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Pilbara rfa ea presentation v3.2 1
1. Pilbara Region Flood Frequency
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Analysis Review
By Jim Davies and Edwin Yip
JDA
Date:
Free Powerpoint Templates 12 November 2012
Page 1
2. Outline of the Presentation
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• Introduction
• Study Area and Flow Data
• Methodology and Results
• Conclusions
Page 2
3. Outline of the Presentation
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• Introduction
• Study Area and Flow Data
• Methodology and Results
• Conclusions
Page 3
4. Outline of the Presentation
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• Introduction
– Background
– Previous Studies
– Scope of this Study
– Source of Information
Page 4
5. Introduction
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Background
•Regional method is for ungauged catchment flood
estimation
•Frequency analysis is estimation of how often a
specified event will occur
•Extreme environmental event such as floods, have
severe consequences for society
Page 5
6. Introduction
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Background (Cont.)
•Couple of advance statistical techniques were
developed since the last two decades after the
publication of ARR1987,
–L-moments were introduced in 1990’s.
•The aim of this study is to review the ARR1987
Index-flood Method of Pilbara utilizing:-
–advance statistical techniques, and
–flow measurement records up to 2012
Page 6
7. Introduction
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Previous Studies
Estimation of design peak discharge for ungauged catchments:
• 1972 US Bulletin 17 – LPIII
• 1975 UK Flood Studies Report – GEV
• 1987 Australia AR&R – LPIII
• 1997 “Regional Frequency Analysis” – Complete Procedure
by Hosking & Wallis - L moments
- Screening of Data
- Regions
- Choice of Distribution
- Estimation of Frequency
Page 7
8. Introduction
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Regions defined in ARR1987
25 years out of date now
Pilbara Region
Gascoyne Region
(firm recommendations
of design discharges
were not made in
ARR1987)
Pilbara Region + Gascoyne Region
= Drainage Division 7
Page 8
9. Introduction
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Pilbara Index-flood Method (ARR1987)
•was developed utilizing 13 stream gauging
stations in Pilbara Region
•Methodology
– Annual Exceedance Series
– Log-Normal distribution (assumed the
generalised skew coefficient was zero)
– Method of Product-Moments
– All 13 catchments to form one Pilbara region
Page 9
11. Introduction
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Pilbara Index-flood Method (ARR1987)
(Cont.)
•Index-flood:
– Design Discharge of 5-year ARI [m3/s]
Q5 = 6.73 x 10-4 A0.72 P1.51
•Parameters in Design Discharge Equation:
– Catchment factor: Catchment Area (A) [km2]
– Climatic factor: Average Annual Rainfall Depth
over the Catchment Area (P) [mm]
Page 11
12. Introduction
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L-Moments (Hosking & Wallis, 1997)
• Sample moment statistics especially skewness
and Kurtosis not reliable (biased) as algebraically
bounded.
• “L-moments” are linear combinations of order
statistics – less subject to bias.
Page 12
13. Introduction
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Software
•R-Project
–with L-moments Packages “lmom” and “lmomRFA”
•The R-Project and L-moment Packages are freely
available
–Website: http://www.r-project.org/
•J. R. M. Hosking is the developer and maintainer of
the L-moment Packages
Page 13
14. Introduction
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EA AR&R Revision Projects: Project 5
“Regional Flood Methods”
Stage 2 Report
PS/S2/015
June 2012
By University Of Western Sydney
To test generic techniques for all Australia
(WA Contributors: JR, NC, LP, MP, JG)
Page 14
15. Introduction
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Project 5 Stage 2 Report June 2012,
General:
• RFFA methods preferred to PRM
• QRT and PRT perform similarly
• PRT preferred due to smoothness
• ROI outperforms fixed regions
• RFFA requires only area and design rainfall intensity data
(easy and simple)
• Arid and semi-arid regions have insufficient data for RFFA;
recommends simplified RFFA (4 regions)
• Trends will be analyzed in Stage III (expected to be
adjustment of ARI’s
Page 15
16. Introduction
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Project 5 Stage 2 Report June 2012
Western Australia Specific
–146 catchments (gauging stations)
•Kimberley: 14 stations
•Pilbara: 12 stations
•South West: 120 stations
–Area Range 0.1 to 7,405 km2
Page 16
17. Introduction
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Project 5 Stage 2 Report June 2012
• Pilbara Region 0.1 to 1,000 km2
• Fixed region (all 12 stations)
• QRT Q2, Q5, Q10, Q20, Q50, Q100
– Function of Catchment Area and Rainfall Intensity
• PRT M, S, G
– Function of Catchment Area, Rainfall Intensity, forest
area, and stream density
Page 17
18. Introduction
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Project 5 Stage 2 Report June 2012
Flow records from 12 gauging
stations in Drainage Division 7
were selected and analyzed in
“ARR Revision Projects -
Project 5 Regional Flood
Methods Stage II”
Source: Rahman, A., Haddad, K., Zaman, M., Ishak, E., Kuczera, G. and Weinmann, P. E. (2012).
