MW Normal - Bass Coast Shire Council

Bass Coast Planning Scheme
Amendment C82
Land Subject to Inundation Overlay
Expert Witness Statement
Powlett River
Prepared by Dugald Baird
September 2014
About the Author
Dugald Baird has prepared this expert witness statement with regards to the Powlett
River Land Subject to Inundation Overlay in the Wattle Bank and Wonthaggi area for the
October 2014 Panel Hearing into the Bass Coast Amendment C82.
Dugald has over 10 year’s experience in flood management. Dugald’s area of expertise
include the analysis and practical implications during the construction of drains, channels,
waterways, retarding basins and wetlands to ensure flood protection of both rural and
urban areas. Dugald has worked on significant urban developments in metropolitan
Melbourne and surrounds including Caroline Springs, The Hunt Club in Cranbourne,
Spring Ridge Wetland Retarding Basin in Wallan, Jackson’s View Estate Wetland
Retarding Basin in Drouin and many more.
Mr Baird has almost 10 years of service with Melbourne Water where he remains a
current employee. He has experience in the areas of planning, building and maintenance
of drainage assets constructed for and maintained by Melbourne Water. His current role
is in the Development Planning Team, which focuses on ensuring all new developments
within Melbourne Water’s catchment management boundary achieve a 1 in 100 year ARI
storm event protection.
Prior to this, Dugald was employed by RHA in Victoria as East Team Leader involved in
civil construction of drains, channels, waterways, retarding basins and wetlands.
In preparing this report the following documents have been reviewed:
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•
•
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Bass Coast Shire Council Amendment C82 Explanatory Report
Casey Planning Scheme Amendment C143 Panel Report
Wellington Planning Scheme Amendment C33 Panel Report
Bass Coast Shire Council Position Paper July 2014
A 15 minute Community Consultation session was attended on 15 April 2014.
Disclaimer
The views, expertise and opinions expressed in this paper are Dugald Baird’s personal
opinions based on his professional knowledge and experience. Dugald’s opinions are in no
way representative of the companies he is currently employed by or has been employed
by in the past.
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Contents
Introduction
4
Issues
1.
2.
3.
4.
Inaccurate/Incomplete Flood Planning, Research and Mapping
Best Practice Floodplain Modelling/Management
Flooding not Addressed in Amendment C82
Community Consultation
5
7
9
13
Conclusion
14
References
15
Appendix 1
Media Article Detailing Heslops Road flooding
Page 3 of 18
16
Introduction
Bass Coast Shire Council (BCSC) proposes to change their planning scheme to amend the
existing boundaries of the Land subject to Inundation Overlay (LSIO) within their
municipality bounds thus impacting what landowners can do on their properties. It has
been communicated to the landowners that the modifications are required to mitigate
potential riverine flooding risk from the Bass River, the Powlett River and coastal
inundation.
Recent changes to zoning which increase urbanisation and subsequent runoff, as well as
the 1 in 100 year average recurrence interval (ARI) storm event that occurred in 2012,
are contributing drivers for these changes. Prior to these proposed changes, the author
is not aware of any riverine flooding to recent developments, however existing issues
such as land locked due to Powlett River flooding have not been addressed in the new
amendments.
This report does not focus on Bass River or predicted future coastal inundation as it is
outside of the landowners’ impacted area; however the overall issues such as inaccurate
planning, research, mapping/modelling and ineffective community consultation may well
be applied to all areas that are part of this amendment. This report focuses on rural
inundation, in particular, riverine flooding from the Powlett River in the Wattle Bank and
Wonthaggi area.
The report will look at gaps in the proposed amendment and discuss best practice
stormwater and flood management to ensure that protection for flood prone areas is
equitably applied to all affected parties.
Page 4 of 18
Issues
1. Inaccurate/Incomplete Flood Planning, Research
and Mapping
The statutory authorities responsible for the collection of flood information and for the
land use planning in flood affected areas is Council and floodplain management
authorities; in this case BCSC and West Gippsland Catchment Management Authority
(WGCMA).
According to the Victorian Planning Provisions Practice Note, the definition of mainstream
flooding is:
‘Heavy rainfall produces surface run-off which flows into streams and rivers. When there is
large amounts of run-off, Water overflows the river banks on to adjacent low-lying land
causing flooding.’
All of BCSC’s literature refers to the mapping of mainstream flooding contributing from
the Powlett River; however no delineation exists between flooding that may occur due to
stormwater runoff from land and riverine flooding.
When questioned on boundaries and particularly flood inundation extents covering some
properties and excluding others, the response from Wayne Gilmore at the WGCMA was:
‘it seemed like a good place to stop.’
