1 Overview of Unsteady Flow Modeling With HEC-RAS Gary W. Brunner, P.E.

2 Introduction l Overview l New Geometric Features for HEC-RAS l Geometric pre-processor l Boundary and initial conditions l Unsteady flow simulation manager l Post-processor l Additional graphics/tables to view results

3 Overview l Common geometry and hydraulic computations for steady & unsteady flow l Using the UNET equation solver (Dr. Robert Barkau) l Can handle simple dendritic streams to complex networks l Able to handle a wide variety of hydraulic structures l Extremely fast matrix solver

4 New Geometric Features for RAS l Existing Geometric Features all work for unsteady flow (XS, bridges, Culverts, inline weirs/spillways) l Lateral Weirs/Spillways l Storage Areas l Storage Area Connections (weirs, gated spillways, and culverts) l Pump Stations

5 Pre-processing Geometry l For unsteady flow, geometry is pre- processed into tables and rating curves n Cross sections are processed into tables of area, conveyance, and storage n Bridges and culverts are processed into a family of rating curves for each structure n Weirs and gated structures are calculated on the fly during unsteady flow calculations n Pre-processor results can be viewed in graphs and tables

6 Cross Section Properties Plot Property Table RS = Conveyance/1000 (cfs) Storage (cu ft) Elevation (ft) Legend Conv. Channel Conv. Valley Conv. Total Storage

7 Cross Section Properties Table

8 Bridge Hydraulic Properties Plot

9 Boundary and Initial Conditions l Boundary conditions must be established at all ends of the river system: n Flow hydrograph n Stage hydrograph n Flow and stage hydrograph n Rating curve n Normal depth

10 Boundary and Initial Conditions l Interior boundary conditions can also be defined within the river system: n Lateral inflow to a node n Uniform lateral inflow across a reach n Ground water interflow n Time series of gate openings n Elevation controlled gate n Navigation Dams n Observed internal stage and/or flow hydrograph

11 Boundary and Initial Conditions l Initial conditions must be established for the entire system: n Specify flows and perform a steady flow backwater analysis n Read in flow and stage at every node from a previous run, “hot start” file

12 Unsteady Flow Simulation Simulation Manager 1. Define a Plan 2. Select which programs to run 3. Enter a starting and ending date and time 4. Set the computation settings 5. Press the Compute button

13 HEC-RAS Computation Window Geometric Pre-Processor Unsteady Flow Simulation Post Processor Computational Messages

14 Simulation Options l Stage and Flow Output Locations l Flow Distribution Locations l Flow - Roughness Change Factors l Seasonal Roughness Factors l Friction Slope Method l Output Options: n Write out Restart File n Detailed Log level output

15 Simulation Options- Continued l Encroachments - Method 1 Only l Dam Breaching l Levee Breaching l Mixed Flow Regime l Checking Data Before Computations l Viewing Computation Log File

16 Calculation Options and Tolerances

17 Post-processing Results l Used to compute detailed hydraulic information for a set of user-specified time lines and an overall maximum water surface profile. l Computed stages and flows are passed to the steady flow program for the computation of detailed hydraulic results

18 Viewing Unsteady Flow Results l All of the output that was available for steady flow computations is available for unsteady flow (cross sections, profile, and 3D plots and tables). l Stage and flow hydrographs l Time series tables l Animation of cross section, profile and 3- dimensional graphic

19 Stage and Flow Hydrograph

20 Time Series Table

21 Animation of Profile Plot

22 HEC-RAS Demonstration