Regional flood methods for Australia, ARR Revision Project 5 Stage 2 Report, Engineers Australia,
Report No. P5/S2/015 Page 18
19. Introduction
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Scope of this Study
•To develop design equations for Index-flood (Q5)
to estimate design peak discharges for ungauged
catchments
–utilizing the updated stream flow measurement records
•To review the frequency factors of ARR1987 Index-
flood method to Pilbara
–utilizing the updated stream flow measurement records
–utilizing advance statistical techniques
Page 19
20. Introduction
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Scope of this Study (Cont.)
•To compare the design discharges between this
study and other studies
–ARR1987
–“Design Flood Estimation in Western Australia” by David
Flavell (2012) (Flavell 2012)
–“ARR Revision Projects - Project 5 Regional Flood Methods
Stage II” by Ataur Rahman and others (2012) (ARR P5 S2)
Page 20
21. Introduction
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Source of Information
•Department of Water
– Daily maximum flow measurement records
– Location of stream gauging stations
•Bureau of Meteorology
– Average Annual Rainfall Depth
•ARR1987
– Design Rainfall Intensity
Page 21
22. Outline of the Presentation
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• Introduction
• Study Area and Flow Data
• Methodology and Results
• Conclusions
Page 22
23. Study Area and Flow Data
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Page 23
24. Study Area and Flow Data
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Study Area
•Whole Drainage Division 7 (i.e. Division of Indian
Ocean) including 10 River Basins as listed follow:-
– Greenough River (701),
– Murchison River (702),
– Wooramel River (703) ,
– Gascoyne River (704),
– Lyndon-Minilya Rivers (705),
– Ashburton River (706),
– Onslow Coast (707),
– Fortescue River (708),
– Port Hedland Coast (709), and
– De Grey River (710)
Page 24
25. Study Area and Flow Data
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709 - Port Hedland Coast
707 - Onslow Coast
710 - De Grey River
705 - Lyndon-Minilya
Rivers
708 - Fortescue River
706 - Ashburton River
704 - Gascoyne River
703 - Wooramel River
702 - Murchison River
- Selected Stations (60)
701 - Greenough River
Page 25
26. Study Area and Flow Data
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World Maximum Flood
Maximum Floods in Pilbara Region
Yule River (1975)
Ashburton River
(1997)
Sherlock River (1971)
Fortescue River (2004)
Nullagine River (2002)
Robe River (2009)
Sherlock River (1984) Portland River (1984)
Source: Flavell, D. 2012, “Design flood estimation in Western Australia”, Australian Journal of
Water Resources, Vol. 16, No. 1, pp. 1-20, http://dx.doi.org/10.7158/W11-865.2012.16.1 .
Page 26
27. Study Area and Flow Data
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Catchment Gauging
Rank River
Area (km2) Station No.
1 (largest) 86,777 Murchison River 702001
2 74,432 Gascoyne River 704139
3 71,387 Ashburton River 706003
4 71,212 Gascoyne River 704193
5 69,278 Gascoyne River 704194
6 50,007 De Grey River 710003
7 43,098 Ashburton River 706209
8 34,775 Gascoyne River 704195
9 29,752 Fortescue River 708006
10 19,613 Lyons River 704196
Page 27
28. Study Area and Flow Data
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Catchment Gauging
Rank River
Area (km2) Station No.
