Post on 12-Mar-2020
Dam Breach Analysis – 1D vs. 2D
PREPARED FOR:
2018 KAMM CONFERENCE
Prepared By: Mario G. Sebastiani
Civil & Environmental Consultants, Inc.
September 19, 2018
Importance of Being Prepared
1D vs. 2D Modeling
Representative Project Overview
1D vs. 2D Results Comparison
Overview
Introduction
-
10,000
20,000
30,000
40,000
50,000
60,000
70,000
High Significant Low Undetermined
15,498 11,882
60,705
2,495
Nu
mb
er
of
Dam
s
Hazard Potential
Dams by Hazard Potential
-
1,000
2,000
3,000
4,000
5,000
Yes No Not Required
4,288 3,902
3,692
Nu
mb
er
of
Dam
s
Emergency Action Plan (EAP)
Number of Significant Hazard Potential Dams with an EAP
Statistics from the National Inventory of Dams
27,380
Introduction
2,565 1,853 1,857 2,188
3,774 4,120
11,902
20,257
13,600
5,521 4,599 4,125
-
5,000
10,000
15,000
20,000
25,000
Before 1900 1900-1909 1910-1919 1920-1929 1930-1939 1940-1949 1950-1959 1960-1969 1970-1979 1980-1989 1990-1999 Since 2000
Nu
mb
er
of
Dam
s
Dams by Completion Date
Statistics from the National Inventory of Dams
Introduction
“By failing to prepare, you are preparing to fail.”
- Benjamin Franklin
2D vs. 1D Modeling
Definitions
▪ 1D Modeling
Solves the fully dynamic St. Venant
equations of conservation of mass and
momentum along a singular dimension.
▪ 2D Modeling
Solves the fully dynamic St. Venant
equations of conservation of mass and
momentum along two dimensions.
What’s the difference?
2D vs. 1D Modeling
Hydraulic Modeling Utilizing HEC-RAS 2D
▪ 1D Advantageso Fewer geometric data are required
o Shorter computational timeo In-bank flows computed more efficiently
o Relatively smaller output files
o Hydraulic structures (2D uses culvert eqns)
▪ 2D Advantageso Flowpaths do not need to be predefined
o Provides realistic depiction of flow throughout a systemo Perform 1D and 2D modeling within the same unsteady flow model allows users to model larger river systems, 1D where appropriate (main river) and 2D
modeling in areas that require a higher level of hydrodynamics
o Flowpaths can change with flow deptho Cross-momentum of flow splits is accounted for (significant for road systems)
o Losses due to 2D effects (i.e. bends, flow separations, etc.) automatically included within computations
o Floodplain storage is implicitly defined
o Inputs and outputs can be defined spatially in GIS-type environments (better data continuity)
o Does not require extraction of cross sections from survey data
o Detailed Flood Mapping and Flood Animations – based on underlying terrain, each cell can be partially wet/dry reflected in the mapping and animations
o Can provide results directly for mapping flood extents and inundation depths, velocities, and safety hazards
2D vs. 1D Modeling
Hydraulic Modeling Utilizing HEC-RAS 2D
▪ When is 1D Okayo Locations where flow isn’t required to spread (uni-directional flow)
o Well-defined channel/overbank systems (defined valleys)
o Simply-connected floodplains where flow in main channel is well connected to flow in the overbank and both are primarily uni-directional
o When elevation data of only limited quality/quantity are available
▪ When is 2D Preferableo Anywhere flow is expected to spread
o Urbanized Areas
o Wide Floodplains
o Downstream of Levee Breaks
o Downstream of Upground Reservoir Breaks
o Wetland Studies
o Lake or Estuary Studies
o Water Quality and Sediment Transport
2D vs. 1D Modeling
Hydraulic Modeling Utilizing HEC-RAS 2D
▪ 1D or 2D?o What is the length-to-width ratio of the
project area? (> or < 3:1?)
o Does the project have features that force
flow to rapidly contract or expand?
o What kind of output animations are
needed to convey the results to the
stakeholders?
