© 2014 HDR, Inc., all rights reserved.

Comparison and Utilization of 1D, 2D, and 3D Hydraulic Models on a Complex

Diversion Structure

Brinton Swift, P.E.

Project Partners Coastal Resource and Protection Agency U.S. Army Corps of Engineers HDR The Water Institute of the Gulf BCG Engineering Moffatt & Nichol Dynamic Solutions GeoEngineers Fugro

Hydraulic Model Overview Application of Hydraulic Models Example of Hydraulic Modeling on Projecto Project Needso Model Selectiono Model Resultso Model Coordinationo Lessons Learned

Recommendations

Presentation Overview

Hydraulic Models 1 Dimensional Modelso Cross Section Based Depth Averaged

• Steady or Unsteady Modeling Approaches

2 Dimensional Modelso Grid or Mesh Based Depth Averaged

3 Dimensional Modelso Structured or Unstructured Grid or Mesh

0 200 400 600 800 1000 1200-30

-20

-10

0

10

20

30

30%_Channel Plan: Full_Open 5/27/2015

Station (ft)

Ele

vatio

n (N

AV

D88

) (ft)

Legend

EG Max WS

WS Max WS

Crit Max WS

Ground

Levee

Bank Sta

.015

1 Dimensional

2 Dimensional

3 Dimensional

1 Dimensional Modelo Steady or Unsteady Riverine Systemso Flow Primarily One Directiono Minimal Split Flow

2 Dimensional Modelo Shallow Floodplain Flowo Braided or Split Flow Conditionso Minimal Depth Varied Velocity (Sand Bars,

River Bends, etc) 3 Dimensional Modelo Complex Riverine Systemso Flow Around Structureso Depth Varied Velocities

General Application Of Hydraulic Models

1 Dimensional

2 Dimensional

3 Dimensional

Modeling For Mid Barataria Sediment Diversion Large Scale Sediment Diversion on Mississippi

River Goalso Divert 15,000-75,000 cfs of Water and Sando Maximize Land Building and Habitat Creation in

Barataria Basino Reduce Impacts to Environment and Residentso Limit Impacts to Navigation

Modeling Needso Identify Optimum Channel Sizeo Determine Impacts to Barataria Basin Hydraulicso Understand Inlet Hydraulicso Optimize Inlet Sediment Capture

Modeling Approacho 1 Dimensional Analysis

• Optimize 10% Channel Hydraulics• Investigate Channel Sediment Conveyance• Review Gate Operation and Bridge Impacts

o 2 Dimensional Analysis• Look at Impacts to Barataria Basin• Review Channel Geometry Hydraulic Impacts• Couple River and Basin Models

o 3 Dimensional Analysis• Identify Complex Hydraulics around Intake, Control Structures,

and Transitions• Provide Better Understanding of Hydraulic Losses• Determine Sediment Capture Impacts

o Additional Models• Water Quality• Storm Surge• Wave• Delta Land Building

Modeling for Mid Barataria Sediment Diversion

Mid Barataria 1 Dimensional Model HEC-RAS Unsteady Modelo Upstream Stage Boundaryo Downstream Normal Depth Boundaryo Approximate Expansion of Flow into Barataria

Basin Benefitso Many Iterations of Geometric and Boundary

Conditionso Runs very quickly

Limitationso Doesn’t capture dynamics of structures and outfall

HEC-RAS 2D Modelo Barataria Basino Linked River, Channel, Outfall Model

• 1-Mile Outfall Area

Benefitso Easy to set upo Relatively fast model run timeso Large model domaino Stable platform

Limitationso More difficult to run iterations of geometryo Doesn’t capture depth varied velocities around

structures

Mid Barataria 2 Dimensional Model

Mid Barataria 3 Dimensional Model FLOW3D CFD Modelo Investigated Inlet Combinationso Linked River, Channel, Outfall Modelo Investigated Hydraulic Losses

Benefitso Capable of modeling complex hydraulics of inlet,

tracers, and particle trackingo Fairly easy to set up with the right solid files

Limitationso Long model run timeso Slightly more unstable

1 Dimensional HEC-RAS Modelo Ran over 150 hydraulic models and 30

sediment transport models.o Identified long initial long term deposition rates

in the diversion channelo Created relationship curves for diversion

channel geometry and velocitieso Investigated sensitivity to Barataria Basin water

surface elevations

Mid Barataria Model Results

2 Dimensional HEC-RAS Model Compared with 3 Dimensional FLOW3D Model

Mid Barataria Model Results

2 Dimensional HEC-RAS3 Dimensional FLOW3D

2 Dimensional HEC-RAS Model Compared with 3 Dimensional FLOW3D Model

Mid Barataria Model Results

2 Dimensional HEC-RAS

2 Dimensional HEC-RAS

3 Dimensional FLOW3D

2 Dimensional and 3 Dimensional in Good Agreement

1 Dimensional model clearly not in good agreemento Upstream energy losses appear to not be

capturedo Flow is definitely varied between the 3 inlet

channels

Mid Barataria Model Results Comparison

Mid Barataria Model Coordination Inlet Losseso Much greater than expected ~ 2 fto Adjusted HEC-RAS model for inlet losses

HEC-RAS Ineffective Flow Areaso Adjusted based on 3D model results

Mid Barataria Model Coordination

MBSD

1574815346

1490514456

14065.4*13674.8*

13284.2*12893.6*

12503

1198611523.6*

11140.2*10756.8*

10373.4*9990.*

9606.60*9223.2*

8839.8*8456.4*

8073.*7689.6*

7306.2*6922.8*

6539.4*6156

56535289

496342903989

3709 3442

2974

MBSD_Channel

Upstream End Transition

Ineffective Flow Boundaries

3 Dimensional FLOW3D

1 Dimensional HEC-RAS

Water Surface Elevationso Excellent agreemento Allowed Iterations of Channel Geometry,

Operation, Assumptions• Promising results required confirmation with 2

Dimensional and 3 Dimensional Models

Mid Barataria Model Comparison

Mid Barataria Modeling

Lessons Learnedo Terrain is importanto Time step is importanto Grids are important, you can go overboard!o Model planning is essentialo Significant hydraulic losses need to be considered

around structures Next Stepso Linked hydraulic model with full Barataria Basino Project specific geomorphic modelingo Physical Models (LSU & CPRA Small Scale

Mississippi River Model)o Water quality models for Barataria Basin

Each type of model is very useful Understand strengths and weakness of

each model Plan modeling approach well in advance

with entire project team Understand the system features! Sanity check everything!

Hydraulic Modeling Recommendations

Questions?