Flood Risk and Asset Management
using HEC-WAT with FRA
Compute Option
Michael K Deering, P.E., D.WRE
Senior Hydraulic Engineer
Hydrologic Engineering Center, CEIWR-HEC
International Workshop to
Discuss the Science of Asset
Management
9 December 2011
US Army Corps of Engineers
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Flood Risk Management with HEC-WAT
with FRA Compute Option
● Systems Approaches and USACE Guidance
● Introduction to the HEC-WAT
● Introduction to HEC-WAT with FRA compute option
● Economic and Performance Metrics
● Columbia River Treaty HEC-WAT/FRA Application
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Need for System Approaches with
Risk Analysis
● ER 1105-2-100, Planning Guidance Notebook, 22 April 2000, requires
systems approaches, "The planning process shall address the Nation’s water
resources needs in a systems context…"
● ER 1105-2-101, Risk Analysis for Flood Damage Reduction Studies, 3
January 2006, requires risk analysis for all flood damage reduction studies,
"All flood damage reduction studies will adopt risk analysis…“
● EC 1105-2-409, Planning in a Collaborative Environment, 31 May 2005,
provides revised procedures for conducting Corps water resources planning,
"Collaboration is the keystone of the Corps watershed approach…"
● USACE Campaign Plan, Goals 1 - 4, require comprehensive systems
approaches that include integrated sustainable solutions where decisions are
risk-informed
BUILDING STRONG®
Watershed Analysis Tool (HEC-WAT)
An overarching interface that allows the PDT to perform water resources
studies in a comprehensive, systems based approach by building,
editing and running models commonly applied by multi-disciplinary
teams and save and display data and results in a coordinated fashion.
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Environmental
Hydrology
Flood Damage
Reservoir
Hydraulics
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HEC-WAT Framework
HEC-HMS
Plug-In
HEC-ResSim
Plug-In
HEC-RAS
Plug-In
HEC-FIA
Plug-In
HEC-HMS
HEC-ResSim
HEC-RAS
HEC-FIA
HEC-WAT
Simulation
With Default
Program
Order
Model Results (simulation.dss)
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Interactive Schematic
Computation
Editors
Output Displays
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HEC-WAT Model Integration
● Integrate model and tools used during the analytical
process







Hydrology - HEC-HMS, GeoHMS
Reservoir Operations - HEC-ResSim
Hydraulics - HEC-RAS, GeoRAS
Economics - HEC-FIA
Environmental - HEC-EFM
Statistical - HEC-SSP
Other software - GSSHA, FLO-2D, ADH, RiverWare
● Share data across models
● Involve modelers early in the study process; encourages
a team approach
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Development of FRA Compute Option
● CEIWR-HEC began researching and creating a tool within the
WAT that would perform risk management with parameter
sampling and a life-cycle approach.
● Provides a systems and life-cycle approach to plan formulation
for assessing risks and uncertainties in simple systems as well
as complex, interdependent systems.
● Provides an effective tool for risk communication.
● FRA will apply the Monte Carlo simulation & allow for a lifecycle type computation of consequences (economic and lossof-life) and associated performance indices.
● Incorporate new computational methodologies.
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HEC-WAT Framework with FRM Compute Option & Cost Analysis
Frequency
Sampler
Plug-In
Fragility
Sampler
Plug-In
HEC-RAS
Plug-In
Spreading
Plug-In
HEC-FIA
Plug-In
Cost
Plug-In
Freq
Sampler
Fragility
Sampler
HEC-RAS
Spreading
Model
HEC-FIA
CSRA
Frequency
Breach
Hydrographs
Inflow
Hydrograph
Set
Hydrograph
Sets
Depths,
Velocities
per Grid
Model Results (simulation.dss)
Net
Benefit
Sampler
Damage
Sets
Model
Convergence
?
Expected
Net Benefit,
CDF
Benefits
No
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FRA Monte Carlo Sampling Sequence
● For each project alternative, a single scenario of the project
life cycle (e.g., 50 years) is simulated by sampling annual
maximum flood events for the duration of the life cycle.
 For agricultural damage, may sample season by
season within each year, or sample a time of
occurrence.
● Hydrologic Sampling
 Sample Historic Pool of events with associated
Hydrograph Set or
 Sample from frequency curve and hydrograph sets
● Sample System-Wide Fragility Functions
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FRM Monte Carlo Sampling Sequence
(Continued)
●Route Hydrograph Set
 Consequence
Area (CA) system Failures are based on hydraulics
and fragility curves
 Hydrographs will get adjusted as Dictated by Spills/Failures based
on hydraulic model
 Determine Flow and Stage at all Consequence Areas
●2D Spreading can be performed in areas where
needed
●Compute Damage/Loss-of-Life for all Consequence
Areas
●Repeat
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FRM Sampling Sequence
Computing EAD by Event Sampling
Hydrograph sets
Peak Discharge (cfs)
Reservoir Analysis
Channel Hydraulics
Levee Behavior
Simple
Monte Carlo
Simulation
Exceedance Probability
stage
Spreading Model
Inundation Mapping
Structure Inventory
Damage to Structures
Random choice of
probability U[0,1]
to "generate" event
Method 1
One Realization
damage
Damage(i)
After all realizations are computed
you now have EAD:
1 N
EAD  Dam age(i)
N i 1
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Hydrologic Sampling - Method 2
● pull out an event,
use all its
hydrographs, put it
back…SHAKE
keep
events
whole
● pull out an event,
use all its
hydrographs, put it
back…SHAKE
100-year
1
200-year
500-year
8
12
22
6
7
15
18
5
20
14
4
10
21
13
19
2
16
9
17
3
● pull out an event,
use all its
hydrographs, put it
back…SHAKE
11
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20-years of 50-year life-cycle
after drawing 50 random U[0,1] values
600000
500000
400000
200-year
event
300000
200000
100000
0
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Inflow Qi
Inflow Qi
FRM Load Distribution
Time
Time
Qi
Qb
(ft)
Reservoir 1
Stage
Reservoir 2
Qo
Outflow Qo
Probability of
Levee Failure
Inflow Qi
Li
Time
Time
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Inflow Qi
Inflow Qi
Inflow Spreading and Consequences
Time
Li
Probability of
Levee Failure
Cn+1
Inflow Qi
Stage
(ft)
Time
Time
Cn
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Consequence Analysis - Inundation
Mapping on Structure Inventory
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Risk Communication
● Life-Cycle Economic Performance
● Annual Exceedance Probability
● Conditional NonExceedance Probability
● Long-Term
Exceedance Probability
● Loss-of-Life
● Risk Maps
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EAC1 = Ctot / 500
EAC2 =Ctot / 2*500
EACn = Ctot / n*500
EACn+1 - EACn < Tol ?
Example Realization of Project Life-Cycle
COSTS
6/18/2010
Project First Cost
9/17/2022
Repair for Event 1
5/8/2030
Repair for Event 2
8/8/2011
O&M each year
N
EACn+2 = Ctot / (n+2)*500
Y
9/17/2042
Repair for Event 3
1/17/2035
Scheduled Rehab
of Pump Station
EADw/o- EADw = DR
12/18/2053
Repair for Event 4
BNet = DR - EAC
2010
2060
8/7/2021
Flood Event 1
5/18/2029
Flood Event 2
2/1/2042
Flood Event 3
3/1/2053
Flood Event 4
FLOOD DAMAGES
Y
N
EAD1 = Dtot / 500
EAD2 = Dtot / 2*500
EADn = Dtot / n*500
EADn+1 - EADn < Tol ?
EADn+2 = Dtot / (n+2)*500
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Life-Cycle Transients in HEC-FRM






