revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green
TRANSCRIPT
![Page 1: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/1.jpg)
Revised Intensity-Frequency-
Duration (IFD) Design Rainfalls
Estimates for WA
Janice Green
Bureau of Meteorology 24 October 2012
![Page 2: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/2.jpg)
IFD Revision Team
• Team members
– Cathy Beesley *Chris Lee
– Fiona Johnson *Maria Levtova
– Catherine Jolly *William Tall
– Garry Moore *Max Monahan
– Cynthia The *Damian Chong
– Karin Xuereb *Murray Henderson
*Ceredwyn Ealanta
– Mike Hutchinson (ANU) (Honorary team member)
– University of Western Sydney
– Student contractors
![Page 3: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/3.jpg)
Current IFDs – AR&R87
![Page 4: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/4.jpg)
Current IFDs – AR&R87
![Page 5: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/5.jpg)
Current IFDs – CDIRS On-line
![Page 6: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/6.jpg)
Current IFDs – CDIRS On-line
![Page 7: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/7.jpg)
Current IFDs – CDIRS On-line
![Page 8: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/8.jpg)
Current IFDs – CDIRS On-line
![Page 9: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/9.jpg)
Current IFDs
• Developed by Bureau of Meteorology over 20 years ago
• Used a database comprising information primarily from the Bureau’s network of daily read and pluviograph stations
• Adopted statistical techniques considered appropriate at the time
• Focus of the IFDs was the design of structures on relatively large rural catchments and therefore durations of less than five minutes were not considered necessary.
![Page 10: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/10.jpg)
Current IFDs – Adopted Approach
Aspect ARR87
Data BoM stations only
Record length ~ up to 1983; 7500 daily read > 30 years; 600 pluviographs > 6 years
Frequency analysis Annual maximum series; method of moments; Log-Pearson Type III
Daily to sub-daily Principal Component Analysis
Mapping Subjective (meteorological analysis)
Frequency ARIs 1 year to 100 year
Duration 5 minute to 72 hour (3 day)
Dissemination Maps; HAS; CDIRS on-line
Climate change Stationary climate assumed;
climatic trends negligible effect on IFDs
![Page 11: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/11.jpg)
Choice of variables
Gridding technique
Basic approach
Rainfall data
Series of extreme values
Frequency Analysis
Gridding
Annual Maximum Series
Choice of fitting technique and distribution
Extraction of L-moments
Supplementing of sub-daily statistics
Establishment of data base – Bureau and Water Regs
Quality controlling of data
Dissemination Outputs
Medium
Regionalisation Index rainfall approach
Regions of Influence
![Page 12: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/12.jpg)
Data base
• Bureau of Meteorology Australian Data Archive for Meteorology (ADAM )
– Contains 19711 daily read rainfall stations (both open & closed) for period from 1800 to 2011
– Contain 1467 continuous stations – both pluviograph & TBRG
• Water Act 2007 identified the Bureau’s new responsibilities including collecting and publishing water information
• Water Regulations 2008 provided ready access to rainfall data collected by other organisations
• In particular, data from dense continuous rainfall networks operated by urban water utilities and councils:
– ~350 daily read rainfall stations
– ~2175 continuous rainfall stations
![Page 13: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/13.jpg)
Spatial coverage of daily read rainfall stations
![Page 14: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/14.jpg)
Spatial coverage of continuous rainfall stations
•
![Page 15: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/15.jpg)
Data base
• Finalisation of data base
– Initially December 2010
![Page 16: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/16.jpg)
Data base
• Finalisation of data base
– Initially December 2010
![Page 17: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/17.jpg)
Data base
• Finalisation of data base
– Initially December 2010
– Updated to December 2011
![Page 18: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/18.jpg)
Data base
• Finalisation of data base
– Initially December 2010
– Updated to December 2011
![Page 19: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/19.jpg)
Data base
• Finalisation of data base
– Initially December 2010
– Updated to December 2011
– Updated to March 2012
– ?????
