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

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Presentation on theme: "L-1621/Klipsch98 1 Importing HEC-2 Data Into HEC- RAS What you need to know…"— Presentation transcript:

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

2 L-1621/Klipsch98 2 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 What you should know first…

3 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?

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

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

6 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.

7 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…

8 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.

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

10 L-1621/Klipsch98 10 Cross Section Conveyance Calculations Cross Section Conveyance Calculations –HEC-RAS Method: subdivisions at n-value break points. n1n1 n2n2 n3n3 n4n4 A 1 P 1 A 2 P 2 A ch P ch A 3 P 3 K lob = K 1 + K 2 K ch K rob = K 3

11 L-1621/Klipsch98 11 –HEC-2 Method: subdivisions at every ground point. n1n1 n2n2 n3n3 n4n4 A2P2A2P2 A 3 P 3 A ch P ch A 6 P 6 K lob = K 1 + K 2 + K 3 + K 4 K ch A 4 P 4 A 5 P 5 A 7 P 7 A 1 P 1 A 8 P 8 K rob = K 5 + K 6 + K 7 + K 8

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

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

14 L-1621/Klipsch98 14 Critical Depth Calculations Critical Depth Calculations 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.

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

16 L-1621/Klipsch98 16 Bridge Hydraulics Bridge Hydraulics 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

17 L-1621/Klipsch98 17 HEC-2’s Special Bridge Method – Low Flow HEC-2’s Special Bridge Method – Low Flow 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.

18 L-1621/Klipsch98 18 HEC-2’s Special Bridge Method – Pressure Flow HEC-2’s Special Bridge Method – Pressure Flow 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.

19 L-1621/Klipsch98 19 HEC-2’s Normal Bridge Method HEC-2’s Normal Bridge Method 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.

20 L-1621/Klipsch98 20 Culvert Hydraulics Culvert Hydraulics 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.

21 L-1621/Klipsch98 21 Floodway Determination Floodway Determination HEC-RAS –Methods 1-3 –Method 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.

22 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


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