Watershed Variables (HMS, RAS)
Operational Variances (ResSim, RAS)
Diminished structure values after event (FIA)
Increasing Structure values during rebuild (FIA)
Diminishing levee/component fragility over time (RAS)
Increased stability after O&M, repair, or rehabilitation (RAS)
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Net Benefits with Uncertainty
● EADw/o- EADw = DR
(DR=Damages Reduced)
● BNet = DR – EAC
(EAC=Expected Annual Cost)
● Determine BNet probability distribution by sampling DR
and EAC distributions
Expected annual
benefit and
cost ($’000)
Net benefits ($’000)
Benefits
Cost
Mean
Std. dev.
Prob. Net
benefit is>0
20’ levee
355
300
55
68
25’ levee
500
400
100
30’ levee
570
550
Channel
375
Detention basin
Relocation
Plan
Net benefit that is exceeded with
specified probability ($’000)
0.75
0.50
0.25
0.80
8
54
99
88
0.88
45
104
164
20
116
0.55
-62
14
91
300
75
74
0.83
19
72
120
325
275
50
96
0.70
-17
50
113
355
250
105
63
0.97
62
100
145
BUILDING STRONG®
Annual Exceedance Probability - AEP
● Key element in defining the performance of a plan. It
is the probability that a specific capacity or target
stage will be exceeded in a given year. For levees,
the chance of failure or exceedance in any given
year.
● HEC-WAT calculates AEP at every grid cell and
structure


AEP in this instance is probability of ground stage
being equaled or exceeded
Creating a flood map from this data will be a simple
raster calculation within a GIS program
BUILDING STRONG®
CNP or Assurance
●The index that a specific target (e.g. the top of a
levee) will not be exceeded, given the occurrence of
a specific flood event.
100
90
25
20
80
15
70
87% of AEPs
for 70' are
less than 1%
60
10
83
5
0
76
70
1.81 2.07 2.33 2.59 2.85 3.11 3.37 3.63
64
58
50
52
46
40
0
30
10
20
87% of 1%
stages are less
than 70'
20
10
0
99
90
75
50
25
10
5
2 1 .5 .2 .1
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Long Term Exceedance Probability
●The probability that one or more flood events will
occur within a specified time period or the likelihood
the target stage will be exceeded in a specified time
period. The calculations are made directly using the
binomial distribution (see EM 1110-2-1415).
Long-Term Exceedance Probability = 1 – (1-AEP)n
AEP = annual exceedance probability
n = term of interest (e.g., thirty years)
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Loss of Life
●HEC-FIA can do Life
Loss estimation.
Care needs to be
taken to make
parameters match
real life data
(warning systems,
population
characteristics, flood
evacuation plans)
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HEC-WAT Application
Columbia River Treaty Study
● From HEC-WAT the FRM
compute option will be used to
calculate the expected annual
damage for the assumed post2024 base condition.
● The models that are part of
HEC-WAT watershed are being
developed with the flexibility to
evaluate numerous hydrologic
scenarios, including climate
change, and numerous
operational modifications during
any time period.
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FRM
AEP Grid
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Conclusion
● USACE will conduct risk assessments in a systems
context
● HEC-WAT/FRM will be a tool that performs these
calculations
● It will include systems approaches, event sampling,
alternative analyses, structural and non-structural
analyses, parameter sampling, life-cycle cost and
economic analysis, loss-of-life, agricultural damage
analyses.
● Could be used nationwide for levee evaluations,
levee assessments, and planning and design
studies.
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QUESTIONS?
www.hec.usace.army.mil
US Army Corps of Engineers
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