![Page 20: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/20.jpg)
Quality Control
• Previous work had undertaken QCing on a largely manual basis
• Enormous amount of data that needed to be quality controlled
– > 20 000 daily read stations - Bureau
– > 1500 pluviograph stations – Bureau
– ~350 daily read rainfall stations – Water Regulations
– ~2175 continuous rainfall stations – Water Regulations
• Disparate amount and type of QCing undertaken by data providers
• Necessitated automating as much of QCing as possible
• However still required manual QCing using Bureau’s Quality Monitoring System (QMS)
![Page 21: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/21.jpg)
QCing daily read data
• Quality Controlling of daily read data:
– Infilling of missing data
– Disaggregation of flagged accumulated daily rainfall totals
– Detection of suspect data, identification and correction of:
• Unflagged accumulated totals
• Time shifts
– Identification of gross errors - data inconsistent with neighbouring records but not either of the above two categories
– Manual correction gross errors identified as having a high probability of being incorrect
![Page 22: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/22.jpg)
QCing daily read data using QMS
![Page 23: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/23.jpg)
QCing of continuous data
• QCing of continuous rainfall data considerably more complicated:
– significantly more data due to shorter time step
– sparsity of continuous station network means fewer stations with which to compare
– small rainfall depths extremely difficult to QC
• Needed to reduce amount of data to be QC’d to a manageable amount
• Developed approach QC’d the PDS
– 5 x number of years of record
• Durations of:
– 5, 10, 15, 30 minutes
– 1, 2, 3, 6, 12 hours
– 1, 2, 3 days
• Number of PDS values to be QC’d > 1,000,000
![Page 24: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/24.jpg)
QCing continuous data
• Issues with Continuous Rainfall Data
– Time shifts of clock - DINES
– Missed pulses – TBRG
• QCing procedure compared values to:
– AWAP (Australian Water Availability Product) gridded daily rainfall data
– Co-located or nearby daily read stations
– AWS (Automatic Weather Stations)
– Synoptic stations
![Page 25: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/25.jpg)
Trialling of frequency distributions
• Frequency analysis
– Previously adopted Log-Pearson Type III fitted by method of moments
– Used 58 Bureau long-term continuous rainfall stations to trial a range of distributions
• From each of the 58 continuous rainfall stations extracted both the AMS and the PDS
![Page 26: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/26.jpg)
Trialling of frequency distributions
• AMS & PDS extracted for durations of :
– 6, 12, 18, and 30 minutes
– 1, 2, 3, 6, and 12 hours
• Calculated L-moments and fit five distributions:
– Generalised Logistic (GLO)
– Generalised Extreme Value (GEV)
– Generalised Normal (GNO)
– Pearson Type III (PE3)
– Generalised Pareto (GPA).
• Assessed goodness of fit using Hosking and Wallis (1997) goodness of fit measure ZDist
![Page 27: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/27.jpg)
Trialling of frequency distributions
• AMS
– the GEV gave the most acceptable fit for all durations except 3 and 12 hours
– however, with the exception of the GPA, the other distributions also showed acceptable fits
• PDS
– the GPA gave the most acceptable fit for all durations
![Page 28: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/28.jpg)
Extraction of L-moments
• L-moments used to summarise statistical properties of AMS and PDS
– Index rainfall (mean)
– L-skewness
– L-CV
• L-moments expected to be more robust against large outliers in the data, particularly for the higher order moments.
• To reduce uncertainty in the parameter estimates, minimum station record lengths have been adopted
– 30 years for daily rainfall stations and
– 9 years for sub daily rainfall stations.
![Page 29: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/29.jpg)
Estimation of sub-daily rainfalls
• Shift in focus to urban design on small catchments necessitating the provision of IFD estimates for durations as short as one minute
• Far fewer continuous rainfall stations than daily read rainfall stations
![Page 30: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/30.jpg)
Spatial coverage of daily read rainfall stations
![Page 31: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/31.jpg)
Spatial coverage of continuous rainfall stations
•
![Page 32: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/32.jpg)
Derivation of short duration IFDs
• Need a method to improve spatial coverage of sub-daily data
• Most commonly done using information from daily stations
– Statistics of sub-daily data are inferred from those of daily data
• Techniques adopted include:
– Factoring of the 24 hour IFDs
– Principal component analysis (PCA)
– Partial least squares regression (PLSR)
![Page 33: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/33.jpg)
Derivation of short duration IFDs
• However, major weakness of the previously adopted approaches is their inability to account for:
– Variation in record lengths from site to site
– Inter-station correlation
• An approach that avoids these problems is Bayesian Generalised Least Squares Regression (BGLSR)
![Page 34: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/34.jpg)
Approach to be adopted
• Statistics to be derived (predictands) are:
– Index rainfall (mean)
– L-skewness
– L-CV
• Predictors to be used are:
– Location (latitude & longitude)
– Elevation
– Slope
– Aspect
– Distance from coast
– Mean annual rainfall
– Index rainfall, L-skewness & L-CV at 24, 48 & 72 hours
![Page 35: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/35.jpg)
Regionalisation
• Regionalisation recognises for stations with short records
– considerable uncertainty when estimating the parameters of probability distributions and
– short records can bias estimates of rainfall statistics
• Overcome by combining information from multiple rainfall stations
– more accurate estimates of the probability distribution parameters can be made
![Page 36: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/36.jpg)
Regionalisation
• Index rainfall approach adopted to do this (Hosking & Wallis)
• Station point estimates have been regionalised using a Region of Influence Approach (ROI).