Representative Project Overview
Four Eagles Lake – Camden,
Ohio
▪ 25.5-acre reservoir at normal pool
▪ 45-foot high, 620-foot long
embankment
▪ 3.1 sq mi drainage area
▪ High Hazard Dam
Four Eagles Lake Dam
Representative Project Overview
Representative Project Overview
Project Overview Aerial Map
Representative Project Overview
Project Overview Hillshade Map
Project Overview
Dam Breach Assumptions/Parameters
Feature/Parameter Value
Maximum Embankment Height 45 feet
Length of Dam 620 feet
Crest Width 18 feet
Crest Elevation 957.96 feet
Reservoir Area at Top of Dam 42 acres
Storage Capacity at Top of Dam 616 acre-feet
Principal Spillway TypeConcrete weir with baffled
chute
Principal Spillway Crest Elevation 947.46 feet
Storage Capacity at Principal
Spillway Elevation255 acre-feet
Reservoir Area at Principal Spillway 25.5 acres
Emergency Spillway TypeGrass-lined open channel with
3H:1V side slopes
Emergency Spillway Crest Elevation 952.46 feet
Four Eagles Lake Dam Characteristics
Dam Breach Assumptions/Parameters
Summary of Breach Results
Scenario PMF
Pool Elevation at
Breach,
Initial (ft)
957.77
Time Breach Occurs 13:04
Breach Type Piping
Storage Volume at
Breach (ac-ft)608.61
Discharge at Dam, Peak
(cfs)63,063
Probable Maximum Flood
HEC-RAS Geometry Map
1D 2D
2D: 10-foot by 10-foot grid
2D Results – Inundation Boundary
2D Results – Inundation Boundary
2D Results – Inundation Boundary
2D Results – Inundation Boundary
2D Results – Particle Tracing
2D Results - Particle Tracing
2D Results - Particle Tracing
2D Results - Particle Tracing
2D Results - Particle Tracing
2D Results – Time Series
2D Results – Time Series
2D Results – Inundation Boundary
2D Results – Inundation Boundary
2D Results – Inundation Boundary
1D vs 2D Results – Inundation Boundary
1D vs 2D Results – Inundation Boundary
1D vs 2D Results – Inundation Boundary
1D vs 2D Results – Inundation Boundary
1D vs 2D Results – WSEL Profiles
840
850
860
870
880
890
900
910
920
930
940
100 2100 4100 6100 8100 10100
WS
EL
(fe
et)
Station
PMF Breach - Water Surface Elevation Profiles(Entire Downstream Reach)
2D
1D
1D vs 2D Results – WSEL Profiles
840
845
850
855
860
865
870
875
880
885
100 1100 2100 3100 4100 5100
WS
EL
(fe
et)
Station
PMF Breach - Water Surface Elevation Profiles(Downstream End of Study)
2D
1D
1D vs 2D Results – Velocity Profiles
0
5
10
15
20
25
30
100 200 300 400 500 600
Velo
cit
y (
fps)
Station
1D vs 2D Velocity
1D
2D
1D vs 2D Results – Velocity Profiles
0
5
10
15
20
25
500 600 700 800 900 1000
Velo
cit
y (
fps)
Station
1D vs 2D Velocity
1D
2D
1D vs 2D Results – Velocity Profiles
0
2
4
6
8
10
12
14
16
18
1200 1400 1600 1800 2000 2200
Velo
cit
y (
fps)
Station
1D vs 2D Velocity
1D
2D
1D vs. 2D Modeling
1D or 2D? Which one should we use?
1D vs. 2D Modeling
Hydraulic Modeling Utilizing HEC-RAS 2D
“All models are wrong, but some are useful.”
-George E. P. Box
“For every complex problem there is an answer that is clear, simple, and
wrong.”
-H.L. Mencken
Questions
Thank You
Mario G. Sebastiani
Water Resources Engineer- Civil & Environmental Consultants, Inc.
msebastiani@cecinc.com | P: 513.985.0226