1330 quest for consistently incorrect models...
TRANSCRIPT
The Quest for Consistently Incorrect Models
Nick Brown
21-08-2012
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1.5 Million People
6000 km2
1.5 Million People
6000 km2
7500 Staff
7500 Staff
6 modellers
AC Stormwater Unit
• 140 people
• Projects
• Operations
• Consents
• Planning
– Predict flooding
– $70M/annum capital works to address flooding
b1
Slide 14
b1 brownn2, 19/08/2012
3rd July 2012
• 100 year event in Auckland
ARI
10 Minute
Duration
ARI
20 Minute
Duration
ARI
30 Minute
Duration
ARI
60 Minute
Duration
ARI
120 Minute
Duration
ARI
180 Minute
Duration
3 July 2012
Recent 100 Year Events
3 July 2012
28 Jan 2011
Recent 100 Year Events
3 July 2012
28 June 2000
28 Jan 2011
Recent 100 Year Events
3 July 2012
28 June 2000
28 Jan 2011
30 Dec 1988
Recent 100 Year Events
3 July 201222 May 1985
28 June 2000
28 Jan 2011
22 May 1985
30 Dec 1988
Recent 100 Year Events
3 July 201222 May 1985
30 June 1979
28 June 2000
28 Jan 2011
22 May 1985
30 Dec 1988
Recent 100 Year Events
Expect 100yr Event every
3 Years
3 July 201222 May 1985
30 June 1979
28 June 2000
28 Jan 2011
22 May 1985
30 Dec 1988
Recent 100 Year Events
Expect 100yr Event every
3 Years
Expect significant Event >20 times per year
The Modelling
Model Reviews
• ~50 Models reviewed
• Many many problems
• <1 in 3 useable
Model Reviews
3 Categories
• Less than Ideal
• Theoretically Correct
• Good model – wrong scope
Model Reviews
3 Categories
• Less than Ideal
• Theoretically Correct
• Good model – wrong scope
Less than Ideal
• Pervious & Impervious - same runoff
• Catchment Boundary wrong
• Model extents wrong – starts below area of interest
• Upstream storage not considered
• No reticulation included
• Schematisation poor
• Survey data not used
Pond outlets
1m1
05
0 m
m
1m1
05
0 m
m
D=1050 mm
C=3300 mm
D=1050 mm
C=3300 mm
Reality = 1050mm Orifice Modelled as 3300mm Weir
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Weir Discharge (l/s)
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
90% more flow
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
190% more flow
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
280% more flow
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
380% more flow
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
470% more flow
0
5,000
10,000
15,000
20,000
25,000
30,000
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Water Level (m)
Dis
cha
rge
(l/
s)
Horizontal Orifice Weir Discharge (l/s)
2m less head
2D Rapid Flood Hazard
200 m3/s too low
Calibration
Gauge
Gauge
Calibrated travel time 2 hrs
Gauge
Calibrated travel time 2 hrs
Gauge
Calibrated travel time 2 hrs
Gauge
Calibrated travel time 2 hrs
Calibrated travel time 0.5 hrs
Gauge
Gauge
Calibrated travel time 0.2 hrs
Gauge
Calibrated travel time 0.2 hrs
10 m/s
Gauge
Calibrated travel time 0.2 hrs
10 m/s
10 m/s for 9.58 Seconds
Not for 600 Seconds
Hydrographs - Hydrology
Model Cross Sections
25.0
25.5
26.0
26.5
27.0
27.5
28.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0Chainage
Ele
va
tio
n
Model Cross Section
25.0
25.5
26.0
26.5
27.0
27.5
28.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0Chainage
Ele
va
tio
n
Model Cross Section
Surveyed
25.0
25.5
26.0
26.5
27.0
27.5
28.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0Chainage
Ele
va
tio
n
Model Cross Section
Surveyed
Water Level
Storage
0
1000
2000
3000
4000
5000
6000
7000
23.4 23.6 23.8 24 24.2 24.4 24.6 24.8 25 25.2 25.4
elevation m
sto
rag
e v
olu
me m
3
0
1000
2000
3000
4000
5000
6000
7000
23.4 23.6 23.8 24 24.2 24.4 24.6 24.8 25 25.2 25.4
elevation m
sto
rag
e v
olu
me m
3
0
1000
2000
3000
4000
5000
6000
7000
23.4 23.6 23.8 24 24.2 24.4 24.6 24.8 25 25.2 25.4
elevation m
sto
rag
e v
olu
me m
3
75% more
volume
Culverts
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Flow (m3/s)
He
ad
Wa
ter
Dep
th (
m)
MOUSE ModelModel
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Flow (m3/s)
Hea
d W
ate
r D
ep
th (
m)
MOUSE Model Culvert ManualModel
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Flow (m3/s)
Hea
d W
ate
r D
ep
th (
m)
MOUSE Model Culvert Manual
Flow 11.5 m3/s
MOUSE model 3.5 m
ModelModel
Model
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Flow (m3/s)
Hea
d W
ate
r D
ep
th (
m)
MOUSE Model Culvert Manual
Flow 11.5 m3/s
MOUSE model 3.5 m
Culvert Manual 6.0 m
Difference 2.5 m
2.5m
Model
Model