51 198 Sthn Fortescue River 708004
52 174 Robe River 707001
53 128 Tanberry Creek 709006
54 78 Sherlock River 709009
55 77 Five Mile Creek 710002
56 50 Harding River 709002
57 49 Harding River 709007
58 41 Kanjenjie Creek Trib. 708009
59 34 Buller River 701006
Nokanena Brook
60 (smallest) 0.13 701601
Catch
Page 28
29. Study Area and Flow Data
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Design Rainfall Intensity 35
from ARR1987 [mm/hr]
(1hour duration, 2-years ARI)
30
27.5
25
22.5
20 18 16
20
Page 29
30. Study Area and Flow Data
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DoW Hydrographic Work – Rating Curve
•“Water Depth” vs “Flow Discharge” derivation
using discharge measurement and HEC-RAS
modelling
•See paper in AHA Conference 2010 Perth by:-
–Michael Harris and Leith Bowyer
–Ross Doherty
Page 30
31. Study Area and Flow Data
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Ashburton River
Page 31
32. Study Area and Flow Data
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Ashburton River
Page 32
33. Study Area and Flow Data
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Maitland River
Page 33
34. Study Area and Flow Data
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Maitland River
Page 34
35. Outline of the Presentation
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• Introduction
• Study Area and Flow Data
• Methodology and Results
• Conclusions
Page 35
36. Methodology and Results
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Methodology - For Extreme Discharges
1)Extract the AM series of stations in study area from flow
measurement data of DoW
– The quality of the measurement records were reviewed, poor
quality records were discarded
– The data in AM series was reviewed to ensure no two sequent
data is due to same storm event
– Only the stations with AM series containing at least 10 years of
data are selected in this study
(60 out of 90 stream gauging stations were selected in this
study)
Page 36
37. Methodology and Results
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Methodology - For Extreme Discharges (Cont.)
2)Divided 3 hydrological regions according to
catchment areas, the 3 regions are (after Hosking and Wallis
(1997)):-
–Small Area Region (19 gauging stations) – “S”:
• catchment area ≤ 1,000 km2
–Medium Area Region (25 gauging stations) – “M”:
• 1,000 km2 < catchment area ≤ 10,000 km2
–Large Area Region (16 gauging stations) – “L”:
• catchment area > 10,000 km2
Page 37
38. Methodology and Results
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Hosking and Wallis (1997), page 180
“Nonetheless, we emphatically reject the possibility of
performing regional frequency analysis with the entire
set of sites being treated as a single region. The main
reason is that the theory and practice of hydrology
imply that the frequency distribution is likely to depend
on the drainage area of the basin. Regional frequency
analysis should therefore be applied only to regions
whose basins cover a fairly small range of drainage
area.”
Page 38
39. Methodology and Results
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Hosking and Wallis (1997), page 180
“A further point is that in regional frequency analysis
there is little to be gained by using regions containing
more than about 20 sites. A reasonable starting point
for regional frequency analysis would therefore be a
subdivision of the set of sites, according to their
drainage areas, into groups of not much more than 20.”
Page 39
40. Methodology and Results
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Methodology - For Extreme Discharges (Cont.)
3)Sub-divide regions “S”, “M”, and “L” according to their statistical
homogeneity,
– Gauging stations with H-statistic < 2.0 were considered that they
could belong to same sub-region
– The number of stations in each sub-regions should not be much
more than 20
– discordance test based on L-moment ratios was performed to
ensure no existence of discordancy dataset in sub-regions
(sub-regions S1 to S3; M1 to M3; L1 to L3; were formed)
Page 40
41. Methodology and Results
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Methodology - For Extreme Discharges (Cont.)
4)Best-fitted frequency distribution for each sub-regions
– The best-fitted frequency distribution was considered to be the
one with the smallest absolute value of Z-statistic
– Candidate frequency distributions are:-
• Generalized Logistic,
• Generalized Extreme Value,
• Generalized Normal,
• Pearson Type III, and
• Generalized Pareto
Page 41
42. Methodology and Results
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Best-fitted
Selected
Sub-Region H-Statistic Distribution
Gauging
Name (< 2.0) (Z-Statistic)
Stations
(close to 0)
706207*, 709002,
709006, 709007, Pearson Type III
S-1 1.326
709009, 709010, (0.108)
710004
701003, 701004, Generalized
S-2 701005, 701006, 1.733 Logistic
701601, 704002
(-0.350)
704001, 704003, Generalized
S-3 704004, 707001, 1.682 Pareto
708009, 708227
(1.384)
* see later plot
Page 42
44. Methodology and Results
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Best-fitted
Selected
Sub-Region H-Statistic Distribution
Gauging
Name (< 2.0) (Z-Statistic)
Stations
(close to 0)
701002, 701011,
Pearson Type III
L-1 701012, 702001, 0.548
703002 (0.024)
704139, 704193, Generalized
704195, 704196,
L-2 706003, 706209, 0.855 Pareto
710003 (-0.260)
708002, 708003, Pearson Type III
L-3 708015, 708223 1.195
(0.998)
Page 44
45. Methodology and Results
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Methodology - For Extreme Discharges (Cont.)
