9/12/2014

1

© 2014 HDR, Inc., all rights reserved.

TESTING AND USE OF HEC-RAS

2D FOR FEMA PMRsBy

Mark Forest, P.E., CFM and Mitch Blum, P.E.

Overview

Example Simulations

Modeling Demonstration

FEMA Applications

Some of the example graphics provided by

the Corps of Engineers, Hydrologic

Engineering Center

9/12/2014

2

Overview

2‐dimensional Hydrodynamic Flow Routing

Within Unsteady Flow HEC‐RAS

Similar to the use of a Storage Area

Linked 1D/2D Capability

Independent 2D Domain

Full Saint Venant or Diffusion Wave

Equation Solution Options

Implicit Finite Volume Solution Algorithm

1D and 2D Coupled Solution Algorithm

Unstructured or Structured Computational

Meshes with Variable Sizes in Domain

Detailed Hydraulic Table Properties for

Computational Cells and Cell Faces

Multi‐Processor Based Solution Algorithm

64 Bit and 32 Bit Computational Engines

What?

Source: HEC

9/12/2014

3

Need for 1D/2D Integrated

Modeling Tool

o Integration with HEC-RAS

1D Elements

oCorps Mission Needs

• Levee breach mapping

• Dam breach mapping

• Robust 2D solutions

oPost-Process w/o

Independent Software

• RAS Mapper Compatible

Why?

Source: HEC

Alpha Version 1 – April 2013

Alpha Version 2 – Aug 2013

Beta Version – May 2014

Revised Beta – June 2014

5.0 Release - Fall 2014

When?

9/12/2014

4

1D/2D Integrated Modeling

Tool

oPublic Domain

oNo License Fees

oRAS Mapper Compatible

Alternatives

oNew Code v. Existing Codes

Unique Approach to 2D

Solution

How is it Different?

Computational Mesh with Sub-

Grid Terrain Data

Gridding Process Defines

Hydraulic Property Tableso Elev-Wetted Perimeter (Face)

o Elev-Area (Face)

o Roughness (Face)

o Elev-Volume (Cell)

Cell Face is Detailed Cross

Section

Able to Capture Complex

Hydrodynamics

How is it Different?

Source: HEC

Source: HEC

9/12/2014

5

Computational Efficiency

Same Detail as Finer Mesh

Models with Larger Grids

Example Run Times:

Example River37800 Cells, 25 Foot Grid Size

Diffusion Wave Solution

Simulation Duration: 3 Days

Time step: 3 Seconds

Run Time: 8.5 Hours

Tidal Basin Example52,919 Cells, 1000 Foot Grid Size (1900 square miles)

Full Momentum, Tidal Boundary

Simulation Duration: 17 Months

Time step: 2 Minutes

Run Time: 16 Hours (laptop) 9 hrs (modeling comp)

Advantages

Source: HEC

Source: HEC

Sub-Grid Level Detail

Computationally Efficient

Multi-Processor Solution

64 and 32 Bit Compatible

Validation Process

Advantages

Source: HEC

Source: HEC

9/12/2014

6

Pre-Processing Capability

o1D (in process)

o2D Mesh Processes

Post-Processing Changes

Will Replace GEO-RAS

oGEO-RAS will no longer be

supported after RAS Mapper

is completed (probably v. 5.1)

Output Limited in Beta, full

function in release version

RAS Mapper

Source: HEC

Multiple 2D Domains

Much Faster Run Times (2 to 3

times compared to Alpha version)

Connections Include Storage Area

Connections, lateral/inline

structures

Internal Hydraulic Structures

Inside 2D Area (Roads, Levees,

Dams, etc.)

Overflow calculated with 2D

Equations, Not Weir

1D Element Not Required

Beta Version

Source: HEC

Source: HEC

9/12/2014

7

1 Manning’s n Value per domain

RAS Mapper functions in process

Output limited to Max and Min

Depth Grid, Animation, HDF files

and some grid data.