10 m/s velocity
MOUSEModel
4 m/s velocity
Culvert Manual
Velocity & Inlet Losses
HERE
HERE
HERE
HERE
Normal Manhole
Wrong Node Type
• 2D outfall
• outlet
Theoretically Correct
10
11
12
13
14
15
16
17
18
19
0 10 20 30 40 50 60 70
Without Bank Marker, n = 0.08
10
11
12
13
14
15
16
17
18
19
0 10 20 30 40 50 60 70
Without Bank Marker, n = 0.08
With Bank Marker, n = 0.08
10
11
12
13
14
15
16
17
18
19
0 10 20 30 40 50 60 70
Without Bank Marker, n = 0.08
With Bank Marker, n = 0.08
With Bank Marker and
Distributed Roughness
Channel n = 0.04 &
Floodplain n = 0.12
Stream Conveyance Estimation
11
12
13
14
15
16
17
18
19
0 1000 2000 3000 4000 5000 6000 7000
Stream Conveyance
Ele
va
tio
n
Without Marker, n = 0.08
Stream Conveyance Estimation
11
12
13
14
15
16
17
18
19
0 1000 2000 3000 4000 5000 6000 7000
Stream Conveyance
Ele
va
tio
n
Without Marker, n = 0.08 With Marker, n = 0.08
Stream Conveyance Estimation
11
12
13
14
15
16
17
18
19
0 1000 2000 3000 4000 5000 6000 7000
Stream Conveyance
Ele
va
tio
n
Without Marker, n = 0.08With Marker, n = 0.08With Marker and Distributed Roughness, Channel n = 0.04 & Floodplain n = 0.12
Stream Conveyance Estimation
11
12
13
14
15
16
17
18
19
0 1000 2000 3000 4000 5000 6000 7000
Stream Conveyance
Ele
va
tio
n
Without Marker, n = 0.08With Marker, n = 0.08With Marker and Distributed Roughness, Channel n = 0.04 & Floodplain n = 0.12
2 ¼ > Flow @ same Elevation
10
11
12
13
14
15
16
17
18
19
0 10 20 30 40 50 60 70
Without Bank Marker, n = 0.08
27 Habitable
Floors Flooded
10
11
12
13
14
15
16
17
18
19
0 10 20 30 40 50 60 70
Without Bank Marker, n = 0.08
With Bank Marker, n = 0.08
9 Habitable
Floors Flooded
10
11
12
13
14
15
16
17
18
19
0 10 20 30 40 50 60 70
Without Bank Marker, n = 0.08
With Bank Marker, n = 0.08
With Bank Marker and
Distributed Roughness
Channel n = 0.04 &
Floodplain n = 0.12
0 Habitable
Floors Flooded
Good Model Wrong Scope
• Grid to large for ground slope
126 m
116 m
10m Elevation change across grid
126 m
116 m
10m Elevation change across grid
121.2 m Predicted Flood Level
Review Summary
• Easily double or halve flow
• Results precise but not accurate
• Floodplains wrong by +/- 3m
• Results cannot be used to set building floor levels
• Results cannot be used to scope projects
The Plan
• Outsource commodity work
• Specifications are for commodity work
• Keep high risk work in-house
• Review all models (external & internal)
• Create Specification & standard review method
• Rolling 10-15 year programme to model all catchments
Model Quality
Best PracticePoor
Model Quality
Best Practice
a
Poor
Consultants
Hydrology
Model Quality
Best Practice
a
Poor
Consultants
HydrologyHydraulics
Model Quality
Best Practice
a
bbb
Poor
Consultants
Model Quality
Best Practice
a
bcbb
Poor
Consultants
Model Quality
Best Practice
a
d
bcbb
Poor
Consultants
Model Quality
Best Practice
a
d
e
bcbb
Poor
Consultants
Model Quality
Best Practice
a
d
e
Specifications
bcbb
Poor
Consultants
Model Quality
Best Practice
a
d
e
Specifications
bcbb
Poor
Consultants
Model Quality
Best Practice
a
d
e
Specifications
bcbb
Poor
Consultants
Model Quality
Best Practice
a
d
e
Specifications
bcbb
Poor
Consultants
Loss
Model Quality
Best Practice
a
d
e
Specifications
bcbb
Poor
Consultants
Loss
GAIN
Model Quality
Best Practice
a
d
e
Specifications
bcbb
Poor
Consultants
Loss
GAIN
Minimum NOT Maximum Standard
Specifications
• Mix of Specification and Guideline
– Instruction and Advice
• Basis for modelling contracts
• Details modelling process
• Updated as needed
• Basis for commodity work
• Allows best practice to be captured so you know which model was produced using which understanding of best practice
What do they Cover
• Flood Modelling
• Rainfall/Runoff method
• Hydraulics
• Report structure
• Deliverables
• Modelling Process
• Content and look of maps
• Includes standard council model review form
Summary
• We don’t know everything
• We do know something
• We don’t know necessarily what is right
• Specification sets a minimum standard
• To manage a modelling and capital works programme need consistency
• Provide consistently incorrect models
Questions
What they don’t cover
• Continuous simulation
• Modelling of non-extreme events
• LID modelling
• Stream erosion
• Geomorpholigical change assessment
• Blockage scenarios
What they are weak on
• Options analysis
• Flood Damage assessment
• Flood Hazard Assessment
• Report mapping format