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7/29/2019 David Whyte - A Comparison of 1d 2d Modelling
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Comparing 1D and 2D modelling implications of outcomes for
development planning and appro
David WhyteSenior Engineer, Aurecon
Nina BarichProgram Leader, Develop Works,Waterways, Melbourne Water
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INTRODUCTION
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A brief discussion of some of the available 1D
flood modelling software Required data input, the model set-up and
assumptions
The importance of good data
Differences in defining flood model extents
Case Study comparison
Assessing impacts of development
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FLOOD MODELLING BASICS
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Flood
Hydrology model and a Hydraulic model
Catchment routing hydrology software
RORRAFTS, WBNM, URBS
1D hydraulic software HEC-RAS, MIKE-11, X
SWMM, DRAINS
2D and 1D-2D coupled hydraulic software M
(MIKE Flood), TUFLOW, XP-2D, SOBEK, RMA-
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Importance o
Models are an approximation. The more accurate th
the closer the simulation will be to representing rea
Common Issues
Inaccurate LiDAR/survey
Poor identification or definition of important
Lack of calibration data
Unknown dimensions for hydraulic structure
Lack of stage-storage information for dams
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Example of good and poor survey definition
Well defined
levee
Poorly d
embank
road
Well de
channe
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Comparing 1D, 2D and 1D-2D couple
1D models
well defined channel and floodplain
flow predictable and predominantly in one direction
2D models
complex interactions between main channel and floodplain
multi-directional and numerous flowpaths within the floodplai
1D-2D coupled models
allows a 1D representation of channels and pipes with a 2D mo
floodplain topography
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Comparing 1D, 2D and 1D-2D couple
1D (left) and
(right)
Representat
Open Chann
(Source: USACE Enginee
River Hydraulics 1994)
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Comparing 1D, 2D and 1D-2D couple
The choice of model will depend on:
The purpose of and desired outcome of the s The level of accuracy required
The available data
Available budget; and Available skills to use or interpret the softwa
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CASE STUDY
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C
Rural catchment in western
Melbourne
Several dams, grassed channels androad culverts
Catchment Area = 3.2km2
Hydrology Modelled using RORB
Hydraulics Modelled using HEC-RAS
Comparison Model using MIKE
FLOOD
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C
Catchment
Overview
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C
1D Model
Network
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C
88
114
88Br
Down stream
1119
1105
1081
1046
1020
958930 841
807777
721
672
635
547 407
381235
6030
Main
Stream 65
65
Up stream
2988
2932 2872 2812 27522633
2551
25142357
2306
2276
2238
22052169
21192076
202319511884
1855
MainS
tr
eam6565
Resevoir
0 50 100 150 200 250245
246
247
248
249
250
251
Station (m)
Elevation(m)
Legend
EGPF#1
WSPF#1
Crit PF#1
Ground
Bank Sta
.05 .05 .05
0 100 200 300235.2
235.4
235.6
235.8
236.0
236.2
236.4
236.6
236.8
Station (m)
Elevation(m)
.05 .05
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C
2D Model Grid
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C
1D Network -
2D Model Grid
Coupled
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C
1D Model
Flood Extents
Results
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C
1D 2D
Coupled
Model Flood
Extents
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C
Comparison
of FloodExtents
E l ti d l
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Evaluating developme
and/or flood mitigatio
1D alter a portion of the cross-section
2D
insert the footprint of the design in the
grid
Whether 1D or 2D - the ability to accurately
represent the development proposal will ulti
depend on the resolution of the model set-u
E l i d l
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Evaluating develop
and/or flood mitig
Example Development Area 1D Model Setup
114
88
Down stream
1119
1105
1081
1046
1020985
958
930
900870841
807777
753
721
700
672
635
578522441 407
38
0 200 400 232.4
232.6
232.8
233.0
233.2
233.4
233.6
233.8
234.0
Station (m)
Elevation(m)
.05 .05
Evaluating developm
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Evaluating developm
and/or flood mitigat
Larger 1D cross-section spacing 2D Model Setup
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CONCLUSION
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C
Good data is important
Choice of model must be fit for purpose Model set-up and resolution is importa
Future use of the model should be cons
Greater understanding leads to better
outcomes
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Question And Answer