5)Estimate parameters of each selected
station for their best-fitted frequency
distribution
6)Estimate the extreme discharges (QY, Y =
2-, 5-, 10-, 20-, 50-, 100-year ARI) of every
stations in each sub-regions
Page 45
47. Methodology and Results
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Methodology - For Frequency Factors
7)Define the peak discharge in 5-year ARI (i.e. Q5)
as the “index-flood”, in regions “S”, “M”, and “L”
8)Make the peak discharges dimensionless by
dividing them by Q5, (i.e. QY / Q5)
9)Calculate different Frequency Factors for different
ARIs in each region,
– “Frequency Factor” is the mean of [QY / Q5] over all
stations and in regions S, M, and L
Page 47
48. Methodology and Results
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Medium Area Region
Small Area Region
Large Area Region
Page 48
49. Methodology and Results
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Methodology - For Design Discharge Equation (Q5)
10)Catchment factors and climate factors for each
selected station:-
–Catchment Area (A) [km2]
–Average Annual Rainfall Depth (P) over the catchment
area between year 1946 to year 2005 [mm/year]
–Design Rainfall Intensity (IDuration, ARI) over catchment
area [mm/hr] of ARI 2- and 50-year (1hr, 12hrs, 72hrs)
Page 49
50. Methodology and Results
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Methodology - For Design Discharge Equation (Q5)
(Cont.)
11)Develop design discharge equation for Design Discharges of
5-year ARI (Q5) in regions S, M & L using catchment factors
and climate factors,
– Stepwise Variable Selection and Multiple Variables Linear
Least Square Regression were performed
– The reasonability and simplicity of the design discharge
equation are considered
– The number of climate and catchment factors kept to a
minimum, they should also be easy to obtain by end-users.
Page 50
51. Methodology and Results
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Results (Cont.)
For Small Size Region
(i.e. catchment area ≤ 1,000 km2)
Design Discharge Equation:
Q5 = 8.26*10-9 A0.703 I1hr,2yrs5.798
Frequency Factors:
ARI 2 yrs 5 yrs 10 yrs 20 yrs 50 yrs 100 yrs
FF 0.34 1.00 1.64 2.43 3.84 5.37
Page 51
60. Outline of the Presentation
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• Introduction
• Study Area and Flow Data
• Methodology and Results
• Conclusions
Page 60
61. Conclusions
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Conclusions
•Design discharges from JDA 2012 can be
applied to whole Drainage Division 7
– ARR1987 and Flavell 2012 cannot generate satisfactory
design discharges in Gascoyne Region
– Doubt about equations from ARR P5 S2 can be applied in
river basin 702, 703, 705, and 710
• No stations were selected at those river basins in the
equations development
Page 61
62. Conclusions
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Conclusions (Cont.)
•Design discharges from JDA 2012 can
be applied to a wide range of
catchment area
– ARR P5 S2 cannot generate satisfactory
design discharges in large catchment
area
• Stations with maximum catchment area of
1,000 km2 were selected
• The catchment areas in Pilbara are large in
particular in downstream areas, say as large as
80,000 km2
Page 62
63. Conclusions
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Conclusions (Cont.)
•The design equations of JDA 2012 is simple and
easy to apply,
– only catchment area and design rainfall intensity are
required in the design discharge equations
– The parameters are easy to obtain
Page 63
64. Conclusions
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Conclusions (Cont.)
•ARR 1987 often over estimated the data (except
river basins 709, 710)
Page 64
65. Study Area and Flow Data
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709 - Port Hedland Coast
707 - Onslow Coast
710 - De Grey River
705 - Lyndon-Minilya
Rivers
708 - Fortescue River
706 - Ashburton River
704 - Gascoyne River
703 - Wooramel River
702 - Murchison River
- Selected Stations (60)
701 - Greenough River
Page 65
66. Conclusions
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Conclusions (Cont.)
•Flavell (2012) may mis-represent due to changes
to measured DoW Flow Data
Page 66
67. Conclusions
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Conclusions (Cont.)
•Method will need recalibrate for revised IFD,
published at H&WR Symposium November 2012
Page 67
