Overview of Unsteady Flow Modeling With HECRAS Gary

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

Introduction 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 l 2

Overview 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 l 3

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

Pre-processing Geometry l For unsteady flow, geometry is preprocessed 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 5

Cross Section Properties Plot Property Table RS = 138154. 4 700 Legend Conv. Channel Elevation (ft) 690 Conv. Valley Conv. Total 680 Storage 670 660 650 0 1000 2000 3000 4000 5000 6000 7000 Conveyance/1000 (cfs) Storage (cu ft) 6

Cross Section Properties Table 7

Bridge Hydraulic Properties Plot 8

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 9

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 10

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 11

Unsteady Flow 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 12

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

Simulation Options 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: l n Write out Restart File n Detailed Log level output 14

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

Calculation Options and Tolerances 16

Post-processing Results 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 l 17

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

Stage and Flow Hydrograph 19

Time Series Table 20

Animation of Profile Plot 21

HEC-RAS Demonstration 22