• Trialled various approaches => ROIs defined as circle which is expanded until it includes 500 station years of record
• Circular ROIs defined with distance defined in three dimensions
– Latitude
– Longitude
– Elevation
![Page 37: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/37.jpg)
Region of influence
![Page 38: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/38.jpg)
Region of influence
![Page 39: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/39.jpg)
Region of influence
![Page 40: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/40.jpg)
Gridding
• Regionalisation gave estimates of GEV parameters at all station locations
– Combined with the mean of the AMS (index) at that site to estimate rainfall quantiles for any required exceedance probability.
• However IFD estimates required across Australia, not just at station locations.
• Results of the analyses needed to be extended in some way to ungauged locations.
![Page 41: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/41.jpg)
Gridding
• Translation from point to gridded rainfall estimates carried out with thin plate smoothing splines implemented using ANUSPLIN.
• ANUSPLIN (Hutchinson 2007) was chosen to grid the GEV parameters so that IFD estimates are available for any point in Australia.
• GEV parameters are being gridded in ANUSPLIN, as:
– earlier testing showed little difference in quantile estimates if point parameter or point rainfall depths gridded.
– Gridding rainfall parameters gives more flexibility in the choice of exceedance probabilities that can be extracted and
– requires fewer grids to be processed in ANUSPLIN.
• Appropriate level of smoothing chosen through generalised cross validation by minimising the predictive error of the fitted surface
![Page 42: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/42.jpg)
Interpolation – point to grid
MEAN GRID
SCALE GRID
SHAPE GRID
![Page 43: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/43.jpg)
Gridding
Index Alpha
Kappa
![Page 44: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/44.jpg)
Y = 1 in 2 AEP Y = 1 in 5AEP
Y = 1 in 10 AEP Y = 1 in 20 AEP
Y = 1 in 50 AEP Y = 1 in 100 AEP
Interpolation – point to grid
MEAN GRID
SCALE GRID
SHAPE GRID
![Page 45: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/45.jpg)
ANUSPLIN Output Example
![Page 46: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/46.jpg)
Outputs
• Revised IFDs will be provided as depths in millimetres (not intensities)
• Revised IFDs will be provided for standard durations of:
– 1, 2, 3, 4, 5, 10, 15, 30 minutes
– 1, 2, 3, 6, 12 hours
– 1, 2, 3, 4, 5, 6, 7 days
– advice provided for IFDs < 1 minute and > 7 days
![Page 47: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/47.jpg)
Outputs
• Revised IFDs will be provided for standard EY and AEPs of :
– 1EY (1 Exceedance Per Year) } New AR&R probability
– 50%, 20%, 10%, 5%, 2%, 1% AEP } terminology
• Revised IFDs also provided for sub-annual recurrences eg 2EY
• Revised IFDs blended with CRCFORGE estimate to enable smooth curve to be derived to an AEP of 0.05%
![Page 48: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/48.jpg)
Revised IFDs
• Revised IFDs will be disseminated
– In electronic form
– Via new web page accessed from Bureau of Meteorology website
• Release of new webpages in 2 Phases
![Page 49: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/49.jpg)
Phase 1
• Phase 1
– Revised IFDs for single point
– For standard durations & EY/AEPs
– Functionality of Phase 1 web pages => same as current CDIRS web page
– CDIRS and IFD 2012 run in parallel for ~ 6 months
![Page 50: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/50.jpg)
Protoype
![Page 51: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/51.jpg)
Phase 2
• Phase 2
– Multiple locations
– Dynamic map
– Duration range filters
– Uncertainty limits
– Temporal pattern
– Areal reduction factors
– Climate change adjustments
– Non-standard durations & EYs & AEPs
– Rainfall frequency curve to 0.05% AEP
![Page 52: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/52.jpg)
Outputs
• Climate Change
– Revised IFDs will be for current climatic regime
– AR&R Revision Climate Change Research Strategy has been developed
– Objective to identify research priorities to enhance understanding of how projected climate change may alter the behaviours of factors used to estimate design floods
![Page 53: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/53.jpg)
Outputs
• Climate Change
– Identified 5 research themes:
• Rainfall intensity-frequency-duration relationships
• Rainfall temporal patterns
• Continuous rainfall sequences
• Antecedent conditions (including baseflow)
• Simultaneous extremes
– Research to be undertaken over both short term (Stage 1 – one year) and longer term (Stage 2 – four years)
– Stage 1 of first two themes funded by GA
![Page 54: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/54.jpg)
More information….
Leave your business card
Janice Green
(02) 6232 3558
or
![Page 55: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/55.jpg)
Protoype
![Page 56: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/56.jpg)
Protoype
![Page 57: Revised intensity frequency-duration (ifd) design rainfalls estimates for wa - janice green](https://reader033.vdocuments.site/reader033/viewer/2022060109/55576f6dd8b42a94728b54e7/html5/thumbnails/57.jpg)
Protoype