When questioned if the overlay was a result of localised flooding caused from stormwater
runoff or riverine flooding from backwatering of the Powlett River, the WGCMA
representative said that they did not track every flow path because they did not have
time. They also acknowledged that minimal field assessment was undertaken and that
the majority of the LSIO was primarily developed using desktop assessments.
It is my opinion that very minimal consultation with landholders was undertaken during
the formation of the LSIO and all emphasis has been placed on desktop assessment with
little regard for local knowledge of on-ground issues. I believe that the map for my local
area is incorrect based on my local knowledge of flow and flood regimes. Creating the
LSIO based primarily on desktop assessment without a hydrological model and a
hydraulic model is inaccurate and fraught with risk and potential liability issues.
The BCSC Position Paper implies that the Wellington Planning Scheme Amendment C33
and Casey Planning Scheme Amendment C143 provide justification that the methodology
used in the Bass Coast Planning Scheme Amendment C82 is appropriate. Both
Amendment C33 and Amendment C143 had more rigorous processes than Amendment
C82.
The Bass Coast Amendment C82 is inadequate because:
•
•
•
•
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No flood model was created
The desktop study was not sufficient due to poor quality aerial photography
There was no estimate of flows from localised catchments
No estimation of flood depth and flow velocities have been provided
The delineation of flood extent is based on an individual’s interpretation of a poor
desktop analysis, not industry accepted science and procedure.
Page 5 of 18
The Casey Amendment C143 recommends that:
‘It is essential that the analysis leading to the definition of LSIO boundaries is rigorous.’
The information presented to date provides little rigor in the formation of Amendment
C82. The delineation of flood extent needs to be developed based on standard and
accepted industry practices and without fear or favour.
When identifying flood prone areas it is essential that detailed modelling based on
science is developed and this information becomes a key input into calculating flood
levels, flow patterns and water behaviour. This information forms a clear and justifiable
base line and allows for future modification as more in-depth data becomes available.
Page 6 of 18
2. Best Practice Floodplain Modelling/Management
The overall methodology and processes used in creating Amendment C82 is primitive in
comparison to today’s standards and practices in flood modelling. My understanding of
the development of the LSIO is that it is based on unscaled low resolution photography
transposed onto satellite imagery.
Collection of detailed survey data is a basic and necessary process in determining
floodplain management. There seems to be some misunderstanding of the term LiDAR
used by BCSC and WGCMA to validate the formation of the LSIO. The suggestion to rely
solely on LiDAR to predict inundation because other flooding information is not available
is not industry accepted science and procedure. I also believe the term LiDAR is being
used to confuse the general public.
LiDAR stands for Light detection and ranging. LiDAR is a technology that uses laser
pulses to generate large amounts of data about the physical layout of terrain and
landscape features.
All varieties of LiDAR operate using the same basic principle. The LiDAR instrument fires
rapid pulses of light (laser pulses) at the landscape and a sensor mounted on the
instrument measures the amount of time taken for each light pulse to bounce back.
Because light moves at a constant and known speed, the LiDAR instrument can then
calculate the distance between itself and the target with high accuracy.
By rapidly repeating the process, the LiDAR instrument builds up a complex 'picture' of
the terrain it is measuring.
LiDAR does not produce a flood extent or establish flood levels it simply forms a
topographical map.
The Bass Coast Amendment C82 position paper (p4) states that:
“recent flood amendments that have relied on LiDAR mapping include Casey C143 and
Wellington C33.”
The Casey Amendment C143 did not rely solely on LiDAR mapping but did more
extensive modelling which included:
i.
ii.
iii.
iv.
Production of topographic information for the area being mapped
Estimation of the magnitude of flows along drainage parts
Estimation of flood depths and flow velocities along the drainage lines
Delineation of flood extent and determination of properties subject to flood
inundation
The information used during the Wellington C33 Amendment included:
i.
ii.
iii.
iv.
extensive scaled aerial vertical photography of the flood waters during two
different events
A GHD report – Rosedale Flood Warning Upgrade Project 2002
Melbourne University Centre for Environmental Applied Hydrology – Gippsland
Lakes Flood Level Modelling Project 2004
SMEC – Port of Sale Hydrological Study 2004
Page 7 of 18
BCSC’s justification and key point is that the LSIO is a planning permit trigger only. This
trigger requires the community to engage a licence surveyor to undertake extensive and
expensive work which may or may not be required because the overlays were not based
on current industry best practices. Economic impacts on land owners such as noncoverage for flooding or increased insurance premiums are also a consequence.
How can the community have confidence that this trigger is accurate given the primitive
development methodology and gaps in the mapping? How can the community have
confidence in a referral organisation who does not undertake adequate modelling before
making decisions on flooding?
