be imported… • Tell HEC-RAS how to identify the cross sections as they are imported… L-1621/Klipsch98

8. Use the Geometry and Steady Flow Editors to review the imported data*. • The note below will appear whenever an HEC-2 data set that contains bridge or culvert data is imported. This is a reminder that bridges and culverts are not handled in the same way in HEC-RAS as they are in HEC-2. You will need to check that the data has been interpreted correctly. L-1621/Klipsch98

9. Computational Differences between HEC2 & HEC-RAS • Cross Section Conveyance Calculations • Critical Depth Calculations • Bridge Hydraulics L-1621/Klipsch98

10. n1 n3 n4 n2 A1 P1 A2 P2 A3 P3 Ach Pch Klob = K1 + K2 Krob = K3 Kch Cross Section Conveyance Calculations • HEC-RAS Method: subdivisions at n-value break points. L-1621/Klipsch98

11. n1 n3 n4 n2 A2P2 A3 P3 A4 P4 A7 P7 A6 P6 A5 P5 Ach Pch A1 P1 A8 P8 Krob = K5 + K6 + K7 + K8 Klob = K1 + K2 + K3 + K4 Kch • HEC-2 Method: subdivisions at every ground point. L-1621/Klipsch98

12. To choose the conveyance subdivision method to use, select Steady Flow Analysis… from the Simulate menu: L-1621/Klipsch98

13. Select Conveyance Calculations… from the Options menu of the Steady Flow Analysis editor • And select your method… L-1621/Klipsch98

14. HEC-RAS Parabolic Method Secant Method Used if parabolic method… Does not converge. Finds a value at the top of a levee or at an ineffective flow elevation. HEC-2 Parabolic Method Uses first local minimum it finds. Critical Depth Calculations L-1621/Klipsch98

15. To choose, first select Critical Depth Computation Method… from the Options menu of the Steady Flow Analysiseditor: • Then select the method: L-1621/Klipsch98

16. HEC-RAS 4 Low Flow Methods Energy Momentum Yarnell WSPRO 2 Independent High Flow Methods Energy Pressure &/or Weir HEC-2 2 Low Flow Methods Normal (Energy) Special (Yarnell) 2 High Flow Methods dependent upon Low Flow Method Energy Pressure & Weir Bridge Hydraulics L-1621/Klipsch98

17. HEC-RAS All methods (including Yarnell’s) use actual bridge geometry to determine flow area Each pier is defined and located individually Bridge opening is determined by geometry. HEC-2 Trapezoidal approximation of bridge opening used to determine flow area Single equivalent width pier centered within trapezoid Net flow area input for pressure flow. HEC-2’s Special Bridge Method – Low Flow L-1621/Klipsch98

18. HEC-RAS Fully submerged or upstream-only submerged. Bridge opening based on geometry. Weir profile is the union of the cross section and bridge deck. HEC-2 Fully submerged condition assumed Net flow area input for pressure flow. Weir profile is defined by BT or X2 data – not cross section. HEC-2’s Special Bridge Method – Pressure Flow L-1621/Klipsch98

19. HEC-RAS Piers are defined separate from the deck or ground. The deck data must have a spatial relationship to the cross section(s) but need not match ground points. HEC-2 Piers were defined as part of the cross section data or deck data. Each BT data point was required to match a cross section GR point. HEC-2’s Normal Bridge Method L-1621/Klipsch98

20. HEC-RAS Wide variety of shapes available: Box Pipe Arch Pipe Low & High Profile ConSpan Ellipse Vertical horizontal Multiple culverts of different shapes and sizes can be placed at a single crossing. HEC-2 2 Shapes available: Box Pipe Multiple barrels of only one shape and size can be used at a single crossing. Culvert Hydraulics L-1621/Klipsch98

21. HEC-RAS Methods 1-3 Method 4 0.01 ft. accuracy Method 5 Optimizes for Water Surface or Energy or Both. Floodway determination is independent of blocked obstructions. HEC-2 Methods 1-3 Method 4 Parabolic Interpolation Method 5 Optimizes for a change in Water Surface Method 6 Optimizes for a change in Energy X3 encroachments override ET floodway determination. Floodway Determination L-1621/Klipsch98

22. What can HEC-RAS do that HEC-2 cannot? • Mixed Flow • Multiple Openings • Momentum computation at bridges and junctions • Complex dendritic streams and looped networks • Blocked Ineffective Areas • Normal Ineffective Areas at any station • Blocked Obstructions • Levees • Inline and Lateral weirs and gated spillways • Geometric cross section interpolation L-1621/Klipsch98