Interactive Data Access

• Depth

• Face Velocity

• Node Velocity

• Water Surface

Beta Limitations

New Features

o Detailed 2D Output

o Additional Speed Enhancements

o Mesh Generation Tools

o Spatial n Value

o Additional Sediment Transport

Functions (1D)

o Dam Breach Options

• Simplified Physical Breaching

• Breach Width and Time Calculator

• Post-Processing of Breach Data

o RAS Mapper Evolution to Replace

GEO-RAS

HEC-RAS 5.0

Source: HEC

9/12/2014

8

Variable Manning’s n Values

Example Simulations

9/12/2014

9

Installed over

100 Temporary

Gages to

Capture the

Event

Used as Model

Validation

Mississippi/Ohio River Flooding May 2011 – Forced Levee Breach

Source: HEC

Example of the

Stability of

Solution

Full Dynamic

Solution

Complex

Hydrodynamics

Benchmark

data set from

European 2D

model tests

Instantaneous Dam Breach

Source: HEC

9/12/2014

10

Model Development

Terrain Data (VERY IMPORTANT!)

Supplemental GIS Data

HEC-RAS Geometry Setup

o 2D Mesh

o Boundary Conditions

o 1D Element

RAS Mapper

o Terrain Creation and Association

o Map Projection

o Web Imagery

Input and Boundary Conditions

o Flow Input

o Boundary Conditions

Computations

Model Setup

9/12/2014

11

Floating Point File

o *.FLT

o Binary Floating Point Values

Derived From

o Grid

o TIN

o ASCII

o Point

Resolution

o Relatively high to capture features

in mesh

Terrain Data

Project Extent

Inflow

Computational Boundaries

GIS Data

9/12/2014

12

2D Flow Area

oGrid Cell Size

Boundary Conditions

o Inflow

oDownstream Boundary

oLateral Boundaries

1D element

HEC-RAS Geometry

Terrain Creation and

Association

Multiple Terrain Support

Flexible Tile

Less terrain file size limits

Map Projection

Web Imagery

RAS Mapper

9/12/2014

13

2D Boundary Conditions

oStage Hydrograph

oFlow Hydrograph

oRating Curve

oNormal Depth

Multiple Boundaries

Available

Initial Conditions

oFlow – 1D

oElevation – 2D

Input and Boundary Conditions

Preprocessor

o2D Hydraulic Tables

Unsteady Flow Simulation

oDiffusion Wave

oFull Momentum

Post Processor

oDepth Grid Animation

Floodplain Mapping

oMax Depth Grid

Computations

9/12/2014

14

Diffusion Wave and Full Momentum Solution Comparison

FEMA Applications

9/12/2014

15

Bifurcated Flow Patterns

Rigid Boundary

Overland Flow

Complex hydrodynamics

Depends on Which 2D Model

Not all 2D Models are Comparable

Hydraulic Structures may be better solved

with 1D

When is a 2D Model Applicable?

When is a 2D Model Not Applicable?

Floodways?

Unsteady Solutions?

Downstream Impacts Not Accounted For?

What is Different With Unsteady?

Differences in Hydrologic Analysis Methods

Differences in Model Detail

o Cross Section Spacing

o Lateral Flows

o Internal Boundary Conditions

Model Stabilization

NFIP Regs Developed in a 1D World

9/12/2014

16

6 Communties

CTP Lead by Carson Water

Subconservancy District

Carson River PMR

70 miles

Community Coalition Process Defined a

Regional Floodplain Management Strategy

Lessons Learned from Truckee River

Goal is to Manage the System as a System

Hydrologic Impacts as Important as

Hydraulic Impacts

Carson River PMR

9/12/2014

17

Unsteady Flow

Method 1 Available in RAS, Method 4 is Not

Convert to Steady Flow for Use in Method 4

Refine using Method 1 in Unsteady

Need to Account for DS Flow Changes

Carson Example – Flow changes up to 0.4

feet

Need to Ask Ourselves:

If it requires a 2D model, does floodway

concept apply?

So What About Floodways

1D Model Assumptions

o Flow breakouts/lateral weirs

o Ineffective flow assumptions

o Geometry developed from 2’ contour data

Using a 2D Model to Inform a 1D ModelSand Creek LOMR

Model Results and Observations

o Results animation*

o Right bank flow breakouts and backwater

o Velocity time series

o Left bank circular flow pattern

o Ineffective flow assumptions

Next steps

o 2D model results used for 1D model refinement

9/12/2014

18

QUESTIONS?