This proposed LSIO seems rushed and the BCSC and WGCMA approach is inadequate.
However, a solution could be to defer the declaration until additional and credible
processes in line with current industry practices are undertaken.
The WGCMA need to develop a hydrological model and a hydraulic model.
Inundation mapping is based on combining the flood levels with topography and flood
levels are determined based on hydraulically modelling the flows, which are calculated
using various hydrologic methods of computation such as the rational method or RORB.
If this LSIO was correctly established flood predictions would have been produced using a
program such as HEC-RAS or TUFLOW, which removes the personal interpretation and
influence and makes the process accountable and able to be reviewed. None of this
information has been disclosed and it appears to have not been calculated for this LSIO.
HEC-RAS, the Hydrologic Engineering Centre’s River Analysis System (US Army Corps
engineering hydraulic modelling software), is currently among the most popular computer
models and is free. Other models such as TUFLOW combine 1D and 2D components to
derive flood depths across both river channels and entire floodplains.
Recent developments in computational flood modelling have enabled more sustainable
and accurate flood predictions. Various computational flood models have been developed
in recent years. These can be either 1D models (flood levels measured in the channel) or
2D models (variable flood depths measured across the extent of a floodplain).
The rainfall over a number of months in 2012 was quite heavy. The Bureau of
Meteorology records show that early May 2012 would have been a good cross reference
point to add credibility to flood data but neither data nor evidence has been presented.
Similarly, multiple scaled vertical photography during this time to build up a more
detailed picture would also have increased integrity of the process.
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3. Flooding Not Addressed in Amendment C82
It is my opinion that there are substantial inconsistencies in the approach to determining
the extent of inundation from which the proposed amendment to the LSIO is based.
These inconsistencies are likely to result in errors in the extents of flooding inundation.
One such example of an error in the inundation extents is demonstrated in the LSIO
proposed for Heslops Road and Korumburra – Wonthaggi Road. The flooding that
occurred along Heslops Road and Korumburra - Wonthaggi Road during June 2012 was
the result of a 1 in 100 year ARI storm event. The flooding resulted in significant
amounts of water from the Powlett River not only engulfing Heslops Road, resulting in
closure several times during 2012, but also over the Korumburra-Wonthaggi Road. There
are news reports and photographic evidence highlighting the closure of Heslops Road and
Korumburra-Wonthaggi Road due to Powlett River flooding. Refer Appendix 1 for one of
the news reports.
Figure 1 Detail of Map 7 Powlett Rv-West Creek 1 LSIO featuring Heslops Road.
In these three locations the flood extent has not included Heslops Road or any land to
the south.
The LSIO boundary depicts these roads as being “flood free” in a 1 in 100 year ARI storm
event. If correct research was conducted, advice had been taken from local knowledge
and modelling developed, the Powlett River–West Creek LSIO would have included roads
and land to the south.
Figure 2: clearly shows the intersection of Korumburra-Wonthaggi Road and Heslops
Road being closed due to flooding. Personal observations during the time indicated that
farm gates, fences and road side delineators (white posts) were completely covered by
floodwater. The direction and flow of the flood water can be clearly seen on all sides of
Korumburra–Wonthaggi Road and Heslops Road extending extensively into the
surrounding properties.
Page 9 of 18
Figure 2: Sentinel Times front page photo of flooding over Korumburra-Wonthaggi Road and
Heslops Road - June 2012.
Council clearly states in its position paper (p8) that:
“Riverine flooding can be long lasting and cause severe disruption to residents cut off by
floodwater.”
Despite this position and statement from BCSC, no modifications to Map 7 Powlett RvWest Creek 1 have been undertaken.
There are other anomalies in the Wattle Bank area. Most of the modifications to the LSIO
have been undertaken in the Wattle Bank/Lance Creek area with selected properties
experiencing some reductions and others complete reductions despite flood water being
present.
Figure 3 Detail of Map 8 Powlett Rv-Outtrim 1 LSIO featuring Wattle Bank.
Page 10 of 18
Figure 4: Image of Property A in Wattle Bank showing originally proposed and amended LSIO
boundary
Figure 4 shows the proposed flood extent in this area (the yellow line) follows a property
boundary, but if we look at the photo provided for the area (Figure 5) there is water
around the dam and a large clump of trees blocking the view of the land.
Figure 5: Arial photo of Property A in figure 4 - Wattle Bank, showing the water is over the
amended boundary line.
Trees obscuring view
Flood water appears behind trees in this area
The reliance on a photo that is of relatively low quality that has significant areas
obscured by vegetation is fraught with risk and liability issues. This yellow line clearly
does not reflect the topography of the land.
Making an assumption on an obscured view based on ability or previous experience
cannot give a true indication of what lies on the other side of the trees. ‘Groundtruthing’ was needed in this situation.
Another example is with Property C in Wattle Bank. Figures 6 show significant amounts of
water on the property but these were not picked-up under aerial photography and LiDAR
because trees and vegetation were obscuring the view and no ‘ground-truthing’ was
conducted.
Page 11 of 18
Figure 6 Photo of Property C looking East from Desmond Road culvert.
Clear parameters need to be put in place to identify which properties are included and
which properties are excluded. If Property C on Desmond Road is excluded then the
section of our Property B which is feed by overflowing water from Property C and the
local road should also be reduced in size.
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4.
Community Consultation
It is my opinion the level of community consultation was inadequate for the C82
Amendment because of the large geographical area, the high number of objections and
financial implications that impact on residents. The information about the amendment is
difficult to find, unreliable and confusing. Residents have been provided with minimal
time to consider the impacts of this amendment and are often asking for additional
clarification. The community consultation process consisted of a mail drop providing a
basic letter about the amendment and an invitation to attend a 15 minute meeting with
the authority.
The Amendment C82 was placed on public exhibition between 13 March 2014 and 2 May
2014. This included Easter and school holidays when people are typically away.
In my opinion the meeting was not to a standard that should be expected by the
community from an authority to whom they pay rates. When questioned on why the
meetings were set up this way the Council response was “because that is all we have to
do”.
Council were not transparent in the implementation of the LSIO amendment. When asked
“what was the driver for the change and the implementation of the LSIO”, the response
was “it is a Melbourne Water requirement”. This is clearly not the case as the Powlett
River is well outside of Melbourne Water’s catchment management boundary. The
residents were further confused at why a Melbourne Water representative was not
present for this meeting if it was in fact a Melbourne Water requirement.
Residents were provided with no prelude to the meeting and during the allocated 15
minute time slot were shown images of the WGCMA proposal. At the meeting two
proposals where displayed, the BCSC proposed layer and the WGCMA amended layer.
This made the discussion very difficult as I was placed with a WGCMA person who
discussed their proposal only. When questioned how I should respond to the amendment,
I was advised to consider only the current council position and was not given any
information on how BCSC came up with their LSIO.
When questioned about how they came up with the levels and extents for the proposed
WGCMA LSIO, the WGCMA was relying on the one photo shown to me. I was told all
affected properties were not visited during the formation of the amendment and no field
surveys were undertaken.
No explanation or overview was given about how the planning system works and no
supporting information was provided. There was no discussion about the Ordinance
changes or even where to obtain this information. Residents were left to try to find
information on their own.
The BCSC has since adopted the WGCMA amended layer without going through what I
believe is a reasonable public consultation process. BCSC continually receives one the
lowest annual community satisfaction results in the state – perhaps reviewing their
consultation processes with issues such as these may improve their results.
During the Casey C143 Amendment - extensions of time was granted and extensive
community consultation / visitations where undertaken. This is in stark contradiction to
the current proposal where a significant change was implemented through acceptance of
WGCMA revised boundary and then referred straight to Panel with minimal community
consultation.
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Conclusion
There is a current LSIO over the Powlett River which has allowed development to proceed
without any flooding issues. Given the lack of technical information, flood modelling,
accurately detailed maps and high resolution aerial photography, as well as what I
believe is inadequate due process; this modified LSIO should not be implemented until a
fairer and more rigorous process has been followed. The current LSIO should be
maintained until the following has occurred:
1. Develop a comprehensive flood model in consultation with the community so the
community can have confidence that a fair and equitable process has been followed.
2. The flood model should include as a minimum:
• A hydrological model and a hydraulic model
• Clear parameters
• Volumes and estimation of flood depths
• Direction of water flows
• Topography of the land
• Justifiable delineation of flood extent and flood level which has undergone an
independent peer review
• Extensive scaled aerial vertical photography of the flood waters during two
different events.
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References
Bass Coast Planning Scheme Amendment C82 Explanatory Report
Casey Planning Scheme Amendment C143 Panel Report
Wellington Planning Scheme Amendment C33 Panel Report
Bass Coast Shire Council Position Paper July 2014
Daily Rainfall – 085041 – Bureau of Meteorology
Victorian Planning Practice Note: Applying the flood Provisions in Planning Schemes August 2000
Monash University engineering
http://eng.monash.edu.au/civil/research/centres/water/rorb/
LiDAR definition taken from CSIRO website www.csiro.au
Sentinel Times Newspaper Tuesday, 26 June 2012
Page 15 of 18
Appendix 1
Sentinel Times Newspaper Article Tuesday, 26 June 2012
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